Influence of matric suction on the results of plate load tests performed on a lateritic soil deposit
| Autor: | L David Suits, TC Sheahan, YD Costa, JC Cintra, JG Zornberg |
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| Rok vydání: | 2003 |
| Předmět: | |
| Zdroj: | Repositório Institucional da USP (Biblioteca Digital da Produção Intelectual) Universidade de São Paulo (USP) instacron:USP |
| Popis: | The performance of foundation systems on unsaturated soil deposits is considerably influenced by variations of the negative pore-water pressure (i.e., matric suction) distribution within the soil mass due to local microclimate conditions. Although significant understanding has been gained in the last few decades on the behavior of unsaturated soils, the use of unsaturated soil mechanics concepts in the interpretation of field tests has not been incorporated into the state-of-practice. As a consequence, conservative foundation engineering principles are used in practice in regions where unsaturated soil conditions prevail. For example, direct use of field test results (e.g., from plate load tests) obtained during a dry season in unsaturated soil deposits may lead to the selection of unconservatively high design parameters at the site. On the other hand, ignoring altogether the beneficial impact of matric suction on the bearing capacity of soils may lead to unnecessarily expensive foundation systems in tropical, arid climates. This paper investigates the influence of soil suction on the results of plate load tests conducted at a depth of 1.5 m on a structured, naturally occurring lateritic soil. Ten tests were carried out under different soil suction conditions. Matric suction was monitored during plate load testing using tensiometers installed at the bottom of the testing pit up to a depth equal to one plate diameter (0.80 m), which is generally recognized as the influence zone in which significant stress variation occurs (Terzaghi and Peck 1948). The results provide insight into the influence of soil matric suction on ultimate bearing capacity and settlement rate of plate load tests performed on lateritic soils. Background Although the notion that the presence of negative pore-water pressures (matric suction) in the soil influences the behavior of foundations is not new, there is only limited information reported in technical literature dealing with the quantification of this problem. A brief description of previous research on this topic regarding shallow footings is presented below. Bearing capacity loss associated with the soil saturation has been commonly accounted for through the use of different values of unit weight of the soil (� ) that arise due to total or partial submersion. Other soil parameters such as the effective cohesion ( c� ) and the effective internal friction angle ( �� ) are usually assumed to play a minor role. Considering the submerged unit weight of the soil is about 50 % of the moist unit weight, Terzaghi and Peck (1948) stated that the bearing capacity of shallow footings could be approximately reduced by 50 % if the water level rises from a depth equal to the footing width below the footing to the surface. Meyerhof (1955) proposed an analytical model for estimating the bearing capacity of shallow foundations based on the variations of the soil unit weight and taking into consideration the possibility of partial submersion. The groundwater table is assumed to lie between the foundation base and the lower portion of the soil failure surface. The value of unit weight of soil to be used is defined as |
| Databáze: | OpenAIRE |
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