小应变下土体刚度非线性分析的试验研究

精确的试验测试显示,土体在小应变下呈非线性作用,用常规的室内试验和传统的线弹性分析方法不能真实描述土的刚度变化,只能采用原位试验和非线性分析方法来确定。基于Bolton等人提出的平面应变下不排水膨胀试验的非线性分析理论,研究了剑桥自钻式旁压试验过程中土体刚度随应变的变化规律,并与线性分析结果进行了对比。试验和分析结果表明:小应变下土体刚度具有高度的非线性,随应变的增加发生衰减,但在不同应变区间衰减程度不同;土体割线模量值大于切线模量值,其差值随应变的增加逐渐减小;传统的线性分析低估了土体弹性作用范围和强度,而采用非线性分析能确定不同应变下土的刚度参数,真实反映土的非线性作用特点。

Non-linear analysis of stiffness of soils under small strain

The highly precise measurements of deformation of soils in the field and laboratory have shown that the response of these soils is non-linear under very small strains.The soil behaviors can not be realistically described by the normal laboratory tests and traditional linear elastic analysis,and then it is vital to use the in-situ tests and non-linear analysis to do so.Based on the theory of non-linear elastic/perfectly plastic analysis for plane strain undrained expansion tests proposed by Bolton et al.,experimental investigation on the decay of stiffness with strain during the Cambridge self-boring pressuremeter tests is carried out,and a comparison between the non-linear analysis and the linear elastic analysis is drawn.The results of test and analysis indicate that the stiffness of soils exhibits non-linear behaviors under very small strain and falls with the increasing strains,but the amplitude of decrease varies in different ranges of strain.The secant modulus of soil is usually larger than the tangent one,but the value of differences decreases with the increasing strain.It is apparent that the simple linear elastic solution greatly underestimates the range of the elastic response and the strength of soil.On the contrary,the value of stiffness corresponding to various strains can be deduced by non-linear analyses,which reflects realistically the non-linear behaviors of the soil under small strain.