Rock Mixture Research Articles

Analysis on mechanical properties and evolution of mesostructure of soil–rock mixture samples from contact network perspective

Analysis on mechanical properties and evolution of mesostructure of soil–rock mixture samples from contact network perspective

Analysis of Strength and Compression Damage Characteristics of Soil Rock Mixture Based on Geopolymeric Reaction

Geopolymers was a common means of solidifying soil which can improve the overall strength of the soil. In order to further explore the strength and damage characteristics of the soil-rock mixture under the action of gel coagulation, this paper analyzed the compressive strength of the soil-rock mixture under different stone content through the unconfined compressive strength test. The results illustrated that when the amount of stone was small, the compressive strength decreases linearly with the increase of the amount of stone, and increased with the increase of the amount of geopolymer; According to discrete element method, using PFC2D software, to simulate the microscopic deformation and mechanical properties of the specimen during compression. The increase of stone content would magnify the damage of the soil when it reached the failure, but it did not necessarily increase the overall soil mass numerically. The strength of the soil would be greatly improved when the stone content reached a state that could form a skeleton structure.

Granular discrete element simulation of the evolution characteristics of the shear band in soil–rock mixture based on particle rotation analysis

Based on the 3D laser scanning technology, the surface morphologies of the rock blocks collected from the soil–rock mixture (S–RM) were scanned. The numerical model of the S–RM with different rock block proportions were established. To study the deformation and failure characteristics of the S–RM during the formation and evolution of the shear band, the numerical large-scale direct shear tests under different normal stresses were performed on these S–RM samples, the failure points were recorded by the detection of contact failure. Base on the step accumulation of particle’s spin, the rotation angles of rock blocks were monitored in the simulation. A parameter $${P}_{\theta }$$ is introduced to describe the evolution characteristics of the shear band. Results show that the, $${P}_{\theta }$$ of the S–RM with the rock block proportion of 60% is obviously greater than the others. The formation and evolution process of the shear band in the S–RM was consistent with the evolution process of the local particle’s rotation. The rotation of the soils always preceded the rotation of the rock blocks, which reflects the “bully” deformation characteristic of S–RM in the shear band formation process. In the form of the failure distribution, the interior failure of the S–RM with low rock block proportions was mainly the thin band-shaped destruction between the soils. However, higher rock block proportion caused more interactions between soils and rock blocks in the S–RM, and the destruction presented a thick cloud-like distribution. The shear fractures in the soils and tensile fractures along the contact planes between soils and rock blocks are the main failure pattern of S–RM under shear tests.

Shear properties and pore structure characteristics of soil–rock mixture under freeze–thaw cycles

Soil–rock mixtures (S-RMs) are widely distributed in the shallow surfaces of cold regions that experience frequent freeze–thaw cycles, considerably threatening the stability of the soil–rock slopes on both sides of the road. We examine the S-RM shear strength and deformation characteristics under different freeze–thaw cycles through experiment and simulation. Nuclear magnetic resonance (NMR) was used to analyze the influence of freeze–thaw cycles on the internal pore structure of S-RM and establish the internal relationship between pore structure and shear characteristics under freeze–thaw cycles. Results show that the shear strength parameters of S-RM first decrease, then increase, and finally decrease as the number of freeze–thaw cycles increases; besides, the vertical expansion range of cracks gradually increases during shearing with the number of cycles. Porosity first increases, then decreases, and increases again with the number of freeze–thaw cycles. NMR results showed that S-RM pores had fractal characteristics. According to the fractal dimension, the soil particles inside the sample formed larger aggregates after the first freeze–thaw cycle. After the second–third freeze–thaw cycles, the agglomerated soil particles gradually disintegrate and tend to homogenize. The soil particles cover the surface of the gravel under the skeleton deformation to form an inclusion structure. The subsequent increase in the number of freeze–thaw cycles causes the soil particles attached to the gravels to gradually peel off.

