Mechanical behavior of sandstone during post-peak cyclic loading and unloading under hydromechanical coupling

This paper investigates mechanical behaviours of sandstone during post-peak cyclic loading and unloading subjected to hydromechanical coupling effect, confirming the peak and residual strengths reduction laws of sandstone with water pressure, and revealing the influence of water pressure on the upper limit stress and deformation characteristics of sandstone during post-peak cyclic loading and unloading.Regarding the rock strength, the experimental study confirms that the peak strength σ_(p) and residual strength σ_(r) decrease as water pressure P increases. Especially, the normalized strength parameters σ_(p)/σ_(pk) and σ_(r)/σ_(re) was negatively and linearly correlated with the P/σ_(3). Moreover, the Hoek-Brown strength criterion can be applied to describe the relationship between effective peak strength and effective confining stress. During post-peak cyclic loading and unloading, both the upper limit stress σ_(p(i)) and crack damage threshold stress σ_(cd(i)) of each cycle tend to decrease with the increasing cycle number. A hysteresis loop exists among the loading and unloading stress–strain curves, indicating the unloading deformation modulus E_(unload) is larger than the loading deformation modulus E_(load). Based on experimental results,a post-peak strength prediction model related to water pressure and plastic shear strain is established.

Corrigendum to “Mechanical behavior of sandstone during post-peak cyclic loading and unloading under hydromechanical coupling”[Int J Min Sci Technol 33(8)(2023)927-947]

The authors regret that ‘Houquan Zhang’applies to remove his name and affiliation from the author list because he thought that he didn't make enough great contributions to this paper,just dis-cus:sion about the outline for the paper writing and some revision suggestions.The correct author list and affi liations are updated as above.

A modified method of discontinuity trace mapping using three-dimensional point clouds of rock mass surfaces

This paper presents an automated method for discontinuity trace mapping using three-dimensional point clouds of rock mass surfaces.Specifically,the method consists of five steps:(1)detection of trace feature points by normal tensor voting theory,(2)co ntraction of trace feature points,(3)connection of trace feature points,(4)linearization of trace segments,and(5)connection of trace segments.A sensitivity analysis was then conducted to identify the optimal parameters of the proposed method.Three field cases,a natural rock mass outcrop and two excavated rock tunnel surfaces,were analyzed using the proposed method to evaluate its validity and efficiency.The results show that the proposed method is more efficient and accurate than the traditional trace mapping method,and the efficiency enhancement is more robust as the number of feature points increases.

Three-dimensional distinct element modeling of fault reactivation and induced seismicity due to hydraulic fracturing injection and backflow

This paper presents a three-dimensional fully hydro-mechanical coupled distinct element study on fault reactivation and induced seismicity due to hydraulic fracturing injection and subsequent backflow process,based on the geological data in Horn River Basin,Northeast British Columbia,Canada.The modeling results indicate that the maximum magnitude of seismic events appears at the fracturing stage.The increment of fluid volume in the fault determines the cumulative moment and maximum fault slippage,both of which are essentially proportional to the fluid volume.After backflow starts,the fluid near the joint intersection keeps flowing into the critically stressed fault,rather than backflows to the wellbore.Although fault slippage is affected by the changes of both pore pressure and ambient rock stress,their contributions are different at fracturing and backflow stages.At fracturing stage,pore pressure change shows a dominant effect on induced fault slippage.While at backflow stage,because the fault plane is under a critical stress state,any minor disturbance would trigger a fault slippage.The energy analysis indicates that aseismic deformation takes up a majority of the total deformation energy during hydraulic fracturing.A common regularity is found in both fracturing-and backflow-induced seismicity that the cumulative moment and maximum fault slippage are nearly proportional to the injected fluid volume.This study shows some novel insights into interpreting fracturing-and backflowinduced seismicity,and provides useful information for controlling and mitigating seismic hazards due to hydraulic fracturing.

