水平曲线外文翻译资料

Horizontal Curve

A horizontal curve is one which connects two tangents occurring in the plane of alignment of the road . These curves are laid out as if they were in horizontal plane , although they may be on a grade . The following trems describe Particular kinds of horizontal curves :

（1）Simple curve . Simple curves are circular arcs .

（2）Compound curve . Compound curves consist of two or more Simple curves possessing a common tangent at any points of meeting which turn in the same general direction and have their centers on the same side of the line . Any two adjacent areas must , of course , have different radii if they are to be a compounded pair rather than a single simple curve .

（3）Reverse curve . Reverse curves are similar to Compound curves except that their centers are on opposite sides of the line and their direction of turning is opposite to each other . The radii of the separate component arcs may be equal or unequal . Reverse curves are frequently called S-curves .

（4）Spiral . A Spiral is a parabolic type of curve used as a transition from a tangent to a circular curve , or from a circular curve to another circular curve of different radius .

The following information relative to the elements of a simple （circular）curve is presented simple for convenience .

a. Radius of the curve is designated by R .

b. Point of curvature , PC , is the point at which the curve begins .

c. Point of tangency , PT , is the point at which the curve ends .

d. Point of intersection , PI , is the point at which the two tangents to the curve intersect .

e. Intersection angle , I , is the deflection angle between the tangents and is equal to the central angle at O between the radii drawn from the PC and PT .

f. Tangent distance , T , is the distance along the tangent from the PI to PC or PT .

g. Length of arc , L , is the length of the arc from the PC to the PT . The length of the arc （L）, in stations , is equal to I/D , Where D is the degree of curve . In the field , it is measured as the sum of its 100-foot chords , plus any subchords occurring at its PC or PT in chaining 100-foot stations around the curve . However , on curves of short radius , chords of 25 feet or shorter are used so that L will not differ appreciably from the actual arc length . Chords of 100feet may be used for curves up to 8ordm; , 50-foot chords up to 16ordm; , 25-foot chords up to 32ordm; , and 10-foot chords for over 32ordm; .

h. Long chord , C , is the straight line distance from the PC to the PT .

i. External distance , E , is the distance from the PI to the midpoint of the curve .

j. Middle ordinate , M , is the distance from the midpoint of the curve to the midpoint of the Long chord .

k. Tangent offset , t , is the offset distance perpendicular from the tangent to any Point on the curve .

l. Deflection angle , d , is the deflection angle from a tangent to chord and equal to oneself the central angle subtended by the chord .

The minimum desirable radius of curvature is intimately related to the extent to which curves may be safely superelevated to counteract the centrifugal force of vehicles traveling on the curve . Complete superelevation to balance the centrifugal force of vehicles , disregarding the effect of friction between the tires and the roadway surface , may be determined by the formula

e＝Vsup2;╱15R

in which : e——the superelevation , in feet per foot of width .

V——the speed of the vehicle , in miles per hour .

R——the radius of the curve , in feet .

Because of the fact that on curves the rear wheels of motor vehicles do not ordinarily travel on the same radius as the front wheels , it is desirable to widen traffic lanes on sharp curves . The theoretical amount of widening required may be calculated as follows :

W＝R－radic;Rsup2;－Lsup2;

in which : W——the widening required for one traffic lane , in feet

L——the wheelbase , in feet .

The widening for n traffic lanes is

W＝n（R-radic;Rsup2;-Lsup2;）

Additional width is required for the overhang of the turning vehicle and because of the space required for maneuvering a vehicle on a curve . This additional widening is not susceptible of accurate evaluation . It varies as the speed , however , and for two lanes the following expression has been accepted extensively

V╱radic;R

For one lane half of this additional widening is required , and the following formula for complete widening has been adopted widely :

W＝n(R－radic;Rsup2;－Lsup2;＋V/lt;2radic;Rgt;)

Construction of stabilization

For mix-in-place work the Construction of a stabilized pavement course consists of the pulverization and preparation of the soil or material to be stabilized ，the spreading and mixing of the stabilizer and water with the soil ,and the compaction , shaping and curing of the stabilized layer . Successful stabilization depends largely upon the care taken in each of these aspects .

For plant mix work , a stationary mixing plant , usually employing continuous mixing , is used to proportion and mix the stabilizing agent , water and gravel or crushed rock and the mixed material is transported to the site in trucks laid by means of a self-propelled paver .

Failures in stabilized materials are generally more pronounced and more costly to repair than those in unstabilized ones-factors often combining to bring undeserved discredit upon the process . Particular care is needed, therefore , to provide a well compacted subgrade and good drainage . Similar care is needed in stabilization itself to ensure thorough mixing in the intended proportions , adequate compaction and good surface preparation .

The princi

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