Cyclic Triaxial Test to Measure Strain-Dependent Shear Modulus of Unsaturated Sand

2017

Geotech. Test. J.

The dynamic properties of a clean sand under different degrees of saturation were investigated using a modified custom built Direct Simple Shear (DSS) apparatus at the University of New Hampshire. The specific characteristics of the DSS were presented, and the testing procedures were discussed. The device used the axis translation and tensiometric techniques to control the matric suction in the soil specimen. The investigation on F75 Ottawa Sand showed a decrease in shear modulus and an increase in damping by increasing the shear strain over the tested range of strains for various degrees of saturation: dry, saturated, and partially saturated. The modulus reduction in the applied range of medium shear strains regardless of the degree of saturation demonstrated the capability of the DSS in consistently capturing the changes of dynamic properties. Experimental results indicated that the matric suction can have a substantial effect on the stiffness of the soil. However, the extent of this effect may depend on the induced strain level of the effective stress in unsaturated soil. In addition, partially saturated specimens resulted in lower dynamic compression.

Section: Materials and Testing Methodssupporting

confidence: 82%

Section: Effective Stress In Unsaturated Soilsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Cyclic Direct Simple Shear Test to Measure Strain-Dependent Dynamic Properties of Unsaturated Sand

2017

Geotech. Test. J.

“…[9][10][11][12] and determining the strain-dependent modulus using cyclic triaxial systems [e.g. 13,14]. These studies consistently reported a higher modulus in unsaturated soils.…”

Section: Dynamics Of Partially Saturated Soilssupporting

confidence: 56%

Suction-controlled dynamic simple shear apparatus for measurement of dynamic properties of unsaturated soils

2016

E3S Web Conf.

Self Cite

Abstract. State variables such as confining pressures and the degree of saturation can have a profound effect on the dynamic properties of a soil. These dynamic properties are essential when performing seismic response analysis of geotechnical systems in the phreatic zone. In order to accurately obtain these properties, laboratory testing using a Dynamic Simple Shear system is often implemented. This paper concentrates on the advancements and modifications of a custom-built dynamic simple shear system at the University of New Hampshire to accommodate soils with unsaturated conditions by employing axis translation technique. Tests could be performed under drained (constant suction) or undrained (constant water content) conditions. The procedure for preparing an unsaturated soil sample and testing is discussed, followed by the methods for interpreting the data and the challenges involved. Preliminary data confirms the ability of the system to control and track suction during the cyclic simple shear test. Suction in unsaturated soil increased the shear modulus and decreased the damping ratio comparing with those in dry and saturated conditions.

“…Inter-particle suction in partially saturated soils increases the effective stresses on the grain skeleton [31]. This, in turn, yields to different soil dynamic properties including small-strain and strain-dependent shear modulus and damping [32][33][34][35][36][37][38][39][40][41][42][43]. As a result, seismic wave propagation mechanisms may vary in partially saturated soil layers [44] that would lead to a different seismic site response [30,[45][46][47][48][49].…”

Section: Introductionmentioning

confidence: 99%

Centrifuge tests to assess seismic site response of partially saturated sand layers

Mirshekari

Soil Dynamics and Earthquake Engineering

2017

Self Cite

Seismic response of unsaturated soil layers may differ from that of saturated or dry soil deposits. A set of centrifuge experiments was conducted to study the influence of partial saturation on seismic response of sand layers under scaled Northridge earthquake motion. Steady state infiltration was implemented to control and provide uniform degrees of saturation profiles in depth. The amplification of peak ground acceleration at the soil surface was inversely proportional to the degree of saturation, especially in low period range. The cumulative intensity amplification of the motion was also higher in unsaturated soils with higher suctions. The lateral deformation and surface settlement of partially saturated sand with higher stiffness were generally lower than that in dry soil. Although neglecting the effect of partial saturation in sand layers might be conservative with respect to seismic deformations, it may result in underestimating the surface design spectra.