Journal of Geotechnical and Geoenvironmental Engineering

A fully instrumented experiment was conducted to investigate the soil-structure interaction of single short, stiff laterally loaded piles. A hollow steel pipe pile with a diameter of 102 mm, a thickness of 6.4 mm, and a length of 1.524 m was installed in well-graded sand and subjected to increasing lateral load. The pile and surrounding soil were fully instrumented using advanced sensors, including flexible shape acceleration arrays, thin tactile pressure sheets, and in-soil null pressure sensors. The sensors attached to the pile were used to develop the compressive soil-pile interaction pressures and the lateral displacement along the pile length. The tactile pressure sheet sensors provided the soil-pile interaction compressive pressures on the circumference of the pile at a specific depth and along the length of the pile. The measured soil-pile interaction compressive pressures combined with the measured lateral displacement along the pile length were used to develop the soil-pile interaction force-displacement relationships ($p\text{-}y$ curves) using direct measurements. In addition, the in-soil null pressure sensor measurements were used to develop the distribution of horizontal stress changes around the pile as the lateral pile displacement increased. When appropriate, the measured results were compared with data and methods available in the literature.

The influence of time-dependent concrete behavior on the performance of top-down excavations is evaluated in light of the observed responses during construction of One Museum Park West (OMPW), a 53-story reinforced concrete tower. Performance during construction was recorded at five instrumentation stations, which included strain gauges in the concrete floor slabs used as lateral bracing during the top-down excavation sequence and inclinometers adjacent to the walls. Top-down construction was simulated with a 3D numerical model of the basement system in which concrete material time-dependent effects were considered, but not the stress relief caused by excavation or other construction activities. Time-dependent concrete response in the floor slabs and the passive resistance developed by the soil as the wall deforms due to concrete time-dependent effects are included in the model. The concrete time-dependent properties related to shrinkage, creep, and aging of the material used in the basement floor slabs are determined by means of standard concrete practice methods. The development of concrete strength and stiffness with time is compared with compressive strength tests on concrete cylinders from construction concrete reports for the concrete used in the floor slabs. Computed lateral deflections of the perimeter pile walls and strains in the floor slabs arising only from concrete material time dependence are compared with the results of performance data collected from inclinometers and strain gauges installed at five instrumentation stations. In this way, the relative contribution of concrete time-dependent effects and excavation-induced movements to the observed lateral wall movements during the top-down stages are determined and conclusions are drawn concerning the design and performance of the top-down support system at OMPW.

The Natomas basin is a 21,450-ha area north of downtown Sacramento, California. The developed area relies on levees for flood protection along its perimeter. The western boundary is a 29.9-km-long levee that protects the area from flooding by the Sacramento River. Since its construction over a century ago, this levee has experienced a myriad of performance issues. From 2008 to 2011, a team of engineers completed design and construction of remedial measures with the objective of ending the historic performance issues. Along one stretch, the Sacramento River and levee make a sharp bend at a constant levee radius of approximately 515 m. During the design processes, the levee was analyzed using a two-dimensional plane strain model despite this relatively sharp convex bend. This paper presents a review of the plane strain and axisymmetric formulations in which it is shown that the radial (horizontal) scale of the axisymmetric formulation is not arbitrary and requires additional planning by the modeler. A comparison of the results (seepage gradients and computed factor of safety for stability) from numerical modeling of levees using plane strain and axisymmetric formulations through the use of a case history is then presented. The computed gradients for the convex axisymmetric case are higher than those computed using a plane strain formulation. For the cross sections used in this study, the increase is greater than previously reported. Moreover, the increase is not systematic and is unique to each cross section.

Tensile strength of soil plays an important role in controlling the cracking and tensile failure of many earth structures. In this investigation, a direct tensile test apparatus was developed to determine the tensile strength of compacted clayey soil over a broad range of water contents (4.3–28.5%) and with different dry densities ($1.5–1.7\mathrm{Mg}/{\mathrm{m}}^3$). The results show that the tensile strength of compacted clayey soil significantly depends on water content. The tensile strength characteristic curve (TSCC) exhibits one peak value occurring at the critical water content $w_c$ around 11.5%. With increasing water content, the tensile strength increases at the dry side of $w_c$ and then decreases at the wet side of it. Generally, with the increase of dry density, the tensile strength also increases. Moreover, a modified model is proposed to describe the tensile strength characteristics of compacted clayey soil, and it is validated by the obtained test data.

