Engineering behaviour of in situ cored deep cement mixed marine deposits subjected to undrained and drained shearing

The deep cement mixing(DCM)is used to improve the capacity and reduce the settlement of the soft ground by forming cemented clay columns.The investigation on the mechanical behaviour of the DCM samples is limited to either laboratory-prepared samples or in-situ samples under unconfined compression.In this study,a series of drained and undrained triaxial shearing tests was performed on the in-situ cored DCM samples with high cement content to assess their mechanical behaviours.It is found that the drainage condition affects significantly the stiffness,peak and residual strengths of the DCM samples,which is mainly due to the state of excess pore water pressure at different strain levels,i.e.being positive before the peak deviatoric stress and negative after the peak deviatoric stress,in the undrained tests.The slope of the failure envelope changes obviously with the confining pressures,being steeper at lower stress levels and flatter at higher stress levels.The strength parameters,effective cohesion and friction angle obtained from lower stress levels(c′0 andφ′0)are 400 kPa and 58°,respectively,which are deemed to be true for design in most DCM applications where the in-situ stress levels are normally at lower values of 50-200 kPa.Additionally,the computed tomography(CT)scanning system was adopted to visualize the internal structures of DCM samples.It is found that the clay pockets existing inside the DCM samples due to uneven mixing affect markedly their stress-strain behaviour,which is one of the main reasons for the high variability of the DCM samples.

Evolution model and failure mechanisms of rainfall-induced cracked red clay slopes:insights from Xinshao County,China

Red clay landslides are widely distributed worldwide,resulting in severe loss of life and property.Although rainfall-induced red clay slopes have received extensive attention,the role of cracks in the evolutionary process of red clay slopes and their connection to failure mechanisms is still poorly understood.A comprehensive approach integrating field investigation,laboratory tests,and numerical simulations was conducted to study the 168 red clay landslides in Xinshao County,China.The results show that red clay is prone to forming cracks at high moisture content due to its low swelling and high shrinkage properties.The failure mode of red clay slopes can be summarized in three stages:crack generation,slope excavation,and slope failure.Furthermore,the retrospective analysis and numerical simulations of the typical landslide in Guanchong indicated that intense rainfall primarily impacts the shallow layer of soil within approximately 0.5 m on the intact slope.However,cracks change the pattern of rainfall infiltration in the slope.Rainwater infiltrates rapidly through the preferential channels induced by the cracks rather than uniformly and slowly from the slope surface.This results in a significant increase in both the depth of infiltration and the saturated zone area of the cracked slope,reaching 3.8 m and 36.2 m^(2),respectively.Consequently,the factor of safety of the slope decreases by 13.4%compared to the intact slope,ultimately triggering landslides.This study can provide valuable insights into understanding the failure mechanisms of red clay slopes in China and other regions with similar geological settings.

Numerical manifold method for thermo-mechanical coupling simulation of fractured rock mass

As a calculation method based on the Galerkin variation,the numerical manifold method(NMM)adopts a double covering system,which can easily deal with discontinuous deformation problems and has a high calculation accuracy.Aiming at the thermo-mechanical(TM)coupling problem of fractured rock masses,this study uses the NMM to simulate the processes of crack initiation and propagation in a rock mass under the influence of temperature field,deduces related system equations,and proposes a penalty function method to deal with boundary conditions.Numerical examples are employed to confirm the effectiveness and high accuracy of this method.By the thermal stress analysis of a thick-walled cylinder(TWC),the simulation of cracking in the TWC under heating and cooling conditions,and the simulation of thermal cracking of the SwedishÄspöPillar Stability Experiment(APSE)rock column,the thermal stress,and TM coupling are obtained.The numerical simulation results are in good agreement with the test data and other numerical results,thus verifying the effectiveness of the NMM in dealing with thermal stress and crack propagation problems of fractured rock masses.

