Journal of Geotechnical and Geoenvironmental Engineering

Dynamic soil-structure interaction effective stress analyses are performed to identify key trends in the settlement of buildings with shallow foundations affected by soil liquefaction. Over 1,300 analyses are performed by systematically varying subsurface conditions and building properties while applying 36 earthquake motions. Shear-induced soil deformation mechanisms govern during strong shaking, whereas volumetric-induced deformation mechanisms contribute more significantly after shaking. The analytical results identify the key parameters controlling shear-induced building settlement due to liquefaction. The relative density of the liquefiable layer is the key soil engineering property, and its thickness and depth are important soil profile characteristics. Building contact pressure is the most important building parameter, and building width is also important. The ground motion intensity parameters that correlate best with building settlement are standardized cumulative absolute velocity, Arias intensity, and 5% damped 1-s spectral acceleration. The postliquefaction bearing capacity factor of safety indicates when large building settlements are possible.

Soil setup is defined as the increase in axial resistance of driven piles after end of driving (EOD). Very recently, over the last five years, the time-dependent increase in axial resistance of prestressed concrete piles (PSC) driven into mainly cohesive soils of Louisiana, due to setup, was systematically quantified using measured field tests. Based on the collected data of thirty PSC test piles (TP) during driving and following load tests, it was observed that soil setup is significant and continues to develop for a long time after EOD. This study will first present the development of analytical models to estimate soil setup after EOD followed by a procedure to determine the resistance factor of a pile setup in accordance with the load and resistance factor design (LRFD) methodology that targets a specific reliability index. The analytical models were developed from 70 clayey soil layers of twelve instrumented test piles. The soil setup resistance was predicted using the developed analytical models at four different time intervals (i.e., 30, 45, 60, and 90 days) after EOD in order to perform the LRFD calibration. The calibration was performed using the first order second moment (FOSM), first order reliability method (FORM), and Monte Carlo simulation (MCS) method on thirty test piles (i.e., twelve instrumented test piles and eighteen noninstrumented test piles). The statistical database showed that log-normal distribution can be used to properly describe the probabilistic characteristics of predicted setup resistance by the developed analytical models and the resistance factor was calibrated with a target reliability index, $\beta$, of 2.33. The calibration showed that the resistance factor due to soil setup was 0.35.

Uplift resistance is a key parameter against upheaval buckling in the design of a buried pipeline. The mobilization of uplift resistance in dense sand is investigated in the present study based on finite-element (FE) analysis. The prepeak hardening, postpeak softening, density-dependent, and confining pressure–dependent soil behavior are implemented in FE analysis. The uplift resistance mobilizes with progressive formation of shear bands. The vertical inclination of the shear band is approximately equal to the maximum dilation angle at the peak and then decreases with upward displacement. The force–displacement curves can be divided into three segments: prepeak, quick postpeak softening, and gradual reduction of resistance at large displacements. Simplified equations are proposed for mobilization of uplift resistance. The results of FE analysis, simplified equations, and model tests are compared. The importance of postpeak degradation of uplift resistance to upheaval buckling is discussed.

Limited uniform settlement of a building subject to liquefaction may not affect the living conditions of the residents immediately after an earthquake. However, even some small nonuniform settlement can cause serious disruptions to residents’ normal life. Because most residents of inexpensive houses cannot afford expensive retrofitting measures against this problem, different possible countermeasures against seismic nonuniform settlement of buildings are proposed, and their performance is evaluated in this study. The proposed mitigations should be not only technically promising but also economically affordable for residents of private houses. The proposed mitigations are (1) installation of sheet-pile walls around the building’s foundation with limited lowering of the groundwater level; (2) installation of diagonal drains under the foundation accompanied by limited lowering of the groundwater level; and (3) limited surface ground improvement. The experimental results showed some differences between the performances of the proposed mitigations in non-uniformly loaded buildings compared with cases of uniformly loaded buildings. It is observed that installation of sheet-pile walls is not a promising countermeasure against tilting of the structures even though it reduces the total settlement. The liquefied sand in the area surrounded by the sheet piles and the building’s foundation could easily deform, resulting in tilting of the building. In contrast, installation of drains reduced both settlement and tilting of structure by providing a nonliquefied column of soil under the foundation. Surface ground improvement also reduced both total settlement and tilting of the structure. However, its efficiency in reduction of the uniform settlement was found to be mostly dependent on the length of improvement rather than its depth, whereas the depth of improvement plays an important role in reduction of the tilting.

