Journal of Geotechnical and Geoenvironmental Engineering

The piezocone penetration test (CPTU) is commonly used to identify a soil’s profile and estimate its material properties. Depending on the soil type, ranging from clay to sand, undrained, partially drained, or drained conditions may occur during cone penetration. In silt and sand–clay mixtures, the CPTU penetration is characterized by partially drained conditions, which are often neglected in data interpretation. The effect of drainage on CPTU measurements has been mainly studied experimentally. Numerical analyses are rare because taking into account large soil deformations, soil–water and soil–structure interactions, and nonlinear soil behavior is still a challenging task. This paper presents and discusses numerical simulations of CPTU in saturated soils with the two-phase material point method. Soil behavior is described with the modified cam clay model. This study investigates the effects of pore pressure dissipation during penetration, cone roughness, and horizontal stress state, comparing the results with experimental data. The paper discusses the effect of neglecting partial drainage in deriving the shear strength parameters for silty soils and suggests a procedure to estimate the consolidation coefficient for performing CPTU at different penetration rates.

This article investigates the hydraulic performance of geosynthetic clay liner (GCL) overlapped seams subjected to nonuniform stresses due to a wrinkle in an overlying geomembrane. The performance when the GCL seam was parallel to and directly below a wrinkle depended on the width of the GCL seam relative to the deformed wrinkle. When both ends of the seam were confined under vertical stress from the deformed wrinkle, there was no evidence of preferential flow along the seam, and the magnitude of flow was slightly smaller than the case with just a single intact GCL panel beneath the wrinkle. Flow through the GCL seam when perpendicular to a wrinkle was mostly affected by the presence and distribution of supplemental bentonite. With no supplemental bentonite, flow was 370 times greater than that through an intact GCL panel beneath the wrinkle. Application of $400\mathrm{g}/\mathrm{m}$ of supplemental bentonite piled along the center of the seam decreased the flow by more than two orders of magnitude compared with having no supplemental bentonite.

This study investigated the effects of polymers on the small-strain stiffness behavior of high volume Class-F fly ash–kaolinite mixtures. The shear wave velocity ($V_s$) and its anisotropy of organically modified fly ash–kaolinite mixtures were evaluated using a self-developed floating wall type consolidometer bender element (BE) testing system. Both synthetic polymers [polyethylene oxide (PEO)] and biopolymers (xanthan gum and chitosan) were used to modify the stiffness of fly ash–kaolinite mixtures. Shear waves generated and received by bender elements were measured to quantify the small-strain stiffness of the organically modified fly ash–kaolinite mixtures in three orthogonal directions, i.e., $vh$, $hv$, and $hh$. The results suggested that (1) as the fly ash content increased, $V_s$ increased, while the $V_s$ anisotropy, in terms of shear wave velocity ratio $V_{s-hh}/V_{s-vh}$, decreased; (2) a threshold fly ash content concept, which corresponds to the onset of continuous contact chains between fly ash particles throughout the specimen, was used to distinguish the kaolinite-dominated zone from the fly ash-dominated zone of $V_s$ and $V_s$ anisotropy behavior; (3) the introduction of fly ash was also found to enhance the cross-anisotropy of fly ash–kaolinite mixtures; (4) the addition of PEO and chitosan increased the $V_s$ of the fly ash–kaolinite mixtures, while the addition of xanthan gum decreased the $V_s$; and (5) all three polymers were found to decrease the $V_s$ anisotropy of the fly ash–kaolinite mixtures.

Measured loads in centrifuge tests on piled embankments were compared with values calculated by three analytical arching models. The Zaeske and Van Eekelen models use sets of arches that give the direction of the load transfer, and result in an increasing load on the soft soil with increasing embankment thickness or surcharge load, which matches the measurements. The Svanø model, however, assumes that the load on the soft soil remains constant with increasing embankment thickness or surcharge load, thereby being transferred directly to the piles. Therefore, the Zaeske and Van Eekelen models match the measurements better than the Svanø model. The Van Eekelen model slightly overestimates the pile efficiency for relatively thin embankments, but matches the measurements better than the Zaeske model for increasing embankment thickness or surcharge load.

From results of a recent series of centrifuge model tests, this paper investigates the effects of shape and embedment on the performance of rocking footings. Rectangular and H-shaped footings are considered. Previous studies have characterized the performance of rectangular rocking foundations on sand and clay, but few studies have systematically characterized the effects of footing shape. The effect of shape and embedment are correlated to detrimental aspects of performance (residual settlement or uplift) and beneficial aspects of performance (hysteretic energy dissipation and recentering). The new results are compared with previously reported results. For rectangular footings rocking in their strong direction, it is found that the susceptibility to residual settlement and uplift increases as the length-to-width ratio increases. For H-shaped footings, susceptibility to settlement and uplift increases with the missing area ratio. The factors that lead to increased recentering also tend to lead to decreased energy dissipation.

