Effects of Cyclic Variations of Pore Pressure on the Behaviour of a Gneiss Residual Soil
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ORIGINAL PAPER
Effects of Cyclic Variations of Pore Pressure on the Behaviour of a Gneiss Residual Soil Olavo F. Santos Jr.
. Willy A. Lacerda
. Mauricio Ehrlich
Received: 23 July 2019 / Accepted: 11 May 2020 Ó Springer Nature Switzerland AG 2020
Abstract Many slope failures in residual soils have been attributed to increased soil pore pressure. During the rainy season, water infiltration occurs, which can lead the slope to rupture by increasing the pore pressure. However, some landslides have been observed with pore pressures below those required for failure. Hypotheses for such ruptures include the occurrence of creep or fatigue due to cyclic variations in the piezometric level on the slope. This paper presents a study on the effect of pore pressure on the behaviour of the residual soil of the Soberbo hillside in Rio de Janeiro, Brazil, subjected to monotonic and cyclic pore pressure. Triaxial tests that simulate the increasing piezometric level (constant shear drained— O. F. Santos Jr. (&) Federal University of Rio Grande Do Norte – UFRN Centro de Tecnologia - Av. Senador Salgado Filho, 300 Lagoa Nova, Natal, RN CEP 59078-970, Brazil e-mail: [email protected]; [email protected] W. A. Lacerda COPPE – Federal University of Rio de Janeiro, Centro de Tecnologia - Bloco B - Sala 101 - Ilha do Funda˜o, Caixa Postal 68506, Rio de Janeiro, RJ CEP: 21941-972, Brazil e-mail: [email protected] M. Ehrlich COPPE – Federal University of Rio de Janeiro, COPPEUFRJ, Centro de Tecnologia - Bloco B - Sala 101 - Ilha do Funda˜o, Caixa Postal 68506, Rio de Janeiro, RJ CEP: 21941-972, Brazil e-mail: [email protected]
CSD tests), drained creep (DC-CSD tests) and cyclic pore pressure variation (CPP tests) in slopes were carried out. The CSD test results showed that the failure due to increasing pore pressure is essentially dilatant and confirmed the peak strength obtained from conventional drained triaxial tests. Sudden failure was observed in all CSD tests at the end of the pore pressure increase phase. The results show that the failure of the slope may occur due to drained creep and the loss of soil shear strength under cycling pore pressure. Keywords Pore pressure Constant shear drained tests Tropical soils Creep Rain-induced failure
1 Introduction Residual soils are commonly found in tropical regions since high temperatures and abundant rainfall create favourable conditions for chemical reactions that decompose rock, transforming it into soil. The combination of deep highly weathered soil, steep slopes and intense rainfall make tropical regions more prone to mass movements. Landslides are considered one of the most important environmental problems in hilly tropical areas, and most landslides are rain-induced. During rainy periods, water infiltration may provoke a significant increase in soil pore water pressure.
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Geotech Geol Eng
Brand (1981) suggested that this phenomenon could be represented by triaxial tests and proposed that the field stress path of a soil
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