The Stability Response Study Of Cast-in-situ Thin Wall Pot Pile In Dealing With Soft Foundation Of Bridges Head

My country is in the stage of fast development of highway now, and the car-jumping problem of bridge approaches is important problem in highway construction, it is nearly impossible to resolve this problem completely by usual treating-methods. the invention of cast-in-situ thin wall tube pile provides a fully new method which solves the problem. basing on the problem existed in current research, the paper does priority studies by test-in-situ of typical road section together with the model analysis, the paper is the most systemic and all-sided research on the cast-in-situ thin wall tube pile technology since it appeared. Through the research, a fully and deeply comprehension on the technology of thin wall tube pile reinforcing soft base at the end of a brige is achived, and a important theoretical foundation is set for the promoting and the applying of this technology.First, this paper has carried on scientific analysis to the engineering geology characteristic and the engineering geology structural feature of soft bases in Zhejiang,it provides a scientific and reasonable division about soft bases structure according to the effect of soft base reinforced by the thin wall tube pile for the first time, there is a generalized analysis basing on many kinds of tests-in-situ at two different soil layer structural unit, the technology advance and the good quality character of cast-in-situ thin wall tube pile is promulgated, the calculation method and the formula of normal value of its limited load-bearing capacity are obtained, and the method of taking control of its quality is proposed.Next, the paper takes the lead to promulgate the reflection of the soil layer at the process of being a pile, it is proved fully that the soil layer's physical mechanics characters and the facial soil layer's load-bearing capacity have a varying degree improvement and enhancement after reinforced by the thin wall tube pile, this conclusion comes out of the studies in two layers soil structural unit, in view of the fact that thin wall tube pile has similar influence to similar stratum, the conclusion above is suitable approximately for three layers soil structural unit, that is to say, the conclusion above has widespread serviceability. The paper uses the basis instant subsidence model experiment to prompt the rule and characteristic of basis' instant subsidence for the first time,then carries on the soft bases' response to thin wall tube pile through the stress and the deformation testing of the basis reinforced by thin wall tube pile, it reveals the factors that influences the pressure of the earth between the piles, the pressure of the earth and the pile, and the pored water pressure of the earth between the piles, at the same time, it reveals the rules of it changing with load, and tells us the basic reason why the total settlement is less in three layers soil structural unit than in twos.Third, the paper promulgates the technical characteristic of the thin wall tube pile through the study on tests-in-situ: its body intensity is high, has a significant effect in lateral retaining, limites the lateral deformation of ground soil, reduces the squeezing of the road ground, enhances the anti-slide stability and the distortion stability of the ground soil. The thin wall tube pile's load-bearing capacity is high, it will increase the strength of the ground soil greatly. When it is used in two Layers soil unit that is made up of "upper hard soil and lower thick mud", it will transfer the compressed deformation of lower thick mud into upper hard soil with the effect of the pile's side friction, it is equal to increas the thickness of the upper hard soil, resultly, it reduces the deformation of the weak underlying stratum greatly, it has a sound effect to reduce the compressed deformation of the road ground, and the same to prevent car-jumping at the end of a bridge and prevent the displacement of the bridge stand.Fourth, the paper carries on correlation analysis on the establishment of the cover, the function of the geogrills, the establishment of transition region and so on, it reveals the relevant rules, proposes to enlarge the pile spacing, reduce the pile number, increase the cover area, in order to display the thin wall tube pile's load-bearing capacity fully, more part of the load is withstanded by the pile body, while less part is withstanded by the earth between the pile, this action will result in reducing the subsidence of the compound ground, cutting down the cost of projects. On the work of thin wall tube pile together with geogrills , it can equalize the stress of the foundation, reduce the unequal settlement .In the author's view, in order to avoid second car-jumping at the end of a bridge enhenced by thin wall tube pile, it is necessary to set a transition region, it can realize by changing the length of piles and the space between the piles. Besides, the paper propose a new way to reinforce the soft base by thin wall tube pile together with reinforce the road ground by graded gravels and sands using water-flushed, this thought is practiced for the first time in south Hangzhou highway,it is proved to be good.Fifth, starting with the standard analysis and the calculation method of the soft base's subsidence, the paper carries on research on the subsidence controlling and calculation method, proposes the calculation model of compound ground reinforced by thin wall tube pile; the paper for the first time establishes the BP artificial neural networks model of the soft base's subsidence reinforced by the thin wall tube pile, using the artificial neural networks which has the advantages such as the powerful learning property and high unlineal reflection capability , self-organization and self-suitability, high fault tolerance, parallel processing, distributional knowledge storage, then according to the SVM model's advantage in small sample, unlineal and multi-dimensional pattern recognition question, the paper provides a new way to resolve the small sample, unlineal and multi-dimensional pattern recognition problem of the soft base's subsidence at the end of a bridge, and this is proved tentatively.Finally, the paper carries on the economical and technical analysis to the cast-in-situ concrete thin wall tube pile, according to the analysis, this technology is proved to have the following merits: compared to the plastic plate pile, soft base reinforced by the thin-wall tube pile, with less settlement, no need of preloading, short period of filling and so on. Only talking about the unit cost of treating, the thin wall tube pile's cost is high, but considering of the construction cycle and the maintenance cost while using, for the road sections with lower foundation strength and higher demand of settlement while using, the thin-wall tube pile is superior to reinforce the soft bases. Compared to powder-spurt pile, the thin-wall tube pile is superior in all sides such as reinforcement depth, settlement, boadbed's stability, and its construction quality is reliable, means of detection is simple and rapid, the cost is lower, especially in the road sections where the soft base's depth is more than 15 meters, the thin-wall tube pile play a irreplaceable role. The strength and stiffness of the soft base reinforced by the thin wall tube pile is greatly enhanced, so the thin wall tube pile is suit to the road sections needing rapid filling, no need of overloaded preloading, it has a incomparable superiority to the plastic plate pile and powder-spurt pile, its economic and social benefits is also very obvious. The tests of the thin wall tube pile fully demonstrate its double performance: a good carrying performance and effective in preventing the soft ground lateral slip.It is proved by experimental research and application that cast-in-situ concrete thin wall tube pile belongs to thin wall structure, the advantages of fast to be a pile, short construction period, automatic soil dump, no mud pollution, saving concrete materials, high capacity and so on. The technology of using the thin wall tube pile at the end of a bridge to treat high filling soft bases is novel, scientific and rational and easy to implement. The settlement of the soft base reinforced by the thin wall tube pile is small. The invention of this technology brings a new breakthrough to solve the problem of car-jumping at the end of a bridge, provides a new way to high-grade highway, as well as other buildings to strengthen the soft soil ground, it deserves widespread promotion.At the end of the paper, the author lists the issue to further study, such as the shape of pile boot, the theory of deformation controlling, developing the technical specifications of thin wall tube pile, reducing the design strength of concrete ,equipment improving and so on.