Soil-rock Mixture Research Articles

A 3D DEM modeling of soil-rock mixture considering spatial distribution orientation of blocks

Spatial distribution orientations of blocks can cause significant errors in the discrete element model (DEM) calculation of soil-rock mixture (SRM). To avoid this error, spherical harmonic (SH) series whose harmonization degrees fixed at 15 were proposed for block reconstruction. This research refers to the case-history of a deep excavation rift valley spanning from the Mabian to Zhaojue section of the Leshan-Xichang Expressway, mainly containing moderately-weathered silty mudstone, in the Leshan City, Sichuan Province, China. The appropriate degree of finite-term SH series is selected by the volume, surface area. 100 blocks were scanned on site, and sphericity and angularity of the blocks were calculated. The sphericity and angularity of 50 reconstructed blocks were considered for the error analysis of SH method. Moreover, stochastic polyhedron method was considered for comparing different block reconstructions. The maximum block placement angle was defined to control the spatial distribution orientations of the blocks. Large scale direct tests were carried. Numerical simulations of large-scale direct shear tests were conducted to study the influence of the spatial distribution orientations of the blocks on the mechanical properties of the SRMs. The results revealed that the finite-term SH series fixed at 15 accurately reflected the shape characteristics and mechanical behaviors of actual blocks. The spatial distribution orientations of the blocks had a minimal impact on the friction angle and cohesion of SRM constructed through the SH method. The SRMs developed via the SH method exhibited marginal variations in contact force and anisotropy index of contact across diverse block placement strategies. The evolution of coordination number was closer when employing the SH method under varied block placement methods. Blocks reconstructed by the SH method, could mitigate errors in DEM calculation caused by the spatial distribution orientations of the blocks.

Experimental study on shear properties and resistivity change of soil-rock mixture

Experimental study on shear properties and resistivity change of soil-rock mixture

Correction to: Effectiveness of high-energy dynamic compaction on Layered soil-rock mixture geomaterials based on field test

Correction to: Effectiveness of high-energy dynamic compaction on Layered soil-rock mixture geomaterials based on field test

Effectiveness of high-energy dynamic compaction on Layered soil-rock mixture geomaterials based on field test

Effectiveness of high-energy dynamic compaction on Layered soil-rock mixture geomaterials based on field test

A new combined finite-discrete element method for stability analysis of soil-rock mixture slopes

PurposeThe purpose of this paper is to propose a new combined finite-discrete element method (FDEM) to analyze the mechanical properties, failure behavior and slope stability of soil rock mixtures (SRM), in which the rocks within the SRM model have shape randomness, size randomness and spatial distribution randomness.Design/methodology/approachBased on the modeling method of heterogeneous rocks, the SRM numerical model can be built and by adjusting the boundary between soil and rock, an SRM numerical model with any rock content can be obtained. The reliability and robustness of the new modeling method can be verified by uniaxial compression simulation. In addition, this paper investigates the effects of rock topology, rock content, slope height and slope inclination on the stability of SRM slopes.FindingsInvestigations of the influences of rock content, slope height and slope inclination of SRM slopes showed that the slope height had little effect on the failure mode. The influences of rock content and slope inclination on the slope failure mode were significant. With increasing rock content and slope dip angle, SRM slopes gradually transitioned from a single shear failure mode to a multi-shear fracture failure mode, and shear fractures showed irregular and bifurcated characteristics in which the cut-off values of rock content and slope inclination were 20% and 80°, respectively.Originality/valueThis paper proposed a new modeling method for SRMs based on FDEM, with rocks having random shapes, sizes and spatial distributions.

Failure mechanism of a tunnel in a soil–rock mixture based on a new combined finite–discrete element method

