Effect of burial depth of a new tunnel on the seismic response of an existing tunnel

Burial depth is a crucial factor affecting the forces and deformation of tunnels during earthquakes.One key issue is a lack of understanding of the effect of a change in the buried depth of a single-side tunnel on the seismic response of a double-tunnel system.In this study,shaking table tests were designed and performed based on a tunnel under construction in Dalian,China.Numerical models were established using the equivalent linear method combined with ABAQUS finite element software to analyze the seismic response of the interacting system.The results showed that the amplification coefficient of the soil acceleration did not change evidently with the burial depth of the new tunnel but decreased as the seismic amplitude increased.In addition,the existing tunnel acceleration,earth pressure,and internal force were hardly affected by the change in the burial depth;for the new tunnel,the acceleration and internal force decreased as the burial depth increased,while the earth pressure increased.This shows that the earth pressure distribution in a double-tunnel system is relatively complex and mainly concentrated on the arch spandrel and arch springing of the relative area.Overall,when the horizontal clearance between the center of the two tunnels was more than twice the sum of the radius of the outer edges of the two tunnels,the change in the burial depth of the new tunnel had little effect on the existing one,and the tunnel structure was deemed safe.These results provide a preliminary understanding and reference for the seismic performance of a double-tunnel system.

Ground stability of underground gateroad with 1 km burial depth： A case study from Xingdong coal mine, China

This paper presents an integrated investigation of the ground stability of a deep gateroad with a 1 km burial depth based on a field test, case studies, and numerical modelling. In situ stress measurements and mechanical properties tests were first conducted in the test site. Then, the deformation behavior, stress and yield zone distributions, as well as the bolts load of the gateroad, were simulated using FLAC3D software. The model results demonstrated that the soft rock properties and high in situ stress were the main factors for the deep gateroad instability, and the shear slip failure induced by the high stress was the primary failure model for the deep rock mass. In addition, the unsuitable support patterns, especially the relatively short bolts/cables with low pre-tensions, the lack of high-strengthen secondary supports and the unsupported floor strata, also contributed to the gateroad instability. Subsequently, a new combined supporting strategy, incorporating longer bolts/cables, yielding ring supports, and grouting measures, was proposed for the deep gateroad, and its validity was verified via field monitoring. All these could be a reference for understanding the failure mechanism of the gateroad with 1 km burial depth.

Effect of tillage and burial depth and density of seed on viability and seedling emergence of weedy rice

Weedy rice(Oryza sativa f. spontanea) is one of the three worst paddy weeds in most rice growing areas. The unexpected heavy infestation is derived from a persistence of soil seed bank of weedy rice, which the shattered seeds chiefly feed back to. Information on soil seed bank dynamics is imperative to predict the infestation of weeds. In the present paper,the effect of rotary tillage on weedy rice seed bank structure was studied first, and a burial experiment of marked seeds was conducted to observe the overwintering survival, seed viability and seedling emergence of weedy rice. The results showed that the proportion of weedy rice seeds in deeper soil increased but seedling emergence decreased with increasing plowing depth. The viability of weedy rice seeds decreased as the burial duration time extended but more slowly in deeper soil layers. Additionally, there was no significant effect of burial density on seed viability. Moreover, the logistic model fitted well(R^2≥0.95, P≤0.01) with the depressive trends of seed viability with increasing burial time under all burial depths and densities which can provide us further information about seed survival. In field experiments, number of seedling emergence significantly decreased as seed burial depth increased, conversely, proportion of seedling emergence increased as seed burial density decreased. This study has important implications for determining strategies for weedy rice management by exhausting its seed bank through the alteration of tillage practices.

