Advances in stability analysis and optimization design of large underground caverns under high geostress condition

The demand for underground space and sustainable energy has driven the need for underground structures.Large underground caverns,being an underground structure carrier,offers a feasible solution.However,the stability analysis and optimization design of large underground caverns is always a great challenge due to the high geostress,complicated rock condition,and high sidewalls and large spans in size.By collecting and reviewing a large amount of relevant research literature from 1970 to 2023,the efforts on the advances in stability analysis methods and optimization design of large underground caverns are described,then the research trends in this field through keywords were found and typical deformation and break modes of large underground caverns with high geostress are summarized.The review reveals that stability analysis and optimization are the recent active research topics.There are seven typical deformation and break modes of large underground caverns under high geostress,four stability analysis methods and four theories of optimization design of large under-ground caverns.With the progress of science and technology and society,intelligent design,mechanized con-struction and greening construction are the development trend in this field.The research results can provide a constructive reference for the stability analysis and optimization design of large underground caverns under high geostress.

Distribution patterns of rock mass displacement in deeply buried areas induced by active fault creep slip at engineering scale

Active fault creep slip induces deformation of rock mass buried deeply in fault zones that significantly affect the operational safety of long linear projects passing through it.Displacement distribution patterns of rock masses in active fault zones which have been investigated previously are the key design basis for such projects.Therefore,a discrete element numerical model with different fault types,slip time,dip angles,and complex geological features was established,and then the creep slip for normal,reverse,and strike-slip faults were simulated to analyze the displacement distribution in the fault rock mass.A disk rotation test system and the corresponding laboratory test method were developed for simulating rock mass displacement induced by creep slippage of faults.A series of rotation tests for softand hard-layered specimens under combined compression and torsional stress were conducted to verify the numerical results and analyze the factors influencing the displacement distribution.An S-shaped displacement distribution independent of fault dip angle was identified corresponding to reverse,normal,and strike-slip faults.The results indicated that the higher the degree of horizontal extrusion,the softer the rock mass at the fault core,and the higher the degree of displacement concentration in the fault core;about 70%of the creep slip displacement occurs within this zone under 100 years of creep slippage.

Tree failure modes influenced by the characteristics of tree and its root distribution caused by debris flows

Forests play an important role in controlling the formation and movement processes of debris flows.They contribute to soil stabilization,regulation of soil water content,and act as robust structures impeding the downstream progression of debris flows.On the positive side,trees,to some extent,can intercept debris flows and effectively mitigate their velocity by increasing flow resistance.On the negative side,trees may suffer damage from debris-flow hazards,characterized by the generation of substantial quantities of wood fragments and consequential ramifications such as river channel blockage,resulting in backwater rise.In extreme cases,this blockage collapse can lead to instantaneous discharge amplification,thereby adversely impacting urban safety and impeding sustainable development.Therefore,in order to grasp the effects of tree characteristics on tree failure modes,the tree failure modes and corresponding parameters,diameters at breast height(DBH)and root-soil plate size,were identified and recorded through the post-event field investigation in Keze Gully,a region prone to debrisflow events in Sichuan,China,respectively.To investigate the impact of spatial variability in tree root distribution on tree failure modes,the root crosssectional area ratio(RAR),root density(RD),root length density(RLD)and soil detachment rate(SDR)were obtained.The findings indicated that:(1)Tree characteristics reflect the interactions of debris flows and trees,and influence the tree failure modes ultimately.The root distribution characteristics influence the size and shape of the root-soil plate to affect the resistance of trees.(2)Compared to burial and abrasion,stem breakage and overturning are the predominant modes of tree failure in debris-flow hazards.Trees with a smaller DBH primarily experience stem breakage and bending,and trees with a larger DBH mostly experience overturning.(3)The root-soil plate shapes of overturned trees,affected by the root architecture and root growth range,are generally semielliptical or semicircular,and the horizontal and vertical radii increase with DBH,but the correlation between the root-soil plate’s breadth-depth ratio and DBH is low.(4)The biomass and RAR decrease with distance.The RAR distribution exhibit the order of upslope direction>downslope direction>lateral direction.The coarse root biomass significantly increases with DBH,but no clear trend in fine root biomass.(5)The roots can significantly enhance the soil erosion resistance,but the erosion resistance of coarse roots is not as significant as that of fine roots.The erosion resistance increases with DBH,and follows the order of upslope direction>downslope direction>lateral direction.The results could provide new insights into the influences of tree and root distribution characteristics on tree failure modes during debris flows.

