The Study On Model Experiment Of Long-short-pile Composite Foundation In Different Young's Modulus And Pile Length

With the theoretical and technologic development of composite foundation, many new types of composite foundation have been used in design and construction. The long-short-pile composite foundation is one of them. Long-short-pile composite foundation is a kind of foundation treatmenttment could both increase the bearing capacity of composite foundation, and can effectively reduce the settlement, and economic benefits is good, it developed and applied rapidly in engineering practice. As a new ground treatment method, it is developed by our engineer, acoording to local conditions and engineering experience.In response to these circumstances , this subject relies on the National Natural Science Fundation project "The Long-short-pile Composite Foundation Deformation Behavior Analysis and Experimental Study" (project number: 50678110) and Taiyuan Science Bureau university students innovative undertaking project "The Study on Long-short-pile Composite Foundation Design of High-raise Building", a series of model experiment on the sand soil has been done(including different Young's modulus of long and short piles, different length of long and short piles), the long-short-pile composite foundation's work mechanism has been conducted, the following conclusions have been made. 1. The long-short-pile composite foundation bearing deformation characteristics are mainly shown by the long pile, the long pile not only plays the influential role in the load bearing aspect, but also is the main component that controls the settlement. The settlement characteristics of composite foundation are related to the length and modulus of the long pile.2. Short pile is the auxiliary pile. Due to its flexibilty, the short pile has larger deformation, upper loads can not effectively pass down. It played a secondary part in bearing load and controlling settlement, and is not sensitive to the impact of external factors.3. The largest axial force's level of long and short pile in different position is different, the corner pile is largest, the side pile is next, the center pile is smallest. But the rule of the largest negative skin friction's level is conversed. The rule of pile-soil load-sharing's is that long pile is largest, soil between piles is next, short pile is smallest.4. Under the same arrangement, and as long piles grow rigid, composite foundation total settlement significantly reduced. Rigid pile axial force increased significantly, pile-soil stress ratio and the pile load distribution ratio also increased significantly.5. Under the same arrangement, with the growth of flexible short-pile composite foundation total settlement decreased. Flexible pile axial force increases, pile-soil stress ratio and the pile load distribution ratio did not change significantly.6. Under the same arrangement, with the long-pile's modulus increasing , composite foundation settlement declines. Rigid pile axial force increases, pile-soil stress ratio and the pile load distribution ratio increases.7. Under the same arrangement, with the short-pile's modulus increasing, composite foundation total settlement did not change significantly. Short-pile axial force increased, pile-soil stress ratio and the pile load distribution ratio did not change significantly.