Study On The Application Of Micro-steel Pipe Piles Composite Soil Nailing Wall In Jinxiucheng Foundation Excavation Of Eastern Outskirts Of Chengdu

In the eastern suburbs of Chengdu Minjiang alluvial plains of the River Ⅱ, Ⅲterraces expansive soils are widely developed, because the complex nature ofexpansive soil engineering," water softening " feature is particularly significant,foundation pit supporting in the region is difficult. Micro-steel pipe piles Compositesoil nailing have been initially applied in expansive soil areas in Chengdu. Based on aspecific project of the Jinxiucheng Foundation Excavation， use the on-siteinvestigations, laboratory testing, field monitoring, numerical simulation andtheoretical analysis to study a variety of methods, get the following conclusions andunderstanding:(1) According to the indoor experiment results of field sampling: JinxiuchengFoundation Excavation soil excavation site of expansive soil with water before themoisture content is about26%, c=32kPa, φ=20°, the water moisture content ofabout29%, c=15kPa, φ=11°, the water softening, its strength index than softeningthe soil is not more than50%lower; strength parameters c sticky cohesive force andfriction angle φ moisture content showed a linear relationship.(2) The Jinxiucheng pit deformation overall is big, the deformation valueexceeds the alarm value,11points more than double the alarm value of deformationvalues; The east of the west side of north and south on both sides of the pitdeformation is the largest, second, deformation is relatively small; Deformation ismainly focused on the initial excavation and the fourth layer excavation of the twoconditions.(3) The main reason is: the deformation of foundation pit is given priority to withexpansive soil foundation soil, under the action of "water" softening due to largedeformation;Initial excavation construction time is too long, soil nail and the surfaceis not completed in time, lead to foundation pit exposed for a long time, Micro-steelpipe Piles advance supporting is less effective.(4) The Micro-steel Pipe Piles Composite soil nailing Wall used in chengduexpansive soil foundation pit,the soil nailing active strengthening coordination withpassive role play is good, is the main stress components; Assume the bending momentof small steel pipe pile itself, advance supporting of foundation pit soil and reinforcement effect in general, as the secondary stress component; Surface does notdirectly under soil pressure, the main function and the soil to closed will into theoverall structure, soil and the retaining wall is an integral part of. Three each other,form a unified whole have the effect of foundation pit supporting.(5) The Micro-steel Pipe Piles Composite soil nailing Wall supportingtechnology in splendid city in the foundation pit have played an important role inguarantee security and stability of the slope of foundation pit, illustrates the basicsupport method suitable for chengdu expansive soil area. But has the problem of largedeformation, but also the existence of easy overall buckling under the influence ofwater hazard, need further research and improvement.