Construction of the Silverline Courthouse Station in South Boston involved 18-m-deep excavations at a site underlain by more than 24 m of normally and lightly overconsolidated Boston blue clay (BBC). The excavations were supported by 27-m-deep floating diaphragm wall panels and five levels of preloaded cross-lot bracing. This paper compares the measured performance of the excavation support system with the Class A finite-element (FE) predictions prepared during the original design phase and with the results of Class C analyses using information obtained during construction. The numerical analyses used data from a special test program of laboratory and in situ tests at a nearby site. The analyses represent coupled consolidation within the soil mass and the anisotropic stress-strain-strength properties of BBC using the MIT-E3 soil model. The Class A analyses generally overestimate the lateral wall deflections and underestimate the measured strut loads, as preloading was not included in the original FE model. However, they provide remarkably consistent predictions of the measured soil deformations, including settlements, lateral spreading, and subgrade basal heave. The Class C analyses refine the stratigraphic section, in situ pore pressures, construction time frame, and strut preloads using the data available at the time of construction but make nominal changes in soil properties. With these limited changes, the Class C model is able to achieve excellent agreement with the measured data.

A new type of slope-stabilization structure has been developed in recent years, which uses a grouted pipe pile group and pile-head connection beams to form a pile-soil frame structure. In this research, field lateral loading tests on one $2\times 5$ and two $3\times 5$ grouted steel-pipe pile groups were carried out at a highway slope-stabilization site. The tests simulated the performance of slope-stabilization pile groups subject to lateral soil movements caused by surcharge fill loading behind the pile groups. Through the measurements of pile and soil displacements, pile strains, and earth pressures, the loading behavior of these grouted steel-pipe pile groups was studied, taking the number of pile rows, row spacing, and pile spacing as variables. At the same pile spacing and row spacing, the maximum displacement of a $3\times 5$ pile group was only 35–55% of that of the $2\times 5$ pile group. The deformations of the soil between the piles were approximately the same as those of the piles. The earth pressure was the largest on the rear piles and smallest on the front piles. The maximum bending moment of the rear piles occurred near the pile head, while the maximum bending moments of the middle and front piles were near the sliding surface of the test slope.

Shallow geothermal heat exchangers integrated in structural pile foundations have the capability of being an efficient and cost-effective solution to cater for the energy demand for heating and cooling of built structures. However, limited information is available on the effects of temperature on the geothermal energy pile load capacity. This paper discusses a field pile test aimed at assessing the impact of thermomechanical loads on the shaft capacity of a geothermal energy pile. The full-scale in situ geothermal energy pile equipped with ground loops for heating/cooling and multilevel Osterberg cells for static load testing was installed at Monash University, Melbourne, Australia in a sandy profile. Strain gauges, thermistors, and displacement transducers were also installed to study the behavior of the energy pile during the thermal and mechanical loading periods. It has been found that the pile shaft capacity increased after the pile was heated and returned to the initial capacity (i.e., initial conditions) when the pile was allowed to cool naturally. This indicated that no losses in pile shaft capacity were observed after heating and cooling cycles. A variance in average vertical thermal strains was observed along the upper section of the pile shaft at the end of the heating periods. These were almost fully recovered at the end of the cooling periods, indicating that they are of an elastic nature. Pile average circumferential strains were found to be relatively uniform at the end of the heating and cooling periods and did not change with depth. They, also, were fully recovered during the cooling period. It was also observed that the increase of temperature during the heating periods prompted the pile shaft to expand radially. Subsequently, as the pile cooled down, the pile shaft slowly contracted and returned closely to its original condition, suggesting a thermoelastic behavior.

Kinematic bending of elastic single fixed-head piles in continuously inhomogeneous soil is explored in both static and dynamic regime. A generalized parabolic function is employed to describe the variable shear modulus in the inhomogeneous stratum, which can simulate both cohesive and cohesionless soil deposits. The problem is treated numerically by means of rigorous elastodynamic finite-element analyses and simplified beam-on-dynamic-Winkler-foundation (BDWF) formulations. A novel expression is proposed for the active length of a pile in inhomogeneous soil, by means of kinematic interaction considerations. This allows an alternative interpretation of kinematic soil-pile interaction along an effective depth, contrary to existing definitions in which soil response is evaluated at a specific location. Following this interpretation, a design formula for kinematic pile-head moments is derived for both static and dynamic loading. A new dimensionless parameter is identified to govern dynamic pile bending, which allows a straightforward assessment of frequency effects in pile design.

A numerical model, called CSTCRS1, is presented for coupled one-dimensional consolidation and solute transport under constant rate of strain (CRS) loading conditions. The consolidation algorithm accounts for vertical strain, general constitutive relationships, relative fluid velocity, changing compressibility and hydraulic conductivity during consolidation, and an external hydraulic gradient. The solute transport algorithm accounts for advection, dispersion, linear and nonlinear sorption, and equilibrium and nonequilibrium sorption. Soil compressibility is rate-independent and as such CSTCRS1 is more appropriate for less-structured soils. The model is based on a dual-Lagrangian framework that separately tracks the motions of sold and fluid phases. The development of CSTCRS1 is first described, and is followed by verification checks. Numeric examples are then presented to illustrate the effects of initial contamination distribution, transport conditions, applied strain rate, initial specimen height, and drainage and concentration boundary conditions on solute transport for CRS consolidation.

