Experimental Study On Bearing Characteristics Of Existing Building Pile Foundation Under Excavation Condition

With the construction of China’s large-scale rail transportation, development and utilization of underground space has entered a stage of rapid development. At the same time, with the increase of the number of vehicles, no underground parking lot and other facilities have defects in the use of functional buildings increasingly apparent, for the development of underground space requirements will be more urgent. The core technology of building underground space development is the pile foundation underpinning and earthwork excavation. Pile foundation underpinning the development of underground space is bound to make the excavation of earth pile decreases, pile foundation is exposed, it will not only affect the pile lateral friction resistance and end resistance of the pile, the pile foundation ultimate bearing capacity will change, so the structure of the settlement, and then affect the safety of buildings. At present domestic and foreign researches in this area are mostly concentrated in the pile, the method is limited to the finite element simulation, therefore, the existing condition of bearing is very necessary for experimental study on the characteristics of building pile foundation excavation.In this paper, the model tests of different excavation depths are carried out by changing the length of pile and the diameter of the pile. Through the test, (1) before the excavation of pile top load-settlement rules and axial force of pile, pile side friction resistance, pile end resistance variation were studied. The single pile of characteristic value of bearing capacity; (2) the conditions of pile top settlement, pile shaft axial force variation excavation and pile top load by pile, pile-soil interface to foundation soil in the transfer rules. The results can be drawn as following:(1) for single pile, increasing the pile length and pile diameter can reduce the settlement of pile top under the same load, and increasing the pile diameter is more obvious. Under different pile top load, the pile body is compressed and the axial force of the pile is gradually decreased from the pile top along the pile body. Pile Cemo resistance with the pile top load increase will be a corresponding increase, early days increases greatly, the latter increases dramatically reduced. (2) with the increase of the depth of excavation, the settlement curves all appear steep drop points ". Increasing the length of the pile, the critical excavation depth can be increased, but the ratio of the excavation is decreased, and the diameter of the pile is increased, and the change of the excavation ratio is small. The excavation ratio of several kinds of pile type is between 0.33-0.40. (3) with the increase of the depth of excavation, the pile body lateral friction resistance will increase correspondingly. In each excavation 50mm, the side resistance decreases 1%-3%, and the end resistance remains basically unchanged or changed very little when it is close to the critical excavation depth.In this paper for muti pile,by changing the pile length, pile diameter and pile numbers three parameters were studied under different excavation depth. Through the test, (1) of multi pile foundation excavation of pile top load-settlement rules and axial force of pile, pile side friction and end resistance variation, received a terrible pile of characteristic value of bearing capacity; (2) studied multi pile in excavation conditions of pile top settlement rules and pile axial force and load transfer law. Through the test results can be obtained:(4) for multi pile, changing the pile length, pile diameter and pile three parameters, the failure of excavation than are in 0.5; increasing the pile diameter to reduce settlement and increase the critical excavation effect is more obvious than that of, and increase of pile length and number of the effect was not significant.