Roof collapse mechanism of weak surrounding rock for deep-buried tunnels under high geostress conditions

High geostress,a typical attribute of tunnels located at significant depths,is crucial in causing stress-induced failure and influencing the stability of the tunnel crown.This study developed an analytical method for the failure mechanism that occurs in deep-buried tunnel roofs,taking into account the influence of geostress.The limit analysis theory was utilized for deriving analytical solutions about the geometry of the collapsing surface and the limit supporting pressure.The collapsing surface obtained by the analytical solution was validated by the findings of the physical model test,which shows a high level of agreement with the actual one.An extensive investigation was done to explore the effects of the lateral pressure coefficients,the tunnel buried depth,the geological conditions of the surrounding rock,the long-short axis ratio,and the size of the tunnel profile.The findings indicate that an increase in the lateral pressure coefficient from 0.5 to 1.5 results in a reduction in the height of the collapsing zone by 2.08 m and the width of the collapsing zone by 1.15 m,while simultaneously increases the limit supporting pressure by 18.9%.The proposed upper bound method accurately determines the limit supporting pressure and the geometry of the collapsing surface,which aligns well with the results acquired through numerical modelling and on-site monitoring in actual engineering applications.The proposed analytical method can serve as a reference for similar crown failure issues of deep-buried tunnels.

Dissolution mechanism of a deep-buried sandstone reservoir in a deep water area:A case study from Baiyun Sag,Zhujiang River(Pearl River)Mouth Basin

Dissolution mechanism and favorable reservoir distribution prediction are the key problems restricting oil and gas exploration in deep-buried layers.In this paper,the Enping Formation and Zhuhai Formation in Baiyun Sag of South China Sea was taken as a target.Based on the thin section,scanning electron microscopy,X-ray diffraction,porosity/permeability measurement,and mercury injection,influencing factors of dissolution were examined,and a dissolution model was established.Further,high-quality reservoirs were predicted temporally and spatially.The results show that dissolved pores constituted the main space of the Paleogene sandstone reservoir.Dissolution primarily occurred in the coarse-and medium-grained sandstones in the subaerial and subaqueous distributary channels,while dissolution was limited in fine-grained sandstones and inequigranular sandstones.The main dissolved minerals were feldspar,tuffaceous matrix,and diagenetic cement.Kaolinization of feldspar and illitization of kaolinite are the main dissolution pathways,but they occur at various depths and temperatures with different geothermal gradients.Dissolution is controlled by four factors,in terms of depositional facies,source rock evolution,overpressure,and fault activities,which co-acted at the period of 23.8–13.8 Ma,and resulted into strong dissolution.Additionally,based on these factors,high-quality reservoirs of the Enping and Zhuhai formations are predicted in the northern slope,southwestern step zone,and Liuhua uplift in the Baiyun Sag.

Fisher discriminant analysis model and its application for prediction of classification of rockburst in deep-buried long tunnel

A Fisher discriminant analysis （FDA） model for the prediction of classification of rockburst in deep-buried long tunnel was established based on the Fisher discriminant theory and the actual characteristics of the project. First, the major factors of rockburst, such as the maximum tangential stress of the cavern wall σθ, uniaxial compressive strength σc, uniaxial tensile strength or, and the elastic energy index of rock Wet, were taken into account in the analysis. Three factors, Stress coefficient σθ/σc, rock brittleness coefficient σc/σt, and elastic energy index Wet, were defined as the criterion indices for rockburst prediction in the proposed model. After training and testing of 12 sets of measured data, the discriminant functions of FDA were solved, and the ratio of misdiscrimina- tion is zero. Moreover, the proposed model was used to predict rockbursts of Qinling tunnel along Xi＇an-Ankang railway. The results show that three forecast results are identical with the actual situation. Therefore, the prediction accuracy of the FDA model is acceptable.

Comparison of vibrations induced by excavation of deep-buried cavern and open pit with method of bench blasting

The measured data of vibrations induced by excavation of deep-buried cavern and open pit with method of bench blasting were analyzed by Fourier Transform and Wavelet Transform,and the characteristics of vibrations induced under these two circumstances were studied.It is concluded that with the similar rock condition and drilling-blasting parameters,vibration induced by bench blasting in deep-buried cavern has a higher main frequency and more scattered energy distribution than that in open pit.The vibration induced by bench blasting in open pit is mainly originated from the blast load,while the vibration induced by bench blasting in deep-buried cavern is the superposition of vibrations induced by blast load and transient release of in-situ stress.The vibration induced by transient release of in-situ stress increases with the stress level.

