Application And Study Of Self-Balanced Loading Test In Longhua Songhua River Superbridge

With the development of national economy, the construction oflarge-scale building for example high-rise building , large-scale bridgeand so on have been constructed, as key foundation on this type ofbuilding——large-sized cast-in-place pile is applied more and morewidespread. Designation of full diameter cast-in-place is satisfied withengineering load and economic security, the determination of pilebearing capacity is the key whether the whole pile foundation is satisfiedwith engineering request. At present, the methods for determining pile bearing capacity arestatic loading test, self-balanced loading test, low strain dynamic test,high strain dynamic test, statnamic test and simulation test. The methodsare used in lots of projects and gain some products. But the traditionalstatic loading test need the special counterforce system. It has thedisadvantages of big counterforce system, long time for preparing test,big quality working, high expense and the rigorous request of testingground. With the increasing of high architecture and big bridgeconstruction, the single pile bearing capacity is bigger and bigger, so it isdifficult to do static loading test and gain the exact data of pile capacity. Incontrast, dynamic test is more convenient and quickly. But the researchand application of static and dynamic test of the latest ten years indicatethat the dynamic tests also have some experience composition. It is anew technique and it is in developing. The dynamic test is a complementof static test ,it can be used as a method of pile checking and can notreplace the static test. Statnamic method includes the merit of static testand dynamic test and it is popular in the world. But the study of thismethod is lack in our country. The stimulation method can stimulate theactual project properties and gain the pile bearing capacity, but theundisturbed sample is hard to get in long pile testing. The self-balancedloading test is widely used as a new pile loading test. The advantagesare: the equipment is simple, the expense is low and it can test thebearing capacity of super tonnage and super long pile.This paper is based on the self-balanced loading test of LonghuaSonghua River super bridge, The main research content is: ①Theresearch of engineering geology condition and property. Through thedetailed engineering geology survey, make the engineering geologyclear, especially the lithology and the thickness of the stratum. Do theresearch of the physic and mechanic property of the stratum and providethe foundation for the location of balanced point. ②Do the self-balancedloading test of the test piles in pier1 and pier2 and calculate the date.Gain the ultimate bearing capacity, lateral friction and tip resistance ofthe piles. The design of the project is according to the date. ③Do theresearch of the type of Q-S curve and the property of inner force of piles,the property of lateral friction and tip resistance, the relation betweenlateral friction and the displacement, and give the bearing property ofcast-in-place pile in mud stone base. ④Contrast analysis is presentedbased on the Q-S curve and the property of the lateral friction, draw theconclusion that the Q-S curve and the degree and numerical of thelateral friction have the close relationship of the construction technics andthe construction quality of the pile. The longer the pore forming is, thebigger the specific weight of mud fluid is, the thicker the mud is canreduce the side friction of pile, and increase the relative displacementbetween pile and soil which is needed by the exertion of side friction.⑤The existing method for transferring the self-balanced testing curve totraditional static testing Q-S curve is not exact when the upper and lowerparts of pile do not reach the ultimate bearing capacity simultaneously.This paper Integrates the testing date of 3# and 5# pile, transform themeasured curve to the static loading test curve according to thedisplacement coordination method.The paper not only have the guide significance for the project butalso have the reference value for the cast-in-place pile in mud stonebase in the other region. This paper Integrates the testing date of 3# and5# pile, transform the measured curve to the static loading test curveaccording to the displacement coordination method. This gives a newway in the self-balanced loading test: make the loading box in thedifferent position of the piles, gain the ultimate lateral friction of everystratum and ultimate tip resistance, and then transform the measuredcurve to the static loading test curve according to the displacementcoordination method.