红层软岩变形特性及基床系数取值试验研究

Experimental study on deformation characteristics and coefficient of subgrade reaction of red mudstone

岩体变形特性及基床系数与基础内力、最终变形量和变形的均匀性直接相关,合理确定基床系数值对高层特别是超高层建筑至关重要。以成都市某超高层建筑论证为依托,针对建筑物持力层中风化泥质软岩,在井下平洞内进行不同压板尺寸和形状的平板载荷试验,并取得原位试样进行室内岩块单轴抗压强度、常规三轴压缩试验和直接剪切试验,根据室内及原位试验资料分析了岩体单轴抗压强度、弹性模量、承压板尺寸与基床系数的关系。结果表明:地基基床系数具有随地基岩石单轴抗压强度增加而增加的趋势;较小承压板试验数据离散性较大,较大压板试验数据离散性较小;如果红层软岩基床系数按照规范建议的黏土或砂土经验公式进行修正,会引起较大误差;红层软岩(中等风化泥岩)地基的基床系数与载荷板尺寸间呈双曲线型经验关系,据此建议对建筑物红层软岩地基基床系数进行修正;对红层软岩采用500 mm方形承压板试验获取的基床系数离散性较小。

The deformation characteristics of rock mass and the coefficient of subgrade reaction are directly related to the internal force,final deformation and deformation uniformity of foundation.Determination of reasonable coefficient of subgrade reaction is important for high-rise buildings,especially super high-rise buildings.Taken a super-high-rise building in Chengdu as example,plate loading tests of red-bed soft rock foundation with different plate sizes and shapes were carried out.Besides,the uniaxial compressive strength test(UCS),conventional triaxial compression test and direct shear test of red-bed mudstone were carried out.Based on the results of laboratory and in-situ test,the relationship between UCS,elastic modulus,bearing plate size and coefficient of subgrade reaction were analyzed.The results show that the coefficient of subgrade reaction has a tendency to increase with UCS of rock,and the smaller the bearing plate size is,the more discrete test data will be obtained.The coefficient of subgrade reaction of red-bed mudstone obtained by 500 mm square bearing plate test is recommended.It is found that the coefficient of subgrade reaction of red-bed mudstone layer has a hyperbolic empirical relationship with the plate size.If the coefficient of subgrade reaction of red-bed mudstone layer is modified according to the empirical formula of clay or sand recommended by the code,it will cause a large error.Therefore,it is suggested that the coefficient of subgrade reaction is modified based on the hyperbolic empirical relationship.