Effects of seepage pressure on the mechanical behaviors and microstructure of sandstone

Surrounding rocks of underground engineering are subjected to long-term seepage pressure,which can deteriorate the mechanical properties and cause serious disasters.In order to understand the impact of seepage pressure on the mechanical property of sandstone,uniaxial compression tests,P-wave velocity measurements,and nuclear magnetic resonance(NMR)tests were conducted on saturated sandstone samples with varied seepage pressures(i.e.0 MPa,3 MPa,4 MPa,5 MPa,6 MPa,7 MPa).The results demonstrate that the mechanical parameters(uniaxial compressive strength,peak strain,elastic modulus,and brittleness index),total energy,elastic strain energy,as well as elastic strain energy ratio,decrease with increasing seepage pressure,while the dissipation energy and dissipation energy ratio increase.Moreover,as seepage pressure increases,the micro-pores gradually transform into meso-pores and macro-pores.This increases the cumulative porosity of sandstone and decreases P-wave velocity.The numerical results indicate that as seepage pressure rises,the number of tensile cracks increases progressively,the angle range of microcracks is basically from 50-120to 80-100,and as a result,the failure mode transforms to the tensile-shear mixed failure mode.Finally,the effects of seepage pressure on mechanical properties were discussed.The results show that decrease in the effective stress and cohesion under the action of seepage pressure could lead to deterioration of strength behaviors of sandstone.

Effects of dry-wet cycles on the mechanical properties of sandstone with unloading-induced damage

Sandstone is the fundamental material in various engineering and construction projects.However,the mechanical integrity of sandstone can be compromised by initial unloading damage resulting from activities such as engineering excavations.Furthermore,this degradation is further exacerbated under periodic dry-wet environmental conditions.This study investigated the effects of dry-wet cycles and unloading on the mechanical properties of jointed fine sandstone using uniaxial and triaxial compression tests.These tests were performed on rock samples subjected to varying unloading degrees and different numbers of dry-wet cycles.The results demonstrate that with an increase in the unloading degree from 0%to 70%,there is a corresponding decrease in peak stress ranging from 10%to 33%.Additionally,the cohesion exhibits a reduction of approximately 20%to 25%,while the internal friction angle experiences a decline of about 3.5%to 6%.These findings emphasize a significant unloading effect.Moreover,the degree of peak stress degradation in unloading jointed fine sandstone diminishes with an increase in confining pressure,suggesting that confining pressure mitigates the deterioration caused by dry-wet cycles.Additionally,as the number of dry-wet cycles increases,there is a notable decline in the mechanical properties of the sandstone,evidencing significant dry-wet degradation.Utilizing the Drucker Prager criterion,this study establishes a strength criterion and fracture criterion,denoted as σ_(1)(m,n) and K_(T)^(Ⅱ)(m, n), to quantify the combined impacts of dry-wet cycles and unloading on jointed fine sandstone,which provides a comprehensive understanding of its mechanical behavior under such conditions.

Prediction of Ground Vibration Induced by Rock Blasting Based on Optimized Support Vector Regression Models

Accurately estimating blasting vibration during rock blasting is the foundation of blasting vibration management.In this study,Tuna Swarm Optimization(TSO),Whale Optimization Algorithm(WOA),and Cuckoo Search(CS)were used to optimize two hyperparameters in support vector regression(SVR).Based on these methods,three hybrid models to predict peak particle velocity(PPV)for bench blasting were developed.Eighty-eight samples were collected to establish the PPV database,eight initial blasting parameters were chosen as input parameters for the predictionmodel,and the PPV was the output parameter.As predictive performance evaluation indicators,the coefficient of determination(R2),rootmean square error(RMSE),mean absolute error(MAE),and a10-index were selected.The normalizedmutual information value is then used to evaluate the impact of various input parameters on the PPV prediction outcomes.According to the research findings,TSO,WOA,and CS can all enhance the predictive performance of the SVR model.The TSO-SVR model provides the most accurate predictions.The performances of the optimized hybrid SVR models are superior to the unoptimized traditional prediction model.The maximum charge per delay impacts the PPV prediction value the most.

