考虑锯齿状节理的桩岩界面模型试验研究

Laboratory Testing Study on Concrete-rock Interface with Sawtooth Joint

针对嵌岩灌注桩嵌入软弱岩层的工况,考虑成桩过程中桩岩界面的剪胀效应,采用常法向刚度边界条件(CNS)模拟软岩对桩身的侧向变形约束,开展了模拟桩岩界面侧阻力发挥的室内大尺寸直剪模型试验.将桩-岩接触面的粗糙体简化为规则的三角形锯齿,根据不同的半波长分别制作了砂岩和混凝土试样,得到了剪切荷载、剪切位移、法向荷载和法向位移之间的关系曲线.试验结果表明,软岩锯齿的法向剪胀角随着剪切位移的增加呈非线性减小,且界面抗剪强度的发挥与法向约束刚度、粗糙体半波长和剪切位移等密切相关;同时,在考虑软岩表面锯齿的弹性压缩对界面剪胀角影响的基础上,采用幂函数拟合了软岩抗剪强度的经验关系式.最后,将试验结果与现有理论模型结果对比,表明了现有模型忽略桩岩界面剪胀角的非线性变化将高估嵌岩灌注桩侧阻力的发挥,这在实际工程中将偏于不安全.

In consideration of the weak rock conditions of rock-socketed piles and taking the dilatancy of the interface into account,the constant normal stiffness conditions(CNS)were applied to simulate the lateral constraints provided by weak rock,and laboratory model tests were conducted to inquire the mobilization of the side resistance.The asperity of the concrete-rock interface can be idealized as regular sawtooth asperities,and sandstone and concrete specimens were manufactured with different half-chord lengths,respectively.The relevant measurements were observed,such as shear load,shear displacement,normal load and normal displacement.In addition,the observations showed that the dilatancy angle of the interface gradually decreased with the development of shear displacement.The shear strength of interface is closely related with the normal constant stiffness and the half chord of the rough body as well as the shear displacement.Based on the consideration of elastic compression of the asperity,the empirical relationship for the shear strength of weak rock was fitted by power functions.On the other hand,the observations were compared with the predictions of an existing theoretical model,and it was shown that the theoretical model can overestimate the side resistance of the rock-socketed piles,due to the disregard of nonlinear variation of the dilatancy angle.