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.

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.

Effects of returns on composition,microstructure and mechanical properties of GH4169 superalloy

To recycle the returned alloy effectively, effects of returns proportion on alloy composition, microstructure and compression properties of superalloy GH4169 were studied by means of scanning electron microscopy(SEM), energy dispersive spectroscopy(EDS) and thermal-mechanical simulator. The results show that returns addition has no significant effect on the main alloy elements content and the principle precipitates, but increases the volume fraction of Al_2O_3 inclusions, resulting in the increase of oxygen level of GH4169 alloy. Returns addition does not change the elastic and plastic deformation process at room temperature or at 1,150 °C, but high returns proportion GH4169 alloy shows improved compression strength and yield strength. The alloy with 100% returns shows a maximum compression strength 1,153.45 MPa at room temperature, while the alloy with 80% returns has a maximum value 69.3 MPa at 1,150 °C. Returns addition increases fluctuation range and reduces the stability of yield strength and compression strength of GH4169 alloy at room temperature. It is noted that the volume fraction and the size of Al_2O_3, and the fraction of Laves phase reach their maximum values in the GH4169 alloy with 60% returns, which exhibits maximum yield strength of 516.65 MPa at room temperature and 62.17 MPa at 1,150 °C.

Effect of returns on microstructure and mechanical properties of Al-Cu based alloys

It is well known that maximal utilization of the returns can be beneficial for cost reduction,preservation of natural resources and protection of the environment,by making them into recycled Al-Cu alloys.In this study,the influences of returns on the microstructure and mechanical properties of Al-Cu alloys have been investigated by means of optical microscopy and scanning electron microscopy.The results showed that the returns could be used to produce recycled Al-Cu alloys with fine and uniform microstructure and excellent mechanical properties,including ultimate tensile strength,yield strength and ductility.It was found that the maximum performance of the recycled Al-Cu alloy in their properties could be achievable when the returns content was 20wt.%,which gave 219 MPa,87.16 MPa and 12.15% at as-cast state,and 525 MPa,445.3 MPa and 14.14% after heat treated,in their tensile strengths,yield strengths and elongations,respectively.These values were much higher than those of primary alloy.

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.

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.

Nitrogen Deep Placement Combined with Straw Mulch Cultivation Enhances Physiological Traits,Grain Yield and Nitrogen Use Efficiency in Mechanical Pot-Seedling Transplanting Rice

To assess the effects of straw return coupled with deep nitrogen(N)fertilization on grain yield and N use efficiency(NUE)in mechanical pot-seedling transplanting(MPST)rice,the seedlings of two rice cultivars,i.e.,Yuxiangyouzhan and Wufengyou 615 transplanted by MPST were applied with N fertilizer at 150 kg/hm2 and straw return at 6 t/hm2 in early seasons of 2019 and 2020.The experiment comprised of following treatments:CK(no fertilizer and no straw return),MDS(deep N fertilization and straw return),MBS(broadcasting fertilizer and straw return),MD(deep N fertilization without straw return),MB(broadcasting fertilizer without straw return).Results depicted that the MDS treatment significantly increased the rice yield by 41.69%-72.22%due to total above-ground biomass,leaf area index and photosynthesis increased by 54.70%-55.80%,38.52%-52.17%and 17.89%-28.40%,respectively,compared to the MB treatment.In addition,the MDS treatment enhanced the total N accumulation by 37.74%-43.69%,N recovery efficiency by 141.45%-164.65%,N agronomic efficiency by 121.76%-134.19%,nitrate reductase by 46.46%-60.86%and glutamine synthetase by 23.56%-31.02%,compared to the MB treatment.The average grain yield and NUE in both years for Yuxiangyouzhan were higher in the MDS treatment than in the MD treatment.Hence,deep N fertilization combined with straw return can be an innovative technique with improved grain yield and NUE in MPST in South China.

基于Pro_MECHANISM刨床急回机构建模及运动仿真

急回机构能实现机械工作行程的匀速慢行和空回行程的快速退回,提高了工作效率、改善了机构运动和动力性能。运用Pro/E软件对急回机构进行三维实体建模及装配,并运用Pro_MECHANISM进行机构运动仿真分析,得出机构的位移、速度、加速度随时间变化的曲线。

Lubrication characteristics of external return spherical hinge pair of axial piston pump or motor under combined action of inclination and offset distance

External return mechanism is a mechanical structure applied to axial piston pumps.To study its lubrication characteristics,the Reynolds equation applied to an external return spherical hinge pair was deduced based on the vector equation of relative-motion velocity of the external return spherical hinge pair under the influence of external swash plate inclination and offset distance.The results show that the total friction,axial leakage flow,and maximum value of the maximum oil-film pressure increase with increasing pump-shaft speed and decrease with increasing offset distance in one working cycle when the external-swash-plate inclination is constant.However,the varying offset distance has little effect on the axial leakage flow.The maximum value of the maximum oil-film pressure decreases with increasing external-swash-plate inclination and the total leakage flow increases with increasing external-swash-plate inclination in one working cycle when the offset distance is constant.It can be seen that the abovementioned parameters are important factors that affect the lubrication characteristics of external return spherical hinge pairs.Therefore,the complex effects of different coupling parameters should be comprehensively considered in the design of the external return mechanism.

