Granite Slopes Research Articles

Effect of Wet‐Dry Cycles on the Loading–Unloading Damage of Granite

ABSTRACTInvestigating the effect of wet‐dry (W‐D) cycling on loading–unloading damage is crucial for ensuring the stability of granite slopes in mountainous areas prone to strong earthquakes. This study conducted a series of W‐D cycling and loading–unloading tests on granite samples, complemented by weight measurements, wave velocity assessments, and nuclear magnetic resonance (NMR) tests on samples subjected to W‐D cycling. The results indicated that W‐D cycling reduced the mechanical properties of granite and increased the irreversible strain, dissipated energy, and number of acoustic emission (AE) counts during loading–unloading. The increase in the number of W‐D cycles led to a significant rise in the number of small‐scale, intergranular, and transgranular microcracks and the gradual formation of middle‐scale and large‐scale microcracks. W‐D cycling weakened the granite because of crystal expansion and contraction as well as mineral dissolution, whereas loading–unloading damaged the granite through inconsistent deformation resulting from the varying hardness of different minerals. This study provides a foundation for understanding the formation mechanism of seismically cracked slopes under the combined effects of rainfall and earthquakes.

Hydrologic infiltration mode of completely decomposed granite slopes under the influence of gas-saturated fractures retardation and diversion

Hydrologic infiltration mode of completely decomposed granite slopes under the influence of gas-saturated fractures retardation and diversion

Characteristics of preferential flow suffosion of soil-rock interface in spherical weathered granite slopes

Characteristics of preferential flow suffosion of soil-rock interface in spherical weathered granite slopes

Disintegration Characteristics of Highly Weathered Granite under the Influence of Scouring

In South China, due to climatic factors, highly weathered granite is distributed across a large area and easily disintegrates after encountering water, causing many geological disasters and other problems. To determine the disintegration mechanism of highly weathered granite in South China, disintegration tests were carried out on highly weathered granite in the Fuzhou area under different immersion durations, cycle times, and flow rates, with the help of a self-designed disintegration test device. Moreover, the disintegration mechanism of the highly weathered granite was revealed using nuclear magnetic resonance (NMR) technology. The results demonstrated an increase in the cumulative relative disintegration with prolonged immersion time and the number of dry-wet cycles. Beyond a certain flow rate, the cumulative relative disintegration amount stabilized. There was a strong correlation between the steady disintegration rate and immersion time (or dry-wet cycles). The disintegration process of the highly weathered granite was divided into three stages: rapid, moderate, and stable disintegration. Notably, disintegration primarily occurred around the large pores. This study revealed that the variation in the immersion time (or wet-dry-scouring cycles) was fundamentally linked to changes in the relative volume of the large pores in the rock samples. These findings provide valuable insights for predicting and mitigating surface disasters on highly weathered granite slopes.

The Slope Failure of Weathered Granite Boulders by Using the Finite Element Method

An assessment of weathered granite profile of a research area at Mukim Senai, Kulai, Johor was conducted using PLAXIS 2D method. The slope stability of weathered granite is closely related to the geometric strength of the slope, slope height, soil type (sand or clay), slope gradient and depth to determine factor of safety. The aim of this research is to model and determine the factor of safety of the weathered granite slope with homogeneous characteristics using Plaxis 2D. In addition, it also aims to analyses and correlate the effect of shapes, size and distribution of boulders to the safety factor of the slope. Finite Element Method (FEM)) had been used through the application of PLAXIS 2D software. By comparing between the 2 methods that have been analyzed, safety factors for the slopes analyzed together with groundwater data is less safe. The Safety Factor has found less than 1.5 indicates a slope prone to landslides.

Study on Fluid–Solid Coupling Numerical Simulation and Early Warning of Weathered Granite Landslides Induced by Extreme Rainfall

Rainfall is the main factor inducing landslides. Clarifying rainfall-induced landslides’ mechanisms and establishing adequate warning and prevention measures are crucial for regional disaster prevention and sustainable development. The weathering degree of fully weathered granite slopes is high, and the engineering mechanics property is poor, so it is easy to lose stability under extreme rainfall conditions. In this paper, the Fanling fully weathered granite landslide in Laoshan Scenic Spot in eastern China is taken as the research object, and the fluid–solid coupling landslide numerical model is established using ABAQUS 2022. The numerical simulation is carried out under five different rainfall intensity and time conditions, and the seepage field response, deformation response, and stability of the slope are analyzed. The research results indicate that (1) the fully weathered granite landslide in Fanling is a thrust-type landslide, and the response of horizontal deformation is greater than that of vertical deformation. (2) Compared with a long-term small rainstorm, a short-term heavy rainstorm is more harmful, and the slope is more prone to instability and damage. (3) The established unstable and under-stable rainfall warning curves for fully weathered granite landslides can provide a reference for the warning and prevention of similar regional landslides.

