基于SARIMA-ARCH的电量预测模型

电量预测是供电单位购电的重要依据,是电力经济稳定运行的根本基础。提出采用SARIMA-ARCH融合模型对某地区售电量进行预测。首先,采用季节时间序列分析方法(SARIMA)对月度电量时间序列进行建模,通过ACF和PACF图筛选确定出最佳模型阶数,得到季节性时间序列模型(SARIMA)基础预测模型;提取模型残差的波动性,建立自回归条件异方差(ARCH)模型;最后,将SARIMA-ARCH模型与常规SRIAM和ARIMA的预测值进行对比分析。结果表明,SARIMAARCH混合模型的预测精度较高。

Arch structure effect of the coal gangue flow of the fully mechanized caving in special thick coal seam and its impact on the loss of top coal

Based on the characteristics of the top coal thickness of the fully mechanized caving in special thick coal seam,the long distance of coal gangue caving,as well as the different sizes of the coal gangue broken fragment dimension and spatial variation of drop flow,this paper uses laboratory dispersion simulation experiment and theoretical analysis to study the arch structure effect and its influence rule on the top coal loss in the process of coal gangue flow.Research shows that in the process of coal gangue flow,arch structure can be formed in three types:the lower arch structure,middle arch structure,and upper arch structure.Moreover,the arch structure has the characteristics of dynamic random arch,the formation probability of dynamic random arch with different layers is not the same,dynamic random arch caused the reduction of the top coal fluency;analyzing the dynamic random arch formation mechanism,influencing factors,and the conditions of instability;the formation probability of the lower arch structure is the highest,the whole coal arch and the coal gangue arch structure has the greatest impact on top coal loss.Therefore,to prevent or reduce the formation of lower whole coal arch structure,the lower coal gangue arch structure and the middle whole coal arch structure is the key to reduce the top coal loss.The research conclusion provides theoretical basis for the further improvement of the top coal recovery rate of the fully mechanized caving in extra thick coal seam.

Improved method for determining active earth pressure considering arching effect and actual slip surface

To determine the distribution of active earth pressure on retaining walls, a series of model tests with the horizontally translating rigid walls are designed. Particle image velocimetry is used to study the movement and shear strain during the active failure of soil with height H and friction angle φ. The test results show that there are 3 stages of soil deformation under retaining wall translation: the initial stage, the expansion stage and the stability stage. The stable sliding surface in the model tests can be considered to be composed of two parts. Within the height range of 0.82 H-1.0 H, it is a plane at an angle of π/4+φ/2 to the horizontal plane. In the height range of 0-0.82 H, it is a curve between a logarithmic spiral and a plane at an angle of π/4+φ/2 to the horizontal. A new method applicable to any sliding surface is proposed for active earth pressure with the consideration of arching effect. The active earth pressure is computed with the actual shape of the slip surface and compared with model test data and with predictions obtained by existing methods. The comparison shows that predictions from the newly proposed method are more consistent with the measured data than the predictions from the other methods.

Pile-soil stress ratio in bidirectionally reinforced composite ground by considering soil arching effect

To discuss the soil arching effect on the load transferring model and sharing ratios by the piles and inter-pile subsoil in the bidirectionally reinforced composite ground, the forming mechanism, mechanical behavior and its effect factors were discussed in detail. Then, the unified strength theory was introduced to set up the elastoplastic equilibrium differential equation of the subsoil under the limit equilibrium state. And from the equation, the solutions were derived with the corresponding formulas presented to calculate the earth pressure over and beneath the horizontal reinforced cushion or pillow, the stress of inter-pile subsoil and the pile-soil stress ratio. Based on the obtained solutions and measured data from an engineering project, the influence rules by the soil property parameters (i.e., the cohesion c and internal friction angle φ) and pile spacing on the pile-soil stress ratio n were discussed respectively. The results show that to improve the load sharing ratio by the piles, the more effective means for filling materials with a larger value of φ is to increase the ratio of pile cap size to spacing, while to reduce the pile spacing properly and increase the value of cohesion c is advisable for those filling materials with a smaller value of φ.

Traveling wave effect on the seismic response of a steel arch bridge subjected to near fault ground motions

In the 1990s, several major earthquakes occurred throughout the world, with a common observation that near fault ground motion （NFGM） characteristics had a distinct impact on causing damage to civil engineering structures that could not be predicted by using far field ground motions. Since then, seismic responses of structures under NFGMs have been extensively examined, with most of the studies focusing on structures with relatively short fundamental periods, where the traveling wave effect does not need to be considered. However, for long span bridges, especially arch bridges, the traveling wave （only time delay considered） effect may be very distinct and is therefore important. In this paper, the results from a case study on the seismic response of a steel arch bridge under selected NFGMs is presented by considering the traveling wave effect with variable apparent velocities. The effects of fling step and long period pulses of NFGMs on the seismic responses of the arch bridge are also discussed.

