Journal of Geotechnical and Geoenvironmental Engineering

This paper describes the influence of sample disturbance on laboratory undrained shear strength tests used for pile capacity calculations of driven close-end pipe piles, referencing an approach based on the stress history and normalized soil engineering properties (SHANSEP) for estimating the side resistance of pipe piles in cohesive soils. The SHANSEP technique provides a rational basis for relating the soil overconsolidation ratio (OCR) to the normalized side resistance overcoming the problems related to sample disturbance. Sample disturbance of soils with $\mathrm{OCR}<2$ is identified as a significant factor affecting the selection of values of side resistance for pile design. The empirical record of load test sites was modified to remove test data that were likely affected by sample disturbance effects from the current database referencing the SHANSEP-based approach to provide a reliable set of reference undrained strengths and measured side resistance values, which produces an equivalent new undrained (alpha) format with limited sample disturbance effects. This equivalent alpha approach is then related to current alpha methods showing the effects of sample disturbance on the undrained strength values, corresponding alpha values, and corresponding calculated pipe pile side resistance capacity. Data with less disturbance effects and subsequently higher undrained strength are shown to result in lower alpha values as compared to current values. Improved methods of sampling and testing, the use of in situ tests to determine undrained strengths without disturbance effects, and calculated undrained strengths developed from oedometer tests need an alpha format matching the improved site characterization or the calculated pile capacity could be overestimated using the better samples and better site characterization.

Four polyethylene based vapor barriers and six different geomembranes were examined for their diffusive properties with respect to benzene, toluene, ethylbenzene, and xylenes (BTEX). All four vapor barriers performed comparably. Of the geomembranes tested, high-density polyethylene (HDPE) showed the greatest diffusive resistance to BTEX, while polyvinyl chloride (PVC) showed the least, LLDPE (linear low-density polyethylene), CSPE (chlorosulphonated polyethylene) and two KEE/EIA (ketone ethylene ester/ethylene interpolymer alloy) geomembranes all performed similarly, bounded by HDPE and PVC. Based on data collected at 22, 30, and 40°C, Arrhenius relationships are presented for the six geomembranes. Each geomembrane was evaluated for performance as a diffusive barrier in a landfill cover scenario. Each vapor barrier and two geomembranes were evaluated, through contaminant transport modeling, for performance as a diffusive barrier to vapor intrusion into a warehouse and substantial potential differences in performance are reported.

This paper presents an innovative grouted ground improvement pile alternative (biogrouted pervious concrete pile). Biogrouting is a potential ground improvement technique that utilizes soil bacteria to induce calcium carbonate (${\mathrm{CaCO}}_3$) precipitation to cement soil particles. The most commonly investigated biogrouting method is microbial-induced carbonate precipitation (MICP). Previous large-scale applications of MICP have encountered practical difficulties including bioclogging, which results in a limited zone of cemented soil around injection points and heterogeneous distribution of ${\mathrm{CaCO}}_3$. The research presented in this paper focuses on evaluating the feasibility of MICP biogrouting of a limited soil zone surrounding permeable piles to improve their responses when subjected to axial compression loading. To investigate this, two instrumented pervious concrete piles with diameters of 76 mm and lengths of 1.07 m with and without MICP biogrouting were subjected to compression loading at the Soil-Structure Interaction (SSI) facility at Lehigh University, Bethlehem, Pennsylvania. The pervious concrete pile serves as an injection point during the MICP biogrouting. The mechanical responses of the pile and surrounding soil were analyzed, along with shear wave (S-wave) velocity, moisture content, and ${\mathrm{CaCO}}_3$ and ammonium contents of the surrounding soil. The results presented in this paper demonstrated that the limited MICP-improved zone around pervious concrete piles improved the load-displacement response, load transfer, and pile capacity under compression loading.

Many forensic studies conducted after catastrophic earthquakes revealed severe damages to pile foundations caused by bedrock fault movement. The mechanism behind these pile foundation failures is not yet fully understood. In this study, two centrifuge model tests are carried out on a single pile and on a group of three piles in sand subjected to normal faulting. The surface settlement profile and additional internal forces of the piles are measured. The surface settlement profile in sand could be well fitted and predicted with a profile function (error function). The single pile, which is located in a differential settlement zone, is displaced, and the pile top rotates toward the hanging wall, inducing an additional bending moment along the pile. The pile group is then forced to rotate toward the hanging wall because the three piles are well connected to the pile cap. Driven by the movement of the two additional piles and a pile cap in place, the pile on the footwall side experiences greater displacement and bending moment than it does when it is only for a single pile. Due to relative downward displacement of the surrounding soil, negative shaft friction is mobilized and the middle pile could fail in tension. Both the downward drag force in the middle pile and the working load are transferred to the other two piles, resulting in pile failure that exceeds the ultimate capacity.

