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AbstractA series of consolidated and drained (CD) triaxial tests were carried out to compare the shear behavior of calcareous sands with that of siliceous sands, in terms of the stress–strain–volume change and void ratio paths. Through nonlinear fitting of test data, the variation in the shear strength, mobilised friction angle, excess frictional angle and void ratio at various characteristic states (CHSs) was analyzed in a quantitative manner. The shear strength is expressed by a power function for the calcareous sand and a linear function for the siliceous sand. Both the mobilised and excess friction angles are fitted by a binary function about the relative density and confining pressure, and the range and value of mobilised friction angle of calcareous sand are larger than those of siliceous sand. The characteristic state lines (CHSLs) of siliceous sands are approximately a straight line in the compression plane, but those of calcareous sands exhibit strong nonlinearity. [ABSTRACT FROM AUTHOR]

This study centers on the crucial determination of the mobilized friction angle between soil and various materials, including steel and concrete, to enhance the modeling of soil-structure interaction. The primary objective of the current investigation was to assess the interfacial friction between calcareous and silica sands when interacting with concrete or steel surfaces. To achieve this, direct shear tests were conducted to examine the impacts of relative density (Dr), surface roughness (Rn), and shearing direction. The test results reveal that the shear strength of calcareous sand surpasses that of silica sand when considering a specific Rn. Furthermore, the interface friction of both sand types escalates with an increase in normal stress and Rn, with higher values observed in interactions with steel plates. Notably, the friction angle ratio (the interaction friction angle over the pure sand friction angle) demonstrates minimal dependence on the sand type. The most pronounced divergence in the friction angle ratio is evident at the maximum Rn value, which increases alongside Rn values for both calcareous and siliceous sands. With increasing Rn values, the maximum shear strength, contingent on normal stress and relative density, also rises. The influence of relative density on the interaction friction angle diminishes with escalating surface roughness. [ABSTRACT FROM AUTHOR]

The shear strength and resistance of granular materials are critical indicators in geotechnical engineering and infrastructure construction. Both sliding and rotation influence the energy evolution of soil granular motion during shear. To examine the effects of particle rotation on shear damage and energy evolution in granular systems, we first describe the transformation of irregularly shaped particles into regular shapes via geometrical parameters, ensuring the invariance of energy density and density. We then analyze the impact of particle rotation on shear-stress variation and energy dissipation through a shear energy evolution equation. Additionally, we establish the relationship between the shear-stress ratio and normal stress, considering particle rotation. Finally, we verify the influence of particle rotation on energy evolution and shear damage through shear tests on irregular calcareous sand and regular silica-bead particles. The results indicate that granular materials do not fully comply with the Coulomb strength criterion. In the initial shear stage, most of the external work is converted into granular rotational-shear energy, whereas in the later stage, it primarily shifts to granular sliding-shear energy. Notably, the sensitivity of the granular rotational energy to a vertical load is significantly greater than that of the granular sliding energy. [ABSTRACT FROM AUTHOR]

AbstractTo reveal the influence of rubber particles on the mechanical properties of calcareous sand under the large-displacement shear effects of earthquakes and waves, indoor ring shear tests were conducted on rubber particle-calcium sand mixtures. The effects of rubber particle size and content on the mechanical properties of calcareous sand were studied via indoor ring shear test. Then, based on PFC3D, a numerical model of a ring shear test that can restore the shape of calcareous sand particles is established, and a mesomechanical analysis of mixed sand is carried out. The results showed that the effect of the rubber particle content on the crushing characteristics and strength of calcareous sand was significant and that the effect of the particle size was small. The rubber content causes a gradual decrease in the peak strength and particle crushing rate and increases the deformation stability of the mixed sand. The softening coefficient and relative crushing rate were significantly reduced to 0.01–0.06 and 0.28–1.2%, respectively, at 40% rubber content. The numerical simulations and experimental results were in good agreement. An increase in the rubber content significantly influences chain development, which explains the macroscopic mechanical properties of mixed sand at the fine level. [ABSTRACT FROM AUTHOR]

