深长变径搅拌桩荷载传递规律的试验研究

采用一种新型的地基处理方式--变径水泥土搅拌桩，处理了浙江省湖州地区深达20多米的深厚软土地基，通过对载荷试验和桩身应力实测资料的分析，研究了深长变径搅拌桩的承载特性和荷载传递机制。研究表明，受到桩身强度的限制，荷载沿桩身传递限定在一定范围内；由于桩径的变化，桩身应力在变截面处出现了应力集中现象；桩身轴力沿深度逐渐衰减，且在变径位置以上桩体衰减速率较下部快；最大侧摩阻力发生在桩顶附近，在变径处附近由于扩大头端承作用而锐减，但变径位置以下一定深度范围内的桩侧摩阻力得到提高；扩大头端承力随桩顶荷载的增加而逐渐变大，但占总荷载的比例不大，桩侧摩阻力仍提供了大部分的承载力，因此变径水泥土搅拌桩属于有支点端承力的摩擦桩。结合3种不同单桩破坏模式，提出了深长变径搅拌桩的单桩极限承载力计算公式，经过试算发现与现场试验结果相差在10%以内，计算结果可靠，可推广应用于实际工程中。

Field test research on load transfer law of long soil-cement deep mixing columns with different cross-sections

The soil-cement deep mixing column with different cross-sections is a kind of newly soft soil foundation treatment methods. Since special modifications have been made towards those drawbacks which exist in traditional deep mixing columns, the the soil-cement deep mixing column with different cross-sections exhibits good foundation treatment effect and thus has been gradually popularized in China recently. Based on in-situ static load tests in subsoil of Huzhou, the bearing capacity and load transfer mechanism of long soil-cement deep mixing columns with different cross-sections are studied. The result shows that load transfer is limited to a certain range due to soil-cement strength of column body. Stress concentration appears at the position of cross-section variation. Axial force decreases with depth. The maximum lateral friction resistance occurs at the top of column. The lateral friction resistance below varied cross-section decreases sharply due to the end resistance effect of the varied cross-section. But the lateral friction resistance of the lower part of the column is improved. The base resistance below varied cross-section increases with total load. Compared with the value of lateral friction, base resistance is less. So this column is a type of friction column with base resistance below varied cross-section. Based on three failure models of single column, the ultimate bearing capacity calculation of long soil-cement deep mixing columns with different cross-sections parts is proposed.