Journal of Geotechnical and Geoenvironmental Engineering

The predesign geotechnical investigation for closure of the Operating Industries, Inc. (OII) Superfund site landfill significantly advanced the state of the art for solid waste landfill engineering. Contributions to solid waste landfill engineering from the OII predesign geotechnical investigation include a solid waste classification system, a method for in situ measurement of waste unit weight, an enhanced understanding of the mechanical properties of solid waste, including unit weight, compressibility, shear strength, shear wave velocity, and equivalent linear shear modulus and equivalent viscous damping, and a methodology for seismic stability and deformation analysis of the waste mass. Many of the procedures and waste property relationships developed for the OII predesign geotechnical investigation remain the state of practice today for solid waste landfill engineering.

Surface fault rupture can be damaging to structures built on or near active faults if the hazard is not addressed properly. Fault-induced angular distortion and lateral ground strain can cause beams to yield and eventually lead to structural collapse. When avoidance is not possible, geotechnical mitigation strategies can be used. These strategies include spreading fault displacement over a large area, causing the structure to respond with rigid-body movement, and diverting the fault rupture around the structure. The effectiveness of these strategies can vary from protecting life safety to preventing significant damage and can be effective for a range of dip-slip fault displacements. Earth fills should be sufficiently thick and ductile to prevent the underlying fault dislocation from developing at the ground surface. Thick RC mat foundations proved to be especially effective in shielding the superstructure from the damaging effects of the underlying ground movements. Although more challenging to implement because they require excellent fault characterization, several fault diversion strategies have also proved effective at protecting structures from fault movement.

A large amount of field and experimental data has been devoted to rectangular excavations thus far. In contrast, very few data were available for cylindrical excavations, especially those with large diameters in thick soft clay deposits. Via a comprehensive instrumentation program on a $100\text{-m-wide}\times 25.89\text{-m-deep}$ unpropped (self-supported) cylindrical excavation constructed by the bottom-up method in Shanghai soft clay, the characteristics of this large-sized circular excavation were extensively investigated. This cylindrical shaft was a part of a large-scale deep foundation pit excavated by the central-island technique. The investigated items included (1) lateral wall deflections, (2) vertical wall movements, (3) lateral ground movements, (4) ground settlements, (5) subsurface settlements, (6) basal heaves, (7) vertical column movements, (8) column stresses, and (9) variation of pore pressures along depth and artesian water levels. Analysis of the field data indicates that discharging of the deep artesian water was one of the key factors affecting the excavation behaviors. The influence zone of basal heave caused by soil removal (stress relief) reached very deep soil layers, far beyond the depths reported in literature. Column movement and stress were shown to be reliable indicators of the relative movement between basal soils, diaphragm walls, and interior columns. Finally, the comparisons of this study with other bottom-up excavations in Shanghai, including 11 cylindrical excavations, 92 building basement excavations, and eight metro station excavations, demonstrate that self-supported (unpropped) cylindrical excavations had much stronger capabilities of resisting deformation than both multipropped regular basement excavations (in terms of deformation magnitudes) and long and narrow metro station excavations (in terms of scale of influence zones). For cylindrical shafts, their diameters, and not wall penetration ratios, played a dominant role in the determination of excavation behaviors. However, when the shaft diameter reached 90 m or more, the advantage of cylindrical shafts over rectangular pits in constraining wall deflection was no longer obvious.

Because of its large size ($\mathrm{30,000}\hspace{0.17em}{\mathrm{m}}^2$ in plan), the 17.85- to 25.89-m-deep foundation pit of the 492-m-high Shanghai World Finance Center building was excavated by the central-island technique, i.e., bottom-up construction of the central cylindrical shaft first and then top-down construction of the peripheral rectangular pit. As part of the comprehensive study on the characteristics of this large-scale foundation pit, this study mainly focuses on the behaviors of the peripheral pit via the following investigated items: (1) lateral wall deflections; (2) vertical wall movements; (3) lateral ground movements; (4) axial forces in the cast floor slabs and braced struts; (5) lateral earth pressures on both sides of retaining walls; (6) variation of pore pressures along depth and deep artesian water levels; (7) ground settlements; (8) subsurface settlements; (9) basal heaves; (10) vertical column movements; and (11) column stresses. To explore the potential effects of pit sizes on the excavation behaviors, field data from another 33 top-down excavations in Shanghai were also included for comparison. The comprehensive comparisons show that in addition to the well-known factors (e.g., excavation depths, supporting system stiffness, and factor of safety against basal heave), pit sizes in plan played a key role in determination of the pit behaviors. The large-scale pits with the areas in plan of $\mathrm{30,000}–\mathrm{50,000}\hspace{0.17em}{\text{m}}^2$ experienced wall deflections and ground settlements three to five times those of regular building basement and metro station excavations with the sizes in plan no more than $\mathrm{6,000}\hspace{0.17em}{\mathrm{m}}^2$, and the corresponding influence zones behind the large-sized pits were also much wider. Different from the braced struts that just carried the load because of soil removal in the proximity, the floor slabs sustained the load induced by exposure of the entire retaining wall along the depth. For the top-down excavations in Shanghai soft clay, the lateral earth pressure envelopes behind the retaining walls were trapezoidal, but their magnitudes were significantly smaller than those predicted by the methods available in the literature, and the corresponding peak values occurred at a greater depth. The influence zones of basal heave caused by soil removal (stress relief) extended much deeper below the excavation bases than those assumed in the conventional slip circle basal stability models.

