The influence of particle morphology and breakage on the strength of sandy soil

Abstract

With the increasing global energy shortages and the expanding exploitation of marine energy resources, geotechnical engineers have encountered numerous challenges related to pile driving in calcareous sand-dominant offshore seafloors. These issues are related to the low strength and high susceptibility to particle breakage of calcareous sands when used as a foundation material. Additionally, large quantities of calcareous sands are utilized in offshore land reclamation projects, serving as the primary foundation material for various infrastructural developments. The unique properties of calcareous sands, such as high susceptibility to particle breakage, can significantly influence the settlement behaviour, impacting the long-term stability of such structures. The primary objective of this study is to examine the influence of both particle breakage and morphology on the strength and settlement behavior of calcareous sands. To provide a comparative framework, river sand—one of the most commonly used construction materials from terrestrial sources—was also included in the analysis. While both calcareous (CS) and river sands (RS) are originated from aquatic environments, they exhibit significant differences in their morphological features and susceptibility to crushing, offering valuable insights into how these factors could affect their mechanical performance. Sand specimens with different initial relative densities, and in different particle size ranges were prepared. To investigate the influence of particle breakage and morphology on the deformation of sandy soils under load, a series of one-dimensional consolidation tests under the vertical effective stress of up to 7.2 MPa were carried out. To investigate the influence of particle breakage and particle morphology on the shear strength of sandy soils, a series of consolidated drained (CD) triaxial compression tests were conducted under the effective confining pressure of up to 800 kPa. To achieve a more precise and comparable quantification of particle morphology, specimens were analysed using the dynamic image analysis (DIA) techniques both before and after the tests. This approach allows for a detailed assessment of morphological parameters and offers an alternative approach to quantify particle breakage. The quantified particle breakage results can then be compared with those obtained from traditional sieving methods, ensuring a more comprehensive and accurate analysis of particle behaviour. To analyse the initiation and progression of micro-mechanical processes such as particle breakage, acoustic emission (AE) recording techniques were employed in conjunction with the one-dimensional consolidation experiments. This innovative application allowed for a detailed examination of the deformation behaviour of calcareous sand samples, offering insights into distinguishing different microactivities such as particle sliding and breakage. Furthermore, the technique enabled the quantification of the intensity of these micro-activities, providing a novel method to assess the internal processes that influence the mechanical response of calcareous sands. The main contributions of this research include a comprehensive analysis of the mechanical behaviour of calcareous sands under varying initial relative densities and particle sizes. The influence of particle breakage on compressibility and strength have been quantitatively evaluated. Additionally, the study advances the quantification of morphological changes occurring during both compression and shearing of sandy soil, and validates a novel method for assessing particle breakage based on morphological parameters. An innovative aspect of this research is the application of AE recording technique, which facilitated the differentiation and quantification of microscopic activities in calcareous sands. This research also offers valuable insights into how particle breakage and morphology affect the overall strength characteristics of sandy soil.