中文摘要：

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。

英文摘要：

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.