Journal of Geotechnical and Geoenvironmental Engineering

Dispersive soils are highly susceptible to erosion, particularly when they are used as a base soil for the core of an earth dam. To prevent migration of the core material, the required filter must be designed and properly positioned in the structure. A study was carried out to assess the adequacy of the existing filter design criteria in controlling core materials that are not only dispersive but also broadly graded and are commonly available for use in the construction industry. The criteria of $D_{15f}/d_{85}\le 5.5$ and $D_{15f}\le 0.28\mathrm{mm}$, each with a reasonable factor of safety, were found to be applicable for the broadly graded, highly dispersive soils from Group 1 and Group 2, respectively. The criteria of $D_{15f}/d_{85\mathrm{reduced}}\le 9$ for the soils of Group 1, $D_{15f}/d_{85\mathrm{reduced}}\le 7$ for the soils of Group 2 with significant clay content, and $D_{15f}/d_{85\mathrm{reduced}}\le 2$ for the soils of Group 2 with significant silt content were also found to be acceptable. Thus, the required $D_{15f}$ size of a filter reduces with the increasing dispersivity of the corresponding base soil. The dispersivity prevalent in the base soils requires the required no-erosion filter boundaries for the soils of Group 2 to be lowered—more so than for the soils of Group 1. Furthermore, the constriction-based criterion of $D_{c35}/d_{85}^{*}\le 1.25$ was found to be acceptable for the base soils of Group 1 with high dispersivity, with the corresponding filter having a relative density of 75%. However, for the base soils of Group 2, the criterion of $D_{c35}/d_{85}^{*}\le 1.0$ was found to be acceptable; for the highly dispersive type, the required criterion was $D_{c35}/d_{85}^{*}\le 0.5$. Further tests were carried out by simultaneously considering the effects of the changing particle size distribution (PSD) and the percent dispersion (D) of the base material on the required no-erosion filter boundary, resulting in the new criterion of $D_{15f}/d_{85}=10.0\exp (-0.009D)$ for the soils of Group 1. However, for the soils of Group 2, the effect of changing the $d_{85}$ on the required no-erosion filter boundary was not as profound as the effect of changing dispersivity, resulting in different no-erosion filter boundaries for the various ranges of dispersion.

External water level variations, such as rapid drawdown or flood loading, change the internal pore pressures in an embankment as a result of changes in the boundary conditions. Three different effects result: (1) changes in water pressure on the slope change the seepage boundary conditions, (2) changes in the total stress applied by the weight of the water on the slope change the confining pressure on the soil, and (3) changes in the stabilizing load from the reservoir cause changes in shear stress. Uncoupled transient seepage analyses, which consider only the first effect, are increasingly being advocated as an appropriate means to calculate pore pressures for effective stress stability analyses following water level changes. This paper discusses the limitations of uncoupled transient seepage analyses for calculating pore pressures during drawdown, explains the requirements for more appropriate analyses, and gives examples that show the errors incumbent on the use of uncoupled analyses.

Steel bar mat is a common reinforcing material in mechanically stabilized earth (MSE) walls. The current method to calculate the pullout capacity of these materials is an empirical-based formulation found in AASHTO and Federal Highway Administration (FHWA) design guidance documents. The accuracy of the current formulation is evaluated using a large database of laboratory pullout tests including data that were not available at the time the current model was developed. A new model is proposed, and it is shown to have advantages over the current formulation particularly when pullout capacity design and analysis will be carried out in a load and resistance factor design (LRFD) framework. Calibration of the new model and quantitative comparisons of the accuracy of the two models are evaluated using statistical characteristics of bias values where bias is the ratio of measured pullout capacity to predicted pullout capacity. The accuracy of both models is evaluated for two cases: (1) when project-specific pullout data are not available (the typical case) and presumptive default coefficients must be used; and (2) when project-specific laboratory pullout box data are available. The influence on calibration outcomes of data sets corresponding to markedly different soils and test methodology is demonstrated in the paper. The data reported in the paper are a necessary precursor to future LRFD calibration of the pullout limit state in the internal stability design of bar mat reinforced soil walls.

This paper presents the modeling of the phenomenon of collapse upon wetting using the effective stress approach. To this purpose, Bishop’s effective stress equation is applied in addition to an elastoplastic framework for the volumetric behavior of unsaturated soils. Bishop’s parameter $\chi$ is obtained from a porous-solid model that is able to simulate the soil-water retention curves during wetting-drying cycles. The proposed framework includes the hysteresis of the retention curve and to some extent the hydro-mechanical coupling of unsaturated soils. This model is able to reproduce quite precisely the phenomenon of collapse upon wetting using a single valued compressibility index. It also represents a unifying framework for saturated and unsaturated soils.

