基于针入度与PG分级的沥青胶结料技术指标对比研究

沥青胶结料是沥青路面的重要组成部分,评价沥青胶结料路用性能的常规方法是针入度方法,美国的战略研究计划(SHRP)开发了一个新的评价沥青胶结料性能的方法,即Superpave沥青胶结料路用性能PG方法,针入度规范的主要技术指标就是沥青的三大指标(针入度、延度、软化点),而沥青胶结PG方法主要指标是高温车辙因子、中温疲劳因子、低温蠕变劲度及最大拉应变等,基于两套规范的差别,从理论方面进行对比研究,研究主要有两个方面,一是从宏观角度对两套规范进行对比,分析其表面的异同,另一方面从每个主要指标进行着手,对比分析其理论方面的异同。     

基于车辙等效的轴载换算关系研究

车辙作为高速公路路面主要病害之一,在我国现行公路沥青路面设计规范中没有纳入车辙指标。目前在国内许多科研机构和学者都在致力于车辙形成机理及车辙预测等方面的研究工作,足尺加速加载试验在公路工程领域是科研费用最昂贵,结果可靠性较接近实际路面状况。通过对野外三种路面结构的加速加载试验,利用车辙等效的关系确定出不同路面结构对应的合理轴载换算指数。将加速加载试验成果与室内车辙试验进行对照,证实室外加速加载试验得出的轴载换算指数与室内试验结果之间的差异。     

An operational UAV-based approach for stand-level assessment of soil disturbance after forest harvesting

The effectiveness of generating virtual transects on unmanned aerial vehicle-derived orthomosaics was evaluated in estimating the extent of soil disturbance by severity class. Combinations of 4 transect lengths (5–50 m) and five sampling intensities (1–20 transects per ha) were used in assessing traffic intensity and the severity of soil disturbance on six post-harvest, cut-to-length (CTL) clearfell sites. In total, 15% of the 33 ha studied showed some trace of vehicle traffic. Of this, 63% of was categorized as light (no visible surface disturbance). Traffic intensity varied from 787 to 1256 m ha^?1, with a weighted mean of 956 m ha^?1, approximately twice the geometrical minimum achievable with CTL technology under perfect conditions. An overall weighted mean of 4.7% of the total site area was compromised by severe rutting. A high sampling intensity, increasing with decreasing incidence of soil disturbance, is required if mean estimation error is to be kept below 20%. The paper presents a methodology that can be generally applied in forest management or in similar land-use evaluations.     

Combined effects of soil texture and machine operating trail gradient on changes in forest soil physical properties during ground-based skidding

Wood extraction by heavy machinery has always been associated with soil disturbance in mountain forests,and the degree of soil degradation is influenced by several factors,including site and soil characteristics,soil moisture,type of equipment used,and number of machine passes.The effects of ground-based skidding operations on the physical properties of soils with different texture were evaluated at different levels of traffic frequency and trail gradient at two sites in an Iranian temperate forest.The treatments included combinations of three different traffic frequencies(3,8,and 14 passes of a rubber-tired cable skidder),three levels of trail gradient(10%,10%–20%,and20%) and two soil texture classes,clay loam(Site 1) and sandy loam(Site 2).The average gravimetric soil moisture at the time of skidding was 23%(Site 1) and 20%(Site 2).The average dry bulk density and total porosity of the undisturbed soil(control) were0.71 g cm~(-3) and 73.3% at Site 1(clay loam) and 0.86 g cm~(-3)and 59.1% at Site 2(sandy loam),respectively.At site 1(fine-textured soil),rutting began after three passes of the skidder,whereas at site 2(coarse-textured soil),rutting occurred only after eight passes.Independent of the traffic frequency and trail gradient,machine impact on the fine-textured soil caused greater increases in bulk density and rut depth compared to that on the coarse-textured soil.After three skidder passes and independent from trail gradients,dry bulk density at Site 1 increased by 54.8% compared to that of the undisturbed control,and the increase was 45.5% at Site 2.Therefore,medium to fine-textured soils are more susceptible to compaction than coarse-textured soils.Such soils,especially when moist,should be protected using brush mats created from harvesting residues during the forest processing phase.     