This study conducts a series of large-scale pullout tests to explore the pullout behavior of the biaxial geogrid-calcareous sand interface. It investigates the effects of normal stress, relative density, and embedded length on the interface pullout behavior of geogrid reinforcement in calcareous sand. In addition, this research examines changes in interface shear strength and the interface friction coefficient. The interface interaction mechanism of geogrid reinforcement in calcareous sand and the evolution of pullout force-clamp displacement curves are determined. The results indicated that the pullout force-clamp displacement curve primarily exhibits softening and hardening behaviors. The passive resistance of the geogrid mesh significantly influences the softening behavior, while shear friction predominantly affects the hardening behavior. The interface friction coefficient ranged from 0.28 to 0.88 for embedded lengths of 300 − 460 mm. The effects of relative density and embedded length on interface cohesion are more pronounced than those on the interface friction angle. When the embedded length increased from 300 to 460 mm, the rise in interface cohesion ranged from 42.0% to 47.7%, whereas the increase in internal friction angle ranged from 9.5% to 14.5%. [ABSTRACT FROM AUTHOR]

To explore the feasibility of geogrid reinforcement as a promising countermeasure to improve the liquefaction and post-liquefaction resistance of calcareous sand, extensive undrained monotonic and multi-stage triaxial tests were performed on unreinforced and geogrid reinforced calcareous sand with different relative densities. The test results illustrate that pore pressure generation curves of unreinforced and reinforced calcareous sand gradually evolve from S-shaped to hyperbolic-shaped with the increase in relative density, cyclic stress ratio, and effective confining pressure. Following this, a pore pressure model applicable to both unreinforced and reinforced calcareous sand is proposed. The liquefaction resistance of calcareous sand increases with the increase in relative density, whereas an elevated cyclic stress ratio increases its liquefaction susceptibility. A virtually unique relationship can be observed between the liquefaction resistance normalized to the product of phase transformation strength ratio and relative density against the number of cycles for triggering liquefaction, providing an effective means of early assessing sand liquefaction resistance. Moreover, the geogrid exhibits excellent reinforcement efficiency in enhancing the liquefaction resistance of calcareous sand at relative densities of 50% and 70%. During the post-liquefaction stage, increasing relative density and geogrid reinforcement can accelerate the recovery of stiffness and strength for liquefied calcareous sand and improve the post-liquefaction strength. In general, geogrid reinforcement is considered a good alternative to densification for improving the engineering properties of calcareous sand and offers great application prospects in marine engineering construction. • The effects of geogrid reinforcement and relative density on the liquefaction and post-liquefaction behaviors of calcareous sand are investigated. • A pore pressure model applicable to both unreinforced and reinforced calcareous sand is proposed. • The inclusion of geogrid enhances the liquefaction resistance of calcareous sand. • Increasing relative density and geogrid reinforcement accelerate the recovery of stiffness and strength for liquefied calcareous sand and improve the shear strength during the post-liquefaction stage. • Geogrid reinforcement is considered a good alternative to densification for improving the engineering properties of calcareous sand and offers great application prospects in marine engineering construction. [ABSTRACT FROM AUTHOR]

Stress-induced anisotropy in calcareous sand can cause an uneven displacement in island reef engineering. In this study, stiffness, as a quantitative indicator, is explored to reveal the stress-induced anisotropy in calcareous sand. Based on the discrete element method, the stiffness anisotropic characteristics of calcareous sand during shearing, as well as the impact of particle breakage, are investigated by numerical simulations. Both the macro and micro responses, i.e., the maximum shear modulus, contact normal, strong and weak contact normal force, and the direction of particle breakage, are explored for calcareous sand with different particle breakage ratios. The results show that calcareous sand exhibits notable anisotropy during shearing, with the maximum shear modulus in the vertical direction (deviatoric stress direction) being significantly greater than that in the horizontal direction. Moreover, the higher the particle breakage rate, the lower the stiffness and its anisotropy. The micro-mechanism results indicate that the primary particle breakage during the shearing process occurs in the vertical direction. That is, the particle breakage weakens the strong contact force in the vertical direction, leading to a redistribution of the strong contact forces from the vertical direction to other directions. This redistribution mainly manifests in a decrease in the anisotropy of contact normal and contact vector within the sample, as well as a decrease in the proportion of strong contact forces in the overall contacts. This, in turn, reduces the shear strength and stiffness of calcareous sand, particularly in the vertical direction, and results in a decrease in the maximum shear modulus and its anisotropy. The maximum reduction can be up to 50% of the original value. These insights can provide a certain theoretical support for the uneven displacement and long-term stability of calcareous sand for islands and reefs. [ABSTRACT FROM AUTHOR]

