Granite Residual Soil Research Articles

The Effect of Organic and Inorganic Modifiers on the Physical Properties of Granite Residual Soil

As a kind of highly weathered special soil in South China, granite residual soils (GRS) feature high strength and high void ratio in a dry environment, so they tend to disintegrate in water and cause geological disasters including collapse. Therefore, modifying GRS for higher strength has become a hot spot. Glass fiber reinforced soils boast fewer cracks, higher energy absorption, and residual strength. This study aims to analyze the reinforcement effect of glass fibers on GRS with inorganic and organic solutions and its environmental feasibility. The inorganic solution contains silicon ion and sodium ion at the ratio of 1 : 4 (hereinafter referred to as Si : Na = 1 : 4 solutions), and the organic one is a modified polyvinyl alcohol solution (hereinafter referred to as SH solution). The reinforced samples were subjected to plate and impact load tests, SEM, and XRD analysis to investigate their mechanical properties, microcharacteristics, and the components produced. Results indicate that the reinforcement effect of glass fibers on GRS under Si : Na = 1 : 4 solutions was better than that of SH solutions. After being reinforced by Si : Na = 1 : 4 solutions, the samples reached maximum impact resistance. SEM results show that glass fibers bond more soil and form an integral structure; thereby the strength was improved as glass fibers share external impact load. XRD results show that geopolymer and alkali-activated materials and potassium feldspar were formed. Geopolymer and alkali-activated materials are pollution-free, inorganic polymers featuring viscosity and high compressive strength. Potassium feldspar is an aluminosilicate mineral with high strength and stable chemical properties, which can adhere to more granules and form a stronger whole structure with geopolymers playing a role. Therefore, it is feasible to reuse these soils sustainably by reinforcing them with glass fibers and the best Si : Na = 1 : 4 solutions. This study finds a new direction for recycling and reusing construction waste, GRS.

3D quantitative characterization and flow simulation of granite residual soil based on CT scanning

<p indent="0mm">This paper aims to reveal the water transport mechanism in soils with macropores. Based on the combination of the X-ray CT scanning and image processing technologies, a three-dimensional (3D) equivalent pore network model (PNM) with macropores (&gt;0.15 mm) is constructed, and the size of the optimal representative volume unit (REV) is determined to be 300×300×300. Then, the quantitative characterization of the topological structure of the macropore space is carried out followed by the PNM single-phase flow and the 3D macropore water-gas two-phase flow simulation. The results show that there are more pores with smaller pore diameters, and more than 80% of the pores are concentrated within <sc>0.15–1.00 mm.</sc> The pore topological space structure is quite different, and the coordination number is mainly less than 20, but some can reach more than 60. The average coordination number of pores is between 3–7, and the average connected pore radius is greater than <sc>2.00 mm.</sc> The single-phase flow simulation find that the complexity of the pore structure and the resolution of X-ray CT scanning resulted in a certain difference between the simulated and measured permeability, but the difference of the main seepage direction is only 3.81%. The two-phase flow simulation find that the front edge of flow is almost linear at the beginning of seepage, then it tend to be fingering, and finally, it become irregular. The residual gas in the pores is mainly distributed in blocks at the edges of pores, dead ends, and sudden changes of pore throats. With the increasing seepage time, the saturation of the water phase shows an upward trend, while the saturation of the gas phase shows a downward trend, then gradually tend to be stable, and finally, the saturation of the water phase and the residual gas phase maintain at 94.92% and 5.08%, respectively. This study can better reveal the meso-seepage mechanism of reconstructed soil, and provide a certain reference for further understanding the law of pore flow in soil.

A Comprehensive Correlation Study of Structured Soils in Coastal Area of South China about Structural Characteristics

Granite residual soil is a common engineering material, and its mechanical properties are of great importance to engineering safety. This kind of soil presents obvious structural characteristics, and many researchers have emphasized the significance of its structural features. According to previous experiments, from a macroscopic perspective, many researchers have investigated the structural relationship between undisturbed and remolded soils, but few studies have considered it in the mesoscopic aspect. Adopting DEM (a mesomechanical simulation method), we can study how the structure affects the mechanical process between undisturbed and remolded soil. Therefore, this paper combines DEM with laboratory tests to study the structural characteristic correlation between undisturbed and remolded soil. The results indicate that a weak cohesion effect exists in undisturbed soil, and the damage of weak cohesion elements accompanies the failure process. Weak cohesion elements in undisturbed soil cause inhomogeneities in deformation, stress state, and damage accumulation, which ultimately causes differences in strength curves. This paper explains the mechanism of the structural effect on mechanical evolution from a mesomechanical perspective. The DEM simulation method proposed in this paper can be applied to structured soils and better guide engineering practice.

