双向搅拌桩加固高速公路软土地基现场对比试验研究

COMPARISON TESTS ON FIELD BIDIRECTIONAL MIXING COLUMN FOR SOFT GROUND IMPROVEMENT IN EXPRESSWAY

针对国内水泥土搅拌桩施工工艺存在的问题,提出了双向水泥土搅拌桩技术。为了分析双向搅拌桩加固高速公路软土地基的处理效果,在同一场地进行了双向搅拌桩和常规搅拌桩试验段工程,对比分析了双向搅拌桩和常规搅拌桩的桩身质量、施工扰动、复合地基承载力和路堤荷载下的工作性状特点。现场试验结果表明,双向搅拌技术能有效地提高搅拌均匀性、消除冒浆现象,并减小搅拌桩施工对桩周土体的扰动;双向搅拌桩桩身质量均匀,桩身强度沿深度变化较小,复合地基承载力高于常规搅拌桩复合地基;填土高度相近时,双向搅拌桩荷载分担比高于常规搅拌桩,地表沉降和坡角处最大水平位移小于常规搅拌桩复合地基,而地基固结速率快于常规搅拌桩复合地基。研究结果表明,双向搅拌桩在高速公路软土地基处理工程中具有很好的应用前景。

With a review of disadvantages of ordinary deep mixing techniques in China, the bi-directional mixing technique is developed and presented. In order to investigate the improving effect and economic benefits of slurry bidirectional mixing column for soft ground improvement in expressway engineering, comparison tests between bidirectional and ordinary deep mixing column sites were conducted in the same geological condition field of Shanghai-Jiangsu-Zhejiang expressway, Jiangsu Province, China. The strength characteristics of columns and behaviors of the composite ground under embankment filling were analyzed. It is indicated from the in-situ standard penetration tests（SPT） and unconfined compression tests on coring samples taken from the column that the strength along the columns with bidirectional mixing technique is almost uniform, while strength with the ordinary deep mixing method decreases rapidly with depth. The bearing capacity of bidirectional mixing column composite ground is higher than that of ordinary deep mixing column composite ground. At the same embankment height, the load sharing ratio of bidirectional mixing column is higher than that of ordinary deep mixing column. The ground surface settlement and the maximum lateral displacement at embankment toe of bidirectional mixing testing section are less than those of ordinary deep mixing method. It is also shown that the excess pore water pressure caused in bidirectional mixing composite ground during the embankment filling is less than that in ordinary deep mixing ground, which is benefit for speeding up the filling in the bidirectional mixing ground. In addition, the bidirectional mixing technique can eliminate grout spill phenomena, decrease the disturbance to surrounding soil and save construction time. The results show that bidirectional mixing technique is an efficient and economic method for soft ground improvement in expressway engineering.