Geo-Congress 2020: Foundations, Soil Improvement, and Erosion

This paper aims to present the design, construction, and quality control of deep foundation for Landmark 81—the current tallest tower in Vietnam and the 14^th tallest tower in the world to be completed in 2019. Before 2015, the project location was used as a dockyard near the Saigon River. Twenty-eight meters (28 m) of very soft clay has almost no load capacity (SPT N-value from 0 to 2) and, combined with the heavy weight of a 461 m tall reinforced concrete building, posed significant challenges for both structural and geotechnical design engineers and contractors. Two fully instrumented test barrette piles with Osterberg cell (O-cell) installation were carried out to study the geotechnical pile capacity. The test results of these 02 test barrette piles have been analyzed and presented. The estimation of foundation settlement including differential settlement and soil-structure interaction analysis was considered. Piles subject to permanent loads (such as dead load, live load, wind load, and especially earthquake load) are analyzed and mentioned in this paper. The paper also describes the shaft grouting technique method, construction sequences, and construction acceptance criteria for this technique. The paper will also draw some conclusions for applying of the same solution to other high-rise buildings in Vietnam and elsewhere in the world.

Caissons are massive foundations having high stiffness which carry large vertical as well as lateral loads. As caissons support lifeline structures, it makes their study very significant. In the current study, numerical modeling of laboratory scale models of caissons was performed using finite element software ABAQUS. The base dimensions of caisson and its depth of embedment were varied keeping other factors same. The caisson dimensions and the soil properties were simulated with the test conditions adopted by Sharda (1975) in the experimental study. Geometric and material non-linearity were taken into account. A code was written in Python for obtaining section forces and bending moment. Lateral soil pressure, load sharing, maximum and minimum base pressures, well displacement, and point of rotation were determined. It was observed on the basis of these computations that the lateral load resistance of caisson increased with both size and embedment depth of caisson. The results were found to be in good agreement with the experimental results of Sharda (1975).

Large diameter caissons used as bridge foundations are generally subjected to transverse loading in terms of horizontal load and overturning moment. Present study demonstrated the moment capacity of caisson foundations embedded in layered cohesive soil by adapting 3D numerical analysis. Validation of the numerical methodology with load test data for layered soil was performed. Effect of several important parameters such as interface roughness conditions and height-to-diameter ratio on the lateral soil reaction profiles for both homogeneous and non-homogeneous soil was investigated. Kinematic mechanisms at failure for different coupling conditions of sliding and rotation of the foundation due to applied lateral load have been discussed in detail. Variation of the depth of rotation for different conditions under lateral loading also has been highlighted in the present analysis.

In this paper, disconnected and connected piled-raft foundations consisting of single pile and 3×3 pile group subjected to both vertical and lateral loads have been analyzed by PLAXIS 3D. The sub-soil profile and pile dimensions are taken from the reported experimental results obtained by another researcher. The validation of the numerical model has been done with the reported experimental results. It has been observed that the vertical settlements of raft and pile head are about 20.33% to 35.20% more than the lateral settlements for both disconnected and connected piled-raft foundations. The disconnected piled-raft foundations of single pile and 3×3 pile group can take lateral loads up to 0.64% and 5.37% of the vertical load respectively. Similarly, the connected piled-raft foundations of single pile and 3×3 pile group can take lateral loads up to 1.14% and 9.71% of the vertical load respectively.

This study investigates the effect of reinforced concrete cracking on the performance of thermo-active piles subjected to traction force. A newly developed finite element code that is within the framework of the load-transfer approach is employed to simulate the response of a single pile subjected to thermomechanical loads. The results suggest that the performance of energy piles is highly affected by reinforced concrete non-linearity. Nevertheless, piles can accommodate thermally imposed strains if ductility capacity is provided. This outcome, in conjunction with the results of previous studies on the non-linear response of interfaces, may be considered for a more rational performance-based design approach of energy piles.

There are different methods proposed for estimating the ultimate axial capacity of the piles using cone penetration test (CPT). These methods represent correlations between CPT data and pile capacity based on different properties such as the pile width, pile type, installation method, soil type, etc. However, there is no perfect pile-CPT method that reflects all the factors affecting these correlations, instead, each pile-CPT method considers some of them. In this paper, the results of 80 pile load test cases of precast prestressed concrete (PPC) piles driven in Louisiana, were studied using seven (7) different pile-CPT methods: LCPC, ERTC3, probabilistic, UF, De Ruiter and Beringen, UWA, and Schmertmann. The results of these methods were compared and their performance was examined for different cases where different percentages of the pile capacity is due to sand layers. The multidimensional unfolding (MDU) technique and the log-normal distribution of estimated to measured pile capacities for these pile-CPT methods were used to develop a novel combined method that enables designers to estimate, more reliably and accurately, the ultimate capacity of driven piles for different soil categories.

There are many situations in which piles have to be provided near slopes. Design procedure based on the p-y approach is well established for piles in level ground. However, the available p-y curves for level ground condition can not be extended directly for sloping ground conditions. Experimental model tests in the laboratory have been undertaken in the present study to investigate the lateral pile response near sloping ground. The paper discusses about the investigation in a series of laboratory tests in dense sand at 72% relative density. The main purpose of the study was to examine the effect of slope angle and edge distance on the pile response. Ground slope was varied as n=1.5, 1.75, and 2 for sloping ground condition. Pile response was obtained for three different positions of pile from the crest of the slope for a specified relative density. The present study was performed to develop a series of p-y curves for single piles through experimental investigations. Pile response for horizontal ground condition was also obtained for quantification of the effect of sloping ground. Displacement and bending moments in the pile increased significantly when the ground surface changes from horizontal to slope. An increase in the edge distance from the slope crest causes reduction in the pile displacement and maximum bending moment.

In conjunction with the construction of the Sagamore Parkway Bridge in West Lafayette, Indiana, a 26-inch-diameter, 100-ft-long, open-ended pipe pile was driven and load tested at the construction site to provide guidance for the foundation design. The soil profile mainly consists of sand-gravel mixtures with gravel content as high as 40–60% at certain depths. The test pile was densely instrumented with a combination of vibrating-wire and electrical-resistance strain gauges. A double-wall instrumentation scheme was used, as it allows independent measurements of the inner shaft resistance from the soil plug and outer shaft resistance. This paper presents the test results in terms of the plug measurement, load-settlement response, development of the plug, annulus and shaft resistances, and profile of the inner and outer unit shaft resistance. The complete dataset consisting of full characterization of soil profile and detailed pile resistance measurements provides great value for the development of the design methods for open-ended pipe piles driven in gravelly sands.

Two production piles were instrumented with pairs of strain gauges to provide information on the combined reliability of the numerical modeling and geotechnical engineering assessment of soil properties in predicting moments and shear forces for auger cast in place (ACIP) pile foundations. The pairs of strain gauges were installed during construction of a 47-story building foundation to define axial loads and moments at eight different depths along the length of the piles. The results of two years of data collection and analysis indicate that ACIP compression piles developed shear forces and moments at depths well below those commonly reinforced in these piles based on conventional analysis. These forces could potentially lead to the structural failure of the piles. The results indicate that for large buildings, ACIP foundation design should include three dimensional geotechnical/structural models capable of defining the forces acting on the piles. Knowing these forces will allow for the design of the piles considering load combinations as defined by ASCE/SEI 7 in the same manner that the other structural elements of the building are currently designed.

The primary objective of the load and resistance factor design (LRFD) method used in the deep foundation geotechnical design industry is to differentiate uncertainties in loading from those existing in the resistance following a probability-based theory. The probability of occurrence associated with loads is reflected by a load factor, γ, and those uncertainties associated with the geotechnical resistance are reflected by the resistance factor, ϕ. The calibration process for deep foundations is completed to determine resistance factors, ϕ, using statistical data regarding loads and geotechnical resistances. One of the important factors used for the calibration process is the bias, λ, defined as the ratio of the nominal resistance determined from results of a full-scale load test, Q_M, to the nominal resistance determined using an agreed predictive model, Q_P. The bi-directional static load test (BDSLT) is widely used to test the deep foundation‘s geotechnical resistance. After the load test is completed, the measured data are analyzed to determine required parameters for construction of the equivalent top-loaded (ETL) curve. The ETL curve is used to evaluate the geotechnical capacity using defined approaches. However, the ETL curve does not always reach 100% or more of the required values for a defined geotechnical resistance determination method. Therefore, extrapolation methods are sometimes required to extend the ETL curve to load and displacement values necessary for a defined method. The extrapolation process will introduce uncertainties which will further impact the calibration process. This paper presents a qualitative assessment of the American Association of State Highway and Transportation Officials (AASHTO), and the Federal Highway Administration (FHWA) predictive models by comparing the predicted nominal resistance to measured nominal resistance using the modified Davisson‘s criteria, 5% relative settlement, and the 10% relative settlement approach with primary focus on drilled shafts. From the comparison analysis, with a coefficient of determination of 80%, the modified Davisson‘s criterion was considered the method of analysis for this study. Furthermore, the extrapolation effect on resistance factors was explored by calibrating these factors using extrapolated and non-extrapolated ETL curves. The calibration process included 30 drilled shaft cases where ETL curves reached displacements equivalent to those determined using the Davisson‘s criteria.