A Case Study of Deep Shaft and Open Face Tunnelling Induced Excessive Ground Settlement in Water Rich Strata in Guangzhou, China

During a shaft and associated sprayed concrete lining (SCL) tunnel construction in a new line of Guangzhou Metro, site monitoring recorded ground surface settlement was much larger than that predicted in the design. This raised the alarm to the safety of an adjacent high-pressure gas pipe. Close-form and analytical calculations and non-coupled and coupled numerical analyses were carried out to back analyze the settlement. It was found the primary contributing factor to the excessive ground settlement is water loss-induced ground consolidation, which is commonly encountered during underground construction in south China where complex strata, such as granite residual soil and fully weathered granite, are present. This paper details the back analysis process and discusses mitigation measures that should be adopted for construction in similar ground in the future.

Compressive Strength of Stabilised Granitic Residual Soil Using Mixture of Pineapple Fibre—Hydrated Lime

Granitic Residual Soil (GRS), referring to the weathered soil from rocks, widely exists all over the world, especially in tropical regions. This type of soil is considered weak for construction due to unsaturated soils and the fact that granitic soil properties can vary from one location to another during formation. As a result, soil stabilisation is necessary. In Malaysia, pineapple fibre (PA fibre) is one of the most widely available waste materials. Chemical stabilisation technology is an attractive stabilisation technique that has been successfully used as a soil stabilising agent for many years. Hydrated lime (HL) is an activation agent and is very commonly used to replace cement application in soil stabilisation. Utilising HL and PA fibre as a soil stabilising agent is an economical and sustainable option as HL contains high pozzolanic characteristics that make it more suitable and reliable to stabilise soil, and PA fibre has high specific stiffness and strength. This study uses the replacement portion of the GRS with stabilising agents—HL and PA fibre, aiming to achieve Malaysia’s green technology goals by balancing economic expansion and environmental privilege. However, the aim of this study is to determine the effect of HL–PA fibre mixture replacement on the performance of mechanical and physical properties enhancements of GRS. GRS is the control sample whereas HL and PA fibre are used as binders. The unconfined compressive strength with the curing period was tested. The result showed that for untreated GRS, the moisture content, Atterberg limit, and specific gravity were 9.44%, 37.3%, and 2.3%, respectively, while the maximum dry density was 1.55 g/cm3 and the optimum moisture was 13.5%, according to the compaction test. Due to weathering conditions, the soil was classified using the Unified Soil Classification System (USCS) as well-graded sand soil, based on the sieve analysis. Sieved soil of 2 mm was used to stabilise the GRS mix with HL and PA fibre. The resulting UCS showed that 0 curing days increased strength by 31%, while 7 curing days increased strength by 26% before decreasing the strength by 8.4% to 9%.

Prediction of Matrix Suction of Unsaturated Granite Residual Soil Slope Based on Electrical Conductivity

To study the relationship between matrix suction and conductivity in unsaturated granite residual soil and realize the matrix suction prediction of soil slope based on conductivity, laboratory and field tests are carried out on undisturbed soil at different depths of the Yandou village landslide in Sanming City, Fujian Province, China. Through physical and chemical property analysis, soil-water characteristic curves and electric parameter matrix suction prediction models for unsaturated granite residual soil at different depths of the target area are obtained. Based on the proposed model, the matrix suction distribution of on-site soil slope is predicted and the dynamic response law under the influence of artificial rainfall is studied. The results show that: (1) The transverse conductivity, average structure factor, average shape factor, and anisotropy coefficient of unsaturated soil are related to the soil saturation degree. By considering the above parameters, the comprehensive structure parameter Re is introduced and its functional relationship with matrix suction is established. (2) Under artificial simulated rainfall, the saturation, hysteresis of the conductivity parameters, and matrix suction response of the slope occurs, which is controlled by soil depth, permeability and rainfall intensity. The matrix suction is distributed in layers on the profile and its recovery rate is slower than saturation. The suction contour map shows a parabola shape with the opening downward. (3) The relationship between the conductivity parameters of the residual soil slope and matrix suction is further revealed and a new method to indirectly measure matrix suction is proposed. Its feasibility is verified based on field tests, which is of great significance to landslide monitoring and early warning.