Analysis of evaporation of high-salinity phreatic water at a burial depth of 0 m in an arid area

High-salinity phreatic water refers to which with total dissolved solids（TDS）>30 g/L. Previous studies have shown that high salinity phreatic water evaporation is different at different depths. High salinity phreatic water evaporation under 0 m depth is the basis of the high salinity phreatic water evaporation studies. In this study, evaporation of high-salinity phreatic water at a burial depth of 0 m in arid area was investigated. New insights were gained on evaporation mechanisms via experiments conducted on high-salinity phreatic water with TDS of 100 g/L at 0 m at the study site at Changji Groundwater Balance Experiment Site, Xinjiang Uygur Autonomous Region in China, where the lithology of the vadose（unsaturated zone） was silty clay. Comparison was made on the data of high-salinity phreatic water evaporation, water surface evaporation(EΦ20) and meteorological data obtained in two complete hydrological years from April 1, 2012 to March 31, 2014. The experiments demonstrated that when the lithology of the vadose zone is silty clay, the burial depth is 0 m and the TDS is 100 g/L, intra-annual variation of phreatic water evaporation is the opposite to the variation of atmospheric evaporation EΦ20 and air temperature. The salt crust formed by the evaporation of high-salinity phreatic water has a strong inhibitory effect on phreatic water evaporation. Large volumes of precipitation can reduce such an inhibitory effect. During freezing periods, surface snow cover can promote the evaporation of high-salinity phreatic water at 0 m; the thicker the snow cover, the more apparent this effect is.

Wintering Swan Geese maximize energy intake through substrate foraging depth when feeding on buried Vallisneria natans tubers

Background: Foraging theory predicts that animals select patches that offer the highest net rate of energy gain. Hence, prey distribution patterns and spatiotemporal heterogeneity play important roles in determining animal feeding patch selection. For waterfowl foraging on buried aquatic plant tubers, the distribution and biomass of these plant organs vary with depth in the substrate. Since excavation costs also increase with depth, the energy intake of the animals foraging on these plants is highly sediment depth dependent. Methods: Here, using observations of Swan Geese (Anser cygnoides) foraging on Vallisneria natans tubers, we test our hypothesis that geese feeding on tubers buried at intermediate sediment depth maximize their daily energy intake because of the interaction between tuber size and abundance with depth. To do this, we measured the distribution patterns of buried Vallisneria tubers under both undisturbed conditions and post-exploitation by geese (i.e. giving-up conditions). We investigated the relationship between tuber size and burial depth, and total tuber biomass within each sediment layer in undisturbed and exploited plots. Finally, we compared modelled Swan Goose daily energy intake feeding on Vallisneria tubers buried at different sediment layers (1–10, 11–20 and 21–30 cm below the surface). Results: Dry weight of Vallisneria tubers linearly increased with burial depth, while average total dry weight density of tubers showed a unimodal relationship, peaking at intermediate levels. Not surprisingly, Swan Geese foraged most intensively on tubers buried at intermediate sediment depths, where they maximize their daily energy intake. Our results support our hypothesis that Swan Geese feeding on tubers at intermediate depths maximize their daily energy intake. Conclusions: Our study is the first to quantify foraging strategies of Swan Geese during the wintering period, emphasizing the importance of plant traits on foraging selection of belowground foragers.

Characteristic strength and acoustic emission properties of weakly cemented sandstone at different depths under uniaxial compression

As coal mining is extended from shallow to deep areas along the western coalfield,it is of great significance to study weakly cemented sandstone at different depths for underground mining engineering.Sandstones from depths of 101.5,203.2,317.3,406.9,509.9 and 589.8 m at the Buertai Coal Mine were collected.The characteristic strength,acoustic emission(AE),and energy evolution of sandstone during uniaxial compression tests were analyzed.The results show that the intermediate frequency(125-275 kHz)of shallow rock mainly occurs in the postpeak stage,while deep rock occurs in the prepeak stage.The initiation strength and damage strength of the sandstone at different depths range from 0.23 to 0.50 and 0.63 to 0.84 of peak strength(σ_(c)),respectively,decrease exponentially and are a power function with depth.The precursor strength ranges from 0.88σ_(c)to 0.99σ_(c),increases with depth before reaching a depth of 300 m,and tends to stabilize after 300 m.The ratio of the initiation strength to the damage strength(k)ranges from 0.25 to 0.62 and decreases exponentially with depth.The failure modes of sandstone at different depths are tension-dominated mixed tensile-shear failure.Shear failure mainly occurs at the unstable crack propagation stage.The count of the shear failure bands before the peak strength increases gradually,and increases first and then decreases after the peak strength with burial depth.The cumulative input energy,released elastic energy and dissipated energy increase with depth.The elastic release rate ranges from 0.46×10^(-3)to 198.57×10^(-3)J/(cm^(3)s)and increases exponentially with depth.