Scour is the removal of soil around bridge supports due to water flow during floods. One of the major problems with scour is in the case of unknown bridge foundations. Bridges with unknown foundations are listed in the National Bridge Inventory as having insufficient data for scour evaluation, particularly regarding foundation depth. Knowing the foundation depth is a critical component of scour risk assessment. Multiple nondestructive testing methods are currently used to determine the depth of unknown bridge foundations; however, many methods are hindered by the type of substructure. An advantage of using near-surface geophysical methods, specifically electrical resistivity (ER) and induced polarization (IP) imaging, is that the inversion processes yield subsurface images, thereby allowing the depth and, to a lesser extent, the foundation type to be seen. Unlike a majority of existing testing methods, ER and IP imaging do not physically use the structure so they are applicable to simple and complex foundation structures. In this paper, results of ER and IP imaging tests performed at the Texas A&M University National Geotechnical Experimentation Site, on a bridge with known foundation depth and a bridge with unknown foundation depth are presented. The applicability of ER and IP imaging to determine substructure characteristics for unknown bridge foundations is also discussed. A probability of nonexceedance estimate for predictions using IP is given to quantify IP imaging reliability.

This paper presents the results of a series of shake table tests of two 460-mm-diameter columns supported on 1.5-meter-square shallow rocking foundations. The tests were conducted using the Large Outdoor High-Performance Shake Table of the Network for Earthquake Engineering Simulation at the University of California at San Diego. The first specimen was aligned with the uniaxial direction of shaking, and the second was positioned in a skew configuration. The specimens were placed inside a soil-confining box 10.1 m long and 4.6 m wide with a 3.4-m height of clean sand compacted at 90% relative density. Three series of tests were performed; each had different groundwater and backfill conditions. The test protocols included up to six historical ground motions and resulted in peak drift ratios up to 13.8%. For peak drift ratios up to 6.9%, the rocking foundations performed very well, with residual drift ratios between 0.5 and 0.9% depending on the backfill conditions and with minimal settlements and no structural damage.

Hollow bar micropiles are becoming a popular option for foundation retrofitting because of their fast installation and effectiveness as both a foundation system and ground improvement at the same time. This paper presents a field study and numerical investigation of the lateral behavior of single hollow bar micropiles embedded in stiff silty clay deposits. Two monotonic and six cyclic lateral load tests were conducted on four micropiles, and the results were used to calibrate/verify a numerical model that was then used in a numerical investigation. The observed load-displacement curves demonstrated that the micropile behavior was flexible and was governed by the properties of soil along a depth equal to 10 times the pile diameter. The parametric study suggested that hollow bar micropiles can carry moderate lateral loads with proper reinforcement configurations and pile head fixity condition. During cyclic loading, the micropile head stiffness degraded initially as the number of load cycles increased. However, the stiffness reached a constant value after a specific number of cycles at the same load amplitude and at different cyclic load amplitudes.

Compressibility of recycled materials including bottom ash (BA), foundry slag (FSG), foundry sand (FSD), recycled asphalt pavement (RAP), recycled pavement material (RPM), recycled concrete aggregate (RCA), and recycled asphalt shingle (RAS) mixed with glacial outwash sand (GOS) was evaluated using one-dimensional (1D) compression tests. Results showed that except RCA, compressibility of all the compacted recycled materials is higher than that of the compacted GOS. Different compression mechanisms were attributed to each recycled material depending on the type, composition, and morphological characteristics of the particles. Bituminous recycled materials including RAP, RPM, and RAS-GOS mixtures exhibited relatively higher compressibility compared with nonbituminous recycled materials. At a constant vertical effective stress (${\sigma }_v^{\prime }$), compression of the recycled materials increased over time with strain rates that are higher for bituminous recycled materials compared to nonbituminous recycled materials. The vertical strain rates (${\dot{\epsilon }}_v$) of all the recycled materials log-linearly increased with increasing ${\sigma }_v^{\prime }$. The slope of the $\log {\dot{\epsilon }}_v-\log {\sigma }_v^{\prime }$ curves, termed stress coefficient of compression, is independent of the elapsed time after loading. The stress coefficient of compression indicates degree of stress dependency for compression and is different for each recycled material. Secondary compression ratio is a power function of ${\sigma }_v^{\prime }$ indicating that an embankment constructed with recycled materials settles at different rates along the embankment height. Temperature rises increased compressibility of the compacted RAP and RAS-GOS mixtures. On the other hand, thermal preloading significantly reduced the compressibility of the compacted RAP and RAS-GOS mixtures. Construction of embankments containing bituminous materials such as RAP, RPM, or RAS is recommended during summer to induce thermal preloading and reduce long-term settlement. Long-term settlements of typical highway embankments constructed with the recycled materials used in this study were below the allowable limit.

