Reliability Design for Longitudinal Slope Length of Expressway

The significance and the strategies of applying the reliability design method of longitudinal slope length in expressway engineering were explored in this study.The objective is to offer insights that can be beneficial for designing longitudinal slope lengths in contemporary expressway projects,with a focus on enhancing their reliability and safety.

Comparison of Slope Length Factor Extraction in Hillslope Soil Erosion Model with Different DEM Resolutions

In this study, non-cumulative slope length(NCSL) calculation method and spatial analytical calculation(SAC) method were respectively applied to extract slope length and slope length factor from 10 sample areas, which are located in Ansai County, north Shaanxi Province. The comparison of computation precision between variable DEM resolutions showed that NCSL was superior to SAC entirely. And the results were best when the DEM resolutions were 5 and 10 m. Besides, the results of slope length factor were nearly the same under the two conditions. So DEM of 10 m resolution can be used to extract slope length.

Uncertainty of Slope Length Derived from Digital Elevation Models of the Loess Plateau, China

Although many studies have investigated slope gradient uncertainty derived from Digital Elevation Models(DEMs), the research concerning slope length uncertainty is far from mature. This discrepancy affects the availability and accuracy of soil erosion as well as hydrological modeling. This study investigates the formation and distribution of existing errors and uncertainties in slope length derivation based on 5-m resolution DEMs of the Loess Plateau in the middle of China. The slope length accuracy in three different landform areas is examined to analyse algorithm effects. The experiments indicate that the accuracy of the flat test area is lower than that of the rougher areas. The value from the specific contributing area(SCA) method is greater than the cumulative slope length(CSL), and the differences between these two methods arise from the shape of the upslope area. The variation of mean slope length derived from various DEM resolutions and landforms. The slope length accuracy decreases with increasing grid size and terrain complexity at the six test sites. A regression model is built to express the relationship of mean slope length with DEM resolution less than 85 m and terrain complexity represented by gully density. The results support the understanding of the slope length accuracy, thereby aiding in the effective evaluation of the modeling effect of surface process.

Comparison of the Effects of the Different Methods for Computing the Slope Length Factor at a Watershed Scale

The slope length factor is one of the parameters of the Universal Soil Loss Equation(USLE)and the Revised Universal Soil Loss Equation(RUSLE)and is sometimes calculated based on a digital elevation model(DEM).The methods for calculating the slope length factor are important because the values obtained may depend on the methods used for calculation.The purpose of this study was to compare the difference in spatial distribution of the slope length factor between the different methods at a watershed scale.One method used the uniform slope length factor equation(USLFE)where the effects of slope irregularities(such as slope gradient,etc.)on soil erosion by water were not considered.The other method used segmented slope length factor equation(SSLFE)which considered the effects of slope irregularities on soil erosion by water.The Arc Macro Language(AML)Version 4 program for the revised universal soil loss equation(RUSLE).which uses the USLFE,was chosen to calculate the slope length factor.In a parallel analysis,the AML code of RUSLE Version 4 was modified according to the SSLFE to calculate the slope length factor.Two watersheds with different slope and gully densities were chosen.The results show that the slope length factor and soil loss using the USLFE method were lower than those using the SSLFE method,especially on downslopes watershed with more frequent steep slopes and higher gully densities.In addition,the slope length factor and soil loss calculated by the USLFE showed less spatial variation.

Rangeland hillslope lengths:A case study at the Walnut Gulch Experimental Watershed,southeastern Arizona