Evolution and modeling of mine water inflow and hazard characteristics in southern coalfields of China:A case of Meitanba mine

In this paper,the hydrogeological characteristics in the southern coalfields of China are first briefly outlined.Then,taking the Meitanba mine as an example,the evolution and modeling of mine water inflow are studied.Finally,the hazard characteristics related to mine water and mud inrush are analyzed.The results show that the main mine water sources in the Meitanba mine area are groundwater,surface water and precipitation.The evolution of mine water inflow with time indicates that the water inflow is closely related to the development of karst structures,the amount of water from rainfall infiltration,and the scope of groundwater depression cone.The mine water inflow increases with time due to the increase in mining depth and the expansion of groundwater depression cone.Using the big well method and following the potential superposition principle,a hydrogeological model considering multi-well interactions has been developed to predict the mine water inflow.Based on the monitored data in the Meitanba mine area over a period of nearly 60 years,it is found that with increasing mining depth,the number of water and mud inrush points tended to decrease.However,the average water and mud flow rate per point tended to increase.

Effect of mineralogy on friction-dilation relationships for simulated faults:Implications for permeability evolution in caprock faults

This paper experimentally explores the frictional sliding behavior of two simulated gouges:one,a series of quartz–smectite mixtures,and the other,powdered natural rocks,aiming to evaluate and codify the effect of mineralogy on gouge dilation and frictional strength,stability,and healing.Specifically,velocity-stepping and slide-hold-slide experiments were performed in a double direct shear configuration to analyze frictional constitutive parameters at room temperature,under normal stresses of 10,20,and 40 MPa.Gouge dilation was measured based on the applied step-wise changes in shear velocity.The frictional response of the quartz–smectite mixtures and powdered natural rocks are affected by their phyllosilicate content.Frictional strength and healing rates decrease with increasing phyllosilicate content,and at 20 wt.%a transition from velocity-weakening to velocity-strengthening behavior was noted.For both suites of gouges,dilation is positively correlated with frictional strength and healing rates,and negatively correlated with frictional stability.Changes in the permeability of gouge-filled faults were estimated from changes in mean porosity,indexed through measured magnitudes of gouge dilation.This combined analysis implies that the reactivation of caprock faults filled with phyllosilicaterich gouges may have a strong influence on permeability evolution in caprock faults.

Determination and applications of rock quality designation(RQD)

Characterization of rock masses and evaluation of their mechanical properties are important and challenging tasks in rock mechanics and rock engineering. Since in many cases rock quality designation （RQD） is the only rock mass classification index available, this paper outlines the key aspects on determination of RQD and evaluates the empirical methods based on RQD for determining the deformation modulus and unconfined compressive strength of rock masses. First, various methods for determining RQD are presented and the effects of different factors on determination of RQD are highlighted. Then, the empirical methods based on RQD for determining the deformation modulus and unconfined compressive strength of rock masses are briefly reviewed. Finally, the empirical methods based on RQD are used to determine the deformation modulus and unconfined compressive strength of rock masses at five different sites including 13 cases, and the results are compared with those obtained by other empirical methods based on rock mass classification indices such as rock mass rating （RMR）, Q-system （Q） and geological strength index （GSI）. It is shown that the empirical methods based on RQD tend to give deformation modulus values close to the lower bound （conservative） and unconfined compressive strength values in the middle of the corresponding values from different empirical methods based on RMR, Q and GSI. The empirical methods based on RQD provide a convenient way for estimating the mechanical properties of rock masses but, whenever possible, they should be used together with other empirical methods based on RMR, Qand GSI.

Overview of Wound Features and Treatment in Wenchuan Earthquake Victims

Objective: “5.12” Wenchuan Earthquake killed 70,000 people and left more than 90,000 people injured seriously. This study was to analyze the wound features and early treatments in Wenchuan earthquake victims and investigate treatment strategies in major disasters, to provide a reference to future disaster rescue. Methods: Total of 1420 earthquake patients who were admitted to Deyang People’s Hospital, Sichuan Province from May 12-30, 2008 were enrolled in the study. The wound features and early treatment were retrospectively analyzed. Results: Among 1420 patients, there were total 1821 injuries. In which, there were 1089 cases with single site injury (76.69%) and 331 cases with multiple injury (23.31%);injuries of limb, body surface and soft tissue were more than that of other sites;injury of single site was larger than that of multi-site (P < 0.01);most of the earthquake patients were admitted to hospital within 2 days after earthquake (68.80%), whose number was more than those at other times (P < 0.01);the number of the earthquake patients in 19 - 45 age group was more than that of other groups (P < 0.01);most of patients were treated within 12 hours after injury (P < 0.01). Conclusion: In disaster rescue, rescue speed is the key point. And the “golden time” and emphases of rescue should be within 2 days after earthquake;the principle of damage control surgery should be followed in the rescue. Enhancing mutual and self help practice and first-aid training at usual times may save more lives.

