湿陷性黄土模型试验相似材料研制与单桩负摩阻力模型试验研究

DEVELOPMENT OF SIMILAR MODEL MATERIAL OF COLLAPSIBTE LOESS AND RESEARCH ON NEGATIVE SKIN FRICTION OF PILE FOUNDATION IN COLLAPSIBLE LOESS REGION

湿陷性黄土模型试验相似材料一直是地质力学模型试验相似材料研制的瓶颈,限制了湿陷性黄土地区模型试验的开展。本文基于Monte Carlo方法,采用空中自由下落技术,研制出了能够模拟湿陷性黄土的模型试验相似材料。在研制出湿陷性黄土相似材料的基础上,进行单桩负摩阻力模型试验,探讨在湿陷性黄土地区广泛存在于桩基工程中的负摩阻力。研究结果表明:桩身轴力沿桩身大致呈"B"形态分布,中性点位于湿陷性土层与砂层的交界处。在自重湿陷作用下,桩顶的沉降远小于土体的湿陷变形,桩侧负摩阻力沿深度增大,在中性点处达到峰值。在浸水1h内,摩阻力随时间大致呈"D"形态分布。在整个测试阶段,负摩阻力出现了第二次峰值,曲线分布呈"β"形态。由于负摩阻力的作用,使桩顶产生0.54mm的沉降变形。本文的研究方法和成果可为分析湿陷性黄土地区桩基的受力特性提供参考。

The model test material of collapsible loess is the bottleneck of similar material model research in geo- mechanics, which has limited application of model tests in loess area. A similar material of model test for collapsible loess is developed by airfall technique based on Monte Carlo method. A single pile foundation model test is carried out to investigate the negative skin friction of the pile under the effect of self-weight collapsibility. The research re- sults show that the axial force along the pile of different time roughly appeared as the shape of ＂B＂. The neutral point is located between the modeled collapsible soil and sands. The settlement of the top of pile is far less than col- lapse deformation of the soil due to the effect of self-weight collapsibility. The negative frictional resistance of the pile increases along the depth and reaches the peak at the neutral point. The frictional resistance along the pileroughly appears as the shape of ＂D＂when immersing water for 1 hour. Through out the testing phase, the negative friction reaches a second peak and the curve distributes as the shape of ＂β＂ . The settlement of the top of pile is a- bout 0.5dmm due to the frictional resistance. The experimental research methods and results can provide references for similar projects.