A database of the mechanical behavior of 25 natural sands was compiled from the existing literature. Particle shape and size analysis, obtained by dynamic imaging analysis, for each material in the database has subsequently been linked to its mechanical properties; selected sands were also subject to interferometry study for particle surface roughness measurements. This paper reviews the effect of the particle shape properties of these sands on their Critical State and stiffness parameters, introducing a new parameter to optimize the correlations.

Box culverts can be subjected to considerable induced earth pressure from overlaying structures and foundations. Therefore, the effect of surface foundations on soil pressures around box culverts needs to be properly investigated and incorporated into the analysis and design of culverts. In this study, the effect of a surface foundation on the response of box culverts was investigated experimentally and numerically. A series of centrifuge tests were performed to evaluate the additional soil pressures around box culverts installed in sand due to adjacent surface foundations. The experimental results were used to calibrate and verify a two-dimensional (2D) numerical model developed using computer software. This model was then used for a parametric study to investigate the effect of the relative foundation location on various aspects of the culvert response. The soil pressures, culvert bending moments, and soil-culvert interaction factors were all considered for different soil depths and surface foundation locations. The results from this analysis were used to establish charts that can aid in assessing the effect of surface foundations on box culvert behavior.

New, alternative in situ ground improvement techniques are necessary to address increased performance demands and growing environmental concerns of traditional grouting methods. To date, the controlled use of microbiological processes has demonstrated promise in the ability of microbes and their activity to address this need. A particular form of biological improvement is the use of biofilms, an organic accumulation of cells and extracellular polymeric substances (EPS), in saturated soils. By adhering and accumulating on particle surfaces, biofilms can cause clogging of the pore volume and induce significant reductions in permeability. The void-filling nature of biofilms allows for possible field applications to control groundwater, heal leaks, and prevent internal erosion in structures such as earth dams and levees. This laboratory study investigated the growth characteristics and robustness of biofilm-treated sands. Experimental results indicate that biofilms are capable of reducing permeability of saturated sands by 100-fold or more after only two to three weeks of nutrient treatment. These improvements can be maintained indefinitely with continued nutrient treatments, after which a gradual return to initial conditions occurs. Permeability reductions were shown to remain stable in a variety of adverse conditions including two months of starvation, reverse flow, and fluctuating hydraulic gradients. Further tests indicated that biofilm growth in this study was highly heterogeneous, with the majority of clogging occurring near the inlet face. The results of this study show strong potential for the use of biofilms to reduce permeability, but future studies are required to improve uniformity as the process is scaled to field applications.

Downslope bentonite erosion in four geosynthetic clay liners (GCLs) with granular bentonite (denoted GCL1–GCL4) left covered only by a black high-density polyethylene (HDPE) geomembrane for 3.6 and 4.7 years was recently published. Reported herein are the results of a field study of the potential for erosion for seven new test sections over a 28-month period. These include four previously unstudied GCLs: two with powdered bentonite (GCL5 and GCL6), one with polymer-enhanced granular bentonite (GCL7), and one multicomponent product installed coating-up (GCL8). One GCL (GCL2) known to experience erosion below an exposed black geomembrane was installed beneath both a black and a white exposed geomembrane and also in a section where the composite liner was promptly covered by 0.3 m of gravel. After 28 months, there was significant erosion of GCL2 and GCL7, but no significant erosion of GCL5, GCL6, GCL8, or GCL2 covered by 0.3 m gravel.

This paper presents the results of a full-scale field test program of driven timber displacement piles for the purpose of densification of loose, potentially liquefiable sands and silty sands. Both conventional and experimental timber piles fitted with prefabricated drains to help densify contractive soils during pile installation were assessed in this study. The piles were installed in groups with center-to-center spacing of two to five pile head diameters. Measurements of cone penetration tests (CPTs) revealed the variation of postinstallation increases in penetration resistance with decreases in pile spacing. Additionally, long-term measurements showed that pile spacing–dependent reductions in cone penetration resistance following installation can occur, which have been attributed to relaxation of horizontal stresses. Rough relationships between the average area replacement ratio and change in corrected cone tip resistance were developed. Pre- and postimprovement standard penetration tests conducted in each of the treated zones confirmed the long-term degree of densification noted using the CPT. Measured pre- and postinstallation shear wave velocities indicated that the soil fabric of the previously aged sands was effectively destroyed and that a reduction of small strain stiffness is possible in tandem with densification. The experimental findings in this paper may be broadly applied to displacement piles constructed of materials other than timber.

Mechanically stabilized earth (MSE) walls reinforced with geosynthetic have been used extensively in highway projects around the world. Typical vertical spacing of geosynthetic reinforcement used in the design of an MSE wall is 0.6 m. This large reinforcement spacing requires a high reinforcement connection strength and may result in wall-facing bulging in the practice. To alleviate such problems, use of secondary reinforcement between primary reinforcement layers was proposed. However, this idea was not verified in the field. In this study, three MSE wall sections reinforced with geogrid layers were constructed and monitored in the field: (1) an MSE wall section with uniaxial geogrid layers as primary and secondary reinforcement; (2) an MSE wall section with uniaxial geogrid layers as primary reinforcement and with biaxial geogrid layers as secondary reinforcement; and (3) an MSE wall section with uniaxial geogrid layers as primary reinforcement only (i.e., the control section). Earth pressure cells, inclinometer casings and probes, and foil-type strain gauges were used in these three test wall sections to measure vertical and lateral earth pressures, accumulated lateral wall-facing deflections, and strains of primary and secondary geogrid layers during construction, respectively. The results from monitoring these three MSE wall sections were analyzed. The test results demonstrated the effects of secondary reinforcement on the improved performance of MSE walls, including reduced accumulated wall-facing deflections, a more uniform lateral earth pressure distribution, and reduced tensile strains in primary geogrid layers.