Spatiotemporal deformation characteristics of Outang landslide and identification of triggering factors using data mining

Since the impoundment of Three Gorges Reservoir(TGR)in 2003,numerous slopes have experienced noticeable movement or destabilization owing to reservoir level changes and seasonal rainfall.One case is the Outang landslide,a large-scale and active landslide,on the south bank of the Yangtze River.The latest monitoring data and site investigations available are analyzed to establish spatial and temporal landslide deformation characteristics.Data mining technology,including the two-step clustering and Apriori algorithm,is then used to identify the dominant triggers of landslide movement.In the data mining process,the two-step clustering method clusters the candidate triggers and displacement rate into several groups,and the Apriori algorithm generates correlation criteria for the cause-and-effect.The analysis considers multiple locations of the landslide and incorporates two types of time scales:longterm deformation on a monthly basis and short-term deformation on a daily basis.This analysis shows that the deformations of the Outang landslide are driven by both rainfall and reservoir water while its deformation varies spatiotemporally mainly due to the difference in local responses to hydrological factors.The data mining results reveal different dominant triggering factors depending on the monitoring frequency:the monthly and bi-monthly cumulative rainfall control the monthly deformation,and the 10-d cumulative rainfall and the 5-d cumulative drop of water level in the reservoir dominate the daily deformation of the landslide.It is concluded that the spatiotemporal deformation pattern and data mining rules associated with precipitation and reservoir water level have the potential to be broadly implemented for improving landslide prevention and control in the dam reservoirs and other landslideprone areas.

Erosion control of Chinese loess using polymer SH and ryegrass

The China Loess Plateau is subjected to severe soil erosion triggered by intense rainfall,resulting in significant harm and losses to both human society and the natural surroundings.In this study,a novel technique for managing loess erosion is introduced,which involves the utilization of a combined polymer SH and ryegrass.A comprehensive series of tests were undertaken,including rainfall erosion tests,disintegration experiments,and scanning electron microscopy examinations,to assess the accumulative sediment yield(ASY),disintegration ratio,and microstructural features of both untreated and treated loess samples.The results showed a significant reduction in ASY with increased dry density of untreated loess.Furthermore,the combined technique effectively controlled erosion,limiting ASY to 266.2 g/cm^(2)in 60 minutes.This was approximately one-sixth,one-ninth,and one-fifteenth of the ASY in SH-treated loess(L-SH),ryegrass-treated loess(L-R),and untreated loess,respectively.It resisted disintegration better than ryegrass alone but slightly less than SH.This improvement was due to the combined effect of SH and ryegrass,which reduced raindrop impact,improved loess microstructure,and boosted ryegrass growth.The innovative technique holds the potential to be applied as a field-scale technique in the Loess Plateau region of China.

Predicting dynamic compressive strength of frozen-thawed rocks by characteristic impedance and data-driven methods

In cold regions,the dynamic compressive strength(DCS)of rock damaged by freeze-thaw weathering significantly influences the stability of rock engineering.Nevertheless,testing the dynamic strength under freeze-thaw weathering conditions is often both time-consuming and expensive.Therefore,this study considers the effect of characteristic impedance on DCS and aims to quickly determine the DCS of frozen-thawed rocks through the application of machine-learning techniques.Initially,a database of DCS for frozen-thawed rocks,comprising 216 rock specimens,was compiled.Three external load parameters(freeze-thaw cycle number,confining pressure,and impact pressure)and two rock parameters(characteristic impedance and porosity)were selected as input variables,with DCS as the predicted target.This research optimized the kernel scale,penalty factor,and insensitive loss coefficient of the support vector regression(SVR)model using five swarm intelligent optimization algorithms,leading to the development of five hybrid models.In addition,a statistical DCS prediction equation using multiple linear regression techniques was developed.The performance of the prediction models was comprehensively evaluated using two error indexes and two trend indexes.A sensitivity analysis based on the cosine amplitude method has also been conducted.The results demonstrate that the proposed hybrid SVR-based models consistently provided accurate DCS predictions.Among these models,the SVR model optimized with the chameleon swarm algorithm exhibited the best performance,with metrics indicating its effectiveness,including root mean square error(RMSE)﹦3.9675,mean absolute error(MAE)﹦2.9673,coefficient of determination(R^(2))﹦0.98631,and variance accounted for(VAF)﹦98.634.This suggests that the chameleon swarm algorithm yielded the most optimal results for enhancing SVR models.Notably,impact pressure and characteristic impedance emerged as the two most influential parameters in DCS prediction.This research is anticipated to serve as a reliable reference for estimating the DCS of rocks subjected to freeze-thaw weathering.