We use the results of pseudo-static and seismic load tests on centrifuge model piles to investigate the effects of improved zone size on the soil-pile interaction mechanisms in cement-improved soft ground. In deriving the p-y curves that are typically used for modeling the soil-pile interaction, we implemented a modified bending moment curve-fitting procedure that accounts for discontinuities inherent in the distribution of soil reaction at the interface of the improved and unimproved soils. Our experimentally derived p-y curves show the influence of the improved layer on the behavior of the underlying soft clay layer and vice versa. The standard p-y curves performed reasonably well for estimating the stiffness of the largest improved zone but over-predicted the stiffness of the smallest improved zone. The standard p-y curves also showed good agreement with the backbones of the seismic p-y curves in the soft clay away from the improved zones. We evaluated the reliability of a simplified pseudo-static analysis for a seismic excitation and obtained satisfactory results for the largest improved zone. Our analyses reveal the dominant nature of kinematic interactions in the response of the improved piles.

Current driven pile design procedures for H-piles in intermediate geomaterials (IGMs) normally utilize static analysis methods developed for soils (i.e., sands and clays) for estimating side resistance. The purpose of this paper is to assess the performance of α- and β-methods on shaft resistance estimation using 17 test piles driven into IGMs in Wyoming. The necessary pile and geomaterial details were retrieved from an electronic database known as WyoPile. The estimated shaft resistances were compared with that obtained from dynamic load testing results and signal matching analyses results. Ratios of measured to estimated resistances were determined and the associated uncertainties expressed in terms of the coefficient of variation (COV). The comparison identified inconsistent performance of the existing α- and β-methods with relatively high COVs of 1.28 and 0.80, respectively. α and β coefficients were therefore calibrated against IGM properties using regression techniques. The improved α- and β-methods, along with their calibrated design coefficients, were verified using five independent test piles. Due to small sample sizes, the performance of the calibrated α- and β methods could not be conclusively assessed.

To convert strain to internal force, it is conventionally assumed that both the foundation‘s composite-section elastic modulus, E, and total cross-sectional area, A, are known. However, only the product EA, the foundation‘s axial rigidity, is needed. Using applied test loads and measured strains, the incremental rigidity (“IR”) method determines the relationship between axial rigidity and strain at individual strain gage levels. From this relationship, measured strains can be converted to internal forces without having to know either a deep-foundation element‘s elastic modulus or its cross-sectional area. This paper reviews several published methods commonly used to estimate elastic modulus, cross-sectional area, internal stress, and internal force in a deep-foundation element. The assumptions, uncertainties, and limitations of each method are discussed. The IR method for converting strain to internal force in an instrumented static loading test is presented, including assumptions, uncertainties, limitations, and best practices associated with method.

A valuable objective of performing static loading tests on deep foundations is to determine load-transfer response. Integral to this objective is determining internal forces at various locations within the deep-foundation element. These internal forces are usually obtained from strain measurements. Using applied test loads and measured strains, the incremental rigidity (“IR”) method determines the relationship between axial rigidity, EA, and strain at each strain gage level. This paper presents results from a number of instrumented static loading tests where the IR method was used to convert measured strains to internal forces. Various illustrations, conclusions, and lessons learned from application of the IR method to these case histories are presented. Topics presented include the strain dependence of rigidity, interpretable versus non-interpretable IR results, the strain magnitudes required to yield interpretable IR results, the use of at- or above-grade strain gages, the benefit of averaging test load and strain values, determining variable rigidities within an apparently uniform pile, determining rigidities at non-interpretable strain gage levels, and applying the IR method to complex geometries. Results from a closed-end concrete-filled steel pipe pile are presented which indicate that the elastic modulus of concrete may increase linearly with depth in the pile.

A common method for predicting ultimate shaft resistance of pile foundation in sandy soils is based on the use of effective stress and utilizing a beta-coefficient (β) that incorporates the soil-pile interface effects. The β is a function of coefficient of lateral earth pressure (defined as the ratio of the effective radial stress acting on the pile wall to the effective overburden stress, σ‘v) and the interface friction angle between pile wall and the soil. In the case of the self-drilling HBMs, the diameter of the formed pile is not known. The diameter of the HBMs varies significantly as the central hollow-bar penetrates soil at various rates and grout pump flow rates. The soil types and existing density also play an important role in forming the diameter. TITAN Injection Pile or HBM manufacturer company “Ischebeck” introduced a new term describing a widening value “a”. This value quantifies the difference between diameters of the formed HBM and the used drill-bit. The “a” value ranges from 0.8-inch (20 mm) minimum for any type of soil to 2.0 inches (50 mm) for sandy soils and 3 inches (75 mm) for gravelly soils. However, the effect of installation parameters on the formation of diameter of HBM is not addressed in previous studies. Therefore, utilizing field-measured data, work presented herein examined the effect of both the installation parameters and soil conditions on the formed HBM diameter. Multivariate regression analysis was used to develop models to predict the formed diameter of HBMs used to assess the axial pullout capacity of HBMs. Eight HBMs, four instrumented and four non-instrumented, were used in the study. The field testing program included installation of micropiles to a depth of 25 ft. (7.62 m) while varying the drill-bit insertion rate (I_R) and the grout flow rate (Q_R). In addition, the installation methods included HBMs that were continuously drilled and grouted with neat grout water-cement ratio (w/c) of 0.4, and others that were first drilled and grouted continuously with thinner grout (w/c-0.7) and then flushed from bottom to top with thicker grout (w/c-0.4). The eight HBMs were tested for ultimate pullout capacity. Four of those instrumented HBMs were retrieved after the load testing to measure the formed diameter per foot of installation. The back-calculated diameter and pull-out test data were used multivariate regression analysis to predict the diameter of those non-instrumented and non-retrieved HBMs.

Circular and semi-circular shaped pipe pile cell foundations were constructed in a river and on its levee to support a new expressway viaduct Tokyo, Japan. The piles were 59.5 m (195 ft) long and 800 mm (31.5 in) in diameter and designed to be embedded in a dense sand layer. In order to safely install the length of the interlocked pipe piles under the existing girder, piles were hydraulically pressed into the ground and repeatedly spliced with mechanical joints. The press-in piling operation with water jetting successfully accomplished highly accurate installation.

Since 2016, a developer in Tampa, Florida, has been involved in a major facility expansion, which includes new parking garages, an elevated Porte Cochere, a central utility plant, a three-story low-rise expansion, and a new 17-story hotel tower. Constructing the expansion structures while maintaining an operational facility presented its own set of unique complications. Because of numerous geotechnical challenges, extensive coordination was required among the design team, ownership, specialty subcontractors, and general contractor to meet the rigorous project demands. The challenging subsurface conditions included highly variable strength characteristics typical of the underlying Tampa limestone formation, karst features within the formation, and the potential for destabilization of the working platform by construction-induced subsidence related to the selected foundation or ground-improvement system installation. All these factors needed to be considered and implemented with regard to potential impacts to adjacent structures supported on a variety of foundation systems. Geologic anomalies such as zones of highly atypical depths to the limestone bearing stratum and interbedded zones of variable infill materials were also encountered. These conditions required specialized construction techniques and a highly skilled team working together. To accomplish the project goals, a number of geotechnical solutions were used including drilled shafts, augered cast-in-place (ACIP) piles, micropiles, vibro-replacement stone columns, and low-mobility grouting as well as deep soil-mixing, tiebacks, and chemical-grout stabilization for support of excavation. To effectively implement a wide range of foundation and ground-improvement solutions, an extensive subsurface investigation was performed followed by comprehensive load testing. Production-phase non-destructive testing for each of the various foundation components was included along with supplemental load testing. An overview of the development concept and a description of each of the geotechnical challenges encountered, the approaches formulated, and subsequent use of each solution is presented here. Additionally, load-test results for drilled shafts will be compared to load-test data from other parts of the Tampa Bay region to highlight the complexity of the project. Non-destructive test results will validate the specialized construction techniques that were required. The paper will provide a case study of how the various subsurface challenges typical to the Tampa region can be overcome in a practical manner through proper communication and planning while meeting the schedule and coordination demands of the project.

