ESTIMATING RELATIVE DENSITY OF SANDY SOILS
ESTIMATING RELATIVE DENSITY OF SANDY SOILS
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DOI：
10.3208/sandf.46.299
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发表时间：
2006-06
影响因子：
3.7
通讯作者：
M. Hatanaka;Lei Feng
中科院分区：
文献类型：
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作者：
M. Hatanaka;Lei Feng
摘要以Fc≤20%，D50≤1.0 mm, Dmax≤4.75 mm的优质细砂至中砂相对密度样本为样本，研究了基于SPT n值、有效覆盖层应力和土壤级配特征估算砂质土相对密度的3种经验关联的适用性。所有未受干扰的样品均采用原位冷冻法回收。Meyerhof方法（1957）估计的相对密度在实测值的+15%~-45%范围内。Tokimatsu和Yoshimi（1983）对Meyerhof方法（1957）进行了改进，考虑了细粒含量对SPT n值的影响。Tokimatsu和Yoshimi的方法（1983）估计的相对密度在实测值的+25%~-20%的范围内。修正了Meyerhof方法（1957）对相对密度的低估。相反，相对密度的高估比Meyerhof方法更为显著。Kokusho et al.（1983）提出的方法估算的相对密度即使在相对密度大于60%的致密砂中，也在实测值的+20% ~ -35%范围内。Meyerhof的方法（1957）和Kokusho等人（1983）提出的方法有一个共同的缺点，即当SPT n值低于8左右时，它们会极度低估细砂到中砂的相对密度。这些方法在估计相对密度时误差较大。本研究提出了一个简单的经验相关性（Eq.(10)），基于归一化SPT n值N1来估计细砂到中砂的相对密度。在0 ~ 50的范围内，所提出的方法估计的相对密度在N1测量值的+15% ~ -30%的范围内。总体而言，与Meyerhof方法（1957）和Kokusho等人（1983）的方法相比，本文方法估算相对密度的误差更小。基于SPT勺样中未受干扰样品的细粒含量数据，再次将本文提出的方法与前三种方法进行了比较。基于上述数据库，本文方法估计的相对密度在实测值的+15% ~ -10%范围内。从总体上看，该方法在相对密度估计上误差最小。考虑到SPT样品中细粒含量的影响，对提出的方法进行了修正（式（16））。基于细粒含量的改进方法估算的相对密度几乎在实测值的+10% ~ -10%范围内。与以往的三种方法相比，本研究提出的两种经验相关法在估计相对密度时误差较小。所提方法估算的相对密度范围与实测值范围（40% ~ 90%）吻合较好。本研究提出的经验相关性适用于Fc≦20%，D50≦1.0 mm, Dmax≦4.75 mm的细砂至中砂。
ABSTRACT The applicability of three previous empirical correlations proposed for estimating relative density of sandy soils based on the SPT N-value, effective overburden stress and soil gradation characteristics was investigated in the present study by using a data base of relative density obtained from high quality undisturbed samples of fine to medium sand with Fc≦20%, D50≦1.0 mm and Dmax≦4.75 mm. All undisturbed samples were recovered by in-situ freezing method. The relative density estimated by Meyerhof's method (1957) was in the range of +15%~-45% of the measured values. Meyerhof's method (1957) was modified by Tokimatsu and Yoshimi (1983) by considering the effect of fines content on the SPT N-value. The relative density estimated by Tokimatsu and Yoshimi's method (1983) is in the range of +25%~-20% of the measured values. The underestimation of relative density of Meyerhof's method (1957) was modified. On the contrary, the overestimation of relative density is more significant than Meyerhof's method. The relative density estimated by the method proposed by Kokusho et al. (1983) is in the range of +20% to -35% of the measured values even for dense sand with a relative density larger than 60%. Meyerhof's method (1957) and the method proposed by Kokusho et al. (1983) have a common disadvantage that they will extremely underestimate the relative density of fine to medium sand for SPT N-value lower than about 8. The errors in estimation of relative density by these methods are large. A simple empirical correlation (Eq. (10)) was proposed in the present study to estimate the relative density of fine to medium sand based on the normalized SPT N-value, N1. The relative density estimated by the proposed method is in the range of +15% to -30% of the measured values for N1 in the range between 0 and 50. As a whole, the proposed method is less in errors for estimating relative density compared with those estimated by Meyerhof's method (1957) and the method proposed by Kokusho et al. (1983). Based on a data base of undisturbed samples with data of fines content obtained from the SPT spoon samples, the method proposed by the authors is again compared with the three previous methods. The relative density estimated by the proposed method based on the above data base is in the range of +15% to -10% of the measured values. Among four methods, as a whole, the proposed method shows the least errors in estimation of relative density. The proposed method was also modified (Eq. (16)) by taking into account of the effect of fines content of SPT samples. The relative density estimated by the modified method based on the fines content is almost in the range of +10% to -10% of the measured values. Two empirical correlations proposed in the present study are less in errors of estimating relative density compared with three previous methods. The range of relative density estimated by the proposed method is well consistent with the range of the measured values (40% to 90%). The empirical correlations proposed in the present study should be applied to fine to medium sand with Fc≦20%, D50≦1.0 mm and Dmax≦4.75 mm.