Journal of Geotechnical and Geoenvironmental Engineering

With the increasing use of augered cast-in-place and drilled displacement piles in new construction, it is important that proper design parameters be incorporated when evaluating pile performance using reliability-based design methods. Although augered piles can be distinguished from bored piles, including drilled shafts, and driven piles by the magnitude of the effective stress changes they produce in the vicinity of the pile during construction, the current design methods for augered piles generally use the same design methods as those used for bored or driven piles. To enhance the efficiency of the augered piles, a unique design method must be developed. This paper focuses on developing a design methodology for axially loaded augered piles installed in predominately sandy soils using the t-z method. To develop the design parameters for augered piles, back-calculation of the t-z parameters was conducted using static load–test data. The data from 17 static pile load tests conducted on augered piles from construction sites were obtained. Load-settlement and load-transfer curve fittings were performed using the t-z model to back-calculate a set of soil-pile interfacial and tip parameters, along with their variability. Correlations of the back-calculated t-z model parameters with the standard field investigation data were conducted, and the most-promising correlations were incorporated into the t-z model–based design methodology. Subsequently, the t-z method for augered pile design was evaluated by comparing the predicted and measured load-settlement and load-transfer curves. In addition, the t-z method was used to perform probabilistic load-settlement analyses and obtain resistance factors applicable to the load and resistance factor design approach.

The use of jet grouting columns to increase the bearing capacity and reduce the settlements of foundations is dealt with, the aim being to formulate a complete design procedure where theoretical analyses and site observations are combined. The study is based on experimental results reported in the literature, which show that jet grouting columns are able to transfer high vertical loads to the surrounding soil but also that structural collapse may locally occur because of a sudden narrowing of their cross sections and/or poor soil cementation. Noticeable attention has been then given to these aspects by interpreting the results of full-scale tests specifically performed to investigate the characteristics of jet grouting columns and their mechanical interaction with the surrounding soil. The results of this analysis form the basis of a numerical method developed to simulate the response of vertically loaded rafts supported by arrays of columns. The nonlinear load-settlement response of axially loaded columns is modeled with the load-transfer curves method customized to account for the irregular shape of jet grouting columns. Extension of the analysis to the whole reinforced foundation is accomplished by considering the mutual interaction between the columns and the upper concrete raft. The variation of column properties is statistically evaluated from the results of field trials, simulated with probabilistic models and introduced into the calculation with a Monte Carlo simulation technique. The main advantages of the proposed method is that the design limit load of the foundation can be expressed in terms of acceptable probability of failure and that the uncertainty arising from the jet grouting process can be experimentally quantified and rationally introduced in the analysis. Benefits and limitations of reinforcement with jet grouting are finally discussed by applying the proposed method to a case study.

Resistance factors are developed for drilled shafts for a design method based on soil variables. The uncertainties associated with the design variables and equations were systematically quantified, and Monte-Carlo simulations were performed to obtain the distributions of the shaft and base capacities. Both the base and shaft capacities were found to follow normal distributions, and the applied dead and live loads were assumed to follow normal and lognormal distributions, respectively. Reliability analysis was then performed to obtain the limit state and nominal resistances and loads for a variety of soil profiles and pile dimensions. The optimal dead- and live-load factors were subsequently obtained from the analysis. The optimal resistance factors were then adjusted for use with the load factors recommended by the Federal Highway Administration.

