Study On Shallow Reinforcement Technology Of Gravel Pile Composite Foundation In Loess Areas

Nowadays gravel pile composite foundation is widely used in northwest loess foundationtreatment. It should be noticed that gravel pile composite foundation has relatively weakbearing capacity because it mainly depends on the loess around piles. In recent years, shallowreinforcement technique is increasingly used to improve the bearing capacity of gravel pilecomposite foundation. However, the theory of shallow reinforcement is far from sufficient,hindering its long-term development. In this paper, relying on the National Natural ScienceFoundation of China “Optimization Mechanism of Multivariate Pile Composite Foundationand Topology Optimization Methods for the Pile Layout”, taking gravel pile compositefoundation in the loess areas as research object, an indoor model test and theoretical analysisabout surface compaction and exchange filling were undertaken on the shallow reinforcement,which provided theoretical supports for the development of shallow reinforcement technologyin loess areas. The main contents of this paper are as follows:1. Through comparing the P~S curves with different reinforcement depth, it could befound that the shallow reinforcement had an obvious effect on the increase of bearing capacityfor gravel pile composite foundation. More specially, the strengthening extent increased withthe increases of reinforcement depth. Compared with the gravel pile composite foundationwithout shallow reinforcement, the bearing capacity increased195%,216%,248%respectively under1D,2D,3D reinforcement depth.2. With the increases of upper load, pile-soil stress ratio increased firstly then decreased.With the increases of reinforcement depth, pile-soil stress ratio showed a trend of decline.Besides, pile stress went up with the increase of load until reaching a certain value,accompanied with swelling phenomenon. Therefore, above analysis indicated that the bearingcapacity of gravel pile composite foundation increased with the rise of reinforcement depth.3. By the observation of piles destroyed in the model test, with the increases ofreinforcement depth, it could be found the position of swelling area on gravel piles moveddown. Meanwhile, the swelling degree reduced.2D distance away from the loading plate edge,the cracks appeared whose development mainly included three stages: subtle cracks, initialdevelopment and rapidly expanding.4. Based on the Brauns theory, a calculation method about bearing capacity of gravel pile was introduced. By adding synthesize equivalent deformation modulus, the loess’s bearingcapacity under different reinforcement depth were deduced. Finally, combining the bearingcapacity’s calculation formula of gravel pile and loess among piles, the bearing capacity ofgravel pile composite foundation could be calculated.5. The bearing capacity formulas were verified correctness and effectiveness throughcomparison between measured and calculated values about bearing capacity6. The application of gravel pile composite foundation shallow reinforcement techniquein practice engineering was preliminarily discussed in this paper.