Levees are very challenging engineering structures to study, in part because they are not typically well-engineered structures. Unfortunately, there is little to no guidance as to how to evaluate the seismic vulnerability of levees. This study focuses on systematically studying the dynamic response of levees using a wide range of input ground motions and developing a simplified procedure for the liquefaction triggering evaluation of earthen levees, accounting for the dynamic response of the levee. The study was based on three levee sites representative of three select California Central Valley regions; however, because floodplains tend to generally have similar depositional environments, the study can be extended to other regions as long as some of the principal characteristics are still applicable. A wide range of input ground motions was used to capture and assess the variability in response and performance because of multiple possible earthquake scenarios. Two aspects of the dynamic response and performance of earthen levees are presented in more detail: the site and topographic effects on the peak ground acceleration, and the shear stresses and the cyclic stress ratios for a series of profiles throughout the levee sites. A simplified methodology for assessing the factor of safety against triggering of soil liquefaction is developed, and recommendations for applying the methodology are presented and discussed.

Deep soil mixing (DSM) to form in-ground shear walls has been used to remediate against the potential effects of earthquake-induced liquefaction on many projects. A grid pattern of soil-cement walls act as a confined shear box, which can provide additional shear stiffness and strength for sites to withstand liquefaction. Current design practice for DSM grids commonly relies on the strain compatibility assumption, where the DSM walls and confined soil are assumed to experience the same shear strain. In this paper, the distributions of shear stresses and strains in liquefiable soil deposits treated with DSM grids are investigated using three-dimensional linear elastic finite-element analyses of unit cells. Parametric analyses are performed for a range of geometries, relative stiffness ratios, and dynamic loadings. These linear elastic results provide a baseline against which future nonlinear modeling results can be compared, but they are also sufficient for demonstrating that shear stress reductions are less than predicted by the assumption of shear strain compatibility. Modifications to the shear strain compatibility equation are presented, which improve its agreement with the results of these analyses.

The design of soil nail systems used in engineering practice is either based on conventional soil mechanics or empirical procedures, and generally ignores the influence of matric suction. An experimental program was conducted to investigate the influence of matric suction on the pullout capacity of soil nails installed in compacted sand under both saturated and unsaturated conditions. Pullout tests were performed on soil nails installed vertically, horizontally, and at an inclination of 15° to the vertical in a specially designed test box. A strong relationship was observed between the pullout capacity and matric suction. A semiempirical method is proposed for the estimation of the pullout capacity of soil nails by using the average matric suction value and the saturated soil strength parameters, $c_a^{\prime }$ and $\delta$. There is a reasonably good agreement between the measured and estimated pullout capacity of soil nails using the results of the present research program as well as the data from the literature.

Various empirical equations have been proposed to estimate the unconfined compressive strength ($q_u$) of cement-treated soils based on the proportions of water, cement, and clay or based on measured early strength. Most equations provide only a point estimate of $q_u$ and no measure of uncertainties associated with the estimation. As the design’s safety level is governed by the uncertainties involved, it is essential to quantify uncertainties associated with the estimation. The coefficient of variation (COV) is taken as a measure of uncertainties. It is straightforward to estimate the mean and COV of $q_u$ based on a single parameter. Similar estimation based on multiple parameters, which may be intercorrelated, is not as straightforward. This paper aims to integrate multiple parameters (water-to-cement ratio, cement content, and 7-day strength) that may contribute to the estimation of 91-day strength using a multivariate normal distribution. The multivariate normal model can be used to derive the mean, COV, and the 95% confidence interval of 91-day $q_u$ at given values of the governing parameters. This confidence interval provides richer information on $q_u$ than the single value provided by most empirical equations. Results show that incorporating more parameters in the estimation of $q_u$ reduces the bias and the COV; thus, a more accurate estimate is obtained. Data of stabilized dredged fill (SDF) from a real land reclamation project are used to demonstrate the approach.

A probabilistic analysis of the face stability of a pressurized tunnel is undertaken in this article. First, two existing velocity fields based on the limit analysis theory are briefly described. They allow one to compute the values of the critical pressures of collapse and blowout of a pressurized tunnel face in cases of both frictional and nonfrictional soils. These models, which have the great advantage of a low computational cost, are validated by comparison with a computationally expensive numerical model. Then, an efficient probabilistic method called collocation-based stochastic response surface methodology (CSRSM) is applied on these velocity fields to perform the uncertainty propagation. This method makes it possible to compute the probability of failure of the tunnel face against both collapse and blowout. In the case of a frictional soil, it appears that the blowout of the face is extremely unlikely and that the collapse is the only probable failure mode. On the contrary, in a purely cohesive soil, it appears that both failure modes are likely to appear and should be considered in the analysis. Finally, this paper presents a discussion concerning the application of the proposed probabilistic method for an economic and safe design of a pressurized shield.

