Cross-Section Design

I. Cross Section Composition

General Components

(1) lane: a general term for all kinds of vehicles on the road, including Fast Lane and slow lane.

(2) shoulder: it is located at the edge of the road lane to the edge of the roadbed, with a certain width of the band structure.

(3) Middle Belt: the highway and the first-level highway are used to separate the road frame components of the opposite vehicle and are usually set in the middle of the lane.

 

Special components

(1) Slope Lane. (2) acceleration and deceleration lanes. (3) Wrong lane. (4) Emergency Parking belts. (5) hedging lanes.

 

Cross-section width of highway at all levels

(1) the cross section of the highway embankment is divided into two types: integral and separate.

Integral: driveway, middle belt, shoulder, Emergency Parking belt, climbing Lane, acceleration and deceleration lane, etc.

Separate: place the upstream and downstream lanes on different planes, and the middle section is in the form of widening with the terrain.

(2) The cross-section of the secondary Highway Embankment includes the road lane, shoulder, and Slope Lane. When fast and slow lanes are separated, you can set the right side of the hard shoulder according to your local experience.

(3) the cross section of the subgrade of level 3 and Level 4 consists of the Road Lane, road shoulder, and wrong lane.

 

Highway Subgrade width

(1) width of integral Subgrade

Width of integral subgrade of all levels of Highway

Highway Grade		Expressway
Design speed (km/h)		120			100			80
Number of lanes		8	6	4	8	6	4	6	4
Subgrade width (m)	General Value	42.00	34.50	28.00	41.00	33.50	26.00	32.00	24.50
	Minimum value	40.00	--	25.00	38.50	--	23.50	--	21.50

Highway Grade		Level 1 Highway
Design speed (km/h)		100		80		60
Number of lanes		6	4	6	4	4
Subgrade width (m)	General Value	33.50	26.00	32.00	24.50	23.00
	Minimum value	--	23.50	--	21.50	20.00

Highway Grade		Level 2 Highway		Level 3 Highway		Level 4 Highway
Design speed (km/h)		80	60	40	30	20
Number of lanes		2	2	2	2	2 or 1
Subgrade width (m)	General Value	12.00	10.00	8.50	7.50	6.50 (double lane)	4.50 (single lane)
	Minimum value	10.00	8.50	--	--	--	--

(2) Split subgrade width

Width of separate subgrade of Expressway and Level 1 Highway

Highway Grade		Expressway
Design speed (km/h)		120			100			80
Number of lanes		8	6	4	8	6	4	6	4
Subgrade width (m)	General Value	22.00	17.00	13.75	21.75	16.75	13.00	16.00	12.25
	Minimum value	--	--	13.25	--	--	12.50	--	11.25

Highway Grade		Level 1 Highway
Design speed (km/h)		100		80		60
Number of lanes		6	4	6	4	4
Subgrade width (m)	General Value	16.75	13.00	16.00	12.25	11.25
	Minimum value	--	12.50	--	11.25	10.25

2. Cross-section Urban Roads

The roadway, sidewalks, green belts and separation belts and other components.

 

Arch

1. Arch Form

There are four types of arch: parabolic, straight line, line, and hyperbolic.

(1) Parabolic Arch

Relatively smooth, beautiful shape, no road peaks, the middle part of the road slope is relatively small, the slope on both sides is large, is conducive to the elimination of rain. However, the cross slope in the middle of the parabolic arch roadway is too gentle, and the traffic is easy to concentrate. This makes the central road surface easy to be damaged, and the cross slope in the road is different, making the construction difficult.

Common Parabolic Arch: 1. secondary parabolic arch (the secondary arch is suitable for medium and low-level roads with a pavement width less than 12 m, while the horizontal slope is relatively large. The disadvantage is that the horizontal slope near the central line is too gentle, the horizontal slope on both sides of the road is too large, which is not conducive to driving); 2. improved secondary parabolic arch (this arch form is suitable for the cross section of urban roads in hybrid driving of motor vehicles and non-motor vehicles. It is characterized by relatively uniform horizontal slope changes and moderate horizontal slopes between the middle and the side of the road, conducive to drainage and driving on the whole width); 3. semi-cubic parabolic arch (this arch form is similar to the improved secondary parabolic arch form, but the luzhong cross slope is a little slow, suitable for asphalt concrete, cement concrete or asphalt gravel pavement whose pavement width is less than 20); 4. correction of three parabolic arch (this form of arch meets the drainage requirements, and improve the shortcomings of part of the luzhong slope is too gentle, suitable for all types of pavement with a horizontal slope less than 3% ).

