Journal of Geotechnical and Geoenvironmental Engineering

Numerical limit analyses have been used to evaluate the stability of the 17th Street Canal I-wall levee during Hurricane Katrina. The potential formation of a water-filled gap along the canal-side soil-wall interface at failure is included in both the lower- and upper-bound formulations. The analyses replicate published two-dimensional (2D) cross sections and soil properties developed in forensic investigations carried out by the Interagency Performance Evaluation Task Force (IPET) and by the Independent Levee Investigation Team (ILIT). The current results provide an independent basis for understanding and evaluating the proposed failure mechanisms and demonstrate that a water-filled gap is a necessary condition for the critical I-wall failure mechanism. Further limit-analysis calculations produce credible estimates of the surge elevation that caused failure of the 17th Street Canal I-wall as well as predictions of a consistent failure mechanism. The numerical limit analyses show clearly how differences in the stability of the I-wall are linked to different interpretations of the stratigraphy and undrained shear strengths by IPET and ILIT. The analyses also show that effects of a thin layer of weak organic clay as postulated by ILIT are not necessary to explain the I-wall failure.

Empirical correlations provide estimates of parameter values for preliminary design, verification of laboratory shear test data, and confirmation of back-analysis of a failed slope. The empirical correlations presented herein use liquid limit, clay-size fraction, and effective normal stress to capture the variability and stress-dependent nature of drained residual and fully softened strength envelopes. This paper describes the testing and analysis used to increase the number of data points in the existing correlations, expand the residual strength correlation to include an effective normal stress of 50 kPa, and develop correlations between values of liquid limit and clay-size fraction measured using sample processed through a No. 40 sieve (ASTM procedure) and values derived using ball-milled/disaggregated sample. In addition, equations are presented to express the empirical correlations used to develop a spreadsheet that estimates the residual and fully softened friction angles based on entered values of liquid limit and clay-size fraction.

The liquefaction response of partially saturated loose sands was experimentally investigated to assess the effect of partial saturation on the generation of excess pore water pressures. An experimental setup including a cyclic simple shear liquefaction box was devised and manufactured. The box includes pore pressure and displacement transducers as well as bender elements and bending disks to monitor the response of partially saturated specimens. Uniform partially saturated specimens with controlled density and degree of saturation were prepared by wet pluviation of powdered sodium perborate monohydrate mixed with Ottawa sand. The reaction of the sodium perborate with pore water released minute oxygen bubbles, thus reducing the degree of saturation of the specimens. The uniformity of a specimen was confirmed with S wave velocity measurements and a high-resolution digital camera. The P wave velocity measurements could only confirm the presence of partial saturation but not the degree of saturation. Partially saturated specimens with varying relative densities and degrees of saturation when tested under a range of cyclic shear strains do not achieve initial liquefaction defined by maximum pore pressure ratio ($r_{u,\text{max}}$) being 1.0. For a given degree of saturation and cyclic shear strain amplitude, the larger the relative density, the smaller is $r_{u,\text{max}}$. For a given degree of saturation and relative density, the larger the shear strain amplitude, the larger is $r_{u,\text{max}}$. The excess pore pressure ratio ($r_u$) can be significantly smaller than $r_{u,\text{max}}$ depending on the number of cycles of shear strain. Tests on the sustainability of partial saturation under upward flow gradient and base excitation led to the conclusion that the specimens remained partially saturated without significant change in the degree of saturation. Based on the experimental test results presented in this paper, an empirical model for the prediction of $r_u$ in partially saturated sands under earthquake excitation is presented in a companion paper.