PPP项目回报机制选择研究——以高速公路PPP项目为例

PPP项目回报机制的选择对于保障PPP项目顺利推进具有重要意义。在分析高速公路PPP项目回报机制选择影响因素的基础上,采用fsQCA方法,以我国55个高速公路PPP项目为样本,分析政府付费、使用者付费、可行性缺口补助等三种回报机制对应的内外部因素作用路径,总结归纳了PPP项目回报机制的选择原则,并以兴延高速公路为例进行验证说明。

农作物秸秆资源化利用问题及发展策略研究

分析了我国现阶段农作物资源化利用存在的附加值低、农户积极性不高、筹资难、农业机械化发展不均衡、人才缺乏等问题,研究适合我国农作物秸秆资源化利用的发展策略及措施,以推动我国农作物秸秆资源化利用。

1LF-5型液压翻转犁的设计与试验

为推动玉米秸秆还田保护性耕作农艺的发展,设计了一种集土壤耕作技术、玉米秸秆还田技术于一体的1LF-5型液压翻转犁,一次作业既翻转了土层、松碎了土壤,又可将土壤表层的玉米秸秆与作物残茬翻入土层下,形成隔层进行还田;同时,犁体受到突发外力冲击时,安全装置自动生效,使犁柱绕固定轴栓旋转,从而保护犁体与犁柱的安全。田间试验表明:1LF-5型液压翻转犁的平均耕作深度稳定为33.45cm,平整度为20mm,变异系数在3.166%~3.535%之间;在第1工况下,翻转犁的耕宽平均值为220.75cm,耕宽的变异系数范围为1.21%~1.71%;在第2工况下,翻转犁的耕宽平均值170.1cm,耕作宽度的变异系数范围为1.26%~1.68%;植被覆盖率平均值为89.97%,土垡破碎率为72.27%。机具满足国家标准GB/T14225对于耕作质量的各项要求,也满足翻耕农艺要求。

基于Theil不等系数IOWAO组合模型的黑龙江省秸秆还田机械化程度预测

玉米、水稻等作物收后秸秆处理一直是农业生产中亟待解决的问题,机械化秸秆还田是作物收后秸秆处理的重要手段,也是保护黑土资源的重要措施。结合相关文献,提出基于协整性检验的单一预测模型选择和基于误差指标最小的最优组合预测模型选择关键环节;运用协整性检验方法确定二次函数模型、ARIMA模型、H-W无季节模型作为秸秆还田机械化程度预测的单一模型;依据误差绝对值和最小法、Shapley法和基于Theil不等系数IOWAO法构建三种组合预测模型,采用误差平方和(SSE)、平均绝对误差(MAE)、均方误差(MSE)、平均绝对百分比误差(MAPE)、均方百分比误差(MSPE)五个误差指标比较模型精度,确定采用基于Theil不等系数IOWAO的组合模型为最优预测作物秸秆还田机械化程度模型。结果表明,2022-2026年黑龙江省秸秆还田机械化程度将稳步提升,平均每年增加4.52%,2026年将达到74.19%,比2021年提升22.62%;2022年以后,黑龙江省秸秆还田机械化程度将进入快速发展期。为制定和实施机械化秸秆处理政策提供理论依据,为保护和恢复黑土资源生产能力提供重要支撑。

汽车后大灯镜壳大型薄壁精密注塑模设计

根据汽车后大灯镜壳的结构特点,设计了一副大型薄壁精密注塑模具。模具采用定模成型内表面、动模成型外表面及动模侧向抽芯机构,有效地解决了成型塑件脱模困难问题;模具采用三级定位机构,显著提高了模具刚度和寿命;模具采用随形水路温度控制系统,成型周期降低了10%,成型塑件最大变形量下降了20%,成型塑件的尺寸精度达到了设计要求的MT3;模具采用推杆先复位机构,有效地消除了滑块和推杆汽相撞的风险,保证了侧向抽芯机构安全可靠。模具投产后运行平稳,成型塑件尺寸稳定。