Many available stabilisers and reinforcements have been used to enhance the mechanical characteristics of silica sand. So far, many studies have been carried out to understand the influence of various old and new additives such as natural and synthetic fibres or traditional stabilisers on the mechanical characteristics of silica sands. However, there is minimal study on the mechanical characteristics of stabilised or reinforced calcareous sands. The main focus of the current study was to evaluate the influences of relative density (Dr), Portland cement (C) content, rice husk ash (RHA) content and synthetic polypropylene fibre (PPF) content on the mechanical characteristics of a calcareous sand, which were: Dr [30%, 80%], C [0, 3%, 5%, 7.5%], RHA [0, 7%, 7.5%, 10%], and PPF [0%, 1%]. For this purpose, direct shear tests have been conducted on treated calcareous sand subjecting to three curing times (7, 14, and 28 days). The test results indicate that adding cement, rice husk ash and polypropylene fibre increases the shear strength and reduces the volumetric strain under shear loading. Thespecimens containing 7.5% cement and 7.5% RHA generally exhibited the highest shear strength and the lowest volumetric strain. Relative density, cement content, RHA content, fibre content and curing time have more important effects on the cohesion than the friction angle of treated specimens. [ABSTRACT FROM AUTHOR]

A series of monotonic and multidirectional cyclic simple shear tests were performed on reconstituted fiber-reinforced calcareous sand specimens prepared by the dry deposition method, at a relative density of approximately 50%, considering the effects of fiber contents and cyclic stress levels. The peak shear strength, the linkage between monotonic and cyclic behaviors, liquefaction resistance, and pore pressure responses of calcareous sand with and without fiber reinforcement were analyzed. The results indicate that both unreinforced and fiber-reinforced calcareous sand exhibit limited flow instability behavior and the peak shear strength increases with the increase in fiber content under monotonic loading. The inclusion of fibers and increasing fiber contents can improve the liquefaction resistance of calcareous sand under cyclic loading. A linear relationship was found between the normalized liquefaction resistance of reinforced sand and the number of cycles for triggering liquefaction, and the prediction of liquefaction resistance of fiber-reinforced calcareous sand with various fiber contents can be conveniently achieved according to the linear relationship. The pore pressure prediction model considering the effect of fiber contents was proposed, which was capable of effectively simulating the pore pressure generation of fiber-reinforced calcareous sand. [ABSTRACT FROM AUTHOR]

Calcareous sand fractures easily, has poor mechanical properties, and usually needs to be stabilized for engineering applications using additives. In this study, nano-MgO was used to enhance the mechanical properties of cement-stabilized calcareous sand (CCS). Unconfined compressive strength (UCS) and unconsolidated undrained (UU) triaxial shear tests were conducted on nano-MgO-modified CCS (MCCS) specimens, and the microscopic mechanism was investigated using scanning electron microscopy and X-ray diffraction. Finally, models to predict the UCS and shear strength of MCCS were formulated. The results showed that the addition of nano-MgO can enhance the strength and stiffness of CCS, with MCCS reaching its maximum strength of 2.1 MPa at 28 days when the nano-MgO content was 1%. Furthermore, the deviatoric stress first increased and then decreased as the nano-MgO content increased, reaching its maximum value when the nano-MgO content was 1.5%. The optimal nano-MgO content obtained from the UCS tests was different from that obtained from the UU tests. This improvement in CCS strength was due to the nano-MgO filling and cementation of hydrates such as Mg7Si8O22(OH)2, Mg(OH)2, and CaAl2Si3O10(H2O)2. However, too much nano-MgO reduces the strength of CCS because the nano-MgO expands during hydration. [ABSTRACT FROM AUTHOR]