Structural failures of soil-nailed structures occasionally occur due to the poor integrity of soil nails. The objective of this study was to evaluate soil nail integrity by estimating the installed length and grouted ratio of the soil nails using longitudinal waves. Laboratory experiments were performed using steel bars as well as partially and fully grouted steel bars with different lengths. Field experiments were conducted for in situ soil nails in slopes. The generation and measurement of longitudinal waves were achieved using a hammer and an accelerometer, respectively. The results showed that the velocity of the longitudinal wave along the grouted steel bars in air was the same as that of the grouted steel bars in soil and was less than that of steel bars. The longitudinal wave velocity along the grouted steel bar decreased with an increase in the grouted ratio. The installed lengths of in situ soil nails were evaluated on the basis of the longitudinal wave velocity along the fully grouted steel bar. The results of this study suggest that the relationship between the velocity and the grouted ratio can be a useful indicator for evaluating the integrity of soil nails with different lengths and those connected by the coupler.

A baseline study was conducted to evaluate the influence of the composition of the enzyme-induced carbonate precipitation (EICP) treatment solution on the efficiency of carbonate precipitation. EICP is an emerging biogeotechnical ground-improvement technique in which calcium carbonate is precipitated from an aqueous solution within the soil pores. A solution consisting of 1 M urea, 0.67 M calcium chloride (${\mathrm{CaCl}}_2$), and $3\mathrm{g}/\mathrm{L}$ urease enzyme (reported activity $\mathrm{3,500}\mathrm{U}/\mathrm{g}$) was identified as the preferred composition of the solution for EICP treatment of soil, because that concentration of ingredients results in high precipitation mass, high precipitation efficiency, and high enzyme efficiency. It was also shown that effluent from EICP treatment may be used as a source of ${\mathrm{CaCl}}_2$ and urea but cannot be used as a source of urease enzyme. Adding calcite seeds facilitates densely agglomerated calcite crystal formation. Unconfined compression tests on EICP-treated specimens rinsed with deionized water to flush organic matter and ammonium chloride from the specimens suggest that there may be a threshold carbonate content above which the strength dramatically increases. The strength of EICP-treated soil is influenced not only by the amount of carbonate precipitation and but also by the method of preparation and by particle packing. Rinsing of the EICP-treated specimens with deionized water was found to cause dissolution and flushing of organic matter and ammonium chloride salt precipitates.

The purpose of this paper is to present a simple analytical model to describe the flow of a dilute colloidal silica dispersion through a porous medium column. The model presents the movement with time of the interface between the dispersion and the water it displaces, the velocity of the interface, and the time-varying discharge through the medium. The effects of both viscosity difference and density difference of the displacing dispersion are included. Results of the model compare favorably with measurements of flow through sand columns 0.914 and 3.05 m long. The viscosities of the dispersions were approximately twice those of the water they displaced and the density was about 8.3% higher. The model is expanded by using a numerical scheme to predict the interface velocity for dispersions having linear and exponential time-varying viscosities.

Strong earthquakes threaten civil structures through ground shaking and, sometimes, due to the outcrop of the causative fault. A number of hybrid foundation schemes that have been found helpful in protecting a structure against strong shaking are evaluated with respect to their effectiveness in reducing the impact of tectonic displacements as well. A series of physical model tests are conducted on hybrid foundations combining (1) footings, designed to provide seismic protection (isolation) through rocking, with (2) a number of belowground interventions hopefully capable of diverting the fault rupture and limiting structural distortion. Fault rupture propagation within a stratum of dense dry sand is simulated at a scale of 1:15 using a custom made 3-m-long split box. The performance of hybrid foundation systems embedded in sand is compared with that of the same footing without interventions. Finite-element modeling is also used and, after validation against experimental results, is used in a parametric study on the effectiveness of the proposed interventions and the potential optimization of their geometry.

Preloaded foundation capacity has recently been a topic of major interest in offshore foundation engineering. The increase in undrained shear strength due to preloading and consolidation enables the foundation to resist a larger environmental load, thereby reducing the size of the footprint. This paper investigates the shape and size of the VHM (i.e., vertical, horizontal, and moment) capacity surface of a skirted circular foundation by comparing both the no-preload and the post-preload responses using coupled small strain finite-element analyses. The influence of the distribution of in situ undrained shear strength, the magnitude of vertical preload, and the duration of consolidation on the foundation’s combined capacity are considered. An approach to estimating the post-preload VHM capacity surface of the skirted circular foundation is provided using a new set of formulations that are compared with available solutions for other foundation geometries and soil conditions.