Observations of the performance of basement walls and retaining structures in recent earthquakes show that failures of basement or deep-excavation walls in earthquakes are rare even if the structures were not designed for the actual magnitude of the earthquake loading. For instance, no significant damage or failures of retaining structures occurred in the recent Wenchuan earthquake in China (2008) or in the subduction earthquakes in Chile (2010) and Japan (2011). To develop a better understanding of the distribution and magnitude of the seismic earth pressures on cantilever retaining structures, a series of centrifuge experiments were performed on model retaining and basement structures with medium dense cohesionless backfill. This paper provides a general overview of the research program and its results. Two sets of centrifuge-scale experiments were carried out on the centrifuge at the Center for Geotechnical Modeling at UC Davis. Three different types of prototype retaining structure were modeled in this research effort as follows: (1) a nondisplacing cross-braced (basement) structure with a stem stiffness of $5.92\times {10}^{10}\mathrm{lb}\text{-}{\mathrm{in}\mathrm{.}}^2$ per ft width ($5.57\times {10}^{05}\text{\hspace{0.17em}kN-}{\mathrm{m}}^2$ per m width) and $1.04\times {10}^{10}\mathrm{lb}\text{-}{\mathrm{in}\mathrm{.}}^2$ per ft width ($9.79\times {10}^{04}\text{\hspace{0.17em}kN-}{\mathrm{m}}^2$ per m width); (2) a nondisplacing U-shaped cantilever structure with a stem stiffness of 5.92 and $1.04\times {10}^{10}\mathrm{lb}\text{-}{\mathrm{in}\mathrm{.}}^2$ per ft width ($9.79\times {10}^{04}\text{\hspace{0.17em}kN-}{\mathrm{m}}^2$ per m width); and (3) a free standing, cantilever retaining wall with a stem stiffness of $2.4\times {10}^{10}\mathrm{lb}\text{-}{\mathrm{in}\mathrm{.}}^2$ per ft width ($2.26\times {10}^{05}\text{\hspace{0.17em}kN-}{\mathrm{m}}^2$ per m width). Overall, for the structures examined [i.e., wall heights in the range 6.1–9.15 m (20–30 ft)], the centrifuge data consistently show that the maximum dynamic earth pressure increases with depth and can be reasonably approximated by a triangular distribution. This suggests that the result of the dynamic earth pressure increment acts near 0.33H above the footing as opposed to 0.5–0.6 H recommended by most current design procedures. The current data also suggest that cantilever walls can resist ground accelerations up to 0.4 g if designed with an adequate static factor of safety.

This paper describes the results of a laboratory investigation performed on clean sand and low-plasticity silty sands, recovered at different locations of the bank stretch at Scortichino, which was affected by serious damages following the 2012 Emilia Romagna earthquake in Italy. A comprehensive cyclic simple shear (CSS) testing program was undertaken to evaluate the liquefaction potential and pore pressure response of silty sand layers, which form the subsoil at the site. A series of undrained CSS tests were carried out on undisturbed samples by applying an initial static driving shear stress before cyclic loading (nonsymmetrical tests), with the aim of gaining a better understanding of the role played by a static preshearing on the observed liquefaction phenomena. The results obtained prove that, in nonsymmetrical cyclic loading tests, low-plasticity silty sands tend to be more susceptible to liquefaction than in symmetrical cyclic loading tests. The onset of liquefaction occurs by large shear strains, and not by complete loss of effective stress resulting from the pore pressure buildup.

The effective preconsolidation stress (${\sigma }_p^{\prime }$) of clay is classically determined from one-dimensional consolidation tests on undisturbed samples but a first-order approximate value can be estimated from its plasticity and water content characteristics. In this paper, initially a twofold simple empirical model for predicting ${\sigma }_p^{\prime }$ that bifurcates at an overconsolidation ratio (OCR) of 3 is developed, and then its validity and generality are evaluated using an external (independent) validation data set that includes 500 records from 50 different sites. The proposed model is accompanied by a discriminant function that uses water content and plasticity characteristics to separate soils with $\mathrm{OCR}<3$ (contractive) versus soils with $\mathrm{OCR}\ge 3$ (dilative). The results of applying the new and existing simple empirical models to the validation data set indicate that the predictive capability of the new model is quite superior to prior existing approaches that have unacceptable performance.