The mechanical properties and failure characteristics of soil–rock mixtures (SRMs) directly affect the stability of tunnels constructed in SRMs. A new SRM modelling method based on the combined finite–discrete element method (FDEM) was proposed. Using this new SRM modelling method based on the FDEM, the mechanical characteristics and failure behaviour of SRM samples under uniaxial compression, as well as the failure mechanism of SRMs around a tunnel, were further investigated. The study results support the following findings: (1) The modelling of SRM samples can be achieved using a heterogeneous rock modelling method based on the Weibull distribution. By adjusting the relevant parameters, such as the soil–rock boundaries, element sizes and modelling control points, SRM models with different rock contents and morphologies can be obtained. (2) The simulation results of uniaxial compression tests of SRM samples with different element sizes and morphologies validate the reliability and robustness of the new modelling method. In addition, with increasing rock content, VBP (volumetric block proportion), the uniaxial compressive strength and Young’s modulus increase exponentially, but the samples all undergo single shear failure within the soil or along the soil–rock interfaces, and the shear failure angles are all close to the theoretical values. (3) Tunnels in SRMs with different rock contents all exhibit X-shaped conjugate shear failure, but the fracture network propagation depth, the maximum displacement around the tunnel, and the failure degree of the tunnel in the SRM roughly decreases via a power function as the rock content increases. In addition, as the rock content increases, such as when VBP = 40%, large rocks have a significant blocking effect on fracture propagation, resulting in an asymmetric fracture network around the tunnel. (4) The comparisons of uniaxial compression and tunnel excavation simulation results with previous theoretical results, laboratory test results, and numerical simulation results verify the correctness of the new modelling method proposed in this paper.

Mechanical Characterization of Soil–Rock Mixture Under Varying Block Parameters, Matrix Properties and Matrix Water Content Using Destructive and Non-Destructive Testing

Mechanical Characterization of Soil–Rock Mixture Under Varying Block Parameters, Matrix Properties and Matrix Water Content Using Destructive and Non-Destructive Testing

Investigation of Particle Gradation Effect on Soil-Rock Mixture Using Direct Shear Test

Soil-rock mixture (SRM) is a special geomaterial that is composed of soil and a certain percentage of rock blocks with various sizes and strengths. It has high structural strength and renewable resources that are used as filler in subgrade, construction material and embankment dams. However, the mechanical properties of the soil-rock mixture are sophisticated owing to the complicated interaction between soil and rock particles. Previously, many experimental investigations were conducted to focus on shear behaviours and the influencing factors of SRM. Yet, limited w ork has been done to underline the effect of particle size distribution towards SRM shear strength parameters. Thus, this study conducted an SRM shear test with three different kinds of gradation and rock block percentages. Various soil densities, porosities and different framework structures have resulted from different rock particle concentrations. From the results, the well-graded SRM shows a non-linear trend of cohesion value while uniformly graded and gap-graded SRMs shows contradicting trend respectively. The result and analysis in this study are especially useful in analysing its influence on the shear strength parameters of SRM with different rock block percentages.

A novel approach to stability analysis of random soil-rock mixture slopes using finite element method in ABAQUS

A novel approach to stability analysis of random soil-rock mixture slopes using finite element method in ABAQUS

A new macro- and micro- coupling model of barrier dam soil

Barrier dams are widely distributed worldwide. It is highly important to accurately evaluate the safety and emergency response of barrier dams. However, the stressstrain relationship of barrier dam soil, which is an important issue for the safety evaluation of barrier dams, has not been elucidated clearly because of its complex composition and wide particle gradation. Based on the proposed macro- and micro- coupling modeling scheme, a series of CT triaxial tests were carried out on barrier dam soil to observe the macroscopic and microscopic behavior. Based on the particle displacement distribution, a fabric evolution rate was proposed as an index to describe the evolution of fabric behaviors. A significant correlation was detected between the shear band fabric evolution rate and the macroscopic mechanical properties of the soil. The fabric evolution equation, modulus evolution equation and Poisson's ratio evolution equation were proposed to set up a new macro- and micro- coupling model for barrier dam soil. The model has only five parameters that have definite physical meanings and can be easily determined by a series of triaxial tests. The validity of the proposed model was verified by different types of tests of barrier dam soil and soilrock mixtures. The model can reasonably describe the fundamental properties of barrier dam soil with wide particle gradation. The proposed model established by macro- and micro- coupling modeling considers the relationship between macroscopic mechanical properties and microscopic fabric behavior, which is suitable for barrier dam soils with wide particle gradations.

