Journal of Geotechnical and Geoenvironmental Engineering

A reevaluation is presented of two factors that can strongly affect the estimation of liquefaction resistance for clean sands under high effective overburden stresses $\left({\sigma }_v^{\prime }\right):$ the relation used to normalize penetration resistances to a ${\sigma }_v^{\prime }$ of 1 atm (i.e., $C_N)\text{,}$ and the adjustment factor for the effects of ${\sigma }_v^{\prime }$ on cyclic resistance ratio (i.e., $K_{\sigma })\text{.}$ These two factors have been investigated in a number of ways and several relations exist for each of them. An improved $C_N$ relation is developed based on cone penetration theory and validation against calibration chamber test data for both cone penetration and standard penetration tests. A relative state parameter index $\left({\xi }_R\right)$ is shown to provide a consistent theoretical framework for interrelating the penetration and cyclic loading resistances. It is subsequently shown that the $C_N$ and $K_{\sigma }$ relations are interrelated through the sand properties and relative density $\left(D_R\right)$ in ways that have compensating effects on the predicted cyclic resistance. The derived relations provide an improved representation of the effects of high ${\sigma }_v^{\prime }$ levels, and reduce the conservatism that results when some established relations are extended to ${\sigma }_v^{\prime }$ levels higher than they were calibrated for.

This paper presents the results of six centrifuge model tests of liquefaction and earthquake-induced lateral spreading of fine Nevada sand using an inclined laminar box. The centrifuge experiments simulate a gently sloping, 10 m thick stratum of saturated homogeneous sand of infinite lateral extent and relative densities ranging from 45 to 75%. Such idealized models approach some field situations and they provide significant general insight into the basic mechanisms and parameters influencing the lateral spreading phenomenon. The layer was subjected to lateral base shaking with prototype peak acceleration ranging from 0.20 to 0.41 g, a frequency of 2 Hz, and duration of approximately 22 cycles. The simulated field slope angle was 5°. The model deposits were all saturated with a viscous fluid 50 times more viscous than water, so that testing under the increased gravitational field (50 g) produced a deposit with the prototype permeability of the same fine-grained sand saturated with water in the field. Detailed discussions and comparisons of the six centrifuge tests are included. The observed effects of relative density $D_r$ and input peak acceleration $a_{\max }$ on the following measured parameters are summarized: thickness of liquefied soil $H_1\text{,}$ permanent lateral displacement $D_H\text{,}$ and ground surface settlement S. Comparisons and discussions are also presented on the effect of permeability for a $D_r=45\%$ deposit. This is done by comparing the results reported herein using a viscous pore fluid, with other published centrifuge tests where a similar deposit using the same model soil, also tested at 50 g and shaken with the same input motion, was saturated with water, thus simulating a prototype sand having 50 times the permeability of the fine sand reported in this paper.

This study focused on the behavior of a large-diameter burial pipe with special reference to its stability against flotation subject to soil liquefaction. Centrifugal modeling technique was used where the results are presented for a total of eight shaking table tests conducted on the burial pipe in a laminar box under $\mathrm{30g}$ gravitational field. The ground was prepared with Nevada sand at a relative density of 38% and shaken with a sinusoidal wave at an amplitude of $0.5g\text{.}$ The use of a viscous fluid in a saturated soil deposit satisfied the time scaling relationships of both dynamic and dissipation phenomena. The centrifugal modeling technique simulated flotation of pipeline as the soil liquefied. A technique that used gravels and geosynthetic material was used to mitigate flotation. The response of the soil deposit, in terms of acceleration and excess pore pressure, was investigated. The uplifting of the pipe, earth pressure response and ground surface deformation were also presented. Based on the test results, a design procedure was proposed for the burial pipe in resisting flotation due to soil liquefaction. The deadweight and stiffness of the gravel unit, which was confined by geosynthetic, were important items in design.

Taylor’s stability chart is the main tool used for engineering analysis of simple homogeneous slope stability problems. It is likely that this situation will continue in the future. One of the main deficiencies of Taylor’s original presentation is that it does not provide a convenient, general tool for establishing the critical slip circle associated with a given stability problem. Critical circles define the extent of the potentially unstable zone, and this information is quite useful in many practical situations. The present work completes Taylor’s classical investigation of stability of homogeneous slopes, and presents the tools necessary in order to establish not only stability numbers (safety factors), but also critical slip circles associated with those numbers. The information defining critical slip circles is presented in a simple chart form which is convenient for practical applications.

In this paper, by combining the geographic information systems (GIS) spatial analysis function and a hydrologic analysis and modeling tool with a column-based three-dimensional (3D) slope stability analysis model, a new GIS grid-based 3D deterministic model has been developed for slope stability analysis. Assuming the initial slip as the lower half of an ellipsoid, the identification of the 3D critical slip surface in the 3D slope stability analysis is performed by means of a minimization of the 3D safety factor using Monte Carlo random simulation. By using this hydrologic analysis and modeling tool, dividing the whole study area into slope units, and taking each slope unit as a study object, the minimum 3D safety factor for each slope unit can be obtained, and the landslide hazard can then be mapped for the whole study area.

