University:
Massachusetts Institute of Technology
Course:
1.322 | Soil Behavior
Academic year:

2019
Views:

430

Pages:

39
Author:

razkorak36n

I STRESS-STRAIN-STRENGTH BEHAVIOR OF COHESIONLESS SOILS Subheadings and Content: Drained Shear (σ' = 0) 3.5 3 Components of Strength (Rowe 1962) 7-8 4 Combined Effects of Dr & σ'₁ 9-14 4.1 Overview + Fig 2-4 Plum Sheets A-E 4.2 State Parameters 4.3 Bolton (1986) 4.4 Soil models MIT-SI Undrained Shear : CIUC Effects of σ' etc 2.1 Toyoura Sand Data & MIT-SI Predictions 1 2.2 MIT Data on MFS (Sheets MFS-4 to 10) 5 (ARO project on frozen sands) Undrained Shear: Other Factors 3.1 Inherent Anisotropy (CIUC after Ke S1) 6 3.2 CIU vs CAU, TC, TC' etc 4 Sheets: MFS-4 to 10 Sands I (Drained Shear) Subheadings and Content: Mini-Problem: Questions on Drained Shear of Sands (Rowe) What is the difference (if any) between: a) constant volume (ϕ_cv) b) Can CD/CU tests be used steady state (ϕ_ss) with equal confidence crated state (ϕ_cs) to obtain ϕ_cs/ϕ_ss for φ' = 0? In Rowe's (1962) model of strength components of ϕ': a) What is the physical significance of ϕ'_p and how is it obtained? b) How do ϕ'_p, ϕ'_f may as a f(Ψ) for CI/CD tests? Graph: A graph is present with axes labeled ϕ' and Ψ. ϕ'_p, ϕ'_f, and ϕ'_t are marked on the graph. How does ∂ϕ'/∂log σ'_rt (pressure sensitivity) vary with increasing: a) Dr b) D₅₀ c) Particle crushing strength? What are the main problems in estimating ϕ'_p (TC) for a natural SW-SM sand a) Using correlations with ϕ'? b) Using Bolton's (1986) eqn? For the MIT-S1 model of sand behavior: a) What does it use to replace the VCL of clays and how is this reference line obtained? b) How good is it at predicting for Toyoura sand... (1) The location of the CSL? (2) ϕ'p 1 RD along σ' as f(Dr) compared to Bolton (1986)? 4.2 State Parameter, Ψ (Been & Jefferies 1985; Been et al. 1991) Subheadings and Content: 1. Definition: Ψ = e - e_ss of same τ_oct, σ'_oct, SSL = reference state Positive Ψ → dilative behavior Negative Ψ → contractive behavior 2. Examples of "unique" correlation between Ψ and shear behavior See Sheet C1 for actual correlations Fig. 15: Decreasing Ψ → increasing rate of dilation at peak strength Fig. 16: ... 3. Problems with application in practice a) Slight variation in particle size distribution can have a large effect on location of the SSL (e.g., Sheet C1, Fig. 7 for uniform medium sand with 0, 2, 5% fines, -#200) b) Whether or not drained shear from I & in will produce the same SSL, CSL is still controversial. Sheet C2, Fig. 12 indicates that drained shear with - does not reach SSL (maybe due to non-conforming conditions (shear planes) in test specimens) c) Get marked curvature in CSL at stresses above significant crushing, e.g., Sheet C2, Fig. 8, 11 & 12 Conclusion: Excellent concept (especially for teaching), but difficult to use quantitatively in practice.

Stress-Strain-Strength Behavior of Cohesionless Soils

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