中文摘要：

变径水泥土搅拌桩是一种新型的地基处理方式,它针对传统水泥土搅拌桩存在的诸多弊端进行了相应的改进.通过对试验区变径水泥土搅拌桩进行几组单桩复合地基载荷试验,研究了变径水泥土搅拌桩复合地基的承载特性及桩身荷载传递机理.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深度范围内;由于桩径的变化,桩身应力在变径处发生了应力集中现象;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;最大桩侧摩阻力则发生在载荷板下4D-6D（D为扩大头桩径）处,在变径处下部有限范围内的桩侧摩阻力由于扩大头端阻作用而锐减;扩大头端承力开始随荷载的增加而线性增大,随后趋于稳定;在其他条件相同时,扩大头端承力随扩大头高度的增加而减小,而桩土应力比随扩大头高度的增加而增加.

英文摘要：

The soil-cement deep mixing column with different cross-section parts is a new kind of soft soil foundation treatment methods. Since special modifications have been made against those drawbacks which exist in traditional deep mixing columns, the soil-cement deep mixing column with different cross-section parts 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 in Zhejiang province, the beating capacity and load transfer mechanism of single column composite foundation of 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 depth of 4D -6D below the loading plate （D is diameter of upper column）. The lateral friction resistance below varied cross-section decreases sharply due to the end resistance effect of the varied cross-section. The end resistance under varied cross-section increases with the total load in the beginning, then it tends to be stabilized. As the length of upper column part increases under the same condition, the end resistance under varied cross-section decreases, but the column-soil stress ratio increases.