Experimental Study on Mechanical Behavior of Unsaturated Silty Sand in Constant Equivalent Granular Void Ratio
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ORIGINAL PAPER
Experimental Study on Mechanical Behavior of Unsaturated Silty Sand in Constant Equivalent Granular Void Ratio Erfan Chali . Mohammad Maleki
Received: 24 November 2018 / Accepted: 14 August 2020 Springer Nature Switzerland AG 2020
Abstract In this paper effect of fine mineralogy on mechanical behavior of unsaturated silty sand in different fine contents and divers confining pressure has been studied. All samples were molded with constant equivalent granular void ratio well-known parameter already proposed for characterizing silty sand behavior in saturated state. This manner of study allow to investigate also the validity of equivalent granular void ratio concept in unsaturated state. For this purpose, a series of triaxial tests were performed on the sand specimens with different percentages of silt in the undrained saturated (CU) and unsaturated (CW) conditions. The results showed that the material types and aggregate distribution of the fines have enormous effects on the silty sand behavior. In addition, the shear strength in the unsaturated specimens changed as a function of the initial applied matric suction. A fewer performance of equivalent intergranular void ratio in the case of unsaturated state in comparison of saturated states was observed. Keywords Matric suction Silty sand Equivalent intergranular void ratio Fine content
E. Chali M. Maleki (&) Department of Civil Engineering, Bu-Ali Sina University, Hamedan, Iran e-mail: [email protected]
1 Introduction Natural sands usually contain some fines contents. These fines can be either clay or silt. Effect of silt on mechanical behavior of sand has been discussed by a great number of authors in literature (e.g. Kuerbis et al. 1988; Koester 1994; Lade and Yamamuro 1997; Thevanayagam 1998; Polito 1999; Thevanayagam et al. 2002; Xenaki and Athanasopoulos 2003; Bouckovalas et al. 2003; Naeini and Baziar 2004; Yang et al. 2006; Rahman and Lo 2008; Rahman et al. 2012; Nguyen et al. 2015). These studies show that the fines has considerable effects on the sand behavior. So that at a given constant void ratio and confining pressure increase in non-plastic fine up to a certain fine content (known as threshold fine content) undrained shear strength of soil deceases. However, adding fines content beyond threshold value, an increase in undrained shear strength is observed. Mitchell (1976) paid attention for the first time to the effect of the inactive fine role in transferring the forces applied on the sand structure. On this basis an index known as skeleton void ratio was used for characterizing sand containing low values of nonplastic fine by several authors (e.g. Kuerbis et al. 1988; Georgiannou et al. 1990; Pitman et al. 1994; Thevanayagam 1998). The skeleton void ratio has the following expression:
E. Chali e-mail: [email protected]
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Geotech Geol Eng
eg ¼
e þ fc 1 fc
ð1Þ
In which e is the soil void ratio and fc is the fines content. For a given constant skeleton void ratio,
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