A systematic series of temperature-controlled oedometer tests on intact and remolded samples of sensitive clay from two depths has been performed. The focus is on studying the temperature effects on the emerging creep rate for a relatively small temperature range, that is, 5°C–25°C, during incremental heating and decremental cooling tests with steps of 5°C. An efficient testing scheme has been developed that exploits the simultaneous testing of several samples. Furthermore, the testing scheme is designed such that no excess pore pressures are generated in the samples during temperature change. The creep rate for intact samples proved to be very sensitive to a temperature change, with the largest effects found for stress levels above the apparent preconsolidation pressure. Heating increments showed larger increases in creep rate than cooling decrements. Both, however, led to a significant change of creep rate in the intact clay samples. In contrast, the reference tests on remolded samples of the same clay that were reconstituted to the in-situ stress state did not show much sensitivity to temperature change. The latter leads to the conclusion that the significant thermal creep triggered in sensitive clays is primarily an effect of the apparent bonding of the natural clay.

In situ characterization of dynamic soil characteristics by means of surface wave tests frequently involves the determination and inversion of dispersion and attenuation curves. The inverse problem is formulated as a non-linear least-squares problem minimizing the misfit between theoretical and experimentally obtained dispersion and attenuation curves, which is often solved using gradient-based techniques. A new analytical and computationally efficient methodology is presented for the determination of the sensitivities of the Rayleigh and Love phase velocities and attenuation coefficients with respect to the shear wave velocity, the dilatational wave velocity, the material damping ratios in volumetric and shear deformation, and the thickness of the layers. The expressions are based on the direct stiffness method for elastodynamic wave propagation. The proposed analytical method requires only a fraction of the calculation cost of the dispersion and attenuation curves. Sensitivities of Rayleigh dispersion and attenuation curves are computed for four soil profiles, including two shallow soil profiles, a very deep profile, and an inverse profile with a soft layer trapped in between two stiffer layers. Results obtained with the proposed method are shown to be in perfect correspondence with sensitivities reported in the literature and obtained with a finite difference method.

Extensive damage to offshore and port structures supported on piles behind a quay wall has been frequently reported as a result of soil liquefaction and lateral spreading in earthquakes. This study aims to explore the dynamic behavior of a soil-pile-quay wall (SPQW) system subjected to liquefaction-induced lateral spreading in terms of experimental investigation, numerical simulation, and global sensitivity analysis (GSA). A large-scale ($1g$) shake-table experiment on a SPQW system is presented in detail, including sensor arrangement, model configuration, and experimental results. Typical liquefaction phenomena, such as sand boils and ground settlement, were observed during the test. The shake-table experiment results were used to validate a three-dimensional (3D) nonlinear finite-element (FE) model developed for dynamic analysis of a fully coupled soil-water system. This FE model accounts for the interactions of the soil, pile, and quay wall through explicitly modeling them as an integrated system. Based on the validated FE model, a GSA was performed to further investigate how variations in system properties influence the dynamic responses of the SPQW system. The GSA with high computational efficiency was implemented using the polynomial chaos expansion (PCE) surrogate model, and the GSA results indicate the relative importance of modeling parameters, which provides insightful information about the system behavior. The presented work provides useful guidance on experimental and numerical simulations of typical SPQW system.

When heavy rainfall, such as that associated with tropical storms, falls on steep hillsides, shallow landslides are often one of the damaging consequences. To assess landslide potential from heavy rainfall, a strategy of combined numerical simulation and field monitoring of variably saturated hillslope conditions is developed. To test the combined method, hillslope hydrologic data from paired field monitoring sites in western North Carolina are examined. The hydrologic data collected from the field monitoring site where no shallow landslide has occurred is used to identify and calibrate the hydromechanical parameters used in a numerical ground water flow model. The identified parameters are then used to simulate landslide potential at the two hillslopes during heavy rainfall associated with hurricanes Frances and Ivan (HFI) that impacted western North Carolina in 2004. Results identify the timing of instability at the shallow landslide site and show that the stable site remains stable during rainfall associated with the HFI tropical storms. Thus, the results demonstrate the effectiveness of combined numerical modeling and field monitoring to evaluate landslide potential under variably saturated conditions.

This paper investigates a basement excavation adjacent to running metro tunnels and underground pipelines in Shanghai soft soil. The zoned excavation technique was adopted to control the deformations caused by excavation. The excavation site was divided into three parts and successively constructed in the order of Zones A, B, and C with the bottom-up method. The field data of retaining walls, struts, columns, surrounding ground, pipelines, and metro tunnels were monitored and analyzed in terms of lateral and vertical deformations throughout the whole construction process. The data indicates that the wall deflection and column heave in Zones B and C were smaller than those in Zone A. The ground surface settlements near the metro lines were effectively reduced by the zoned excavation technique. The deformations of the metro tunnels and pipelines were well controlled within the acceptable limits. A general relation between wall deflection and the excavation area was also proposed based on this and 15 similar cases.