Evaluation of soil arching effect due to partially mobilized shear stress in piled and geosynthetic-reinforced embankment

In piled and geosynthetic-reinforced(PGR) embankment, the arching behavior determines the overburden load on piles and subsoils. Placement of geosynthetic is effective in reducing the relative displacement between pile and subsoil. When the mobilized shear stress is less than the shear strength, partially developed arching will occur. Consequently, existing analytical methods, adopting the ultimate shear strength failure criterion, need to be improved. This study developed a simplified 2 D analytical method, which is based on the developing arching effect, to evaluate the load redistribution of the PGR embankment. Then, the influences of embankment height and internal friction angle, subsoil depth, ratio of pile cap width to pile clear spacing(RPC) and geosynthetic tensile stiffness on the critical height ratio, stress concentration ratio, soil arching ratio, geosynthetic tension and axial strain were investigated. This study suggests that a RPC of 1:1.0 and a one-way of single-layer geosynthetic tensile stiffness of 2000 kN/m should be considered as the sensitivity thresholds for the PGR embankment.

Analysis of Soil arching effect for Blind sheet-pile wharf based on ABAQUS

Combined with practical engineering, based on the introduction of soil arching theory, we explore the impact of barrier piles in blind sheet-pile bank connecting structure. Besides, we build a plane strain model by ABAQUS sot＇cware to study the impact of cross section type, the pile spacing and soil properties on soil arching effect. We find that cross section type of the pile has a certain influence on soil stress distribution in front of the barrier piles by comparing circular cross section and rectangular cross section. We also find that clear distance between the barrier piles and cohesive force of the soil have a great influence on that impact. We can increase clear distance between the barrier piles appropriately to improve the efficiency of construction and reduce the proiect cost.

沥青混凝土心墙堆石坝心墙拱效应研究

心墙拱效应是影响土石坝安全稳定运行的重要因素,心墙力学特性复杂且受众多因素的影响,复杂地形地质条件对心墙拱效应具有重要影响。首先对比了直心墙、斜心墙、下直上斜式心墙拱效应的差异,在此基础上选取岸坡坡度、河谷宽度、覆盖层厚度以表征坝体所处的地形地质条件。基于数值计算定量研究复杂地质条件对沥青混凝土心墙拱效应的影响规律。结果表明:心墙应力拱效应主要集中在心墙中部3/4坝高附近及靠近岸坡处;斜心墙应力拱效应相对较小,可以很好地改善心墙的整体受力状况;岸坡变陡,斜心墙整体的拱效应强度增加,应力传递的核心区域由心墙中部拓宽至心墙两岸坡;随着河谷宽度的增加,应力传递的重心逐渐由底部转移到心墙两岸及心墙中上部;斜心墙整体的应力拱效应并非随着河谷宽度的增加单调变化,当坝轴线长度与坝高比值增加到3~4时,河谷产生的河谷效应对斜心墙变形及拱效应的影响大幅下降;随着覆盖层厚度的增加,斜心墙底部的拱效应明显增强,底部的拱效应系数分布逐渐集中化、区域化,容易产生局部破坏。

波纹钢形状与拱效应对加固盖板涵承载力的影响

为了探索波纹钢形状对加固盖板涵承载力的影响及填充混凝土的拱效应形成机制,采用室内试验与数值分析相结合的研究方法,以一个室内模型试验结果为基准,建立了72个箱形、圆弧及其之间的过渡形状的波纹钢加固盖板涵的数值模型,探明了加固体系承载力随波纹钢形状参数的变化规律;基于合理拱轴的概念,探明了填充混凝土的拱效应形成机理,并采用5个数值模型进行了验证。结果表明:拱腋半径保持不变时,加固体系的承载力随着拱顶、侧墙半径的增加而减小;拱顶、侧墙半径不变时,加固体系的承载力随着拱腋半径的增加而增大;提升加固体系承载力最有效的方式是增加拱腋半径,其次是减小拱顶和侧墙半径;填充混凝土的拱效应与荷载类型有关,当波纹钢的形状能保持拱轴连续并且在素混凝土刚性角以内时,加固体系的承载力最高。在设计波纹钢加固盖板涵结构时,应根据实际工程需要综合考虑波纹钢形状与填充混凝土的拱效应,尽量避免紧贴原盖板涵的加固设计。