Cross-hole sonic logging (CSL) is commonly used for the evaluation of the structural integrity of drilled shafts. Cross-hole sonic tomography (CST) is also performed to generate a more detailed image of the suspected defect detected by CSL. CST is more demanding than CSL in terms of both data acquisition and analysis. However, it is reported in the literature that these methods exhibit some limitations in detecting defects of certain geometry within drilled shafts. Recently the full waveform inversion (FWI) technique in non-destructive testing applications has shown promising performance in providing high resolution images of the domain of interest. FWI is implemented by solving an iterative optimization problem that simulates wave propagation through the domain. The choice of starting model is of significant importance to ensure the convergence of the inverted model to a physically meaningful result. In this study the application of FWI as an alternative to CST is investigated through numerical simulations. The focus is primarily on improving the convergence of the inversion by examining a hybrid combination of misfit functions over a range of frequencies for the modeled waveforms. In addition to the choice of the misfit function, this study will investigate the performance of a multi-scale FWI for structural integrity of drilled shafts.

Pile setup is defined as increase of pile capacity with time after the end of initial driving (EOID). Construction costs can be significantly reduced by the incorporation of pile setup in design phase of piles, and has recently been included in the design phase by various states. This study was performed in Alabama, to investigate the pile setup phenomenon for driven piles (i.e., HP pile and PPC pile). The size and geometry of the pile contribute to the amount of setup differently. Load test data was acquired from the Alabama Department of Transportation (ALDOT) of 18 test piles (7 HP piles and 11 PPC piles) driven throughout the region. All the test piles showed a significant amount of setup after EOID. All restrike data were analyzed using signal matching programs CAPWAP and iCAP; and were compared to the PDA in order to analyze setup behavior. The results indicate that setup developed on all test piles (7 H-piles and 11 PPC piles). Logarithmic setup parameter “A” for Skov and Denver (1988) model was back-calculated for these 18 piles. The results showed that the average value of “A” parameter was 0.21. However, the “A” parameter was higher for HP piles compared to PPC piles. The iCAP results indicate that the total axial pile capacity (regardless of pile type or size) increased over time from EOID (setup) by an average of 70% regardless of the soils encountered.

Wind turbine towers and tall trees have comparable components and induce similar loads (vertical, horizontal, and moment loads) on their foundation. In this paper, the possibility of developing a new foundation configuration similar to tree root is explored. Three simplified foundation configurations were identified with six, twelve, and eighteen main roots (MR). Three additional configurations were developed by adding two sub-roots (SR) per MR. Three-dimensional finite element models were created for each configuration in ABAQUS and analyzed by applying design loads. The results showed that the addition of MR contributed to a higher improvement in the performance (differential settlement and horizontal displacement), whereas, the impact of SR was insignificant. The parametric study conducted by varying the size of the taproot (TR) showed that a larger TR resulted in better performance but the impact of the SR was still negligible. Nevertheless, extensive investigation is required to make a better judgment.

Based on current design approaches for highway bridge foundations, the total axial resistance of open-ended steel pipe piles should be chosen as the minimum axial resistance determined for the fully plugged condition and the unplugged (coring) condition. Several studies have been conducted to investigate the plugging condition of the driven pipe piles considering different soil properties; however, there is still a need to investigate the actual behavior of large-scale driven piles and evaluate the axial capacity and plugging condition compared to the design assumptions. To expand the data inventory, this study presents findings from two bridge sites constructed as part of San Diego Freeway (I-405) Improvement Project located between State Route 73 and Interstate 605 in Orange County, California. The bridge abutments and bents are supported by grouped 24-inch-diameter x 0.5-inch wall thickness steel pipe piles. This paper presents the calculated axial capacities that were evaluated using a CPT based direct approach and the subsequent pile driving analyzer (PDA) test results that were performed on production piles to evaluate the capacities. The PDA tests provide insight into the plugging condition of full-scale driven piles from the first hours of pile installation and up to four days after driving. The direct method provided good estimation of the production piles’ axial capacities, and the PDA tests showed variable results in the improvement of the end bearing capacities with time. The findings of this study will be useful for practitioners in driven pile design.

Until recently, accurate long-term measurement of strain, temperature, corrosion potential, and other variables in concrete deep foundations and in superstructure elements has been difficult and costly. However, advancements in sensor technology and wireless data transmission has both simplified data acquisition, increased reliability, improved accuracy, and reduced costs. This technology now provides long term measurements which can be accessed in real time for in-service structures through a cloud-based system. Owners along with other stakeholders can now document and maintain “cradle to grave” records on their structural assets with respect to pre-stress level, post-tensioning level, corrosion, temperature, and several other variables of interest—load transfer from the superstructure to the substructure and effects from scour, sudden impacts, etc. Based on these measurements, design parameters, changes in loading, the effects of possible extreme events, corrosion rates, and other anomalous data can be evaluated in real time. This process allows owners with sufficient time to plan remedial actions which will prevent or at least minimize the risk of catastrophic failure. This paper discusses two case histories for structures constructed in Florida and the Bahamas, including the installation of the system, results from the days of monitoring, and its implications for the future.

These days, it is typical for the height of existing telecommunication towers to be increased to accommodate for the ever-increasing cellular and data demands. This results in considerable increases in uplift force of the tower foundation. To resist the uplift force, in dense granular soils, concrete cast-in-place (CIP) tension piles are typically used adjacent to the tower foundation with a galvanized steel frame to connect the piles to the foundation. However, CIP piles are not only expensive but also require access to larger equipment such as drilling rigs and concrete trucks. These factors can cause additional costs and operational issues during the construction process. Therefore, in this study, as an alternative method to resistance of uplift force, the applicability of helical piles were investigated experimentally and numerically. Six helical piles were installed using a modified installation technique with high torque. The pullout force was measured as the uplift resistance. Furthermore, the total increased uplift capacity of the foundation was analyzed based on 2-dimensional axisymmetric numerical modeling parametrized with soil properties of the site, and a parametric study was performed. These findings suggest that helical piles can be an effective method of resisting the uplift force in dense granular soils created by an extension of a telecommunication tower section compared to CIP piles.

The pile foundations are structural units that transfer the superstructure loads to deep levels where a satisfactory supporting ground or sound formation are encountered. It is quite common to have a group of piles supporting a heavy concentrated load. These groups are designed to support all exerted forces. Piles subjected to lateral loads or pull out forces due to wind or expansive soils need to be checked for stability and adequate strength. The pile settlement is a significant factor that needs to be kept within a small differential range. The work presented in this paper was conducted for a tall building proposed for construction at site underlain by limestone formation. It was aimed at comparing uniform distribution of piles under a thick raft and a rectangular tube-like distribution in which piles are concentrated under exterior shear walls. The structure also included two central columns supported by pile groups. Resistance to different loading conditions including vertical, lateral, and pull-out forces were studied and compared for the two pile configurations. The efficient pile distribution was selected. Comments on the efficient system and the choice criterion are given.

The Xcel Energy W3408 69 kV overhead transmission line was originally constructed in 1934 and extends 2.7 miles (4.3 km) from the Nelson Substation in Wisconsin to the Wabasha Substation in Minnesota, crossing the Mississippi River and its backwaters through the Federal Upper Mississippi River National Wildlife Refuge. The 2.2 miles (3.5 km) of direct embed wood H-frame structures in Wisconsin through the backwaters area was identified by Xcel Energy for rebuild in 2018–2019 due to age and condition. Design and construction challenges include the following: the presence of 22 to 3ft (0.6 to 0.9 m) of standing water over a significant portion of the project; winter ice; environmental/wildlife concerns; a limited service interruption (outage) for the transmission line, and poor soils. The design team selected a high strength conductor, minimizing sag and decreasing the total structure count from 27 to 17. The chosen principal foundation consists of groups of four (4) 3.5-inch (90 mm) outer diameter helical piles connected by a grillage at each structure leg. All required materials could be transported to the structure locations by airboat and installed using specialized marsh equipment without an extended, non-restorable outage of the transmission line. The grillage cap design consists of W-beams interconnecting grouted collars that accept the helical piles and transfer loads from the structure legs. This configuration develops a fixed head condition for the piles. With the use of battered piles, this creates a stiffer load-deflection response thus improving capacity. Drifting and expanding ice loads were addressed by identification of risk-prone areas and development of a secondary foundation system consisting of vibratory steel caissons for the four (4) structures that could not be spotted in low risk areas. These caissons consist of 0.563-inch (14.3 mm) thickness galvanized steel in a dodecagonal shape with a 3.5-ft (1.05 m) outer diameter. They range in length from 56 to 62 feet (16.8 to 18.6 m) and are designed for up to 6.5 feet (1.95 m) of scour potential.

A cross validation between the predictions of a response of an energy pile obtained by the computational and analytical models is presented. The computational model performed a coupled thermal hydro-mechanical finite element analysis. The pile is surrounded by a single soil underlain by bedrock. Two scenarios of the history of temperature change relative to the temperature of a surrounding soil were applied to the pile. During the first loading scenario the pile remained in the net heated state while the second load scenario induced the net cooling state. The net heating induced an upward axial displacement, tensile strain, and compressive stress while the net cooling induced a downward vertical pile displacement, compressive strain, and tensile stress. While the assumptions used by the two models differ to some extent their predictions of the pile vertical displacement along with strain and stress over the range of temperatures show a very good agreement.

