Abstract
The erosion of limestone and calcarenite ridges that existed parallel to the Mediterranean shoreline forms the calcareous sand (CS) formation at the surface layer of Egypt’s northern coast. The CS is often combined with broken shells which are considered geotechnically problematic due to their possible crushability and relatively high compressibility. In this research, CS samples collected from a site along the northern coast of Egypt are studied to better understand its behavior under normal and shear stresses. Reconstituted CS specimens with different ratios of broken shells (BS) are also investigated to study the effect of BS ratios on the soil mixture strength behavior. The strength is evaluated using laboratory direct-shear and one-dimensional compression tests (oedometer test). The CS specimens are not exposed to significant crushability even under relatively high-stress levels. In addition, a 3D finite element analysis (FEA) is presented in this paper to study the degradation offshore pile capacity in CS having different percentages of BS. The stress–strain results using oedometer tests are compared with a numerical model, and it gave identical matching for most cases. The effects of pile diameter and embedment depth parameters are then studied for the case study on the northern coast. Three different mixing ratios of CS and BS have been used, CS + 10% BS, CS + 30% BS, and CS + 50% BS, which resulted in a decrease of the ultimate vertical compression pile load capacity by 8.8%, 15%, and 16%, respectively.
Highlights
Is the surface loaded area; H1 is the sample height after each loading; Hs is the equivalent height of the solid sample; eo is the initial void ratio; ∆H, ∆e, and ∆σ are the settlement, change in void ratio, and normal stress per load step, respectively; and mv is the coefficient of compressibility
The previous verification is conducted to determine the calcareous sand (CS) characteristic parameters that can be used in the finite element analysis (FEA) for the pile loading model presented
This study provides a novel technique to determine the CS characteristic parameters, based on lab test results, that can be used in the FEA for the pile loading model
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Piled foundations for large floating and fixed offshore structures are constructed in CS in many coastal zones, consisting of carbonate particles of various shapes and sizes This type of soil is found scattered around the world, to name a few, Oahu beaches, Barry’s beach, Mediterranean coastal line between Alexandria and Marsa Matrouh cities, Bass Strait southwest coast of Australia, and South China Sea (Nansha Islands) [1,2,3,4,5]. The particle crushing process depends on the particle strength, size, shape, gradation, density, stress anisotropy, etc It causes complexities in estimating engineering properties such as permeability, shear strength, and compressibility of sand soils [25,26]. More details are presented in [29,30,31]
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