砂土中螺旋桩在斜拉荷载作用下的承载性能

为研究斜拉荷载倾斜角度和叶片埋深对螺旋桩极限承载力的影响,基于ABAQUS软件构建了砂土中螺旋桩的有限元模型,通过螺旋桩水平承载机理砂箱试验与竖向拉拔试验数据,对模型的准确性和可行性进行验证。设置4组不同叶片埋深的螺旋桩模型,分别施加不同角度的斜拉荷载,探讨了砂土地基中螺旋桩的承载性能与斜拉角度、叶片埋深的相关性。结果表明:砂土中螺旋桩的极限承载力随着斜拉角度的增大不断减小;当斜拉角度小于30°时,螺旋桩极限承载力与斜拉角度的关系曲线近似呈线性;螺旋桩极限承载力存在一个临界埋深比,当埋深比大于等于4时,承载力不随埋深比的增大而变化。推导了深埋状态下螺旋桩受斜拉荷载作用的极限承载力公式,经验证该公式能较好反映螺旋桩极限承载力随斜拉角度增大而逐渐下降的规律。

埋深和水土含量对松散岩堆抗剪强度的影响

针对松散岩堆剪切力弱会引起滑坡、崩塌等严重自然灾害的问题,运用相似理论,以石英砂为基本岩块、黏性土为填充土,配置相似材料,分别控制不同填充土含量和含水率并进行三轴试验,研究不同埋深下填充土的含量和含水率对松散岩堆抗剪强度的影响。结果表明:填充土的含量和含水率是松散岩堆咬合力和内摩擦角的关键影响因素,咬合力受影响程度更大;填土中的水对于松散岩堆的剪切力起着削弱作用;岩堆剪切力随着埋深的增加而增加,不同埋深处岩堆有相同的最佳填充土含量和含水率;在恒定岩堆土重度情况下,抗剪强度和埋深呈线性关系。

上软下硬复合地层盾构隧道开挖面稳定性分析

针对上软下硬复合地层条件下盾构隧道开挖面的稳定性问题,依托深惠城际2标实际工况,分析不同软硬比及土体参数对开挖面极限支护压力的影响。利用颗粒流数值模拟分析土体的失稳模式,借助极限分析法建立符合开挖面失稳轮廓的理论计算模型,将理论计算结果与既往文献及实际工程进行比较分析。结果表明:当隧道开挖面主动失稳时,变形主要集中在软土层,硬岩层的变形较少;随着开挖面软硬比的增大,隧道开挖面的极限支护压力也增大;开挖面的极限支护压力与隧道埋深比无关,与土体内摩擦角成反比。

大柳塔52606工作面沿空留巷围岩走向非均匀破坏机制研究

大柳塔煤矿沿空留巷工作面混凝土墙及煤柱受力变形与煤层埋深呈现明显相关性,为获取埋深影响留巷侧围岩非均匀破坏的机制,以52606工作面开采为背景,采用相似材料模拟实验和理论分析的方法对岩层垮落结构及应力分布规律进行研究。结果表明,埋深增加,对应的周期来压步由10 m逐渐增加至约20 m。支承压力应力升高区范围增加,应力集中系数增加,应力峰值位置距离工作面距离减少。工作面顶板裂隙密度增加,不利于在埋深大区域形成支撑结构,不利于留巷稳定。埋深较大的终采线侧垮落角为34°,埋深较小的开切眼侧垮落角为43°。垮落角减小悬臂结构长度增加,破碎围岩支撑力减弱导致埋深大区域巷道发生大变形。

