Settlement Character Of Composite Foundation For T-shaped Mixng Piles In The Guangzhou Nansha Area

When building the highway or the main city’s road in the Guangzhou Nansha area, large settlement and obvious differetial settlement are happened, which seriously affect the normal use of the highway. TO resolve these problems, a new type of pile,the T-shaped mixing pile,is used and to reinforce soft soil of Guangzhou Nansha area. For the T-shaped mixing pile is used in the Guangzhou Nansha area in the first time, its settlement characteristics of composite foundation is analyzed necessarily to verify its reinforcing effect. The survey data of the Guangzhou Nansha area and results of field test are analyzed and the results is showed:the soft soil of the Guangzhou Nansha area has high water content, void ratio, high compressibility, low shear strength, coefficient of consolidation, consolidation of a long time, high sensitivity, large disturbances and so on. Pore pressure gauge、Settlement gauge and soil pressure box are buried in T-shaped mixing pile composite foundation and the composite foundation settlement is monitored on the embankment load. The test results is obtained:with the increase of the embankment load, the soil stress、pile stress on the top of pile and the pile-soil stress ratio increase gradually. After increasing embankment load, the pile-soil stress ratio does not increased. The settlement of the T-shaped mixing pile composite foundation is different greatly on the different strata. Because a silty clay,which has a good engineering geological conditions, is being in the soft soil of the test section, the composite foundation settlement of the T-shaped mixing pile changes with depth. The settlement difference between6.1m depth and7.3m depth, located in the silty clay above, is about10mm and between9.0m depth and7.3m depth, located in the silty clay is less than1.0mm. The settlement of the T-shaped mixing pile composite foundation is calculate by different theories, and the results is showed:the settlement of reinforcement area in the composite foundation, which is about7.67mm, is relatively small, and the reinforced area’s average settlement of pile’s variable cross-section above is about2.44mm and of pile’s variable cross-section following is5.39mm. But the settlement of the subjacent bed,about187.7mm, is relatively large, and the settlement of the subjacent bed mainly occur in the muddy soil, accounting for more than90%the total settlement of the subjacent bed.Through combining of the engineering geological characteristics of the soft soil in the Guangzhou Nansha area、site monitoring and numerical analysis, the settlement characteristics of the T-shaped mixing pile’s composite foundation is analyzed, and the results is obtained:the main settlement of T-shaped mixing pile’s composite foundation is occured in the subjacent bed and the reinforced area’s settlement is relatively small. The main settlement of the reinforced area is happened in the muddy soil layer and of the subjacent bed is occured above the silty clay layer. For the actual monitoring value is less than the calculated value in the T-shaped mixing pile’s composite foundation, the theoretical calculated value should be amended when designing embankment reinforcement project in the the Guangzhou Nansha area. The settlement correction factor(Ψ s), which is required in the technical specification for T-shaped bidirectional deep mixing column composite foundation, shall be taken as0.85.