過圧密粘土のセン断応力 : 変位特性におよぼす過圧密比の影響(農業工学科)

実験結果から次の点が明らかになった。1)ピーク以後のτ∿D曲線の形状は解析的に次式で表わされる。[numerical formula]ここに, b, cは過圧密比や土性によって決まる定数, τ_f, D_fはピーク強度とそれに対応する変位を示す。2)過圧密状態におけるτ∿Dの挙動は試料の持つ応力履歴によって大きく影響される。すなわち過圧密の程度が高い土ほど, 固結化が進み, 強度の増加とピーク後の強度低下が顕著である。3)ピーク強度と変位の比(τ_f/D_f), ブリトル指数(I_B), 初期変形係数(E_i)等のτ∿D曲線の形状係数と過圧密比とは相関関係が極めて高い。
It is a well-known fact that if an overconsolidated clay is strained beyond failure, its strenght will decrease and finally reach a certain constant value, the ULTIMATE STRENGTH (it is referred to especially as the RESIDUAL STRENGTH under slow drained shear test), which will remain constant for further straining. For the overconsolidated plastic clays the drop in shear strength after failure is very significant. In order to investigate the relation between stress-displacement behaviour after passing the peak i. e. rate of progressive reduction in strength from the peak to the ULTIMATE (or RESIDUAL) condition and degree of overconsolidation, a series of direct shear test has been conducted under each different conditions of overconsolidation ratio (the ratio of preconsolidation stress to effective normal stress, n_p=P_0/σ) respectively for P_0=constant, σ=constant and n_p=constant. From the test results the following points were clarified. 1. The general shape of the stress-displacement curve (τ∿D curve) of the postpeak can be expressed analytically by [numerical formula] where b and c are constant on the overconsolidation ratio and the materials. 2. The stress-displacement behaviour of the state of overconsolidation is greatly dependent on the stress history of the sample-the higher the overconsolidation ratio, the stiffer the soil. 3. The shape factors of the stress-displacement curve, initial tangent modulus (Ei), ratio of stress to displacement at failure (τf/Df) and brittle index (I_B), seem to be well expressed as a function of the overconsolidation ratio.