Accurate estimation of the soil thickness distribution in steepland drainage basins is essential for understanding ecosystem and subsurface response to infiltration. One important aspect of this characterization is assessing the heavy and antecedent rainfall conditions that lead to shallow landsliding. In this paper, we investigate the direct current (DC) resistivity method as a tool for quickly estimating soil thickness over a steep (33–40°) zero-order basin in the Oregon Coast Range, a landslide prone region. Point measurements throughout the basin showed bedrock depths between 0.55 and 3.2 m. Resistivity of soil and bedrock samples collected from the site was measured for degrees of saturation between 40 and 92%. Resistivity of the soil was typically higher than that of the bedrock for degrees of saturation lower than 70%. Results from the laboratory measurements and point-depth measurements were used in a numerical model to evaluate the resistivity contrast at the soil-bedrock interface. A decreasing-with-depth resistivity contrast was apparent at the interface in the modeling results. At the field site, three transects were surveyed where coincident ground truth measurements of bedrock depth were available, to test the accuracy of the method. The same decreasing-with-depth resistivity trend that was apparent in the model was also present in the survey data. The resistivity contour of between 1,000 and 2,000 $\Omega$m that marked the top of the contrast was our interpreted bedrock depth in the survey data. Kriged depth-to-bedrock maps were created from both the field-measured ground truth obtained with a soil probe and interpreted depths from the resistivity tomography, and these were compared for accuracy graphically. Depths were interpolated as far as 16.5 m laterally from the resistivity survey lines with root mean squared error (RMSE) = 27 cm between the measured and interpreted depth at those locations. Using several transects and analysis of the subsurface material properties, the direct current (DC) resistivity method is shown to be able to delineate bedrock depth trends within the drainage basin.

A new tunnel auxiliary method, the pressure-induced inflatable pipes method, is proposed in this paper. It utilizes the concept of cavity expansion for tunnel reinforcement by forming an umbrella arch on the roof of the tunnel. When each inflatable pipe is inserted and expanded by pressure in the boreholes of the umbrella arch, the ground around the borehole can be compacted so that the stress conditions above the tunnel perimeter are changed favorably. To verify the reinforcement effect of this new concept, a pilot-scale chamber test, numerical analysis, and trapdoor test were performed and compared. In the pilot-scale chamber test, three types of inflatable pipes were tested to check their capability for expansion and each type of pipe was demonstrate to function correctly by expanding only in the intended direction. Numerical analysis of a tunnel and the applied trapdoor tests using the inflatable pipes were also performed to determine the reinforcement effects of the proposed technique. The results imply that the new method with three-directional inflatable pipes can contribute to reducing tunnel convergence and face settlement.

Over the last few decades, extensive research has been conducted to investigate fault-rupture propagation induced by faulting through uncemented soil. While it has long been realized that many natural soils are cemented, relatively few publications have been devoted to investigating fault-rupture propagation in cemented soil. Moreover, preexisting fracture in soil may be reactivated during earthquakes, and its influence on fault-rupture propagation is not fully understood. In this study, three centrifuge model tests are reported on investigating fault-rupture propagation induced by normal faulting in uncemented clay and cemented clay with and without a preexisting fracture. Preliminary numerical analyses of the centrifuge tests are also carried out to study the mechanism of fault-rupture propagation in these three ground conditions. Ground deformation was dominated by a shear mechanism in uncemented clay, and a shear zone along the projection of the bedrock-fault plane was observed. On the other hand, a bending deformation mechanism was identified at the ground surface in cemented clay with and without a preexisting fracture. In the presence of cementation, two main ruptures were observed, where one initiated at the cemented ground surface and propagated downward toward the center of the cemented clay, whereas the other initiated at the bedrock fault and propagated upward. The presence of a fracture in cemented clay was found to initiate a fault rupture at the tip of the preexisting fracture.

An analysis is presented for evaluation of the pullout capacity of sheet reinforcement subjected to oblique pullout force considering that the subgrade soil is represented as a two-parameter linear-elastic Pasternak model and the reinforcement as inextensible. Use of the Pasternak model makes the oblique pullout analysis more realistic. The orientation of the reinforcement at the pullout end is found to be different from the direction of the pullout force and depends on the shear modulus of the subgrade soil. A parametric study is carried out to evaluate the effect of various factors, such as the modulus of the subgrade reaction, shear modulus of the subgrade, angle of interface shear resistance, and the obliquity of the pullout force on the magnitude and direction of the reinforcement force and the end displacement. For the first time, oblique pullout results have been compared with direct measurements of the reinforcement inclination in the vicinity of the failure surface available in the literature, and the experimental data compare well with the present analysis. Model tests on single and multiple sections of sheet and strip reinforcements are also performed to study the suitability and applicability of the present analysis in the design of reinforced soil walls.

