Abstract

Coarse-grained soils are preferably used in geotechnical infrastructure projects such as retaining walls and highway embankments due to their superior drainage and frictional properties. However, such materials are not always available on or near the construction site. Given the limited availability, high cost, and transportation issues associated with coarsegrained fill, using the locally available marginal soil for the various infrastructure projects becomes essential. Marginal soils are soils with a high percentage of fines that can be cohesive or non-cohesive. The primary concern with marginal soil is its low permeability, which causes excess positive-pore water pressure evolution during load application. As a consequence, the soil loses shear strength over time. Previous researchers have provided some information on the dynamic behaviour of marginal soils in terms of cyclic strength and pore pressure development. However, more research is needed to understand the dynamic response of compacted marginal soils in terms of cyclic resistance ratio (CRR) using field and lab data. Therefore, an attempt has been made in this study to evaluate the cyclic resistance of compacted marginal soil (clayey sand) by performing stress-controlled cyclic simple shear (CSS) tests in the laboratory and Standard Penetration Test (SPT) and Dynamic Cone Penetration Test (DCPT) in the field. The cyclic strength of marginal soil has been determined as Cyclic Resistance Ratio (CRR) by using laboratory (CSS) and field (SPT, DCPT) test data.

Abstract

Analysis of shallow foundations, pavements, and slabs-on-grade requires adequate site characterization of the nearsurface soils. Key properties required for the above are the soil stiffness and its nonlinearity. In this paper, we present the results of field site characterization at a coastal aeolian sand site located in Villa El Salvador, Peru, where large storage tanks are being proposed to be supported on concrete slabs-on-grade and shallow ring foundations. The site characterization included standard penetration tests (SPT), dynamic cone penetrometer (DCP) tests, lightweight deflectometer (LWD) testing, and geophysical tests such as multichannel analysis of surface waves (MASW), seismic refraction, and electrical resistivity. The paper focuses on estimating elastic soil stiffness (Es) values on the main bearing layer of the tanks. The observed large variability of Es estimates was associated with inherent soil variability at the site, the in-situ test method, and the use of empirical correlations between Es and different in-situ tests. Good elastic soil stiffness estimates for the bearing layer (Upper SP sand) were required to make reliable estimates of absolute and differential settlements for the tanks. Due to soil nonlinearity, the elastic stiffness values from the different methods decreased with increasing levels of shear strains associated with each test. Accordingly, the highest elastic stiffness values were from the MASW, followed by the LWD, and the lowest from SPT-based correlations. The soil stiffness estimates using SPT-based correlations yielded the highest variability due to the high uncertainty and low confidence of the empirical correlations between Es and SPT field values.