消费者风险厌恶的运费险分担机制与供应链定价研究

考虑消费者的退货行为、风险厌恶态度和运费险价值敏感,建立零售商承担、消费者承担、零售商与消费者共同承担、零售商与制造商共同承担4种不同运费险承担方式的Stackelberg价格博弈模型,研究供应链的定价决策和在线零售商的最优退货运费险策略。研究表明:低退货率和高运费险敏感性有助于提高供应链的整体利润;低退货率时,在线零售商主动为消费者购买运费险优于消费者自行购买;运费险的分担机制不能实现供应链协调。

回油盖隧道式二次抽芯机构注塑模设计

为解决塑件局部区域复杂特征的脱模困难问题,在注塑模具设计时首先采用局部特征分区域办法将局部难脱模特征集中分离出来,而后依据脱模方向的分布情况再进行同向集成分类,针对各集成后的脱模方向设计单次或多次抽芯机构,即脱模方向集成分类脱模设计法,从而有效地解决塑件脱模方向众多而导致的塑件整件或局部区域脱模设计困难问题。基于上述设计原理,结合润滑盒回油盖塑件的脱模设计困难问题,创新设计了一种隧道式二次抽芯机构。在该机构中,利用一根斜导柱驱动主成型块内的隧道滑块转向驱动主成型块内的另一成型活动块先完成第一次抽芯,此过程中主滑块与主成型块分离,而主成型块维持不动;然后该斜导柱再继续驱动主滑块带动主成型块完成第二次抽芯来实现塑件局部区域的脱模。结合机构运动力学分析,在该机构的结构设计中,主滑块与主成型块的闭合锁紧由楔紧块两侧不同斜角的斜面进行锁紧,其斜角分别为23°和25°,相应地,主滑块的斜导柱斜角取20°,用此参数设计的两次抽芯机构顺利地克服了塑件局部区域脱模机构设计困难难题,应用于塑件模具上,较好地实现了塑件的自动化注塑生产。塑件的模具结构为一种单点点浇口三板模具,一模一腔布局。

“返家乡”社会实践工作常态化、长效化研究

“返家乡”社会实践工作是共青团中央面向全国青年学生开展社会实践育人工作的新探索新拓展,引导青年学生在社会实践中增长知识、提高技能、接触社会和丰富阅历。要建立“返家乡”社会实践工作常态化、长效化发展的机制体制,服务学生成长成才。

返乡农民工群体在广东区域协调发展中的积极作用——基于内在机理与政策取向视角

在地理区位、经济基础和产业政策等不同条件的影响下,广东区域差距愈发明显。与此同时,粤东西北地区一定规模的农民工群体因珠三角地区就业受阻而选择暂时返乡。研究发现,返乡农民工群体具有生产者、消费者和传播者三重身份,将会为粤东西北地区带来物质资本、人力资本、社会资本和情感资本四项稀缺性资源,其对于粤东西北地区高质量发展以及全省区域协调发展均是不可或缺的。在返乡创业就业中,该群体能够激活四项资本的巨大潜能,有助于粤东西北地区实施乡村振兴战略,推进新型城镇化。要从政府、市场、返乡农民工群体和中介组织四个维度共同发力,发挥返乡农民工群体在乡村振兴和新型城镇化建设中的积极作用,助推广东区域协调发展。

农民工返乡创业带头人成长演进机制研究

农民工返乡创业带头人是乡村振兴中重要的人才资源之一,是推动农村经济发展,促进农民增收的重要力量。运用扎根理论研究方法,以广东省清远市16名返乡创业农民工带头人典型案例为样本,通过三步编码法对案例资料进行提炼,构建了农民工返乡创业带头人成长演进的“特征—欲望—意向—行为”模型。农民工返乡创业带头人案例在创业特征、创业欲望、创业意向、创业领导、创业行为等方面存在共同的特征。地方政府应通过提升创业能力、加大激励力度、优化改善创业环境、强化领导力培训、加强返乡创业带头人科学管理等手段,进一步优化农民工返乡创业带头人的培育路径。

基于多元合作机制促进大学生返乡创业对策研究

影响大学生返乡创业的因素是多元的,也是结构性的。引导和促进大学生返乡创业,应加强高校与地方政府、企业和全社会的协同合作。在高校层面,应深化教育教学改革,提升大学生返乡创业意愿;在政府层面,应完善角色职能,强化大学生返乡创业政策支持;在企业层面,应发挥协同作用,为大学生返乡创业提供帮助;在社会层面,应调动各方资源力量,厚植返乡创业文化土壤。