Dynamic Properties of Calcareous Sands from Urban Areas of Abu Dhabi

Abstract

Abu Dhabi (ABD) has recently developed its national building code that mandates dynamic analysis of large structures to seismic loadings. Large strain dynamic properties such as shear modulus (G) and damping ratio (D) of local undisturbed calcareous sands are not available. Designers are compelled to choose degradation models from studies on calcareous sands of other regions that are usually reconstituted. This research presents for the first time large strain dynamic properties of calcareous sands of urban ABD. Undisturbed samples are collected from different areas of urban ABD and are tested in cyclic triaxial (CT) devices fitted with bender elements (BE). The dynamic properties as functions of confinement are curve fitted with power models, whereas their variation with shear strain level is curve fitted with hyperbolic models. The results are compared with findings of previous studies on calcareous and silica sands. The results indicate that dynamic properties of all samples degrade with shear strain at almost the same rate irrespective of their spatial distribution. The proposed degradation models can therefore be used in dynamic analyses. The results from this study show smaller rates of degradation in dynamic properties compared to other studies on similar sands. The change in low-strain shear wave velocity (Vs) with confinement is significant among the tested samples; therefore, a site-specific evaluation of Vs is recommended. The dynamic properties of calcareous sands of ABD and previous studies however exhibit larger degradation with shear strain and a smaller increase in confinement compared to silica sands.

Continuous Evaluation of Shear Wave Velocity from Bender Elements during Monotonic Triaxial Loading

“…Low-strain Vs is required to classify sites for seismic analysis, and corresponding amplification factors for ground accelerations are determined. Dynamic properties are typically obtained by conducting field and laboratory tests (Khan et al [ 1 ]; Khan et al [ 2 ]; Khalil et al [ 3 ]; Irfan et al [ 4 ]). These tests have various limitations and testing biases related to boundary conditions, assumptions, attainable strains and frequencies (e.g., Khan et al [ 1 ]; Clayton et al [ 5 ]).…”

“…The outcomes of the studies are contrary to expectations, which caused more interest; the main reasons for the unexpected results are still not fully understood, but should be in order to better design future experiments. Typically, Vs as a function of shear strains is measured with a combination of resonant column (RC) and cyclic triaxial (CT) devices which require additional resources (e.g., Khan et al [ 1 ], Khalil et al [ 3 ]). Bender elements (BE) have been extensively used to determine low-strain Vs (Dyvik and Madshus [ 10 ], Shirley and Hampton [ 11 ], Viggiani and Atkinson [ 12 ], Kuwano and Jardine [ 13 ], Gu et al [ 14 ], Khalil et al [ 3 ]; Irfan et al [ 4 ]).…”

Dynamic Shear Modulus and Damping of MICP-treated Calcareous Sand at Low Strains

“…For example, the small-strain shear modulus and damping ratio of calcareous sand under isotropic or anisotropic stress consolidated state have been studied [22][23][24][25]. The effects of confining stress, pore ratio, relative density, grading and particle size, and particle breakage on the dynamic properties are discussed [21,[25][26][27][28][29]. Morsy et al [26] found the effect of void ratio on shear modulus was more pronounced at low void ratios and maximum shear modulus increased as the void ratio decreased.…”

“…Hassanlourad et al [28] studied the shear behavior of calcareous sand through drained and undrained triaxial tests and reported the effect of particle breakage on specimen response. Khalil et al [29] performed a series of bender element and cyclic triaxial tests to study the low-strain and large-strain characterization of calcareous sand and terrigenous sand.…”

“…Although, the dynamic shear modulus and damping ratio at low strains have been extensively studied on natural soil and cement stabilized soil [22,26,[29][30][31][32][33][34], considerably less information is available for the dynamic response of marine soil like calcareous sand at different MICP--treatment levels. It is necessary to understand how the shear modulus and damping ratio of MICP-treated calcareous sand varied with shear strain and other factors for engineering application.…”