矩形闭合地下连续墙基础负摩阻力模型试验研究

Model tests on negative skin friction of rectangular closed diaphragm wall foundation

矩形闭合地下连续墙基础(简称闭合墙基础)是一种新型的桥梁基础。通过单片墙与矩形闭合墙的对比性浸水模型试验,对闭合墙基础负摩阻力的作用机理以及浸水后闭合墙基础的竖向承载性状进行了研究。试验研究结果表明:单片墙与闭合墙基础的中性点深度比在0.34～0.64之间,与现场试验实测结果十分接近,且闭合墙基础的中性点位置比单片墙的低。负摩阻力分布曲线大致呈抛物线型,与桩基现场浸水试验结果相似。由于闭合墙基础良好的整体性和防渗特性,当墙周土层浸水发生湿陷变形,土芯不会受到水的影响,因此在负摩阻力作用下,内摩阻力与承台土反力能够得以发挥。闭合墙基础所有竖向荷载均由外侧正摩阻力、内摩阻力以及端阻力和承台土反力四者共同分担,能够有效地阻止墙身附加沉降的继续发展。在相同的湿陷性黄土地层且浸水条件相同的情况下,闭合墙浸水后的附加沉降小于单片墙,表现出良好的抗沉降特性,在一定程度上能减小负摩阻力对桥梁工程的危害。

Rectangular closed diaphragm wall foundation is a new type of bridge foundation. The mechanism for negative skin friction and the bearing behaviours of closed diaphragm walls after immersion were studied through model tests. It was observed that the neutral plane depth ratio of diaphragm walls was 0.34-0.64, and the neutral plane depth of closed diaphragm walls was lower than that of single diaphragm wall. Distribution curves of negative skin friction were similar to parabola, as was also found in some field test studies. With good integrity and anti-seepage capacity, there was no effect of water on soil core, then, the inner shaft resistance and soil resistance under the cap were developed well. So the working load and downdrag load of closed diaphragm walls were shared by the inner shaft resistance, outer shaft resistance, toe resistance and soil resistance under the cap. Additional settlement of closed diaphragm walls was smller than that of single diaphragm wall in the same loess stratum under the same immersion condition. The good anti-settlement capacity of diaphragm walls could reduce the hazard of negative skin friction in bridge engineering.