Biostimulated microbially induced carbonate precipitation (MICP) is an innovative soil improvement approach utilizing indigenous ureolytic microbes to hydrolyze urea. The objective of this study is to investigate the effect of biochar amendment on the shear strength of biocemented calcareous sand through the biostimulation approach. Biochar powder produced from softwood forestry residues with a maximum size of 0.045 mm was used. The specimens were prepared at two initial relative densities (i.e., 16.2% and 54.6%) and four biochar contents (i.e., 0%, 0.1%, 0.3%, and 0.5% by weight), and a series of direct shear tests were conducted at five normal stress levels (i.e., 50, 100, 200, 400, and 600 kPa). The cementitious content, peak shear strength characteristics, and microstructural features were determined during and at the end of the tests. The results indicate that the amendment of biochar in biocemented sand could increase its overall cementitious content. It is also found that whether biochar amendment could enhance shear strength depends on the biochar content, cementitious content, and initial relative density. The higher initial relative density (54.6%) and moderate biochar content (0.3%) are favorable conditions for greater sand shear strength enhancement provided by biochar. Microscopically, the biochar powders are embedded within biocementation. Mechanistically the effects of biochar on the shear strength of biocemented sands are (1) increasing cementitious content, (2) creating weak points inside biocementation, and (3) reducing interparticle friction. [ABSTRACT FROM AUTHOR]

For the island and reef project formed by filling calcareous sand, the problems of wide particle size distribution (PSD) and complex mechanical properties have to be faced. Therefore, in order to provide basic mechanical parameters for the construction of the island and reef project, triaxial shear tests were carried out on calcareous sands with five different typical PSDs. The results showed that as particle gradation became narrower, the axial strain corresponding to the strain-softening point all showed a decreasing trend and their differences gradually decreased; the confining pressure has a significant impact on the volumetric deformation modulus of calcareous sand with a wide PSD. The cohesion of calcareous sand showed a positive correlation with non-uniformity and curvature coefficients, while the variation of an internal friction angle showed a parabolic law; the internal friction angle also changes in the parabola with the change of fine particle contents. Furthermore, by establishing the PFC3D discrete element model, it was found that the numerical simulation results were in good agreement with the test results, which verifies the feasibility of the numerical simulation and the rationality of the mesoscopic parameter calibration. It was discovered that the wider the particle gradation range, the greater the axial strain corresponding to the critical coordination number; the sample with a narrow gradation interval was more likely to present a rotating displacement field to form a penetrating shear band. This study can provide design parameters for stability analysis of high and steep slopes in calcareous sand sites.

In this text, a method to use CO2 for the treatment of calcareous sand is presented. Carbon dioxide solidification-bacteria (Streptomyces microflavus) was obtained by screening and applied to the mechanical strengthening of calcareous sand through a microbial mineralization/carbonization process. Experiments in both liquid phase and sand were carried out. The optimal mass ratio of carbon dioxide solidification-bass cteria to calcium oxide was found to be 2:1. The optimal dosage of bacterial powder was 30% of the total dry sand mass. Using the optimal recipe, the average uniaxial compressive strength of treated sand columns was 3.67 MPa and the average permeability coefficient was 4.90 × 10−3 cm/s. Compared to the other microbial induced carbonate precipitation (MICP) approaches, the proposed method does not release harmful by-products such as ammonia. The chemical composition and microstructure of the treated calcareous sand were characterized by powder X-ray diffraction (XRD) and scanning electron microscopy (SEM). The XRD results showed that the CO2 carbonized product contained mainly calcite. [ABSTRACT FROM AUTHOR]

