This paper presents results of small scale physical model tests on an instrumented rigid retaining wall subjected to 1-D shaking and effectiveness of EPS (expanded polystyrene) geofoam to reduce seismic earth pressures. Two different boundary conditions viz., retaining wall with and without hinge at the base were considered during experiments. Initial application of 50 kPa static surcharge, followed by seismic load in the form of a stepped sinusoidal acceleration in the range of 0 to 0.7 g was applied in increments of 0.045 g, each increment being applied for 5 seconds at 3 Hz frequency. The seismic earth pressure distribution was observed nearly hydrostatic in the case of retaining wall with hinge, without geofoam inclusion. Whereas, for the retaining wall without hinge, the observed seismic earth pressure distribution was curvilinear with maximum pressures in the upper half of the retaining wall. Provision of 10D (10 kg/m3) EPS geofoam reduced the total lateral force on the retaining wall by about 23% and 28%, for retaining wall with and without hinge, respectively. It was observed that, boundary conditions are mainly influenced the earth pressure distribution in both the cases, with and without geofoam provision.

View full abstract

In this paper, the application potential of expanded polystyrene (EPS) geofoam as a vibration screening material in an in-filled trench has been investigated under circular machine loading. Circular machine foundations are commonly used for the foundations of reciprocating engines, compressors, turbines, generators etc. The numerical analysis is performed using two-dimensional finite element method under dynamic condition. The present analysis considers the foundation bed as linearly elastic, isotropic and homogeneous soil deposit. The inclination of the trench is also considered as a special parametric study. The vertical displacement amplitudes of the ground vibrations are analysed at different pick-up points along the ground surface to determine the amplitude reduction factor (ARF).

View full abstract

In this study, series of experimental test were conducted on geocell type of reinforcements for its implementation to improve the strength of soft ground. The ground for test pit has less tensile strength than normal ground, which causes problems like subsidence of ground or weakening of bearing capacity. From the series of large soil box with geocell experiment varying filling materials and geocell shapes, the effect of geocell shape and filling material characteristics on bearing capacity of geocell reinforced soil layers was evaluated. Based on the result, reinforcement of bearing capacity and stress distribution effect of the sub-ground according to increase of loading was analyzed under the conditions including height, width, and shape of geocell, and types of filling materials. Evaluation of bearing capacity based on a large soil box test suggested that the ultimate bearing capacity with the maximum reinforcement increases by four to eight times in comparison with natural ground, and the largest ultimate bearing capacity is given in geocell shape of 1:1.2 (width: height) which is filled with sand, and to be 1:0.8 (width: height) when filled with sedimentary clay. Also, the maximum earth pressure in reinforced ground decreases 50% up to 60% in comparison with unreinforced ground because of dispersion of lower stress.

View full abstract

Soft clay is normally avoided during construction due to its low bearing capacity and high susceptibility of consolidation. The safe bearing capacity of soft clay is considerably increased with insertion of geocells at suitable depth from the foundation. Although it is known that geocell reinforced soft clay behaves differently in confined and unconfined conditions, but a detailed study is not reported yet. Moreover, the behavior of geocell reinforced soft clay under dynamic loading is also not properly studied. Extant of increase in bearing capacity of soft clay due to insertion of geocells is also not known. Present research is intended to study a series of static and cyclic triaxial tests to understand the effect of geocells on modification of strength parameters and dynamic properties of soft clay. Both confined and unconfined tests have been done considering actual site condition. It is observed that under unconfined conditions, the geocells will compress resulting in increase in strain, whereas, under confined condition, the geocells will stiffen the soil resulting in increase in stress. It is also observed that maximum improvement in axial stress is achieved when the geocells are placed at a depth of one fourth of the loading diameter. However, position of geocells does not have a significant effect on stress strain curve in unconfined condition. It is observed that the shear modulus increases and the damping ratio decreases due to insertion of geocells. A study has also been conducted to obtain the effect of geocells on modification of residual strength after cyclic loading. It is observed that reduction of strength due to cyclic loading is much less due to insertion of geocells.

View full abstract

In this study, it was intended to clarify the compressive properties of soils mixed with deformable particles such as waste tire chips. Generally, in the case of soil mixed with deformable particles such as rubber, it is thought that two more compression components; the compression of the deformable particle themselves and the following reduction of pore space, add to the ordinary volumetric compression. Therefore, a series of one-dimensional compression tests were executed using rubber and aluminum chips to estimate these additional compression components. In the experiment, the specimen pore space was saturated with water, and the drainage was measured to estimate the pore space volume change. As a result, it was found that the pore space reduction caused by the deformation of rubber chips was far larger than the compression of the rubber chips themselves. It was also confirmed that the compression of rubber arises most extremely in the early stages, and that the rubber is hardly compressed any more even if the compressive stress increases subsequently.

View full abstract

In this study, evaluation of in-situ compressive stiffness of backfilling ground reinforced with fiber was discussed. A model ground made at the test field by backfilling with Liquefied Stabilized Soil (LSS) reinforced with fiber amount of 0 and 20 kg/m³ was subjected to portable Falling Weight Deflectometer (FWD) tests at curing time of 28, 56 and 84 days, respectively. The stiffness was estimated by Young’s modulus E_P.FWD calculated from K_P.FWD-value as the coefficient of subgrade reaction. In parallel, in order to obtain the tangent Young’s modulus E_tan in deviator stress and axial strain (q -e_a) curve, a series of Consolidated–Undrained triaxial compression tests under the conditions at constant strain rate, constant deviator stress (partial creep test), and changed strain rate during monotonic loading have been carried out for specimens prepared by trimming LSS retrieved from the model ground by block sampling. Based on the test results, the relationship between the E_P.FWD and E_tan was discussed. It is considered that the K_P.FWD-value is able to estimate the stiffness of backfilling ground by LSS reinforced with fiber.

View full abstract

Sand reinforced with randomly oriented short polypropylene fibers (fiber reinforced sand, fibrosand, FRS) was tested to determine creep characteristics. This study is a part of research aimed at encouraging FRS application in subsoils, embankments and retaining wall constructions. Natural non-treated sand was used as a base material. Commercially available polypropylene fibers of 12 mm in length were used as reinforcement. Fiber content accounted for 0.93 %. Twin samples of FRS were put to creep tests using the two curve method. The test results were analyzed and checked with the use of ageing, hardening and hereditary creep theories. The results of a prolonged creep test on the samples under constant load were used to fit the creep parameters by the FORE method. The methodology and creep test results on FRS are given and discussed in the paper.

View full abstract