Evaluation of urban underground space resources using digitalization technologies

Exploitation and utilization of urban underground space resources is gaining increasing attention in cities’sustainable development.Due to the attributes of fragility and irreversibility,urban underground space resources can be extremely vulnerable to damage and it is often difficult in restoring their original state once damaged.Therefore,scientific and reasonable evaluation of urban underground space resources is of vital importance in urban planning and development.This paper first describes the content and methods for the evaluation of urban underground space resources,and introduces the digitalization technologies to handle the problems of strong subjectivity,low efficiency and rough precision encountered when using traditional evaluation tools.Then,the related concepts and main technologies for digitalization were demonstrated and an intelligent GIS-based engineering geology system was built.Based on the drilling information in Changzhou City,stratum standardization and 3D modeling of strata,underground structures and pipelines were conducted in the built intelligent system.Finally,with the help of spatial overlay analysis in the GIS-based platform and a combination of other digitalization technologies,the urban underground space resources of Changzhou City were evaluated.Maps of geological suitability were produced,which provide scientific guidance and reference for the exploitation and planning of urban underground space resources in Changzhou City.In addition,site selection for key projects was conducted based on the evaluation results using this platform.

Aspects of rock permeability

Effective evaluation of rock permeability is required in different energy,engineering and environmental projects.Although much research has been conducted on rock permeability,it is still one of the most difficult tasks for practicing rock engineers to accurately determine rock permeability.Based on a comprehensive literature review,this paper outlines the key aspects of rock permeability by presenting the representative values of the permeability of different rocks,describing the empirical and semi-empirical correlations for estimating the permeability of rocks,and discussing the main factors affecting the permeability of rocks.The factors discussed include stress,depth,temperature,and discontinuity intensity and aperture.This paper also highlights the scale effect on rock permeability,interconnectivity of discontinuities,and anisotropy of rock permeability.This paper provides the fundamental and essential information required for effective evaluation of rock permeability.

A simple method for evaluating liquefaction potential from shear wave velocity

The simplified procedure using shear wave velocity measurements is increasingly used to evaluate the seismic liquefaction potential of soils.This procedure is based on finding the boundary separating the liquefactionand non-liquefaction cases through the analysis of liquefaction case histories,following the general format of the Seed-Idriss simplified procedure based on standard penetration test(SPT)data.It is noted that many assumptions have been made in the simplified procedure.This paper develops a simple method for evaluating the liquefaction potential of soils from shear wave velocity by using the optimum seeking method to directly analyze the liquefaction history data and quantify the influence of major factors affecting the liquefactions potential of soils.The factors considered are the earthquake magnitude,the vertical effective overburden stress,the shear wave velocity,the peak acceleration at the ground surface of the site,and the fines content of the soil.The most important factor has been identified as the shear wave velocity.The developed method uses the measured data directly and in a very simple way.Neither stress-correction of shear wave velocity nor calculation of cyclic shear stress as in the simplified procedure is required.Comparisons indicate that the developed simple method has a higher success rate for evaluating liquefaction potential of soils than the simplified procedure.A case study is presented to illustrate the application of the developed simple method and further confirms its accuracy.

Evaluation of rock mass deformability using empirical methods-A review

Evaluation of rock mass deformability is an important but very challenging task in the analysis and design of underground structures in rock.Although various empirical(correlation)methods have been developed for determining the deformation modulus of rock masses,they come in many forms and are scattered in different sources.It is often difficult,time-consuming,or even impossible for a practitioner to find appropriate information to determine the deformation modulus of rock masses for a particular project.Therefore,this paper first provides a comprehensive review of the different empirical methods for determining the deformation modulus of rock masses.Then a comparative analysis and discussion is carried out on the accuracy and main issues of these methods.Since many of the empirical methods for determining the deformation modulus of rock masses need to use the deformation modulus of intact rock,the various empirical methods for estimating the deformation modulus of intact rock are also reviewed.In addition,this paper highlights the scale effect on rock mass deformability,the effect of confining stress on rock mass deformability,and the anisotropy of rock mass deformability.Overall this paper outlines the key aspects of rock mass deformability and provides the fundamental and essential information required for effective evaluation of rock mass deformability using the empirical methods.