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试验证明,在桩周围的土壤相对于桩产生很小的向下的变位,就会对桩产生下曳力,这下曳力一般称为负摩擦力。在工程设计中,如果不考虑或过低估计负摩擦力,就会导致建筑物产生过大的沉降,甚至破坏。特别是对于穿过软土地基而言,更是这样。如果对负摩擦力估计过大,致使桩的承载能力降低,就会增加工程的造价。因此恰当地确定负摩擦力的大小是必要的。影响摩擦力的因素很多,综合以往的试验和实践经验,主要有以下几个方面: 1.桩周土沉降与桩之间产生相对位移大(包括土壤固结过程的压密变形),负摩擦力也大,但相对位移达到某一定值时,负摩擦力不再增加。 2.桩穿过的软土层越厚,负摩擦力值越大。 3.桩的允许沉降量大,负摩擦力相对减小。 4.纯粘土或含少量砂的粘土,负摩擦力小。 5.土壤含水量低抗剪强度高,桩表面摩擦力增加。作为土建设计来说,负摩擦力的大小必须有个具体
Tests have shown that a small downward displacement of the soil around the pile with respect to the pile generates a downward drag on the pile, which is generally referred to as negative friction. In engineering design, if you do not consider or estimate the negative friction too low, it will lead to excessive settlement or even damage to the building. This is especially true for passing soft soils. If the negative friction force is estimated to be too large, the bearing capacity of the pile will be reduced, which will increase the cost of the project. Therefore, it is necessary to properly determine the magnitude of negative friction. There are many factors that affect the friction, and the previous experiments and practical experience are mainly summarized in the following aspects: 1. The relative displacement between pile settlement and the pile is large (including the compaction deformation of the soil consolidation process), negative friction The force is also large, but when the relative displacement reaches a certain value, the negative friction no longer increases. 2. The thicker the soft soil layer the pile passes through, the greater the negative friction force. 3. The allowable settlement of the pile is large and the negative friction force is relatively reduced. 4. Pure clay or clay containing a small amount of sand, the negative friction is small. 5. Low soil moisture content High shear strength and increased pile surface friction. As a civil design, the negative friction must have a specific size