| Karst is a geographical phenomenon caused by the long-term corrosion of carbonates rocks by underground water. Karst should be a trouble for the underground part of construction and designation of our infrastructure. As wide spread in China,many provinces will meet these problems, such as Yunnan and Guizhou where the solvable carbonates rocks exist everywhere. As to Gangxi province, this phenomenon is even treated as a resources of touring. The same question comes to Jiangxi, mainly in Shanggao, Pingxiang and Yichun. Problems come into birth in bridge and civil construction because its over-active.Jiangxi is a less-developed region of central China, its infrastructrure construction is still to be completed. The construction scale of freeway, railway and urban bridges will increase rapidly in recent years, and it sould be made clear that the construction of roads will be more likely to occur above caves. Therefore it is not illustrated clearly in the codes about how the carrying capability of piles in karst areas is calculated. That is saying we can only find a conventional instead of special formulation about rock-socketed-pile in our codes, which is unreasonable to a controversy karst area.To give a guidance to the designation of bridge substructrure, and to build a reliable basis for the calculation of carrying ability of piles above caves, the research of this area should be elevated to a general, formular level.Basing on the karst characteristics in Jiangxi, this article discussed some questions about rock-socketed-pile in karst areas, the main contains are as below:(1)Detailed statistics of the geography features under bridges of a freeway in construction in Jiangxi, and summary about the karst condition in that area;(2)Discussion of the principle of the transferance of rock-socketed-pile and the condition for its break;(3)Choosing expanded Drucker-Prager model as the constitutive model of rock and build a simulation of rock-socketed-pile with ABAQUS, a finite element software.(4)Numerical analysis about the susceptibility of some cave parameters, theresults are as follow: a) piles embedded in roofs of cave break in two ways:destruction from the top caused by the compress and destruction from the bottom caused by the tensile, if the edge of the pile and the cave approach each other, damage also can be easily caused by shear stress; b) roofs of caves in different height share a similar carrying capability, but the horizontal size of the cave seem to have apparent impact on carrying capability; c) if the thickness of roof is small(below 4m), the embedded depth should be as small as well, if the thickness is between 5m and 8m,the embedded length of 0.5~1.0m seem to be suitable; d) the bear capability can be calculated similarly in a fomulation, which is tried to fit in.(5)Giving some advises about construction and designation of bridges in karst areas. |
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