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TPMCorrelationPhiNcorr - ¢ ’{deg 4 151 0(fl qc/a’y1...

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Unformatted text preview: ¢ ’ {deg} 4 151 0 (fl qc /a’y1,/ 00/0 Comp/AW by Roby/son and Campane/la {/983) 4c, = 4,, K/OO/av'a/ [/2 a-Jo /'n /rPa 6 8/0. 40 4c/ WP!” 20 60 Figure 19.5 Empirical correlation between friction angle dp’ of sands and normalized push cone tip penetration resistance. ory (de Beer 1948, Meyerhof 1961, Janbu and Senneset 1974, Durgunoglu and Mitchell 1975, Mitchell and Keaveny 1986). Data compiled by Robertson and Campa- nella (1983) are plotted in terms of go, in Fig. 19.5. The correlation is mainly applicable to normally consolidated young sand deposits composed of quartz and feldspars. It underestimates by several degrees the friction angle of compressible carbonate sands with crushable particles, and it overestimates by several degrees the friction angle of overconsolidated or aged sands with values of of", higher than those in normally consolidated young deposits (Schmertmann 1975). The correlation between (13' and (N060 in Fig. 19.6 is based on various proposals for the relationship between d)’ and standard penetration blow count N (Peck et a1. 1953, De Mello 1971, Schmertmann 1975, Stroud 1988). It underestimates d)’ for calcareous sands with crushable (Stroud 1988). Figure 19.6 also includes relations between (b’ and (N060 determined from the empirical correlation in Fig. 19.6 together with qC/Nm values of 400 and 500 kPa for sand deposits. The two different empirical correlations between d)’ and qc and between d)’ and N60, which have originated from separate databases, lead to comparable values of d)’ for sands. 19.2 Drained Shear Strength of Cohesive Soils The drained shear strength of normally consolidated cohe- sive soils is defined by the friction angle (b’, as follows: s = 0’ tan cb’ (19.6) The effective normal stress 0" on the plane of shear is determined by the total normal stress and the equilibrium particles and overestimates d)’ for overconsolidated sands . Coarse Era/fled Sam/s ¢’ (deg) ~F/‘ne GIG/fled Sands 25 20 40 (IV, lgo 50 Figure 19.6 Empirical correlation between friction angle d)’ of sands and normalized standard penetration blowcount. hydrostatic or steady porewater pressure condition. The friction angle d)’, which corresponds to a more or less random arrangement of particles, is mainly a function of the clay mineral content and clay mineralogy of the composition. Values of d)’ for the full range of clay com- positions are shown in Fig. 19.7. Among the pure clay minerals, sodium montmorillonite (consisting of filmy particles) has the lowest value of d)’, whereas attapulgite (with interlocking fibers) exhibits the highest value. Typi— cal values-of 43’ for soft clay, stiff clay, and shale constit— uents are in the range of 25° to 35°, 20° to 35°, and 15° to 35°,-respectively. The water—filled and rough surface— ...
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