Partial saturation in sands attributable to the presence of gas bubbles (not capillarity) can be encountered naturally in the field because of the decomposition of organic matter, or it can be induced for liquefaction mitigation. An empirical model (RuPSS) was developed to predict the excess pore pressure ratio ($r_u$) in partially saturated sands subjected to earthquake-induced shear strains. The model is based on experimental test results on partially saturated sands. Cyclic simple shear strain tests were performed on specimens prepared and tested in a special liquefaction box. Excess pore pressures were measured for a range of degrees of saturation $40\%<S<90\%$, relative densities $D_r=20-67\%$, and cyclic shear strains $\gamma =0.01-0.2\%$. The test results demonstrated that partially saturated sands achieved a maximum excess pore pressure ratio ($r_{u,\text{max}}$) when large enough cycles of shear strain were applied. The excess pore pressure ratio ($r_u$) that partially saturated sand can achieve under a given earthquake-induced peak shear strain and the number of equivalent cycles of application can be significantly smaller than $r_{u,\text{max}}$. Therefore, the empirical model was developed in two stages. In the first stage, $r_{u,\text{max}}$ was related to $S$, $D_r$, and shear strain ($\gamma$). In the second stage, a model was developed relating $r_u$ to $r_{u,\text{max}}$, shear strain amplitude ($\gamma$), effective stress (${\sigma }_v^{\prime }$), and earthquake magnitude ($M$). This paper presents the equations that define the predictive models for $r_{u,\text{max}}$ and $r_u$. Through these equations, plots for $r_{u,\text{max}}$ and $r_u$ are provided for ranges of soil and earthquake parameters for ease of use in engineering applications. To illustrate the implementation of the empirical model for predicting $r_{u,\text{max}}$ and $r_u$, an example is presented in which a partially saturated sand layer experiencing a peak earthquake-induced shear strain was analyzed, and the pore pressure response of the sand was evaluated using both the predictive equations and the plots.

Ground reinforcement anchorages are a means of ensuring the stability of a wide range of structures and retaining walls. The performance of an individual anchorage depends on the tensile load that the anchorage is carrying but this will change over the anchorage’s life span, so it is therefore necessary to have some way of measuring this load. A nondestructive technique, ground anchorage integrity testing (GRANIT), in which impulse responses of anchorages are determined to evaluate whether load transfer is maintained, has previously been developed for anchorages in rock. This research examines the possibility of extending this to soil anchorage systems. In this work, implementation of a model nondestructive testing system is tested using a geotechnical centrifuge. Load distributions along centrifuge model anchorages are measured and found to reduce gradually within the fixed length, as is the case with rock. Anchorage frequency responses to impulse loads are then evaluated to validate the consistency of the results obtained. Various anchorage inclinations and fixed lengths are also investigated, showing that inclined anchorages contain a greater range of frequencies in their signature response. The practical importance of these results is that nondestructive testing may be usable for anchorages in soil as well as anchorages in rock. Further investigation is necessary to refine the relationship between anchorage load and response frequencies. This may be accomplished using centrifuge modeling.

This paper presents the results from four centrifuge experiments modeling light, nonaqueous phase liquid (LNAPL) migration in a sandy soil. These experiments were performed to evaluate the performance of a soil-cement wall used as a containment barrier and to investigate the effects of groundwater flow on LNAPL migration behavior. Centrifuge modeling experiments were performed at 30 g to simulate 80 days of LNAPL migration through the soil. Pore water pressure measurements and video recordings were used to evaluate the LNAPL migration behavior. Results show that in all tests, the water level was depressed because of the large volume of LNAPL confined between the walls. When groundwater flowed, the LNAPL migrated faster and deeper than when there was no groundwater flow. As a result, the depth of a soil-cement wall should be designed to a greater maximum depth to account for the groundwater-flow effects. In addition, numerical simulations were performed and validated with the centrifuge test results. Both methods showed a good agreement as they provided similar behavior of the LNAPL migration and confirmed the effective performance of the soil-cement wall as a containment barrier.

Lot JC3 of the Xianmen Airport Highway Project in China involved building a twin-tube tunnel with each tube serving three-lane one-way traffic. The existence of 79 overlying buildings brought great challenges to the tunnel construction. To safeguard these buildings, two building blocks located above the nearby tunnel portal were approved by the owner of the project to be the trial blocks. Compensation grouting was adopted for ground settlement compensation at this lot. Free-field compensation grouting tests were conducted to derive the suitable grouting parameters. Pretreatment to reinforce the ground prior to the tunneling passage, concurrent grouting to compensate the excessive settlements during the tunneling passage, and regrouting to uplift the distorted buildings after the tunneling passage were designed to protect the trial blocks. According to the monitoring data of the trial blocks and the ground, the characteristics of the soil-structure interaction were studied and the criteria for the safety of the structures were therefore determined.

