Upper bound solutions of stability factor of shallow tunnels in saturated soil based on strength reduction technique

Based on the upper bound theorem of limit analysis,the factor of safety for shallow tunnel in saturated soil is calculated in conjunction with the strength reduction technique.To analyze the influence of the pore pressure on the factor of safety for shallow tunnel,the power of pore pressure is regarded as a power of external force in the energy calculation.Using the rigid multiple-block failure mechanism,the objective function for the factor of safety is constructed and the optimal solutions are derived by employing the sequential quadratic programming.According to the results of optimization calculation,the factor of safety of shallow tunnel for different pore pressure coefficients and variational groundwater tables are obtained.The parameter analysis shows that the pore pressure coefficient and the location of the groundwater table have significant influence on the factor of safety for shallow tunnel.

Rock Strength Estimation Using Several Tree-Based ML Techniques

The uniaxial compressive strength(UCS)of rock is an essential property of rock material in different relevant applications,such as rock slope,tunnel construction,and foundation.It takes enormous time and effort to obtain the UCS values directly in the laboratory.Accordingly,an indirect determination of UCS through conducting several rock index tests that are easy and fast to carry out is of interest and importance.This study presents powerful boosting trees evaluation framework,i.e.,adaptive boosting machine,extreme gradient boosting machine(XGBoost),and category gradient boosting machine,for estimating the UCS of sandstone.Schmidt hammer rebound number,P-wave velocity,and point load index were chosen as considered factors to forecast UCS values of sandstone samples.Taylor diagrams and five regression metrics,including coefficient of determination(R2),root mean square error,mean absolute error,variance account for,and A-20 index,were used to evaluate and compare the performance of these boosting trees.The results showed that the proposed boosting trees are able to provide a high level of prediction capacity for the prepared database.In particular,itwas worth noting that XGBoost is the best model to predict sandstone strength and it achieved 0.999 training R^(2) and 0.958 testing R^(2).The proposed model had more outstanding capability than neural network with optimization techniques during training and testing phases.The performed variable importance analysis reveals that the point load index has a significant influence on predicting UCS of sandstone.

Strength criterion of porous media: Application of homogenization techniques

The present paper aims at giving some general ideas concerning the micromechanical approach of the strength of a porous material. It is shown that its determination theoretically amounts to solving a nonlinear boundary value problem defined on a representative elementary volume(REV). The principle of nonlinear homogenization is illustrated based on the case of a solid phase having a Green’s strength criterion. An original refinement of the so-called secant method(based on two reference strains) is also provided. The paper also describes the main feature of the Gurson’s model which implements the principle of limit analysis on a conceptual model of hollow sphere. The last part of the paper gives some ideas concerning poromechanical couplings.

Limit equilibrium method(LEM) of slope stability and calculation of comprehensive factor of safety with double strength-reduction technique

When the slope is in critical limit equilibrium(LE) state, the strength parameters have different contribution to each other on maintaining slope stability. That is to say that the strength parameters are not simultaneously reduced. Hence, the LE stress method is established to analyze the slope stability by employing the double strengthreduction(DSR) technique in this work. For calculation model of slope stability under the DSR technique, the general nonlinear Mohr–Coulomb(M–C) criterion is used to describe the shear failure of slope. Meanwhile, the average and polar diameter methods via the DSR technique are both adopted to calculate the comprehensive factor of safety(FOS) of slope. To extend the application of the polar diameter method, the original method is improved in the proposed method. After comparison and analysis on some slope examples, the proposed method's feasibility is verified. Thereafter, the stability charts of slope suitable for engineering application are drawn. Moreover, the studies show that:(1) the average method yields similar results as that of the polardiameter method;(2) compared with the traditional uniform strength-reduction(USR) technique, the slope stability obtained using the DSR techniquetends to be more unsafe; and(3) for a slope in the critical LE state, the strength parameter φ, i.e., internal friction angle, has greater contribution on the slope stability than the strength parameters c, i.e., cohesion.

CHOICE OF FILLING MATERIALS AND TECHNIQUES IN XINQIAO PYRITE MINE

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Process parameters optimization for friction stir welding of RDE-40 aluminium alloy using Taguchi technique

Taguchi approach was applied to determine the most influential control factors which will yield better tensile strength of the joints of friction stir welded RDE-40 aluminium alloy. In order to evaluate the effect of process parameters such as tool rotational speed, traverse speed and axial force on tensile strength of friction stir welded RDE-40 aluminium alloy, Taguchi parametric design and optimization approach was used. Through the Taguchi parametric design approach, the optimum levels of process parameters were determined. The results indicate that the rotational speed, welding speed and axial force are the significant parameters in deciding the tensile strength of the joint. The predicted optimal value of tensile strength of friction stir welded RDE-40 aluminium alloy is 303 MPa. The results were confirmed by further experiments.