In saturated clean medium-to-dense cohesionless soils, liquefaction-induced shear deformation is observed to accumulate in a cycle-by-cycle pattern (cyclic mobility). Much of the shear strain accumulation occurs rapidly during the transition from contraction to dilation (near the phase transformation surface) at a nearly constant low shear stress and effective confining pressure. Such a stress state is difficult to employ as a basis for predicting the associated magnitude of accumulated permanent shear strain. In this study, a more convenient approach is adopted in which the domain of large shear strain is directly defined by strain space parameters. The observed cyclic shear deformation is accounted for by enlargement and/or translation of this domain in deviatoric strain space. In this paper, the model formulation details involved are presented and discussed. A calibration phase is also described based on data from laboratory sample tests and dynamic centrifuge experiments (for Nevada sand at a relative density of about 40%).

This paper presents the results of nondestructive integrity tests (NDTs) and axial static load tests on drilled shafts constructed in varved clay at the National Geotechnical Experimentation Site in Amherst, Mass. The shafts were constructed with built-in defects to study: (1) the effectiveness of conventional NDT methods in detecting construction defects and (2) the effect of defects on the capacity of drilled shafts. Defects included voids and soil inclusions occupying 5–45% of the cross section as well as a soft bottom. Nine organizations participated in a blind defect prediction symposium, using a variety of NDT techniques. Most participants located defects that were larger than 10% of the cross sectional area. However, false positives and inability to locate smaller defects and multiple defects in the same shaft were encountered. Static load tests indicated that (1) minor defects had little or no effect on skin friction; (2) a soft bottom resulted in a 33% reduction in end bearing relative to a sound bottom; and (3) reloading resulted in a 20–30% reduction in the geotechnical capacity.

Anchor pull-out tests were performed on seven instrumented full-scale low-pressure grouted anchors installed in weathered soil at the Geotechnical Experimentation Site at Sungkyunkwan University. Anchors were 165 mm in diameter and embedded 9 to 12 m in weathered soil. Four were compression type and three were tension anchors. Performance tests, creep tests, and long term relaxation tests were performed and the results are presented. The characteristics of grout-soil and grout-strand interface were investigated and presented. From the measurements, a load transfer mechanism for tension and compression ground anchors was investigated and evaluated by a simple beam-spring numerical model.

Recently, there has been substantial interest in the enhancement of refuse decomposition in landfills, which results in increased settlement. In this paper, changes in waste compressibility as a function of the state of decomposition are reported. Samples representative of residential refuse were decomposed under conditions designed to simulate decomposition in both control and bioreactor landfills. Twenty four one-dimensional oedometer tests (63.5 mm cell) were performed on refuse prepared in laboratory-scale reactors for measurement of primary (Cc) and secondary $(C_{\alpha i}\text{,}$ representing creep, and $C_{\beta i}\text{,}$ representing biological) compression indices. The state of decomposition was quantified by the methane yield and the cellulose (C) plus hemicellulose (H) to lignin (L) ratio. The magnitude of compressibility was shown to increase as refuse decomposed and compressibility parameters were correlated with the state of decomposition. Initial settlement increased with decreasing $(C+H)/L$ ratio while the creep index was fairly independent of the state of decomposition. The coefficients of primary compression (Cc) for bioreactor samples showed an increasing trend with decreasing $(C+H)/L$ ratios. Cc increased from 0.16 to 0.36 as $(C+H)/L$ decreased from 1.29 to 0.25, and similar values of Cc were obtained with control samples at similar $(C+H)/L$ ratios. The creep index range was estimated at 0.02–0.03 for control and bioreactor samples in various states of decomposition. The magnitude of the biological degradation index $\left(C_{\beta i}\right)$ depended on the degradation phase with the highest value of 0.19 obtained during the phase of accelerated methane production. Proposing a single Cc for landfill settlement calculations may lead to inaccurate predictions. Properties of each waste sublayer will change as a function of the decomposition stage, and dominating processes with appropriate compressibility parameters should be applied to individual sublayers.

This paper describes the use of an instrumented dilatometer (IDMT) equipped with sensors designed to record the continuous displacement of the membrane, the total pressure, and the pore water pressure. The IDMT was tested in the Connecticut Valley Varved Clay at the University of Massachusetts—Amherst National Geotechnical Experimentation Site. The results, presented in terms of profiles of pore pressure during insertion, corrected pressures, dilatometer indices, and shear modulus are compared to results from the standard dilatometer, the self-boring pressuremeter, the seismic cone, and the seismic dilatometer. The results from the tests suggest that the IDMT can be used to provide accurate and cost-effective values of unload–reload modulus and, the complete pressure–displacement curve could potentially be used to develop improved correlations for strength and initial in situ stresses. In addition, the continuous pressure–displacement response and the pore pressure measurements provided insight into the mechanics of the dilatometer expansion in partially drained conditions.