One of the main problems of carbonate sands is the fragile nature of particles and their susceptibility to breakage. Carbonate sands are affected by volumetric strain even at low stress levels, which is not the case with silicate sands. By defining a simple breakage model, the current study develops an elastoplastic critical state constitutive model that considers the impact of particle breakage on the mechanical behavior of carbonate sands. The particle breakage model depends on mean effective stress and critical breakage stress, which is assumed to correspond with the precompression pressure of soil in the oedometer test. In the proposed model, critical state line movement with the breakage parameter (alpha) considers the particle breakage effect. Based on the unified clay and sand model (CASM), a novel dynamic yield surface with a shape parameter affected by particle breaking has been created. Certain modifications are made to the modified Cam-Clay stress dilatancy to predict the behavior of carbonate sand. The current model has only ten parameters that simulate the carbonate sands' behavior even at high-stress levels without any breakage test. Experimental data with different soil densities, loading stress paths, and stress levels were compared with the model, and the results demonstrated satisfactory conformance.

Carbonate sand, widely distributed in coastal regions, presents challenge due to its high stress-dependent and time-dependent (creep) compressibility. While soil stabilization techniques have traditionally focused on enhancing the strength of carbonate sand, the evaluation on the compressibility performance of cemented carbonate sand remains a critical aspect for most envisaged practical applications. In light of recent developments in self-healing approaches for soil stabilization, this study investigated the potential of calcium alginate/Tung oil capsules to mitigate compressibility in carbonate sand. The encapsulated Tung oil serves as a healing agent, gradually releasing within the sand matrix when subjected to void ratio changes during compaction, hardening and bonding sand grains after a 30-day drying. Long-term stepwise one-dimensional compression tests were conducted on both clean sand and sand-capsule composite with different initial relative density and particle size. The overall and stress-dependent compressibility was reduced for fine sand-capsule composite, while capsules had adverse effect on the compressibility of medium and coarse sand-capsule composite. Capsules could not reduce the creep but increase the elastic response of all sand-capsule composites. The Tung oil bonding could reduce the compressibility by preventing particle breakage of sand during loading. The stabilization mechanism of capsules in carbonate sand with different particle size was further investigated through thermal analysis, CT scan and microscopic analysis, revealing that the compressibility mitigation by capsules depended on the amount of Tung oil release from capsule, which was controlled by the pore structure of sand-capsule composite.

The shear modulus degradation curve in normalized shear modulus vs. shear strain plane presents crucial information about the cyclic and/or dynamic response of soil, especially for undrained conditions. This study introduces an analytical shear modulus degradation model specifically for carbonate sand subjected to high-amplitude cyclic loading associated with marine geostructures. Unlike hard-grain siliceous sand, carbonate is soft and crushable under low confining conditions. To address this, we utilize a generic analytical shear modulus degradation model and enhance it for carbonate sand. The model coefficients are first calibrated based on existing cyclic experiments on carbonate sand collected from various offshore regions around the world, without taking into account the particle crushing effect. Later, cyclic undrained tests are numerically simulated, accounting for the particle-crushing effect using a bounding surface plasticity soil model. The simulation results show a noticeable shift in the shear modulus degradation curves while accounting for the particle breakage compared to non-crushable sands, irrespective of cyclic stress ratio conditions. Based on the numerical simulations, the analytical model is further refined through evolving characteristics of sand gradation (i.e., coefficient of uniformity). The proposed model is validated with separate experimental results of carbonate sand subjected to different confining pressures.

Engineers have limited control over the process of soil formation, which can pose challenges when it comes to constructing structures such as dams, pavements, rail tracks, and foundations. To address this issue, a study was conducted to examine the mechanical properties of Hormoz Carbonate Sand and Firoozkooh Quartz Sand No 161. The goal was to predict the settlement, particle breakage, and shear strength of these sands. Tall oedometer and direct shear tests were conducted in a drained condition and the samples were prepared with the dry pluviation method in two different relative densities (30% as loose and 80% as dense) and consolidated under various confining pressures. The results revealed that in dense specimens, the particle breakage index increased as the porosity decreased. In the tall oedometer tests, it was observed that the vertical applied stress decreased with increasing height of the soil sample. Additionally, particle breakage decreased with depth in the samples, corresponding to the decreasing vertical applied stress. Furthermore, direct shear tests were performed on soil samples of different heights (0.5, 1, 1.5, 2, and 3 cm) using a direct shear apparatus. It was found that in the lower sample heights (0.5, 1, 1.5 cm), a greater amount of breakage occurred due to a higher percentage of soil volume placed in the shear zone. The results also indicated that increasing the shearing rate led to a reduction in the particle breakage index.

Using an energy-based approach and a wide range of marine silt content (SC), along with simulating different field conditions, a systematic experimental study was conducted through a series of strain-controlled cyclic triaxial tests on the undrained cyclic response of saturated Konarak carbonate sand-silt mixtures that originated from the northern coasts of the Oman Sea. The results revealed that the trend of variation in capacity energy (cumulative dissipated energy required to initiate liquefaction, Wliq) of sand-silt mixtures versus variation in SC was highly dependent on the relative density (Dr). Using the concepts of equivalent intergranular void ratio (e*) and equivalent interfine void ratio (ef*), a new relationship was proposed to estimate the Wliq of the Konarak sand-silt mixtures under different field conditions. To take into account the effects of SC, the energy-based pore water pressure model model proposed by Jafarian et al. (2012) was revised with modified calibration parameters. Similarly, as there exists a distinct relationship between energy dissipation and the excess pore water pressure generation during cyclic loading, a significant correlation is also observed between energy dissipation and stiffness degradation for carbonate soil.

For mooring systems, the relationship between chain axial resistance and confining stress affects the tension transfer of embedded mooring chain, and an effective width parameter Et was adopted to reflect the complex geometry of the chain. However, the relationship in carbonate sand is fully understood. Designed as an element test, monotonic and cyclic loading tests were conducted to investigate the variation of chain axial resistance with confining stress under different conditions in South China Sea carbonate sand. Peak effective width parameter and secant coefficient were particularly analyzed to describe the gradual mobilization. The results show that the Et value in South China Sea carbonate sand has a mean increase of 15% compared with Pingtan quartz sand, which makes the chain harder to pull into the carbonate sand. The irregular particle shape may contribute to the higher axial resistance. In cyclic tests, the peak post-cyclic Et-m is larger than that of monotonic test under lower confining stress but is smaller under higher stress. This paper provides some references to chain profile prediction in the carbonate sand.