粉土循环累积应变和残余动模量的试验研究

粉土地基上建造的铁路或公路在交通荷载作用下易产生各种病害,导致基础设施不能正常工作。为研究交通循环荷载作用下粉土的累积变形和动力性能,针对钱塘江粉土开展一系列的循环三轴试验,探讨土体物理条件(相对压实度、含水率)和应力特征(频率、围压、动应力比)等对粉土累积轴向应变、动模量和阻尼比等的影响。试验结果表明,钱塘江粉土的临界动应力比约为0.11,当轴向动应力小于临界动应力时,粉土的动模量变化很小,相应的累积轴向应变也很小;当动应力超过临界动应力后,土样的动模量快速下降,残余动模量约为初始弹性模量的20%,同时,动模量和阻尼比随着累积轴向应变(或名义振次)的发展变化显著。粉土的动模量和阻尼比在归一化后可得到统一规律:在轴向应变(或名义振次)小于一定值时,动模量几乎不变,而后呈指数形式衰减,最终趋于稳定值;粉土阻尼比随着轴向应变(或名义振次)的发展呈指数关系增长。

Experimental study of cumulative axial strain and residual dynamic modulus of silt soil

Traffic loading from trains or vehicles will cause damages in transportation infrastructure constructed on silt soil, and consequently result in reduction of transportation infrastructure’s availability. In order to investigate cumulative deformation and dynamic behaviors of silt soil under large cycles of traffic loading, a series of dynamic triaxial tests have been conducted on Qiantang River silt soil. Effect of soil’s physical properties, such as relative compaction(RC), water content and loading features, and loading frequency, confining pressure and cyclic stress ratio(CSR) on soil’s axial strain, dynamic modulus, damping ratio have been discussed based on the test data. The results show that the critical cyclic stress ratio(CSR) of Qiantang River silt soil is about 0.11. When the applied dynamic stress is below the critical dynamic stress, silt soil’s dynamic modulus shows very little reduction; and the cumulative axial strain is very small. When dynamic stress exceeds the critical dynamic stress, soil’s dynamic modulus reduces quickly, and the residual dynamic modulus can reach about 20% of the initial elastic modulus. Meanwhile, the dynamic modulus and damping ratio change significantly with the axial strain. The test data on silt soil’s dynamic modulus and damping ratio show a uniform conclusion after normalization on the data. Silt soil’s dynamic modulus almost keeps constant when the axial strain (or the normalized cycle number) is less than a threshold value, and decreases exponentially when beyond it and reaches a stable value ultimately. The damping ratio develops exponentially with the axial strain (or the normalized cyclic number).