Spatial structural characteristics of the Deda ancient landslide in the eastern Tibetan Plateau:Insights from Audio-frequency Magnetotellurics and the Microtremor Survey Method

It is of crucial importance to investigate the spatial structures of ancient landslides in the eastern Tibetan Plateau’s alpine canyons as they could provide valuable insights into the evolutionary history of the landslides and indicate the potential for future reactivation.This study examines the Deda ancient landslide,situated in the Chalong-ranbu fault zone,where creep deformation suggests a complex underground structure.By integrating remote sensing,field surveys,Audio-frequency Magnetotellurics(AMT),and Microtremor Survey Method(MSM)techniques,along with engineering geological drilling for validation,to uncover the landslide’s spatial feature s.The research indicates that a fault is developed in the upper part of the Deda ancient landslide,and the gully divides it into Deda landslide accumulation zoneⅠand Deda landslide accumulation zoneⅡin space.The distinctive geological characteristics detectable by MSM in the shallow subsurface and by AMT in deeper layers.The findings include the identification of two sliding zones in the Deda I landslide,the shallow sliding zone(DD-I-S1)depth is approximately 20 m,and the deep sliding zone(DD-I-S2)depth is 36.2-49.9 m.The sliding zone(DD-Ⅱ-S1)depth of the DedaⅡlandslide is 37.6-43.1 m.A novel MSM-based method for sliding zone identification is proposed,achieving less than 5%discrepancy in depth determination when compared with drilling data.These results provide a valuable reference for the spatial structural analysis of large-deepseated landslides in geologically complex regions like the eastern Tibetan Plateau.

Numerical and theoretical study of large-scale failure of strata overlying sublevel caving mines with steeply dipping discontinuities

The deformation and fracture evolution mechanisms of the strata overlying mines mined using sublevel caving were studied via numerical simulations.Moreover,an expression for the normal force acting on the side face of a steeply dipping superimposed cantilever beam in the surrounding rock was deduced based on limit equilibrium theory.The results show the following:(1)surface displacement above metal mines with steeply dipping discontinuities shows significant step characteristics,and(2)the behavior of the strata as they fail exhibits superimposition characteristics.Generally,failure first occurs in certain superimposed strata slightly far from the goaf.Subsequently,with the constant downward excavation of the orebody,the superimposed strata become damaged both upwards away from and downwards toward the goaf.This process continues until the deep part of the steeply dipping superimposed strata forms a large-scale deep fracture plane that connects with the goaf.The deep fracture plane generally makes an angle of 12°-20°with the normal to the steeply dipping discontinuities.The effect of the constant outward transfer of strata movement due to the constant outward failure of the superimposed strata in the metal mines with steeply dipping discontinuities causes the scope of the strata movement in these mines to be larger than expected.The strata in the metal mines with steeply dipping discontinuities mainly show flexural toppling failure.However,the steeply dipping structural strata near the goaf mainly exhibit shear slipping failure,in which case the mechanical model used to describe them can be simplified by treating them as steeply dipping superimposed cantilever beams.By taking the steeply dipping superimposed cantilever beam that first experiences failure as the key stratum,the failure scope of the strata(and criteria for the stability of metal mines with steeply dipping discontinuities mined using sublevel caving)can be obtained via iterative computations from the key stratum,moving downward toward and upwards away from the goaf.

Swelling behaviors of heterogeneous red-bed mudstone subjected to different vertical stresses