Microscopic Evolution of Pore Characteristics and Particle Orientation of Granite Residual Soil in One-Dimensional Compression

This study investigates the microstructural changes of granite residual soil (GRS) upon compression, the aim being to understand further the deformation mechanism from a microscopic perspective and establish the relationship between the mechanical behavior and microstructural characteristics of GRS. By means of (i) experimental compression tests with different loadings and (ii) scanning electron microscopy (SEM), the structural evolution of GRS during compression tests is investigated systematically from both macroscopic and microscopic perspectives. Microstructural characteristics including particle morphology, pore size distribution, and particle preferred orientation are investigated specifically through SEM quantification methods. With an obvious turning point, thee–log σv′curve for natural GRS approaches the intrinsic compression line gradually when the vertical pressure exceeds the preconsolidation pressure, which indicates the significant influence of cementation bonding on the mechanical behavior of intact GRS. At the microscopic scale, the deformation of natural GRS is attributed to the compression and transformation of large pores, while the deformation of remolded GRS is also related to the transformation from mesopores to small pores. Upon compression loading, particles show higher preferred direction angle perpendicular to vertical loading, thereby facilitating the preferred orientation. With increasing vertical loading, the microfabric can no longer sustain the initial alignment pattern and tends to be rearranged and reoriented into a more stable and stronger structure. This study offers guidance for the deformation analysis of subgrade related to GRS.

Evolution of disintegration properties of granite residual soil with microstructure alteration due to wetting and drying cycles

Evolution of disintegration properties of granite residual soil with microstructure alteration due to wetting and drying cycles

The Interaction Effect of Particle Composition and Matric Suction on the Shear Strength Parameters of Unsaturated Granite Residual Soil

The Interaction Effect of Particle Composition and Matric Suction on the Shear Strength Parameters of Unsaturated Granite Residual Soil

Experimental Study on the Mechanical Properties and Disintegration Resistance of Microbially Solidified Granite Residual Soil

Microbially induced calcium carbonate (CaCO3) precipitation (MICP) is an emerging soil-treatment method. To explore the effect of this technology on granite residual soil, this study investigated the effects of the mechanical properties and disintegration resistance of microbially cured granite residual soil under different moisture contents by conducting direct shear and disintegration tests. The curing mechanism was also discussed and analyzed. Results showed that MICP can be used as reinforcement for granite residual soil. Compared with those of untreated granite residual soil, the internal friction angle of MICP-treated granite residual soil increased by 10% under a moisture content of 30%, while its cohesion increased by 218%. The disintegration rate of the MICP-treated granite residual soil stabilized after a maintenance time of 5 days under different water contents. Therefore, we provide the explanation that the improvement of the shear strength and disintegration resistance of granite residual soil is due to CaCO3 precipitation and the surface coating.

The Effect of Length and Content of Fiber on Glass Fiber and Basalt Fiber‐Reinforced Granite Residual Soil

Fiber‐reinforced soil boasts fewer cracks, higher energy absorption, and higher residual strength. With the well‐established concept of carbon neutralization, it is necessary to reduce the dependence on high carbon‐emitting reinforcement materials such as cement and concrete. The need for resource recycling has led to the development of reusing construction waste as the raw material for slope and embankment reinforcement. The purpose of this study is to analyze the reinforcement performance and environmental feasibility of glass and basalt fiber on granite residual soil with the content of 3%, 4%, and 5% and the length of 6 mm, 9 mm, and 12 mm. The reinforced samples were subjected to static impact load tests and SEM analysis to study its mechanical properties, microcharacteristics, and structure before and after reinforcement. Results show that the incorporation of 3% glass fibers of 6 mm has the best reinforcement effect on GRS, while the incorporation of 4% basalt fibers of 6 mm also has a good reinforcement ability. Glass fiber performs better than basalt fiber under the optimal content and length. SEM results indicate that glass fibers bind the soil particles more closely, thereby increasing their friction and leading to higher compressive strength. When the length and content of fiber exceed a certain range, the fibers are prone to cross and knot and fail to fill between soil particles, so the fiber and soil particles are separated, which lowers the strength of the soil. It is concluded that both glass fiber and basalt fiber can be well used for reinforcing GRS for higher bearing capacity and fewer cracks at the given proportion and length. Fiber length and content were considered when reinforcing GRS with different fibers in this study.