Cross walls are commonly used in some Asian countries like Japan and Taiwan for constraining the excavation-induced ground settlements as well as mitigating the subsequent building damages. To quantify the effect of cross walls, 22 case histories, including 11 excavations with cross walls and 11 excavations without cross walls, are collected in this study. It is found that cross walls can effectively reduce ground settlements by minimizing wall displacements—the maximum wall displacements for cases with cross walls are within $0.1\%H_e-0.35\%H_e(H_e=\text{excavation depth})$, compared with those for cases without cross walls being within $0.3\%H_e-0.8\%H_e$. Case histories show that the spacing of cross walls has a major effect on wall displacements. A physical model is proposed to predict the system stiffness in the presence of cross walls. Based on the data points in the collected case histories and the proposed stiffness model, a regression model that is capable of predicting maximum wall displacements is further developed. This model is applicable to cases with or without cross walls and is found to perform reasonably well over independent validation case histories.

Recent experiments have shown that exogenous bacteria can be introduced into soil for the purpose of inducing calcite precipitation. A series of tests are documented in this paper that demonstrate that natural indigenous bacteria can also be stimulated to induce calcite precipitation with measurable changes in geotechnical properties. Tests reported in this paper include a microcosm experiment with cone-penetration testing and cyclic triaxial shear tests. These experiments demonstrate that indigenous bacteria can induce significant quantities of calcite precipitation, that calcite precipitation can result in measurable changes to geotechnical soil properties, and that the cyclic resistance ratio can be increased substantially with moderate levels of calcite precipitation. Using indigenous bacteria to modify soil properties is a significant step in making biomodification of soils economically viable.

Liner systems are increasingly being used to protect the environment from contaminated waste. At the same time, society is increasingly insisting on estimates of the probability that these liner systems will fail to achieve their design objectives, one of which is to limit hydraulic flow from the contaminated region to acceptably small levels. This paper presents a methodology to estimate the probability of excessive hydraulic flow, considering the spatial variability of the soil composing the liner (its mean, variance, and correlation length) as well as the liner thickness. Semiempirical equations predicting the mean and variance of the effective hydraulic conductivity of the liner, based on theory and calibrated by random finite-element method simulations, are presented and used to investigate the probability that a liner exceeds regulatory hydraulic flow requirements. The proposed methodology is illustrated by an example.

This study explores the elastoplastic deformational behavior of gravelly soils. A series of drained triaxial tests with controlled stress paths [conventional triaxial compression (CTC) and conventional triaxial extension (CTE)] were conducted using large specimens composed of gravelly soils. Experimental results reveal that the elastic and plastic deformation of gravelly soils exhibits the following characteristics: (1) the elastic shear modulus stiffens under increase of hydrostatic loading; (2) during the CTC tests, plastic deformation occurs before the failure state, and the influence of confining pressure on the plastic strain is insignificant; (3) through the CTE path, the shear strain dominates the plastic deformation; (4) based on the distribution of plastic flows, the gravelly soils follow the nonassociated flow rule; and (5) this study proposes a possible geometry of plastic potential surface for gravelly soil, which includes two parts: an approximately horizontal line and an elliptic surface in the $p-\sqrt{J_2}$ plane.

Negative skin friction (NSF) can induce an increased compressive force on piles, called dragload, and additional pile settlement caused by the downward pull of the soil, called downdrag. To investigate the efficiency of shielding effects on dragload and downdrag of piles, centrifuge tests have been carried out to study the shielding mechanisms created by installing sheet piles sleeves around an existing pile in consolidating ground. The effects of various shielded lengths have also been investigated. Comparisons between centrifuge test results and finite-element (FE) analyses are made and discussed. Based on centrifuge tests, it is clear that the shielding effect on the dragload decreases only gently with a decrease in the shielded length, whereas the shielding effect on the downdrag decreases exponentially with a decrease in the shielded length. Numerical simulations of the centrifuge model tests on the sleeved center piles reveal that the observed shielding effects on the center pile are attributed to the stress transfer from the consolidating soft soil to the sheet pile sleeve. As consolidation proceeds, the relatively stiff sheet piles sleeve hangs up the soil, leading to a significant reduction in the vertical and horizontal effective stresses in the soil and in the NSF on the center piles. The deeper the depth, the greater the hang-up effects. Thus, the shielding effect increases with the shielded length of the center pile. The reduction in the NSF on the center piles protected by the sheet pile sleeve is more significant than the reduction in the NSF from the sacrificial piles with the same shielded length.

