Suction effects on a compacted clay under non-isothermal conditions

Abstract

The paper presents the results of an experimental study on the effects of suction and temperature on the volumetric behaviour of an unsaturated soil. Statically compacted Boom clay samples have been used in the testing programme, which has been performed using an oedometer apparatus with simultaneous control of suction and temperature. Suctions up to 0·45 MPa and temperatures up to 808C have been applied. Special measures have been taken to control and minimise the problems associated with phase changes and vapour migration at high temperatures. A comprehensive experimental programme has been carried out, including isothermal tests with control of vertical stress, suction and temperature, non-isothermal tests under constant suction, and isothermal swelling pressure tests. Testing samples at two compacted soil densities provides observations concerning a wide scope of behaviour ranging from collapse to swelling behaviour on wetting. Test results obtained at 808C have been compared with those of tests performed at room temperature (228C). Based on these comparisons, thermal effects on a variety of features of behaviour such as swelling potential, swelling pressure, collapsibility, shrinkage strains, compressibility, stress path dependence and degree of strain reversibility are presented and discussed. Although the basic behaviour is similar at high and low temperatures, various significant differences are identified concerning mainly swelling strains developed during wetting and compressibility with respect to loading. Swelling pressure test results indicate that the high-temperature samples yield at a lower stress than that observed in room-temperature samples, suggesting that the stress domain bounded by the main yield surface reduces as temperature increases-a behaviour feature shared with saturated soils.

Thermo-mechanical behaviour of a compacted swelling clay

“…The same phenomena have been observed by Romero et al (2003) , PI = 27%), also in an oedometer. Saix et al (2000) performed compression tests in a triaxial cell at constant suction (4.9 kPa) and temperature (30 -70°C) on a clayey silty sand ( % 25 = L w , PI = 10.5%).…”

“…With compacted FEBEX bentonite, Romero et al (2005) observed that the stiffness upon loading at 14 MPa suction increased with temperature. On the contrary, with compacted Boom clay, Romero et al (2003) noticed that the compression index is larger at higher temperatures, but the swelling index seemed to be temperature independent. In terms of thermal volume changes, Saix et al In order to understand better the thermo-mechanical behaviour of unsaturated soils, in the present work, unsaturated compacted MX80 bentonite was studied using a suctiontemperature controlled isotropic cell.…”

Effect of thermal history on the properties of bentonite

“…Pusch et al (1990) and Cho et al (2000) showed that increase in temperature induced increase in the swelling pressure of bentonite. Romero et al (2003) studied the effects of temperature in controlled-suction swelling pressure test for compacted Boom clay. They concluded that the values of swelling pressure at each equilibrium suction (i.e., 4500, 2000, 600 kPa and saturated condition) at 22 0 C are more than those at 80 0 C.…”

A new triaxial apparatus for testing soil water retention curves of unsaturated soils under different temperatures

“…In the limited literature on this topic, temperature-controlled oedometers, isotropic and triaxial apparatuses were developed and used. In the first reported systematic study on temperaturecontrolled tests on unsaturated soils, Romero et al (2003) presented experimental results about the suction and temperature effects on the volumetric behavior of compacted Boom clay. In this study, a temperature-controlled oedometer apparatus placed inside a thermostatic silicone oil bath was used.…”