Updated 21 Feb. 2010
The suction-controlled Direct Shear Test is an advanced laboratory teaing method to study the shear strength of unsaturated soils as affected by the soil suction. Although initially considered as a research laboratory tool, suction-controlled direct shear test is increasingly being used in the geotechnical engineering practice to investigate the shear strength of unsaturated soils.
Soils in many cases are unsaturated in their natural state. It means that the pores are filled not only with water (liquid) but also partly with air (gas). The co-existence of the these two phases in unsaturated soils generates the soil suction. In simple words, the total suction in the soil refers to the potential of soil water and it can be measured in terms of the partial vapor pressure of the soil water [1,2]. Total soil suction has two components: (i) osmotic suction, (ii) matric suction. Osmotic suction is linked to the water solute potential and usually is neglected in unsaturated soil mechanics. Matric suction represents the liquid tension tension generated through the interaction of soil water and the soil matrix and it is defined as the pressure difference between the soil water and the surrounding gas. Soil suction influences the mechanical behaviour of unsaturated soils, including the shear and the compression properties. Accordingly, shear behaviour of unsaturated soils shall be assessed under controlled-suction condition.
Description and test procedure
The apparatus is similar to direct shear test apparatus with the exception that it allows controlling the suction in the soil sample. The total soil suction refers to the potential of soil water and has two components: osmotic suction (often neglected) and matric suction defined as the pressure difference between the soil water and the surrounding gas. The existing types of suction-controlled direct shear test apparatus commonly use the axis translation method  which allows controlling the matric suction. The method is based on imposing and controlling positive air and water pressure in the soil sample (higher than atmospher pressure).
- Richards, B. (1965). Measurement of free energy of soil moisture by the psychrometric technique using thermistors. In Moisture equilibria and moisture changes in soils beneath covered area, pages 39–46, Australia, butterworths.
- Fredlund, D. and Rahardjo, H. (1993). Soil mechanics for unsaturated soil. John Wiley & Sons, Inc.
- Hilf, J. (1956). An investigation of pore-water pressure in compacted cohesive soils. PhD thesis, Technical Memorandum 654, University of Denver, Colorado.
- Specification and main features of a commercially available Saturated / Unsaturated shear box ,GDS Instruments, UK
- Direct Shear Testing of Unsaturated soils, Megaris, Electronics and Electromechanics Systems, Itay
- Illustration of a Direct Shear Test for Unsaturated soils and typical results of suction effects on interface shear strength, Tariq B. Hamid
- Experimental unsaturated soil mechanics, Pierre Delage, Proc. 3rd Int. Conf. on Unsaturated Soils, UNSAT’2002, (3) 973-996, Juca JFT, De Campos TMP, Marino FAM, Recife, Brazil, Balkema
- Recent developments in the techniques of controlling and measuring suction in unsaturated soils, Pierre Delage & Enrique Romero and Alessandro Tarantino, Keynote Lecture, Proc. 1st Eur. Conf. on Unsaturated Soils, Durham, 33-52, CRC Press.st Eur. Conf. on Unsaturated Soils, Durham, 33-52, CRC Press.
Where to get Suction-Controlled Direct Shear Test services
No corporate member providing this service is available yet.
You provide this service and want to become a member? Join Now.
Where to buy Suction-Controlled Direct Shear Tes equipment
No corporate member providing this equipment is available yet.
You sell this equipment and want to become a member? Join Now.Related experimental results on Database
- GDL006: Direct shear and compression behaviors for an unsaturated compacted soil with water content and matric suction measurement, D.Hormdee, H. Ochiai & N. Yasufuku, Advanced Expertmental Unsaturated Soil Mechanics - Tarantino, Romero & Cui (eds), pp. 177- 184 Access