Journal of Geotechnical and Geoenvironmental Engineering

A series of biaxial (plane strain) experiments were conducted on three sands under low (15 kPa) and high (100 kPa) confining pressure conditions to investigate the effects of specimen density, confining pressure, and sand grain size and shape on the constitutive and stability behavior of granular materials. The three sands used in the experiments were fine-, medium-, and coarse-grained uniform silica sands with rounded, subangular, and angular grains, respectively. Specimen deformation was readily monitored and analyzed with the help of a grid pattern imprinted on the latex membrane. The overall stress-strain behavior is strongly dependent on the specimen density, confining pressure, sand grain texture, and the resulting failure mode(s). That became evident in different degrees of softening responses at various axial strains. The relationship between the constitutive behavior and the specimens' modes of instability is presented. The failure in all specimens was characterized by two distinct and opposite shear bands. It was found that the measured dilatancy angles increase as the sand grains' angularities and sizes increase. The measured shear band inclination angles are also presented and compared with classical Coulomb and Roscoe solutions.

The behavior of a peat from Mercer Slough in Bellevue, Wash., was investigated by a program of field and laboratory testing. The peat was very soft, very weak, and highly compressible. Water contents averaged approximately 600% and in situ shear wave velocities were measured at 12–30 m/s. Cyclic triaxial and resonant column testing indicated that the modulus reduction and damping behavior of Mercer Slough peat was significantly influenced by strain amplitude and effective confining pressure and was weakly influenced by loading frequency and overconsolidation ratio. Comparison of the behavior of Mercer Slough peat with other highly organic soils suggests a trend of increasing linearity and decreasing damping with increasing effective confining pressure. Site response analyses indicated strong response at low frequencies with spectral shapes that differ significantly from the standard shapes implied by current codes.

An experimental study was conducted to evaluate factors affecting flow rates past soil-bentonite (SB), geomembrane (GM), and composite geomembrane-soil (CGS) vertical cutoff walls. Intact walls and walls containing defects (inadequate keys, windows, and poor joint seals) were studied. For intact cutoff walls, CGS walls had the lowest flow rate, followed by SB and GM walls. CGS walls typically had flow rates as much as 100 times lower than comparable GM walls. Flow rates increased by a factor of 2–160 when the GM walls contained defective joints or the SB walls contained permeable windows. For all wall types, an effective key was required to achieve low flow rate past the wall. For GM walls, under seepage was not effectively controlled when the GM was placed in direct contact with the aquitard. Flow rates for GM walls placed in direct contact with the aquitard were nearly equal to the aquifer flow rate without a wall. Better control of underseepage was possible with SB and CGS walls placed in direct contact with the aquitard because the soft bentonitic backfill conformed to the surface of the aquitard. Hydraulic conductivity of unsealed joints in GM walls was estimated from flow rates past GM walls where a portion of the joint was unsealed. These hydraulic conductivities ranged between 1.8 × 10⁻⁴ and 5.6 × 10⁻³ cm/s.

An accurate prediction of bearing capacity of shallow foundations on granular soils has been historically complicated by effects due to scale of the foundation. These effects are due to the nonlinear strength behavior of the granular soil and the phenomenon of progressive failure. The former can be conveniently accounted for by strength-dilatancy relationships. It is proposed that the effect of progressive failure on ultimate bearing capacity can be described in terms of the relative dilatancy index inherent in strength-dilatancy relationships. A design approach to bearing capacity based on these considerations is presented. The approach is calibrated using bearing capacity results from studies spanning the past 20 years. The solution is shown to work well for the sands examined and is useful in that the proposed process by which strength parameters are determined reduces, or may eliminate, the need for laboratory or in situ shear testing, while increasing the accuracy of the predictions made when compared to conventional methods.

