Journal of Geotechnical and Geoenvironmental Engineering

How the design and actual founding depths of foundations correspond to the variability of geological conditions has long been a concern. This paper evaluates the spatial variability characteristics of as-built and estimated founding depths of driven steel H piles with reference to the spatial variability characteristics of geologic profiles at a weathered soil site in Hong Kong. Spatial variability characteristics are evaluated in terms of variance and scale of fluctuation. The variability of three founding depth indicators, i.e., the depth of Grade-III bedrock, the depth of standard penetration test blow count “N” of 200 blows/0.3 m (SPT-200), and the depth of completely decomposed granite over the site was estimated. It is found that pile founding depths exhibit greater variations than those of the geologic profiles due to the presence of design model errors, judgment errors, and construction effects. The as-built founding depths are mostly between the SPT-200 profile and the Grade-III bedrock profile. The variances of as-built pile length are similar to those with depth of SPT-200 but less than those with depth of Grade-III bedrock. The scale of fluctuation of as-built pile length is on the order of 20 m when kriging is used and 10 m when kriging is not used, which are less than those with depths of SPT-200 and Grade-III bedrock.

Three-dimensional finite element analyses were performed to study the behavior of piles in sloping ground under undrained lateral loading conditions. Piles of different diameter and length in sloping cohesive soils of different undrained shear strength and several ground slopes were considered. Based on the results of the finite element analyses, analytical formulations are derived for the ultimate load per unit length and the initial stiffness of hyperbolic $p\text{-}y$ curves. New $p\text{-}y$ criteria for static loading of piles in clay are proposed, which take into account the inclination of the slope and the adhesion of the pile-slope interface. These curves are used through a commercial subgrade reaction computer code to parametrically analyze the effect of slope inclination and pile adhesion on lateral displacements and bending moments. To validate the proposed $p\text{-}y$ curves, a number of well documented lateral load tests are analyzed. Remarkable agreement is obtained between predicted and measured responses for a wide range of soil undrained shear strength and pile diameter, length, and stiffness.

This paper presents a theoretical study of Biot flow–induced damping in saturated soil during shear wave excitations. The solid skeleton is treated as equivalent linear. Biot flow–induced damping is evaluated for the cases of resonant column tests and site response analysis, based on the spectral response of a soil column/layer under harmonic torsional/horizontal excitations. Closed-form analytical solutions indicate that Biot flow–induced damping is hydraulic conductivity and frequency dependant. At the first resonance in a resonant column test, Biot flow–induced damping is dependent on a dimensionless hydraulic conductivity parameter K. For K within the range of 0.01 to 100, corresponding to coarse sands and clean gravels, Biot flow–induced damping may have an important contribution to total soil damping, especially at small strain levels. For site response analysis, Biot flow–induced damping should be considered for coarse sands and clean gravels, but can be practically neglected for fine sands, silts, and clays. The effects of soil porosity, mass coupling, and non-Poiseuille flow on Biot flow–induced damping are discussed.

A series of drained tests for sands with inherent fabric anisotropy were conducted with an automatic hollow cylinder apparatus. The samples were subjected to cyclic rotation of principal stress axes while the magnitudes of effective principal stresses were maintained constant. The evolution of strain components and the volumetric strain with number of cycles, the relationship between the shear stress and shear strain components, and the flow rule of sands were investigated. It is found that plastic deformation is induced due to principal stress axes’ rotation alone without variation in the magnitudes of effective principal stresses. The contractive volumetric strain accumulates steadily with the increasing number of cycles; however, its accumulation rate is lowered with its progressive accumulation. The results also exhibit obvious noncoaxiality between the directions of strain increment and stress, and the noncoaxiality shows segmentation characteristics during the rotation of principal stress axes. Meanwhile, special attention was paid to the significant role of the intermediate principal stress parameter $b$ $\left[b=\left({\sigma }_2^{\prime }-{\sigma }_3^{\prime }\right)/\left({\sigma }_1^{\prime }-{\sigma }_3^{\prime }\right)\right]$ in the deformation behavior of sands during cyclic rotation of principal stress axes. It is found that the volumetric strain and the shear modulus ratio of the $j\text{th}$ cycle to the first cycle increase with the increase in the $b$ value under otherwise identical conditions. The effects of the relative density, effective mean normal stress, and deviatoric stress ratio on sand deformation behavior are also addressed in this work.

This paper presents an investigation into the seepage hydraulics of a layer of subballast filter subjected to cyclic loading in a fully saturated environment. A multilayer mathematical approach was used to predict the time-dependent permeability of this filter, with a reduction in porosity as a function of compression under cyclic loading, and the amount of base soil $\left(<150\mu \text{m}\right)$ trapped within the filter voids being the two main aspects of this proposed model. Laboratory test results conducted on a novel cyclic loading permeameter apparatus were used to validate the proposed model. The family of equations that are an integral part of the proposed model are then presented in the form of compact visual guidelines anticipated to provide a more practical tool for railway design practitioners.

