Laboratory Investigation on Particle Breakage Characteristics of Calcareous Sands

Qingsheng Chen,Sanjay Nimbalkar,Wan Peng,Gaoliang Tao,Ronghu Yu,Xiaodong Hu

doi:10.1155/2021/8867741

Abstract

Many studies have demonstrated the fragility of calcareous sands even under small stresses. This bears an adverse influence on their engineering properties. A series of laboratory tests were carried out on poor-graded calcareous sands to investigate the crushability mechanism. Einav’s relative breakage and fractal dimension were used as the particle breakage indices. The results show that the particles broke into smaller fragments at the low-stress level by attrition which was caused by friction and slip between particles. In contrast, particles broke in the form of crushing at the relatively higher stresses. The evolution of the particle size was reflected by the variation in Einav’s relative breakage and fractal dimension. As testing commenced, the breakage index rapidly increased. When the stress was increased to 400 kPa, the rate of increase in the breakage index was retarded. As the stress was further increased beyond 800 kPa, the rate of increase in the fractal index became much smaller. This elucidated that the well-graded calcareous sands could resist crushing depending on the range of applied stresses. Based on the test findings, a new breakage law is proposed.

Highlights

Calcareous sands are rich in calcium carbonate or other insoluble carbonate products. ese sands are mainly distributed in the continental shelf, the coastline of the tropical/ subtropical climate between latitude 30° north and 30° south, the Southern China Sea, and the Red Sea
It was found that the surfaces of calcareous sands were irregular and the internal structure was porous. is was evident from the compression test data in which the increased stresses led to a larger finer fraction. e particle breakage at low-stress level was in the form of attrition or crushing caused by friction and slip between particles, as well as the particle splitting as a result of specimen compression occurred at the high-stress level
Particle breakage of calcareous sands occurs under small stresses commonly encountered in the field

Summary

Introduction

Calcareous sands are rich in calcium carbonate or other insoluble carbonate products. ese sands are mainly distributed in the continental shelf, the coastline of the tropical/ subtropical climate between latitude 30° north and 30° south, the Southern China Sea, and the Red Sea. Einav [27] assumed that soil particles would undergo complete fragmentation in the shear process and defined the relative breakage in terms of the relative distance of the current grain size distribution from the initial and ultimate distributions. E micromorphology of calcareous sands with a single particle size was studied by scanning electron microscope (SEM) tests, and the mode of particle breakage was described. Scanning electron microscope (SEM) tests were conducted to observe the microscopic images of the original calcareous sand with different particle sizes (4, 3, 2, 1, 0.5, and 0.25 mm). In this experiment, the sputtering speed is 10 mm/min and the sputtering time is 60 s. It was found that the surfaces of calcareous sands were irregular and the internal structure was porous. is was evident from the compression test data in which the increased stresses led to a larger finer fraction. e particle breakage at low-stress level was in the form of attrition or crushing caused by friction and slip between particles (refer to the location indicated in Figure 4), as well as the particle splitting as a result of specimen compression occurred at the high-stress level

Particle Breakage Index

Findings

Conclusions