This paper outlines a test program in southern Sweden for measurement of the vibration induced in the ground and railway embankment by high-speed trains, together with a rigorous numerical model developed for the prediction of embankment/ground response. In this formulation the ground is modeled as a layered viscoelastic half-space, and the railway embankment is modeled as a viscoelastic beam excited by the moving loads of the train. The model uses the Kausel-Roësset Green's functions to calculate the soil stiffness matrix at the ground-embankment interface and assembles it with the dynamic stiffness matrix of the embankment. The solution is carried out in the frequency domain, and the time histories of the motions are derived through a Fourier synthesis of the frequency components. Numerous simulations of train-induced vibration are presented for the ground conditions and embankment parameters at the test site and compared with measured records. The simulations agree well with the measurements, both in qualitative and quantitative terms. In particular, the large ground deformations registered for train speeds exceeding 140 km/h are reproduced by the simulations. With the help of the prediction model, the effectiveness of a remediation measure for the mitigation of ground vibration is explored.

Volume change in argillaceous sediments can take place due to either swelling of expansive clay or gypsification of anhydrous calcium sulfate. Gypsification offers a variety of serious geotechnical hazards such as high swell pressure, floor heave in tunnels, massive rock uplift in dams, and damages to light structures and pavements. Some of these phenomena have been observed in the Arabian Gulf coastal region, where the behavior of local argillaceous sediments is controlled by severe climatic and environmental conditions. Based on laboratory investigation of natural and synthetic samples, this paper studies the influence of gypsification of anhydrite on the engineering behavior of calcareous expansive clay.

Strong motion records at five vertical array sites in Japan are used to examine soil shear modulus and material damping as a function of shear strain during large earthquakes. Acceleration data from the sites are processed directly for evaluation of site shear stress-strain hysteresis curves for different time windows of the record. Results of the analysis demonstrate a significant nonlinear ground response at the sites with surface peak ground accelerations exceeding 90 gal. The results of shear stress-strain hysteresis curves are also used to estimate variation of soil shear modulus and material damping characteristics with shear strain amplitude at each site. The identified shear modulus-shear strain and damping ratio-shear strain relationships are in general agreement with published laboratory results. These response interpretations are also compared with the results of a frequency-domain analysis by using the spectral ratio (uphole/downhole) technique. There is general agreement between the time- and frequency-domain results. The results illustrate the significance of the site nonlinearity during strong ground motions as well as the accuracy of the dynamic soil properties obtained from laboratory tests.

Safe and economical storage of tailings is now a major consideration in the operation of many mining operations. Tailings in slurried form, particularly if they have a significant clay content, can take a very long time to consolidate under the action of self-weight consolidation alone. However, if the operation is located in an area of high potential evaporation, this can be used to accelerate the rate of tailings densification. This paper presents a study of the evaporation behavior of a clayey tailings slurry deposited into an evaporation pond in the southwest of Western Australia. Over a six-month period, the rate of evaporation from the tailings surface was monitored using the Bowen Ratio method and the microlysimeter method. This was compared with the evaporation from a Class A pan located nearby. The tailings underwent very significant cracking as drying proceeded, and it was found that these cracks had a significant influence on the overall rate of evaporation once the top surface of the deposit started to desaturate. A large strain consolidation model was used to model the behavior, and the algorithm used in this model to include the effects of evaporation is shown to provide a reasonable prediction of the observed evaporation behavior.

The effects of tube sampling disturbances on undrained shear characteristics of reconstituted samples of three coastal soils were investigated. The values of undrained shear strength s_u and initial tangent modulus E_i were reduced, whereas axial strain at peak deviator stress ε_p increased because of a disturbance caused by penetration of samplers. Disturbances also reduced initial effective stress ${\sigma }_{\mathit{i}}^{\mathit{\prime }}$ and pore pressure changes considerably. The changes in soil parameters between the “in situ” and “tube” samples depended markedly on the geometry of samplers used to retrieve tube samples. Values of s_u, E_i, and ${\sigma }_{\mathit{i}}^{\mathit{\prime }}$ of samples were reduced, whereas the values of ε_p increased with an increasing area ratio (or decreasing external diameter to thickness ratio) and an increasing outside cutting edge angle of the samplers. Different reconsolidation procedures were adopted to assess the suitability of reconsolidation of tube samples to recover in situ properties. It was found that the K₀-reconsolidation of tube samples to vertical effective stresses equal to 1.5 and 2.5 times the in situ vertical effective stress produced the best overall estimate of in situ characteristics.