Bulletin of Engineering Geology and the Environment最新文献

This paper presents a new equation to design rock pillars in underground excavations. The study is based on rigorous statistical analysis of empirical databases and equations used in the engineering design process. The new formula has three fitting functions that consider the rock mass quality, the shape of the rock pillar, and the scale effects. The new equation has two distinctive advantages: (1) It takes into account the Rock Mass Rating of Bieniawski-1989 (RMR_B89), and (2) It unifies the strength of the intact rock, scaling the strength of laboratory tests to the scale of rock pillars. The results suggest that the proposed new formula (and corresponding fitting formulae) provide better estimations than empirical approaches, at both the laboratory and rock pillar scale levels. Specific recommendations to use the equations are based on the rock mass quality, geometrical properties, and spatial location of the rock pillars. The premise of this study was to overcome the three main disadvantages of empirical formulae used in the engineering design of rock pillars: (1) disregarding of the rock mass quality of rock pillars in the formulation. (2) Dependency on local site geomechanical conditions (site conditions dependent equations). (3) The non-uniformity between the intact rock strength measured in the laboratory and the pillar strength. The results of this work provide a step forward in the design of rock pillars, structures engineered with the natural in-situ rock mass, to sustain underground openings, and guarantee safe underground excavations.

In the Wenchuan seismic disturbed region, the landslide sediment transfer has seriously damaged the vegetation. On the contrary, the vegetation recovery can improve the post-seismic slope instability by the root reinforcement effect and reduce landslide sediment transfer. However, due to limited earth observations, it remains elusive that the dynamic response of hillslope landslide sediment transfer to ecological environment recovery in earthquake disturbed area. We analyzed the prolonged evolution of landslide sediment transfer potential (LSTP) and surface recovery in epicentre of Wenchuan earthquake using the standardization landslide sediment transfer potential index (SIH) and normalized difference vegetation index (NDVI), respectively. As well, the dynamic relationship between landslide sediment transfer and vegetation recovery is discussed. We found that the LSTP in regions between Gengda and Caopo was dominated by high and extreme levels between 2008 and 2013, and it gradually enhanced during this period, which poses a negative impact on vegetation recovery. On the contrary, the LSTP continued to decline after 2013, which provided a positive impact on vegetation recovery, and average NDVI recovered at a rate of 0.05 yr⁻¹. In recent years, more than 78.33% of the study area was dominated by moderate and slight LSTP, and the NDVI has almost returned to pre-earthquake levels, which provides a linear impact on decay of landslide erosion and landslide sediment supply for channel. However, the species that breed slowly (trees) will gradually rehabilitate for a longer period, so the impact of vegetation restoration on landslide sediment reduction needs further long-term observation.

Climate change and frequent earthquakes influence the surface deformation of landslides and further lead to catastrophic event. However, due to the deficiency effective long-term monitoring data for landslides, it is difficult to quantitatively analyze the actual impact of the changing local environment on landslide deformation. In this study, we quantitatively analyzed the effects of rainfall and earthquakes on landslides deformation in Zhouqu County, China, using Multi-Temporal Interferometric Synthetic Aperture Radar (MT-InSAR) technique. The results showed that in recent years, the unstable areas and the fastest deformation velocity of the five occurred landslides (Suoertou, Daxiaowan, Xieliupo, Zhongpai and Qinyu landslides) studied have significantly increased. Meanwhile, the time series displacement data of five landslides showed that the deformation trend changed from a steady state to an accelerated state. Furthermore, our findings revealed that an augmentation in precipitation not only exacerbated the incidence of rainstorms, thereby facilitating the occurrence frequency of devastating landslides, but also demonstrated a correlation between annual precipitation and variations in the deformation trend of landslides. Smaller values of the magnitude (reciprocal), depth, and epicentral distance resulted in greater surface displacement of the landslide; conversely, larger values resulted in smaller surface displacement. These quantitative correlations suggest that, due to the perpetual alterations in the environment, landslides are progressively transitioning from a state of relative stability to one of heightened activity.

Rainfall has been recognized as a key factor in triggering landslides. However, it is not entirely clear why many landslides have been triggered by slight-to-moderate rainfall. The Mudui landslide that occurred in Sichuan Province, China, on June 22, 2020, exemplifies the evolution of landslides induced by seasonal rainfall, which can cause substantial damage to infrastructure. This landslide was a deep-seated debris slide with a volume of approximately 0.64 million m³. It occurred in colluvial deposits, which are heterogeneous soil–rock mixtures with high permeability that easily retain water. On the basis of detailed site investigations and various monitoring data—including interferometric synthetic-aperture radar (InSAR), ground-slope and subsurface-slope deformation monitoring, and hydrogeological monitoring—we investigated the landslide-triggering mechanism along with pre- and post-landslide kinematics and assessed the effects of remedial works. The results show that both the soil water content and the slope deformations have significant seasonal characteristics. The soil water content decreases during dry seasons and increases during rainy seasons. Correspondingly, the deformation rates increase with the onset of rainy seasons and decrease with the onset of dry seasons. The landslide area underwent progressive deformations linked to groundwater seepage, inducing a continuous deterioration of the soil body. Finally, prolonged rainfall triggered the landslide of the deteriorated soil mass. The results indicate that the adverse effects of long-term seasonal soil-water-content fluctuations need to be take into account in analyzing slope instabilities in colluvial deposits.