Photogrammetric Technique-Based Quantitative Measuring of Gravity Erosion on Steep Slopes in Laboratory: Accuracy and Application

Quantitative measuring of gravity erosion contributes to a better understanding of soil-mass failure occurrence and prediction. However, the measurement of gravity erosion requires the continuous monitoring of the objective terrain, due to its occurrence, usually within seconds, and combination with hydraulic erosion. The photogrammetric technique can quickly obtain terrain data and provide a new method for measuring gravity erosion. Based on a continuous high-overlapping image-acquisition equipment, a Structure-from-Motion-Multi-View-Stereo (SfM-MVS)-integrated workflow, and volume calculation, a new working methodology was established for measuring gravity erosion on steep granitic slopes in the laboratory. The results showed a good match between the digital point clouds derived from SfM-MVS-integrated workflow and terrestrial laser scanning (TLS), achieving millimeter-scale accuracy. The mean distance between the point clouds derived from TLS and SfM-MVS was 1.13 mm, with a standard deviation of 0.93 mm. The relative errors among the volumes calculated by SfM-MVS and TLS or the conventional oven-drying method were all within 10%, with a maximum error of 9.3% and a minimum error of 0.2%. A total of 213 gravitational erosion events were measured in the laboratory by using the SfM-MVS method, further confirming its feasibility.

Influence of Rainfall Intensity and Slope on the Slope Erosion of Longling Completely Weathered Granite

Serious slope erosion occurs in the distribution areas of fully weathered granites, and rainfall intensity and slope gradient are important factors affecting slope erosion. In this study, we investigate the erosion characteristics of Longling completely weather granites with a focus on the effects of rainfall intensity and slope gradient. Based on an indoor 60-min simulated rainfall test, we selected four slope gradients (10°, 20°, 30°, and 40°) and three rainfall intensities (50, 80, and 110 mm/h) for evaluation. A total of 12 groups of tests were conducted to analyze the erosion and surface hydrodynamic characteristics of the completely weathered granite slope. The results indicate a significant positive correlation between rainfall intensity and slope gradient, and the correlation between rainfall intensity and flow velocity became stronger as the slope gradient increased. The peak sediment yield rate represents the moment at which the change in slope shape is maximized. After the peak appears, the slope will no longer undergo great deformation, and the sediment yield rate will decrease and then become stable. Finally, rainfall intensity and slope gradient, which are the two key factors that determine slope flow velocity, are described using a binary function. The findings provide a reference for the study of slope erosion in completely weathered granites.

Numerical investigation of the seismic dynamic response characteristics of high-steep layered granite slopes via time–frequency analysis

Numerical investigation of the seismic dynamic response characteristics of high-steep layered granite slopes via time–frequency analysis

Development of training image database for subsurface stratigraphy

ABSTRACT Image-based stochastic simulation methods, such as multiple point statistics (MPS), can be viewed as a physics-informed Bayesian learning approach, which samples typical stratigraphic patterns from a single training image for onward conditional modelling of subsurface stratigraphy. A training image is essentially a prior geological model, which comprises representative stratigraphic connectivity at the site of interest. One key difficulty hindering wide application of image-based geological modelling methods is the lack of qualified training images. In this study, a systematic framework is proposed to develop training image databases for conditional simulations of subsurface stratigraphy. Collected training images can be further categorised based on three key factors, namely, geological origin, site location and application scenario. As a pilot study, a total of 54 geological cross-sections, mainly interpreted by experienced engineering practitioners, for weathered granite and tuff slopes in Hong Kong are collected and compiled as two training image databases. To demonstrate value and application of the established training image databases, subsurface stratigraphy for real weathered granite slope examples are used as illustrative examples, and stratigraphic uncertainty is also quantified. Results indicate that training image databases are of great significance for subsurface stratigraphy and uncertainty quantification, particularly when only limited site-specific data are available.