双层地下连续墙土压力的现场实测研究

南京某超深基坑工程采用异形围护结构双层地下连续墙进行施工,双墙间土体处于非极限平衡状态,土压力分布演变形式及墙土间相互作用机制并不明确。为探明深基坑开挖施工引起的双墙间有限土体的土压力变化规律及墙外侧土拱效应对土压力分布的影响,采用现场实测分析结合物理模型计算的方法开展研究。首先,通过现场试验在土层中布设土压力监测点,获取基坑开挖过程中墙间土压力演变规律;其后,建立考虑土体分层的曲面锥形土拱模型,计算侧土拱发展引起的墙外土压力变化量,并结合试验数据的参数反演和误差分析对模型计算结果的准确性展开讨论。研究结果表明:基坑开挖施工对双墙间土体的影响总体呈现为挤压变形,有限土体受到的侧向约束作用有助于进一步发挥土体的抗剪强度;基坑开挖各工序中土方开挖过程对地层扰动最为显著;侧土拱效应进一步增大了浅层土体挡土墙侧土压力,而中深层土体中几乎没有侧土拱发展;考虑侧土拱效应的土压力计算结果较传统水土分算的Coulomb理论计算方法与现场实测结果更加吻合。本研究可为异型围护结构的深基坑工程设计及施工提供思路与建议。

火灾下面内约束钢筋混凝土简支双向板力学响应机理

现有分析方法对火灾下面内约束简支双向板的开裂、变形响应以及面内约束导致抗火性能降低的机理缺乏合理解释,本文应用ABAQUS有限元软件对火灾下面内约束钢筋混凝土简支双向板的温度场和热力耦合场进行了三维实体有限元分析,在实验验证基础上进行参数分析,探究钢筋和混凝土的挠度、应力变化规律和力学响应机理.结果表明:在火灾下,面内约束力削弱了板的倒拱效应与拉力膜效应,导致抗火性能显著降低.单向和双向面内约束、长宽比、荷载比的增大均会缩短板的倒拱效应与拉力膜效应阶段的时间.

砂土边坡桩间水平土拱机理与演变规律离散元分析

抗滑桩等非连续支挡结构在边坡工程中依靠土拱效应安全经济地发挥支护功能。鉴于不同类型砂土的力学性质差异较大,为揭示密砂与松砂土质边坡抗滑桩桩间水平土拱机理与演变规律,采用离散元方法(DEM)模拟支挡砂土水平土拱的成拱过程。在传统力链分析的基础上,提出通过筛选高应力颗粒来研究土拱的形成过程,进一步从细观角度对不同工况土拱效应进行分析,以揭示“应力拱”和“位移拱”的演化过程。研究表明:密砂和松砂中的水平土拱的动态演变过程均表现为3个演化阶段,分别对应于密砂和松砂的剪切性状,即应变软化和应变硬化现象,揭示了砂土边坡桩间土拱效应的演变规律。此外,讨论了宏-微观DEM模拟参数对土拱形成过程与土拱效应性能的影响,结果表明拱跨对于荷载传递效率的影响最大。

桩承式加筋垫层路堤荷载分担改进计算模型

桩承式加筋垫层路堤中的关键荷载传递机制是多种现象的组合,包括路堤填土中的土拱效应、加筋垫层的张拉膜效应和地基土的支撑作用,然而,目前针对此方面的研究尚不完善。本文首先以考虑土体被动土压力发挥程度及桩间土应力非均匀分布改进的Hewlett土拱模型为改进载体;其次,假定加筋垫层为上、下部受均布荷载作用的简支梁,截面拉应力完全由加筋体承担,压应力完全由垫层材料承担,同时考虑地基土反力与梁最大挠度相关,引入地基反应系数,从而建立改进的桩承式加筋垫层路堤荷载分担计算模型;最后,通过工程实例与模型参数分析,验证本文计算模型的可靠性与准确性。研究结果表明:在路堤填筑过程中,土拱效应逐渐完全发挥,促进路堤荷载向桩体转移;随着地基土固结,桩体承担的路堤荷载也在逐渐增大;路堤填土高度、填土内摩擦角、桩间距对桩体荷载分担影响较大,加筋体抗拉模量对其影响较小。