Ti Coating on Magnesium Alloy by Arc-Added Glow Discharge Plasma Penetrating Technique

Arc-added glow discharge plasma penetrating technique is a new surface coating method. With the help of vacuum arc discharge, a cold cathode arc source continually emits ion beams of coating elements with high currency density and high ionizing ratio. As the ion bombard and diffusion working on, the surface of the parts form deposited layer, penetrated layer and hybrid layer. Under lab condition, a commercial magnesium alloy Az91 had been coated with Ti film layer with the aim of improving its’ anti-corrosion performance. This paper mainly summarized our studies on the testing and analyzing of the coating layer. The composition and microstructure of the coating layer had been analyzed by means of X-ray diffraction (XRD) and glow discharge spectrum (GDS), and the surface appearance had been surveyed by scanning electronic microscope (SEM). The adhesion strength between film and matrix had been evaluated by experiments of sticking-tearing. The results indicated that the coated layer on magnesium alloy were homogeneous, dense and robustly adhered.

Effects of Gas Metal Arc Welding Techniques on the Mechanical Properties of Duplex Stainless Steel

The study has compared the effect of gas metal arc welding techniques on some mechanical properties of duplex stainless steel. The samples after welded were given post weld heat treatment (quenching in engine and neem oil). After the analyses, it was established that duplex stainless steel can be weld successfully using gas metal arc welding process (GMAW). Both Lubricating oil and neem oil can serve as quenching medium for post welding heat treatment of duplex stainless steel. The results of the studies also show that welding and heat treatment really affect the mechanical properties of the alloy;the control strength was 811.47 MN/m2 while that of the welded samples ranged from 177.07 to 257.32 MN/m2. The control impact energy was 162.70 J, while that of the welded samples ranged from 38.64 J to 56.20 J. The research also shows that the stress relief heat treatment gives better strength (A3 = 331 MN/m2) compared to those that were quenched in lubricating oil (A2 = 329 MN/m2) and neem oil (A1 = 222 MN/m2), but the reverse is the case in terms of toughness.

焊丝成分对超高强装甲钢焊接接头组织与性能的影响

利用气体保护电弧焊工艺完成了4.5 mm和9.0 mm超高强装甲钢的焊接,研究了焊丝(MG70S-6和ER307Si焊丝)成分对接头组织与性能的影响,通过光学显微镜(OM)、扫描电子显微镜(SEM)、能谱分析(EDS)、X射线衍射(XRD)等表征方法对焊接接头各区域进行微观组织和物相结构的分析,并测试了接头的硬度分布、拉伸性能和冲击韧性。结果表明,焊接接头成形质量良好,无明显未熔合、气孔、裂纹等缺陷,焊缝区组织为片状马氏体、针状铁素体和少量粒状贝氏体,完全淬火区组织为马氏体和贝氏体,不完全淬火区组织为马氏体和铁素体,回火区析出网状渗碳体。焊接接头的热影响区软化现象较为明显,接头难以达到与母材等强,断裂主要发生在焊缝区,呈现出脆性断裂特征。采用ER307Si焊丝焊接的9.0 mm装甲钢接头的焊缝室温冲击功达到94 J,完全满足使用要求。

CFG桩在公路软土地基处理中的应用研究

为提高软土地基承载力和稳定性,论文依托实际工程,将水泥、粉煤灰、赤泥和再生砖骨料作为原材料制作CFG桩,将其应用于软土地基中,形成复合地基,并通过室内试验检测新拌混凝土立方体的抗压强度,评价CFG桩的力学性能。研究结果为,当赤泥掺量为10%,粉煤灰掺量为10%,再生砖骨料掺量为40%时,3 d、7 d和28 d抗压强度分别为22.63 MPa、16.98 MPa和33.96 MPa,不仅满足强度性能要求,还提高了建筑固体废弃物的再生利用率。最后,总结了CFG桩在软土地基处理中的施工技术要点。