The Minnesota Department of Transportation (MnDOT) has engaged in several driven pile instrumentation and performance monitoring projects to evaluate the pile response during construction, during and subsequent to axial load testing, and in the years following construction. The intent of the load testing program at this site was to save time and money on driven pile installation by driving the piles to a relatively shallow dense layer of sand, rather than driving through that layer to a deeper deposit of dense sand and rock. This paper describes a project in Clearwater, Minnesota, where a production pile was instrumented immediately after installation, with measurements recorded in the weeks and years to follow, including during the execution of a static load test conducted on the pile. The paper includes site investigation data from both traditional borings (with SPT tests conducted) and cone penetration soundings at the site. Information from the high-strain dynamic monitoring tests and the complete response of the pile during the axial static load test is provided, along with short-term and long-term performance data through the duration of construction and in the initial years following project completion, respectively. The results of the static load test are important to document for local and regional calibration efforts. The construction and extended performance data provide a basis for several interesting observations. Lessons learned from this project are shared to help advance the state of practice in driven pile design.

Thermomechanical behavior of energy piles is of great interest to the researchers, these days. In this paper, by considering different conditions for the mechanical behavior of the surrounding soil, an analytical approach is presented to determine the ultimate bearing capacity of the energy piles embedded in dry and saturated sandy soils under the application of the mechanical loads and imposing heating and cooling to the soil-pile system. In addition to analytical solution, a FEM software ABAQUS is implemented to simulate the bearing capacity of the energy piles in 3D condition. Then by making comparison between the analytical and numerical results, the functionality of the implemented approaches is evaluated for estimating the ultimate bearing capacity of the energy piles. Results are considered to be useful for engineering practical purposes as well as for the research works on this subject.

Laboratory model test results for the ultimate bearing capacity of a circular surface foundation of diameter B supported by a dense sand layer of limited thickness ($H$) and subjected to inclined loading have been presented. For these tests, the $H/B$ ratio for the sand layer was varied as 0.3, 0.5, 1.0, 2.0, 3.0, and 5.5 (which is considered large depth for sand). The load inclination (α) to the model foundation with respect to the vertical was kept at 0°, 5°, 10°, and 20°. For a given load inclination, the average inclined ultimate load per unit area, $q_{u(H/B,\alpha /\varphi )}$, decreases with the increase in $H/B$. The ultimate average inclined load per unit area becomes constant [i.e.$q_{u(\alpha /\varphi )}$] beyond a critical value of ($H/B$) ≈ ($H/B$)_cr. For the tests ($H/B$)_cr was about 3. Based on the model test results, an empirical nondimensional reduction factor, R, has been developed to estimate the average inclined ultimate load per unit area at a given $H/B$(≤ 3) from that obtained for the case at larger $H/B$[i.e.$R=q_{u(H/B,\alpha /\varphi )}/q_{u(\alpha /\varphi )}=f(H/B,\alpha /\varphi )$].

In this study, a database was developed to house reliable results from 43-plate load tests conducted on different types of compacted soil, including load-displacement responses and other information about soil and testing conditions. Using information from that database, resistance factors were developed for shallow foundations based on the prevalent first order second moment reliability approach. The resistance factors were calculated for common equations used to calculating the soil bearing capacity such as Terzaghi, Meyerhof, and Hansen. The calibration was based on comparing the calculated capacity with actual field measurements acquired from the plate load tests. After calibration, it was found that the resistance factors for footings placed on medium dense sand vary from 0.54 to 0.69. Resistance factors for other types of soil were also provided to cover a wide range of reliability indices.

Emergent innovative foundation types for wind turbine generators may interact with surrounding soil in a complex manner that cannot be easily or reliably evaluated with traditional and simplified industry-standard methods. Simulations employing numerical methods and a suite of study cases can be used to estimate the geotechnical performance of such foundations and to complete their structural design. In this paper, one such innovative foundation system for wind turbine generators is evaluated using 3D finite element continuum modeling. The foundation considered is a proprietary anchored grade-beam system. The grade beams are post-tensioned, segmental, and precast and are arranged in a star-pattern around a central hub to which the turbine steel tubular tower is connected. Earth anchors are fixed to the outer ends of the beams. Modeled features of the foundation included: (a) earth anchor system, (b) post-tensioning of grade-beams, and (c) anchor bolts in the tower connection. A total of seven (7) loading cases were analyzed to check foundation performance for: (a) rotational and horizontal stiffness, (b) lift-off, (c) overturning, (d) subsurface shear failure, (e) beam-aligned extreme load, and (f) beam-skewed extreme load. Though a continuum approach can provide a better approximation of the response of the foundation-soil system under wind loads as compared to simpler methods, there are challenges that need to be addressed for numerical evaluation to be successful. This paper discusses and proposes approaches to address the following modeling challenges: proper wind load transfer from structure to surrounding soil and assessment of foundation lift-off and overturning when using a continuum model. Of twenty-eight (28) simulations varying site/soil conditions, satisfactory performance was found for lift-off, overturning, global stability, and rotational stiffness. However, computed shear stiffness for the foundation did not meet industry requirements for two loading cases which utilized lower-bound values for concrete and soil characteristics.

This paper presents the results of a class C numerical blind prediction based on a large-scale shaking table test which was recently conducted at UCSD on a shallow foundation located on top of liquefiable soils. The organized blind prediction was focused on predicting the liquefaction-induced permanent settlements at multiple locations at free-field as well as on the foundation and comparing them with those measured during the test. Eight teams submitted predictions which were carried out using a wide range of software platforms, constitutive soil models, and element types. The accuracy of blind prediction submissions was evaluated in terms of root-mean-square error (RMSE) and the team with the lowest RMSE was ranked 1st and declared as the winner of the blind prediction. This paper discusses the observed bias trends of the predicted settlements in terms of the extent of underestimation and/or overestimation.

Generally, the first choice in the selection of a foundation for buildings and other structures is a shallow foundation because it is typically more economical and easier to construct than a deep foundation. However, shallow foundations are usually considered to settle more than deep foundations. This is a fallacy as well-designed shallow foundations do not settle more than well designed deep foundations. To calculate the settlement of shallow foundations on sands, the most critical parameter is the soil modulus. This parameter is influenced by a number of factors and the range of variation is large. Comparison between observed settlement and measured settlement can help to calibrate the soil modulus which best matches the settlement measurements. In this article, a probability analysis based on a database of 315 shallow foundation settlement records on sand “TAMU-SHAL-SAND” is presented. The foundation width in the database varies from 0.30 m to 135 m with a mean of 7.76 m and a standard deviation of 9.42 m. The SPT N values are between 2 blows per foot (bpf) to 60 bpf with an average of 23.68 bpf and a standard deviation of 13.26 bpf. Using the database, scatter plots of predicted vs measured settlement are presented. In addition, a probability plot is presented with the probability that the predicted settlement will be less than the measured settlement on the vertical axis and a prediction multiplier on the horizontal axis. The results can help the practitioner decide at which level of probability to operate. The data show that using E (kPa) = 1,000 N(bpf) give a settlement which has a 90% probability of being larger than the measured settlement.

Calculation of immediate settlement plays a very important role in the design of foundations and geostructures when they are supported in granular soils. Soil strength and stiffness mechanisms associated with immediate settlements can be studied via full-scale load tests following Schmertmann (1993) conical load test method, which has been proven successful and practical to study settlements in granular soil deposits. The test consists of constructing a conical mound of granular fill placed at its angle of repose to create an approximate 12.3 m diameter 4.2 meter-high cone. This paper presents first the site characterization of a site near the University of Central Florida campus mainly in terms of CPTs, SPTs, and DMTs. These tests were used to calibrate constitutive soil model parameters for finite element models intended to recreate the conical load sequence. Numerical simulations using hardening soil and hardening soil enhanced with small strains constitutive models were developed to simulate the loading sequence of a Schmertmann conical load test and draw conclusions regarding the variables involved in the problem: stiffness and construction sequence of the conical loading, stage construction sequence of loading, relative density and stiffness of supporting granular soils, and horizontal influence zones.

