Residual strength of softened Shimajiri mudstone (Department of Agricultural Engineering)

(1)すべり面付近の新鮮軟化泥岩の圧密降伏応力はPy=10^/cm^2前後にある。(2)軟化泥岩の繰返しセン断試験結果からピーク強度定数はCdf=1.20∿1.55^/cm^2,φdf=19∿22°, 残留強度定数はCdr=0,φdr=17∿19°の範囲にある。(3)セン断破壊面が十分発達した自然分離面ではCdr=0,φdr=17°, 作成分離面ではCdr=0,φdr=15°となる。(4)軟化泥岩のブリトル指数は, σ_n=1∿5^/cm^2に対しおよそI_B=80∿50%となり, Py/σ_nとの関係ではI_B=44.2log Py/σ_n+32.5が成り立つ。(5)完全軟化粘土の正規圧密セン断から得られたφ_Nf=23°, φ_Nr=19°は分離面で求めたφdrよりも大きめである。Drained shear tests were performed with shear box on intact softened mudstone, fully-softened clay, natural joint, and specimen with pre-cut plane. The following results have been obtained : 1. The consolidation yield stress of intact softened mudstone is about 10kg/(cm)^2. 2. Residual strength was determined with the common procedure of reversal shear tests. After 5-cycle shear tests no further reduction of strength occurred in the intact softened mudstone. Consequently the tests were not carried further than 5-cycles. 3. The shear tests on the intact softened mudstone show the peak strength parameters of Cdf=1.20-1.55kg/(cm)^2 and φdf=19-22°, and the residual strength parameters of Cdr=0 and φdr=17-19°. 4. The displacement necessary to reach the residual strength along natural joint and precut plane of specimen is smaller than that of intact sample : a single cycle of reversal shear test is sufficient to reduce the strength to a value very near to the residual one. 5. The shear tests on the natural joint and the specimen with pre-cut plane show the residual strength parameters of Cdr=0 and φdr=17°, and Cdr=0 and φdr=15°, respectively. 6. The brittleness index of the intact softened mudstone ranges from 0.8 to 0.5 as σ'_n changes from 1 to 5kg/(cm)^2,and the index is related to Py/σ'_n as follows : I_B=44.2log Py/σ'_n+32.5. 7. The friction angles of fully-softened clay are slightly larger than those along the joint and pre-cut plane