The mechanical properties of calcareous sands are very different from those of terrestrial sands as the particle crushing occurs under low confining pressure. If the calcareous sand is used as the foundation materials, engineering problems such as the uneven settlement of the foundation are prone to occur. In this paper, the Polyurethane foam adhesive (PFA) is used to improve the calcareous sand through the unconsolidated undrained (UU) large-scale triaxial test. The shear strength of PFA solidified calcareous sand under different PFA content and confining pressure was studied. In order to facilitate engineering design, this paper evaluates the strength parameters of PFA solidified calcareous sand, including peak strength, internal friction angle and cohesive force, followed by the SEM microstructure test to reveal the micro-mechanism of PFA improved curing. The experimental results show that the shear strength and deformation resistance of the solidified calcareous sand improved significantly by addition of PFA. Furthermore, SEM studies revealed that the PFA is mainly wrapped around the surface of the sand particles or filled between the sand particles, which manifests in the form of improved cohesion which ultimately results in overall improvement in strength of soil PFA mixture. [ABSTRACT FROM AUTHOR]

Fine-grained calcareous silt interlayers with a non-uniform thickness are distributed discontinuously in the hydraulically reclaimed foundation of island-reefs in the South China Sea. Because of their high compressibility and low strength, these interlayers commonly cause differential foundation settlement and result in the cracking of buildings, which poses a potential safety hazard. In this study, consolidated-drained triaxial shear tests were conducted to investigate the effect of fines content (FC) on the shear strength of calcareous sand. The brittleness index and dilatancy coefficient were introduced to quantify the strain-softening and dilatancy of calcareous sand. The mechanism by which the FC affects the calcareous sand strength was revealed in terms of the particle shape and soil structure. Under a constant effective confining pressure, an increase in FC led to a gradual decrease in peak strength, a weakening of strain-softening characteristics, less dilation, and a linear decrease in apparent cohesion for calcareous sand. The internal friction angle of calcareous sand peaked at a FC of 10%. Compared with quartz sand, calcareous sand has the more irregular particle shape. An increase in FC weakened the interlocking between calcareous sand particles, which decreased the shear strength. The research results are of great significance for slope stability analysis and for the foundation treatment of island reefs. [ABSTRACT FROM AUTHOR]

Calcareous sand, a special type of sand commonly used for the construction of coastal engineering in tropical coasts, is usually required to be strengthened due to its poor engineering mechanical properties. Microbially induced carbonate precipitation has been proved to be a promising method for this purpose. A higher cementation level generally leads to a greater strength enhancement, but tends to cause brittle failure of bio-cemented calcareous sand, which in turn brings great potential risks for the coastal engineering. Therefore, the shear behaviour, especially the brittle behaviour, of bio-cemented calcareous sand needs to be understood properly, and taking some measures to improve its brittle behaviour is also necessary. In this regard, a series of triaxial compression tests were conducted to study the shear behaviour of bio-cemented calcareous sand with various cementation levels, and the waste rubber particles are used to improve the brittle behaviour of bio-cemented calcareous sand. The test results show that the shear strength of bio-cemented calcareous sand increases with the increase in cementation level, and the brittle behaviour is significant gradually. The waste rubber particles contribute to improve the brittle behaviour of bio-cemented calcareous sand, reducing the dilation of bio-cemented calcareous sand and slowing the changes in dilatancy with the increment of stress. [ABSTRACT FROM AUTHOR]

Calcareous sands have abundant intraparticle pores and are prone to particle breakage. This often leads to poor engineering properties, which poses a challenge to coastal infrastructure construction. A study using bio-cementation to improve the engineering properties of calcareous sand is presented in this paper. The macro- and microscopic properties of bio-cemented calcareous sand were characterized by drained triaxial tests and scanning electron microscopy observations. Experimental results show that the precipitated calcium carbonate can effectively fill the intra- and interparticle pores and bond adjacent particles, thus enhancing the shear strength of calcareous sand. The special structures (e.g. abundant intraparticle pores and rough surface) and mineral components (i.e. calcium carbonate) of calcareous sand are beneficial for improving bacterial retention in soil, which leads to a relatively uniform and dense calcium carbonate distribution on the sand particle surface, exhibiting a layer-by-layer growth pattern. This growth pattern and the abundant interparticle pores would result in less effective calcium carbonate. The strength enhancement of bio-cemented calcareous sand is significantly lower than that of bio-cemented silica sand at the same calcium carbonate content, which may be caused by the differences in the following: (a) soil skeleton strength; (b) the amount of effective calcium carbonate; and (c) interparticle pore-filling of calcium carbonate. [ABSTRACT FROM AUTHOR]

