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Direct shear properties of a compacted soil with known stress history
Published in H. Rahardjo, D.G. Toll, E.C. Leong, Unsaturated Soils for Asia, 2020
The stress state variables for an unsaturated, in situ profile consist of the net total stress and matric suction. Two stress variables in terms of effective stresses control the behavior of the unsaturated soil. The stress history of a soil is commonly determines using a one-dimensional oedometer test. Predicting of the stress history of an unsaturated soil is difficult. Stress history is defined in terms of the preconsolidation pressure and current overburden effective stress in saturated soils. It is difficult to define over-consolidation ratio for natural unsaturated soils or artificially compacted unsaturated soils. This study used total stress ratio instead of overconsolidation ratio for a compacted unsaturated silty soil. Total stress ratio is defined as the ratio of compaction pressure to current confining pressure. As total stress ratio not included matric suction, total stress ratio is completely not the expression of present of stress states of unsaturated soils.
Consolidation settlement and analysis
Published in Buddhima Indraratna, Ana Heitor, Jayan S. Vinod, Geotechnical Problems and Solutions, 2020
Buddhima Indraratna, Ana Heitor, Jayan S. Vinod
Preconsolidation pressure is defined as the maximum pressure the soil has experienced in the past. A careful evaluation of preconsolidation pressure is important for the computation of consolidation settlement. An estimate on the preconsolidation pressure can be obtained from the graphical procedure proposed by Casagrande (1936). The pressure can also be used as a limiting pressure for controlling long term settlements in overconsolidated soils.
Soil Mechanics
Published in P.K. Jayasree, K Balan, V Rani, Practical Civil Engineering, 2021
P.K. Jayasree, K Balan, V Rani
Preconsolidated clay or overconsolidated clay: A clay is said to be precompressed or preconsolidated or overconsolidated if it has ever been subjected to a pressure in excess of its present overburden pressure. The temporary overburden pressure to which a soil has been subjected and under which it go consolidated is known as preconsolidation pressure.
Tunnelling-induced surface settlement: on the choice of soil constitutive model
Published in European Journal of Environmental and Civil Engineering, 2021
Sara Rachdi, Emad Jahangir, Michel Tijani, Ahmed Rouabhi
An initial preconsolidation pressure has to be specified for the considered soil models. It was determined from the overconsolidation ratio defined for the structure level as: where is the in situ vertical effective stress. Bangkok stiff clay represents an overconsolidated clay with an estimated overconsolidation ratio of approximately 4 (Sayed, 2018). In Paris, the most challenging sections are going to be excavated in an overconsolidated clay with an OCR between 3.4 and 6 (Vuillaume & Jacquard, 2018) under the Seine river. The reference simulations were then performed with OCR = 4. The average void ratio of 1.2 reported in (Surarak et al., 2012) was adopted. The initial effective vertical and horizontal stress were calculated through a unit weight of the saturated clay γ = 20 kN/m3 with earth gravity g = 9.8 m/s2 and initial horizontal to vertical effective stress ratio Hence, the initial stress state corresponds to an isotropic geostatic stress state for the reference simulation.
Experimental comparison of electroosmotic consolidation of wenzhou dredged clay sediment using intermittent current and polarity reversal
Published in Marine Georesources & Geotechnology, 2018
Hongtao Fu, Ziquan Fang, Jun Wang, Jinchun Chai, Yuanqiang Cai, Xueyu Geng, Jinqiang Jin, Fangyi Jin
The use of polarity reversal for soil improvement was first proposed by Wan and Mitchell (1976), who obtained more uniformly distributed water content and higher shear strength by reversing polarities. Lo et al. (1991) conducted a field pilot test and demonstrated that pumping at the cathode was eliminated by the appropriate design of electrodes and polarity reversal. The increase in soil shear strength was demonstrated as the expansion of the effective strength envelope and increase in the preconsolidation pressure. Moreover, Gray and Somogyi (1977) believed that polarity reversal exhibited predominate effects in restricting the soil temperature as well as potential loss. However, the experimental results of Ou et al. (2009), Kaniraj and Yee (2011), and Tao et al. (2015) obtained with Taiwan clay, an organic soil from the central Sarawak region of Malaysia, and Hangzhou clay, respectively, demonstrated the inferior EO effects of polarity reversal over continuous conduction. Therefore, the validity of polarity reversal in improving EO efficiency is still controversial because the role of polarity reversal remains unclear.