甘蔗收获机切割器入土切割深度监控系统设计与试验

入土切割是降低甘蔗收获机破头率的重要方法。为了实现甘蔗收获机切割器随地面起伏自动调控入土深度,保持切割器入土深度的一致性,基于4GQ-1型甘蔗收获机,设计一种甘蔗收获机切割器入土切割深度监测与自动控制系统,实现切割器入土深度自动调控及其参数可视化,并通过室内试验和田间试验检验系统的监控性能。室内试验结果表明,监控系统的入土深度监测精度平均值为98.90%,自动控制精度平均值为97.7%,监测精度和自动控制精度达到95.0%以上。田间试验结果表明,在20、30和50mm入土深度的条件下,监控系统的自动控制精度的平均值分别是85.3%、90.6%、94.1%,自动控制精度达到85.0%以上,监控系统总体设计合理,性能良好。研究结果可为甘蔗收获机切割器入土切割深度控制系统研究提供理论参考,对甘蔗收获机优化升级具有重要的参考意义。

陕北地区中深层同轴地埋管取热性能影响因素分析及优化

中深层同轴地埋管地热供热技术在我国北方城镇供热领域兴起并广泛应用。陕北地区地热资源丰富,但地温梯度略低且岩土热物性参数特性不同,地质参数影响中深层同轴地埋管的取热性能。采用OpenGeoSys开源数值模拟平台建立三维中深层同轴地埋管耦合地层传热计算模型,并基于陕北地区典型地质参数,研究不同设计参数对中深层同轴地埋管取热性能的影响及全生命周期技术经济性,优选出地热工程最佳工艺参数。结果表明,中深层同轴地埋管的外管径与埋深增大均能提升取热能力。相较于外管径,埋深对取热能力的提升效果更为显著,埋深从2 500 m增加到3 500 m,取热量增加了77.3%。依据工程实践,当外管外径×厚度大于177.80 mm×9.19 mm时所对应的平均能源成本因其钻井成本陡增而增大。在给定工况参数下,推荐中深层同轴地埋管的最佳外管外径×厚度为177.80 mm×9.19 mm,埋深为3 200 m,此时平均能源成本为0.524元/(kW·h),经济效益最优。

华北平原禹城地区地下水埋深对地下水及土壤水分和盐分分布的试验研究

【目的】研究不同浅层地下水埋深下的土壤水盐分布规律及其对作物产量的影响。【方法】在体积蒸渗仪样地中设置4个地下水埋深处理,分别为G0(无地下水埋深)、G1(地下水埋深40 cm)、G2(地下水埋深70 cm)、G3(地下水埋深110 cm)和G4(地下水埋深150 cm),监测夏玉米在自然蒸发条件下的浅层地下水盐分离子量变化和夏玉米收获后土壤水分和盐分的垂直变化。【结果】(1)地下水埋深越深,表层(0~20 cm)土壤含水率与含盐量越低。与G0处理相比,G1处理和G2处理表层土壤含水率分别显著增加27.54%和26.97%,G3处理增加8.25%,而G4处理仅增加2.18%;G1、G2、G3处理表层土壤含盐量分别增加0.79、0.47、0.43 g/kg,而G4处理则减少了0.01g/kg。G1、G2、G3处理下的盐分主要积累在表层土壤,G4处理主要积累在40~70 cm土层;(2)地下水埋深与表层(0~20 cm)土壤含水率与含盐量呈线性关系,地下水埋深每增加0.1 m,表层土壤含水率降低0.53%,含盐量降低0.065 g/kg。(3)浅层地下水中的主要阳离子为Na^(+)、Mg^(2+),主要阴离子为SO_(4)^(2-)和HCO_(3)^(-),集中降水使浅层地下水中离子由Na-Cl·SO_(4)向Na-HCO_(3)转化;(4)在强烈的地表蒸发下,地下水埋深越浅,地下水中离子浓度上升越快。其中HCO_(3)^(-)浓度在各处理中波动较大,总体呈上升趋势;而NO_(3)^(-)由于施肥的影响,地下水埋深越浅,NO_(3)^(-)在浅层地下水中达到峰值的速度越快,且浓度越高。【结论】增加浅层地下水埋深可有效降低表层土壤水盐量,减小浅层地下水受蒸发、降水的影响。浅层地下水埋深为1.2 m最适宜夏玉米生长,产量最优。研究不同浅层地下水埋深对农田土壤水分和盐分的影响有助于掌握农业生态系统中水盐迁移以及地下水与土壤的相互作用机制,对于防止土壤盐渍化、保障作物产量具有重要意义。

