第三章纵断面设计《路基路面工程》PPT课件

纵断面设计线是由直坡线（Grades）和竖曲线（Vertical Curves)组成 的。
直坡线有上坡(Downgrades)和下坡(Upgrades)，其大小用纵坡(Grade) 和坡长(Grade Length)表示，纵断面上同一坡段两点间的高差与其水 平距离（即坡长，不计斜长）的比值称为纵坡，以百分数计。
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4.纵断面设计的主要任务
根据汽车的动力特性、道路的功能和等级、地形、地质、水文及其 它自然环境的限制，综合考虑工程的技术要求和经济性等诸多因素， 合理确定坡度、坡长和竖曲线半径，并进行纵断面和平面的组合设 计，以便达到行车安全、环保、快速、经济合理及乘客感觉舒适的 目的。
Vertical Alignment is controlled mainly by topography, type of highway, horizontal alignment, performance of heavy vehicles, right of way costs, safety, sight distance, construction costs, cultural development, drainage, and pleasing appearance. General Rules for Establishing Vertical Alignment
In rolling terrain, natural slopes consistently rise above and fall below the road or street grade, and occasional steep slopes offer some restriction to normal horizontal and vertical roadway alignment.
路段时则是指设置超高加宽之前该处标高； （2）改建公路：一般按新建公路的规定办理，也可以采用中央分
隔带中线或行车道中线标高。 （3）城市道路：设计标高可视具体情况，采用中央分隔带边缘、
中线或行车道外侧边缘作为设计标高。
设计标高
设计标高
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n一般公路，路基未设加宽超高前的路肩边缘的高程。
设计标高
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n设分隔带公路，一般为分隔带外边缘。 设计标高
不同纵坡转折处称为变坡点(Vertical Point of Intersection, VPI or PVI)，为平顺过渡要设置竖曲线，按纵坡转折形式的不同，竖曲线有 凹有凸，其大小用半径和水平长度表示。坡度转折处（变坡点）只计 坡度代数差。
PVI-Point of Vertical Intersectionintersection of the two grades
In mountainous terrain, longitudinal and transverse changes in the elevation of the ground with respect to the road or street are abrupt, and benching and side hill excavation are frequently needed to obtain acceptable horizontal and vertical alignment.
PVC-Point of Vertical Curvaturebeginning of the vertical curve
PVT-Point of Vertical Tangency-end of the vertical curve
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3.路基设计标高（Elevations）
( 1）新建公路： ① 高速、一级公路采用中央分隔带外侧边缘标高； ② 二、三、四级公路采用路基边缘标高，在设置超高和加宽
第三章 纵断面设计 Chapter 3 Vertical Alignment
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Contents
Concepts Grades Vertical Curves Combination of Horizontal and Vertical Alignment Methods of Vertical Alignment Design
In level terrain, highway sight distances, as governed by both horizontal and vertical restrictions, are generally long or can be made to be so without construction difficulty or major expense.
Goal-Provide a uniform, comfortable ride and safe vehicle operation Balance cut/fills Grades>=0.5% or 0.3% to prevent drainage problems Check SSD/HSD Check driveway and intersecting road tie-ins Keep simple (few curves, flat curves, gradual grades) Check clearances (over/un Profile
I Concepts
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2.Basic Concepts
（1）地面线(Ground Line)，它是根据中线上各桩点的高程而点绘的一条不规 则的折线，平面线形确定后，地面线自然就唯一的确定下来，对于新建道路而 言，地面线反映了沿着中线地面的起伏变化情况.
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（2）设计线（Vertical Design Line）
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To characterize variations in topography, engineers generally separate it into three classifications according to terrain—level, rolling, and mountainous.