八段锦功法训练对慢性阻塞性肺疾病患者下肢肌力和生活质量的影响

目的:分析慢性阻塞性肺疾病(COPD)患者采用八段锦功法训练对其下肢肌力与生活质量的影响。方法:选取自2022年1月至2024年1月在福建中医药大学附属第二人民医院肺病科进行治疗的84例COPD患者,通过随机数字表法将其分为对照组和观察组,各42例。对照组患者接受呼吸内科常规治疗及护理,观察组患者在对照组基础上配合八段锦功法锻炼。比较干预前及干预6周后两组患者下肢肌力、6 min步行试验(6MWT)、慢性阻塞性肺疾病评估测试问卷(CAT)评分以及不良事件发生情况。结果:干预后,与对照组比较,观察组患者下肢肌力更强,6MWT值更高,CAT评分更低,差异具有统计学意义(P<0.05)。两组患者不良事件发生率比较,差异无统计学意义(P>0.05)。结论:COPD患者采用八段锦功法训练可促进其下肢肌力提升且有助于改善其生活质量,安全可靠。

孔隙结构对黏土持水性及抗剪强度的影响

为研究双峰孔隙结构对非饱和土力学特性的影响,以广西南宁和桂林2种典型双峰孔隙结构黏土为研究对象,分析了其在不同饱和度情况下的抗剪强度特性;辅以滤纸法及核磁共振(nuclear magnetic resonance,NMR)技术探究了2种土体在双峰孔隙结构情况下孔隙水分布状态对强度的影响机理。结果表明:饱和状态下,2种土体试样的T2分布曲线为双峰结构,且土样持水特性整体上均呈现双峰土水特征曲线;2种土体的应力-位移关系变化规律相似,抗剪强度与饱和度密切相关;在饱和度为40%前后土样黏聚力变化趋势发生改变,而内摩擦角则是在饱和度为80%时达到最小值。

冻结温度对不同粒径冻土石混合体劈裂特性的影响

为研究冻结温度与尺寸效应耦合作用下的冻土石混合体巴西劈裂特性,分别对经过-10、-15、-20、-25、-30、-35、-40℃冻结处理后的5~10、10~15、15~20、5~20 mm粒径冻土石混合体试件进行巴西劈裂实验;研究冻结温度和不同粒径块石对试件劈裂抗拉强度的影响规律,并进一步通过数字图像相关技术(digital imagine correlation,DIC)再现了冻土石混合体在巴西劈裂实验过程中的应变场演化过程。实验结果表明:在劈裂拉应力作用下,试件从中心开裂并产生初始裂纹,沿着土石界面向两加载端贯穿试件,试件破裂面裂纹呈弯曲折线型,且块石粒径越大,裂纹越曲折;冻土石混合体在破坏时会经历线弹性变形阶段,并随着拉应力的增大和冻结温度的降低会经历塑性-脆性破坏阶段;试件劈裂抗拉强度具有强温度敏感性,会随着冻结温度的降低而近似线性增加;块石尺寸效应会导致试件强度的差异性,试件劈裂抗拉强度大小依次为5~10、5~20、10~15、15~20 mm粒径试件。

Research progress of heterogeneous structure magnesium alloys:A review

In recent years,a new class of metallic materials featuring heterogeneous structures has emerged.These materials consist of distinct soft and hard domains with significant differences in mechanical properties,allowing them to maintain high strength while offering superior ductility.Magnesium(Mg)alloys,renowned for their low density,high specific strength,exceptional vibration damping,and electromagnetic shielding properties,exhibit tremendous potential as lightweight and functional materials.Despite their advantageous properties,high-strength Mg alloys often suffer from limited ductility.However,the emergence of heterogeneous materials provides a fresh perspective for the development of Mg alloys with both high strength and ductility.This article provided a fundamental overview of heterostructured materials and systematically reviewed the recent research progress in the design of Mg alloys with strength-ductility balance based on heterostructure principles.The review encompassed various aspects,including preparation methods,formation mechanisms of diverse heterostructures,and mechanical properties,both within domestic and international contexts.On this basis,the article discussed the challenges encountered in the design and fabrication of heterostructured Mg alloys,as well as the urgent issues that require attention and resolution in the future.

RSSI和PC-CSI加权融合的指纹定位方法

针对基于RSSI和CSI的指纹定位技术易受环境干扰、定位精度较低的问题,提出了一种基于RSSI指纹和相位修正信道状态信息(phase correct based channel state information,PC-CSI)指纹的加权融合指纹定位技术。基于PC-CSI的指纹定位在传统基于CSI幅值的指纹定位基础上增加相位信息对定位结果进行修正,之后对RSSI指纹和PC-CSI指纹的定位结果加权重定位。实验结果表明,提出的加权融合指纹定位算法与基于CSI的主动定位算法相比,平均定位误差(mean position error,MPE)降低了36.2%,能满足室内定位需求。

