This paper presents a preliminary report on a systematic study of the dilatancy and creep behaviour of rocks in the brittle field, which is of primary importance for crustal processes and underground rock engineering. A comprehensive description is given of the new 8000 KN servo controlled multipurpose triaxial apparatus Three series of tests conducted at the constant strain rates of 5×10–5 sec -1 and 10–5 sec-1 on samples of Fangshan granite and sandstone have been performed at various confining pressures from 17 to 400 MPa and temperatures from 20 to 250°C. In order to study the time dependent deformations in the linear and dilatancy stages more closely, creep tests have been conducted. Two creep tests on Fangshan granite have been carried out using stepwise loading at 100 and 200 MPa confining pressures and a temperature of 7 and 200 °C respectively. Creep test on sandstone at room temperature 25°C and without confining pressure has been carried out also. In this manner the dependence of creep and dilatancy on deviatoric stress and time can be obtained from one sample. The threshold values f* at the onset of dilatancy for creep have been determined from the stress-strain relationships. An analysis of the time dependent processes of dilatancy is presented in connection with structural changes due to crack growth, coalescence and generation. On the basis of the experiments it is concluded that in underground constructions granites are in the brittle field with time effects down to a depth of many kilometers.
In order to get a better understanding such crustal processes as the tectonics of the crust, the genesis of earthquakes, the behavior of engineering constructions at large depths etc, a profound knowledge of the rheological behaviour of rocks in the brittle field at various stress and temperature conditions is desirable. Such a study is very valuable to make theoretical predictions of deep tunnels in heat flow regions under high tectonic stresses. This paper will present a systematic study of the phenomenon of dilatancy. Dilatancy is a volume increase which is due to the effect of deviatoric stresses. It is a common property of granular and polycrystalline materials such as igneous and sedimentary rocks, sand, cohesive soils, concrete, case iron etc. This process is accompanied by large deformations and decrease of strength and thus instability. Therefore such stages near failure must be carefully studied by the geotechnical engineer. The first observations of inelastic volume increases prior to fracture in compression tests on soapstone, marble and dolerite were made by Bridgman (1949); dilatancy was also observed in sedimentary rocks (Handin et al 1963) and in granites. Matsushima (1960) showed that increasing confining pressure reduced the magnitude of dilatancy and the range of truly elastic behaviour was increased; A more systematic study was from the study of many authors as Bridgman (1949), Handin et al (1963), Matsushima (1960), Brace et al (1966). The following findings which are based on constant rate tests at room temperature can be concluded from their works.