Leaching controlling mechanisms of As, Ba, Ca, Cd, Mg, Se, and Sr from soil alone, fly ash alone, and soil-fly ash mixtures were investigated at a pH range of 1.5–14 through geochemical modeling. Results of the pH-static tests from previous studies indicated that As and Se concentrations increased at alkaline conditions, while Ca, Cd, Mg, and Sr concentrations increased when the pH of the aqueous solutions were acidic. Leaching of Ba tended to increase slightly at alkaline pH values. Effluent pH, oxidation-reduction (i.e., redox) potential $E_h$, and element concentrations measured from pH-static tests were used as input data in the geochemical model. Geochemical modeling results indicated that release of the elements, except As and Se, are controlled by the dissolution and precipitation of oxide, hydroxide, sulfate, and carbonate solids of the elements. For a given element, these solids controlling the leaching of elements were very consistent regardless of soil and fly ash types. Model-based predictions indicated that leaching of Mg and Cd were controlled by carbonate minerals, and both carbonate and sulfate minerals were controlling solids for Ca, Ba, and Sr, depending on the pH of the leachate. According to the results of geochemical modeling analyses, leaching of As and Se were controlled by neither the dissolution nor precipitation of oxide, hydroxide solid minerals. The research reported in this paper suggests that the sorption mechanism was most probably controlling the leaching behavior of As and Se elements.

The lateral response of pile foundations in sand is commonly analyzed using the beam on nonlinear Winkler foundation (BNWF) assumption, with load transfer behavior often characterized by the API sand $p\text{-}y$ relationship (where $p$ is lateral resistance, and $y$ is relative displacement between the soil and pile). This relationship was developed for static loading conditions, with cyclic correction factors intended to represent degradation due to many slow loading cycles. However, the model is often applied for dynamic loading conditions (e.g., earthquake shaking) because suitable alternatives have not been formulated. This paper demonstrates that the API sand functional form is not ideal for dynamic analysis of piles, and presents a new functional form that better captures the nonlinear $p\text{-}y$ behavior of piles in sand during earthquake loading. The new functional form is developed using bounding surface plasticity theory and implemented in an open-source finite-element modeling platform that is freely available to users. The proposed $p\text{-}y$ model is shown to capture the experimental response of a pile from a centrifuge test program using calibrated model parameters.

A pile group consisting of four cast-in-place concrete piles was instrumented to measure the induced bending moment along the piles due to excavation of an adjacent slope. The green field lateral soil movement profiles and the lateral pile deflection profiles were monitored by in-soil and in-pile inclinometers, respectively. The unexpected early arrival of a rain storm prior to the year-end monsoon caused the failure of the slope, which resulted in the severe damage of this pile group located at the slope crest. This paper examines the prefailure and postfailure behavior of the pile group and it is demonstrated that considering the uncracked and cracked bending stiffness of the piles is vital when evaluating the progressive damage of the pile group due to slope failure.

This paper presents a field study of the lateral monotonic and cyclic behavior of jet-grouting, reinforced, cast-in-place piles in soft soils. To assess the contribution of the jet-grouting reinforcement, nine instrumented piles were loaded monotonically or cyclically. The test results show that the ultimate lateral-bearing capacity of the cast-in-place pile increases by 64.2–68.9% due to the jet grouting. Moreover, reinforcement by jet grouting significantly reduces the maximum bending moment of the cast-in-place piles and enhances the pile-head stiffness. The tests also demonstrate that the behavior of reinforced piles is satisfactory when subjected to one-way and two-way cyclic loading. The use of jet-grouting, reinforced, cast-in-place piles is a viable foundation option for lateral loading applications.

A test procedure that involved shearing soil specimens at different shear rates was proposed to study the effect of shear rate on the strength recovery of three natural clays. The obtained results indicated that an increase in shear strength occurred when the shear rate decreased. This strength regain was more pronounced for higher plasticity clays, which were sheared at a relatively lower confining pressure of 100 kPa.