A three-dimensional numerical study on the stability of layered rock spillway tunnels in alpine canyon areas

Rock masses in alpine canyon areas exhibit strong heterogeneity,discontinuity,and are subject to strong tectonic effects and stress unloading,leading to extremely complex distribution of in-situ stress.In addition,the occurrence of layered rock masses makes it more complex,with obvious anisotropic mechanical properties.This study proposes a comprehensive method for evaluating the stability of layered rock spillway tunnels in a hydropower station in an alpine canyon.First,the failure criterion and mechanical model of layered rock masses considering the anisotropy induced by the bedding plane and the true triaxial stress regime were established;an inversion theory and calculation procedure for in-situ stress in alpine canyon areas were then introduced.Finally,by using a self-developed numerical tool,i.e.CASRock,the stability of the layered rock spillway tunnel in a hydropower station was numerically analyzed.The results show that,affected by geological structure and stratigraphic lithology,there is significant differentiation in the in-situ stress in alpine canyons,with horizontal tectonic stress as the main factor.The occurrence of layered rock masses in the region has a significant impact on the stability of surrounding rock,and the angle between the bedding strike and the tunnel axis as well as the bedding dip both exert a significant influence on the failure characteristics of the surrounding rock.

Resilience of Wengding,the Phoenix Wa traditional village

The village of Wengding,ancestral home of the Wa ethnic group,considered as China’s last primitive tribe,suf-fered near-complete extinction due to a fire incident in 2021.Historical records indicate that stilt-style buildings,also in Wengding,are highly susceptible to fire.Nevertheless,this has not hindered the long-term existence of these distinctive architectural forms.This study analyses the reasons for the sustained existence of the traditional building forms in Wengding,from the perspective of resilience.The findings indicate that the requirements of the traditional nomadic civilization for rapid construction of dwellings,the communal consciousness toward dis-aster resistance,and the implementation of spatially oriented fire protection measures collectively account for the swift recovery and reconstruction observed in Wengding village after the disaster.These aspects are tangible manifestations of the capacity of the village for resilience.Overall,resilience is essential for the sustainability of such traditional villages in the long term.

Drainage of paddy terraces impacts structures and soil properties in the globally important agricultural heritage of Hani Paddy Terraces,China

Marginalization and abandonment of paddy terraces are widespread,but their effects on the sustainability of subsequent agricultural production are still unknown.Hani Paddy Terraces,included in Globally Important Agriculture Heritage Systems,are threatened by paddy fields drainage.Here,changes in terrace structure,the productivity of topsoil(0-20 cm),and soil water holding capacity at 0-70 cm depth were determined in a case study of Hani Paddy Terraces in Amengkong River Basin in Yuanyang County in Southwestern China,which had been converted into dryland terraces for 2-14 years.Our results showed that:(1)The degree of terrace structures degradation exhibited a U-shaped curve with increasing time since draining,with those drained for 5-9 years having the best structure;(2)Soil productivity index decreased first and then increased with time after conversion;(3)Maximum water holding capacity at 0-70 cm soil depth dramatically decreased after conversion and such trend became increasingly obvious with increasing time since conversion.Our study revealed that drainage of paddy terraces along with associated changes in crop and field management led to an increase in soil productivity,but degradation of terrace structures and a decrease in water holding capacity will inhibit restoration to paddy terraces.These findings enhance the understanding of the biophysical changes due to marginalization in paddy terraces.

Optimizing biochar addition for vermicomposting:a comprehensive evaluation of earthworms’activity,N_(2)O emissions and compost quality

Biochar addition has been widely used in the field to mitigate soil nitrous oxide(N_(2)O)emissions,and can be considered as a potential method to reduce N_(2)O emissions during vermicomposting.However,excessive biochar addition may inhibit earthworms’activity.Thus,it is crucial to clarify the optimum addition volumes of biochar during vermicomposting.This study evaluated the impact of addition of various amounts of biochar(0,5,10,15,20 and 25%of total amount of feedstock)on earthworms’(Eisenia fetida)activity,N_(2)O emission and compost quality during vermicomposting.Compared with the treatment without biochar added,5%of biochar application significantly increased earthworm total biomass(from 177.5 to 202.2 g pot^(−1)),and cumulative burrowing activity(from 47.0%to 52.2%pixel per terrarium).The increased earthworms activity stimulated the vermicomposting process and led to the best quality of compost,which showed the highest total nutrient content(5.38%)and a significantly higher germination percentage of seeds(88%).Although N_(2)O emissions were slightly increased by 5%biochar addition,a nonsignificant difference was found between the treatment with 5%biochar and the treatment without biochar added.On the contrary,20%and 25%biochar addition not only lowered N_(2)O emissions,but also significantly decreased the quality of compost.The results suggest that 5%biochar application is an appropriate amount to improve the quality of compost without significant N_(2)O emissions.

Discrete element method study of hysteretic behavior and deformation characteristics of rockfill material under cyclic loading

Granular geomaterials under different loading conditions manifest various behaviors,such as hysteresis.Understanding their hysteretic behavior and deformation characteristics is the basis for establishing a constitutive relation with excellent performance in deformation prediction.The deformation characteristics of crushable particle materials are analyzed through a series of cyclic loading tests conducted by numerical simulation.The hysteretic behavior is investigated from a particle scale.The increase in particles with contacts less than two may be responsible for the residual strain,and the particle breakage further promotes particle rearrangement and volume contraction.Both the accumulation of plastic strain and the resilient modulus are found to be related to confining pressures,stress levels,cyclic loading amplitudes,and the number of cycles.The plastic strain accumulation can be written as a function of the number of cycles and an evolution function of resilient modulus is proposed.