Study Of Pile Groups-Soil Interaction By Test And Grey Theory

The interaction between pile-box (raft) foundation and ground soil is mainlysuch questions as soil share top load and subsides.Because of the restriction of thecalculation before, when design the foundation and piles, did not consider this relation.Obviously, routine design methold are not accorded with this fact. Compared with topstructure, the foundation is underground and it engender complicated force with therock and soil medium,in addition,rock and soil body itself is dispersed,inequality ,incontinuum and non-linearity,it acquit complicated mechanics characteristicduring the course of constructing and using, its characteristic is too difficult to answerwith pure theory method. It is difficult to analyze with the aid of modern computertechnology to set up model because of ensure material parameter is not easy.With thedevelopment of testing technology , various kinds of stresses and emergency sensingcomponent is produced.It is possible to test and inspect. Testing and monitoring in thecourse of constructing can prove credibility than simple room test. Pile-soil interactionsystem can be regarded as a grey system according to grey theory ,so it is impossibleto use limited observation and normal position test data to study pile -soil interaction bygrey model and grey related theory.It is necessary to study the characteristic and properties of the soil before analyzethe piles-box (raft) interaction. The typical P-S curve appears the exponential functionlaw. According to the grey systematic theory, the grey GM (1,1) model is very suitablein this kind of curve which presents the exponential function,and the modeling methodis simple, veracity is high. So, the author set up the GM(1,1) model of the P-S curveaccording to a lot of test data . This kind of model is tested can accurately which predictthe limite of the soil bear which the weight of strength.The curve of Q-S of pile quietloading test also have the character of exponential function law. So the curve of Q-S ofpile quiet loading test also can set up the GM(1,1)model to forecast. Using some dataof an ascertain skyscraper ,set up the GM(1,1)model.Analyzing the S-T curve of the subside,find this curve is similar to the verhulstliving beings growth curve. According to the basic thought of the grey theory, thesystem that the skyscraper, foundation and ground interaction is a grey system, thesubsided data is a grey chromatic numberes of lines. So, seting up verhulstmodel S⁰(t_n) = A/(1+ Be^(at)_n) with the grey theory law in subsiding amount of thewhole course of the skyscraper, namely model of grey verhulstGM (1,1). Use thesubsiding and observing materials of a certain skyscraper of Chongqing , has proved themodel of verhulst GM (1,1) S(t) = 33.33 (1+ 22.45e?0 .01t) , predicted this buildingfinall subside amount is 33.3mm, much smaller than though equivalence frusta amount76.7 mm and elastic theory 188 mm .Because this projectr constructed in dense sand atcobble, there aren't case foundation rigidity, so 33.3 mm is closer to the actualconditions .After 900 days ,the subside is tending to stability since constructing begain.While estimating the subsiding amount finally, should consider the load which the soilshared. Though bury sensor underground can test the pressure which soil beard. The testusing this method of an ascertain high building in chongqing which proved that even inthe dense sand and cobble of Israel, the soil of quaternary period, soil which underBox-piles foundation still plays a role in sharing the top load. The general soil increasesslowly counts with constructing, the soil is not equality, non-linear along the basis levelof strength, generally loading the centre against strength biggest, other ranges are thesame basically in size .Soil can share 4.57% load at least. In divide into 4.57% top loadwhen redesign according to soil count, may save 14 at least, it can make the soil sharetop load fully through reduce is it increase of interval. Test through the quiet load of soil and piles, observer subside, test of soil pressure,deduced that even in the dense sand and cobble of Israel, the soil of quaternary period,soil which under Box-piles foundation still plays a role in sharing the top load.Becausethis kind interaction can give better together-strength to bear the weight, make buildingand whole project subside stability in the experimental period in the course ofconstructing and using.