Analysis of vibrating characteristics of multi-span continuous skew bridges

To explore the vibrating frequencies and rational impact factors of multi-span skew bridge, the recursive algorithm of vibrating frequency and finite element formulations of static and dynamic analysis are established for uniform section multi-span continuous skew bridge. The first five order frequency changes of equal-span multi-span continuous skew bridge and unequal-span multi-span skew bridge are compared. The interaction of vehicle-bridge system for two-span skew bridge is analyzed. The history curves for deflection and moment of middle-span are presented. The influence of obliquity on dynamic deflection and dynamic moment as well as the influence of vehicle velocity and obliquity on impact factors of deflection and moment are investigated. Results show that the fundamental frequency of multi-span skew bridge is identical to that of single span skew bridge. The higher order frequencies of single span skew bridge are distributed in frequencies of multi-span skew bridge, which mix other vibrating frequencies. The more the span number is, the more the other vibrating frequencies mingle. Obliquity has an important influence on dynamical characteristics of skew bridge. Impact effects of vehicle have no harmonious changing rule with vehicle velocity and obliquity. The impact factors of deflection and moment are different for skew bridge.     

亚热带花生旱坡地的水分动态特征分析

为研究红壤旱坡地的水分动态特征,进行了2001—2003年田间实测。花生旱坡地水分状况随年降水周期和坡位不同变化。0~150cm土壤贮水量大致分为盈余期、消耗期和补充期三个阶段。土壤水势变化与贮水量三阶段相对应,总体由大变小再回升,只是土壤剖面空间从上而下,水势值增大,变幅减小,100cm土层以下近乎常年稳定。在四个水势段出现频率中,水势较高的水势段出现频率越大,顺序为饱和>湿润>亏缺>干旱。饱和－湿润段出现频率比例总体上底土>心土>表土,坡下>坡上;低水势干旱段主要出现在坡上、土壤上层和伏秋干旱季节。旱坡地在雨季有壤中流产生,坡下降雨后深层出现较长时间的饱和区,而坡上深层水势出现较短时间的饱和区或未出现变化;旱季降雨对坡地水分影响较小。     

Analysis on key problems of initiative decompression pre-reinforced structure

In slope engineering, the shear resistance of rock and soil can never be exerted themselves by general pre-reinforced structure, through the coupling mechanism between reinforced structure and slope, an initiative decompression pre-reinforced structure consists of soft stuffing and pre-reinforced structure is presented. The setting and thickness of soft stuffing are both key questions during the design of initiative decompression pre-reinforced structure. On one hand, the setting of soft stuffing assure that parts of initiative decompression pre-reinforced structure cannot interact each other under reinforcing; on the other hand, the thickness of soft stuffing can assure that the shear resistance of rock and soil can be exerted by themselves, the sliding thrust which is endured by pre-reinforced structure alone is changed to be endured by soil and pre-reinforced structure together. Then the sliding thrust endured by pre-reinforced structure minimizes, accordingly the effect of initiative decompression is achieved. In the end, the calculation procedure of thickness is illustrated by a practical project and the result is rational.     

典型岩溶农业区洼地和坡地的元素迁移特征差异

摘要：本文以桂林会仙典型岩溶洼地和坡地两种不同地貌部位为研究点,以石灰岩地质背景条件下的基岩-土壤-土壤水-植物体系统中的元素含量和组成特征为研究对象,探讨不同地貌部位条件下元素的基本特点、制约因素和变化趋势。研究结果表明,在岩溶动力条件的驱动下,岩溶区形成了显著的偏碱环境特征;洼地和坡地土壤剖面元素和土壤水含量特征差异明显,植物对土壤元素的生物吸收系数比较低,属于受氮限制的类型;坡地部位的偏碱富钙和水分胁迫程度更为严重;同一石灰岩地质背景条件下不同地貌部位岩溶系统元素迁移特征差别显著。     