An existing building in California is being structurally modified. As part of the project, new foundations will be constructed adjacent to existing foundations. The level of groundwater is at the base of the foundations. During excavation adjacent to existing footings, cracks appeared on several columns. Survey data indicated that there was no measurable vertical movement of the columns or footings (within the tolerance of the survey), but the columns/footings moved 1/8 inch horizontally toward the excavation. A conclusion was reached that a small rotational movement of the footings occurred due to the excavation adjacent to the footings: the rotational movement induced shear stresses within the columns, resulting in diagonal cracks on the face of the columns. The excavation was completed and immediately backfilled with concrete. Crack gages were installed on columns and indicated that the movement ceased after the initial cracking. A comparison is made of the observed movement and the mechanism that would be expected in a conventional bearing capacity evaluation. In addition, the mechanism of translation of movement of the footing is evaluated relative to the observed deformation and cracking of the column. It is concluded that the observed movements are indicative of deformation consistent with conventional bearing capacity theory, despite a sufficient factor of safety being preserved during the construction activities.

This study offered a novel method for characterizing the soil support in slab-on-grade constructions such as rigid pavements and raft foundations. The method applies to slabs that are instrumented with fiber-optic cables for distributed strain sensing; it is based on analyzing the spatial profiles of slab bending strains generated by randomly applied surface loads. The concept was demonstrated for a synthetic case involving an infinite plate resting on a Pasternak support model. The method was shown to deliver non-destructive, non-disruptive, and load-independent quantitative information on the prevailing soil support. Therefore, it is deemed well suited for long-term health monitoring applications of slab-on-grade constructions. Such monitoring can help facility owners evaluate and intercept external events that undermine the integrity of the structure. In the long-term, continued monitoring of soil support can help the engineering community improve analysis approaches and design decisions concerning soil-structure interaction.

Most marine structures tend to use deep foundations. However, using shallow foundations would be a more cost-effective alternative for some situations, especially for subsea infrastructure. An important factor in the general bearing capacity equation is the shape factors. In this study, the effect of different footing shapes on the bearing capacity of marine soft clay was investigated, with the aid of a transparent soil that permits visualizing deformations within it. Five shapes having the same cross-sectional area and the same material properties were used. The marine soft clay was simulated by a synthetic transparent soil made of magnesium lithium phyllosilicate (MLPS). The undrained shear strength was measured using a miniature ball penetrometer. An embedded seeded plane was employed to track soil movements. Those movements were captured by a high-speed camera, and the resulting images were analyzed using digital image correlation (DIC) methods (aka. PIV). The internal shear strain was determined during different stages of loading. The failure stage was observed through the image analysis and the failure mechanism could be observed. The shape factor for each footing was determined based on the general bearing capacity equation and the ultimate load measured. A comparison between the results and traditional shape factors in common use supports the validity of shape factors proposed by Terzaghi or Meyerhof for marine foundations supported by very soft clay soils.

Settlement of structures built on soils is a subject of considerable interest to practicing engineers since excessive settlement is one of the most important problems in soil mechanics and can lead to serviceability problems or even failure states in the structure‘s foundations. Even though immediate settlement calculation is an important step in evaluating the usage of shallow foundations in cohesionless soils for bridge foundations, differential settlement, and angular distortion are the most effective parameters for the evaluation of bridge foundations. In this paper, the performance of six settlement prediction methods for spread footing foundations is verified by using compiled field data from research projects. Vertical settlements were measured on 20 footings (yielding 10 measurements of differential settlement) from seven bridges in the Northeast U.S. and one bridge in Ohio. The settlement prediction methods selected for settlement calculations for the spread footings on cohesionless soils for each footing site are compared with measured settlement values. The standard penetration test (SPT) is considered in this study for the selected settlement prediction methods. Statistical parameters corresponding to each of the six settlement prediction methods for both differential settlement and angular distortion are evaluated and summarized. The study shows considerable differences in accuracies for the six selected prediction methods. It can be concluded that two prediction methods showed better results than the others. In addition, the distributions of differential settlement for the two selected prediction methods for shallow bridge foundations are examined.

A new primary crusher was built for a copper mine expansion project in the Peruvian Andes. The crusher is housed in a new reinforced concrete structure supported on a 1.8-m thick mat with rectangular plan dimensions of 19 m×38 m. A mechanically stabilized earth (MSE) wall of 30 m height was built around 3 sides of the crusher to facilitate the dumping of rock materials for crushing. A settlement monitoring system was installed on the crusher foundation, and monitoring started when the MSE wall was 10 m high. The new crusher settlements were roughly estimated using the average anticipated loading on the crusher foundation prior to construction. The foundation soil parameters were extracted from SPT blow counts obtained from a hammer with non-standard weight. The measured settlements were smaller than the estimated. In this paper, the settlement calculation was performed using 3D simulation and it considered the MSE wall and crusher loading on the crusher foundation. The calculated settlements from 3D modeling are compared with the measured ones, and they are in reasonable agreement in four corners of the crusher foundation.

The response of soft clays reinforced with single granular columns has been the subject of a number of laboratory-scale and triaxial experimental programs in the past. However, given that granular columns are seldom designed and/or constructed as individual elements, there is a clear need to identify and quantify group effects. The objective of this study is to cater for this need by designing and implementing a triaxial testing program in which soft clay specimens, 14.5-cm in diameter and 29.5-cm long, are reinforced with multiple sand columns and tested in a consolidated drained triaxial setting. Results indicated that at area replacement ratios of 17% and 30%, there was an increase in the ultimate strength of the specimen by 12% and 43%, respectively. It was also shown that stress concentration ratios in the range of 4 to 6 could be mobilized at very low strains. It is anticipated that results from the tests completed in the study will facilitate the development/improvement of design methodologies of soft clays that are reinforced with sand column groups.

This paper presents a comparative study of stabilization of expansive soil using lime pile and lime precipitation technique. Lime precipitation was carried out by sequential permeation of calcium chloride (CaCl₂) and sodium hydroxide (NaOH) solutions through a central hole in the compacted expansive clay. Similarly, lime pile was installed in a central hole of compacted expansive soil. After 30 days of curing, the undisturbed soil specimens were collected from different radial distances for evaluation of physico-chemical, index, and engineering properties. Microstructural changes were captured using scanning electron microscopic (SEM) images and electron dispersive X-ray spectroscopy analysis (EDAX) for both treated and untreated soils. The index and engineering properties of treated soils indicate that the lime precipitation treatment was effective up to a radial distance of 2.5 d from the central hole of diameter, d, while the lime pile treatment was limited to a radial distance of less than 0.8 d.

While using rigid elements to reinforce a soft soil is not a new idea, it was only widely introduced in the North American market about 15 years ago and has gained wide acceptance only in the last few years. It has now been successfully used across the country for very different types of soil profiles and structures. The technique consists of associating a network of vertical rigid inclusions (R.I.—typically made of concrete) primarily installed using a displacement tool with a granular compacted layer (load transfer platform—L.T.P.). Together with the soil surrounding, the inclusions and the load transfer platform create a ground improvement system for all types of structures from buildings, embankments, MSE walls, slabs, rafts, to tanks, and more. This foundation system reduces overall and differential settlements, increases allowable design bearing capacity, and in some cases mitigate liquefaction. This paper will briefly describe the different techniques available in the marketplace for installation of rigid inclusions, the overall theory behind the design of the rigid inclusions ground improvement system, and give an overview of different actual applications of rigid inclusions in various types of soils and for various types of structures with results of long-term monitoring.

Newly dredged clay is commonly hydraulic mud that contains a large amount of fine soil particles and has a higher water content. The dredged clay is often times too soft for the surcharge to be applied. Vacuum preloading technology can be an attractive technology rather than surcharge preloading. In order to better apply vacuum preloading technology to dredged clays, it is necessary to establish a large strain consolidation model. Based on the Gibson‘s one dimensional large-strain theory and Barron‘s free strain theory, and abandoning the equal strain assumption, introducing the negative pore water pressure boundary condition, a large strain consolidation model is established by incorporating the radial and vertical flows and the weight of the soil. The material nonlinearity is considered in the large strain consolidation model. It is found that the nonlinear compression and nonlinear permeability have the significant influence on the consolidation effect. In addition, the large strain vacuum consolidation model is compared with the small strain degradation consolidation model, the two models differ greatly in excess pore pressure dissipation and degree of consolidation. The large strain vacuum consolidation model must be taken into account in the prediction of vacuum preloading effect of dredged clays.

Microbially induced calcite precipitation (MICP) is a bio-mediated soil improvement technique that uses ureolytic bacteria to enable calcium carbonate precipitation. A meter-scale study was performed to investigate knowledge gaps critical for implementation at field-scale, including controlling spatial uniformity, managing ammonium by-products, and minimizing material and energy usage. Three 3.7-meter long columns contained the same alluvial sand and were treated with three different treatment protocols. Two columns received different solutions intended to stimulate native ureolytic microorganisms and a third column was augmented with Sporosarcina pasteurii to investigate the effect of ureolytic activity on cementation spatial uniformity and extent. During treatments, shear wave velocities, hydraulic conductivities, and aqueous solution chemistry were monitored. Following treatments, rinse solutions were applied to all columns to remove ammonium by-products and soil samples were obtained. Results show that stimulation techniques may improve the extent and uniformity of precipitation at meter-scale when compared to the augmentation approach.