After tunnel excavation, inherent cracks within rock masses may be exposed at the free surface of the tunnel, which are referred to as end cracks. Crack growth from the end crack occurs much more easily than that from a crack inside the rock mass. This study conducted compression experiments under true triaxial stress condition, along with numerical simulations, to explore the failure characteristics and mechanical behavior of surrounding rocks containing end cracks near the free surface of the tunnel. The results reveal that compared with the inclination angle of the end crack, the failure pattern of rock is significantly affected by the end crack length. As the end crack length increases, the failure pattern of rock gradually transitions from the mixed tensile-shear fracture to the shear fracture. The peak strength of rock initially decreases and then increases as the end crack length increases. While, the peak strength of rock basically remains unchanged with the increase of the inclination angle, suggesting that the capacity of surrounding rocks containing end cracks near the free surface is primarily influenced by the end crack length. Based on the failure characteristics of surrounding rocks containing end cracks, as obtained from numerical simulations, the support measure of “grouting consolidation + local priority strengthening support” was proposed. The results indicate that the support measure can effectively restrain crack propagation and improve the capacity of surrounding rocks containing end cracks near the free surface.

The tensile strength of expansive soils is crucial to control the formation of cracks within the soil. Analyzing the tensile strength of such soils under different water contents has both theoretical significance and practical engineering applications for ensuring canal slope stability in the Middle Route of South-to-North Water Diversion Project. The expansive soil and cement-modified expansive soil (modified soil) collected from the high fill canal slope were made into samples with a water content of 3% to 24%, respectively, and water holding and splitting tests were conducted on the two soils using a WP4C soil water potential lab instrument (WP4C), pressure plate, and Particle Image Velocimetry (PIV) splitting test system. The results of this study show that with increased water content, the peak splitting load of the samples shows a trend of first increasing and then decreasing, while the peak splitting load and the peak load corresponding to the turning point water content are lower in expansive soils than those in modified soils. Under different water contents, these soils exhibit notable strain softening, and each corresponding load–displacement curve can be divided into linear load increase, tensile failure, and residual stages. According to the displacement vector fields of expansive and modified soil samples, all the fractures are tensile failures. The soil–water characteristic curves of the two types of soil exhibit similar trends. The water content and void ratio of the two soils decrease with increasing suction. This study provides practical guidance for selecting the appropriate water content in canal slope construction.

The present work investigated the macrostructural and microstructural changes in the behavior of two different soil samples collected from Rayaka (Su-1Clay) and Dodka (Su-2Clay) in Vadodara, Gujarat, India, under multi-staged oedometer tests. The microstructural analysis was performed to understand the pore morphology and particle rearrangement for different stress cycles and durations. For interlinking the macroscopic and microscopic data, porosity and void ratio were compared for both levels, and results showed an average deviation of 6%. From the mineralogical data, illite group minerals were predominant in both the samples and similar macroscopic behavior was observed during the multi-staged tests. The pore count was found to be higher during the initial stages of consolidation, as there was no stress involved. The microscopic results for Su-2Clay indicated that the loading patterns, load duration and plane of observations (i.e., parallel or perpendicular to loading) do not influence the circularity of pores and shape ratio. It was observed that the particle rearrangement was influenced by their loading value and duration, plane of observations and loading patterns. As a result, the behavior of most of the particles changed from anisotropic to isotropic as the stress value and time increased.

The soil water retention curve (SWRC) is a crucial indicator in the analysis of percolation. For low plasticity soil containing substances that promote soil expansion and contraction, the volume change behavior of the soil is generally neglected to determine the drying SWRC. Such a procedure is constrained by an underlying assumption that the volume change of the soil is zero or negligible, which consequently limits the precision of seepage simulations. In this study, for the exogenous substance of soil swelling and shrinking, Attapulgite (ATP), the concept of “effective porosity” was introduced to develop a modified SWRC model that takes into account the variation of soil pore space based on the conventional van-Genuchten (VG) model of simulated SWRC. The parameters of the modified SWRC model were determined using a genetic algorithm, which was used to simulate infiltration in the SWMS_2D program to further evaluate the accuracy of the model. The results indicated that the modified model provides a more precise representation of the relationship between soil water content and suction, with error analysis presented outstanding goodness-of-fit. As a critical factor controlling the modeling of soil–water interaction, this modified SWRC model parameters were found to be in good agreement with simulation results of the seepage process of soil water flow over the soil column. The evaluation conducted via the Taylor diagram proved that the model is more precise than the conventional VG model in simulating the seepage process. In particular, the greater the soil volume change caused by exogenous ATP, the superior the performance of the model.

The stability analysis of dangerous rock mass is the key to preventing and controlling dangerous rock mass collapse as a geological disaster. Indeed, it is of great practical significance to propose a scientific and relatively accurate stability computation method for predicting the collapse of dangerous rock mass. Based on conventional limit equilibrium, this study proposes a new theory considering the size effect of dangerous rock mass under various blasting vibration loads to assess its stability. The approach considers dangerous rock mass shape, geometrical size, blasting vibration frequency, and the initial phase of the blasting vibration wave in different directions. Based on the slice method, it establishes the stability analysis and calculation of dangerous rock mass, considering the size effect under blasting vibration. The corresponding calculation program is compiled using MATLAB to carry out calculation examples. The results indicate that the calculated minimum stability coefficients of dangerous rock mass in this study are proximate to those calculated by conventional pseudo-static analysis. However, this study's calculations are slightly larger than those computed by pseudo-static analysis, with a relative difference between 5.1% and 8.2%. The method proposed in this study provides a reference for dynamic stability analysis and evaluation for dangerous rock mass.