成都地区中等风化泥岩地基承载力取值试验研究

Experimental study on bearing capacity of moderately weathered mudstone in Chengdu area

成都地区分布着俗称"川中红层"的中等风化泥岩,规范DB51T5026建议此类泥岩地基承载力特征值fa按岩石单轴抗压强度frk折减法确定,建议取值500~1000 kPa,而实践证明计算方法合宜性差且建议值偏低,但是更为合理的取值研究至今鲜有突破。通过对24个场地约100个原位平板载荷试验与同条件岩石单轴抗压强度试验工程案例进行对比分析,讨论了成都地区中等风化泥岩fa计算公式中ψ值取值及其与fa的相关关系。然后,依托成都高新区在建的某超高层建筑项目,进一步联合原位平板载荷试验(9组)和旁压试验(17孔),探讨了中等风化泥岩地基承载力取值影响因素及旁压实施的可行性。研究结果表明:成都地区中等风化泥岩地基承载力特征值fa普遍在1500~2500k Pa区间,折减系数呈现出随单轴抗压强度增加而递减的趋势,一般为0.37~0.7;对于相似性状的泥岩,平板载荷试验、钻孔旁压试验确定的泥岩fa可互为印证,试验值受承压板直径影响不显著。研究成果建议了成都地区中等风化泥岩地基承载力取值,同时提出了以单轴抗压强度或旁压试验结果作为设计依据的建议,实践证明其具有较强的适用性,对充分发挥红层软岩承载力具有一定的工程意义。

The moderately weathered mudstones in Chengdu area are widely developed.The code DB51 T5026 recommends that the characteristic value of bearing capacity is 500~1000 kPa,which is determined by the reduction method for uniaxial compressive strength of rock.However,the engineering practice proves that the proposed value is low,but there have been few breakthroughs in its researches.We discuss the value of reduction factor and its correlation with fa for the moderately weathered mudstone in Chengdu area,based on the comparative analysis of 24 sites of in-situ load tests and uniaxial compressive strength tests.Furthermore,based on a super high-rise building project under construction in the High-tech Zone of Chengdu,the bearing capacity of the mudstone foundation fa is determined by using the bearing plate tests and the pressuremeter tests.The results show that the values of fa determined by the tests are 1500~2500 kPa.The reduction coefficient of uniaxial compressive strength from high to low can be 0.37~0.7.For the mudstones with the same character,the diameter of the bearing plate has no significant effect on fa;and the values of fa determined by the bearing plate tests and the pressuremeter tests are very similar.The research results put forward the value of bearing capacity of moderately weathered Jurassic mudstone in Chengdu area,and a fast and economic estimation method to determine the characteristic value of bearing capacity of this kind of mudstone foundation.At the same time,the research results have a certain engineering value for giving full play to the bearing capacity of red bed soft rock.