榆林地区岩土体剪切波速与埋深的相关性分析

岩土剪切波速是地质工程、地震工程和工程勘察领域需要涉及到的重要参数之一。以榆林地区218个钻孔数据为研究对象,定量研究了榆林地区Ⅱ类场地常见的6种土类的剪切波速和埋深的关系,通过最小二乘法优化参数,并以拟合优度、根均方误差与中值误差作为评价指标,给出推荐的函数模型和适用范围,并以两个工程场地实测钻孔为例对比了两个常用模型,验证了本文模型的可靠性。结果显示:研究区各类土的剪切波速和埋深都呈较为明显的正相关,不同岩性的埋深和剪切波速的相关性规律应该具体问题具体分析;经过对模型参数优化并对比三种模型评估指标,可知用三次多项式表达更为合适。该研究成果有助于更好的理解岩土体剪切波速和埋深之间的关系,为榆林地区工程项目建设提供参考。

沁水盆地郑庄区块残存煤层气的埋深和构造综合控气模式分析

煤层含气量是影响煤层气勘探开发的重要条件.实际生产中,煤储层地质条件十分复杂,含气量往往受多个因素综合控制.以沁水盆地郑庄区块3^(#)煤层为研究对象,分析其含气量分布特征及控气地质因素,得到以下结论:郑庄区块煤层含气量较高,其分布特征受煤层埋深和构造条件综合作用;在构造条件不发育地区,煤层埋深通过改变储层温度和压力控制煤层气的产生和保存,随着埋深增加,煤层含气量先增加后降低,逐渐由强压力敏感性转变为强温度敏感性;在构造发育区域,煤层含气量受埋深和构造条件综合作用,构造条件通过改变煤层埋深和储层封闭能力引起煤层气的运移逸散,褶皱和断层作用改变煤层埋深,为煤层气运移提供驱动力,伴生的节理是煤层气的运移通道,其走向和密度控制煤层气的运移方向和程度,运移目标区的埋深等储层特征影响煤层气的最终保存.

基于力学仿真分析的PCCP断丝预警及报警阈值评估方法

分析了钢丝的预应力作用机理和管道的破坏过程,提出了一种基于力学仿真分析的PCCP断丝预警与报警阈值评估方法。通过ABAQUS程序建立了PCCP有限元模型,模拟了包括铺设垫层、安装管道、分步回填在内的完整施工过程,计算了不同埋深、不同设计工作压力近百种工况下管道预应力钢丝、钢筒和管芯混凝土的应力状态,提出将管芯混凝土在水锤作用下起裂的最大允许断丝数作为爆管预警阈值,将管道埋地承载力极限状态的最大允许断丝数作为爆管报警阈值,并分析了不同工作内压和埋深条件下PCCP断丝预警与报警阈值之间的关系。