Rangeland hillslopes provide much of the sediment supplied to channel systems and their lengths exert a fundamental constraint on hillslope diffusive processes.However,information regarding lengths of rangeland hillslopes,and how best to estimate them,is limited.In this study,three groups of watersheds(10 in total)were selected from the Walnut Gulch Experimental Watershed according to their geology,soil and vegetation characteristics.Group 1 watersheds were at lower elevations dominated by shrubs,Group 3 were at high elevations dominated by grass,and Group 2 were mixed shrub and grass.Their hillslope lengths were calculated from 1 m-resolution DEMs using three methods:a flow routing algorithm,slope-area relationships,and inverted relationship with drainage density.Parameters that characterize the current watersheds,including Hack's exponent and coefficient,watershed shape coefficient,channel concavity and steepness,and surface roughness,were quantified and related to hillslope lengths.Results shows:(1)estimated hillslope lengths were different for the three methods and between the three groups of watersheds;(2)hillslope lengths that measured from the flow routing algorithm for the ten selected watersheds primarily ranged from 30 to 100 m,with a median value of 63.0 m,which was 20%e50%greater than those derived from slope-area plots or drainage densities;(3)hillslope lengths estimated from the flow routing method were greater in Group 3 watersheds than in Group 2 and then in Group 1 watersheds.We attributed these differences in hillslope lengths to the historic epeirogenic pulses,watershed and drainage network morphology,and differences in vegetation characteristics;(4)measured hillslope lengths from the flow routing algorithm were best correlated with hillslope relief,then surface roughness,channel steepness and concavity.These results would benefit the applications of hydrological and erosion models in rangelands.

Stability analysis of slope in strain-softening soils using local arc-length solution scheme

Soils with strain-softening behavior — manifesting as a reduction of strength with increasing plastic strain — are commonly found in the natural environment. For slopes in these soils,a progressive failure mechanism can occur due to a reduction of strength with increasing strain. Finite element method based numerical approaches have been widely performed for simulating such failure mechanism,owning to their ability for tracing the formation and development of the localized shear strain. However,the reliability of the currently used approaches are often affected by poor convergence or significant mesh-dependency,and their applicability is limited by the use of complicated soil models. This paper aims to overcome these limitations by developing a finite element approach using a local arc-length controlled iterative algorithm as the solution strategy. In the proposed finite element approach,the soils are simulated with an elastoplastic constitutive model in conjunction with the Mohr-Coulomb yield function. The strain-softening behavior is represented by a piece-wise linearrelationship between the Mohr-Coulomb strength parameters and the deviatoric plastic strain. To assess the reliability of the proposed finite element approach,comparisons of the numerical solutions obtained by different finite element methods and meshes with various qualities are presented. Moreover,a landslide triggered by excavation in a real expressway construction project is analyzed by the presented finite element approach to demonstrate its applicability for practical engineering problems.

Study on embedded length of piles for slope reinforced with one row of piles

The embedded length of anti-slide piles for slope is analyzed by three-dimensional elastoplastic shear strength reduction method. The effect of embedded pile length on the factor of safety and pile behavior is analyzed. Furthermore, the effects of pile spacing, pile head conditions, pile bending stiffness and soil properties on length and behavior of pile are also analyzed. The results show that the pile spacing and the pile head conditions have significant influences on the critical embedded length of pile. It is found that the critical embedded length of pile, beyond which the factor of safety does not increase, increases with the decrease in pile spacing. The smaller the pile spacing is, the larger the integrity of the reinforced slope will be. A theoretical analysis of the slip surface is also conducted, and the slip surface determined by the pressure on piles, considering the influences of both soil and piles for slope, is in agreement with the ones in previous studies.

Assessment of soil erosion in the Irga watershed on the eastern edge of the Chota Nagpur Plateau,India

Human activities to improve the quality of life have accelerated the natural rate of soil erosion.In turn,these natural disasters have taken a great impact on humans.Human activities,particularly the conversion of vegetated land into agricultural land and built-up area,stand out as primary contributors to soil erosion.The present study investigated the risk of soil erosion in the Irga watershed located on the eastern fringe of the Chota Nagpur Plateau in Jharkhand,India,which is dominated by sandy loam and sandy clay loam soil with low soil organic carbon(SOC)content.The study used the Revised Universal Soil Loss Equation(RUSLE)and Geographical Information System(GIS)technique to determine the rate of soil erosion.The five parameters(rainfall-runoff erosivity(R)factor,soil erodibility(K)factor,slope length and steepness(LS)factor,cover-management(C)factor,and support practice(P)factor)of the RUSLE were applied to present a more accurate distribution characteristic of soil erosion in the Irga watershed.The result shows that the R factor is positively correlated with rainfall and follows the same distribution pattern as the rainfall.The K factor values in the northern part of the study area are relatively low,while they are relatively high in the southern part.The mean value of the LS factor is 2.74,which is low due to the flat terrain of the Irga watershed.There is a negative linear correlation between Normalized Difference Vegetation Index(NDVI)and the C factor,and the high values of the C factor are observed in places with low NDVI.The mean value of the P factor is 0.210,with a range from 0.000 to 1.000.After calculating all parameters,we obtained the average soil erosion rate of 1.43 t/(hm^(2)•a),with the highest rate reaching as high as 32.71 t/(hm^(2)•a).Therefore,the study area faces a low risk of soil erosion.However,preventative measures are essential to avoid future damage to productive and constructive activities caused by soil erosion.This study also identifies the spatial distribution of soil erosion rate,which will help policy-makers to implement targeted soil erosion control measures.