Failure Patterns and Morphological Soil–Rock Interface Characteristics of Frozen Soil–Rock Mixtures under Compression and Tension

Construction operations in cold regions may encounter frozen geomaterials. In construction, it is important to understand the processes by which geomaterials fail under common loading conditions to avoid accidents and work efficiently. In this work, an artificial frozen soil–rock mixture was used for uniaxial compression and indirect tension loading analysis to investigate macroscopic failure patterns and soil–rock interface crack evolution mechanisms. To further understand and compare the meso-mechanical failure mechanisms of the soil–rock interface, we used two types of rock block particles with different surface roughness for fabricating frozen artificial soil–rock mixtures. Acoustic emission (AE), ultrasonic plus velocity (UPV), and digital microscopy were utilized here to obtain the sample deformation response and analyze the morphology of the soil–rock interface. The results were as follows. From the perspective of macroscopic observation, bulging deformations and short tension cracks represent the main failure pattern under compression, and a tortuous tension crack in the center of the disk is the main failure pattern under indirect tension. From the perspective of microscopic observation, the soil–rock interface will evolve into a soil–rock contact band for the sample containing a rough rock block. The strength of the soil–rock contact band is obviously larger than that of the soil–rock interface. Three main failure patterns of the soil–rock interface were observed: a crack path through the accurate soil–rock interface, a crack path through the envelope of the rough rock block, and a crack path passing through the rough rock block. The experimental results could provide a reference for foundation engineering, especially in pile foundation engineering in cold regions.

A Novel Method of On-Line Coal-Rock Interface Characterization Using THz-TDs

The core problem in unmanned/intelligent working face of coal mining is the automatic adjustment of shearer arm where the coal-rock interface detection is the key. The cutting location of shearer drum affect the proportion of coal and rock powder around the cutting teeth of shearer drum. Therefore, the method of on-line coal rock interface characterization using Terahertz Time Domain spectroscopy (THz-TDs) we proposed aims to estimate the ratio of rock by Terahertz response. Firstly, anthracite and quartz sandstone were uniformly mixed according to 39 different ratios in this study, the samples' responses were obtained by terahertz system, and then the obtained time domain data was converted into frequency domain data by fast Fourier transform. The absorption coefficient spectrum and the refractive index profile of the 39 samples were calculated by optical parametric model. Secondly, corresponding quantitative model between mixed coal/rock powder and THz signal was built by using back propagation neural network (BPNN) and least squares support vector machine (LSSVM). We expected to use the ratio of rock powder detected by the model to estimate the depth of shearer drum teeth embedded in the rock layer. Finally, we found that both two mathematical arithmetic is feasible to quantitatively detect different proportion of coal and rock mixtures. The results show that the depth of shearer drum teeth embedded in the rock layer could be estimated by the novel method, which means the coal-rock interface could be on-line characterized by using THz-TDs and the height of the drum could be adjusted in time.

Quantitative analysis of binary and ternary organo-mineral solid dispersions by Raman spectroscopy for robotic planetary exploration missions on Mars.

The Mars 2020 and ExoMars 2022, rover-based missions are specifically dedicated to the search for evidence of life and will both utilise Raman spectrometers on the surface of Mars. Raman spectroscopy is indeed a valuable analytical technique for planetary exploration that enables in situ characterisation of rocks and soils collected directly from the surface or retrieved as cores and subsequently crushed when extracted from the subsurface with a drill. On Mars, the miniaturised spectrometers will interrogate ancient geological deposits, in order to try and identify hydrated or aqueously altered minerals and organic matter to assess the habitability of Mars. While the identification of relevant hydrous minerals and organic components is the primary analytical objective of the missions, quantifying their abundances would be of particular significance for interpreting past geological conditions (e.g. formation or alteration processes) and for ascertaining the putative presence of biosignatures. Therefore, we have developed quantitative models that enable the quantification of both mineral proportions from crushed mixtures of geological components and spiked mixtures containing organic analytes dispersed in mineral matrices. Based on data normalisation with appropriate standards (internal and external), we demonstrate that robust quantitative models can be (1) applied for solid dispersions of various complexities relevant to planetary exploration; and (2) applied to different Raman set-ups, including an instrument representative of the ExoMars Raman Laser Spectrometer. With important Raman-active minerals (calcite, gypsum, baryte, quartz), we demonstrate that using a correction factor Fϕ2/ϕ1, based on the ratio of apparent Raman scattering coefficients, the relative proportion of minerals in binary mixtures can be accurately determined. Regarding the organics, evaluated in clay-rich sediments (Fe-smectite) and crushed rocks of coarse-grained fraction (>100μm), we establish calibration curves in the concentration range 2-20 wt% for non-resonant compounds (L-cysteine, phthalic acid, adenine) and even lower (<1 wt%) for pre-resonant anthracene. Despite large levels of heterogeneity, the Raman analyses of these solid dispersions verify that quantitative Raman analyses can be performed in the context of robotic exploration studies.