Design of retaining walls for earthquake action is traditionally performed by limit analysis procedures—notably the classical solution of Mononobe-Okabe and its variants. Fundamental assumptions of these methods are (1) the static nature of seismic excitation, (2) the compliance in sliding and/or rocking of the base of the wall, (3) the shear failure of the backfill and the soil-wall interface, and (4) the prespecified point of application of soil thrust. Given the restrictive nature of these assumptions, alternative solutions based on wave-propagation theory have been developed that do not require failure of the backfill and thereby are applicable to nonyielding walls. Because of the complex mathematics involved, the use of these solutions in practice appears to be limited. A special integration technique inspired from the seminal work of Vlasov and Leontiev is presented, which simplifies the analysis by providing closed-form solutions suitable for practical use.

The use of resistivity imaging (RI) in subsurface investigation has increased in recent years. RI is a non-destructive method and provides a continuous image of the subsurface. However, only qualitative evaluation of the subsurface can be obtained from RI. The correlations between RI results and geotechnical engineering properties of soils have become important for site investigation using this method. The primary objective of the current study was to determine the geotechnical parameters affecting electrical resistivity of compacted clays. Understanding the influential factors will be helpful in determining the correlations between RI results and geotechnical properties of soil. The effects of moisture content, unit weight, degree of saturation, specific surface area, percentages of pores, and ion composition on soil resistivity were investigated. Soil samples used were classified as highly plastic clay (CH) according to the Unified Soil Classification System. High-energy X-ray fluorescence tests indicated the presence of high percentages of aluminum, silicon, and calcium ions in the samples. In addition, scanning electron microscope images were analyzed to identify clay structure and the distribution of pores. It was determined that the dominant clay mineral in the soil samples was montmorillonite. Soil resistivity tests were conducted in the laboratory at varying moisture contents and unit weights. Based on the experimental results, the average reduction in soil resistivity was 13.8 Ohm-m for an increase of moisture content from 10 to 20%. Test results indicated that soil resistivity decreased with an increase in moist unit weight. In addition, soil resistivity increased from 4.3 to 14.2 Ohm-m for an increase of surface area from 69.6 to 107.1 m²/g at 18% moisture content and 11.8 kN/m³ dry unit weight. Soil with high surface area required more water for the formation of water film and bridging between the particles. This might cause an increase in soil resistivity with an increase of surface area. Moreover, specific surface area also controlled resistivity when soil resistivity was plotted against calcium ions and pore spaces of the soil samples. Therefore, in addition to moisture content and unit weight, specific surface area of soils was identified as an important factor influencing soil resistivity.

Ground movements caused by deep excavations may potentially lead to building damages in urban cities where the majority of buildings are frame structures. A new damage chart, with two key parameters of the differential settlement and frame dimensions, has been proposed. The chart has been validated against published data, and field measurements have been obtained during the construction of mass rapid transit (North East Line) in Singapore. The proposed chart can be used as an alternative or a supplement to other similar charts. Although the measurement of the frame dimensions is straight forward, the accuracy of the chart highly depends on the predicted building settlement, which still remains a challenge.

The goal of this research is to develop an experimentally validated two-dimensional (2D) finite difference frequency domain (FDFD) numerical forward model to study the potential of radar-based tunnel detection. Tunnel detection has become a subject of interest to the nation because of the use of tunnels by illegal immigrants, smugglers, prisoners, assailants, and terrorists. These concerns call for research to nondestructively detect, localize, and monitor tunnels. Nondestructive detection requires robust image reconstruction and inverse models, which in turn need robust forward models. Cross-well radar (CWR) modality was used for experimentation to avoid soil-air interface roughness. CWR is not a versatile field technology for political boundaries but is still applicable to monitoring the perimeter of buildings or secure sites. Multiple-depth wideband frequency-response measurements were experimentally collected in fully water-saturated sand, across PVC-cased ferrite-bead-jacketed borehole monopole antennae at a pilot-scale facility (referred to as SoilBED). The experimental results were then compared with the 2D-FDFD model. The agreement between the results of the numerical and experimental simulations was then evaluated. Results provide key diagnostic tools that can help to develop the algorithms needed for the detection of underground tunnels using radar-based methods.