Journal of Geotechnical and Geoenvironmental Engineering

Monotonic, static beam on nonlinear Winkler foundation (BNWF) methods are used to analyze a suite of dynamic centrifuge model tests involving pile group foundations embedded in a mildly sloping soil profile that develops liquefaction-induced lateral spreading during earthquake shaking. A single set of recommended design guidelines was used for a baseline set of analyses. When lateral spreading demands were modeled by imposing free-field soil displacements to the free ends of the soil springs (BNWF_SD), bending moments were predicted within $-8\%$ to $+69$ (16th to 84th percentile values) and pile cap displacements were predicted within $-6$ to $+38\%$ , with the accuracy being similar for small, medium, and large motions. When lateral spreading demands were modeled by imposing limit pressures directly to the pile nodes (BNWF_LP), bending moments and cap displacements were greatly overpredicted for small and medium motions where the lateral spreading displacements were not large enough to mobilize limit pressures, and pile cap displacements were greatly underpredicted for large motions. The effects of various parameter relations and alternative design guidelines on the accuracy of the BNWF analyses were evaluated. Sources of bias and dispersion in the BNWF predictions and the issues of greatest importance to foundation performance are discussed. The results of these comparisons indicate that certain guidelines and assumptions that are common in engineering design can produce significantly conservative or unconservative BNWF predictions, whereas the guidelines recommended herein can produce reasonably accurate predictions.

Critical for the seismic safety of immersed tunnels is the magnitude of deformations developing in the segment joints, as a result of the combined longitudinal and lateral vibrations. Analysis and design against such vibrations is the main focus of this paper, with reference to a proposed $70\mathrm{m}$ -deep immersed tunnel in a highly seismic region, in Greece. The multisegment tunnel is modeled as a beam connected to the ground through properly calibrated interaction springs, dashpots, and sliders. Actual records of significant directivity-affected ground motions, downscaled to 0.24 $g$ peak acceleration, form the basis of the basement excitation. Free-field acceleration time histories are computed from these records through one-dimensional wave propagation equivalent-linear and nonlinear analyses of parametrically different soil profiles along the tunnel; they are then applied as excitation at the support of the springs, with a suitable time lag to conservatively approximate wave passage effects. The joints between the tunnel segments are modeled realistically with special nonlinear hyperelastic elements, while their longitudinal prestressing due to the great $\left(7\text{bar}\right)$ water pressure is also considered. Nonlinear dynamic transient analysis of the tunnel is performed without ignoring the inertia of the thick-walled tunnel, and the influence of segment length and joint properties is investigated parametrically. It is shown that despite ground excitation with acceleration levels exceeding 0.50 $g$ and velocity of about $80\mathrm{cm}∕\mathrm{s}$ at the base of the tunnel, net tension and excessive compression between the segments can be avoided with a suitable design of joint gaskets and a selection of relatively small segment lengths. Although this research was prompted by the needs of a specific project, the dynamic analysis methods, the proposed design concepts, and many of the conclusions of the study are sufficiently general and may apply in other immersed tunneling projects.

In this research, centrifuge model pile-load tests were carried out to failure to investigate the behavior of large-diameter bored pile groups with defects. The model piles represented cast-in-place concrete piles $2.0\mathrm{m}$ in diameter and $15\mathrm{m}$ in length. Two series of static loading tests were performed. The first series of tests simulated the performance of a pile founded on rock and a pile with a soft toe. The second series of tests simulated the performance of three $2\times 2$ pile groups: One reference group without defects, one group containing soft toes, and one group with two shorter piles not founded on rock. The presence of soft toes and shorter piles in the defective pile groups considerably reduced the pile group stiffness and capacity. As the defective piles were less stiff than the piles without defects, the settlements of the individual piles in the two defective pile groups were different. As a result, the applied load was largely shared by the piles without defects, and the defective pile groups tilted significantly. The rotation of the defective pile groups caused large bending moments to develop in the group piles and the pile caps. When the applied load was large, bending failure mechanisms were induced even though the applied load was vertical and concentric. The test results confirm findings from numerical analyses in the literature.

