条形基础下格栅加筋地基的细观机理

Meso mechanism analysis of geogrid reinforced foundations under strip footing

格栅加筋地基是在基础下一定深度范围内铺设适当的土工格栅,以此来改善地基承载性能的地基处理形式.基于模型试验,采用三维颗粒流软件(3D particle flow code,PFC^(3D))模型,建立了条形基础下格栅加筋地基的颗粒流数值模型.通过分析地基中整体应力分布、砂土颗粒位移、砂土颗粒接触力、筋材变形及筋土相互作用等,研究了条形基础下格栅加筋地基的承载性能和细观加固机理.结果表明:在条形基础下,格栅能较好地均化上覆条形荷载;格栅主要发挥加筋作用的长度约为1.3~1.5倍基础宽度.格栅加筋地基的主要加固机理为格栅网孔结构的嵌固作用.嵌固作用使得颗粒与格栅协同作用形成一个整体,并进行应力重分布,进而提高整体格栅加筋地基的承载性能.此外,水平格栅的横肋对土体的阻挡力是导致纵肋产生拉力的主要原因.在条形上覆荷载下,格栅的变形存在一个反弯点.格栅对反弯点一侧的土体产生向上的作用力,对反弯点另一侧的土体产生向下的作用力.格栅的张拉膜效应调节了整体地基的不均匀沉降.

The geogrid reinforced foundation is a foundation treatment method to improve the bearing capacity of the foundation by laying appropriate geogrids at a certain depth under the footing.Based on model tests,a 3D particleflow code(PFC^(3D))was applied to simulate the geogrid reinforced foundation under strip footing.The bearing capacity and the reinforcement mechanism of the geogrid reinforced foundation were investigated by an-alyzing stress distribution,sand particle displacement,sand particle contact force,geogrid deformation and geogrid-sand interaction,et al.The results demonstrated that a more uniform loading was applied on the foundation by using the geogrid reinforcement,and the effective reinforcement length was approximately 1.3∼1.5 times of the footing width.The primary reinforcement involved surrounding soil materials to interlock across the ge-ogrid plane.This interlocking enhanced passive resistance,rendering the geogrid-reinforced foundation more integral.Consequently,stress redistribution occurred,leading to an im-provement in bearing capacity.In addition,the lateral restraint of the transverse ribs was the main reason for inducing a tensile force in the longitudinal ribs.The deformation of geogrid had a reverse bending point under the applied loading.An upward and downward force was applied to the sand particles at the two sides of the reverse bending point,respec-tively.The tension membrane mechanism of the geogrid decreased the uneven settlement in the overall geogrid reinforced foundation.