考虑拱效应的复合地层盾构隧道开挖失稳分析

根据盾构隧道开挖面的特点,考虑不同地层、不同隧道埋深条件下土体成拱效应,基于Paik圆弧拱理论建立失稳土体三维极限平衡理论分析模型。将经典三维楔形体模型改进为垂直面水平面均考虑拱效应的失稳土体三维模型,模拟盾构隧道开挖时前方土体的影响范围和影响大小,将上覆土压力计算方法扩展为三维形式,并采用土体条分法给出失稳土体极限平衡公式。最后利用MATLAB编程将模型计算结果与离心试验及其他理论模型进行了对比验证。结果表明:本文力学模型结果与离心试验结论更接近,可更准确地应用于开挖面最小支护压力参数的确定。

早期矫治在青少年下颌后缩畸形中的效果观察及对美学效果的影响研究

目的探讨螺旋扩弓器联合Twin-block矫治器早期矫治在青少年下颌后缩畸形中的效果观察及对美学效果的影响研究。方法将河南大学赛思口腔医院2021年1月至2022年1月收治的65例青少年下颌后缩畸形患者,按照随机数字表法分为两组,对照组33例、观察组32例,对照组早期给予Twin-block矫治器治疗,观察组早期给予螺旋扩弓器联合Twin-block矫治器矫治治疗,比较两组颌面部形态指标、面部美容指标、牙齿咬合力及咀嚼能力。结果矫治后3个月,观察组蝶胺中心-鼻根点-上牙槽座点角(SNA)、蝶鞍中心-鼻根点-下牙槽座点角(SNB)、上牙槽座点-鼻根点-下牙槽座点角(ANB)、下面高(ANS-Me)、上面高(N-ANS)、全面高(N-Me)改善情况均优于对照组(P<0.05);矫治后3个月,观察组上唇角(ALs-FH)、面突角(G-Sn-Pg)、颌沟倾角(Pg B-FH)、颌唇沟角(Li-b-Pos)的改善情况均优于对照组(P<0.05);矫治后3个月,观察组牙齿咬合力、咀嚼能力均优于对照组(P<0.05)。结论螺旋扩弓器联合Twin-block矫治器早期矫治可以有效改善青少年下颌后缩畸形患者的面部形态,提高面部美学效果,改善牙齿咬合力和咀嚼功能。

基于离散元模拟的不同挡土墙位移模式下非极限主动土压力

针对刚性挡土墙主动位移过程中砂土非极限主动土压力问题,利用PFC 2D分别对挡土墙绕墙顶转动(RB)模式、绕墙顶转动(RT)模式和平动(T)模式下砂土主动破坏过程进行模拟分析。分析结果表明,不同位移模式下土体内摩擦角及墙土摩擦角调动规律存在差异。挡土墙主动位移过程中,RB模式下土体破坏从墙顶开始,向墙脚发展,土楔体内部只有靠近墙背侧区域出现主应力偏转现象,并且土楔体中内摩擦角调动值均能达到极限值。RT模式下,土体破坏沿着墙背和滑裂面从墙脚开始,向土体表面发展,墙后土楔体中上部区域主应力偏转角度较大,形成了大主应力拱,与此对应的是该区域内摩擦角调动值相对初始内摩擦角减小。T模式下,土体破坏分别沿着墙背从墙顶向墙脚发展以及沿着滑裂面从墙脚向土体表面发展,墙后土楔体内部会出现小主应力拱,且内摩擦角调动值从初始内摩擦角增加,但达不到极限值。

深覆土梯形拱明洞静力特性及卸荷效果

为研究深覆土条件下梯形拱结构–填土相互作用对周围土压力的影响机制和卸荷机理,明确梯形拱明洞相较于传统矩形明洞的优势,采用室内模型试验和数值模拟相结合的方法,对深覆土梯形拱明洞静力特性及卸荷效果进行分析。结果表明:无减载时,梯形拱明洞两侧回填土沉降大于上方回填土沉降,两侧回填土土压力向明洞上方转移,土压力随着填土高度的增大而增大,基本呈线性变化趋势;减载时,明洞上方回填土沉降大于两侧回填土沉降,回填土内部产生土拱效应,明洞上方回填土土压力向两侧转移,铺设减载层不会改变深覆土明洞结构受力分布,但会极大地减小其内力及变形,并提高结构安全系数;减载后,梯形拱明洞的最大轴力、最大正弯矩和最大负弯矩分别减少17.5%、34.1%、29.9%,最大变形减小32.9%。矩形和梯形两种截面形式下明洞的最大轴力均出现在中隔墙底部,最大正弯矩、最小安全系数和最大变形均出现在顶板中央位置;铺设减载层后两种截面形式拱明洞最小安全系数分别增大42.6%和100.0%,梯形拱明洞安全系数提高的比例更大,效果更显著。该研究可为深覆土梯形拱明洞结构的设计和施工提供理论指导和技术支持。

