Anisotropic small-strain stiffness of calcareous sand affected by sample preparation, particle characteristic and gradation

Abstract

Sands exhibit a directional diversity in shear modulus at small strains, reflecting the anisotropic stiffness behaviour in the structure. In this paper, sample preparation method, particle shape and particle size are considered as parameters to produce samples with various initial fabric. Five preparation methods, namely, air and water pluviation, dry and moist tamping and dry funnel deposition are used to reconstitute the samples. The stiffness anisotropy of calcareous sand and Mol silica sand is quantified by the small-strain modulus G 0 measured in horizontal and vertical planes with the bender element technique in triaxial tests. Test results show that calcareous sands behave as an elastic homogeneous continuum material at small strains. Calcareous samples prepared by the air pluviation method possess the highest anisotropic ratios. The lowest stiffness anisotropy exists in the samples prepared by moist tamping and dry funnel deposition methods. Compared with the anisotropic ratios of the air pluviation samples from the literature, the notably higher values for the calcareous sand in this study are attributed to the lower sphericity. In addition, less prominent stiffness anisotropy is found in calcareous sands with smaller particle sizes (D 50 ).

Predicting the Small Strain Stiffness of a Calcareous Sand Considering Sample Preparation Method and Stress Path

“…n denotes the response of soils to stress variation. From Table 1, the higher A corresponds to the higher shear modulus reported by Shi et al (2020a). It can also be seen that the samples with a higher A always show a lower n. This also verifies the deduction mentioned above since a smaller n means the less strain response of the sample subjected to loading and the stronger structure the sample has.…”

“…The densification is carried out by tapping the mold side with a rubber hammer. Details of the five methods can be found in Shi et al (2019), Shi et al (2020a) and Shi et al (2020b). All the tests are performed at least two times to verify the repeatability.…”

“…Small strain shear modulus, G 0 , is a fundamental parameter in determining the ground movements of many geotechnical infrastructures. Soils like sands and clay behave elastic at the very small strain ranges (≤10 -5 %) in which G 0 can be determined by some indirect measurement techniques, for example, bender element test (Bellotti et al 1996;Pennington et al 1997;Fioravante 2000;Escribano and Nash 2015;Shi et al 2020a). Based on the shear wave velocity measurement in bender element test, G 0 can be evaluated with Eq.…”

Small-strain shear modulus of calcareous sand under anisotropic consolidation

“…The mechanical properties of calcareous sand are always different with those of silica sands due to its special physical characteristics (Cassidy et al, 2002;Coop et al, 2004;Qadimi and Coop, 2007;Xiao et al, 2019b;Xiao et al, 2020;Xu et al, 2020;Tong et al, 2020;Tong et al, 2021;Xiao et al, 2021;Wu et al, 2021). Calcareous sands always exhibit higher irregularity in particle shape, which could promote the stiffness as the result of the stronger grain interlocking compared with that of silica sand at a similar state (Giang et al, 2017;Lv et al, 2019;Rui et al, 2020;Wei et al, 2020;Shi et al, 2021a). The small-strain shear modulus of calcareous sand was captured with the developing of offshore geotechnical engineering in marine areas where the infrastructure such as oil platform and artificial island are built upon the materials (Wang et al, 2011;Van Impe et al, 2015).…”

“…The factors affecting the small-strain stiffness behavior of sandy soils can be summarized: physical properties, e.g., particle shape, size, fine content and gradation (Wichtmann and Triantafyllidis, 2009;Carraro et al, 2009;Yang and Gu, 2013;Choo et al, 2015;Wichtmann et al, 2015;Enomoto, 2016;Goudarzy et al, 2016;Payan et al, 2016;Liu et al, 2020;Shi et al, 2020) and testing environment, e.g., saturation and temperature (Alramahi et al, 2010;Khosravi et al, 2018;Rajabi and Sharifipour, 2018;Wang et al, 2019). The factors affecting soil fabric and stress state such as sample preparation method, cementation, isotropic and anisotropic consolidation and over-consolidation, are also important for 0 G (Jardine, 1992;Fernandez and Santamarina, 2001;Hoque and Tatsuoka, 2004;Sawangsuriya et al, 2006;Lee et al, 2009;Clayton et al, 2010;Lee et al, 2011;Ng and Xu, 2012;Gu et al, 2013;Fioravante et al, 2013;Montoya and DeJong., 2015;Senetakis and Li, 2017;Simatupang et al 2018;Payan and Chenari, 2019;Mendoza-Ulloa et al, 2020;Shi et al, 2021a;Liu et al, 2021;He et al, 2021). Some of the factors, for example, the overconsolidation ratio OCR, can be quantified and introduced into the Hardin equation (Hardin and Black, 1966) to predict 0 G of sand, which is expressed as:…”