In this paper, the pile body tensile stresses distribution pattern during driving is discussed, based on dynamic piling testing results of 13 driven piles attained by the laboratory and in situ tests. These tests indicate that the maximum driving tensile stresses occur in the upper portion of the pile, especially at the initial stages of driving the pile tip seated on soft soils or if the pile foundation is built on a soft foundation. After serious study, it can be concluded that the maximum driving tensile stress often occurs at $(1∕4)l$ ( $l$ stands for the length of pile) from pile top with its value accounts for 50% of the driving compressive stresses at the same cross section. This high driving tensile stress would lead to the occurrence of transverse cracks and even the breakage of the pile, which should claim the attention of the engineer. The tests also demonstrate that high driving tensile stresses often occur due to the usage of a conventional pile cap in the driving of a prestressed concrete (tubular) pile. To the contrary, the tensile stresses tend to diminish within the control tensile stresses $\left(5\mathrm{MPa}\right)$ due to the usage of a new type of disk spring pile cap during driving. Moreover, this new pile cap can prevent driving deviation from alignment, ensure an even distribution of the hammer blow on pile top, and protect the integrity of the pile body.

The oil sands mining industry in Canada has made a commitment to reclaim mining areas to an equivalent capability to that which existed prior to mining. An essential requirement in the design of reclamation covers to meet this objective is that all covers must have a sufficient available water holding capacity (AWHC) in order to supply sufficient moisture for vegetation over the summer moisture deficit typical in the region. AWHC is currently based on static evaluations of wilting point and field capacity under a constant annual evapotranspiration demand. This paper presents an alternative probabilistic approach by which the hydrologic performance of these reclamation soil covers can be assessed. A field-calibrated water balance model is used along with the available historical meteorological record to estimate the maximum soil moisture deficit that a soil cover is able to sustain over the growing season. Frequency curves of the maximum annual moisture deficit are used to assess the probability that a cover is able to provide any particular threshold of moisture demand. The method also allows for a quantification of the predictive uncertainty of the model. The predictive uncertainty is used as a margin of safety to estimate a design value of moisture deficit for various alternative cover designs. This paper recommends procedures for a frequency-based assessment and design of reclamation soil covers in the oil sands industry. This method takes into account climatic variability as well as parameter uncertainty in estimating the soil moisture deficit.

An elastoplastic pressuremeter theory for cohesive soil has been used in the design of construction, such as retaining walls, slope stability, or foundation engineering. This theory takes into account the plasticity along the vertical and horizontal planes and allows for the determination of the conventional limit pressure. We compute here the conventional limit pressure using the Plaxis program to check the validity of the theoretical results. First, we present the theory used for the interpretation of the pressuremeter test in cohesive soil and its extension to the conventional limit pressure, which is defined as the pressure at the borehole wall for a volume increase $\mathrm{\Delta }\mathrm{V}$ equal to the initial volume of the borehole. One of the main results is the theoretical expression of the conventional limit pressure. This volume variation is linked to a radial strain of $\sqrt{2}-1$ . This conventional limit pressure can be directly measured with the pressuremeter, whereas the theoretical limit pressure is expressed as an infinite expansion and cannot be directly measured. Then, we validate this theory by using finite elements, and determine the conventional limit pressure with the Tresca standard model of Plaxis, which is compared to the theoretical expression. Conclusions are drawn on the validity of this new theory which allows the measurement and the control of the shearing modulus and shear strength of the natural soil.

A great number of rock strength criteria have been proposed over the past decades. Of these different strength criteria, the Hoek-Brown strength criterion has been used most widely, because: (1) it has been developed specifically for rock materials and rock masses; (2) its input parameters can be determined from routine unconfined compression tests, mineralogical examination, and discontinuity characterization; and (3) it has been applied for over $20\text{years}$ by practitioners in rock engineering, and has been applied successfully to a wide range of intact and fractured rock types. The Hoek-Brown strength criterion, however, does not take account of the influence of the intermediate principal stress, although much evidence has been accumulating to indicate that the intermediate principal stress does influence the rock strength in many instances. In this paper, a three-dimensional (3D) version of the Hoek-Brown strength criterion has been proposed. The original Hoek-Brown strength criterion is just a two-dimensional (2D) version of the proposed 3D strength criterion. The 3D strength criterion not only inherits the advantages of the original Hoek-Brown strength criterion, but can take account of the influence of the intermediate principal stress. Polyaxial or true triaxial compression test data of intact rocks and jointed rock masses has been collected from the published literature and used to validate the proposed 3D Hoek-Brown strength criterion. Predictions of the proposed 3D Hoek-Brown strength criterion are in good agreement with the test data for a range of different rock types. The proposed 3D Hoek-Brown strength criterion is also compared with a simplified 3D Hoek-Brown strength criterion proposed by Pan and Hudson. The Pan-Hudson criterion cannot be considered a true 3D version of the Hoek-Brown criterion, because it does not reduce to the form of the original Hoek-Brown criterion at either triaxial or biaxial state. The Pan-Hudson criterion underpredicts the strength at the triaxial state, but overpredicts the strength at the biaxial state.