In the past decades, efforts have been made to substitute cementing material for the Portland cement by using industrial byproduct such as ground granulated blast slag (GGBS), from the iron production process. When GGBS is reacting with different alkali-activators, alkali-activated slag (AAS) can produce binding material to filling the gap between aggregates. By adding biochar to the AAS system, the extremely porous structure of biochar enables to reserve water inside and release the water as the hydration process goes on. The gradual release of water can improve the hydration degree of AAS, leading to enhanced mechanical and durability performance. In this study, the admixture of GGBS, hydrated lime, and biochar was applied to stabilize the calcareous sand. The strength of the biochar-enhanced AAS stabilized calcareous sand was measured. The results showed that with the addition of biochar AAS, the stabilized soil doesn‘t compromise on the strength and even shows higher strength in some cases.

The 2001 Nisqually earthquake demonstrated the seismic vulnerability of the Elliott Bay Seawall in downtown Seattle. The Project is to replace a critical portion of the seawall with a seismically stable structure. A key component of the project is to install over 5000 jet grout columns landward of the new seawall as a mitigation to the liquefiable soils. At the early part of the construction, the jet grouting induced significant ground movement and heave, resulting in instability of adjacent structures. A full-scale field test program was conducted to evaluate the jet grouting in the field. The test consisted of monitoring grouting installation methods, pore water pressures, and lateral ground deformations. The paper presents some key findings and conclusions from the investigation, including (1) the jet grouting pressures under varying field conditions and the resulting ground movements, (2) derivation of the rational jet grouting load criteria for design, (3) evaluation of the ground stability walls during jet grouting, and (4) mitigation measures implemented to ensure stability of the adjacent structure and shoreline.

Deep mixing method (DMM) is a ground stabilization technique using lime or cement binders. The DMM has gained increasing applications to minimize ground settlements and increase stability to support structures. However, this ground improvement technique has not yet been used extensively in Manitoba. For the effective design of DMM, mixtures of cement, clay, and water that would produce optimal strength and stiffness are generally determined through laboratory tests. A total of 120 unconfined compression tests were conducted at different amounts of cement in the admixtures, water-cement ratio, and curing periods were conducted on Lake Agassiz clay frequently found in Manitoba. The results were compared with those of Champlain clay found in Ontario and Quebéc and Ariake clay in Japan where extensive data are available. This paper discusses the outcome of the comparison. It was found that the improvement effect of Lake Agassiz clay by DMM is an effective means to increase the strength.

This manuscript presents the stabilisation of black cotton soil (S) with red mud (RM), a by-product of the aluminium industry. The basic geotechnical properties including unconfined compressive strength, swelling pressure, and California bearing ratio test of virgin soil and soil stabilised with red mud have been performed. Strain controlled cyclic triaxial tests on virgin clay samples and soil stabilized with red mud have been carried out at various shear strain amplitudes and at an effective confining pressure of 100kPa. The compressive strength test indicates the increase in strength of treated soil is about 20 to 55% to that of untreated soil for 0, 7, and 28 days of curing periods. California bearing ratio of the optimum mix is found to be increased by 18.5% to 27.30% to that of untreated soil. The suitability of black cotton soil stabilized with red mud for subgrade pavements has been discussed.

Soil-cement columns constructed by the deep mixing method (DMM) can effectively improve soft soil profiles for support of overlying structures. The soil-cement material can have highly variable strength properties resulting from a large number of factors. The difficulty in linking specific factors to soil-cement strength properties makes a reliability analysis using a Monte Carlo simulation approach appropriate. This paper investigates the effect of autocorrelation distance of strength properties on the overall stability of an embankment supported by soil-cement columns. Gaussian random fields of cohesion values are generated in MATLAB to be used in a FLAC finite difference model. Monte Carlo simulations are conducted to produce cumulative distributions of safety factor of the model for two autocorrelation distances. The resulting safety factors are compared and used to demonstrate a statistically significant difference in mean safety factors for different autocorrelation distances. The results suggest that the safety factor may decrease as autocorrelation distance reduces, indicating that deterministic analyses (i.e., as autocorrelation distance goes to ∞) may be unconservative for columns with high variability.

A thick, compressible, high plasticity, alluvial silt deposit along the Delaware River in Philadelphia, required surcharging to facilitate a shallow foundation system. A 10-ft high embankment was constructed across the building pad after installing prefabricated strip drains to expedite the consolidation process. A new mechanical room, which was added after completion of the strip drains, required 20 ft of fill to complete the consolidation at the same time as the rest of the building area. The preloading program was monitored using vibrating wire settlement sensors and drive point piezometers for 6 months and post-surcharge verification tests were also carried out for added assurances ahead of starting construction. The verification tests included standard penetration tests (SPT), cone penetration tests (CPT), flat dilatometer tests (DMT) as well as collecting undisturbed Shelby tube samples for laboratory consolidation testing. The post-surcharge laboratory tests demonstrated a significant increase in preconsolidation pressure or maximum past stress (p'_c). Of the in situ verification tests, however, only the dilatometer test captured the increase in p'_c consistent with the laboratory consolidation test, and none showed an increase in the undrained shear strength due to surcharging.

Soil erosion leads to extensive environmental problems and comprises the serviceability of infrastructure, such as bridges. An environmental friendly method to improve soil erosion resistance is highly desirable. This study investigated the performance of a filamentous fungus, Pleurotus ostreatus, to improve soil erosion resistance. Experimental results indicate that fungal mycelium fiber and exo-polymers improve the soil particle adhesion and the fiber filaments act as soil reinforcements; both improve the soil erosion resistance. Besides, the hydrophobic surface of fungal mycelium reduces the erosion force by flowing water due to a slipping effect at the interface between water and soil. Consequently, fungi demonstrates unique performance in improve the soil erosion resistance.

This paper presents the soil-structure interaction, particularly negative skin friction, of the rigid inclusion columns over a 3.5-year monitoring period. In order to understand the fundamental behavior of rigid inclusions, typical deep foundation and drilled displacement pile approaches were adopted in the analyses. First, the load test results were interpreted to determine the axial capacities and moduli of the rigid inclusion columns. Then, the estimated moduli were used in conjunction with embedded strain gage data in obtaining the axial load distribution profile along the columns from the end-of-construction to post-construction periods, spanning over several years. The strain profile shows that negative skin friction and the neutral plane location progressively developed over time at every instrumented column. Based on that, the neutral plane locations appear to be at 1/2 of the column length, where a stiff clay layer is located. By matching the interpreted loads with the effective stress approach, it was found that the measured β (= K tan δ) could range from 0.6 to as high as 2.8, assuming 80% and 20% of load transfer on upper and lower soil layers, respectively. Theoretical β values were also checked against the measured β. It was found that the ratio of K/K_o arriving at these values was approximately 2.0.

This paper presents a systematic investigation to study the behavior of geogrid-encased stone columns in soft soil under embankment loading. A 3-D finite element model of the embankment was employed to carry out a parametric study on factors like encasement stiffness and encasement length. The result shows significant improvement in terms of settlement reduction, excess pore water pressure generation, and lateral deformation of the column along its length. This study reveals that for the chosen configuration, column encased with geogrid encasement having stiffness beyond 5000 kN/m has an insignificant effect on the performance. Moreover, there is no any substantial improvement beyond encasement length $\left(\zeta =L_{GESC}/L_{OSC}\right)$ of 0.80. It is interesting to note that the failure profile of the column is different at different locations. Encasing the column is beneficial both in reducing the bulging and bending of the column.

Enzyme induced carbonate precipitation (EICP) is a bio-cementation technique and is a new area of Geotechnical Engineering. In this paper, a parametric study was conducted to evaluate and optimize the effect of concentration and activity of urease enzyme and concentration of other chemical constituents (urea and calcium chloride) on EICP process. pH, electrical conductivity (EC), and micro-structure analysis using scanning electron microscope (SEM) imaging were performed. Results indicate that, the precipitation ratio (PR), which is defined as the ratio of mass of precipitated CaCO₃ in test tube and theoretical mass of CaCO₃ is a function of the concentration of urea-CaCl₂ (mol/L) and urease enzyme (kU/L). Rate of change in pH and EC during urea hydrolysis is influenced by urea and urease enzyme concentration. SEM images of CaCO₃ precipitates from solution containing low active urease enzyme (3,500 U/g) showed a disordered and anhedral calcite crystals whereas the high active urease enzyme (40,150 U/g) showed euhedral and agglomerated rhombohedral calcite morphology.