椰丝纤维长度对土体抗剪强度和抗压强度的影响

【目的】探究在客土喷播基材中添加不同长度纤维材料对土体抗剪强度和抗压强度的影响。【方法】采用控制变量的试验方法,以不同长度(1、2、3、4、5 cm)的椰丝纤维和砂土为试验材料,按0.4%(w/w)的质量比混合后进行了室内三轴试验和无侧限抗压试验。【结果】(1)各长度纤维加筋土在各围压下的主应力差峰值强度和抗压强度峰值都大于无纤维加筋的素土;(2)随着纤维长度的增加,主应力差峰值强度、内聚力、内摩擦角和加筋效果系数都呈现出先增加后减少的趋势,且在长度为3~4 cm时,强度达到峰值;(3)随着纤维长度的增加,抗压强度峰值,主应力差强度峰值及破坏后的残余强度都得到明显提升,应力-应变曲线逐渐由应变软化型过渡为应变硬化型。【结论】掺量为0.4%、长度为3~4 cm的椰丝纤维可以有效提升土体的抗剪强度和抗压强度。

公路长大下坡试验路段安全坡长设计分析

以某公路长大下坡试验路段为例,在提出此类路段关键控制指标以及交通事故的发生原因后,构建小客车运行速度预测模型和货车制动毂温度预测模型,采用SPSS软件分析刹车轮毂温度的影响因素以及彼此间存在的影响机制,并预测长大下坡路段安全坡长的取值。经过本次研究,为该类特殊路段的设计工作提供参考,严格控制坡长及相关关键参数,提高长大下坡路段的设计水平,保障车辆行驶安全。

小净距隧道洞口抗震设防研究

为明确净距与岩体等级对隧道洞口段抗震设防长度的影响规律,以云南玉溪宝山高陡边坡段小净距隧道为工程依托,利用FLAC3D有限差分软件建立小净距隧道数值模型,根据室内力学试验确定模型参数,以校正后的汶川地震波作为震动荷载输入,针对震动荷载作用下隧道洞口段围岩稳定性进行分析,探明隧道围岩与支护结构在不同工况下的动力响应特征,进一步确定合理的隧道抗震设防长度。研究结果表明:同一净距条件下,围岩等级越高,衬砌结构位移及轴力、应力的响应值越小,反之亦然;宝山隧道最不利工况条件为Ⅴ级围岩、0.5B净距,在震动荷载作用条件下,隧道峰值位移最大值为62.5 cm,衬砌轴力最大值产生于左、右拱脚处,洞口段峰值达1320 kN,位移曲线下降率升高临界点最大值为78 m(6.0B),最终确定宝山隧道洞口合理设防长度为78 m。

互通立交入口匝道大型车加速车道长度研究

加速车道长度设计是否合理对车辆运行安全至关重要。为提高互通立交入口匝道加速车道长度设计的合理性及车辆运行的安全性,通过分析合流影响区车辆交通特性,基于修正的二阶爱尔朗车头时距分布模型,建立大型车在不同坡度(-2%≤i≤2%)、不同比功率(8~12 kW/t)下的加速车道长度计算模型,重点研究大型车在不同坡度、不同比功率下的加速车道长度。研究发现:坡度、比功率与加速车道长度均成正比。该研究可以为针对大型车的高速公路互通立交加速车道长度相关规范的修订提供参考。

