软岩的应变速率效应研究

对硅藻质软岩试样进行了不同围压和不同加载速率的应变和应力控制式固结不排水三轴试验,试验结果表明,硅藻质软岩具有明显的应变速率效应,加载速率对软岩的强度变形特性有较大的影响。在试验研究的基础上,应用三维弹粘塑性模型,考虑硅藻质软岩的应力–应变关系的时间依存性,模拟了软岩的应变速率效应。数值分析中所采用的参数均由试验确定,对不同应变速率下固结不排水试验的应力–应变关系和有效应力路径的数值计算结果,反映出不同应变速率下软岩的峰值强度和残留强度均随着应变速率的增大而不断提高,与试验结果相吻合;计算结果还反映出与试验结果一致的孔隙水压力变化和应变软化趋势。通过对比分析表明,三维弹粘塑性模型可以较好地描述软岩的应变速率效应。

STUDY ON STRAIN RATE EFFECT OF SOFT ROCK

Consolidated undrained triaxial tests were conducted on the specimens of diatomaceous soft rock under different pressures and different loading rates,with stress controlled and strain controlled respectively. The test results show that the soft rock has obvious strain rate effect,and strain rates during loading have notable influences on the strength and deformation of soft rock. On the basis of tests,considering the time-dependent behavior of stress-strain relation of diatomaceous soft rock,a 3D elasto-viscoplastic constitutive model (3D EVP model) is introduced to simulate the strain rate effect of soft rock. All parameters of the model are determined by tests. The stress-strain relationship and the effective stress path of undrained consolidated triaxial tests under different strain rates were simulated using 3D EVP model. The numerical calculation results reflect that the strength,including peak strength and residual strength,of soft rock improves with the increasing of strain rate;and they are consistent with the tests results. The trend of pore water pressure and strain softening of calculation results also show agreement with test results. Through comparing and analysis,it is found that 3D EVP model is effective to describe the strain rate effect of soft rock.