孔隙水压力与恒定时间对砂岩变形的实验研究

Experimental Analysis on the Deformation of Sandstone under Pore Pressure and Constant Time

探讨三峡库水位在145-175 m之间涨落及蓄水时水压对岩(石)体的变形特性影响。以实验为基础,进行了不同轴向应力(1σ=55.54,34.18和12.82 MPa)条件下,周期孔隙水压力(Pmin=2 MPa,Pmax=6 MPa)与上、下限恒定时间(ΔT=120和240 s)作用下砂岩的变形特性实验。通过分析1ε-T与p-T关系曲线和p-1ε滞回曲线,可知:1ε-T砂岩曲线呈连续正弦波形演化,当孔隙水压力加载时,应变减小;上限恒定时,应变持续减小到谷值;卸载时,应变逐渐增大;下限恒定时,应变持续增大到峰值。砂岩p-1ε滞回曲线的2个阶段变化,一是微孔隙压密阶段,未形成明显的滞回曲线;二是孔隙水压力耦合阶段,形成了稳定的滞回曲线,表现形式由疏变密,并且稳定的滞回曲线呈逆时针演化。还对比了不同轴向应力和不同恒定时间条件下,每个p-1ε滞回曲线的四区段(加载段、卸载段、上限恒定段和下限恒定段)的Δε-n关系曲线。

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（σ1=55.54,34.18,12.82 MPa）,two cyclic pore pressures（Pmin=2 MPa,Pmax=6 MPa） and two kinds of constant time（the upper limit time and the lower limit time（ΔT=120,240 s）.With ε1-T curves and p-T curves,as well as p-ε1 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-ε1 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,Δε-n curves in four sections（loading,unloading,steady upper limit,steady lower limit） of p-ε1 curves were compared and respectively ananlyzed in the condition of various axial stress and different constant time.