淮北平原冻融期和非冻融期及年时段裸地潜水蒸发模拟研究

为进一步揭示淮北平原砂姜黑土和黄潮土裸地冻融期、非冻融期日潜水蒸发变化规律及其与年时段计算结果的差异性,根据五道沟实验站2006~2022年62套原状土(0~5m)蒸渗仪观测资料,采用非线性最小二乘法,分别提出了两种土质3个时段日潜水蒸发量计算修正公式,并得到潜水蒸发极限埋深阈值hm和参数n的取值。结果表明:①两种土质经过修正后的阿维里扬诺夫计算公式计算日潜水蒸发量,较直接用水面蒸发(E601)计算精度提高0.9%~10.2%,其中砂姜黑土计算精度提高0.9%~10.2%。黄潮土计算精度提高3.6%~5.0%;②将潜水蒸发量的计算分成冻融期和非冻融期两个时段来考虑,比直接采用单一年时段潜水蒸发量计算公式,模拟精度有所提高,且两种土质计算精度表现出差异性,砂姜黑土冻融期提升6.6%,非冻融期提升2.8%;黄潮土冻融期提升1.3%,非冻融期提升2.6%;③砂姜黑土和黄潮土冻融期阈值hm分别为0.96、1.18,参数n分别为2.082、2.830;非冻融期阈值hm分别为1.39、1.69,参数n分别为2.236、0.719。采用年时段计算的阈值hm分别为1.23、1.66,参数n分别为2.758、0.740,实际应用时分别取冻融期及非冻融期的值较为合理。

地下水超采区埋深控制指标确定方法的探讨

多年来,地下水的不合理开发利用,引发了区域性地下水超限开采,形成了地下水超采区。地下水超采区是指地下水实际开采量超过可开采量,破坏了地下水的采、补平衡,导致地下水水位持续下降、生态损害和地质灾害频发。为了实现水资源可持续利用,保护和改善区域地下水生态环境,可通过对地下水超采区的地下水取用水总量和地下水埋深两方面进行控制,实现地下水超采区科学治理的目的。本文以四平市区地下水超采区为例,利用年度超采量比例法,分析计算地下水埋深年变幅,确定地下水超采区不同条件下的地下水埋深控制指标,为相关决策提供数据支撑和技术参考。

基于量纲分析的浅埋炸药爆炸地表振动速度试验研究

为研究浅埋炸药爆炸地表质点振动速度的衰减规律,在某试验场开展了多次不同当量和不同埋深的浅地下化学爆炸试验。通过测振系统获得了不同测点处的地面振动速度数据,分析了当量、炸药埋深以及测点距离对浅地下化学爆炸地表质点振动速度衰减的影响。结合量纲分析的方法建立了在介质为冲积土的条件下,预测精度较高的地表质点振动峰值速度计算模型。浅埋爆炸时地表质点振动峰值速度v_(P)与当量Q、装药埋深H和测点距离R有关,并获得了相关的经验公式。所得到的计算模型可为浅埋武器爆炸时的威力和毁伤效果评估提供一定的参考。

某过断层深埋高水头TBM输水隧洞围岩-支护结构响应规律

为了研究过断层深埋高水头敞开式TBM输水隧洞支护结构的响应规律,对不同支护方案下某过断层深埋高水头敞开式TBM隧洞围岩与支护结构的响应规律进行对比分析,选出最合适的支护设计方案。建立TBM隧洞动态开挖-支护精细仿真模型,逐个研究动态开挖-支护中围岩、锚杆、钢拱架、初喷混凝土、二衬的响应规律。结果表明:依次支护管棚、锚杆、钢拱架、固结灌浆、衬砌后,围岩拱顶变形分别降为不支护时的59.4%、32.9%、32.9%、4.1%、3.2%。盾尾离开后各响应突增,增幅逐步减缓且最终趋于稳定,衬砌支护后突降并稳定。锚杆应力分布不均,支护后拱腰处锚杆应力比拱顶增加快,各锚杆应力越靠近洞壁处越大。管棚+锚杆+钢拱架+固结灌浆+初喷+二衬可保证安全,但需固结围岩弹性模量、黏聚力及内摩擦角分别提高1.0、1.0、0.21倍。