北京松山自然保护区天然油松林土壤养分与坡位关系的研究

为了阐明坡位对天然油松林地土壤养分状况的影响,并为华北地区天然油松林地的抚育管理提供科学依据,以北京市松山自然保护区内的健康天然油松林地的土壤为研究对象,对样地内上、中、下3个坡位的土壤主要养分含量进行分析测定,探讨林地内土壤主要养分含量与坡位的关系。结果表明：（1）土壤养分主要在下坡位汇集,各坡位油松林土壤全氮含量和速效钾含量：上坡位>中坡位,而有效磷含量为：中坡位>上坡位。（2）各养分元素主要集中于土壤表层,基本随土层深度的加深而降低;土壤全氮和有效磷含量分别在下坡位和中坡位出现了随土层深度加深而先降低后升高的趋势;（3）土壤速效钾含量在0~20 cm土层深度表现为中坡位出现最低值,而在20~60 cm土层深度表现为中坡位出现最高值。     

东北黑土区植被配置的土壤抗冲性研究

对东北黑土区不同植被配置下的土壤抗冲性及其影响因素进行研究,为水土保持植物选择和配置提供一定理论依据.采用野外采样与原状土冲刷试验相结合的方法.结果 表明:坡位对土壤抗冲性具有一定影响,胡枝子与紫穗槐在不同坡位上的土壤抗冲性不同,且在土层上层(0～10 cm)存在差异,下层(10～20 cm)的变化规律相近;不同植被配...     

Longitudinal Vibrations of a Single Pile in Saturated Viscoelastic Soil

Based on Biot's theory, the longitudinal vibrations of a single pile in saturated viscoelastic soil are investigated in the frequency domain subject to the harmonic load. By the Novak plane strain model, the control equations for the saturated viscoelastic soil are derived. Regarding the pile as the one-dimensional rod model, the vibration equation of the pile is established. Based on the continuity conditions of the pile and soil, the dynamic stiffness and dynamic damping of the pile top are obtained. It is compared with the solution for Novak, and the influence of different physical parameters of the pile and soil on the longitudinal vibrations of the soil and pile system is examined. It is shown that the dynamic characteristics of the pile in the dry soil as well as the saturated soil have some differences; the resonance effect of dynamic stiffness factor and equivalent damping is obvious weakening with the increase of the ratio of the length to radius of the pile. The resonance effect and natural frequency are increasing when the modulus ratio of the pile to soil increases; the interaction coefficient of the flow-solid and the damping ratio of soil skeleton have few influences on the responses.     

农业灌溉作用下黄土边坡失稳引起耕地流失分析

为了明确在大面积农业灌溉作用下，水分入渗土壤进而渗入下部黄土体，改变临空耕地黄土边坡的稳定性状态，造成边坡失稳引起耕地流失的过程。在统计分析甘肃天水耕地流失面积、农田灌溉面积、地质灾害数量和由地质灾害造成耕地流失比例的基础上，在典型地层剖面上采集原状土壤和黄土试样，进行天然状态和灌溉作用下土体的物理力学性质和抗剪强度试验，采用理正岩土边坡稳定性分析系统，利用基于极限平衡条分法的瑞典法进行边坡稳定性定量分析。结果表明：在天然状态下，该边坡稳定性系数为1.074，处于基本稳定状态；而在灌溉作用下，随着水分入渗深度的增加，稳定性系数逐步降低，最后失稳。因农田灌溉仅使土壤层饱和，对该边坡稳定性影响不大；当灌溉水持续入渗使饱和层土体厚度大于2 m时，该边坡稳定性降低一个等级，处欠稳定状态；当饱和层厚度大于10 m时，该边坡失稳，发生滑坡，造成耕地流失。     