露天煤矿非工作帮顺倾软岩边坡稳定性研究

为达到提高露天煤矿顺倾软岩边坡稳定性的目的,结合白音华二号露天煤矿非工作帮为典型顺倾软岩边坡的工程实际情况,采用岩土工程数值模拟软件FLAC^(3D),揭示边坡稳定性的形态效应与尺寸效应;建立了临界坡角与弱层暴露临界长度之间的关系曲线,最终设计了有利于稳定的白音华二号露天煤矿非工作帮边坡空间几何形态。研究结果表明:通过合理控制弱层的暴露长度以及开挖坡角等关键指标,可有效提高露天矿边坡的稳定性,最终确定的白音华二号露天煤矿非工作帮开挖坡角为45°,此时坑底弱层的临界暴露长度约为176 m,边坡即可满足安全要求。

Effects of rainfall intensity and topography on rill development and rill characteristics on loessial hillslopes in China

Rill development is a major soil erosion process that causes severe soil degradation.This study examined the effects of representative rainfall intensities(50 and 75 mm h-1),slope gradients(10°and 150),and slope lengths(7.5 and 10.0 m)on rill development and rill characteristics on loessial hillslopes in China.Loessial soil was collected from the cropland of Ansai Town,Yan’an City,Shaanxi Province.The soil with 28.3%sand,58.1%silt,and13.6%clay was packed into a soil pan to conduct rainfall simulations in 2012.The results showed that the time of the knickpoint occurrence(5-16 min),the rill headcut extension(9-33 min),and the mean headward erosion rate(1.7-5.o cm min-1)were better representative indicators for reflecting the changes in the rill development than other indicators used in this study.For a quick evaluation of the rill erosion severity,the rill coverage ratio(1%-12%,generallyincreasing with an increase in the rainfall intensity)was better than the other indicators for treatments with different rainfall intensities,and the rill width-depth ratio(1.56-2.27,generally decreasing with an increase in the slope gradient)was better than the other indicators for treatments with different slope gradients.Furthermore,the rill inclination angle(8.2°-19.1°,significantly increasing with an increase in the slope length)and rill density(0.19-1.34 m·m-2,generally increasing with an increase in the slope length)were more suitable for evaluating the rill erosion severity on hillslopes with different slope lengths.Therefore,the representative indicators could reflect the differences in the rill development and rill characteristics under different rainfall and topographic situations.The study greatly improved the evaluation of rill erosion severity and the prediction of the development of rills for loessial hillslopes.

基于力法的格构梁节点荷载分配方法及悬臂段长度优化设计

格构梁节点荷载简化分配方法的不足在于无法考虑2个方向的梁上其他节点荷载的影响且对文克尔(Winkler)地基上梁的类型进行了主观假定。为克服格构梁节点荷载简化分配方法的上述缺点,提出了一种基于力法的格构梁节点荷载分配方法。根据节点静力平衡条件及变形协调条件,新的格构梁节点荷载分配方法通过构建并求解线性方程组,能够合理地将作用在节点的集中力分别分配给2个方向的纵梁和横梁。进一步地,引入一个格构梁边坡锚固案例并等比例地增加纵梁和横梁的悬臂长度。不同基床系数条件下,基于新的节点荷载分配方法将格构梁节点荷载分配给纵梁和横梁,然后对各梁单独进行弯矩计算。以悬臂最大正弯矩与跨中最大负弯矩比值的绝对值接近1为评价指标,对格构梁最优悬臂长度进行了评价。节点荷载分配结果表明,随着悬臂长度的增加,分配给纵梁和横梁的荷载逐渐趋于稳定。弯矩计算结果表明,随着基床系数的增大,悬臂长度对格构梁弯矩的影响逐渐减弱。不同边坡基床系数条件下,当悬跨比在0.2~0.4之间时,悬臂各梁最大正弯矩与跨中最大负弯矩趋于均衡。因此,基于力法理论的节点荷载分配方法的提出为格构梁内力的精确分析及悬臂长度优化设计提供了可靠的理论依据。

坡度条件下不同长宽比矩形火源燃烧火焰贴地长度实验研究

利用可变角度实验台,改变斜坡角度(10°~50°)、热释放速率(12.3~24.6 kW)以及燃烧器长宽比(1~6),开展了一系列燃烧实验,研究了火焰贴地长度随这3个因素的演变规律.结果表明,随着斜坡角度、火源热释放速率及燃烧器长宽比的增加,火焰贴地长度增加.对于相同的坡度和火源热释放速率,随长宽比增大,贴地长度增幅范围在65%~105%之间.基于斜坡诱导压差与火羽流浮力共同作用的物理机制分析,并考虑到燃烧器长宽比对火焰卷吸行为的影响,提出了无量纲火焰贴地长度预测模型.