Structure Degradation Induced by Wetting and Drying Cycles for the Hilly Granitic Soils in Collapsing Gully Erosion Areas

The hydrological and mechanical properties of granitic residual soils can be significantly altered by periodical wetting and drying (W-D) cycles. The soil structure degradation induced by W-D cycles can lead to soil mass failure and collapsing gully erosion in granitic hilly slopes in south China. However, limited attempts have been made at a comprehensive investigation of the effects of W-D cycles on the structure degradation of granitic residual soils, especially at the pedon scale. The purpose of this paper is to investigate the structural degradation of granite soils induced by W-D cycles and explore its potential influence on the development of collapsing gully erosion. The granitic soil properties, including hydraulic properties, shear strength, and disintegration characteristics, were performed after W-D cycles. The results indicated that the W-D cycles altered the soil pore structure, leading to variations in soil hydraulic properties. Specifically, with increasing alternate W-D cycles, the initial saturated water content and residual water content decreased, while the saturated hydraulic conductivity increased. Meanwhile, increasing W-D cycles contributed significantly to variations in cohesion and internal friction strength by decreasing the shear strength variables, especially the soil cohesion strength. Correspondingly, soil disintegration was increased during W-D cycles. Furthermore, most degradation of soil structure was recorded within the first two cycles of W-D. The obtained results indicate that the W-D cycles weaken soil structure, increase rainwater infiltration, decrease soil shear strength and disintegration resistance, and accelerate soil erosion. A vicious cycle of granitic slope failure induced by W-D cycles is eventually formed. This study provides useful information about the mechanism of soil mass failure and collapsing gully erosion in granitic hilly slopes.

Giant river-blocking landslide dams with multiple failure sources in the Nu River and the impact on transient landscape evolution in southeastern Tibet

Giant landslides have frequently occurred in deeply-incised valleys during the topographic development of the Tibetan Plateau, and these landslides commonly blocked rivers and in turn affected fluvial processes. The giant Qianjincun landslide, with a volume of ~110 × 106 m3, created the highest natural dam among all the completely river-blocking landslides identified along the trunk of the Nu River in the southeastern Tibetan Plateau. This giant landslide, which developed on a granite hillslope and dammed the river with a height of ~175 m, was dominated by long-term fluvial incision responding to uplift in one of the deepest valleys in the world. The dammed lake was breached around the end of the Dali glaciation (~10 ka), and the deposits remaining in the valley indicated an earlier landslide from the opposite failure source beside the Qianjincun landslide. The Geduicun landslide on the right bank evolved from gravitational deformation of toppling controlled by schist foliations, while the Qianjincun failure on the left hillslope was governed by the seismically-triggered detachment of granite cut by rock joints. The kinematic process of the Qianjincun landslide was numerically investigated under seismic loading, indicating high-velocity sliding from a thousand-meter-high source. In comparison to the soft rock failure preceded by the long-term gravitational effect, the mass movement on the granite slope was catastrophically induced by dynamics with high initial kinetic energy, and the subsequent overwhelming river blockage transiently caused stronger landscape evolution than any other landslides in the catchment. The inventory of river-damming landslides compiled along the trunk of the Nu River suggested a prominent tendency that all the dammings occurred in the region where the relief is greater than 2000 m. The analysis provided the power-law correlations of the geomorphic parameters of dams that can help predict the disastrous effects of future river blockages. The insight into landscape feedbacks between giant landslides and fluvial processes could contribute to effective risk assessments of disaster chains in high-relief reaches.

Molecular Phylogenetics and Trait Evolution in Stigmatodon (Bromeliaceae, Tillandsioideae), an Endemic Genus to Brazilian Rocky Outcrops

