加载速率对密砂应力-应变特性影响的试验研究

Experimental study on effect of strain rate on stress-strain behavior of dense sand

【目的】砂是一种常见的建筑材料,在水利水电工程、交通、海洋和其他土木工程中应用广泛。在不同的工程应用中,砂土经受不同的加载过程和加载速率。因为加载速率效应,砂在相同幅值荷载作用下产生的变形有一定差异。这项研究旨在深入了解不同应变速率三轴剪切条件下砂的应力应变特性。【方法】采用相对密度为0.9的密砂,开展了一系列三轴固结排水剪切试验,在两种不同围压(750 kPa和2000 kPa)下对试样进行固结后,分别采用三种不同的常应变速率(0.00625%/min,0.0625%/min和0.625%/min)进行应变控制排水剪切。根据试验数据,绘制了应力-应变关系发展曲线,分析了应变速率对砂土偏应力和体积应变演化的影响。【结果】结果表明,在本试验采用的恒定应变速率和围压条件下,密砂在轴向应变约为2%时将发生屈服。屈服前,相同轴应变增量对应的土样偏应力增量和体积应变增量对剪切速率比较敏感,特别是体积应变,即加载应变速率较小时获得的土样剪应力较低,但体积应变(收缩)发展量较大。【结论】在屈服前,砂土的模量随着加载速率的增加而增大;但是屈服后,当加载达到大应变(ε1=15%)条件时,应变率对砂土应力变形的影响不明显。另外,在相同围压下,以不同应变率加载的砂样在加载过程中的应力比(q/p)-偏应变关系呈现出一致性。该研究可以提高对砂土力学特性的认识,并为砂土地基上的结构设计和安全评价提供参考。

[Objective]Sand is a common construction material,which is widely used in hydraulic and hydropower engineering,highway subgrade,marine filling,and other civil engineering projects.Sand can be subjected to various loading processes with specific loading rates due to different engineering applications.Because of the rate effect,the deformation of sand under the same amplitude load in the similar process can be different.The purpose of this study is to investigate the behavior of sand sheared at different constant strain rates.[Methods]Dense sand with a relative density of 0.9 was used to carry out a series of triaxial com-pression tests under consolidated-drained conditions.After consolidated under two different confining pressures(750 kPa and 2000 kPa),sand samples were sheared at three different constant strain rates(0.00625%/min,0.0625%/min,and 0.625%/min)respectively.According to the experimental data,the curves of the stress-strain relationship ware presented.The effect of shearing rates on sand′s deviator stress and volumetric strain evolution were examined.[Results]The result shows that the dense sand yields at axial strain of about 2%under all tested constant strain rates and confining pressures.The deviator stress increment and volumetric strain development before yielding are sensitive to the loading strain rate.Shearing under a lower strain rate leads to a lower yielding strength and a higher volumetric strain(contraction).[Conclusion]It can be concluded that the stiffness of sand rises with increased strain rate before yielding,but by the end of loading to a large axial strain(ε1=15%),the strain rate has little effect on sand′s property.However,the tested sand samples loaded with different strain rates exhibit consistent in stress ratio(q/p)-deviatoric strain relationship throughout the loading process under the same confining pressure.The result of this study can enhance our knowledge of soil mechanics and provide references for the design and safety assessment of structures con-structed on sand-based materials.