The Study Of Prestressed Spun Concrete Hollow Square Pile On Bearing Capacity

The prestressed spun concrete hollow square pile is new-type foundation pile in China in recent years. The bearing capacity problems at the stage of design and construction are discussed.By introducing construction technology of prestressed spun concrete hollow square pile, A few important steps which ensures bearing capacity can be understood. The bending tests on prestressed spun concrete hollow square pile are done to study their flexure bearing behavior. The results show that the flexure bearing capacity is close to normal square pile, and is larger than pipe pile, but is more economic for its smaller area. Through comparison of compression tests, the size of square pile hole can be the size of pipe pile. The properties of material is considered when the calculation formula of structure bearing capacity is deduced, especially the calculation formula of shear strength by i-section hypothesis. Some understanding and suggestions are proposed about some calculation formula of structure in current codes.The load test values are analyzed. A few common methods are compared. These methods have limitations of areas and geological conditions.When the end of pile is open, a few common calculation formula of the extreme bearing capacity are analyzed and compared based on theoretical analysis. The vertical bearing capacity formula of the ultimate bearing capacity is deduced in sand or clay concerning plug effect.A varieties of factors which influence on vertical bearing capacity are analyzed by the finite element method. It is shown that the stress and displacement of the prestressed spun concrete hollow square pile are the similar to that of pipe pile under the same area and same length. The ratio of ending bearing capacity increased with increase of block degree. When the load increased, the result of part block is close to finish block. FEM analysis shows that the ratio of length between diameter is the chief influence factor of bearing capacity and displacement among other factors, such as characters of pile-end soil, characters of pile-surrounding soil, modulus of plugged soil, and plugged soil modulus’s influence is be relatively small. The soil plugging effect has little action when the ratio of length between diameter of pile is large, but significant effect to the small ratio of length between diameter.The relationship between piling pressure and bearing capacity is discussed, which demonstrated the end piling pressure is relative with the ultimate bearing capacity. The theoretical formula of piling pressure in clay soils were deduced by spherical cavity expansion theory. Three geological conditions are divided by static penetration test, i.e. sudden, gradul, jumply. The calculation formula of driving resistance in sand is deduced on these conditions. Finally, the economy and reliability are verified by the practical engineerings all around the country. This kind of pile is worth to promote widely. Through more designs and construction practice will be accumulated combining with geological and soils conditions, More economic and social benefits are produced.