In this study,the axial swelling strain of red-bed mudstone under different vertical stresses are measured by swell-under-load method,and the microstructure of mudstone after hygroscopic swelling is studied by mercury intrusion porosimetry(MIP).The weakening coefficient and Weibull distribution function are introduced into the coupling model of mudstone moisture diffusion-swelling deformation-fracture based on finite-discrete element method(FDEM).The weakening effect of moisture on mudstone's mechanical parameters,as well as the heterogeneity of swelling deformation and stress distribution,is considered.The microcrack behavior and energy evolution of mudstone during hygroscopic swelling deformation under different vertical stresses are studied.The results show that the axial swelling strain of mudstone decreases with increase of the vertical stress.At low vertical stresses,moisture absorption in mudstone leads to formation of cracks caused by hydration-induced expansion.Under high vertical stresses,a muddy sealing zone forms on the mudstone surface,preventing further water infiltration.The simulation results of mudstone swelling deformation also demonstrate that it involves both swelling of the mudstone matrix and swelling caused by crack expansion.Notably,crack expansion plays a dominant role in mudstone swelling.With increasing vertical stress,the cracks in mudstone change from tensile cracks to shear cracks,resulting in a significant reduction in the total number of cracks.While the evolution of mudstone kinetic energy shows similarities under different vertical stresses,the evolution of strain energy varies significantly due to the presence of different types of cracks in the mudstone.The findings provide a theoretical basis for understanding the hygroscopic swelling deformation mechanism of red-bed mudstone at various depths.

Modelling of debris-flow susceptibility and propagation: a case study from Northwest Himalaya

The geological and geographical position of the Northwest Himalayas makes it a vulnerable area for mass movements particularly landslides and debris flows. Mass movements have had a substantial impact on the study area which is extending along Karakorum Highway(KKH) from Besham to Chilas. Intense seismicity, deep gorges, steep terrain and extreme climatic events trigger multiple mountain hazards along the KKH, among which debris flow is recognized as the most destructive geohazard. This study aims to prepare a field-based debris flow inventory map at a regional scale along a 200 km stretch from Besham to Chilas. A total of 117 debris flows were identified in the field, and subsequently, a point-based debris-flow inventory and catchment delineation were performed through Arc GIS analysis. Regional scale debris flow susceptibility and propagation maps were prepared using Weighted Overlay Method(WOM) and Flow-R technique sequentially. Predisposing factors include slope, slope aspect, elevation, Topographic Roughness Index(TRI), Topographic Wetness Index(TWI), stream buffer, distance to faults, lithology rainfall, curvature, and collapsed material layer. The dataset was randomly divided into training data(75%) and validation data(25%). Results were validated through the Receiver Operator Characteristics(ROC) curve. Results show that Area Under the Curve(AUC) using WOM model is 79.2%. Flow-R propagation of debris flow shows that the 13.15%, 22.94%, and 63.91% areas are very high, high, and low susceptible to debris flow respectively. The propagation predicated by Flow-R validates the naturally occurring debris flow propagation as observed in the field surveys. The output of this research will provide valuable input to the decision makers for the site selection, designing of the prevention system, and for the protection of current infrastructure.

Centrifuge modeling of unreinforced and multi-row stabilizing piles reinforced landslides subjected to reservoir water level fluctuation

With the construction of the Three Gorges Reservoir dam,frequent reservoir landslide events have been recorded.In recent years,multi-row stabilizing piles(MRSPs)have been used to stabilize massive reservoir landslides in China.In this study,two centrifuge model tests were carried out to study the unreinforced and MRSP-reinforced slopes subjected to reservoir water level(RWL)operation,using the Taping landslide as a prototype.The results indicate that the RWL rising can provide lateral support within the submerged zone and then produce the inward seepage force,eventually strengthening the slope stability.However,a rapid RWL drawdown may induce outward seepage forces and a sudden debuttressing effect,consequently reducing the effective soil normal stress and triggering partial pre-failure within the RWL fluctuation zone.Furthermore,partial deformation and subsequent soil structure damage generate excess pore water pressures,ultimately leading to the overall failure of the reservoir landslide.This study also reveals that a rapid increase in the downslope driving force due to RWL drawdown significantly intensifies the lateral earth pressures exerted on the MRSPs.Conversely,the MRSPs possess a considerable reinforcement effect on the reservoir landslide,transforming the overall failure into a partial deformation and failure situated above and in front of the MRSPs.The mechanical transfer behavior observed in the MRSPs demonstrates a progressive alteration in relation to RWL fluctuations.As the RWL rises,the mechanical states among MRSPs exhibit a growing imbalance.The shear force transfer factor(i.e.the ratio of shear forces on pile of the n th row to that of the first row)increases significantly with the RWL drawdown.This indicates that the mechanical states among MRSPs tend toward an enhanced equilibrium.The insights gained from this study contribute to a more comprehensive understanding of the failure mechanisms of reservoir landslides and the mechanical behavior of MRSPs in reservoir banks.