Study on the progressive fracturing in soil and rock mixture under uniaxial compression conditions by CT scanning

Soil and rock mixture (SRM) is very common in engineering as a type of extremely heterogeneous and anisotropic geological material. SRM is easy to fracture and damage under external forces, which often causes geological disasters, such as landslide and debris flow. Therefore, study on the progressive fracturing of this material is very important for geological engineering. In this paper, uniaxial compression test with real-time computed tomography (CT) scanning was conducted on SRM samples (with rock percentage of 40%). The evolutions of visible fractures, invisible fractures in CT slices, average density and heterogeneity of the sample during loading process were all studied quantitatively. This research finds that invisible fractures occur soon once loading begins, gradually accumulate in elastic deformation stage, and finally form visible fractures in plastic deformation stage. Average density of the whole sample slightly declines, while heterogeneity greatly increases during the evolution of fracturing.

Application of the discrete element method and CT scanning to investigate the compaction characteristics of the soil–rock mixture in the subgrade

The soil–rock mixture (SRM) usually contains a large amount of gravels exceeding 40 mm in size, so the traditional laboratory method cannot directly test its maximum dry density (MD), making it difficult to evaluate the compaction degree of the SRM subgrade during construction. In this paper, a numerical simulation method of the vibration compaction method for the SRM (NSM-VCM) was developed based on a discrete element method (DEM) and CT scanning. Based on the established NSM-VCM, the MD of SRMs with a maximum particle size greater than 40 mm (SRM-G) was investigated comprehensively. Based on the results of laboratory tests and the NSM-VCM, a predictive model and determination method of the MD of SRM-G were developed. Finally, field measurements were conducted to validate the laboratory investigations. The results showed that the maximum error between the MD of the SRM obtained from the NSM-VCM and the laboratory test was 0.1%, indicating that the established NSM-VCM has high predictive accuracy. The MD of SRM-G increases with an increasing maximum particle size and dosage of giant granules. Only when the soil–rock ratio is appropriate can SRM-G form a better skeleton dense structure, which is important for improving the MD and mechanical strength. The maximum error between the estimated MD and the measured MD from the field site is 1.3%, which indicates that the prediction model and method for SRM-G established in this paper have high precision. These results address the issue that the MD of SRM-G cannot be determined in a laboratory.

Experimental study on the prediction model of the cumulative strain of the soil–rock mixture backfill under metro train load

An indoor dynamic triaxial test was performed on the soil–rock mixture (SRM) backfill in Chongqing to study the cumulative strain characteristics of the SRM under the cyclic dynamic loading of the metro train. The effects of different consolidation degrees U, rock block contents P, and effective consolidation confining pressures were then analyzed. Results showed that when and P are the same, the lower the U, the faster will be the increase in cumulative strain. When U and P were the same, the lower the , the greater will be the increase in cumulative strain and the higher will be the cumulative strain stable value of the stability curve. When U and were the same, the lower the P, the faster will be the increase in cumulative strain. An empirical model of the cumulative strain of the SRM considering the influence of U, P, and was established on the basis of the results of the dynamic triaxial tests. The accuracy of the prediction model was verified against the actual test results. This study provides a theoretical basis for the settlement and deformation evaluation of SRM backfill subgrades under metro train cyclic loading.

