拉拔作用下锚杆复合土钉支护协同作用细观机制研究

Mesoscopic mechanisms of collaborative working of composite soil nail-anchor supporting wall subjected to tension

锚杆复合土钉墙支护以机动灵活、支护能力强、工期短、造价低等特点被广泛运用,但是对此支护形式的机制研究,一直落后于工程实践。基于PFC3D离散元数值模拟并结合室内模型试验,从细观层面探究砂土颗粒的位移场、运动轨迹、锚杆抗拔力、土体孔隙率以及剪应力的变化规律,结果表明:在锚杆拉拔过程中,锚板直径越大,其竖向影响范围越大,并呈现出具有收敛性的喇叭口状位移场;锚杆和土钉之间的砂土颗粒以旋转移动和平行滑移为主,可划分为3个区域,但每一区域内颗粒的主要运动形式又不尽相同;在砂土中,当钉锚间距为两倍锚板直径时,锚杆复合土钉协同支护达到最佳效果;同时,在此过程中土体会出现明显的剪胀与剪缩现象,孔隙率变化呈正弦式波动曲线,并且在钉锚协同支护中,最小的孔隙率发生在土钉周围区域;颗粒间的挤压作用和颗粒运动受到土钉阻挡,共同加强了锚杆复合土钉之间的协同作用。该研究成果可为完善锚杆复合土钉支护设计理论提供参考。

Composite soil nail-anchor supporting walls have been widely used in practice because of their flexibility,strong supporting capacity,short construction period and low cost. However,researches of composite soil nail-anchor supporting walls leg engineering practices and the working mechanisms are not fully understood,which may lead to some uncertainties in design. Combining three-dimensional(3D) discrete element method(DEM) and experimental model test,displacement field,motion trace,porosity and shear stress of sand particles as well as anchorage resistance during the process of pulling anchor were investigated at the mesoscopic level. The results reveal that the larger the diameter of the anchorage plate,the larger the vertical influence range,and that the displacement field has a convergent bell-mouth shape. During the process of anchor-pulling,sand particles between anchors and soil nails tending to rotate or slide can be divided into three zones with different particle movements for each zone. When the anchor spacing is twice the diameter of the anchorage plate,the composite soil nailing method can achieve an optimum result. Meanwhile,dilatation and contraction occur in sand. The change of the porosity can be described by sinusoidal wave curve and the minimum porosity appears around the nails. Sand particles are squeezed together and blocked by the soil nails,which enhances the synergistic effect of composite soil nail-anchor supporting system. The results presented in this study may provide useful references for upgrading current design methodology of composite soil nail-prestressed anchor supporting system.