长期动荷载作用下冻结粉土的变形和强度特征

The Features of Strain and Strength of Frozen Silt under Long-Time Dynamic Loading

根据长期动荷载作用下的蠕变试验结果,研究了冻结粉土的变形和动强度特征.试验分3组,第一、二组是小振幅动荷载试验,且第二组的动荷载幅值为第一组的两倍;第三组是大振幅动荷载试验,荷载最小值取接近于零的值,最大值与第一组对应.试验结果表明:各种振幅的动荷载作用下,冻土的累积应变随荷载振动次数的变化规律相同(都包括初始蠕变阶段、稳定蠕变阶段、渐进流阶段)但数值上有差异.在初始和稳定蠕变阶段,第三组试验的累积应变小于第一、二组的,但是第三组试验稳定蠕变阶段的应变速率很大,蠕变曲线迅速进入渐进流阶段,此后其累积应变值大于小振幅动荷载试验的;第一、二组试验的应变幅值随振次的变化规律相似,但与第三组的有明显不同,而且,第三组试验的应变幅值明显大于第一、二组试验的.各种振幅动荷载作用下冻土的残余应变随振次的变化规律相同,且偏移荷载载越大或动荷载振动幅值越大,残余应变越大;冻土的动强度随荷载振动次数的增加而衰减,直至趋于极限动强度,大振幅动荷载试验的极限动强度明显小于小振幅动荷载试验的.

Strain and strength are studied through dynamic creep tests of frozen silt under long-time dynamic loading.Three groups of tests（Test Ⅰ,test Ⅱ and test Ⅲ） are performed.As to Test Ⅰ and Test Ⅱ,the static loadings of both are the same and the dynamic loading of Test Ⅱ is twice as much as that of Test Ⅰ.As to Test Ⅲ,the minimum value of dynamic loading is near zero,and the amplitude of dynamic loading is larger than that of Test Ⅰ and Test Ⅱ.To all the three groups of tests,there are similar changing tendency of cumulative strain（including initial creep stage,steady creep stage and tertiary stage）,but the values are different.The cumulative strain of Test Ⅱ is larger than that of Test Ⅰ during the whole creep course.The cumulative strain of Test Ⅲ is less than that of Test Ⅰ and Test Ⅱ during the initial creep stage and the steady creep stage.However,due to its higher creep strain rate during the steady creep stage and consequently a considerable strain increment,after a shorter steady stage,it moves into the tertiary stage quickly and the strain become larger than that of Test Ⅰ and Test Ⅱ.The strain amplitude of Test Ⅲ is larger than that of Test Ⅰ and Test Ⅱ.The residual strain will be greater when the offset loading or dynamic loading vibration amplitude is larger.The dynamic strength of frozen silt will decrease and trend to a terminal dynamic strength while the vibration times of loading increases.The terminal dynamic strength of Test Ⅲ is obvious less than that of Test I and Test Ⅱ.