定向剪切应力路径下冻结黏土强度特性试验

The strength characteristics of frozen clay under the different principal stress directions

为探索考虑主应力轴方向变化等复杂应力路径下的冻结黏土强度特性,采用冻土空心圆柱仪,在温度为-10℃条件下,对重塑冻结黏土开展一系列主应力轴方向固定不变的定向剪切试验,探讨大主应力轴方向角a、中主应力系数b和平均主应力p值变化对冻结黏土强度特性的影响.通过对广义剪应力-广义剪应变曲线的分析,发现a角和p值变化对冻土的强度及破坏应变都有较大影响,随着a角的增加,破坏时的广义剪应力qJ值先增加后减小,最小值出现在a=75°处,随着p值增加,qJ值先增加后减小;b值变化对强度的影响较小,而对破坏应变有较大影响;广义剪应力-广义剪应变曲线均为弹性塑性应变硬化曲线,且初始线性段的极限应变值在0.5%左右,不受应力路径变化的影响.分析应力与应变之间的关系,建立了定向剪切应力路径下冻结黏土的强度模型方程,进而求得广义剪切模量随应变发展的关系表达式,并发现初始广义剪切模量对冻结黏土应变的发展及破坏应变值有较大影响,且存在一临界值,对于冻结黏土,该临界值为6×105k Pa.a角、b值和p值的变化都会对冻结黏土的强度及变形产生较大影响.

To fully study the strength characteristics of frozen clay under complex stress paths such as the variation of principal stress axis direction,a series of different principle stress direction shear experiments were carried out using the frozen soil hollow cylinder apparatus at a temperature of-10 ℃ to investigate the influence of the major principal stress orientation angle a（ defined in the vertical plane）,the intermediate principal stress ratio b and the mean principal stress p on the strength characteristics of frozen clay. Analyzing the generalized shear stressgeneralized shear strain curves,the results showed that the strength of frozen clay was great influenced by the changes in a angle and p-value,and it was not affected by the changes in b-value. The failure strain was affected by the changes in these three parameters. The styles of stress-strain curves were all elastic-plastic strain harden curves and the range of elastic strain of the curves was about 0.5%,which was not affected by different stress paths. The strength model of frozen clay under different principle stress direction shear experiments was built through analyzing the relationship between stress and strain. Moreover,the relationship about generalized shear modulus EJtand strain was obtained,and the influence of initial shear modulus EJt 0 on EJt-strain curves was also discussed. The threshold value of EJt0 was found and was about 6×10^5 kPa for frozen clay. The changes in a angle,b-value and p-value had great influence on the strength characteristics of frozen clay.