条形荷载下加筋土边坡破坏机制的数值模拟

为了克服模型的尺寸效用,获得加筋与不加筋边坡在条形荷载下的各种性状参数和边坡的破坏机制,建立用于分析和模拟3个大型室内足尺加筋与不加筋边坡破坏机制的数值计算模型。边坡回填材料采用级配较差的粗砂,土体的非线性弹性响应采用Duncan-Chang双曲线模型E-B模式加以描述,破坏准则采用Mohr-Coulomb屈服准则,并采用与屈服条件不相关联的流动法则。加筋材料采用两节点的弹塑性锚索结构单元进行模拟,并采用无厚度的弹簧-滑动系统来模拟筋土之间的相互作用和相对运动。数值计算采用基于有限差分的连续介质快速拉格朗日分析方法(FLAC),分别对与破坏面位置和形态密切相关的节点位移速度向量、塑性区和剪应变速率分布3个参数进行了计算,获得了3个边坡在条形极限荷载下的双楔体破坏机制和极限承载力,与试验结果吻合较好,验证了模型的可行性。在此基础上,对不同的条形荷载位置及不同填土材料强度下边坡破坏机制进行了数值模拟和分析。研究结果表明,无论加筋与不加筋边坡,当条形荷载位置距坡肩的距离减小时,边坡破坏面形态由双楔体过渡到圆弧形;当填土材料强度降低时,破裂面形态转化为圆弧形或对数螺线形。

Numerical simulation of flailure mechaIlism for reinflorced and unreinfbrced slopes under strip footing

A numerical model is developed to simulate and analyze the failure mechanisms of three instrumented,full-scale,reinforced and unreinforced slopes under a strip footing.The backfill material of slopes is poorly graded sand,and it is modeled as a Duncan-Chang hyperbolic nonlinear elasto-plastic material with Mohr-Coulomb yield criterion and non-associated flow rule.The geogrids are modeled as elasto-plastic two-node cable elements.A spring-slider system without thickness is employed to model the interaction between sand and geogrids.The finite-difference-based Fast Lagrangian Analysis of Continua code,FLAC,is employed in the numerical analysis.The displacement,velocity,plasticity indicator and shear strain rate under strip footing are calculated.The ultimate bearing capacity and the dual-wedge failure mechanism of slopes thus obtained are in good agreement with the test results.On the basis of the above analysis,the failure mechanisms for different strip footing positions and different soil strengths are modeled and analyzed.The results indicate: the dual-wedge failure surface of slopes becomes a circular failure surface when the strip footing is near the crest of the slope;and the failure surface is transformed into a circular or logarithmic spiral when the strength of the soil decreases,whether the slope is reinforced or unreinforced.