Abstract— The genus Stigmatodon occurs in vertical and bare granite slopes, typical of the inselbergs of the Brazilian Atlantic Forest. Here, we present the first broad phylogenetic analysis focused on Stigmatodon, sampling a total of 83 terminals, including 16 of the 20 species of the genus and the morphologically similar species of Vriesea. We conducted a phylogenetic analysis using two plastid markers (matK and rps16-trnK) and the nuclear gene PHYC to infer phylogenetic relationships and reconstruct ancestral states for ecological and morphological characters. Our results suggest the monophyly of Stigmatodon as originally circumscribed is only possible with the inclusion of morphologically and ecologically similar Vriesea species. In addition, the morphological and anatomical traits led us to propose a new circumscription for the genus, combining eight species of Vriesea to Stigmatodon as S. andaraiensis, S. freicanecanus, S. lancifolius, S. limae, S. oliganthus, S. pseudoliganthus, S. vellozicolus, and S. zonatus. The stomata positioned above the ordinary epidermal cells, the adaxial water-storage parenchyma with axially elongated cells, the stamens positioned in two groups of three on each side of the corolla, and the tubo-laciniate stigma are exclusive to Stigmatodon in its new circumscription. These new morphological and phylogenetic results constitute a relevant contribution to the taxonomy and evolution of Bromeliaceae, one of the most diverse and ecologically important families of flowering plants of the Neotropics.

Influence of Rainfall Infiltration on Stability of Granite Residual Soil High Slope

The seepage evolution characteristics and stability change rule of granite residual soil inside the high cutting slope under the action of rainfall infiltration were studied. Based on the saturated-unsaturated seepage theory, the numerical simulation of the rainwater infiltration path inside the granite residual soil slope was carried out under the condition of rainwater infiltration. The evolution characteristics of the seepage field of the granite residual soil cutting high slope under the condition of rainfall infiltration were revealed, and the influence of the rainwater infiltration on the stability of the granite residual soil slope was mainly studied. The research results show that with the accumulation of rainfall infiltration, the pore water pressure of the granite residual soil slope increases continuously, and the pore water pressure of the soil below the platform increases the fastest. With the increase in elevation, the water content of the slope presents a wave crest distribution. In the early stage of rainfall, the seepage velocity vector distribution on the slope surface is relatively uniform. In the middle stage of rainfall, the seepage velocity vector is the most dense at the platform, and the rainwater migration rate is accelerated. In the later stage of rainfall, the infiltrated rainwater at the slope angle of the first-level slope spreads to the surrounding area. With the continuous rainfall, the slope stability safety factor gradually decreased unevenly, and after the rainfall stopped, it gradually increased with the rainwater infiltration.

Experimental study on response law and failure process of slopes in fully weathered granites under precipitation infiltration

To investigate the response law and failure process of slopes in fully weathered granites under precipitation infiltration, a typical fully weathered granite slope is selected for sampling in South China. The physical simulation experimental study of rainfall-induced landslide is conducted, in which Weber criterion is used as the similarity criterion for precipitation. The research results reveal that under precipitation infiltration, the fully weathered granite slope responds quickly. Further, the water content increases sharply, and the matrix suction quickly dissipates. After dissipation, the matrix suction transforms into pore water pressure, which accelerates the deformation of the slope. The wet peak has a large infiltration depth in the slope, and the acceleration of the deep part is lower than that of the shallow part. Under the action of precipitation, the fully weathered granite model undergoes four stages of failure. Firstly, gullies and cracks appear; secondly, cracks propagate and link up; then, the soil on the slope surface swells and ruptures; and finally, the slope slides locally until the entire slope creeps, collapses, and transforms into a “soil flow”. It shows that the landslide will be triggered in fully weathered granite slope by precipitation when the precipitation intensity comes up to 155 mm/d, and the landslide occurs at an accumulated precipitation of 304 mm based on the analysis of precipitation similarity. Overall, the results can provide a reliable theoretical basis and abundant experimental data for the prevention, monitoring, and forecasting of geological disasters in granitic areas.

Coupling loss characteristics of N-P-C through runoff and sediment in the hilly region of SE China under simulated rainfall.