玛纳斯河流域沙漠与绿洲过渡带土壤水盐变化特征与规律

土壤盐碱化防治是新疆地区农业乃至社会经济发展的重要任务。在新疆古尔班通古特沙漠南缘选取了两个耕地土壤剖面和一个丘间地原生土壤剖面进行调查,室内测量其土壤粒径、容重、含水率和含盐量,探讨了原生盐碱荒地及开垦农田水盐变化特征与规律,以便为该地区防治盐碱化提供必要的科学依据。调查分析结果表明：（1）土层物理性质的差异对土壤水盐分布特征有较为明显的影响,粘粒及粉粒较多的土层积盐现象更为明显;（2）土层的结构异质性对水分盐分有阻滞作用,导致土壤中存在盐分堆积层;（3）灌溉水导致土体淋溶强度增大,这虽能降低土体中的盐分却增加地下水矿化的风险。建议该地区土壤盐碱化防治应因土层异质性而设置相应的排水措施,灌排结合以达到土壤盐碱化防治乃至保护地下水的目的。     

西南黄壤坡耕地保护性耕作的土壤结构效应

设置两种保护性耕作措施,通过6a持续试验,研究了保护性耕作措施对黄壤结构性状的影响,为西南黄壤地区保护性耕作技术应用与发展提供理论依据。[方法]分别用环刀法、干湿筛法测定土壤容重和土壤团聚体组成,土壤机械组成采用MS2000激光粒度分析仪测定,并计算出土壤孔隙度和团聚体破坏率。 [结果]结果表明：(1)垄播沟覆轮耕与免耕秸秆覆盖两种保护性耕作措施均可降低黄壤容重,增加土壤孔隙,且此作用是由表及里的渐进过程,垄播沟覆措施的土壤容重优化作用要优于免耕覆盖,而免耕覆盖对较深层次土壤孔隙状况优化效果更显著。(2)保护性耕作可提高0～20 cm土壤＞0.25mm干筛团聚体含量,水稳性团聚体含量处理之间差异不显著,但0～20cm层含量略大于20～40cm层。(3)保护性耕作可提高土壤团聚体稳定性,降低团聚体破坏率,免耕覆盖措施对提高土壤团聚体稳定性具有更加显著的效果。[结论]该试验证明了保护性耕作对黄壤土容重、孔隙、团聚体等结构性状有一定的改善作用,这种改善作用是一个非常漫长的由表及里的渐进过程,为西南黄壤地区保护性耕作技术应用与发展奠定了坚实的基础。     

Mechanical Analysis of Herbaceous Plant Strengthening Slope

Since there are the root systems of herbaceous plant in the shallow layer of soil masses of slope, the shallow layer of slope becomes a compound materials made of soil masses and root system.Owing to friction action and tensile resistance action of roots, the shear strength of soil layer with root system is increased.And a comprehensive mechanical analysis of how herbaceous plants strengthen slope was carried out.Not only a mechanical model of interaction between root and soil, but also a quantitative calculation of increase of shear strength and stability coefficient of slope was put forward.As a result, the theoretical basis of herbaceous plant ecological slope protection was provided.     

膜下滴灌条件下不同灌水量对玉米产量及土壤水分的影响

为建立赤峰地区膜下滴灌玉米灌溉制度,指导农业生产,通过连续两年的田间试验,研究不同灌水定额对玉米产量的影响,分析了不同灌水定额的土壤水分动态变化规律,进而讨论了在不同灌水定额条件下玉米的产量、总耗水量、以及水分利用效率的差异。结果表明：膜下滴灌条件下玉米土壤水分运移变化多在60cm土层以上,尤其以0~20cm土层变化最为明显。膜下滴灌玉米产量和全生育期耗水量与灌水定额大小成正比,随灌水量的增加而增加,水分利用效率与之相反。综合连续两年的产量、耗水量及水分利用效率对比分析,认为赤峰地区膜下滴灌玉米的灌水量为150~180mm是较为适宜的,为指导赤峰地区玉米膜下滴灌合理灌溉及增产节水提供理论依据。     