Molecular simulation study on the evolution process of hydrate residual structures into hydrate

The clathrate hydrate memory effect is a fascinating phenomenon with potential applications in carbon capture,utilization and storage(CCUS),gas separation,and gas storage as it can accelerate the secondary formation of clathrate hydrate.However,the underlying mechanism of this effect remains unclear.To gain a better understanding of the mechanism,we conducted molecular dynamic simulations to simulate the initial formation and reformation processes of methane hydrate.In this work,we showed the evolution process of hydrate residual structures into hydrate cages.The simulation results indicate that the residual structures are closely related to the existence of hydrate memory effect,and the higher the contribution of hydrate dissociated water to the hydrate nucleation process,the faster the hydrate nucleation.After hydrate dissociation,the locally ordered structures still exist after hydrate dissociation and can promote the formation of cluster structures,thus accelerating hydrate nucleation.Additionally,the nucleation process of hydrate and the formation process of clusters are inseparable.The size of clusters composed of cup-cage structures is critical for hydrate nucleation.The residence time at high temperature after hydrate decomposition will affect the strength of the hydrate memory effect.Our simulation results provide microscopic insights into the occurrence of the hydrate memory effect and shed light on the hydrate reformation process at the molecular scale.

Bibliometric analysis of research challenges and trends in urban underground space

The utilization and development of urban underground space play a crucial role in optimizing the layout of civic architecture and enhancing the urban ecological environment,which contributes toward increasing the overall carrying capacity and promoting sustainable development in megacities.To delve into the research progress of urban underground space,knowledge maps were created using the information visualization software VOSviewer.The literature was systematically extracted from three prominent databases,namely,Web of Science,Scopus,and China National Knowledge Infrastructure.According to the bibliometric analysis of the co-citation and core words co-occurrence,the trends and challenges of research on urban underground space were identified.As highlighted by the results obtained,it still remains highly challenging to achieve interdisciplinary collaboration in urban underground space research;the research trends of urban underground space consist of collaborative planning and whole life cycle sustainable development,multisource geological data informatization and resource evaluation,infrastructure design optimization,and intelligent construction.The knowledge map,drawn using bibliometric methods,offers a quantitative analysis of literature retrieval across various levels.It is recognized as an essential tool for exploring and identifying challenges and trends in urban underground space.

Failure behavior and strength model of blocky rock mass with and without rockbolts

To better understand the failure behaviours and strength of bolt-reinforced blocky rocks,large scale extensive laboratory experiments are carried out on blocky rock-like specimens with and without rockbolt reinforcement.The results show that both shear failure and tensile failure along joint surfaces are observed but the shear failure is a main controlling factor for the peak strength of the rock mass with and without rockbolts.The rockbolts are necked and shear deformation simultaneously happens in bolt reinforced rock specimens.As the joint dip angle increases,the joint shear failure becomes more dominant.The number of rockbolts has a significant impact on the peak strain and uniaxial compressive strength(UCS),but little influence on the deformation modulus of the rock mass.Using the Winkler beam model to represent the rockbolt behaviours,an analytical model for the prediction of the strength of boltreinforced blocky rocks is proposed.Good agreement between the UCS values predicted by proposed model and obtained from experiments suggest an encouraging performance of the proposed model.In addition,the performance of the proposed model is further assessed using published results in the literature,indicating the proposed model can be used effectively in the prediction of UCS of bolt-reinforced blocky rocks.