Deformation Characteristics of the Shear Zone and Movement of Block Stones in Soil–Rock Mixtures Based on Large-Sized Shear Test

Soil–rock mixtures (SRM) have the characteristics of distinct heterogeneity and an obvious structural effect, which make their physical and mechanical properties very complex. This study aimed to investigate the deformation properties and failure mode of the shear zone as well as the movement of block stones in SRM experimentally, not only considering SRM shear strength. The particle composition and proportion of specimens were based on field samples from an SRM slope along national highway 318 in Xigaze, Tibet. Shear zone deformation tests were carried out using an SRM-1000 large-sized geotechnical apparatus controlled by a motor servo, considering the effects of different stone contents by mass (0, 30%, 50%, 70%), vertical pressures (50, 100, 200, 300, and 400 kPa), and block stone sizes (9.5–19.0, 19.0–31.5, and 31.5–53.0 mm). The characteristics of the shear zone deformation and block stone interactions were monitored by placing aluminum wires and dry ash in holes in the specimens. The results showed that the stone content 30% and 70% were two critical thresholds to determine the deformation characteristics of SRM. Under the conditions of high stone content and large particle size, the stones throughout the shear surface tended to extrude and roll during the shear process. The block stones around the shear surface were mainly affected by dilatancy and exhibited extrusion, particle breakage, and redistribution. The deformation pattern could be considered as be analogous to push-type shear deformation from the back to front or composite shear deformation from the front and back to the middle of the slope. It is of great importance to study the shear characteristics and deformation evolution of SRM to understand the progressive shear process of the sliding zone and the failure mode of landslides.

Study of hidden factors affecting the mechanical behavior of soil–rock mixtures based on abstraction idea

Because of spatial variability and complex compositions, the mechanical test results of natural soil–rock mixtures (SRMs) are often discrete and lack reproducibility, which has greatly restricted the practical application of the experimental findings. The objective of this study was to examine the general mechanical behavior of SRMs under the influences of some hidden factors (e.g., structural parameters, parent rock type and weathering degree). To that end, the abstraction idea was adopted to prepare purified SRM samples. Large-scale triaxial tests were performed on these purified materials. On this basis, the influences of three structural parameters on the mechanical behavior of SRMs were studied. Moreover, the relationship between the shear strength and parent rock type and that between the shear strength and the spatial distribution of rock blocks were quantified. Some additional intrinsic behavior was distinguished from individual experimental phenomena through the comparative analysis of the test data in this study and those reported in the literature. The results show that the hidden factors had significant influences on the mechanical behavior of SRMs. A greater saturated uniaxial compressive strength of rock blocks generally led to a larger shear strength of SRMs. According to the significance of their influences on the shear strength parameters of SRMs, the structural parameters are ordered as: the gradation of rock blocks, the initial dry density of sample and the spatial distribution of rock blocks. The deformation and failure feature of SRMs were considerably affected by the spatial distribution of rock blocks and shear rate. And the shear strength parameters of SRMs were mainly influenced by the content of grains between 40 and 60 mm. The findings of this study would provide useful guidance for engineering practice.

Influence of rock percentage on strength and permeability of tailing-waste rock mixtures

The strength and permeability of tailing-waste rock mixtures directly affect deposits’ stability for an alternative co-disposal technique. In the mixed co-disposal method, the void of the waste rock is filled with tailings, while the waste rock forms the particle skeleton. This method does not only improve deposits stability but also potentially reduces acid pollution. In this study, the rock percentage influence on the shear strength and permeability of tailing-waste rock mixtures was investigated by carrying out large triaxial tests and permeability tests. The shear strength, enhanced strength mechanism, and mixture permeability were analyzed. The results indicate that the shear strength and internal friction angle of the tailing-waste rock mixtures gently increased until the rock percentage reached 30% and then rapidly increased with the further increase of the rock percentage. The permeability coefficient of the mixtures slowly increased until the rock percentage reached 50% and then rapidly increased with the further increase of the rock percentage. The tailings washed out of the waste rock skeleton when the permeability was large. In this paper, 50% of waste rock is recommended for building mixture deposits.

