Statistical Evaluation of Sleeve Friction to Cone Resistance Ratio in Coarse-Grained Soils

The investigation of soil is a particularly important stage of structural design. Cone penetration tests (CPTs) are the most common soil investigation techniques. The results of these tests provide information about the values of cone resistance (qc) and sleeve friction (fs), which correspond to depth. Previous studies have shown that the ratio of sleeve friction to cone resistance depends on the particle size distribution in soil and its use for soil classification. Unfortunately, as an analysis of the literature shows, there is no such classification for coarse-grained soils. This paper presents statistically significant differences in the ratio of fs to qc in coarse-grained soils. Based on the research performed, the proposed coefficients depend on the classification of coarse-grained soils with respect to the size of the soil particles. The data investigated were obtained from study reports on 35 sites (5934 tests) at which the main type of soil was coarse-grained and contained different sizes of particles. Following a statistical analysis, five groups of tested coarse-grained soils, silty fine sand, clayey fine sand, fine sand, medium sand and gravelly coarse sand together with gravel, are derived. The analysed data show statistically significant differences in the ratio of fs to qc considering this particular type of soil. A ratio of fs to qc with a probability of 95% is proposed for sandy soils. The values for silty fine sand, clayey fine sand, fine sand, medium sand and gravelly coarse sand mixed with gravel are 0.009459, 0.010982, 0.009268, 0.008001 and 0.006741, respectively. A linear relationship between the fs and qc indexes is also suggested.