Geological and Geoengineering Properties of the 1997 Yangjia Shan Landslide, Enshi, China

Yangjia Shan instability has been evidenced by the occurrence of the July 16, 1997 landslide. The instability factor which leads to activating the landslide is the intense rainfall;lithology of Luoreiping Formation and the highly weathered slopes’ rocks have played a great role in starting and aggravation. Weathering at the landslide site consists largely of attack on the cement and removal of support of the sandy mudstone and sandstone and decompose of shale. The weathering degree of the rocks decreases vertically with increasing depth from high, medium to slightly weathered corresponding to grade IV, III and II, respectively. The slip surface consists of moderate to highly weathered intercalated layers of sandy mudstone (mudstone) and shale, while, the layer below the slip surface is characterized by dark gray, moderately weathered and thick layered mudstone. The moderate to highly weathered subsurface lithology is probably attributed to the accumulation of the infiltrated rainfall water through fractures and porosity, raising the ground water level and wetting of the sandy mudstone and shale rocks of Luoreping Formation. The wetting contributed more or less to the disintegration of the sandy mudstone and shale, lowered the shear strength and created cracks on the upper part of the slope leading thus to increase the landslide susceptibility. Therefore, the frequency and magnitude of landslide at the study area and its vicinity are expected to increase through the activation of old landslides and triggering of new ones under circumstances similar to those of the past.

Engineering Geological and Geophysical Assessment of the 2009 Jiwei Shan Rockslide, Wulong, China

This study presents the engineering geological and geophysical assessment of the June 5, 2009 Jiwei Shan rockslide, Wulong, China. Jiwei Shan is a part of Wulong karst terrain lithologically, it’s composed of Quaternary Deposits, Jialingjiang Formation, Maokou, Qixia, Liangshan and Hanjiadian Groups (chronologically from younger to older). The surface is highly irregular (pinnached), the rocks contain two sets of fractures, networks of convoluted solution channels and caves and there are large voids filled by soil mantle. It’s a south-north dipping limb of an anticline fold composed of sedimentary rocks, mainly of limestone of variable composition, mudstone and shale and series of limestone deposited with interbedded mudstone and shale. There are two sets of steeply dipping fractures developed in the Maokou and upper strata of Qixia Groups;set one trending EW and set two trending nearly SN directions. The study has been conducted by geological fieldwork, geophysical investigation (Vertical Electrical Sounding), petrographical and scanning electron microscope (SEM) studies and laboratory testing on rock samples collected from Jialingjiang Formation and Maokou and Qixia Groups. The study of the SEM photomicrographs showed that the microcrack propagations in limestone indicated that the increases in crack length and micropores of limestone are indication to the weathering grade increase from II (slightly weathered rock) to grade III and IV (moderately and highly weathered, respectively). The Qixia Group;Middle Layer is highly weathered shale and bituminous interlayer with clear fissility, high porosity, and gently dipping strata, it represents the sliding surface of the rockslide. It’s comparatively weak and strongly weathered compared to the overlain EW and SN fractured stratum. Generally, the tectonic of the study area imposes controls on the rockslide in many ways: created favourable terrain, provided sufficient rockslide prone materials such as highly weathered limestone and shale, weak rocks, created very steep beds which reduced the stability of the highly fractured bedrock of the slope.

Multiscale evolution mechanism of sandstone under wet-dry cycles of deionized water:From molecular scale to macroscopic scale

Water is the most abundant molecule found on the earth’s surface and is a key factor in multiscale rock destruction.However,given the fine-grained nature of rock and the complexity of its internal structure,the microstructural evolution of rock under the action of water has not yet been elucidated in detail,and little is understood about the relationship between the rock structure and solideliquid unit.A variety of techniques were used in this study to track the mechanical properties,pore and crack characteristics,and mineral structure degradation characteristics of sandstone at different stages under the action of deionized water,and the evolution mechanisms of the microstructure were analyzed at the molecular scale.The results showed that during the watererock interaction process,water was adsorbed onto the surface of dolomite minerals and the hydrophilic surface of clay minerals,forming a high-density hydrogen bond network.However,different mineral surface structures had different water adsorption structures,resulting in the strain of the dense clay mineral aggregates under expansion action.Stress concentrated at crack tips under the capillary force of dolomite minerals(very weak dolomite dissolution).These effects resulted in a substantial increase in the number of small pores and enhancements in poreecrack connectivity,and the rock strength exhibited varying degrees of decline at different stages of wet-dry cycles.In general,the results of this paper will help to further elucidate the internal connections between molecular-scale and macroscale processes in rock science.