Hydro-mechanical simulation of the saturated and semi-saturated porous soil–rock mixtures using the numerical manifold method

Dynamics of the widespread saturated and semi-saturated soil–rock mixtures (SRMs) are of importance in practical engineering. In this paper, a numerical manifold model is presented for hydro-mechanical simulation of the saturated and semi-saturated SRMs. In the case of the semi-saturated SRMs, the model is based on the generalized Biot theory involving immiscible two-phase wetting and non-wetting fluids in deformable porous media. The wetting, non-wetting fluid pressure and skeleton displacement are chosen to be primary variables which are related to the wetting and non-wetting saturation and permeability by experimental relationships. For the mechanical problem, the material interfaces between soil and rock are deemed discontinuous by imposing a stick–slip contact constraint using an augmented Lagrange multiplier approach. For the hydraulic problem, the material interfaces are continuous for the fluid pressure and flux fields. Within the framework of the numerical manifold method (NMM), the discretized model including the interfacial discontinuities always can be established using the triangular mesh and the lumped mass representation is always available to increase computational efficiency. Besides the benchmark problems of saturated and semi-saturated porous media, two examples of soil–rock foundation and slope are performed to demonstrate the versatility and robustness of the model and to investigate the hydro-mechanical responses of the porous SRMs.

Influence of water and rock particle contents on the shear behaviour of a SRM

Abstract The contents of both water and rock particles are important factors affecting the mechanical strength of a soil–rock mixture (SRM) filled subgrade in the western mountainous area of China. Therefore, the purpose of this paper is to study the mechanisms of reconstituted landslide deposit samples with different water and rock particle contents by analysing the characteristics of shear strength, volumetric strain and ‘jumping’ phenomenon via large-scale direct shear tests. The results show that the influence of water content on shear strength is greater than the influence of rock particle content under a lower normal stress, and the results are reversed in the case of a higher normal stress. The effect of water content on the equivalent cohesion is bigger, especially for the sample with a high rock particle content. The friction angle of the specimen with same water content increases with the increasing rock particle content, but when the number of rock particles increases to a certain extent, there is a little effect on the friction angle. However, the friction angle decreases with increasing water content at the same rock particle content. Specimens with the same rock particle content change from dilation to compression with increasing water content. Finally, the continuous stage of the ‘intense jumping’ at different water content has been analysed. The ‘jumping’ phenomenon of samples with low water and rock particle content will first strengthen and then weaken the samples with increasing normal stress.

Strain-softening failure mode after the post-peak as a unique mechanism of ruptures in a frozen soil-rock mixture

A large number of traffic systems in China pass through a large area of frozen soil, most of which contains frozen soil–rock mixtures (FSRMs). For a profound understanding of the mechanical behaviours and damage mechanisms of geotechnical and geoenvironmental projects, it is necessary to understand the stress–strain characteristics and failure modes of FSRMs. This study focuses on the uniaxial compression strength (UCS), Young's modulus, and complete stress–strain curve under loading, considering the post-peak behaviour. More than 250 FSRM specimens were tested for UCS evaluations, while considering the effects of different freezing temperatures (−5, −10, −20, −30, and − 40 °C), initial water contents (15.0, 25.0, and 30.0%), and volumetric block proportions (0, 30, 40, 50, and 100%). The stress–strain curve of the FSRM was characterised by six distinct stress levels and deformation stages, different from those of rock or soil in the normal state. Particularly, the turning point from volume compression to expansion was observed after the post-peak, at which superficial cracks were initiated. Ice crystals provided ductility of the FSRM and maximised its load capacity to prevent premature cracks on the FSRM surface. The block stone hindered the linear propagation of cracks. The failure patterns of the FSRM for the UCS evaluation could be classified into four types. The UCS was influenced by mainly the strength of the mixture composed of ice crystals and soil particles and friction and occlusal strength between blocks. Notably, the gradual thawing of the FSRM might cause the largest deformation at the bottom of the active layer in summer and autumn, according to the experimental results. Thus, it is very important to understand the strength characteristics, deformation stages, and failure patterns associated with the geomechanical behaviour of the FSRM for engineering design and applications in a permafrost region.