Internal erosion is a major cause of dam or dike failures and incidents. In this study, laboratory tests were conducted to investigate the deformation of two gap-graded soils during internal erosion and the stress-strain behavior of the soils that experienced loss of fine particles due to internal erosion. An erosion-controlled experimental method was adopted to achieve a designated loss of fine particles during internal erosion by adding a predefined amount of salt into the soil sample during sample preparation and dissolving the salt in water under a controlled stress condition. Both the radial and axial deformations during erosion were measured using a photographic method. Subsequently, drained triaxial compression tests were performed to study the stress-strain behavior of the soils that had lost different amounts of fine particles. The peak friction angle and critical friction angle of the soil decreased with the loss of fine particles. After a significant loss of fine particles, the stress-strain behavior changed from the initially dilative behavior to a more contractive behavior.

Resonant column tests, corresponding to a given input voltage of the drive mechanism, were conducted in torsional mode to examine the effect of vibration cycles on shear modulus ($G$) and damping ($D$) of dry sand with shear strain amplitude in a range of 0.0005–0.05%. Two different relative densities, approximately 61 and 85%, and effective confining pressures, 300 and 500 kPa, were used. The specimens were subjected to a number of vibration cycles ranging from 1,000 to 50,000. The shear modulus and damping ratio, before and after the application of vibration cycles, were determined for several input voltages. An induction of the vibration cycles leads to a continuous increase in shear strain, which causes (1) a decrease in the shear modulus and (2) an increase in the damping ratio. This effect becomes especially more prominent for lower values of relative densities and confining pressures. The modulus reduction and damping curves remained the same after applying vibration cycles.

A new relationship for estimating the in situ at-rest lateral stress coefficient ($K_0$) in sands consisting predominantly of silica particles is derived in this technical note using the calibration chamber test results reported in the literature. Variables in the relationship, in order of significance, are overconsolidation ratio, dilatometer horizontal stress index, and normalized cone tip resistance. Values of in situ $K_0$ estimated with the new relationship generally compare well with $K_0$ determined from self-boring pressuremeter tests. Estimates of $K_0$ in Pleistocene sands are, on average, about 10% higher than in Holocene sands.

The dry surface strength of mine tailings (MT), or mill tailings, is closely related to their dust resistance. To explore biopolymer stabilization of MT to increase their dust resistance, uniaxial and triaxial compression tests are carried out on dry MT specimens treated with biopolymer solutions of different concentrations. The experimental results show that the elastic modulus, unconfined compressive strength (UCS), cohesion, and friction angle of MT all increase after biopolymer treatment, with higher biopolymer concentration leading to a greater increase. This is primarily because biopolymer treatment leads to aggregation of MT particles, creates bonding between biopolymer and MT particles, and forms a cross-linking network binding the detached particles and filling the voids between them, leading to a denser structure. As expected, the elastic modulus also increases with higher confining pressure.

Drained triaxial compression tests were carried out for a well-graded coarse granular soil (CGS) to investigate the effect of the initial specific volume on the location of the critical state line (CSL). A family of parallel CSLs in the $v\sim \log p^{\prime }$ plane was observed for the well-graded CGS, indicating that it exhibited transitional behavior. The degree of transitional behavior was quantified from the relationship between the intercepts of the CSLs and the initial specific volumes, giving a value of 0.59, which indicated a substantially transitional behavior. The observations of the CSL pattern in the CGS illustrated that transitional behavior could be extended to large-sized granular soils, beyond the usual transitional soils that have been observed so far, which generally have gradings between those of clean sand and plastic clay.

A comprehensive model for the index void ratios $e_{\text{max}}$ and $e_{\text{min}}$ of sands is presented. It is based on a large set of previously published sand properties as well as tests on 25 new materials including glass spheres and two types of rice. The new model uses the index void ratios of perfectly uniform spherical glass beads as baselines to which factors accounting for the three most influential intrinsic soil properties are applied. The three properties are particles roundness, $R$, sphericity, $S$, and the coefficient of uniformity, $C_u$. The following three factors led to the new model’s improvement over previous such efforts: (1) use of sands spanning a wide range of $R$, $S$, and $C_u$ values; (2) consideration of the combined and coupled effects of $R$, $S$, and $C_u$; and (3) utilization of a recently developed computational geometry method on digital images to obtain precise values of $R$ and $S$ for large, statistically reliable numbers of particles.