A study on the evolution of microstructure of soil-rock mixtures based on the electrochemical conductive paths model under different rock and moisture content conditions

ABSTRACT To further improve the understanding of the evolution law of the microstructure of SRM in road engineering under moisture and rock content, the electrochemical impedance spectroscopy test under different moisture and rock conditions was carried out. This paper proposed an electrochemical model of different conductive paths based on different cementation states. The impact of rock and moisture content on the characteristic parameters of the conductive path model was analyzed. The results indicated the impedance spectrum curves became more pronounced with the continuous decrease in moisture content and increase in rock content. There was a well-defined exponential relationship between total impedance and both moisture and rock content. The total impedance decreased continuously with increasing moisture content and increased with increasing rock content. The characteristic parameters had practical significance in representing the microscopic structure. The moisture content primarily influenced the variation trends of the representation parameters by altering the channel width, length, and quantity of the continuous pore water solution pathways and the discontinuous rock-soil bonded bodies. The rock content affected the changes by compressing the external and internal pore water solution and soil particles, altering the compression and support between the continuous pore water solution pathways and the block rock framework.

Research on the dynamic resilience characteristics of carbonaceous mudstone soil-rock mixture under wet-dry cycles

Research on the dynamic resilience characteristics of carbonaceous mudstone soil-rock mixture under wet-dry cycles

Effect of gradation on macro-meso shear properties of the alluvial-diluvial soil-rock mixture (ADSRM)

Alluvial-diluvial soil-rock mixture (ADSRM) is a unique geological material primarily consisting of pebbles, gravel, and soil. Gradation design significantly enhances the shear strength of ADSRM, offering significant implications for sustainable construction of transportation infrastructure in mountainous regions. Hence, the N-method of gradation theory was employed for the gradation design of ADSRM fillers in this study. Macro-mechanical testing reveals that the graded sample exhibits significantly higher shear strength, equivalent cohesion, and friction angle compared to the ungraded sample, with more pronounced shear dilatancy. Meso-shear properties suggest that the graded sample has a lower percentage of pore area compared to the ungraded sample, but a higher percentage of small pores relative to total pores, and more crushed rock blocks under the same normal stress conditions. Pore abundance indicates that the majority of pores on the shear plane are oblate in shape. The findings from the equivalent diameter and fractal dimension of the rock block contour suggest improved grinding roundness of rock blocks in the graded sample post-shearing. In summary, the quantity of pores and broken rock blocks primarily impacts the strength and equivalent cohesion of the filler, while the abundance, roundness, shape coefficient, and fractal dimension of rock block contour mainly affects the internal friction angle.

Evaluating thermal conductivity of soil-rock mixtures in Qinghai-Tibet plateau based on theory models and machine learning methods

The thermal property of the scum layer (soil-rock mixtures) has dominant influence on the heat exchange efficiency between the lower rock layer and the upper environment in the open-pit mines of the cold regions. This paper presents a series of thermal conductivity tests (560 samples) on the scum particle to investigate the coupling effects of ice (moisture) content, temperature, and particle size distribution on the thermal properties. Previously reported models (47 empirical or theoretical models) were adopted to predicate the thermal conductivity of soil-rock mixtures in order to validate the evaluation ability of these models under the wide testing ranges. The comparison results indicate that the theoretical models, normalized model and linear/non-linear models all can not fully predict experimental results under the wide testing conditions. Three machine learning algorithms were used in the assessment presentation for the thermal properties of soil-rock mixtures. The performance of three machine learning algorithms were contrastively examined by using three important indexes (the coefficient of determination (R2), the root mean square error (RMSE) and the relative error (RE)). Based on the evaluation results, the performance ranking of three machine learning algorithms can be listed (GA-BP > SVR > RFR). This investigation is a beneficial attempt for the large data analysis to introduce the machine learning method into the determination of the thermal conductivity of soil-rock mixture under complex conditions.

Study on shear surface morphology and failure mechanism of soil-rock mixture under wet-dry cycle action

The present study investigates the failure modes and formation mechanisms of shear surfaces in soil-rock mixtures from various perspectives. Firstly, through in-situ direct shear tests, two main shear failure modes, namely planar and non-planar, are identified. Subsequently, using PFC 2D numerical simulation, an in-depth exploration of the characteristics and causes of these two typical failure modes is conducted. The findings reveal that in the natural state, the material is relatively dry, and the matrix suction within the soil-rock mixture is significant. During shearing, the inter-particle force chains are prone to rupture, exhibiting characteristics akin to brittle failure. This leads to nearly planar shear surfaces, with force chain ruptures primarily localized near the planar regions adjacent to the shear surface. However, after multiple dry-wet cycles, the plastic enhancement of the soil-rock mixture reduces the matrix suction to almost zero. The continuous rupture and reorganization of force chains deepen the shear band under their influence, resulting in non-planar shear surfaces. It is noteworthy that the characteristic point fitting curve of non-planar shear surfaces exhibits a nonlinear trend. In summary, our study elucidates the evolution process and causes of shear surface morphology in soil-rock mixtures, which holds significant implications for understanding their mechanical properties and engineering behavior.