Mechanical Properties of Deep-buried Marble Material Under Loading and Unloading Tests

The mechanical properties are essentially different when rock material is subjected to loading or unloading conditions. In this study, loading and unloading tests with various confining pressures are conducted to investigate the mechanical properties of marble material samples taken from the deep diversion tunnels of Jinping II Hydropower Station. The stress-strain relationship, failure characteristics and strength criterion are compared and analyzed based on the experiment results. The results show： in the loading and unloading test, peak strength, lateral strain, axial strain and plastic deformation increase significantly as the confining pressure increases. Lateral strain increased significantly and obvious lateral dilatancy can be observed to the change of confining pressure; The fracture mode is mainly the single shear fracture for the triaxial compression test and post-peak test, angle between the failure surface and the ends of the rock material becomes smaller as the confining pressure increases. Hock-Brown strength criterion reflects the strength characteristics of marble material under two different unloading conditions, and has some supplementary effects to the rock material of mechanical field.

Numerical simulation of zonal disintegration of surrounding rock in the deep-buried chamber

Zonal disintegration is the phenomenon of cyclical rupture zone and nonrupture zone in the surrounding rock of a deep-buried chamber,which is different from that of a shallow chamber.Based on the finite difference software FLAC3D,the numerical simulation of surrounding rock with different mechanical parameters was conducted by using the SU model(Bilinear Strain-Softening Ubiquitous-Joint).The influences of buried depth,cohesion,and internal friction angle of surrounding rock on zonal disintegration were analyzed to reveal the influence law.The results show that:(1)after the chamber excavation,multiple rupture zones gradually extend from the chamber surface or adjacent periphery to the deep surrounding rock.In the extension process,a single rupture zone may be forked into two or even multiple rupture zones,which cross each other and form the zonal disintegration zone.(2)Zonal disintegration is affected by bothσ(in situ stress)and U_(cs)(uniaxial compression strength).Smaller U_(cs)and largerσwill lead to zonal disintegration.(3)The zoning fracture is not obvious in the case ofσ≤U_(cs).In the reverse case,zoning fracture appears remarkably in the surrounding rock around the chamber.These results reveal the influence law of zonal disintegration and provide theoretical support for the design of deep-buried chambers.

Analytical solution for steady seepage into a circular deep-buried mountain tunnel with grouted zone in anisotropic strata

Due to the existence of a large number of discontinuous fractures and interfaces in tunnel surrounding rocks,the groundwater inflow into tunnel generally presents significant anisotropy.Therefore,it is of great significance to consider the anisotropic permeability when dealing with water gushing-induced engineering accidents in water-rich mountain tunnels with large burial depth.In this study,based on the complex variable method and the seepage flow theory,a theoretical model of water inflow into a deep-buried circular tunnel in a fully saturated,anisotropic and semi-infinite aquifer is developed.The influence of grouted zone,initial support and secondary lining is fully considered.By comparison to the existing analytical methods and numerical results,the reliability of this proposed analytical solution is well validated.It is indicated from the parametric study that the groundwater inflow into tunnel presents an upward trend with an increasing value of the strata permeability in the vertical direction.Moreover,the water inflow rate and the total water head decrease with the growth of the thickness of grouting circle.It is suggested that reasonable grouting thickness and permeability should be controlled to enhance the grouting effect.This study provides a practical method for estimating the water inflow into a deep-buried,grouted and lined mountain tunnel considering the anisotropic strata permeability.

Experimental study on similarity materials for soft rock of deep-buried tunnels

When every parameter is properly scaled down in accordance with some similarity coefficients, it is possible to study the physical-mechanical properties of rock mass with a scale model. To identify the key mechanisms of soft rock in deep buried tunnels, the proper sand, binder and ratio were selected. During the process, the model manufacture technology was introduced and typical tests were done and the results were presented. The physical and meehanieal properties effects caused by each composition were discussed. It is shown that the physical and mechanical properties of chosen ratio material such as uniaxial compressive strength tests, elasticity modulus, tensile strength, internal frictional angle, and Poisson＇s ratio meet with similarity relationship well. The physical and mechanical properties of deep soft rock are simulated successfully.

Forecasting of water yield of deep-buried iron mine in Yanzhou, Shandong

This paper compares analytical and numerical methods by taking the forecasting of water yield of deep-buried iron mine in Yanzhou, Shandong as an example. Regarding the analytical method, the equation of infinite and bilateral water inflow boundary is used to forecast the water yield, and in the case of numerical simulation, we employed the GMS software to establish a model and further to forecast the water yield. On the one hand, through applying the analytical method, the maximum water yield of mine 1 500 m deep below the surface was calculated to be 13 645.17 m3/d; on the other hand, through adopting the numerical method, we obtained the predicted result of 3 816.16 m3/d. Meanwhile, by using the boundary generalization in the above-mentioned two methods, and through a comparative analysis of the actual hydro-geological conditions in this deep-buried mine, which also concerns the advantages and disadvantages of the two methods respectively, this paper draws the conclusion that the analytical method is only applicable in ideal conditions, but numerical method is eligible to be used in complex hydro-geological conditions. Therefore, it is more applicable to employ the numerical method to forecast water yield of deep-buried iron mine in Yanzhou, Shandong.