The presence of mica changes the mechanical behavior of sandy soils. In this study, micro- and macroscale tests are used to explore the unique packing characteristics that develop in mixtures made of round and platy particles, and the effects that mica exerts on small, medium, and large strain parameters. Mixtures are prepared with different mica contents and various mica-to-sand size ratios, $L_{\mathrm{mica}}∕D_{\mathrm{sand}}$ . Results provide a comprehensive characterization of mixtures made of spherical and platy particles. Mica plates change sand packing through pore filling, bridging, ordering, and mica–mica interaction; bridging prevails and leads to open fabrics when $L_{\mathrm{mica}}∕D_{\mathrm{sand}}\ge 1$ . As the mica content increases in mixtures with $L_{\mathrm{mica}}∕D_{\mathrm{sand}}\ge 1$ , the shear-wave velocity decreases and it becomes more sensitive to the state of stress; the constraint modulus decreases; and the peak and residual friction angles decrease. Remixing during disordered granular flow prevents mica alignment and diminishes the otherwise weakening effect of mica on large-strain strength.

The Lower San Fernando dam failure, which took place in 1971, is one of the most reported cases of seismic liquefaction damage in the geotechnical literature. For this reason, it has been analyzed by almost all of the numerical models developed since that year. In this paper, a comparison between numerical simulations, using a new endochronic model, with measured response of this dam during the earthquake of 1971, as well as numerical results previously obtained by other researchers, is presented. The main particularity of this new constitutive law is a nonassociative flow rule, related to a parameter quantifying degradation with shaking duration, in terms of stiffness reduction. It is incorporated in the model to represent soil dilation. Furthermore, contractive, dilative, and collapse trends of soil behavior are jointly embodied into the new developed constitutive law, which has been implemented in a two-dimensional coupled finite-element model. By so doing, the failure mechanism and the critical locations of the dam are identified and compared with field observations, and the approximate time for the beginning of the upstream sand fill slide is determined.

This paper investigates the performance of stone columns in a weak deposit such as peat. It evaluates the effects of reinforcing stone columns by jacketing with a tubular wire mesh and bridging reinforcement with a metal rod and a concrete plug. A series of plate loading tests was conducted on isolated stone columns installed in a soil bed consisting of a peat layer sandwiched between two layers of sand. The load–displacement characteristics of footings supported by stone columns were investigated by applying load to a circular plate supported on: (a) untreated soil; (b) soil treated with stone columns; and (c) soil treated with stone columns reinforced with the above reinforcing techniques. The work has shown that the settlement characteristics of the soil can be improved by installing stone columns and that a significant enhancement in the load–settlement response is achieved when the columns are reinforced by the various methods.

This paper presents the mechanical properties of silicate-grouted sands subjected to creep loadings at low stress levels. Uniaxial compressive tests were performed in order to determine the stress levels of constant creep tests. The uniaxial compressive strength rapidly increased with time over the first 7 days of curing and then approached a constant level. A series of creep tests were performed for three stress levels and viscoelastic theory was employed to assess the creep behavior. During the loading process elastic, plastic, and viscoelastic strains existed together. The recoverable portions contained elastic and time-dependent viscoelastic strains, and both were approximately linear. Test results showed that the magnitude of the instantaneous recoverable strains was independent of the unloading time. A constitutive model to predict the permanent deformation was developed.

This paper describes a development and laboratory evaluation of the light-based high-resolution target movement monitor which can be used to measure convergence at underground excavations with submillimeter accuracy. The monitor is based on unique measurement technology which was developed at the University of Missouri-Rolla. This system has the potential for high accuracy detection and monitoring of positional changes (as small as $0.1\mathrm{mm}$ with the current laboratory implementation) presented by many types of targets located in close proximity to or at far distances from the monitor. The sensitivity of the system to camera resolution and the error analysis as a function of the laser incident angle are described. The system utilizes custom computer processing, a high-resolution camera, and laser light to measure the distance to a target accurately in one dimension, but it can also be used for performing two-dimensional surface profiling or analyzing three-dimensional movement of the target. The ability of this optical system to measure ground movement with submillimeter accuracy will allow for monitoring ground convergence in areas of high traffic or which are inaccessible for the installation of traditional ground movement sensing devices.