输电线路岩石锚杆基础抗拔试验分析

Test and analysis of the uplift resistance of rock bolt foundation in transmission line projects

某输电线路沿途场地内片麻岩、页岩、花岗岩、石灰岩分布广泛,采用岩石锚杆基础。通过25组不同岩石锚杆基础破坏真型试验,试验结果表明:除个例外,τ_(a)、τ_(b)、τ_(s)实测值较大、软质岩石τs实测值较小。采用设计规定中假想的理想45°破坏模式的设计值计算有时偏大,具有较大的不安全性。岩石锚杆基础破坏荷载较小时,上拔位移量很小,地面没有明显变形;随着荷载加大,产生环形裂缝,岩体表面出现细小的裂纹,基础上拔位移量增大;当荷载增大到一定程度时,锚杆基础变形迅速增大,产生以基础为中心放射状裂缝,并向四周逐步发散,裂缝扩展的范围和宽度随着荷载的增加而增大。沿着锚杆与混凝土的握裹体与岩石的结合面的薄弱面产生破坏,锚筋或砂浆柱被拔起;或基础沿环形裂缝与岩石一同拔出,发生整体破坏。研究成果对岩石锚杆基础设计参数和正确指导工程实践具有重要意义。

Gneiss,shale,granite and limestone are widely distributed along one transmission line,and rock bolt foundation is adopted.Through 25 groups of true failure tests of rock bolt foundation,the test results show that,with an exception,the measured values ofτ_(a),τ_(b),τ_(s)are larger than those of soft rock.The design value of the ideal 45°failure mode assumed in the design regulations is sometimes too large to be safe.When the failure load of rock bolt foundation is small,the pull-up displacement is very small,and there is no obvious deformation on the ground.With the increase on the load,ring cracks are produced,and small cracks appear on the rock surface,and the pull-up displacement of the foundation increases.When the load increases to a certain extent,the deformation of rock bolt foundation increases rapidly,resulting in radial cracks centered on the foundation,which gradually spread around,and the cracks expand the extent and width of the spread increase with the increase on the load.Failure occurs along the weak surface of the joint surface between the anchor rod and the concrete and the rock,and the anchor bar or mortar column is pulled out;or the foundation is pulled out along the circular crack with the rock,and overall failure occurs.The research results are of great significance to the design parameters of rock bolt foundation and the correct guidance of engineering practice.