Model Test And Numerical Simulation Of Optimization Of Gravel Pile Composite Foundation

Gravel pile composite foundation can enhance bearing capacity and accelerate consolidation, and has been widely used in foundation treatment. Study has shown the gravel pile can very easily develop lateral deformation which leads to large-scale failure of foundation under vertical loads. The bearing capacity mainly depends on the constraint from the lateral soil. The lateral deformation mainly occurs where the depth is 1 to 3 times the length of pile radius. Recent years, reinforced gravel pile composite foundation emerges as the fast development of geosynthetics. It is gravel pile surrounded by geogrid in certain depth, and it can effectively control the lateral deformation of pile and also enhance the bearing capacity of gravel pile composite foundation. Based on these facts, this paper takes the gravel pile in loess area as study objects and model tests are performed to investigate the effect of reinforced gravel pile composite foundation together with theory analysis and numerical simulation. The work mainly includes:(1) Model test are performed on natural foundation, gravel single pile foundation, gravel pile composite foundation, and reinforced gravel pile composite foundation. From the settlement curves, it is clear that there are 3 stages: elastic, elastoplastic, and plastic stages. Gravel pile composite foundation and reinforced gravel pile composite foundation can both enhance the bearing capacity obviously, with increment of 45.8% and 88.3% respectively.(2) Stress ratios of gravel piles and reinforced gravel piles both increase first before falling afterwards. Considering the lateral deformation after caving, the maximum lateral deformation occurs within the depth of 3 times the length of pile radius, peaking at 1 time the length of pile radius. The lateral deformation emerges at the lower reinforced part. Theoretical calculation reveals the calculated results are the same with the experiment results for gravel pile composite foundation, while the bearing capacity in experiment is smaller for reinforced gravel pile composite foundation.(3) Numerical simulation model is set. Based on the results derived from load-settlement graph, parameters of soil are determined and used in the numerical model.(4) For the gravel pile composite foundation, numerical results show that lateral deformation exist near the 2D region, maximum at depth of about 1.5 times the length of pile radius. Both lateral deformation and settlement decrease when cohesion and friction angle increase. Stress ratio of the gravel pile first decreases and then grows before leveling off at last. When the length of the pile reaches certain vale, increasing the length of gravel would not help to enhance bearing capacity very effectively. The results suggest there is a critical pile length, which is about 4 times of the length of the pile radius according to calculation results.(5) For the reinforced gravel pile composite foundation, numerical results show that the reinforcement can enhance the bearing capacity and reduce the settlement. Increasing the material strength of reinforcement can also help to reduce settlement but with limited extent. Increasing the length of pile shows to useless in enhancing bearing capacity while increasing length of reinforcement can effectively reduce the settlement as well as enhance the bearing capacity. The pile and soil of the gravel pile composite foundation can be seen as a combined structure working together, therefore increasing pile strength without increasing soil strength or simply reinforcing where it is easy to develop lateral deformation but ignoring less sensitive areas can neither be the most efficient ways for reinforcement to elaborate.