扬子鳄发情期昼间行为时间分配及活动节律

2004年5~6月,在安徽扬子鳄国家级保护区红星保护点,对发情期的扬子鳄(Alligator sinensis)进行了昼间行为时间分配和活动节律的研究。扬子鳄的行为谱包括游动、晒阳、停息、吼叫和交配等。就所观察到的几种主要行为统计发现,从7:00到19:00,扬子鳄昼间游动行为占有最大的百分率,达到(34.30±26.27)%;其次是停息行为,为(30.44±18.50)%;再次为晒阳和吼叫行为,分别为(21.04±32.95)%和(14.16±18.97)%。游动行为各时段占有的百分率比较接近,为26.47%~44.83%,但在游动过程中,它们并不是始终保持一种姿势游泳。停息行为存在2个高峰期,分别为9:00~11:00和17:00~19:00时间段;晒阳行为出现在6月3日以后,仅有1个高峰期(11:00~13:00)。吼叫行为的高峰期出现在7:00~9:00时间段;结合夜晚记录发现,21:00~23:00时间段也是一个吼叫高峰。扬子鳄的吼叫次数与水温差存在一定的关系,吼叫次数最多的水温差为3.5℃,在1.5~3.5℃吼叫最频繁。笔者认为,该时期扬子鳄的活动行为主要受繁殖因素的影响。图3参36     

Mitigating effects of slash on soil disturbance in ground-based skidding operations

Reinforcement of skid trails with slash has been shown to reduce soil disturbances, but there have not been any studies documenting the mitigating effects following traffic of harvest equipment traffic on steep mountainous skid trails. The objective of this study was to quantify potentially mitigating effects of slash cover on soil compaction and rutting on skid trails in mountainous hardwood forests. The effects of the placement of no slash (bare soil), light density slash (7.5 kg m^?2) and heavy density slash (17.5 kg m^?2) in a skid trail following one, five, and nine machine passes on both gentle slopes <20% and steep slopes >20% in a downhill skidding operation by a steel-tracked skidder were studied. Bulk density and rut depth increased following harvest equipment traffic on both slope gradients. Compared to bare soils, soil bulk density was not significantly reduced by light slash density; however, soil bulk density was significantly reduced by heavy slash up to five machine passes on steep slopes. Light and heavy slash significantly reduced rut depth in both slope classes. The study revealed a high protective role of slash, particularly on steep skid trails. However, benefits of slash to mitigate soil compaction were limited to five passes, after which the slash deteriorated and only provided benefits against rutting.     

沥青混合料高温车辙直线预估方法

基于统计分析方法，对车辙形成机理及其顼估方法进行探讨．通过对不同级配下橱青混合辩进行系统的车辙试验，全程采集车辙形成过程中的变形数据，对数据分别采用双对数曲线、半对数曲线和直线3种函数进行统计回归分析．结果表明，不同级配类型的沥青混合料车辙形成具有一致的规律性．其不同时刻下变形占总变形的比例基本上一致，变形稳定后变形占总变形的比例也一致．预估值与实测值对比分析表明：采用3种统计分析方法对车辙形成规律进行分析，精度均较高，其中直线预估方法拟合精度最高，计算简便、直观．便于工程采用．     

沥青路面不同层位车辙分布的模拟分析

为了研究沥青路面受到车辆荷载作用产生车辙破坏最严重的结构层,应用数值模拟建立了沥青路面的三维模型,运用瞬态动力学分析沥青路面各个结构层在动态荷载作用下产生的竖向变形量,从而得出受到荷载作用产生车辙破坏最严重的层位,为沥青路面的结构设计提供参考.结果表明:沥青路面产生车辙变形量最大的位置出现在荷载作用的中心线处；在动荷载作用下沥青路面的面层是产生竖向变形最大的结构层.     

A 3D Visco elasto plastic Finite Element Analysis of the Asphalt Pavement Rutting Deformation

Based on the dynamic action between vehicles and pavement, a simplified model of vehicle dynamic loading caused by surface evenness was established. This research made it possible to find a Asphalt Pavement Rutting Prediction method based on the theory of visco elasto plasticity which is the basic theory of the dynamics, and finite element method (FEM). Asphalt pavement rutting was calculated and predicted, and the factors influencing rutting were analyzed and calculated. The good agreement between the calculation results and the testing road data indicate that the rutting prediction method is reasonable and reliable.