Soil carbonation—the process of introducing carbon dioxide gas and an alkali mineral in soil—is a potential alternative to chemically strengthen subgrade materials by cementing the soil matrix. In this study lime (alkali source) was mixed with non-plastic silty sand to investigate the influence of fine content (0, 20, 50%), lime content (1 and 10%), and the carbonation period (3 and 24 hours) on the unconfined compressive strength of elemental soil specimens. Thermogravimetric analyses on select specimens verified that changes in unconfined compressive strength arose due to the carbonation process. Unconfined strengths increased with fine content, lime content, and carbonation period. The fine content and lime dosage had a greater influence on the ultimate strength than the carbonation period, indicating the chemical reaction occurred quickly at the elemental scale. Unconfined strengths up to 1,000 kPa were achieved for silty sand with a 50% fine content, 10% lime, and carbonation period of 24 hours. Approximately 70% of this strength was achieved for a carbonation period of 3 hours for the same soil and lime content. Unconfined strengths no greater than 250 kPa were achieved for specimens tested with lower fine contents.

A site with favorable wind condition may not have suitable subsurface condition for building tall wind turbines. In such situation, it may be economical to improve the subsurface properties to gain net economic advantage. In this study, the effectiveness of ground improvement to support an 80 m tall wind turbine on a piled-raft foundation was investigated using analytical and 3D finite element methods. First, analytical designs were conducted to determine the length of the piles for the assumed raft and pile size and number of piles to meet the safety and serviceability requirements. Three different depths of improvements were considered in the design. Then, 3D FE models of the piled-raft foundations and supporting soils were created and analyzed using ABAQUS. In the FE modeling, the lateral distance was varied in addition to the depth of ground improvement. Both methods show that significant economic advantage can be achieved by improving the ground.

Desiccation cracks in clayey soils when subjected to rainfall events can possess a serious threat to the stability of earthen structures, including embankments, dams, and levees. This research study demonstrates the use of polydimethylsiloxane (PDMS) polymer and plate-like nano-montmorillonite (MMT) in evaluating the desiccation crack formation and healing efficiency in kaolinite-rich soil and a Western South Dakota soil. Laboratory studies were performed to characterize the soils, and engineering tests were performed on the control soil and treated soils containing different percentages of polymer and nano-MMT additives to investigate the cracking-healing phenomenon. The results indicated that the addition of the additives led to substantial changes in crack formation, propagation, and increase healing efficiency. Threshold values on the percentage composition of the polymer and nano-MMT were established. This research highlights the adaptability of novel polymer and nano-MMT additives in relegating the cracking initiation and propagation with self-healing of the desiccation cracks.

Lignosulfonate, a co-product of paper pulp production, has been traditionally used for dust suppression. Over the last decade, a few laboratory studies have reported soil stabilization with lignosulfonate, yet there has been very limited field practice to serve as application of the corresponding laboratory outcomes. In this field demonstration, diluted ammonium-based lignosulfonate was sprayed on a gravel road subgrade with the goal of improving the subgrade‘s strength and durability. In situ tests and documentation were conducted at different periods of the construction to monitor seasonal performance of the stabilized section and to draw lessons learned from the practice. Light-weight deflectometer (LWD) tests and the dynamic cone-penetration (DCP) tests were performed before, one week after, and six months after, the construction. The construction process was documented both visually and in written form. Some critical lessons learned from this demonstration provide recommendations for future studies and benefit relevant practitioners.

The resilient modulus (M_R) is regarded as an important stiffness parameter for pavement design. Determining the M_R of expansive subgrades is critical because of their high swell-shrink potential. Lime stabilization has been adopted to treat expansive subgrade soils in North Texas for decades. Due to severe greenhouse effects of lime use and production, an alternative to lime stabilization has gradually emerged. A liquid ionic soil stabilizer (LISS), an environmentally friendly soil stabilizer can be used as an alternative soil stabilizer for its significant effect in enhancing soil stiffness and strength. However, engineers are still reluctant to accept the use of LISS because of the proprietary patent and limited literature review. In this study, the M_R of expansive soils before and after LISS treatment was evaluated in the laboratory. The LISS used is composed of sulfuric acid, phosphoric acid, surfactant, and water. LISS was diluted in water to treat expansive soils and the soils were cured for 7 and 28 days. The experimental M_R results of expansive soils treated with LISS were validated by comparing them with the results of the M-EPDG model and Ooi et al. (2004) model.

Bio-inspired improvement of soils via enzyme induced carbonate precipitation (EICP) has attracted increasing attention over the past decade. EICP employs the hydrolysis of urea (ureolysis), a process catalyzed by the urease enzyme, to precipitate calcium carbonate (CaCO₃) in the presence of calcium ions. This paper describes a preliminary experimental study on improvement of sand shear strength through the use of EICP along with sodium alginate biopolymer for surficial soil applications. In this research, the sodium alginate biopolymer was used to evaluate the ability of the biopolymer hydrogel to improve EICP by holding the reaction substance around the soil particles. Unconfined compression strength (UCS) test of the treated soils was measured to evaluate enhancement in soil strength. Scanning electron microscope (SEM) imaging was conducted to study the microstructure and identify the presence of crystalline materials in treated sand samples. The results indicate that the incorporation mix of EICP and SA significantly improved the UCS compared to the samples treated with only EICP. The improvement is mainly attributed to the inter-particle bonding effect of both carbonate precipitant and biopolymer.

The thermo-mechanical behavior of saturated clays during a heating/cooling cycle is relevant from the perspective of understanding different types of energy geostructures as well as understanding the use of heat for soil improvement. This paper involves a study of the effect of a heating/cooling cycle on the preconsolidation stress of saturated normally consolidated clays. Although many studies have observed a decrease in preconsolidation stress (thermal softening) after heating of overconsolidated soils, fewer studies have investigated changes in preconsolidation stress of normally consolidated soils. Available thermo-elasto-plastic models indicate that a heating-cooling cycle will lead to thermal contraction and an apparent overconsolidation effect for normally consolidated soils (thermal hardening), but inconsistencies in the literature have been observed. This study involves the use of a thermal triaxial cell to first consolidate kaolinite clay to normally consolidated conditions, apply a drained heating or a heating/cooling cycle, followed by mechanical loading to higher mean effective stresses. The tests presented in this study confirm that cooling also induces an apparent overconsolidation effect on the initially normally consolidated clay, but with a preconsolidation stress greater than that expected from the initial virgin consolidation line before heating. The results are a positive finding regarding the possible use of heat to improve the mechanical response of soft clays.

Low-density cellular concrete (LDCC) was first introduced to the market in the early 1900s and since then has made continuous technological advances. There are two primary types of LDCC: permeable and non-permeable. Both types of cellular concrete offer advantages in different types of geotechnical engineering applications. Because of its unique characteristics of low density, high compressive strength, and high fluidity during placement, LDCC offers an effective solution for a wide variety of engineering applications, and in many cases provides a more cost-effective, labor saving alternative to traditional fill materials. This paper will review the history, characteristics, and technological advances of LDCC, highlighting multiple real-world case studies that showcase the high-performance capabilities of both permeable and non-permeable LDCC.

The present work explores the potential of bio-enzymatic stabilization on two types of soil with extreme characteristics namely, black cotton soil and lateritic soil. Bio-modification was achieved by blending the selected soils with terrazyme. To assess the permanency in strength laboratory tests were carried out for two different dosages (150ml/m³ and 250 ml/m³) as well as curing periods (7, 14, and 28 days) and the results compared. The current work concentrates in understanding the variation in UCS, bearing ratio values, secant modulus, and improvement factor of enzyme treated soils with respect to ageing. In case of bio-modified black cotton soil the improvement factor increased up to 216% when compared with that of laterite soil. Further, the experimental results also indicated that bio-modification was more effective at lower enzyme dosage and increased curing periods. From the experimental investigations the potential of enzyme in achieving economic feasibility was also comprehended.

Sewage sludge is a by-product of wastewater treatment and is typically dewatered and incinerated to reduce its volume prior to landfill disposal. As the residue of incinerating sewage sludge, sewage sludge ash (SSA) can potentially be used in a number of alternative applications depending on its pozzolanic activity. This study first examines the pozzolanic activity of a SSA from a local wastewater treatment facility, Delaware County Regional Water Quality Control Authority (DELCORA) located in southeast Pennsylvania. The SSA was then investigated for possible use for soft soil stabilization. Various dosages of SSA (5%, 10%, 15%, 20%, 25%, and 30%) were utilized to quantify the pozzolanic activity of mortar mixtures. The SSA was found to be capable cementitious material at a dosage up to 10%. The SSA was then mixed with kaolinite clay to investigate its potential for soil stabilization. Unconfined compression strength tests were conducted on control and SSA-stabilized kaolinite clay.

