Study On The Settlement And Reliability Of Composite Foundation With Compound Piles

With the foundation deformation control design principles proposed composite pile foundation more widely used in engineering practice. Composite pile foundation is composed of a variety of different lengths, different pile diameter or pile combination of different materials forming the composite. Wherein the composite foundation formed by a combination of different lengths is called the length of the composite foundation, it is the most widely used composite pile foundation. In general, short pile using discrete material pile piles or flexible, is mainly used to improve the bearing capacity of the foundation carried out. As long pile deformation design master pile, at an increased bearing capacity, the main foundation is to reduce the vertical deformation. Long pile the general stiffness of the pile. Although the composite pile foundation has been widely used in engineering practice, but studies on its mechanism of action and the shape of the work is lagging behind. In this paper, in order to study the length of the working mechanism of pile composite foundation, a series of model test. Study the different length, different pile diameter and different from the pile on the settlement deformation, stress analysis of the pile between the pile and soil stresses and stress ratios in the pile of soil. Mainly in the following conclusions:(1) Increase in long pile length, pile diameter is reduced from the pile settlement control a significant effect.(2) Comparative analysis between soil stress hormone land-based and composite pile foundation, we can see the short pile can effectively improve the bearing capacity.You can pile load transfer to the lower soil, so that no additional stress with different natural foundation and delivery points, the current settlement calculation method is still using the additional stress transfer method the natural foundation.(3) Long pile stress is not the biggest pile, but top of the pile at about one third of the length of pile position of the maximum, which is due to the presence of cushion so that the top of the pile penetration caused by friction from negative. After the maximum stress, due to the soil around the pile friction, pile stress becomes smaller,the upper load gradually transfer to the lower soil layers. When the load is small, the relative movement of the pile soil is relatively small, so the graphics relatively straight,as the load increases, the friction increases, pile stress and attenuation increases rapidly, showing a clear curved pattern. Short pile about the location of maximum stress in the middle of the pile, and then gradually decreases due to frictional resistance.(4) The center of the upper part of the pile length pile soil stress ratio increases at first and then gradually decreased. Because the piles penetrate the upper soil compaction and gradually render strain hardening. The lower half of the pile-soil stress ratio has been gradually increased, indicating that the lower part of the pile with the pile stress underlying layer is compacted, it increasingly difficult to penetrate gradually increases.(5) On the long corner pile-soil stress ratio has been showing an increasing trend,long pile soil around the corner and did not like the center of the pile to give him a long gradual increase of confining pressure, as the load increases, the upper part of the pile between soil stress increases, the angle of the pile soil around the lateral displacement may occur to the other three, but can not form a confining pressure effects. With the foundation deformation increases, corner pile stress increases, while the surrounding soil and can not share more of the load, so the pile-soil stress ratio has been increased.(6) Long pile and short pile stress ratio increases as the load has been increasing,indicating that as the load increases, the piercing long pile more and more difficult,the proportion of their share of the load continues to increase.(7) Long pile with depth is consistent with the pile-soil stress ratio, showing the two big middle small features. Actually, this is a long pile piles master reasons, due to the long pile bears the load transfer to the lower soil mission ends its larger stress,pile-soil stress ratio is larger. Pile soil stress ratio piling is increasingly smaller as the depth increases, working with long pile upper part of the pile-soil stress ratio similar change.Highlights the huge difference of strain caused by the discussion, to accurately grasp the combined pile composite foundation settlement calculation depends on the mechanism which combined pile composite foundation stress field of research is the key. In this paper, the pile body stress and pile soil stress and pile-soil stress ratio onsettlement influence research for settlement calculation method of the foundation. In this paper three kinds of settlement calculation method, standard method and composite modulus method are a problem, is the ideal model of composite foundation compression modulus calculation is not allowed due to pile and pile soil strain and composite modulus method this problem. But if you can obtain the pile body stress And the inter pile soil stress and composite modulus method can get more accurate sedimentation value. In practical engineering, if can be accurately obtained pile thorn quantity, can through the composite modulus method to calculate more accurate sedimentation value. Standard method to calculate the settlement of the accurate, not open around the choice of many empirical coefficient. Although present in all kinds of settlement calculation method, the calculation of the law value is closer to the actual value, but the composite modulus method and elastic mechanics method in the calculation of compression modulus of composite foundation of breakthrough, is expected to be more simple, accurate calculation method.