基于“筋骨并重”理念的郑氏理筋手法对老年桡骨远端骨折患者疗效的影响

目的:观察基于“筋骨并重”理念的郑氏理筋手法对老年桡骨远端骨折患者腕关节功能、腕关节活动度、握力及指夹力的影响。方法:选取2020年6月~2023年6月在我院治疗的桡骨远端骨折患者80例。采用随机数字表法分为观察组和对照组,每组40例。两组患者均接受骨折手法复位夹板外固定进行治疗。对照组给予常规功能锻炼,观察组在对照组基础上给予郑氏理筋手法治疗。比较两组治疗前后腕关节功能评分(PRWE)、臂肩和手残疾功能评分(DASH)、腕关节活动度、握力及指夹力。结果:两组患者治疗前腕关节功能评分(PRWE)、臂、肩和手残疾功能评分(DASH)、腕关节活动度、握力、指夹力比较,差异无统计学意义(P>0.05)。与治疗前比较,两组患者PRWE和DASH评分均明显降低,差异有统计学意义(P<0.05)。两组腕关节屈伸活动度、尺桡偏活动度、前臂旋前后活动度均明显改善,差异有统计学意义(P<0.05)。两组患者握力、指夹力明显增加,差异有统计学意义(P<0.05)。与对照组比较,观察组PRWE评分、DASH评分、腕关节屈伸活动度、尺桡偏活动度、前臂旋前后活动度、握力、指夹力改善更显著,差异有统计学意义(P<0.05)。结论:基于筋骨并重理念的郑氏理筋手法可改善老年桡骨远端骨折患者腕关节活动度,促进肌肉力量恢复,改善腕关节功能,提高患者生活质量,值得临床推广。

下采样体素网格技术在角联锁复合材料损伤失效预测中的应用研究

为解决角联锁复合材料在损伤失效预测时计算量大、计算效率低的问题,采用图像处理方法中常用的下采样体素网格技术,将原体素网格模型中的4~3个网格打包成一个代表性体元进行计算,从而大幅度降低计算量和计算时间。从复合材料的弹性性能、损伤状态和计算时间三个方面与全网格模型进行比较,数值试验结果表明,采用下采样体素网格技术的模型与全网格模型不仅在刚度预测中完全一致,且损伤状态也相仿,同时具有千万级网格模型的CPU时间降低约85%,适用于工程用角联锁结构的高精度、高速率计算。

弹力带在跨栏项目教学中的应用研究

跨栏项目是指运动员以较快速度越过一定数目栏架的运动项目。跨栏运动可以分为四个阶段:起步至第一栏、跨栏间跑、跨栏步、冲刺。影响跨栏成绩的因素主要有身体素质、技能素质,其中身体素质方面主要包括速度、力量和柔韧等,技能方面主要包括跨栏步技术、栏间跑技术和“跑跨”组合能力等。研究目的:验证在跨栏教学应用弹力带教具促进学生学习掌握相关体育知识、技术和技能,以及提高测试通过率的成效。研究方法:本文采用实验法,将弹力带技术应用于跨栏技术练习,对跨栏步技术动作进行分析,研究弹性抗阻对跨栏项目的影响,总结、提出通过弹性阻力训练学习和巩固跨栏技术动作的教学建议。结果表明,在跨栏比赛中,使用弹性阻力可以有效地改善和优化跨栏技术,提高运动水平。建议:在将弹性阻力运用于专业力量的发展时,可以将传统的肌肉群高效的刺激与有针对性的弹性阻力训练相结合,以此促进提高跨栏训练的专业化水平。

乳化沥青冷再生基层施工技术研究

为提高公路维修过程中产生的铣刨废旧沥青混合料利用率,结合实际工程对乳化沥青冷再生技术展开研究。采用5种乳化沥青用量(3.2%、3.7%、4.2%、4.7%和5.2%)和3种水泥剂量(1.0%、1.5%和2.0%)的混合料进行力学性能试验。试验结果得到,采用水泥剂量为1.5%,乳化沥青用量为4.2%,拌和用水量为5.1%时,混合料性能最佳,此时混合料残留稳定度大于75%,动稳定度在5000~6000次/mm,7 d、28 d无侧限抗压强度达到3~5 MPa,路用性能指标均满足技术要求。

低温条件下水泥稳定碎石基层施工技术研究

为改善寒冷地区半刚性基层的使用性能,保证工程质量,论文以实际项目为依托,分析水泥稳定碎石的原材料选择与级配设计,并通过击实试验和无侧限抗压强度试验确定水泥和早强剂的剂量,总结各环节的施工要点。