基于Geo-Slope的抗滑桩加固路堤的数值模拟

依托相关工程背景,运用有限元软件Geo-Slope模拟路堤分层填筑的施工过程,以了解路堤的变形特征.针对填筑过程中出现的滑塌现象,采用抗滑桩加固路堤.选取抗滑桩的桩位、桩身弹性模量、桩长这三个参数进行数值模拟,分析研究出其敏感性为:桩位在坡脚的抗滑桩能有效控制路堤最大水平位移,且更具有可操作性;桩身弹性模量的提高有利于限制路堤最大水平位移;穿过危险滑动面的桩,其桩长对路堤最大水平位移的限制作用不明显.考虑到施工质量控制及成本控制,应该选择合适的桩身弹性模量及桩长.

主动柔性防护网锚杆锚固段长度设计研究

随着我国高速公路建设加速推进,越来越多的高速公路进入到运维期,路堑边坡会出现局部崩塌、岩石风化剥落等现象。对于存在落石风险的岩质边坡,工程中一般采用主动柔性防护网进行防护。文章结合工程实际技术指标,通过简化边坡局部崩塌计算模型,得出路堑边坡主动柔性防护网锚杆锚固段长度的简化算法,为锚杆锚固段的长度设计提供技术支持。

Accelerated recruitment of copepod Calanus hyperboreus in pelagic slope waters of the western Arctic Ocean

Shelf-basin advection is essential to subsistence of the Arctic copepod Calanus hyperboreus population in high basin area. Its abundance, population structure and body size in pelagic layer were investigated with samples collected over a large range in the western Arctic Ocean during summer 2003, to evaluate the geographical variation in recruitment pattern. Calanus hyperboreus was absent from the shallow areas of the Chukchi Sea and most abundant in the slope area between the Chukchi Sea and Chukchi Abyssal Plain（CS-slope）. Total abundance varied between 1 110.0 and 5 815.0 ind./m^2 in the CS-slope area and ranged from 40.0 to 950.0 ind./m^2 in the other areas. Early stages（CI–IV） dominated in the CS-slope area, whereas CV and adult females were frequently recorded only in deep basin areas. Geographical difference of prosome length was most evident in CIII,with average ranging from 2.48 to 2.61 mm at the CS-slope stations and 2.16–2.37 mm at the others. Abundance of early developmental stages（CI–CIV） correlated positively with Chl a concentration, but negative correlation was observed in late stages（CV–adult）. Our results indicated that C. hyperboreus can benefit from primary production increase through accelerated development in the first growth season and the productive CS-slope area is a potential source for slope-basin replenishment.

圆柱滚子轴承次表面裂纹区域应力分布规律研究

圆柱滚子轴承套圈滚道次表面裂纹将改变滚子表面与滚道之间的接触特性,从而影响轴承的工作特性。针对这一问题,研究了次表面裂纹的长度、宽度和倾斜度对裂纹区域应力分布的影响规律。首先,采用有限元方法,建立了轴承滚子与滚道等效接触的计算模型,并将有限元模型与赫兹接触理论的算例计算结果进行了对比,对有限元模型的正确性进行了验证;然后,基于圆柱滚子轴承次表面裂纹的形态特征,提出了含次表面裂纹的滚子与滚道接触有限元计算模型;最后,基于有限元模型,分析讨论了次表面裂纹的深度、宽度和倾斜角度对滚道次表面应力区分布范围的影响规律。研究结果表明:当次表面裂纹的宽度增大时,应力区的深度和宽度都迅速增大;当次表面裂纹的深度增大时,应力区的深度和宽度都迅速降低;当次表面裂纹的高度与宽度一定时,次表面裂纹的倾斜角越大,次表面应力区越小,次表面裂纹对轴承接触特性的影响也越小。