Recompacted completely decomposed granite (CDG) has been relatively well studied in literature. But soil in a natural environment may have some degree of true cohesion, which could be formed through cementation and ageing. To investigate influence of weak cementation on loose CDG behavior, 1% of Portland cement was added to recompacted samples for consolidated undrained (CU) and consolidated drained (CD) tests....[ Read more ]

Recompacted completely decomposed granite (CDG) has been relatively well studied in literature. But soil in a natural environment may have some degree of true cohesion, which could be formed through cementation and ageing. To investigate influence of weak cementation on loose CDG behavior, 1% of Portland cement was added to recompacted samples for consolidated undrained (CU) and consolidated drained (CD) tests.

Influence of artificial weak cementation on static liquefaction of loose CDG was investigated by CU tests. For recompacted CDG specimens with an initial void ratio of 1.0 (a commonly reported in-situ value), substantial wetting collapse was observed during a saturation process. For cemented CDG specimens with the same initial void ratio, no significant volume reduction was observed. Post-yield gradient of consolidation curve (λ_iso=0.170) for uncemented CDG was lower than that 0.308 of cemented one. During undrained shear, both uncemented and cemented CDG showed strain softening behavior with the latter one showing more brittleness than the former. As cementation could increase static liquefaction resistance, mobilized instability friction angle ∅'_inst=22°-29° for uncemented CDG was lower than that 24°-40° for cemented CDG. A new parameter named as pre-yield state parameter is introduced to describe static liquefaction behavior of a cemented soil specimen whose initial state lies within a yield point. State parameter (Been and Jefferies 1985) is used for initial state that falls beyond yield point. Two important static liquefaction parameters: liquefaction potential index and stress ratio at peak point could be expressed in terms of the pre-yield state parameter and the state parameter. The location of instability line (IL) in e-logp' space of both uncemented and cemented CDG may be determined by an OCR value. All ILs seem to be parallel with NCL.

Based on results from CD tests, both uncemented and cemented CDG showed strain hardening behavior. Cemented loose CDG was less contractive than that of uncemented one initially but this initial restrained contraction was released after yield and led to a more significant contraction than an uncemented soil. From both CU and CD tests, it was found that ∅'_cs, for both uncemented and cemented CDG fell in the same range (40°±20°). However critical state line (CSL) for uncemented and cemented CDG showed clear difference in e- Logp' space and it shifted rightward as a result of cementation. Gradient of CSL (λ_c=0.072) for cemented CDG was larger than that (λ_u= 0.04 1 ) for uncemented one.