This paper focuses on understanding the temporal behavior of backward erosion using measurements from densely spaced piezometers during large-scale field experiments in October 2009 and September 2012 at IJkdijk in the Netherlands. Observations and data originate from nearly continuous monitoring of pore-water pressure and visual observations of seepage and sand boils. In 2009, the test progressed to breach (release of reservoir), while in 2012 the test included a vertical geotextile in the foundation to mitigate backward erosion such that the embankment did not breach. Study of pore-water pressure provides indicators of backward erosion (also known as piping) detectable in instrument readings. Temporally and spatially dense pore-water pressure measurements detect two pore-water pressure transitions characteristic to the development of internal erosion, even in piezometers located away from the backward erosion activity. First, the backward erosion causes anomalous pressure decrease in piezometers, even under constant or increasing upstream water level. Later, measurements stabilize as backward erosion extends further upstream of the piezometers, as shown in the 2009 test. In the 2012 test, measurements did not stabilize and the embankment did not breach, likely because of the geotextile installed vertically in the foundation near the downstream toe. The transitions provide an indication of the temporal development and the spatial extent of backward erosion.

A new soil water retention curve (SWRC) equation, generalized from previous models and the latest understanding of soil-water interaction, explicitly accounts for capillary and adsorptive processes. Under the assumption of local thermodynamic energy equilibrium, soil water is one of two types (capillary and adsorptive), and occurs in three retention regimes in the order from high to low matric potential: Capillary, adsorbed film, and tightly adsorbed soil water. A new equation for adsorptive water as a function of matric potential is introduced. The transition between adsorption and capillary regimes is smoothly described with a cavitation probability function imposed on a commonly used SWRC model. Three parameters (adsorption capacity, adsorption strength, and mean cavitation suction) are defined, replacing the commonly used parameters of residual moisture content, pore structure, and residual suction. The soil water retention data for 21 soils, representing a variety of soil compositions, are used to assess the proposed SWRC equation in comparison with other SWRC models. The proposed SWRC equation is shown to be a statistical improvement over other models in both the high and full suction range. The calculated adsorption capacities of these soils accord well with an existing adsorption-capillary based SWRC model and experimental evidence.

If ${\overline{U}}_v>0.50$, Asaoka’s method can be used to evaluate $c_v(s)$ and $s_{cf}$ from settlement data, but the method leads to unsafe results when the data are measured when ${\overline{U}}_v<0.50$ (i.e., $c_v$ much too high and $s_{cf}$ much too low). For field conditions where all data have $({\overline{U}}_v)<0.50$, one cannot predict $s_{cf}$ or estimate $c_v(s)$ solely on the basis of measurements of surface settlement. These conditions require analysis of both piezometer and settlement data together with knowledge of the initial excess pore pressure ($u_0$). With proper instrumentation, Johnson’s incremental time ($\mathrm{\Delta }t$) graphical method can be used to estimate $c_v$ and $s_{cf}$, but this technique tends to be cumbersome and imprecise. Two new techniques (EFM-1 and EFM-2) based on the Laplace Transform are proposed. The accuracy of $c_v$ and $s_{cf}$ estimates using EFM-1 and EFM-2 are evaluated as functions of piezometer location, time, and uncertainty in $u/u_0$.

A method to generate biocementation in sand using the microbially induced carbonate precipitation (MICP) process and calcium source produced from eggshell is presented in this paper. Instead of using calcium chloride or other calcium salts, soluble calcium was produced by mixing eggshell with vinegar and used for the MICP process. The compressive strength and permeability of sand treated using this method were measured using unconfined compression and permeability tests. A comparative study between sand samples treated using calcium produced from eggshell and those using calcium chloride with the same concentration of calcium was carried out. The study shows that the effect of the MICP process using calcium produced from eggshell is just as good as that using calcium chloride. The optimum ratio of eggshell and vinegar for the MICP process was established.

This paper presents an experimental investigation of the relative density on dilative behaviors of clayey sand–fouled aggregates. The large-scale monotonic triaxial tests (TX) were conducted on mixtures in saturated conditions. Values of friction angles were compared with the dilatancy angles to stress the effect of the relative density on shear behaviors. A correlation among the relative density, peak friction angle, the friction angle at the end of the test, and peak stress based on triaxial tests was established. The parameters of the correlation were determined. The findings are expected to improve the understanding of the dilative behavior changes in character as the relative density changes