Stress wave propagation and incompatible deformation mechanisms in rock discontinuity interfaces in deep-buried tunnels

Complex weak structural planes and fault zones induce significant heterogeneity,discontinuity,and nonlinear characteristics of a rock mass.When an earthquake occurs,these characteristics lead to extremely complex seismic wave propagation and vibrational behaviors and thus pose a huge threat to the safety and stability of deep buried tunnels.To investigate the wave propagation in a rock mass with different structural planes and fault zones,this study first introduced the theory of elastic wave propagation and elastodynamic principles and used the Zoeppritz equation to describe wave field decomposition and develop a seismic wave response model accordingly.Then,a physical wave propagation model was constructed to investigate seismic waves passing through a fault,and dynamic damage was analyzed by using shaking table tests.Finally,stress wave attenuation and dynamic incompatible deformation mechanisms in a rock mass with fault zones were explored.The results indicate that under the action of weak structural planes,stress waves appear as a complex wave field decomposition phenomenon.When a stress wave spreads to a weak structural plane,its scattering may transform into a tensile wave,generating tensile stress and destabilizing the rock mass;wave dynamic energy is absorbed by a low-strength rock through wave scattering,which significantly weakens the seismic load.Wave propagation accelerates the initiation and expansion of internal defects in the rock mass and leads to a dynamic incompatible deformation.This is one of the main causes for large deformation and even instability within rock masses.These findings provide an important reference and guide with respect to stability analysis of rock mass with weak structural planes and fault zones.

冬春季生态沟渠对农田径流污染物的净化效果分析

为有效提高冬春季沟渠的净化效率,在原有土质沟渠中增设耐寒植物黑麦草浮毯与填料透水坝构建生态沟渠,分析生态沟渠对农田径流中主要污染物的削减率,对比沿程不同处理段对污染物的净化效果,估算植物吸收对于污染通量降低总量的贡献。结果显示:在冬春季节,生态沟渠对总氮(TN)、硝氮(NO_(3)^(-)-N)、总磷(TP)、化学需氧量(COD)和悬浮物(SS)的总削减率均值分别为29.06%、54.93%、20.76%、54.08%和49.85%。透水坝段的TN和NO_(3)^(-)-N沿程削减率最高;植物浮毯+透水坝段的TP和COD沿程削减率最高;植物浮毯段的SS沿程削减率最高,其对NO_(3)^(-)-N、TP和COD也有较好的净化效果。在降水量达到10 mm以上的9 d内,TN和TP的污染通量降低总量分别为11.43和0.27 kg;黑麦草吸收的氮、磷量分别约占污染通量降低总量的20.6%和55.6%。大雪融化后气温降至0℃以下,可能引起土壤冻融作用,雪水径流中的氮、磷浓度显著升高,此时生态沟渠对径流中氮、磷的净化效果不明显,可利用周边河塘暂存雪水径流,后续结合生态措施对污染物实施强化处理。

农田排水沟除草护坡及生态净化研究综述

对农田排水沟除草护坡及生态净化等方面的研究进行了综述,并对目前主要使用的除草技术,生态护坡技术,以及发展前沿的生态净化技术等方面的国内外相关成果进行总结归纳。然而这些方法都存在技术单一、影响环境等缺点,在对各影响因素的协同作用进行综合系统分析的基础上,提出新的解决思路。对沟道运行面临的问题与需解决的科学问题进行了探讨,旨在为现代农业灌溉排水区域建设提供参考。

