In order to discuss the deformation characteristics of rock mass under different water levels changing between 145 and 175 meter in the Three Gorges reservoir area

an experiment was carried out for the studying sandstone deformation under the conditions of three different axial stresses(σ1=55.54

34.18

12.82 MPa)

two cyclic pore pressures(Pmin=2 MPa

Pmax=6 MPa) and two kinds of constant time(the upper limit time and the lower limit time(ΔT=120

240 s).With ε1-T curves and p-T curves

as well as p-ε1  hysteresis curves

it was found that the curves were continuous sine wave-shaped curves.At first

the strain decreased with loading pore pressure.And then

it decreased to valley value with pore pressure at stable upper limit.Next

it increased with unloading pore pressure and increased to peak value with pore pressure at stable lower limit.The p-ε1  hysteresis curves of the sandstone had two typical stages.And one was caused by the closure of some primary pores and crack under increasing compaction

in which the strain did not form obviously hysteresis curves

and the other was pore pressure coupling stage which showed obvious hysteresis curve in form of the anti-clockwise from the dispersed to the dense.In addition

Δε-n curves in four sections (loading

unloading

steady upper limit

steady lower limit) of p-ε1 curves were compared and respectively ananlyzed in the condition of various axial stress and different constant time .