应力历史对黏土-混凝土界面剪切特性的影响研究

RESEARCH ON EFFECT OF STRESS HISTORY ON SHEAR BEHAVIOR OF INTERFACE BETWEEN CLAY AND CONCRETE

采用大型直剪仪,系统研究法向应力历史对黏土–混凝土界面剪切特性的影响。根据制定的加卸荷方案,对3个粗糙度等级(锯齿高为0,1,2 cm)的黏土–混凝土接触界面先加荷至初始法向应力,再卸荷至剪切法向应力进行剪切。从剪应力–剪切位移曲线、界面最大剪应力、剪胀性3个角度对试验结果进行对比分析。分析结果表明:黏土–混凝土界面剪应力–剪切位移曲线仍大体呈双曲线形式,并未出现应变软化现象。初始法向应力越大,相同剪切位移对应剪应力越大;初始法向应力越大对应的界面最大剪应力越大,根据Mohr-Coulomb准则通过线性拟合得出界面强度参数,并引入界面摩擦有效系数和黏聚有效系数。通过数据对比发现,界面黏聚有效系数随着初始法向应力的增大而增大,而摩擦有效系数则随初始法向应力的增大而减小。剪切过程中3个粗糙度等级的黏土–混凝土界面均发生不同程度的剪胀,界面越粗糙,剪胀量越大。同时,应力历史对界面剪胀性规律有明显的影响,未经历法向卸荷的界面剪切过程开始先剪缩然后再剪胀,而经历法向卸荷的界面剪切一开始便呈现剪胀,且初始法向应力越大,剪胀越明显。

A series of direct shear tests were carried out to study the effect of stress history on shear behavior of interface between clay and concrete.The clay-concrete interfaces of different roughnesses（sawtooth height of 0,1 and 2 cm,respectively） were loaded to an initial normal stress,then unloaded to a normal stress before shearing according to the schemes of loading and unloading.Results are presented for interface shear behavior in forms of shear stress-shear strain curves,vertical strain-shear strain curves and shear strength parameters.Results show that the shape of shear stress-shear strain curves is hyperbolic;and no strain-softening phenomenon was observed in the tests.Higher initial normal stresses offer higher shear stress with the same horizontal displacement.The strength of interface still obeys the Mohr-Coulomb criterion;and the internal friction angle and cohesion can be obtained by fitting lineally.The effective parameters of friction and cohesion are employed to reflect interface strength normalized by the strength parameters of clay.The higher applied initial normal stress offers the lower effective parameter of friction.But the higher effective parameter of cohesion is received for higher applied initial normal stress.The dilation was observed during the process of shearing the interfaces of different roughnesses;the rougher interface offers the higher dilative displacement.Meanwhile,the effect of stress history on dilation law of interface is obvious.For the interface without experiencing normally unloading,it first exhibits a short contraction behavior before dilatation,while directly exhibits dilation for the interface experienced normally unloading.The more significant dilation was found for the higher initial normal stress.