Experimental Study and Variability Analysis of Strength Parameters in Passive Zone Reinforcement of Soft Foundation Pit
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摘要: 基坑被动区加固是有效的变形控制手段，在软土深基坑工程中已广泛应用，但被动区加固体强度参数及其变异性的试验研究较少。武汉地区某软土深基坑被动区采用三轴水泥土搅拌桩加固，为深入研究被动区加固体强度参数及其变异性，进行原位静（动）力触探试验及室内无侧限抗压强度试验，建立被动区加固体原位测试指标与无侧限抗压强度参数的相关关系，并根据建立的经验公式将连续的原位测试数据转换为无侧限抗压强度值，通过数据统计分析探讨被动区加固体强度参数的变异性及分布规律。研究结果表明：被动区加固体的强度比原状土显著增加，但坑底以下20%水泥掺量的实桩部分相比坑底以上10%水泥掺量的空桩部分的桩身强度增加幅度并不明显；被动区加固体不论是空桩段还是实桩段都具有显著的不均匀性，且空桩段变异系数比实桩段更大；空桩段水泥土强度采用指数分布拟合效果更好，而实桩段水泥土强度则近似满足对数正态分布。Abstract: Passive zone reinforcement is an effective deformation control method, which has been widely used in soft soil deep foundation pit engineering, but there are few reports about the measured strength parameters and its variability analysis of the passive zone reinforcement. Based on a soft clay deep foundation pit in Wuhan area, in-situ cone penetration tests, dynamic penetration tests, and laboratory unconfined compressive strength tests were carried out, and its correlation between the laboratory unconfined compressive strength parameters and in-situ test indexes was established for the passive zone reinforcement. Through the established empirical formula, the continuous in-situ test data were converted into unconfined compressive strength values, and the variability and distribution of strength parameters of the passive zone reinforcement were discussed by statistical analysis. The results showed that there were significant differences between the strength of the passive zone reinforcement and the undisturbed clay, compared with the empty pile with 10% cement content above the bottom of the pit, the strength of the solid pile with 20% cement content below the bottom of the pit was not significantly increased. The strength of the passive zone reinforcement has strong nonuniformity in both empty and solid piles, and the variation coefficient of the empty pile was larger than that of the solid pile. The distribution of cement-soil strength for the empty pile with low cement content was fitted by an exponential distribution, while that of cement-soil strength for the solid pile with high cement content was approximately lognormal.
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Key words:
- passive zone reinforcement /
- cement-soil /
- unconfined compressive strength /
- variability
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表 1 原状土物理力学指标
层号 土层名称
γ/（kN·m−3）Es1-2
/MPa直剪（快剪） 有机质含量/% c/kPa φ/（°） 1-2 素填土 18.0 11 9 1-3 淤泥 16.9 2.3 10 4 3.47 2-1 黏土 17.6 3.4 20 10 2-2 淤泥质土 16.8 2.4 12 5 1.88 2-3 黏土 18.4 4.6 23 12 
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表 2 水泥土的实测物理力学指标
土层
名称γ/(kN·m−3) Es1-2/MPa 直剪（快剪） 无侧限抗压
强度qu/MPac/kPa φ/（°） 空桩段
水泥土13.5～19.8 1.66～16.98 12.0～86.5 3.1～37.9 0.040～1.43 实桩段
水泥土14.1～20.2 3.36～12.19 38.3～121.2 13.7～26.7 0.048～1.05
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表 3 现有文献中经验公式汇总
经验公式 地区 适用土层 公式来源 R=0.2048qc+0.232 广东 软土水泥土 钟献科[8] $ {P}_{{\rm{s}}}=10\times {q}_{{\rm{u}}}\times \dfrac{\sqrt{t}}{\sqrt{90}} $ 上海 软土水泥土 杨龙才等[9] qu=(62.04N10+146)/t0.5 软土水泥土 崔家立[16] R=0.138(N′−3.6)0.5 连云港 软土水泥土 邓小宁等[17] qt=8Nt+162lnt–286 连云港 软土水泥土 刘松玉等[11] qt=0.0034Nt2+0.0035Nt+0.172 武汉 软土水泥土 和礼红等[18] 注：qc为7天静力触探锥尖阻力；R为28天龄期无侧限抗压强度；Ps为 t天静力触探比贯入阻力；qu为90天龄期无侧限抗压强度；qt为t天龄期无侧限抗压强度；t为试验时的成桩龄期；N10为t天龄期的轻便动力触探击数；Nt为t天龄期的标贯击数；N′为7天龄期修正后的标贯击数。
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