拉拔承载锚杆合理锚固长度的确定

Determination of Reasonable Anchorage Length of Drawing Bearing Anchor

以锚杆弹性极限承载力公式为基础,分析推导锚杆锚固长度临界值la和界面剪切刚度K1的计算表达式。通过极限承载力与锚固长度的关系曲线进一步探究锚杆合理锚固长度l’a,并结合一个具体实例对计算公式的合理性进行验证。结果表明:在一定锚固范围内,锚杆承载力与锚固长度为正相关关系,但当锚固长度达到临界值时,拉拔力达到最大值,其不再随锚固长度的增加而增大;界面剪切刚度、等效弹性模量、锚杆孔径与锚杆锚固长度临界值有直接关系,其中界面剪切刚度与锚固长度临界值为负相关,等效弹性模量和锚杆孔径与其为正相关;推导的理论计算公式可用于计算锚杆临界锚固长度和合理锚固长度,根据推导结果应取临界锚固长度的0.5倍作为合理锚固长度,此时锚杆能够承担较大荷载,接近极限拉拔力,可以在充分利用锚杆的条件下改善经济效益。

Based on the formula of elastic ultimate bearing capacity of bolts,the calculation formula for deriving the critical anchorage length and the interface shear stiffness is analyzed. Based on the anchorage length threshold,the reasonable anchorage length of the anchor is further explored by the relationship between the ultimate bearing capacity and the anchor length. The rationality of the calculation formula is verified by a specific example. The test results show the following facts.(1) Within a certain anchorage range,the bearing capacity of the bolt is positively correlated with the anchoring length. However,when the anchoring length reaches the critical value,the drawing force is the largest and does not increase with the increase of the anchoring length.(2) The interfacial shear stiffness,equivalent elastic modulus and bolt aperture are directly related to the critical value of bolt anchorage length. The interfacial shear stiffness is negatively correlated with the critical value of bolt anchorage length,while the equivalent elastic modulus and bolt aperture are positively correlated with it.(3) The derived theoretical calculation formula can be used to calculate the critical anchorage length and reasonable anchorage length of the bolt. According to the calculation result,0. 5 times of the critical anchorage length should be taken as the actual anchorage length. At this time,the bolt can bear a large load and approach the ultimate pullout force. It can improve economic efficiency under the condition that the bolt is fully utilized.