Shear Strength Anisotropy of Natural Granite Residual Soil

AbstractA significant feature of residual soil is the presence of a cemented structure and fissures that dominate its anisotropic behavior. Although the anisotropy of some sedimentary soils is well...

Effects of Drying-Wetting Cycles on the Microstructure and Mechanical Properties of Granite Residual Soils

Effects of Drying-Wetting Cycles on the Microstructure and Mechanical Properties of Granite Residual Soils

An Experimental Study on Influence of Grain-Size Composition on Collapsing Erosion of Granite Residual Soil

An Experimental Study on Influence of Grain-Size Composition on Collapsing Erosion of Granite Residual Soil

Small strain stiffness for granite residual soil: effect of stress ratio

Most previous studies have focused on the small strain stiffness of sedimentary soil, while little attention has been given to residual soils with different properties. Most studies also neglected the effects of the deviator stress, which is extensively involved in civil engineering. This note considers the effects of the deviator stress on the small strain stiffness of natural granite residual soil as established from resonant column tests performed under various stress ratios. Although increasing the stress ratio results in a greater maximum shear modulus for both natural and remolded residual soils, remolded soil is more sensitive to changes in the stress ratio, which highlights the effects of soil cementation. The data herein offers new insights to understand the stiffness of residual soil and other weathered geomaterials.

Experimental investigations of hydraulic and mechanical properties of granite residual soil improved with cement addition

Granite residual soil is widely distributed in southeastern China. Notably, this soil easily softens when exposed to water and is easily damaged when subjected to stress, and these characteristics are not conducive to engineering construction and underground space development. In this study, computed tomography(CT), mercury intrusion tests, XRD and SEM techniques are used to examine the improvement of granite residual soil in the Shenzhen area through the addition of cement. The soil micropore structure, saturated permeability coefficient and soil strength characteristics for improved soil specimens with different cement contents (2%, 4%, 6% and 8%) and curing durations (3 d, 5 d and 8 d) are examined. The results show that the pore distribution of granite residual soil has a bimodal structure. In the cement-improved soil, the large pores are eliminated, connectivity of pores is decreased, and number of isolated pores increases. Moreover, the unconfined compressive strength of the improved soil is higher than that of the granite residual soil. The introduction of cement contents of 6% can effectively increase the strength of granite residual soil while decreasing the permeability.

Formation mechanism of collapsing gully in southern China and the relationship with granite residual soil: A geotechnical perspective

Recently, there has been an increase in collapsing gullies in the south of China as one of the most destructive types of soil erosion. Most collapsing gullies are formed on a well-developed granite crust; thus, granite residual soil plays a critical role. However, the extent to which the geotechnical features of residual soil, especially soil disintegration, affects collapsing gully formation is poorly understood. This study performed laboratory disintegration tests on granite residual soil taken from the red soil, sandy soil, and detritus layers of a collapsing gully. The disintegration behaviour was quantified by defining the disintegration ratio, Rd, and three equivalent disintegration rates, vI, vII, and vIII, corresponding to Rd = 10%, 30%, and 50%, respectively. The results revealed that the red soil layer (depth < 1.3 m) and the soil at the shallower depth of the sandy soil layer (depth < 3.0 m) showed similar disintegration behaviours, which were complete (Rd = 100%) and rapid, with vI values in the range of 66.7–266.7%/min. The soil disintegration in the sandy soil layer was characterised by an incremental increase in Rd to 100% within 100 min. The residual soil at the bottom of the sandy soil layer and the top of the detritus layer (depths of 4.0–8.0 m) disintegrated consistently at the first, after which the disintegration rate gradually decreased with vIII lower than 1%/min. The detritus layer soil at a depth greater than 10.0 m showed incomplete disintegration, and the ultimate Rd was approximately 60%. The formation mechanism for the soil disintegration and gully collapse was also proposed. The weakening of cementation triggered the breakup of soil aggregates and led to soil disintegration and the occurrence of a gully collapse. This study provided new insights on gully erosion.