Accelerated carbonation of C2SH based dense concrete

In this work the possibility of producing a CO2 hardened concrete where the binder is a calcium silicate hydrate instead of anhydrous silicates was investigated and the technological parameters for obtaining calcite based products, combining Ca2(HSiO4)(OH) (α-C2SH) hydrothermal synthesis and accelerated carbonation curing were presented. α-C2SH was synthesized in a stirred suspension (water to solid ratio 10, 100 rpm) after 16 h at 200 °C from lime-opoka (silica-calcite sedimentary rock) mixture with molar ratio CaO/SiO2 = 2.0. Pressed cylindrical samples from synthesized binder and its mixtures with sand were carbonated in the CO2 environment at 1.5 MPa and at 45 °C from 8 to 48 h. It was shown that α-C2SH is, in fact, a binder that hardens in a carbon dioxide atmosphere. Compressive strength of the samples carbonated for 8 h was ~10 MPa and with extended curing, reached ~35 MPa and ~60 MPa after 24 and 48 h, respectively. By XRD and STA it was found that most of the α-C2SH sample carbonates within the first 8 h of curing. Amount of CaCO3 continues to grow gradually but steadily for up to 48 h. SEM and 29Si MAS NMR indicated that the compressive strength development is rather more reliant on the calcite crystal growth than silica gel polymerization. Concrete products from binder/sand mixture (1:3 by mass) with a compressive strength of ~25 MPa can be produced when carbonation is performed at 1.5 MPa CO2 pressure, 45 °C, and 24 h duration. α-C2SH binder, compared to Ordinary Portland cement, has a significantly lower negative impact on the environment due to lower amounts of calcareous raw materials and the elimination of high-temperature combustion.

A Monte Carlo Approach to Estimate the Stability of Soil–Rock Slopes Considering the Non-Uniformity of Materials

A soil–rock slope is a heterogeneous slope composed of soil and rocks that is widely distributed throughout the world. In order to accurately analyze the slope stability of soil–rock mixture, based on a Monte Carlo algorithm (fuzzy-based method), a symmetrical stability analyzing method for soil–rock slopes is proposed, considering the dispersion of strength of soil–rock mixtures. In analyzing it, the numerical model is symmetrical to the real soil–rock slope in geometry and material properties. In addition, the effect of rock content to slope stability was studied by this symmetrical method. The specific work of this paper is as follows: (1) The acquisition method of random number series for the Monte Carlo algorithm and the method of slope stability analysis, using the Monte Carlo method, are introduced. (2) According to in situ samples and remade samples, the strength characteristics of soil–rock mixtures were measured with different rock contents, which proved the scatter of strength of soil–rock mixtures. (3) Based on the measured strength parameters of soil–rock mixtures and the slope landslide, the reliability in analyzing results and superiority in calculating time of using the Monte Carlo method to analyze stability of soil–rock slopes are detailed. (4) The stability of soil–rock slopes with different rock content is discussed with the Monte Carlo method, and it is concluded that with the increase of rock content, the stability of a soil–rock slope decreases first and then increases, and the minimum safety factor is acquired at 20% rock content. (5) Based on a large number of calculation examples, the applied situations of the Monte Carlo method to analyze stability of soil–rock slopes are detailed according to sampling results and rock size.

