Study On Bearing Capacity Of Red Weathered Argillaceous Siltstone Foundation In Jiangxi Province

With the vigorous development of engineering construction in Jiangxi Province,more and more buildings,bridges and other engineering projects choose typical weathered red layer as their foundation bearing layer.Up to now,there is no systematic and specialized study on the layered evaluation of the weathering degree of the typical argillaceous siltstone red layer in Jiangxi Province and the determination of the bearing capacity of each weathered layer.As a result,the bearing capacity of the argillaceous siltstone weathering layer,which is widely used as the bearing layer of buildings in the current engineering practice is too conservative,and its natural sufficient bearing resources have not been fully utilized,causing great waste.Therefore,carrying out layered evaluation of weathered argillaceous siltstone and research on bearing characteristics of each weathered layer are important research topics that are closely combined with engineering practice and are actually required for production.Based on domestic and foreign literature and site surveys,collection and statistics of a large number of red bed site investigation data,comprehensive utilization of engineering hydrogeology,indoor and outdoor geotechnical tests,mathematical statistics,and numerical simulation,etc.,with Cretaceous argillaceous siltstone as the research focus,the applicability of the existing foundation bearing capacity determination method to various argillaceous sandstone weathered layers is compared and analyzed.The research results have certain reference value for guiding engineering practice and theoretical research,and enrich the regional soft rock engineering geological theory and engineering practice.Specific work has been carried out in the following aspects:1.Based on the investigation of the geological conditions of the red layer of typical Cretaceous argillaceous siltstone,the applicability of quantitative indexes,i.e.point load strength,SPT and heavy dynamic penetration strikes and elastic wave velocity,in the layered evaluation of the weathering degree of argillaceous siltstone is analysed through tests and mathematical statistics.Take samples to carry out the basic property test and triaxial test of Cretaceous argillaceous siltstone,analyse its strength,deformation,water-physical property and other characteristics;the triaxial test results show that water has obvious degradation effect on the cohesive of remoulded argillaceous siltstone,and the cohesive decreases continuously with the increase of water content under the same degree of compaction;analyse the static disintegration phenomenon of argillaceous siltstone and the change characteristics of the form and particle size of the disintegrating substance.The disintegration resistance index decreased exponentially with the increase of disintegration cycles.2.With the help of numerical simulation and reference to regional stratum conditions,the homogeneous and heterogeneous foundation models are established for parametric analysis.The influence of shear strength index,deformation parameter and foundation width on the bearing characteristics of the foundation is discussed.The error and applicability of different methods to evaluate the bearing capacity of the foundation under different working conditions are compared and analysed,The load settlement curve obtained by numerical simulation is basically consistent with the characteristics of corresponding failure mode。3.The bearing capacity of weathered argillaceous siltstone foundation determined by different methods is compared and analysed.Based on the practice of engineering investigation,a large number of in-situ test results of different weathered zones of Cretaceous argillaceous siltstone in Ganzhou-Fuzhou and other areas are statistically analysed,and the regional statistical relationship of f_ak-N(or N_63.5)are preliminarily fitted.According to the formula:f_ak=15.63N+26.63、f_ak=24.30N_63.5+28.55,the bearing capacity of the corresponding argillaceous siltstone weathering layer can be evaluated according to the in-situ penetration strikes.The reduction coefficient value of moderately weathered argillaceous siltstone is calculated according to the reduction of saturated and natural uniaxial compressive strength.The statistical average value of the reduction coefficient is 0.56 and 0.43 respectively,which are close to the upper limit 0.5 of the reduction coefficient value of"0.2-0.5 for relatively complete rock mass"in the code.