托顶煤巷道锚固“梁-拱”结构分类及顶板冲击失稳机制

我国煤矿托顶煤巷道冲击地压频发,且冲击动载下顶板灾害尤为严重。为探究托顶煤巷道顶板锚固结构类型和冲击失稳机制,以陕西某矿301工作面回风巷道大面积冲击垮顶为工程背景,运用相似实验、理论分析及数据统计等方法,分析了托顶煤巷道围岩应力、位移和巷表加速度的动载响应特征,研究了顶煤厚度与支护构件影响下顶板锚固结构的分类特征,探究了弹性波下托顶煤巷道的应力响应机制,提出顶板锚固“梁-拱”结构的冲击失稳机制,评估了301工作面回风巷道的抗冲能力,并提出了相应的抗冲支护优化方案。结果表明:①冲击动载下托顶煤围岩应力和位移等监测数据验证了顶板存在内、外层的梁或拱形锚固结构,因顶煤厚度增加,顶板内层锚固结构存在由“梁”向“拱”的转换;②基于顶煤厚度与支护构件相对关系,将顶板锚固结构划分为薄顶煤的“叠加梁-拱”、厚顶煤的“组合梁-拱”和特厚顶煤的“组合拱”,建立了厚煤梁由“梁”向“拱”转化的临界厚度指标;③顶板锚固梁结构和锚固拱结构的冲击失稳机制为动静载荷下分别达到其拉伸、剪切强度极限后破坏,锚固“梁-拱”结构对冲击载荷的放大效应受其尺寸影响明显;④特厚顶煤的“组合拱”结构中内层拱承载强度较低,可增加锚杆长度提升内层拱厚,对应的“组合拱”结构的承载能力上升明显,与抗冲能力评估结果相符。

考虑刀土摩擦的砂土盾构隧道开挖面支护压力计算方法

确定盾构隧道开挖面极限支护压力是隧道工程中的核心问题之一。现有研究一般忽略盾构刀盘与主动极限状态时开挖面前方失稳土体间的摩擦效应,导致计算结果偏保守。为了解决此问题,首先,基于梯形楔形体模型,考虑盾构开挖掌子面与前方被切削土体之间的竖向摩擦力、楔形体与上方土柱之间因相对错动引起的横向摩擦力以及隧道埋深对极限支护压力的影响,推导了砂土地层盾构开挖面的极限支护压力计算公式;其次,通过与其他理论方法及试验结果进行对比,验证了本文方法的合理性;最后,讨论了刀土摩擦力在不同工况下对盾构开挖面极限支护压力的影响规律。研究结果表明:在其他参数不变时,开挖面极限支护压力随着刀土外摩擦角增大而逐渐减小,与刀土外摩擦角近似呈线性关系;刀盘土体间摩擦力对维持盾构开挖面稳定具有有利影响,对开挖面极限支护压力的影响不可忽略;适当增大刀盘与前方土体间的外摩擦角可有效增加开挖面的极限稳定性;刀土摩擦力对浅埋情况的盾构隧道开挖面极限支护压力的影响要明显比深埋情况的影响大,在选择盾构掘进刀具时应重点考虑埋深的影响。

基于倾斜滑裂面假设的浅埋盾构隧道松动土压力研究

随着地铁建设的快速发展,隧道上方松动土压力的计算成了隧道工程领域的研究热点,而隧道松动区的确定对松动土压力的计算至关重要。为简便而准确地确定松动区的范围,首先假设松动区的边界为倾斜直线,然后基于Mohr-Coulomb破坏准则并考虑隧道尺寸、埋深等因素的影响推导滑裂角计算式,进而确定隧道周围地层的松动区范围。最后结合松动区土体主应力轴旋转理论以及倾斜滑裂面的假设,推导出滑裂面上的侧压力系数以及隧道松动土压力的计算式。结果表明:滑裂角随土体内摩擦角的增大而增大,随隧道埋深比的增大先减小然后趋于稳定;大主应力轨迹线为圆弧时计算更为简便、更易推广,可采用圆弧形大主应力轨迹的假设计算隧道松动土压力;松动土压力计算式所得结果和实际的试验结果吻合较好,因此该计算式可应用于砂土地质条件下浅埋盾构隧道上方的松动土压力计算。