随机应力循环加卸载三轴试验土的变形稳定状态初探

Preliminary investigation on stable state of deformation of soils in random stress cyclic unloading triaxial tests

为研究土在随机应力幅值循环加卸载条件下的应力-应变关系,基于土样全表面变形数字图像测量系统,以福建标准砂和硅微粉为研究对象进行一系列三轴试验。据此分析土样在不同随机应力循环加卸载过程的应力-应变行为,判断其是否达到变形稳定状态,同时与等应力幅值循环加卸载和阶梯应力幅值循环加卸载试验进行对比。结果表明:无论是恒定应力幅值、阶梯应力幅值还是随机应力幅值加卸载循环,当循环次数超过一定次数后,土样逐渐趋于变形稳定状态,且变形稳定状态对应的循环次数值不同;土在受到超过历史最大应力幅值时,应力-应变关系会回到初次单调加载的应力-应变曲线;在最大应力值小于破坏应力的条件下,应力加卸载时间过程幅值的随机特征,如幅值大小和分布对土的应力-应变行为,包括变形稳定状态没有影响。

In order to study the stress-strain relationship of soil under the condition of cyclic loading and unloading with random stress amplitude,a series of triaxial tests were carried out on Fujian standard sand and silica powder by applying the whole surface deformation digital image measurement system.Accordingly,the stress-strain behavior of soil specimen in different random stress cyclic loading and unloading processes is analyzed,and the stable deformation state of soil specimen is determined.And the they were compared with those of equal stress amplitude cyclic loading and unloading and step stress amplitude cyclic loading and unloading tests.Research results show that no matter the loading and unloading cycles of constant stress amplitude,step stress amplitude or random stress amplitude,when the number of cycles exceeds a certain number,the soil sample gradually tends to the stable state of deformation,and the corresponding cycles of stable state of deformation are different.When the soil is subjected to stress more than the historical maximum stress amplitude,the stress-strain relationship will return to the stress-strain curve at initial loading.Under the condition that the maximum stress value is less than the failure stress,the random characteristics of the amplitude of the loading and unloading,such as the magnitude and distribution of the amplitude,have no influence on the stress-strain behavior of the soil,including the stable state of deformation.