丘陵果园立式螺旋开沟施肥机设计与试验

针对丘陵果园大型开沟施肥机无法进入,小型开沟施肥机因低功率限制无法达到所需开沟深度且功能单一的问题,设计了一种适宜丘陵地区25°坡度地形集开沟、施肥、覆土三大功能为一体的小型立式螺旋开沟施肥机。通过理论分析对开沟装置、施肥装置和覆土装置等关键部件进行了设计。根据丘陵果园土壤板结的特点选择Hertz-Mindlin with Bonding接触模型建立了开沟仿真模型,并以降低开沟旋转功耗、前进功耗、比功为目标,设计Box-Behnken试验对螺旋开沟刀结构参数进行优化。刀具优化仿真试验结果为:螺旋开沟刀的螺旋角、齿数、刃角、齿长分别取17.6°、10、30°、19.76 mm,此时,开沟旋转功耗、前进功耗、比功分别为6.74 kW、0.132 kW、0.165 kW·h/kg。将优化后的螺旋开沟刀试制并开展仿真验证试验,结果表明,试验与仿真测得开沟旋转功耗相对误差为5.6%,说明刀具优化结果正确。整机的田间试验结果表明,施肥机开沟深度稳定性系数、沟底宽度一致性系数、施肥均匀性系数、覆土率分别为96.91%、98.16%、97.08%、77.38%,各项指标均满足农艺要求。

宁夏黄土区稀疏带状山杏人工林土壤湿度动态与影响因素

【目的】以宁夏南部黄土丘陵区带状山杏人工林为例,揭示林带内与带间的不同深度处土壤湿度的时空变化及其关键环境影响因素,为半干旱区林草植被科学管理及雨水资源高效利用提供依据。【方法】2020—2022年,在宁夏彭阳县山杏人工林带内和带间各布设1套200 cm测深的智墒传感器,分层逐时监测土壤体积含水量和土壤温度变化,同时布设1台气象站连续监测近地面降水、气温、空气湿度等气象条件,采用相关分析探究土壤湿度对前1日土壤湿度、土壤温度和气象因子的响应规律。【结果】2020年和2021年为平水年,降水量分别为467.4和440.8 mm;2022年为枯水年,降水量为354.8 mm;土壤体积含水量平均值为平水年(2021年,17.0%)显著高于枯水年(2022年,14.3%)。土壤体积含水量随土层加深呈近线性增加,其斜率表现为林带间高于林带内,平水年高于枯水年。在0~120 cm土层的土壤体积含水量为林带内(15.3%)高于林带间(14.0%),但在120~200 cm土层为林带间(17.6%)高于林带内(16.8%)。在0~60 cm土层的土壤体积含水量变异系数为林带间(42.9%)高于林带内(37.8%),但在60~200 cm土层为林带内(23.2%)高于林带间(19.1%)。土壤湿度变化的季节格局为:相对稳定期(3—4月)、耗损期(5—8月)、恢复期(9—11月)和衰退期(12月—次年2月),最大值多出现在4月,最小值出现在8月(平水年)和12月(枯水年);土壤湿度变化的垂直空间格局为:速变层(0~50 cm)、活跃层(50~90 cm)、次活跃层(90~170 cm)、相对稳定层(170~200 cm)。相关分析发现,土壤湿度日变化相关性最强的环境因子为正相关的前1日土壤湿度和负相关的土壤温度,月变化相关性最强的环境因子为负相关的土壤温度。【结论】宁夏黄土区稀疏带状山杏人工林林带内和林带间土壤湿度在季节和剖面上均表现出较大波动,枯水年比平水年波动的层次更深。综合分析发现前1日土壤湿度、土壤温度、气象因子均是影响枯水年和平水年日及月尺度各剖面层次土壤湿度变化的要素。其中,前1日土壤湿度和土壤温度为主要影响因子;在0~120 cm土层内的土壤湿度为林带内高于林带间。本研究结果对宁夏半干旱黄土区水平沟整地后退化植被科学恢复及土壤水分高效利用有很好的指导意义。

生态沟改良技术及组合工艺净化效果分析

生态沟是一种经济高效、广泛应用于农业面源污染治理的方法,主要由植物、基质和排水沟构成。本研究重点分析了水生植物、微生物、基质、水体流速和水位等环境因子对生态沟净化效果的影响,并梳理了国内外生态沟的改良技术及组合工艺。结果表明,经过结构改良的二级生态沟和沸石屏障生态沟显著提高了总磷、总悬浮物和氨氮的去除效果;几种生态沟的组合工艺能够增强对污水的净化能力,优化生态景观,并且能将碳转化为有机物积累在基质或者生物体内,具有碳汇效应,有助于实现双碳目标。研究结论可为生态沟与其他工艺组合、应用范围的拓展以及工程实践提供参考依据。