Proppant Diagenesis in Carbonate-Rich Eagle Ford Shale Fractures

SummaryProppant diagenesis occurs when minerals form on the proppant surface and/or around the embedment crater at high-temperature and/or high-stress conditions (Weaver et al. 2005). It has been used recently to explain low fracture conductivity in the field as well as the long-term downward trend of laboratory-measured American Petroleum Institute conductivity data (Liang et al. 2015). However, researchers disagree about the source of such overgrowth minerals and the involvement of proppant in the process. In addition, the diagenesis process has not been investigated in the case of carbonate-rich shale formations. Therefore, the objectives of this paper are to experimentally investigate the proppant diagenesis process during hydraulic fracturing of the Eagle Ford Shale Formation and to determine the role of the proppant in the process.Diagenesis was studied after aging a mixture of proppant and formation samples in deionized water for 3 weeks at 325°F and 300 psia. Outcrop cores of the Eagle Ford Shale Formation were crushed and sieved to 50/100 US-mesh size. The ceramic, sand, and resin-coated-sand (RCS) proppants of 20/40 US-mesh size were tested. The proppant surface was studied for mineral overgrowth and/or dissolution before and after aging using scanning electron microscope (SEM) with energy-dispersive X-ray spectroscopy (EDS). The concentration of the cations leached into the solution was measured by analyzing the supernatant samples using inductively coupled plasma (ICP)/optical-emission spectroscopy, while the sulfate-ion concentration was measured using a spectrophotometer. The proppants and the Eagle Ford Shale Formation samples were analyzed after aging separately at the same conditions to explain the sources of the leached ions and the observed overgrowth and/or precipitated minerals.The Eagle Ford Shale was found to be the source of calcium sulfate and calcium zeolite precipitates because of dissolution/precipitation reactions with water. Only the ceramic proppant was found to induce an additional mineral overgrowth of iron calcium zeolite on its surface. Conversely, the sand and RCS proppants did not encounter any precipitates/overgrowth minerals. These proppants only changed the elemental composition of the precipitated zeolite from the formation/fluid interaction, showing increased silicon and decreased calcium and aluminum concentrations. The proppant dissolution was observed with all types of proppants, as indicated by the presence of silicon ions in the solution after aging. A thermodynamic modeling study was conducted and confirmed the possibility of formation of the observed precipitate and overgrowth minerals at the equilibrium state of the rock and proppant mixture in water. Finally, the breaking and peeling of the phenol formaldehyde resin from the RCS proppant particles at static conditions was observed for the first time (to the best of the authors’ knowledge) using the SEM technique.The study contributes to the understanding of the scale formation and the mechanisms that damage fracture conductivity in the Eagle Ford Shale. Results impact the choice of fluid and proppant for fracturing optimization and long-term production sustainability in the Eagle Ford Shale reservoirs.

Effect of gravel content on the sediment transport capacity of overland flow

The sediment transport capacity (Tc) is an important parameter for analysing and controlling soil erosion processes. However, few studies have investigated the Tc of soils containing gravel (grain sizes of >2 mm) on steep slopes. Colluvial deposits on steep slopes in benggang are composed of loose materials with large amounts of gravel. This study aimed to investigate the effects of gravel content on the Tc of overland flow using colluvial deposits with a range of slope gradients and flow discharges in a nonerodible flume (4 m long, 0.12 m wide and 0.1 m high). The experiments were carried out using six gravel mass contents (0, 10, 20, 30, 40, and 50%), four slope gradients (18, 36, 57, and 84%), and four flow discharges (0. 56, 1.11, 2.22, and 4.44 × 10-3 m2 s−1). The experimental results revealed that the measured Tc increased linearly as the gravel content increased. The effects of the slope gradient, flow discharge and gravel content on Tc were significant (p < 0.01). Tc increased following power functions either with slope gradient, flow discharge and gravel content (coefficient of model determination (r2) = 0.96 and Nash-Sutcliffe model efficiency (NSE) = 0.96), or with slope gradient, flow discharge and sediment median grain size (d50) (r2 = 0.98 and NSE = 0.98). The two established power functions facilitated the prediction of the Tc of colluvial deposits in this study. However, the power functions overestimated the predicted Tc values when the measured Tc was less than 1 kg m−1 s−1 and underestimated the values when the measured Tc ranged from 2 to 4 kg m−1 s−1. These findings are helpful for improving the simulation of erosion processes in colluvial deposits and deepening the understanding of erosion mechanisms in soil and rock mixtures. Moreover, the relationship of hydrodynamic variables with Tc on colluvial deposits remains to be investigated in additional in-depth studies.