Seismic displacement of a geosynthetic-reinforced wall with full-height rigid panel facing (Tanata wall) in the 1995 Hyogo-ken Nambu earthquake is calculated using a pseudo-static method based on a 'multi-wedge' failure mechanism. The calculated value of horizontal displacement of the wall is comparable to the measured one. Based on an investigation into the effect of vertical ground acceleration to the seismic displacement of the wall using vertical and horizontal input ground accelerations in recorded seismograms, it is found that the contribution of vertical ground acceleration to the seismic displacement of the Tanata wall is small, because the peak horizontal and vertical ground accelerations are out of phase. Therefore, the use of peak vertical-to-horizontal ground acceleration ratio obtained in an earthquake event for pseudo-static multi-wedge analysis may overestimate the seismic displacement of a geosynthetic-reinforced wall to some extent. The effect of the embedment of the facing on the seismic displacement of the Tanata is also investigated. It is found that the effect of facing embedment to the seismic stability and/or displacement in the case of the Tanata wall is insignificant.
In this paper, geosynthetic reinforced granular fill-soft soil system subjected to a moving load with constant velocity over an infinitely long beam is analyzed. The foundation is assumed as tensionless foundation (to react only in compression). The upper reinforced granular bed is modeled by a rough elastic membrane embedded in Pasternak shear layer overlying a series of compressible Winkler springs representing the underlying soft soil. The parametric studies reveal that the flexural response of the infinite beam as well as of the reinforcement, are greatly affected by the velocity, intensity of load and compressibility of granular fill. The interfacial frictional coefficients, shear modulus of granular layers and coefficient of lateral earth pressure do not significantly affect the response of the beam and the reinforcement for the range of parameters studied.
Quasi-elastic deformation properties of dry, dense Toyoura sand at very small strain level were investigated by conducting a series of triaxial and torsional shear tests on hollow cylindrical specimens. Strains were measured locally by a newly developed pin-typed local deformation transducer. In the tests, effect of end-restraint at the top cap and pedestal on small strain shear modulus that was measured externally by applying small unload /reload cycles in the torsional direction was found to be significant. A new hypoelastic model was proposed to simulate the inherent and stress-induced anisotropies of quasi-elastic deformation properties of sand, considering rotation of principal stress axes from material axes. Good agreements between experimental and simulation data were observed. In the simulation, effect of inherent anisotropy on the quasi-elastic deformation properties of Toyoura sand was found to be small.
In a naturally deposited soil foundation subject to embankment loading, a delayed settlement can often be observed after the embankment's completion, sometimes also showing acceleration over time. Frequently in such cases the soil exhibits an increase rather than a dissipation of excess pore pressure in some of its parts, a phenomenon which cannot be explained by conventional elasto-plastic consolidation theory. In this paper the possible mechanism for this kind of delayed settlement is investigated numerically using a soil-water coupled elasto-plastic computation under plane strain conditions. It is assumed that the soil section contains a medium dense sand layer and highly structured clay layers. A Super/subloading Yield Surface Cam-clay model is used to describe the elasto-plastic behavior of both the sand and the clay with respect to soil structure, overconsolidation and anisotropy. It is found that the delayed settlement behavior occurs under a certain constant embankment load, and persists over a period of 40 years, with increases in the settlement rate accompanied by both dissipation and a rise in excess pore pressure. The cause of this is the softening that co-occurs with the plastic compression of the soil skeleton. In other words, consolidation settlement can be considered as an example of “progressive consolidation with decay of structure”. Some typical characteristics of this delayed settlement behavior are also numerically examined with reference to the height and weight of the embankment, and to soil improvements using sand drains. When the embankment is much lower, the foundation does not undergo delayed consolidation, and when it is higher, the foundation becomes subject to circular slip failure. Soil improvement with sand drains can effectively shorten the length of time up to final settlement.
A series of consolidated drained triaxial compression tests were performed on recycled concrete aggregates to investigate the feasibility of their use as a backfill material for geotechnical engineering structures requiring a high stability while allowing a limited amount of deformation, such as embankments and conventional type and geosynthetic-reinforced soil retaining walls supporting highway and railway. The experimental results showed the following. The compressive strength qmax when well compacted at water content in the vicinity of the optimum water content wopt is similar to that of typical well graded gravelly soil that is categorized as the highest class backfill material. When well compacted at the same energy level, the peak strength and pre-peak stiffness of recycled concrete aggregate is insensitive to changes in the moulding water content relative to wopt. When well compacted around wopt, the effect of confining pressure on qmax is similar to the one of typical well graded gravelly soil, while confined saturation does not have any detrimental effects on the qmax and pre-peak stiffness. With a decrease in the compacted dry density from the maximum dry density at fixed water content around wopt for a given compaction energy level, the qmax and pre-peak stiffness decreases at a very high rate. The viscous property of the recycled concrete aggregate is similar to the one of ordinary type backfill materials. When well compacted around wopt, residual strains by sustained and cyclic loading are not significant.