The compression behavior of Canadian oil sands was investigated by running high-stress oedometer compression tests up to 65 MPa. An X-ray microtomography investigation confirmed the significant disturbance affecting the core samples, showing large pores located between dense intact clusters made up of angular sand grains. Compression tests confirmed the significant effects of disturbance on the compression characteristics, providing a much softer response without any memory of the significant load applied by the 3- to 4-km-thick ice sheet during the Quaternary period. High-stress compression allowed us to bring back the samples close to the in situ estimated porosity, providing compression characteristics (estimated from a loading cycle) close to the intact ones, despite obvious differences in fabric (including the effects attributable to grain crushing at high stress). Creep behavior was also observed, and an estimate of the order of magnitude of the creep strain corresponding to the Quaternary period is provided.

This paper discusses the seismic retrofit of Tuttle Creek Dam near Manhattan, Kansas, including investigations, seismic analyses, design, construction, and stabilization techniques used. Original plans called for stabilization of the upstream and downstream slopes and installation of an upstream cutoff wall to reduce underseepage. However, constructability and dam safety issues, along with the results of refined seismic deformation analyses, led to cancellation of the jet grouted upstream slope stabilization and cutoff wall. Downstream slope stabilization was to be accomplished by jet grouting or soil mixing, but ultimately was accomplished using a self-hardening cement-bentonite (C-B) slurry to construct transverse shear walls. A total of 351 transverse shear walls were constructed along the downstream toe by primarily clamshell equipment. Typical shear walls are 13.7 m long, 1.2 m wide, and extend 18.9 m deep or about 6.1 m into the coarse foundation sands. The walls are spaced at 4.3 m on center along the downstream toe for a replacement ratio of about 29%. In addition to the transverse shear walls, the relief well collection ditch along the downstream toe was replaced with a buried collector system to further improve downstream stability and underseepage control.

This study investigates the kinematic behavior of a clay-mandrel-anchor system during the driving-retrieval process and its influence on the installation of prefabricated vertical drains and clay disturbance. In addition, a new anchor plate with an asymmetric shape is proposed as an alternative for improved anchoring performance and clay disturbance mitigation. To investigate the behavior of the clay-mandrel-anchor system, two-dimensional centrifuge model tests were developed and successfully performed to visualize anchoring kinematics and deformation of the clay layer. The tests demonstrated that the asymmetric anchor plate effectively provides an anchoring mechanism and reduces the degree of disturbance. The conventional anchor has potential risk of delayed anchoring and thus unsuccessful installation. While the amount and extent of clay deformation are obviously affected by the protruding length of the anchor plates into the clay, the protrusion length has less influence on the range of the smear zone than the degree of disturbance in the smear zone. The asymmetric anchor considerably reduces the smear effect, as three sides of the mandrel have minimal protrusion length from the center unlike in the conventional anchors.

To expand the improvement region, a series of electroosmotic chemical tests was performed to study the mechanism of improvement. Results showed that injection of calcium chloride and sodium silicate solutions could improve the soil near the cathode and anode, respectively. Injection of calcium chloride solution for a rational injection time, followed by the injection of sodium silicate solution, could yield a fairly good improvement result for the entire sample. The rational time for the injection of calcium chloride solution could be obtained by selecting the time between the first and second turning points on the relational curve of total drained water volume and injection time. Moreover, appropriate concentrations of injected solutions were studied and were discussed in this paper.

This research investigated the confined flow under hydraulic structures. The hydraulic conductivity of the soil was modeled as a spatially random field, which followed a lognormal distribution. Only porous media that have anisotropic heterogeneity were investigated. Results showed that larger anisotropic heterogeneity ratios (the ratio of horizontal to vertical scale of fluctuation) dramatically increased the seepage flow. This increase of flow was more pronounced at larger coefficients of variations. A similar trend was observed in the case of uplift force, although it was less sensitive to the increase in the anisotropic heterogeneity ratio. Moreover, both the seepage flow and the uplift force tended to their deterministic values as the ratio of anisotropic heterogeneity increased. Results also showed that the exit hydraulic gradient attained its greatest value at particular values of the anisotropic heterogeneity ratio.