Numerical simulation of water-gas two-phase displacement process in unsaturated granite residual soil

Infiltration of current in unsaturated soil is essentially a two-phase flow problem of water displacing air in the process of infiltration. The accuracy of traditional two-phase flow research methods cannot meet the needs of engineering, and it is not conducive to repetitive research. In contrast, the numerical simulation method of multiphase flow at the meso-scale can better simulate the whole dynamic process of water flooding. Mao Huan, Qren and others have achieved great results in the field of pore meso-scale research, but on the one hand, most of them focus on the study of rock multiphase flow, and there are some differences between the research object and the actual pore structure. On the other hand, the widely used pore network model method cannot directly show the change of particle velocity at any time and cannot present the phase interface movement state. In view of this, in order to reveal the dynamic percolation mechanism of water-gas two-phase displacement of unsaturated granite residual soil, this paper selected undisturbed granite residual soil in Fuzhou as the research object and studied the dynamic characteristics of two-phase displacement of undisturbed soil samples by using industrial CT scanning images and Level Set method. The results show that the Level Set method can properly capture the interface position between two immiscible fluids for meso-scale water-gas two-phase displacement simulation. The water-gas two-phase displacement process has the characteristics of large pore preferential flow, and the ‘low around’ phenomenon can easily appear in the higher ground of porosity roundness in general. The displacement rate is mainly controlled by the tortuosity of the channel, displacement speed is relatively high in the straight and wide channel. There is an obvious phenomenon of ‘preferential passage’, and its seepage time is positively correlated with the first rapid and then slow characteristics, and the maximum and minimum growth rate are 10.77 % and 1.90 %, respectively. The velocity distribution of the pore cross-section is related to the pore structure, and the phenomena of 'reflux' and 'flow around' cause the displacement velocity to drop sharply, whose decreasing degree can reach 21.62 %. The maximum displacement resistance appears at the hole wall, and the narrower the hole, the greater the resistance. The displacement efficiency is directly proportional to the displacement pressure difference, and the initial pressure growth effect is significant (up to 25.49 %, and only 1.47 % later). The research results can provide a theoretical basis for the study of the water migration mechanism of porous slopes, and also can enrich the theoretical basis of rainfall-induced landslides and are helpful in preventing natural disasters.

Shear strength parameters of granitic and sedimentary residual soils from the Northern and the Peninsular Malaysia

Reduction of shear strength and negative suction as the soil in a stable slope becomes saturated during prolonged rainy seasons are the two main causes for a stable slope to fail. A total of 148 and 112 effective shear strength parameters were collected from granitic residual soil and sedimentary residual soil respectively at both the stable slopes and slope failures in the Northern Malaysia. Meanwhile a total of 103 and 65 effective shear strength parameters secondary data were also collected from granitic residual soil and sedimentary residual soil respectively in Peninsular Malaysia including Singapore. Because of the natural variability of residual soil as the results of inconsistent weathering process during residual soil formations, the highly variable values of the shear strength parameters were obtained. The objectives of the research are to determine the best fit distributions for the effective shear strength parameters as well as their mean values for the granitic and sedimentary residual soils both in the Northern and the Peninsular Malaysia. It was found that the normal distributions were the best fit distributions for the transformed data of the effective shear strength parameters for granitic and sedimentary residual soils at both locations. It was also found that, the mean values of effective shear strength parameters in granitic and sedimentary residual soils at both locations were almost the same although a slightly lower value for effective cohesion was obtained for sedimentary residual soil in the Northern Malaysia.

Effect of inherent anisotropy on the strength of natural granite residual soil under generalized stress paths

Effect of inherent anisotropy on the strength of natural granite residual soil under generalized stress paths