静载作用下土工格栅加筋防护埋地管道力学性能的实验研究

 针对土工格栅加筋防护埋地管道开展了静力载荷实验，研究管周填土相对密实度(Dr)、管道埋深(H)、筋材长度(L)和层数(n)，以及首层筋材埋深(u)等对埋地管道防护性能的影响。实验结果表明：首层筋材最佳埋深为0.4B(加载板宽)，筋材最佳铺设长度为4D(管道外径)，筋材层数以3～4层为宜；同等条件下随着Dr持续增加，管道极限承载力增加，加载板沉降相应减少，且二者变化率明显降低，表明管周土相对松散时加筋效果愈加明显；同等条件下管道水平和竖向径向变形均随地表载荷增加而增加，且竖直径向比水平径向变形略大，通过增加筋材层数能显著提高土体刚度，能有效地分散管道上方载荷，为管道提供减载保护；管道外壁监测点环向应变值位于－1.5%～1.0%之间，顶部以压缩变形为主，其两侧45°处为压缩和拉伸变形过渡区，而水平径向以拉伸变形为主；随着Dr增加，管周环向应变减小，且应变的对称性愈加显著，表明因Dr增加引起土体自身刚度增加，能有效地限制管道移动及变形。

EXPERIMENTAL STUDY OF MECHANICAL PERFORMANCE OF BURIED PIPES PROTECTED BY GEOGRIDS UNDER STATIC LOAD

A series of tests on mechanical performance of buried pipes protected by geogrids have been carried out under static load. The effects of relative density of soil surrounding buried pipes，Dr，embedment depth of buried pipes，H，length of reinforcement，L，layers of reinforcement，n，and embedment depth of the first layer of geogrid，u，on protection performance of buried pipes are investigated. The tests results show that the acceptable optimum values of u，length and layers of geogrids are 0.4B(B，width of loading plate)，4D(D，external diameter of pipe) and 3～4，respectively. While keeping the remained parameters identical，bearing capacity of buried pipes increases and settlement of loading plate decreases with the increase of relative density，but the rate of change for both decreases remarkably. This indicates that the function of reinforcement at lower relative densities is more effective than higher ones. Horizontal and vertical deformation along diameter direction increase with the increase of load，and vertical deformation is slightly greater than horizontal deformation. Furthermore，greater stiffness for soil surrounding pipes induced by increase of layers of reinforcement can disperse stresses effectively；it provides well effects of load-reduction for buried pipes. Additionally，measured hoop strains around buried pipes range from －1.5% to 1%. Through the measured strain values of buried pipes，it is obtained that compress strains appeared at the crown of pipes，and transition zone for strains changing from compress to tension falls in angle of 45 offside from crown of pipes，but tensile strains occur at the horizontal direction along diameter. When increasing relative density，hoop strains，which appear more obvious symmetrical，decrease. This demonstrates that increasing stiffness of soil itself due to higher relative density can inhibit movement and deformation of pipes.