Experimental study on bearing capacity of moderately weathered mudstone in Chengdu area
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摘要: 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1500～2500 kPa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。Abstract: The moderately weathered mudstones in Chengdu area are widely developed. The code DB51T5026 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.
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图 5 p–s曲线（以02深井300 mm承压板为例）
Figure 5. p–s curves (deep well No. 2, plate diameter 300 mm)
表 1 中等风化泥岩物理力学性质统计表
Table 1 Physical and mechanical properties of rock
统计指标 天然密度/(g·cm-3) 单轴抗压强度/MPa 黏聚力/MPa 内摩擦角/(°) 天然状态 饱和状态 天然状态 饱和状态 天然状态 饱和状态 最大值 2.62 9.67 8.20 1.2 0.85 40.1 38.6 最小值 2.30 2.71 1.56 0.4 0.23 33.7 31.4 平均值 2.48 6.00 3.88 0.8 0.49 37.9 35.5 样本容量 141 51 39 28 17 28 17 
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表 2 岩基载荷试验与单轴抗压强度试验对比
Table 2 Comparison between load tests and uniaxial compressive strength tests
工程名称 工程地点 frk/MPa fa/kPa ψ 停载位移/mm 点数 隆鑫 成华区 4.00 2044 0.51 5.420 3 润都科技 成华区 4.00 1981 0.49 6.760 3 蓉华·上林 成华区 3.05 1841 0.60 3.990 8 1773 0.58 9.730 1861 0.61 8.680 科创中心 成华区 5.00 2263 0.45 18.370 8 东方荟 锦江区 5.00 2157 0.43 3.640 4 东大街项目 锦江区 3.07 1900 0.62 3.520 3 仁恒置地广场 锦江区 3.43 1990 0.58 — 2 航天科技大厦 锦江区 6.00 2880 0.48 — 3 西部国金 锦江区 1.48 843 0.57 10.410 3 融御大楼 锦江区 7.30 3010 0.41 0.562 3 海桐三期 锦江区 7.90 2959 0.37 8.300 4 滨江30号地块 高新区 6.80 2740 0.40 10.700 3 半岛城邦 高新区 4.50 2021 0.45 6.600 9 龙湖世纪城 高新区 2.79 1800 0.65 33.190 8 川大科技园 双流区 3.92 1894 0.48 5.290 3 水电·云立方 龙泉驿 5.98 2400 0.40 5.500 3 视高天府公园 天府新区 6.48 2400 0.37 7.320 3 学府城 天府新区 4.99 2290 0.46 1.420 4 2266 0.45 2.720 2 仁中风华一期 天府新区 5.64 2400 0.43 5.980 6 驿都水岸丽园 天府新区 5.58 2524 0.45 17.500 1 5.00 2162 0.43 18.630 2 东方希望天祥 武侯区 4.39 2000 0.50 1.160 3 海洋乐园 武侯区 6.55 2500 0.38 4.260 6 中邮金融中心 武侯区 5.74 2400 0.42 2.200 3 田园晶品 新都区 3.1 1697 0.55 3.720 6 注： frk为岩石天然单轴抗压强度标准值；fa为承载力特征值；ψ为折减系数。
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表 3 折减系数和承载力特征值建议值
Table 3 Recommended values of reduction coefficient and characteristic value of bearing capacity
frk/MPa ψ fa/kPa 说明 <2 0.7 500~1400 符号意义同表2,岩石单轴抗压强度为天然状态 2~4 0.5~0.7 1400~2000 4~6 0.4~0.5 2000~2400 6~8 0.37~0.4 2400~3000 >8 0.37 >3000
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表 4 研究区中等风化泥岩承载力特征值试验值统计表（承压板载荷试验）
Table 4 In-suit test values of bearing capacity of moderately weathered mudstone in study area
试验点号
竖井编号承压板直径D/mm 原位试验 极限值/3对应荷载fa/kPa 岩体完整性指数Kv 最大加载量/kPa 比例界限对应荷载/kPa 终止条件 裂缝情况 SJ01
（459.06 m）300 9000 3000 趋近试验装置系统极限 无 2400 0.46 500 9600 2400 位移持续增大,不能稳定 无 2400 0.46 800 6300 2700 沉降增大,大于前一级沉降量的5倍 有 2300 0.43 SJ02
（451.15 m）300 7800 2400 变形不能保持稳定 有 2100 0.39 500 10800 2400 变形不能保持稳定 无 2000 0.39 800 11700 2700 沉降增大,大于前一级沉降量的2倍 有 2100 0.39 SJ03
（447.54 m）300 11800 3600 趋近试验装置系统极限 有 2800 0.49 500 9600 3000 趋近试验装置系统极限 有 3000 0.50 800 10800 3600 支硐上壁无法提供足够反力 无 2700 0.43
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表 5 修正折减系数法验证结果
Table 5 Test results of modified reduction coefficient method
竖井编号 编号 fa/kPa frk/MPa 平均frk/MPa ψ 计算值 差异/% SJ01 1 2400 4.9 5.96 0.40 2384 0.6 2 5.8 3 7.19 SJ02 1 2100 3.47 4 0.50 2000 4.7 2 3.78 3 4.39 SJ03 1 2800 6.89 7.1 0.39 2769 1.1 2 8.31 3 8.41
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表 6 旁压试验结果统计表
Table 6 Results of pressuremeter tests
钻孔编号 测试深度/m Pf/kPa P0/kPa fa/kPa 钻孔波速/(m·s-1) 岩体完整性指数Kv JK04 28.5 3002.4 625.2 2377.2 2465 0.380 JK03 21.0 1399.5 350.0 1049.5 1873 0.231 JK10 20.0 1294.2 310.5 983.7 2023 0.256 JK12 13.0 1495.5 311.2 1184.3 2160 0.292 JK12 20.0 2670.0 698.5 1971.5 2204 0.304 JK14 28.0 3753.0 850.6 2902.4 2912 0.507 TL01 26.5 3790.2 849.6 2940.6 2445 0.414 TL03 18.5 4085.1 1120.3 2964.8 2754 0.530 TL05 28.0 2828.4 475.6 2352.8 2542 0.447 TL11 20.5 3715.9 850.6 2865.3 3013 0.469 TL13 16.5 3342.3 942.3 2400.0 2555 0.452 TL13 23.0 2209.1 487.2 1721.9 2241 0.348 TL14 17.5 2300.5 422.1 1878.4 2613 0.473 TL16 14.5 2489.0 475.6 2013.4 2178 0.296 TL16 20.5 2737.9 475.6 2262.3 2824 0.498 TL18 23.0 2590.6 432.2 2158.4 2523 0.441 TL22 23.0 2856.7 511.2 2345.5 2930 0.415 TL25 24.5 2707.0 530.1 2176.9 2347 0.381 TL25 26.0 4773.5 681.2 4092.3 3094 0.663 TL35 23.0 3032.5 625.2 2407.3 2659 0.490 TL37 18.0 2494.4 550.0 1944.4 2690 0.501
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