Q_3原状非饱和黄土的水量变化和临界状态特性

Characteristics of critical state and water volume change for Q_3 unsaturated intact loess

用双室非饱和土三轴仪,对Q3原状黄土进行一系列控制吸力的各向均等压缩及同时控制吸力和净围压的三轴排水剪切试验,分析了吸力,净围压及应力路径对非饱和原状黄土临界状态及水量变化特性的影响,提出了各向均等压缩及三轴剪切应力条件下水土体积比与净平均应力关系的表达式、偏应力与净平均应力临界状态关系模式。研究结果表明:应力路径对非饱和原状黄土水量变化的影响显著,随着净平均应力增大,等向压缩应力条件下处于排水状态,剪切应力条件下视吸力及净围压的大小可能处于吸水或排水状态,不同试验条件下水土体积比与净平均应力或其增量之间对数关系呈二段直线。吸力对偏应力与净平均应力临界状态线的影响皆随着净围压增大而减小,不同吸力(大于0)下水土体积比与净平均应力的对数关系临界状态线皆近似为平行直线。

A series of isotropic compression tests with controlled suction and triaxial drained shear tests with controlled suction and net cell pressure are performed on Q3 intact loess by using a double-walled triaxial test apparatus for unsaturated soils. The influences of the suction, net confining pressure and stress path on the critical state and water volume change of intact unsaturated loess are analyzed. The models describing water ratio versus the net mean stress(ew-p) under isotropic compression and triaxial shear stress, and the critical state lines(CSLs) on the deviator stress versus the net mean stress(q–p) plane are proposed. The results show that the stress path has significant influences on water volume change of unsaturated intact loess. The pore water drains from the specimen under isotropic compression, and with the increase of the net mean stress, the absorbing or draining water depends on the size of the suction and net confining pressure under shear stress. The logarithmic relationships between water ratio and the net mean stress or its increment present a binary linear under different test conditions. The effects of suction on the CSLs of the deviator stress versus the net mean stress(q–p) decrease as the net confining pressure increases. The CSLs of water ratio versus the net mean stress(ew–lnp) are parallel under different suctions which are greater than zero.