黄土丘陵区小流域横断面土壤水分的空间分布特征

以黄土丘陵区的纸坊沟小流域为研究对象,研究了横断面上土壤水分空间变化特征,得出如下规律：①从总体来看,土壤水分含量大致是阴坡高于阳坡,坡下高于坡上,地形起着决定性作用,但植被的影响也非常重要。②在小流域断面水分分布中,乔木林地的平均含水量最低,灌木林次之,草本植被最高。表明丘陵区最适宜的植被应是草本植被和灌木群落。③植被的生长弱化了断面地形变化的影响,刺槐的阴阳坡、上下坡的土壤水分含量趋于接近,柠条的生长良好时的大耗水量也使阴坡和坡下的水分优势减弱,长势良好的草本群落使梁峁坡上的土壤水分状况优于其他坡位。④纸坊沟小流域除阴坡草本植被外,全部有土壤干层的存在,但并不影响植被的正常生长,因此,在植被恢复良好的地区,干层的产生是正常的。     

土壤容重对高产玉米根系生长的影响及调控研究

不同土壤容重不同,其稳定性也不同。土壤容重的变化会引起土壤调节水、气、热能力的变化,提高土壤的自动调节能力可以使土壤肥力水平得以提高并满足植物对生长因子的持续需求。为研究土壤物理性质对玉米高产稳产的影响机理,以耕地棕壤为试验材料,采用盆栽方法,研究不同容重对玉米根系生长指标的影响,并进一步研究了施用不同有机肥量及模拟不同耕作深度对玉米根系生长的调控效果。结果表明:在设计容重范围内,容重增加,根系生长指标都表现为下降,容重大于1.2 g/m3时,不同处理根系生长指标差异显著;当容重大于1.3 g/cm3时,不同处理根系活力差异显著。施用有机肥对高容重土壤调控效果更好,有机质含量为4%与5%的处理差异减小,低容重土壤在所设计的有机质水平内调控效果也都较好。耕层厚度增加可以提高根系生长参数,但与对照相比,差异不显著。所以,对于紧实结构性较差的土壤,改善其调节能力应该通过增施有机肥的方法,紧实结构较好的土壤考虑使用耕翻的办法。     

Numerical Simulation and Field Monitoring Research of Reinforcement Range of Soft Ground on One Side Road Widening Project

As one of common reinforcement measure, cement mix pile is widely used in soft ground treatment of road widen project, while relevant studies on reinforcement range is insufficient. According to the one side road widening project, the cross-section of deep soft ground is analyzed. When fill is simplified as trapezoid load, the conclusion that reinforcement depth of cement mix pile should greater than load breadth can be gained by addition stress distribution. Based on the numerical simulation of different reinforcement measures, the slope stability, road settlement and horizontal deformation are influenced greatly by reinforcement range. Comparison research indicates that when the soft ground from slope toe to road shoulder is strengthened, the improvement effect is obvious. The numerical simulation and field monitoring resules show that reinforcement measure is suitable. Meanwhile, this study can provide reference to similar project.     

客土基盘造林法对滨海盐渍土水盐动态的影响

为了使得客土基盘造林技术在滨海泥质盐碱地造林绿化应用中有充分的理论依据,以河北唐山市南堡开发区盐渍化土壤为研究对象,通过野外试验,研究了客土基盘造林法对滨海盐渍土水盐运移规律的影响,并比较了不同客土配比方式的排盐、降盐效果。结果表明,对照组（未经改造的原状土）土壤含水量变化规律与降水量变化规律相同或稍有滞后,处理组（以不同客土配比方式制作的客土基盘A1、A2、A3、A4）同样受降水规律的影响,但各土层含水量变化幅度差异较大,且峰值的出现时间不同,不同客土配比方式对0~20 cm、40~60 cm土层含水量影响具有显著性差异,对20~40 cm、60~80 cm影响无显著性差异。对照组含盐量变化与含水量变化存在显著负相关关系,观测结束时,返盐程度剧烈;而处理组则无显著相关关系,总体含盐量保持持续降低。4种不同客土配比方式对各土层含盐量变化影响具有显著性差异,平均含盐量均有大幅下降,总体降盐效果：A1>A3>A2>A4,植物根区含盐量下降效果：A1>A2>A4>A3。综合分析,以A1处理方式,即原状土与基质土以1:2配比制作的客土基盘排盐降盐效果最好。     

