Study On Settlement Distortion Characteristics Of Expressway Connection Sections And The Foundation Treatment

The control of the discrepancy settlement between the old road and the widening section is the crucial issue of the expressway widening engineering on soft soil ground. The discrepancy settlement control criterion relates to several aspects such as the placidity and comfort of driving at high speed, smooth drainage, and the crack which may occur during or after widening process. The practice indicates that if the change of the slope in length and breadth of road surface is under 0.5%, the problems above can be avoided, and this can be taken as the control criterion of discrepancy settlement of road widening engineering.The selection of reasonable foundation treatments to reduce the discrepancy settlement between the old and new roadbed is another crucial problem to ensure the engineering quality. We can reduce settlement in two ways: one is to reduce the weight of the road embankments using lightweight filling. And the other is to improve the soil ground such as forming composite ground to enhance the bear weight of the ground and reduce the settlement.The lightweight fillings include coal ash, expanded polystyrene (EPS). SLM light mixture and so on. The practice indicated that the EPS roadbed have advantages of light weight and convenient construction, erection structure will reduce more ground press and land area. This method can reduce the settlement availably and it is an ideal lightweight filling of the widening roadbed.The traditional methods of ground improvement such as cement soil piles have shortages of low strength and short treating depth. To further reduce the discrepancy settlement, we can use the PTC prestressed pipe pile which has higher strength and treating depth. To exert the strength of the piles and soil between the piles sufficiently, one pile cap is put on the top of the pile, and then gravel cushion is above, in the middle of the gravel cushion a layer of steel net is placed, and all these form the pile-net-cushion composite ground. The practice indicated that this method can reduce discrepancy settlement effectively, and enhance the bear weight of the ground. It is the effective foundation treatment of the deep soft soil ground. The finite element method analysis and the practice indicated that the reinforced foundation section can use composite modulus to computer the settlement, and the settlement of the center of the old road must be analyzed under different conditions. This method is economical than traditional cement soil method, and can save cost 20%, and can be spread to road or road widening engineering.