(2) linear Pavement

The two sides are inclined lines, and a curve or easing curve is added near the center line of the roadway. It is usually used on urban roads with a high pavement width greater than 20 m. Advantage: The vehicle tires have relatively uniform contact with the road surface, and the road surface wear is relatively small. Disadvantage: drainage is not as smooth as parabolic.

(3) line-shaped arch

Applicable to urban roads with multiple types of roads. Advantage: during construction, it is easy to smooth and smooth. You can choose a turning point at the most important point of the roadway. If the road surface is sunk after driving, the rain can also be ruled out, it meets the design, construction and maintenance requirements. Disadvantage: There is a spike at the turning point.

(4) hyperbolic Pavement

It is often used to tell highways and high-grade roads.

 

Cross-Section Design

Basic Requirements

The Structure Design of the subgrade should be carried out according to the use requirements and local natural conditions, and the construction conditions, that is, there should be sufficient strength stability and economic and reasonable.

The subgrade design of mountain and chongqiu areas should be based on the local natural adjustment, especially the terrain and engineering geological conditions, select the appropriate cross-section form of subgrade and the roadside slope.

The section form and size of the subgrade should be determined according to the road level, design standards and the provisions of the design task book, as well as the use requirements of the road, and the specific geometric conditions.

The design of the subgrade should take into account the needs of the basic construction of the local farmland, and cooperate with farmland soil change, farmland water conservancy, and irrigation ditches in the aspects of soil taking, waste soil, soil pit setting, and drainage design, minimize waste land occupation to prevent soil erosion and congestion.

 

Cross-section layout

1. Highway cross-section layout

Generally, the layout of a highway is not calculated separately. The section form can be arranged based on the local terrain, geology, water temperature, and excavation conditions, with reference to the typical cross section, the Section Sizes of the luford road width and road frame should be arranged according to the highway level, traffic volume, technical standards and specific conditions according to the provisions in the figure.

2. Cross-section layout of Urban Roads

Deployment principles

(1) The cross section should be in coordination with the nature and composition of the traffic on the road. (2) It should be in line with the nature and characteristics of the road. (3) Coordination and arrangement should be made with natural conditions and buildings along the line. (4) Coordination and arrangement of natural conditions and buildings along the line should be carried out. (5) drainage should be beneficial. (6) It shall meet the needs of diffuse and civil air defense projects on the ground and underground pipelines. (7) short-and long-term integration should be considered.

　　

Layout form

There are four layout modes: (1) single cross section ("one Board"); (2) double cross section ("two boards"); (3) three cross sections ("three plates"); (4) Four cross sections ("four plates ");

 

Cross-section design steps and main achievements

Steps:

1. point the horizontal line of a cross section; 2. according to the provisions of the standards, determine the width of the roadbed, (according to the soil and hydrological conditions to develop the slope of the roadbed slope; according to the drainage requirements to draw up the Side Trench, water cut trench and other dimensions) 3. calculate the ultra-high widening value based on the radius of the curve. 4. Based on the profile design data, the subgrade design table is calculated on a pile-by-pile basis based on the design elevation to complete the subgrade design table. 5. The cross-section design line is displayed based on the subgrade design table. 6. check whether there is sufficient line of sight on the inside of the cross section of the curve, whether obstacles need to be removed, and whether to set up line of sight.

Design results:

According to the highway engineering Basic Construction Project Design Document compilation method, the main achievements and requirements of highway subgrade construction are as follows:

(1) subgrade design table: list the elements of the screen lacking line, longitudinal slope (slope, slope length, slope change point pile number and elevation), Vertical Curve Elements, pile number, ground elevation, design elevation, fill-in height, subgrade width (original width, widening, total width after widening), easing length, super high value (left, right), subgrade edge and design height (left, right) and so on. The design data, shape and size, and the elevation (left and right) of the bottom vertical slope should also be listed during special design of the Side Trench (drainage ditch );

　　

 

　　

Cross-Section Design