This paper presents a numerical investigation of one-dimensional large strain consolidation-induced solute transport for incremental loading (IL) and constant rate of strain (CRS) conditions. Solute transport accounts for advection, diffusion, dispersion, linear and nonlinear sorption, and equilibrium and nonequilibrium sorption, and is consistent with temporal and spatial variations of porosity and seepage velocity in the consolidating soil. Simulations were conducted using material properties for kaolinite clay and indicate that IL and CRS conditions produce significantly different responses during the course of consolidation, including applied stress, rate of settlement, excess pore pressure, and local strain. However, for a given set of initial and boundary conditions, final solute mass outflows and final solute concentration profiles for IL and CRS conditions were generally in close agreement, provided that total elapsed time and final average strain were matched for both loading procedures. Such agreement occurred for varying initial specimen height, initial contamination distribution, loading procedure, transport condition, and applied strain rate. Conversely, solute mass outflows were generally not in close agreement during the course of consolidation, with IL conditions producing higher mass outflow due to higher fluid outflow at the top boundary.

The U.S. Army Corps of Engineers’ blanket theory has been successfully used to evaluate levee underseepage for many years. The method was developed from closed-form analytical solutions based on the principles of groundwater hydrology. More recently, the proliferation of computing resources has made finite-element analysis (FEA) a tool that is easily accessible to many geotechnical engineers. This study compares the results of blanket theory to FEA to delineate conditions in which the two methods provide essentially the same solution. The assumptions inherent to blanket theory are reviewed to provide designers with an understanding of its usefulness and limitations. Guidelines are provided for correctly assigning FEA boundary conditions that are consistent with the assumptions of blanket theory. For cases in which all of the assumptions are satisfied, the volumetric flow rate and excess head at the levee toe predicted by blanket theory were within 10% of those determined by using FEA.

Landfill gas (LFG) collection efficiency is low at many municipal solid waste (MSW) landfills in China. The relevant mechanism and potential solution for this problem are studied through laboratory gas permeability tests on MSW, field LFG extraction tests at a landfill subjected to leachate drawdown, numerical assessment of the LFG collection efficiency at the landfill with different leachate levels, and engineering application of the measures to improve LFG collection. The research work outcomes are as follows: High water content in the food-rich MSW is one of the major reasons causing the high leachate level at many Chinese landfills. High leachate mounds tend to result in a high degree of saturation in waste, and hence a low gas permeability of the waste. Therefore, the LFG collection efficiency at Chinese landfills with high leachate level is lower than expected. A drawdown of leachate level at a Chinese landfill by pumping resulted in a significant increase in the LFG collection rate and the influence radius of LFG extraction wells. The dependence of LFG collection efficiency on the leachate level relative to the total waste thickness was verified and quantified. The leachate level is suggested to be controlled to less than 30% of the total waste thickness to achieve a high LFG collection efficiency. Engineering application at a Chinese landfill indicated that the retrofitted facilities, including deep vertical wells and horizontal drainage trenches, were effective in lowering high leachate level. The drawdown of leachate level resulted in an increase of LFG collection efficiency from 10–20 to 60–90%.

The paper describes a mechanism-based design approach for assessing spudcan penetration in soft nonuniform clay with an interbedded stiff layer. The proposed approach is developed on the basis of the results from a parametric study through large deformation finite-element analyses and validated against centrifuge test data. This can be taken as a “top-down” approach. Design formulas are proposed for assessing the limiting cavity depth and soil plug height. A direct comparison between the predicted profiles using the proposed design approach and the “bottom-up” approach recommended in an ISO standard confirms the benefit of using the former.

Dilatancy influences almost all aspects of the behavior of granular material, ranging from shear strength to stress-strain behavior. However, there is no practical method for estimating the dilatancy angle based on in situ soil properties, although the variables that influence dilatant behavior are well-known. This paper attempts to link the dilatancy angle to preshear mean effective stress and relative density for cohesionless soils. Accordingly, it may be possible to estimate the dilatancy angle by using variables that can be measured or calculated during the soil exploration phase of a design project. For this purpose, an experimental study is conducted on Silivri sand and the obtained results are used to quantify the relationship between dilatancy angle and preshear soil properties. An equation for the dilatancy angle is proposed that requires only two unit-independent soil constants, which can be obtained by conducting triaxial or plane strain tests. Moreover, the proposed dilatancy equation can be combined with a linear relationship between friction angle and dilatancy angle to form a new equation that can be used to estimate the peak friction angle. Thus, a new equation is developed that allows the calculation of the peak friction angle from preshear soil properties. Finally, for verification purposes, the proposed equations for dilatancy and peak friction angles are tested by using available data on other sands and the results are compared with the predictions of available dilatancy equations in literature.