钉形粉喷桩加固海相软土地基的现场试验研究

Field Tests of Soft Marine Clay Foundation Reinforced by T-shaped Bidirectional Dry Jet Mixing Piles

针对常规粉喷桩处理海相软土地基中存在的搅拌不均匀、桩身强度低等问题,提出了钉形双向搅拌粉喷桩的施工工艺.以连云港至临沂高速公路软基处理项目为例,进行了现场单桩施工扰动、单桩静载试验,并对试验过程中的孔隙水压力、土压力等参数进行监测.结果表明:钉形粉喷桩由于上部桩径扩大且进行复搅,使变径深度处的超静孔隙水压力最大,且超过土体的上覆有效应力,单桩施工影响在5～10倍桩体半径范围内;由于增大了上部桩径,承载力比相同直径的双向搅拌粉喷桩和常规(单向)粉喷桩的单桩极限承载力分别提高了36%和76%.因此,钉形粉喷桩具有对施工扰动小、单桩承载力高等优越性.

In order to overcome disadvantages of the marine soft soil foundation treated by the conventional dry jet mixing（DJM） piles,such as mixing non-uniformity of soil cement and low strength of pile body,a technique of using T-shaped bidirectional DJM piles was proposed to reinforce the soft marine clay foundation in Lianyungang area of China.Single pile tests were conducted in a field site of the Lianyungang-Linyi Expressway（Jiangsu Section）.Disturbance effects of DJM during installation and static load test after the construction of the T-shaped bidirectional DJM were analyzed.The dissipation process of the excess pore water pressure after installation,load,and settlement parameters were monitored during the static load test.The results indicate that the excess pore water pressure exceeded the effective overburden stress of the soil during installation,probably due to the larger diameter of upper head of the T-shaped DJM pile and the repeated mixing process.However,excess pore water pressure dissipated quickly just after installation.Single pile installation had an influence scope of 5-10 times the pile radius.The single pile static load test results indicate that,compared to bidirectional and conventional DJM piles with the same diameter,the ultimate bearing capacity of the T-shaped bidirectional DJM pile increased 36% and 76%,respectively.Therefore,T-shaped bidirectional DJM is characterized by high pile strength and high single pile bearing capacity.