褥垫层的位移场特性及其力学机理的试验研究

Experimental study on character of displacement field and mechanics mechanism of the composite ground cushion

褥垫层对复合地基的各部分受力的分配具有调节作用,但其调节的内部机理还不明确,大量的研究还是以假定为基础。为探讨刚性桩复合地基褥垫层在荷载下的位移场变化趋势,利用自制的专利土工模型箱进行加固软土地基的室内模型载荷试验。监测逐级加载下复合地基的沉降规律及桩顶和桩间土的应力分布变化;利用经纬仪测算加载前后标记物的坐标变化,探寻褥垫层的应力场和位移场的动态变化特征,推究褥垫层的工作机理。试验结果表明:群桩复合地基的褥垫层材料总体上朝桩体试验区中心方向移动;褥垫层中从桩体附近的垫层颗粒到距桩体较远处颗粒所受的竖向应力越来越小,颗粒沉降量从桩顶中心向桩间土中心靠近时逐步递增;桩间净距越大,复合地基的整体沉降越大;褥垫层厚度越大,复合地基整体沉降未必增大;越接近试验区中心,桩间土的压缩沉降越大。试验结论为褥垫层优化设计提供了有益参考。

The cushion has the function of allocating load of all parts of composite ground, but the inner mechanism of allocating isn′t clear yet and great deal of study is performed on assumption basis. In order to probe the variation trend of displacement field of cushion of rigid pile composite ground, a laboratory model loading test is carried on the reinforced soft ground through self-created model box. Settlement law of composite ground and the variation of stress distribution among the pile top and the soil between the piles under loading step-by-step are monitored. The variation of coordinate of markers is measured through theodolite before and after loading, the dynamic variation character stress field and strain field of cushion is explored, and then the working mechanism of cushion is deduced. The experimental results show that the cushion material moves towards the center of the testing piles generally;the vertical stress decreases and the settlement rises from the pile center to the soil between piles;the settlement is becoming greater with the increase of distance between piles;the settlement variation tendency is not consistent with the thickness changing of the cushion;the more closer to the center of the testing area, the compressive settlement of soil between piles is larger. These experimental conclusions may provide some useful reference for optimizing design of cushion.