Understanding the mechanical behavior of calcareous sand under repeated loading-unloading is important to engineering design for island-reef underground caverns and pile foundation projects. In this study, we conducted conventional consolidated-drained triaxial shear tests on calcareous sand collected from the South China Sea under different effective confining pressures, and then, we performed multiple sets of triaxial repeated loading-unloading tests on calcareous sands with equivalent physical properties under different deviatoric stress levels and effective confining pressures. Based on the results, we conducted an in-depth investigation of the effects of the loading mode and effective confining pressure on the strain softening behavior and shear strength angle of calcareous sand. We studied the variation in the unloading rebound modulus as the effective confining pressure and deviatoric stress level changed, verified the applicability of the Dunkan-Chang model's estimation equation for the unloading rebound modulus to calcareous sand, and established the relationship among the volume contraction during unloading, the effective confining pressure, and the deviatoric stress level. The results of this study provide an important basis for selecting appropriate parameters for island-reef construction engineering. [ABSTRACT FROM AUTHOR]

Microbial-induced carbonate precipitation (MICP) is an innovative ground improvement technique that utilizes bacteria to induce calcium carbonate precipitation to cement soil particles. In this paper, the interface strength between calcareous sand and steel was improved using the MICP process. The interface shear behavior between MICP-treated calcareous sand and steel was investigated experimentally under different cementation levels and normal stresses. With the increase of CaCO3 content, the peak shear strength increased, accompanied by obvious volume dilation, and the corresponding shear displacement was reduced. The shear band thickness was suppressed greatly from 22.2d50 to 4.4d50 , and the percentage interface slip increased from 77.8% to 95.7%. With the increase of normal stress, the thickness of shear band increased and then remained stable. Both the peak and mobilized strength at 5 mm increased. MICP products changed the interface morphology and led to shear dilation of the sand sample, especially for high cementation levels. However, if the normal stress is large enough, the raised edges on the interface will be cut off and obvious contraction in the local layer near the interface appears. MICP cementation was found to have a remarkable effect on improving the cohesion of the calcareous sand–steel interface according to the Coulomb criterion. [ABSTRACT FROM AUTHOR]

To provide new insights into the liquefaction and post-liquefaction behaviors of calcareous sand with and without geosynthetics reinforcement, a series of multi-stage cyclic triaxial tests were conducted. The geosynthetics employed in this study include geogrid, geotextile, and geotextile-geogrid composite. The multi-stage tests consist of an initial cyclic loading applied to cause liquefaction, followed by undrained monotonic loading without excess pore pressure dissipation. The effect of different arrangements of reinforcement layer on the behaviors of calcareous sand is examined and discussed in this study. The test results indicate that a unique relationship can be observed between the double amplitude axial strain and the pore pressure ratio of calcareous sand, irrespective of the influence of reinforcement layer arrangement, providing an effective means of predicting the strain at a given pore pressure level. The liquefaction resistance of calcareous sand increases with the increase in the number of reinforcement layer and decreases with the increase in the distance from the first layer of reinforcement to the sample's top surface. Compared to geogrid and geotextile, the proposed geotextile-geogrid composite exhibits better efficiency in enhancing the liquefaction resistance of calcareous sand. The reinforcement also accelerates the recovery of strength for liquefied calcareous sand and increases the maximum shear strength of sand at large axial strain during the post-liquefaction stage. • The liquefaction and post-liquefaction behaviors of reinforced calcareous sand are investigated. • The relationship between double amplitude axial strain and the pore pressure ratio is established. • The arrangement of reinforcement layer has a significant influence on the liquefaction and post-liquefaction behaviors of calcareous sand. • The geotextile-geogrid composite exhibits satisfactory efficiency in improving the liquefaction and post-liquefaction characteristics of calcareous sand. [ABSTRACT FROM AUTHOR]