A section of Interstate 95 in Philadelphia, Pennsylvania, was to be widened, requiring new construction of abutments, wing walls, and retaining walls. The overburden consisted of surficial soft/loose alluvium overlying very dense sands and gravels. Jet grouting ground improvement was initially specified to provide acceptable performance of shallow foundations for the proposed structures. However, the relatively small work zones and close proximity to adjacent structures would be problematic for jet grouting operations. An alternative design which featured lightweight cellular concrete backfill was subsequently developed. The premise of the design alternative was to provide a structure that was light enough to minimize vertical deformation and yet heavy enough to provide overturning and sliding resistance required for adequate stability. This paper discusses the developed methodologies used in the design alternative, construction of the design alternative, and results of a settlement monitoring program.

Increase in the moisture content directly affects the geotechnical behavior of all types of soil. Loess is one of the most vulnerable types of soil to the high moisture content conditions in which it can trigger a drastic soil volume reduction. This study shows how the electrokinetics technique, as an innovative in situ solution that changes the physiochemical properties of soil, can contribute to the improvement of Illinois loess collapsibility. For this purpose, undisturbed samples of Illinois loess were collected and remediated by the electrokinetics technique using two different stabilizer agents (nanosilica and salt) in the laboratory. According to the results of standard collapse potential measurements, the efficiency of this method at three different maximum vertical stresses were evaluated. It was observed that the electrokinetics technique is able to significantly decrease the collapse potential of Illinois loess. However, the extent of improvement was not equal for different stabilizer agents at different maximum vertical pressures.

A parametric study that employed the finite element method was performed with the purpose of examining the lateral load response of stiff column-supported footing systems. The influence of different geometry-based variables in their lateral response was examined. The results of the parametric study, presented in the form of the average of the absolute values of the percent changes, showed that the thickness of the load transfer platform, a granular mattress placed above the soil-column composite, was the geometry-based variable with the greatest influence in the lateral response of the stiff column-supported footing systems examined with an average of 47.25%. The geometry-based variable with the least influence was the stiff column spacing with an average of 3.36%.

Twenty years ago, most buildings in the United States were supported by either shallow spread footings or deep foundations. Since then, “intermediate” ground improvement options have increased in use, providing building owners, contractors, and engineers with a host of options each with its own unique design and construction characteristics. Loose sands are now often densified, and soft cohesive soils are reinforced with displacement or replacement aggregate piers prior to shallow foundation construction. For heavier loads and softer soils, the subsurface materials are often now reinforced with “rigid inclusions”, typically consisting of cementitious columnar elements installed by either driven-displacement or drilling methods. Organic soils, such as those typically found in New England, the Upper Midwest, and the Pacific Northwest almost always require “improvement” prior to shallow foundation construction because of their inherent compressibility under even small loads. In certain conditions, the organic materials can be reinforced by non-cemented aggregate piers, provided care is used in the appropriate selection of pier stresses to avoid the pier “bulging” and long-term settlement performance issues. In other conditions, such as when the thickness of the organic soils is large, when the loads are heavy, or when the consequences of settlement are severe, more robust solutions, such as those provided by rigid inclusions are necessary. This paper provides the results of multiple case histories in which organic soils have been reinforced by both confined aggregate and cemented ground improvement elements.

Cement permeation grouting is a soil improvement method applied to increase the strength of a soil body and/or lower its hydraulic conductivity. This method is particularly useful in cases where surface access is limited and where soil disturbance cannot be tolerated, for example when improving soil below an existing structure. Cement permeation grouting has been extensively studied and our understanding of the mechanisms controlling its successful application has improved remarkably over the past decades. However, most of the performed studies consider homogeneous porous media, and understanding the effect of soil heterogeneity on grout propagation is still lacking. In fact, soil heterogeneity is often considered a limitation when trying to apply lab test results to field applications. This paper introduces a 2D grouting setup to research grouting of heterogeneous layered soils. The paper presents preliminary test results demonstrating the effect of soil heterogeneity on grout flow compared to flow in homogenous soils.

Low mobility grouting (LMG) was used to improve the condition of limestone bedrock to support the foundations of a single span bridge in Northampton County, Pennsylvania. Test borings showed the presence to extensive solution activity in the upper rock strata, which was found not suitable for foundation support without improvement. After alternative analysis, it was determined that the preferred foundation system is the improvement of the upper rock strata using LMG. The LMG treatment area was selected as the footprint of the foundation, plus an “allowance” for effective distribution of bearing stresses into the deeper rock mass. Primary and secondary injections were spaced in grid pattern and supplementary injections were added in areas where the distance to the nearest grout hole was excessive. A total of 271 holes were proposed with a design treatment depth of 4.5 m below proposed bottom of footing (BFE). Four verification borings were drilled, two at each abutment, after completion of the 271 injections. Six additional injections were added based on the result of the original injections and the verification borings. The LMG program was designed to achieve a target rock recovery required for foundation support for this bridge. The paper summarizes the construction aspect of spread footing on bedrock improved by LMG in karst and verification of bearing improvement after the LMG. The paper discusses related aspects of the project, including the subsurface conditions, LMG design, and other challenges that were specific to this project. The paper will document how the design was actually implemented and verified, plus the adjustments that were needed to in the field to achieve the goal. This project showed that LMG can be successfully used in karst with proper inspection and on-site adjustment to address variation of subsurface conditions.

Grouting is a frequently used technique for controlling the water inflow and reinforcement of soil and rock. Even though cement-based grouting materials have been well characterized, ongoing improvements of chemical grouting materials create a need to understand the characteristics of these materials in order to increase the efficiency of grouting applications. The purpose of this study is to characterize the selected three common chemical grouting materials by exploring their mechanical performance under varying initial soil conditions. Decision criteria consist of the UCS and slake durability test results, observation of penetration ability, and comparison of the findings. The three chemicals used were acrylate, colloidal silica, and polyurethane. Test specimens were prepared with two different sand gradations and two different initial moisture contents, which were compacted to the same constant density. Cylindrical test specimens were injected using a constant and predetermined injection pressure. Injected specimens were moist-, air-, and wet-cured for 28 days. Thereafter, the specimens were tested, and the stress-strain relationships were developed. Slake durability tests were conducted to characterize the durability of chemically grouted sands subjected to wetting-drying cycles. The results of this study showed that initial grain size and fine content of the soil influenced the resultant strength for acrylate and colloidal silica grouting ma. On the other hand, initial moisture content of soil was solely effective on UCS of acrylate grouted sand. This study found that the effect of wetting-drying cycles on durability was minimum for the polyurethane grouted sands. It may be concluded that use of polyurethane in medium sands and use of acrylate in fine sands can be more effective than the use of acrylate, and colloidal silica for medium sands and the use of polyurethane, and colloidal silica for fine sands.

Erosion rate of soils during a levee or dam overtopping event is a major component in risk assessment evaluation of breach time and downstream consequences. The mechanism and evolution of dam or levee breach caused by overtopping erosion is a complicated process and difficult to measure during overflow due to accessibility and quickly changing conditions. In this paper, the results from flume erosion tests are presented and discussed. The tests were conducted in a 1-m (3-ft) wide flume on four gravel mixes with a median grain size D₅₀ of 5 mm and varying fines content. Each soil sample is prepared by compacting the soil mix near maximum dry density and optimum water content in a box embedded in the flume floor. The box measured 0.45 m wide×1.2 m long×0.18 m deep. A shallow water lidar (SWL) system is utilized to record the evolution of soil erodibility and water depth along the scanned profiles of the test box parallel to the direction of the flow. SWL is a noncontact system that transmits laser pulses from above the water and records the time-delay between top and bottom reflections. Results from the SWL scans indicated that the erosion rate reduces significantly over the duration of the test. This is due to the changes in the hydraulic loading, and also due to the effect of the fines content and large particle size of the mix. Higher fines and clay content results in a lower initial erosion rate, while larger maximum particle size results in a lower erosion rate at the same acting bed shear.

Since its establishment in 1991, Hydraulic Engineering Circular (HEC-18) has been the primary tool for United States transportation agencies to evaluate bridge scour. The empirical relationships in HEC-18 are based on cohesionless soils and have been proven to be overly conservative cohesive soils. To incorporate the scour behavior of cohesive soils in the design manual, the Federal Highway Administration recently developed a scour prediction model for cohesive soil. However, the new model is valid for a very narrow range of cohesive soils, focusing mainly low plastic silts and clays. The objective of this study was to determine significant soil properties that affect the critical shear stress (exerted by the flowing water on soils) for the onset of erosion using a broader spectrum of cohesive soils. A total of 71 soil samples from 27 bridge sites were used for this study. Erosion testing was performed in the erosion function apparatus and soil properties were measured in the field and laboratory for obtaining different variables. Among the various soil properties, percent fines, liquid limit, and electrical resistivity were found to be statistically significant variables for predicting the critical shear stress. For the 71 samples used in this study, liquid limit varied between 26 to 80, plasticity index between 3 to 52, and percent fines between 11 to 100. Therefore, the variables that were found statistically significant in this study can be utilized to build a comprehensive model for critical shear stress, applicable for a broader range of cohesive soils.