The current study analyzes the leachate distribution in the Orchard Hills Landfill, Davis Junction, Illinois, using a two-phase flow model to assess the influence of variability in hydraulic conductivity on the effectiveness of the existing leachate recirculation system and its operations through reliability analysis. Numerical modeling, using finite-difference code, is performed with due consideration to the spatial variation of hydraulic conductivity of the municipal solid waste (MSW). The inhomogeneous and anisotropic waste condition is assumed because it is a more realistic representation of the MSW. For the reliability analysis, the landfill is divided into 10 MSW layers with different mean values of vertical and horizontal hydraulic conductivities (decreasing from top to bottom), and the parametric study is performed by taking the coefficients of variation (COVs) as 50, 100, 150, and 200%. Monte Carlo simulations are performed to obtain statistical information (mean and COV) of output parameters of the (1) wetted area of the MSW, (2) maximum induced pore pressure, and (3) leachate outflow. The results of the reliability analysis are used to determine the influence of hydraulic conductivity on the effectiveness of the leachate recirculation and are discussed in the light of a deterministic approach. The study is useful in understanding the efficiency of the leachate recirculation system.

The stress-strain behavior of clayey soil is time dependent. Laboratory study and constitutive modeling of the time-dependent stress-strain behavior are needed to understand the soil behavior and analyze displacements of reclamation works and foundations on clayey soils. The stress relaxation, as one of the significant time-dependent phenomena in clayey soils, has been observed and examined in excavations and constructions, such as the short-term change in lateral earth pressure after installation of a supporting system. In this study, Hong Kong marine deposits (HKMDs), which are clayey soils, and a sand-mixed bentonite (SMB) soil were investigated in relaxation tests. Relaxations were performed in both the loading stage and the unloading stage. This paper is focused on the testing study and modeling of the time-dependent relaxation behavior of clayey soils. Relaxation tests were carried out to measure the changes of the effective stress with time in one-dimensional (1D) straining condition. A new 1D elastic visco-plastic model considering swelling (1D EVPS) was used to simulate the relaxation tests. Analytical solutions from the 1D EVPS constitutive equations were obtained for relaxation tests. All parameters in this 1D EVPS model were obtained from a conventional oedometer test. The analytical solutions from the 1D EVPS model were used to simulate the relaxation behavior and compare with test data. Good agreement between the simulated curve and the measured data were found.

This technical note assesses the widely accepted Thompson’s equation used to approximate design resilient modulus ($M_r$) for lime-stabilized soils from the results of unconfined compressive strength ($q_u$) testing. There is limited evidence in the literature to support Thompson’s equation relating $q_u$ and $M_r$ for lime-stabilized soils, and other studies have suggested that the relationship provides an excessively conservative approximation for design $M_r$, specifically above $q_u=\mathrm{1,000}\hspace{0.17em}\text{kPa}$. Laboratory $M_r$ and $q_u$ testing was performed on multiple specimens of three lime-stabilized soils. These data reveal that Thompson’s equation provides a lower-bound estimate of $M_r$ from $q_u$ and that Little’s recommended relationship provides a more reasonable match to the data. This study also illustrated a lack of a clear correlation between $M_r$ and $q_u$.

By applying the lower bound theorem of limit analysis in conjunction with finite elements and nonlinear optimization, the bearing capacity factor $N_{\gamma }$ has been computed for a rough strip footing by incorporating pseudostatic horizontal seismic body forces. As compared with different existing approaches, the present analysis is more rigorous, because it does not require an assumption of either the failure mechanism or the variation of the ratio of the shear to the normal stress along the footing-soil interface. The magnitude of $N_{\gamma }$ decreases considerably with an increase in the horizontal seismic acceleration coefficient ($k_h$). With an increase in $k_h$, a continuous spread in the extent of the plastic zone toward the direction of the horizontal seismic body force is noted. The results obtained from this paper have been found to compare well with the solutions reported in the literature.

This paper focuses on the effects of particle size distribution on shear strength of accumulation soil. A series of direct shear box tests and triaxial tests were performed to characterize the shear strength of the accumulation soil. Results from the direct shear tests indicate that the range of the angle of shearing resistance of the accumulation soil is 33.5–54.6°, and those from the triaxial tests indicate that the angle is 37.2–50.7°. The basic properties of the soil, such as median particle diameter, coefficient of uniformity, and gravel content, were used to analyze the effects. The angle of shearing resistance is generally increasing with increasing median particle diameter and gravel content and decreasing with increasing coefficient of uniformity.