Soil total carbon (TC), phosphorus (P), and nitrogen (N) exports from the weathered granite slopes are greatly influenced by the complex hydrological processes and terrain factors. In this study, the coupling loss characteristics of N-P-C via runoff and sediment were studied with two soil tanks under simulated rainfalls. Three soils respectively derived from the tillage layer (T-soil), laterite layer (L-soil), and sand layer (S-soil) were employed to determine the interactions of hydrology and topography on N-P-C exports under three rainfall intensities (1.5, 2.0, and 2.5 mm/min). The erosion degree of different soils displayed an order of S-soil > L-soil > T-soil. The results showed that surface flow was the main runoff form for L- and T-soil, while underground flow was predominant for S-soil. There was a linear correlation between sediment and surface flow (R2 > 0.78). Surface flow was the dominant pathway of P loss via runoff with underground flow being an important supplementation, and the main P loss pattern switched between dissolved phosphorus (DP) and particle phosphorus (PP) during the experiment. However, P lost via eroded sediment accounted for more than 94% of the TP loss amount. N presented an opposite trend to P and was mainly lost via underground flow. The main N loss form in surface and underground flow was NO3--N. Underground flow was the predominant total nitrogen (TN) loss pathway for S- and L-soil, followed by sediment and surface flow. For T-soil, TN lost via runoff was much greater than that carried by eroded sediment. TC for S-soil was mainly lost via underground flow while that for L- and T-soil was mostly lost via surface flow. Both N-P loss loads in surface flow and P loss load in underground flow were positively correlated with TC loss load (p < 0.05), indicating that the presence of organic matter brings about more nutrient losses. These results expand our understanding of the combined effects of rainfall intensity and erosion degree on runoff and sediment yields as well as N-P-C losses from the bare weathered granite slopes of SE China.

A study on the rainfall infiltration of granite residual soil slope with an improved Green-Ampt model

A study on the rainfall infiltration of granite residual soil slope with an improved Green-Ampt model

Variations of soil hydraulic properties along granitic slopes in Benggang erosion areas

As soil hydraulic characteristics, including near-saturated hydraulic conductivity and water retention, influence slope stability and erosion development, this study aimed at the spatial distribution patterns of hydraulic properties along the Benggang slopes for a better understanding of the development mechanisms of Benggang erosion in southern China. Near-saturated hydraulic conductivity and soil water retention at different slope positions in two typical Benggang erosional areas were determined by the in situ infiltration test using tension disk infiltrometer and laboratory test using the high-speed freezing centrifuge method. The soil hydraulic conductivity, effective macropore, and pore size parameter, Gardner α, in lower slopes were greater than those in upper and middle slopes. From upper to lower slope, the total water flow showed an increasing trend in pores > 1 mm in diameter, in contrast to a decrease in pores between > 0.33 mm and < 0.5 mm in diameter, and < 0.33 mm in diameter. The effective macroporosity values in measured soils were statistically greater (p < 0.05) in the lower slope than in the upper or middle slope. Meanwhile, the soil water retention of lower slopes was lower than that of upper and middle slopes, and the lower slope had higher unsaturated hydraulic conductivity than the upper or middle slope. Erosion degree showed significant (p < 0.05, p = 0.016) influence on the soil hydraulic conductivity and effective macropore. Moreover, the soils on the severe erosion slope drain faster than that on the slight erosion slope, and the unsaturated hydraulic conductivity decreased faster on the severe erosion slope than on the slight erosion slope. Vertical differentiation of granitic soil properties is the main factor influencing the soil hydraulic properties of the two slopes with a different erosion degree, while the macropores are the main factor influencing the soil hydraulic properties in different slope positions. Spatial variation may affect the rainwater infiltration during rainfall and soil water redistribution after the rainfall and finally affect the soil mass failure of the collapsing wall.

Woody Vegetation Succession and Prediction of the Occurrence Cycle of Shallow Landslides on Steep Granite Slopes

We investigated woody vegetation succession and the rate of topsoil development on shallow landslide scars on steep granite slopes in Kagoshima Prefecture, Japan. We used our results to predict the occurrence cycle of shallow landslides. For this study, nine shallow landslide scars of ≥40º were selected. The age of the scars ranged from 2 to 49 years. We installed 5 m × 5 m quadrats in the scars and conducted a field study. The results showed that woody vegetation in the quadrats had a smaller Fisher-Williams index of diversity and the rate of evergreen broad-leaved trees than a climax forest. Accordingly, the succession of woody vegetation in the quadrats was not at the level of a climax forest. The rate of topsoil development, based on the relationship between topsoil depth and the time since the occurrence of the shallow landslide, was 0.25 cm/year. Thus, the occurrence cycle of shallow landslides, based on the topsoil depth needed to generate a shallow landslide and the rate of topsoil development, ranged from 200 to 300 years (average 248 years). Our method was effective for predicting the occurrence of shallow landslides on steep granite slopes.

Hydrologic Infiltration Mode of Completely Decomposed Granite Slopes Under the Influence of Gas-Saturated Fractures Retardation and Diversion

Hydrologic Infiltration Mode of Completely Decomposed Granite Slopes Under the Influence of Gas-Saturated Fractures Retardation and Diversion