During a self-boring pressuremeter test (SBPMT), a cylindrical cavity is expanded from finite radius. With this view, a method for estimating volumetric strains in expanding plastic zone based on finite strain analysis is developed to solve the problems related to expansion of cylindrical cavity from a finite radius in sands. Using finite strains, average value of volumetric strains in the plastic zone is calculated at various values of circumferential strains (εθθ) ranging up to about 30%, when the value of angle friction (φ) is varying between 25 and 45 degrees and the value of rigidity index (Ir) is varying between 5 and 1000. The dimensional cavity expansion factor (F"q) is calculated using cavity expansion theory to develop F"q versus εθθ curves at various values of φ and Ir. In the companion paper, Gupta (2005), this method has been applied to analyze the SBPM tests performed in sands for determining φ, Ir, and modulus of deformation (E) at different stress levels.
Self-boring pressuremeter test (SBPMT) data has been analyzed based on cylindrical cavity expansion method and dimensionless cylindrical cavity expansion factors (F"q) to determine angle of friction, rigidity index (Ir) and modulus of elasticity (E). Then, based on a hyperbolic model, secant modulus (Esf), secant modulus at 50 percent failure stresses (E50), and initial modulus (Ei) have been determined. Reasonable values of angle of friction, initial modulus (Ei), and secant modulus of deformation at failure (Esf) have been determined for sand deposits located in different geographical regions. The secant modulus (E50) determined by this method compares well with unload-reload modulus, Er, determined from unload-reload cycle of the SBPM tests.
Isotropic compression tests have been performed on two fine sands. Specimens of Nevada sand were prepared by air pluviation and by funnel deposition followed by tapping to relative densities of 30, 50, 70, and 90%. Specimens of Santa Monica Beach sand were prepared by air pluviation to a relative density of 90%. All specimens exhibited cross-anisotropic behavior, both in terms of total strains and in terms of unloading strains. Small pressure cycles performed during loading and unloading were used to study elastic behavior. The inclination angles of the total and plastic strain increment vectors relative to the hydrostatic axis in the principal stress space were used to express and to study the evolution of cross-anisotropy in the sand deposits. In the context of elasto-plastic constitutive modeling, the variation of the inclination of the plastic strain increment vector was further characterized by a rotation of the plastic potential surface as a means to capture the inherent cross-anisotropic behavior observed in such sand deposits.
A series of undrained cyclic torsional shear tests was conducted to investigate liquefaction properties of Toyoura sand under low confining stress. Hollow-cylindrical specimens were prepared by air pluviation at a relative density of about 55%. After being saturated, they were anisotropically consolidated to an effective vertical stress of 9.8, 29.4 and 98.1 kPa, while keeping the effective horizontal stress to be half of the vertical one. They were subjected to undrained cyclic torsional shear without allowing any vertical displacement of the top cap. The amplitude of the cyclic shear stress was kept constant with correction for the effects of membrane force on the measured values. The liquefaction resistance was found to increase with the decrease in the confining stress, while correction for the effects of membrane penetration did not significantly affect this tendency. Analyses of the test results revealed that the liquefaction properties were affected by the mobilization of shear resistance under extremely low effective stress states and the stress level-dependency of shear modulus that was normalized by the confining stress. Finally, by introducing a concept of apparent increase in the effective mean principal stress, a simplified procedure to estimate the liquefaction resistance under low confining stresses was proposed.
This paper aims to investigate the effect of consolidation time on the shear modulus of volcanic coarse-grained soils with different degrees of particle breakage. A series of bender element and cyclic triaxial tests was performed on volcanic coarse-grained soils under isotropic consolidation at different consolidation times. The simplified cyclic triaxial test has been proposed in order to clarify the effect of consolidation time on shear modulus. A good agreement among test results obtained from the simplified cyclic triaxial test, conventional cyclic triaxial test and bender element test can be observed. The test results also show that the rates of increase in the shear modulus due to consolidation for volcanic coarse-grained soils depend strongly on the degrees of particle breakage. In addition, empirical equations for predicting the time-dependent behavior of the shear modulus were also proposed based on the test results.