| Xiang-Liou basin is a DiWa basin, large areas of which is covered with Red beds soft rock composed of argillaceous gravellystone, silty mudstone and mudstone with the features of weak diagenetic process and susceptiable to weathering and easily be disingtegrated. This rock is widespread during Cretaceous in Changsha-Zhuzhou-Xiangtan area. In recent years, rock-socket piles are widely used for bridges and high-rise buildings and skyscraper in Red beds, but there are few integrated test reports on it, which restrain people's full understanding to rock-socket piles' bearing mechanism. To know deeply the engineering property of Red beds is precondition of using it effectively,So researching on the engineering characteristics and bearing behavior of piles socketed in Red beds are of great significance for the planing and construction of Chang-Zhu-tan economic integration.Based on analyzing and referring literatures from home and abroad, this thesis conludes the geological condition and study actuality of Red beds in Xiang-Liou basin;Theoretical analysis and study to its physical and mechanical property had been made with a series of trials;Problems such as bearing behavior and mechanism of piles socketed in Red beds had been studied by employing field test with numerical simulation too.Some conclusions have been corned to as follows:(1) The development characteristics and spatial-temproal variability characters of Cretaceous red layer in Xiang-Liou basin have been researched focus on the distribution, the period stratum and rock type classification, the progress of geological environment. It has presented that the Red bed's project intensity mainly influenced by follow geology environmental condition-basin structure, lithology characteristics, stratum features, water medium physical-chemistry condition, geologic structure, the improving methods are put forward too.(2) Problems such as determinating the wreathing belt, the bearing capacity, the compressive strength and evaluating the properties for construcation meterials have been researched with a series of tests including X-ray technique, permeability test, expansion test, disintegration test, thermal conductivity test, compression test, direct shear test, wave velocity measurement, load test, high pressure pressurement test(PMT). On the basis of laboratory and in-situ test data, the correlation equations are established for characteristic parameters of dynamic and static properties of Red beds with synthetical analysis of multi-parameter, much efficient information about rock werthering and strength is achieved in this paper.(3) The vertical static load test is adopted to investigate 4 large-diameter rock-socket pile in Red layer, in which the variation of axis force in piles is measured by sliding micrometer and strain gauges. Hence, the bearing capacity behavior, load transfer mechanism, the lateral friction and end bearing are researched in this paper. According to the test results, the load transfer performance of rock-socket pile is similar to that of end-bearing friction pile, the Q-s curves are slowly varying. The pile length, covering and soil around pile are all important to the load transfer mechanism and action of lateral friction. For the natural structure of red layer, the critical displacements of piles are 2～6mm and the tested result is much higher than those recommended by the Specifications, which indicates that the shaft resistance is strengthened, while lateral friction and end bearing can not display simultaneously.(4) The developments about side resistance of socketed pile in weak rock and responsing mechanism of side resistance are presented in detail. Testing study is made on the lateral resistance of socketed pile in argillaceous siltstone, which includes straight shear test, side resistance test in rock, high pressure pressurement test (PMT) and stress detector. Through testing and analysis, it is found that the side resistance of red beds evaluated with Technical Code for Building Pile Foundation (JGJ94-94) is quite lower. And then the difference and influence factors for test results have been discussed also. An improved parameter formula is given to calculate the lateral resistance of embedded section with uniaxial compressive strength standard value under natural moisture, and it's reduced coefficient is 0.15 to 0.30. The results is deserved to be applied to practical problems such as those on soft rocks. (5)The mechanism of bearing at the tip of rock-socket pile is researched with theories of destroying relation to rock. The available methods of calculationin specification are compared and the difference between the end resistances determined by different mithods are studied. The limitation of the way recommanded by the current Code in measuring the end capacity of rock-socketed piles in Red beds are demonstrated firstly, and then on the basis of analysis to all kinds of influential factors and summarization to the testing data, the load transfer function and a new formulae to estimate end capacity are put forward by means of linear fiting.(6)A review on the research of the bearing behavior of rock-socketed pile is taken, and a brief introduction is made about theories and design mothods. An improved formula is given to calculate the total resistence of embedded section, which is comparatively agree with the practice and is instructive for design and deep study. With considering diameter, length and strength of rock at the same time, orthogonal experimental design and sensitivity analysis are used in the design of socketed pile in Red beds to make it both reliable and economical.(7)Based on the static load test of practical engineerimg, the pile-soil-rock interaction of rock-socket pile in Red bed were simulated by using finite element method. The influence factors of the ultimate capacityof rock-socketded pile such as the diameter of pile, the modenm of pile, the property of superstratum soils and rock in base, the length of rock socketed are analyzed, the results of analysis can be used in the design and theory resarch.
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