Experiments on triaxial mechanical properties of soft coal containing gas

Taking briquette specimens composed by soft coal with outbursting trends as research object, systematic research of the influence on triaxial mechanical properties of soft coal containing gas caused by confining pressure and gas pressure is done. The results show that confining pressure can significantly affect mechanical properties of soft coal containing gas, the compression phase of soft coal containing gas is obvious and the triaxial strength is increased gradually as confining pressure is increased; the influence on elastic modulus and shape of stress-strain curve is not obvious. The triaxial strength of soft coal containing gas shows decrease trend as gas pressure is increased; the influence on strength of soft coal containing gas caused by gas pressure is obvious when the confining pressure is smaller, but it is not obvious when the confining pressure is bigger. the influence caused by gas pressure on elastic modulus and deformation of yield step is not obvious; gas pressure has not only obvious mechanical effects,but also have chemical action on soft coal containing gas; stress-strain curve of soft coal containing gas can be expressed by conic, the influence caused by gas pressure can be considered as equivalent confining pressure effects.     

Discussion on Methods for Determining Cracking Angle of Rock Slope

Many mountainous cities are facing slope problems during project construction. At present, there are two methods to determine cracking angle for rock slope, namely, the method from "Technical Specification for Retaining Structure in Excavation" and the method from "Handbook of Engineering Geology". However, there is obvious difference between cracking angles of rock slope by these two methods. In this paper, the theoretical formulas of these two methods are derived and compared. Based on analyzing the results of FLAC numerical simulation for soft rock slope, it is concluded that the cracking angles of rock slope determined by the "Handbook of Engineering Geology" are more reasonable and safe.     

土体抗剪强度指标变异水平对边坡稳定安全系数取值的影响

针对传统的边坡稳定极限平衡方法不能考虑土体抗剪强度指标变异性影响的问题,基于极限状态的概率分析原理,采用Monte-Carlo法对均质路堤边坡的稳定性开展了可靠度计算,讨论了稳定安全系数一定的条件下边坡失效概率随土体抗剪强度指标变异水平的变化规律,分析了安全系数与边坡可靠指标的对应关系及其随土体抗剪强度指标变异水平的变化特征。研究表明：边坡可靠度受土体抗剪强度指标变异性影响显著,呈现出随土体抗剪强度指标变异水平提高而急剧减小的趋势;为保证边坡具有相同的可靠性,安全系数的取值应与土体抗剪强度指标的变异性相适应,据此提出了基于可靠指标和土体抗剪强度指标变异水平的安全系数取值原则及其对应的三参数函数关系式。     

辽西北沙地流动沙丘土壤水分时空变化特征研究

以辽西北沙地流动沙丘为对象,研究了土壤水分运动的时空变化特征。结果表明：流动沙丘土壤含水率的时间变化与降雨有密切关系,春季土壤含水率较低,为0.1%~3.1%;夏季土壤含水率较高,为2.5%~5.1%;秋季土壤含水率略高于春季,为2.2%~3.6%。土壤含水率垂直变化位为：0~10cm土壤含水率变异程度较大,受降雨和蒸发影响强烈;10cm~80cm变异程度相对小些;80cm~120cm土壤含水率比较稳定。流动沙丘不同部位的土壤含水率受干沙层厚度频繁变化和降雨量影响显著,阴坡底含水率＞阳坡底＞阳坡中＞丘顶＞阴中。