道路生态滤沟回填黄土毛细持水特性试验研究

市政道路生态滤沟雨季积水渗透、旱季保墒是基本功能,而黄土生态滤沟回填土的设计无据可依,常导致景观植被雨季渍害或旱季枯死。为此,通过对重塑黄土进行小尺寸毛细水上升高度试验、大尺寸持水特性模型试验以及非饱和数值分析研究。结果表明:当干密度分别为1.3 g/cm^(3)、1.4 g/cm^(3)时,土柱的最终毛细水上升高度均可达到100 cm。土柱高度超过20 cm后,其含水率基本保持稳定,稳定含水率分别为30.0%、28.0%;在重塑黄土毛细水上升过程中,存在一个暂态饱和区,其中干密度越小,孔隙比越大,大孔隙数量增多,毛细吸力减弱,导致水分迁移速率较慢,同时被湿桥封闭的大气泡数量也较多,因此暂态饱和区的持续时间较长。对于1.3 g/cm^(3)的土柱,其湿润锋时程曲线的模拟值与实测值基本吻合。综合考虑黄土地层稳定的天然平均干密度、毛细水上升高度及其持水特性以及生态滤沟回填土在后期将经历反复的渗透固结与毛细作用,采用1.2 g/cm^(3)作为回填控制干密度,以确保市政道路生态滤沟中的植土在旱季仍能维持植被生长所需的土壤湿度。

胜利山柳沟北部油区长8致密砂岩开发对策研究

胜利山柳沟北部油区存在油层能量利用不足、井场状态不理想、注采井网不完善等问题,在很大程度上影响了油田的开发效果。基于此,针对低渗透油藏的特征,通过考虑地层压力的合理维持、采用菱形反九点井网形式、综合经济评价确定井网密度,以及物质平衡方法计算合理注采比等措施,实现了更加经济高效的油田开发。最终提出的开发调整方案有助于提高地层压力、优化井网结构,以及保障油田的可持续开发。这些调整为新建产能提供了可行的方案。

河套灌区农业高效节水与面源污染防控技术

针对河套灌区水资源短缺、农业面源污染严重等问题,从不同空间尺度和治理环节入手开展灌区农业高效节水与面源污染源头防控技术研究。研发了针对污染源头的农田水肥盐药调控管理技术模式(包括除草剂残留研究与用量推荐、土壤水氮盐和作物生长对水肥管理的响应、减量膜上秋浇技术及次生盐渍化土壤微生物改良技术)、针对农田排水的富氧生态沟渠截污净化技术模式和区域尺度的面源污染空间解析识别技术,并集成构建了贯穿源头控污—过程削污—区域查污—系统调污的高效节水型农业面源污染防控技术体系。基于现状研究和新发展理念提出了河套灌区水土资源领域研究的几点认识,相关成果为河套灌区高质量发展提供了重要支撑,对同类型灌区具有重要借鉴意义。

带状砂沟模式下土壤入渗过程模拟研究

[目的]探究土壤质地类型和砂沟结构参数对土壤入渗过程的影响,为砂沟集雨工程设计、运行和管理提供科学依据。[方法]基于HYDRUS-2D/3D软件,建立带状砂沟模式下土壤水分运动数学模型,利用室内试验验证模拟带状砂沟模式下土壤入渗过程的可靠性。在此基础上,模拟分析不同影响因素下带状砂沟模式下土壤累积入渗量和湿润锋运移变化过程。[结果]模拟结果与实测数据无显著性差异且一致性良好,表明所建模型及其求解方法能够有效获取带状砂沟模式下不同时刻土壤累积入渗量和湿润锋运移距离数值;均质土壤填充带状砂沟存在明显的增渗效应。原土质地、砂沟距、砂沟宽和砂沟深均对增渗率有较大影响,增渗率随原土饱和导水率和砂沟距的增大而减小,随砂沟宽和砂沟深的增大而增大;土壤湿润锋轮廓呈下低上高的U形,随时间的延长,U形侧边湿润锋逐渐靠近砂沟交汇面,顶部平台逐渐消失;原土质地对湿润锋运移距离影响较大,湿润体随原土饱和导水率的增大而增大;砂沟深对湿润锋的形态和分布影响较大,随砂沟深度的增大,U字体型垂向拉伸,左侧湿润深度显著增大,右侧湿润深度变化微弱;砂土质地、砂沟距和砂沟宽对湿润锋运移距离影响较小。[结论]带状砂沟土体构型能够显著提高土壤入渗能力,土壤质地类型和砂沟结构参数对土壤累积入渗量和湿润锋运移距离均有不同程度影响。

双层隔震梁结构关键施工技术

以北京市城市规划设计研究院新建业务综合楼为载体,针对狭窄环境下核心筒结构隔震支墩、地下结构劲性双层隔震框架梁、超高隔震沟外墙等关键施工部位,合理地进行隔震支座与主体结构的节点深化,优化隔震支座与框架结构的连接工艺措施,调整隔震沟外墙与支护结构的施工工艺,重视韧性结构关键节点的质量与安全,取得了良好的技术经济效益,值得类似项目借鉴。