This paper concerns the problem of designing standard artificial tunnels for rock boulder protection. The proposed approach consists in uncoupling the problem of the dynamic response of the granular dissipative soil cushion placed on the top of artificial tunnels from the dynamic response of the reinforced concrete structure underneath. An already conceived elasto-viscoplastic constitutive model capable of simulating the penetration process of the boulder within the soil stratum and reproducing the force acting on the boulder is briefly described. Its simplified one-dimensional formulation is outlined. A modified version of the model, taking into account large displacements occurring when either impacts on loose granular soils or high energetic content impacts on dense sand strata are considered, is also introduced. To validate the approach, some in situ test results are numerically simulated. A simplified numerical approach is proposed for obtaining the evolution with time of both impact force and boulder penetration, bypassing the use of the rheological model. This goal is achieved by introducing some abaci obtained numerically with reference to an ideal dense sand soil stratum of reference.

Analytical solutions for conservative solute diffusion in one-dimensional double-layered porous media are presented in this paper. These solutions are applicable to various combinations of fixed solute concentration and zero-flux boundary conditions (BC) applied at each end of a finite one-dimensional domain and can consider arbitrary initial solute concentration distributions throughout the media. Several analytical solutions based on several initial and BCs are presented based on typical contaminant transport problems found in geoenvironmental engineering including (1) leachate diffusion in a compacted clay liner (CCL) and an underlying stratum; (2) contaminant removal from soil layers; and (3) contaminant diffusion in a capping layer and underlying contaminated sediments. The analytical solutions are verified against numerical solutions from a finite-element method based model. Problems related to leachate transport in a CCL and an underlying stratum of a landfill and contaminant transport through a capping layer over contaminated sediments are then investigated, and the suitable definition of the average degree of diffusion is considered.

Rainfall, hydrological condition, and geological formation of slope are important contributing factors to slope failures. Parametric studies were carried out to study the effect of groundwater table position, rainfall intensities, and soil properties in affecting slope stability. Three different groundwater table positions corresponding to the wettest, typical, and driest periods in Singapore and four different rainfall intensities (9, 22, 36, and 80 mm/h) were used in the numerical analyses. Typical soil properties of two main residual soils from the Bukit Timah Granite and the sedimentary Jurong Formation in Singapore were incorporated into the numerical analyses. The changes in factor of safety during rainfall were not affected significantly by the groundwater table near the ground surface due to the relatively small changes in matric suction during rainfall. A delay in response of the minimum factor of safety due to rainfall and a slower recovery rate after rainfall were observed in slopes from the sedimentary Jurong Formation as compared to those slopes from the Bukit Timah Granite. Numerical analyses of an actual residual soil slope from the Bukit Timah Granite at Marsiling Road and a residual soil slope from the sedimentary Jurong Formation at Jalan Kukoh show good agreement with the trends observed in the parametric studies.

A manually operated penetrometer (DMS) fitted with cylindrical (T-bar) and ball penetrometer tips was developed for measuring the profiles of undisturbed and remolded undrained shear strength within box-core samples. This paper summarizes the findings of a series of miniature penetrometer tests and vane shear tests that were carried out on reconstituted clay from a local site in Western Australia. The aim of the tests was to evaluate the potential of the DMS in characterizing the shear strength of seabed surficial sediments. It was found that the DMS gave essentially identical T-bar and ball penetration resistances but these were up to 17% lower than the net cone resistance. From the comparison between the T-bar and ball penetration resistance and the shear strengths measured from vane shear tests, average $N$ factors of 11 and 14 were obtained for intact and fully remolded conditions, respectively. The test results suggest that the DMS is a reliable and efficient means of obtaining intact and remolded shear strength profiles.

Large-scale one-dimensional compression tests were performed in order to analyze the influence of gravel on the compression properties of gravel-mixed decomposed granite soils. After adjusting the gravel contents of the said soil, specimens compacted at a certain level of compaction energy and water content were tested. Based on the test results, it was observed that when gravel-mixed decomposed granite soil was compacted at the same energy level, there existed a specific gravel content at which the dry density was maximum and which also produced the minimum compression index. Furthermore, an expression based on two-phase mixture theory was proposed to quantitatively evaluate the effects of gravel content through a material parameter calculated using the theory, and the estimated compression curves agreed very well with the results of the experiments.

Stabilizing piles have been used extensively over the past few decades to support unstable slopes. A new simplified method is described to analyze the stability level of a strain-softening slope reinforced with stabilizing piles. An equivalent principle is proposed to account for the three-dimensional effect of the piles on the stability level of slopes. The formulation is derived on the basis of the displacement distribution assumptions of the slope by extending the simplified Bishop slice method. The parameters can be easily determined by element tests. This method is used on a real-world slope to discuss the influential factors. The results show that the slope geometry and pile layout, which includes pile spacing, pile location, and pile depth, have a significant effect on the safety factor and critical slip surface of the reinforced slope. The stability level of a strain-softening slope is dependent not only on the strength parameters but also on the stress-strain relationship of soil.