Numerical Investigation of Soil–Rock Mixture Landslide Runout by Random Field and Finite Elements

Numerical Investigation of Soil–Rock Mixture Landslide Runout by Random Field and Finite Elements

Computational model for the thermal conductivity of soil-rock mixture

Soil-rock mixture (S-RM) consists of a mixture of soil and crushed rocks, and their thermal conductivity is highly important in underground engineering. Currently, research on thermal conductivity is primarily focused on soil and rock individually, with minimal attention given to S-RM thermal conductivity. This paper aims to develop a model capable of accurately calculating the thermal conductivity of S-RM by conducting an in-depth analysis of the macrostructure of soil and crushed rocks. First, a series-parallel model of S-RM was developed based on the series-parallel concept of resistors. Second, considering that the intermixing of fine-grained soil and coarse-grained crushed rocks during the fabrication of S-RM results in reduced porosity and elevated saturation - factors that influence thermal conductivity - a refinement has been applied to the generalized thermal conductivity model proposed by Côté and Konrad. The proposed modified model of thermal conductivity is applicable to the S-RM. Finally, the modified model was proven to have high accuracy in predicting the thermal conductivity of S-RM through testing.

Ultrasonic properties and damage expression of frozen soil-rock mixture with various block conditions

Ultrasonic properties and damage expression of frozen soil-rock mixture with various block conditions

Study on the variation of the permeability coefficient of soil–rock mixtures in fault zones under different stress states

AbstractAs the first gold mine discovered at the sea in China and the only coastal gold mine currently mined there, Sanshandao Gold Mine faces unique challenges. The mine's safety is under continual threat from its faulted structure coupled with the overlying water. As the mining proceeds deeper, the risk of water inrush increases. The mine's maximum water yield reaches 15 000 m3/day, which is attributable to water channels present in fault zones. Predominantly composed of soil–rock mixtures (SRM), these fault zones' seepage characteristics significantly impact water inrush risk. Consequently, investigating the seepage characteristics of SRM is of paramount importance. However, the existing literature mostly concentrates on a single stress state. Therefore, this study examined the characteristics of the permeability coefficient under three distinct stress states: osmotic, osmotic–uniaxial, and osmotic–triaxial pressure. The SRM samples utilized in this study were extracted from in situ fault zones and then reshaped in the laboratory. In addition, the micromechanical properties of the SRM samples were analyzed using computed tomography scanning. The findings reveal that the permeability coefficient is the highest under osmotic pressure and lowest under osmotic–triaxial pressure. The sensitivity coefficient shows a higher value when the rock block percentage ranges between 30% and 40%, but it falls below 1.0 when this percentage exceeds 50% under no confining pressure. Notably, rock block percentages of 40% and 60% represent the two peak points of the sensitivity coefficient under osmotic–triaxial pressure. However, SRM samples with a 40% rock block percentage consistently show the lowest permeability coefficient under all stress states. This study establishes that a power function can model the relationship between the permeability coefficient and osmotic pressure, while its relationship with axial pressure can be described using an exponential function. These insights are invaluable for developing water inrush prevention and control strategies in mining environments.

Predicting permeability coefficient in soil-rock mixtures using parameters from the negative exponential continuous grading equation

Soil-rock mixtures (SRMs) are widely utilized for embankment filling of highways in mountainous areas. The permeability characteristics of SRMs must be investigated as mountain highways are often exposed to strands of rainwater subjected to extreme rainfall. For the same species of SRM, its permeability is determined by its pore distribution and grading characteristics, which can be considered as an expression of particle grading and pore parameters. The predictive model of the SRMs permeability coefficient encompassing gradation coefficients and porosity was proposed based on the negative exponential continuous gradation equation and the Kozeny–Carman model. The applicability of the prediction model was verified based on the existing literature and performing SRMs seepage tests. The findings indicated that the permeability coefficient formula for SRMs established on the particle grading parameters and porosity was reasonable. Nevertheless, its current applicability is limited to the prediction of permeability coefficients for continuously graded SRMs. Consequently, further investigation is required to assess the suitability of the model for intermittently graded SRMs.