The shear characteristics of calcareous sand, a typical deposit in the South China Sea, could significantly influence the safety and stability of marine structures. Previous studies showed that many factors, such as temperature and surface roughness, could affect the mobilized shear strength between the calcareous sand and steel surface. Therefore, studies on the shear behaviors of the steel-sand interface under various thermal conditions are necessary. In this study, a new multifunctional sediment shear system has been developed and employed to investigate the shear performance. For this purpose, steel plates with different surface roughness were tested under various normal stress values, shear displacement rates and temperatures. Shear strength and deformation were analyzed using test data to reveal the relationships between several factors and the shear strength of the steel-sand interface. Results from test demonstrate that the interfacial shear strength on rough steel interfaces will be 1.45–3.15 times higher than that on the smooth steel interface. Besides, the shear strength of the interface rises significantly with the roughness of the steel plate. The peak friction angle increases rapidly at the start and then tends to stabilize with the increase of normalized roughness. The interfacial shear strength could be enhanced in low-temperature environments but would reduce in high-temperature environments, e.g. the energy pile, particularly under low normal stress. The shear displacement rate also has a positive effect on the interface shear strength for most cases in this study. Finally, a new nonlinear function is proposed to describe the peak friction angle ratio of foundation interface to consider the effect of temperature and shear displacement rate reasonably. • A new multifunctional sediment shear system has been developed and employed to investigate the shear performance of steel and calcareous sand. • Steel plates with different surface roughness were tested under different normal stresses, shear rates and temperatures. • A new nonlinear function is proposed to describe the peak friction angle ratio of foundation interface. [ABSTRACT FROM AUTHOR]

Calcareous sand containing weak particles originated from the deposition of skeletal residue of marine organisms is susceptible to significant particle crushing under compression and shearing. The breakage of grains results in excessive deformation and foundation failure. This study focuses on the mechanical properties and particle crushing of calcareous sand retrieved from Nansha Island, South China Sea. A series of isotropically drained and undrained triaxial compression tests were performed on reconstituted calcareous sand samples at different initial densities and at a wide range of confining stresses. The amount of particle crushing for calcareous sand after shearing was measured and quantified. Experimental results demonstrate that the shear response of calcareous sand had been well interpreted within the critical state framework. The amount of particle crushing for calcareous sand increases with increasing density and confining stress. Compared with the undrained condition, a larger amount of particle crushing of calcareous sands is observed in the drained triaxial compression test. Stress-dilatancy curves exhibit similar varying tendency for calcareous sand. Multiple critical state lines for calcareous sands with different initial densities are identified in the void ratio and logarithm of the mean stress plane. Considering the variation in stress ratio at the critical state induced by particle crushing, all stress paths are normalized to determine the state bounding surface for calcareous sand at varying densities and stresses. • Particle crushing for calcareous sand is jointly governed by density, stress level, and drainage condition. • Particle crushing-induced position shift of critical state line is observed for calcareous sand. • Bounding state surface is identified for calcareous sand at various initial densities. [ABSTRACT FROM AUTHOR]

The irregular particle shape is the significant feature of calcareous sands. It is known that calcareous sands generally show a higher liquefaction resistance than that of quartz sands, but the contribution of particle shape to the liquefaction resistance has not been well understood. In this paper, the particle shapes of calcareous sand, quartz sand and steel ball were quantitively assessed. Then, undrained monotonic and cyclic simple shear tests were conducted to investigate the influence of particle shape on the liquefaction resistance. The particle size and shape before and after simple shear were compared to assess the particle breakage. It is found that the degree of particle breakage is quite small, the surface grinding is the main mode, and the particle shape keeps almost unchanged during cyclic simple shear. Irregular sand particles show slow accumulation of excess pore pressure and need more cycles to trigger liquefaction in cyclic tests. It also shows the liquefaction resistance has a good linear correlation with the overall regularity of sand particles. Based on the fitting parameters, the liquefaction resistance of sand samples with different particle shapes can be directly obtained by the provided overall regularity of the sand particles. • Effect of particle shape on shear strength of calcareous sands during monotonic shear. • Effect of particle shape on liquefaction resistance of calcareous sands during cyclic shear. • Contribution of particle breakage to monotonic and cyclic behaviours of calcareous sands. [ABSTRACT FROM AUTHOR]