where С1пр – diseconomies from traffic stopping along bypass, along the whole road per day (traffic time-out, damage of perishables etc),

2. Arrangement of profile subgrade with prefabricated surface laying along the whole road under reconstruction.

With intensity from 1000 and more motor cars per day, and also at unfavorable soil conditions and higher moistening there are constructed truck prefabricated surfaces allowing multiple use. Prefabricated surfaces from reinforced slabs are used more often. The advantages are for slabs structure with simple smooth contour of upper and low surfaces, with the simplest butt arrangements. At high intensity there are constructed solid surfaces from reinforced slabs.

The length of laid and operated road surface is equal to the road –building section length. Prefabricated reinforced surfaces provide traffic passing along bypass without intervals and with the smallest speed reduction. Diagram of bypass arrangement with prefabricated slabs is in fig. 2.9.

Ramp with prefabricated surface is divided into three plots. On the first one there is made a demounting of already used surface, on the second one (main) – there is traffic, the third section is prepared for traffic passing placing the surface from elements delivered from the first section. The complex of elements of prefabricated surfaces should provide the section laying approximately 2 times bigger than factually operated bypass. The operation duration of laid surface on the place depends on main work flow velocity on the road under reconstruction and number of ramps from it.

Fig. 2.9. Diagram of bypass arrangement with prefabricated slabs

1 – rehabilitated road; 2 – section under reconstruction; 3 – section of dismantle prefabricated surface; 5 – section of prefabricated surface laying; 6 – surface slabs transportation.

Where Ссз is the cost of subgrade construction on bypass including ramps onto main road; L – length of the section with prefabricated surface; Сп – cost of production of prefabricated blanket of 1km length; N – number of blanket assemble

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and dissemble during the whole period of works; См – summarized cost of assembly and removal of one section blanket; Сэ – cost of maintenance and repair of 1km of bypass.

At economic estimation of this variant it is necessary to check that the number of designed assembles and disassembles of N –prefabricated blanket is not exceeded the number of allowed one according to technical characteristic of these blankets. In opposite case it is necessary to foreseen repeated expenses for additional slabs purchase.

3. Motor cars passing along the half of the road

This variant is for the cases when there is no possibility to construct bypasses near the road under reconstruction because of the considerable bogginess, mountain relief, roadside development or plantings. At this variant a road base is constructed along the whole road side width and an additional traffic line is arranged.

While observing this variant there are no expenses for the bypass arrangement, but there are additional expenses because of the rise of the works cost in cramped conditions and also the expenses for the preventions of the places of works and traffic regulation. There are appeared the losses because of the periodical vehicles idles at shuttle method of traffic passing. Diagram of traffic regulation along the half of the road is given in fig. 2.10.

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Fig. 2.10. Diagram o traffic regulation along the half of the road

1 – traffic light; 2 – motor car meter, 3 – plot of working, 4 – traffic lane.

In the crossing points from double-lane traffic to single-lane traffic there are placed traffic lights and motor car meters. At green light signal in point No1 a motor car meter is on and the information about the number of the vehicles passing by the meter transmitted onto analogical meter placed in point No2.

At red light in point No1 traffic starts after the green signal on. It lights in the case when the number of the vehicles passing by the meter in point 1 in second point direction will be recorded by the meter in point No2.

Or meters and traffic lights power there are usually used small capacity power

plants.

Sum of the expenses is:

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Where Сэ – expenses for maintenance and repair of the lane along which the traffic passes; Ссд – additional expenses (rise in cost) during operation along the half width of carriage part of the road; Срд – expenses for traffic regulation; Спр – loss from periodical traffic idles at by turn pass of single side traffic.

Replacement of reconstruction by new construction

At significant traffic intensity it is reasonable to observe the problem of new road construction instead of reconstruction. In this case the existing road at the period of new road construction will play the role of bypass.

Such decision is typical at the road of categories II or III reconstruction into the road of category I. On different sections of one road under reconstruction there are can be applied different methods of traffic provision.

While deciding the problem of the operations some variants of general schemes of traffic organization are usually analyzed and compared. Minimum of summarized expenses and losses are taken as criteria of the choice. These expenses should be appropriated in the estimate for road reconstruction.

UNIT III

PERFORMANCE OF WORKS ON RECONSTRUCTION OF THE ROADBED

3.1.Double side (symmetrical) widening, advantages and disadvantages.

3.2.Single side (nonsymmetrical) widening, advantages and disadvantages.

3.3.Peculiarities of roadbase widening on slopes.

3.4.Technology of operation of widening:

а) technology of operation of fillings;

б) technology of operation of cavities widening. 3.5. Suitability of soils, their disposition.

While motor way constructing there is arranged new road base on the sections of road alignment, significant increasing of curves radius in the plan, on the sections of settlements bypasses, bypasses of landslips, screes.

“Health” roadbase is usually tried to use during the process of reconstruction. The absence of hanging horizons of water (high water) caused by the unfavorable disposition of filter and impenetrable soils proning to frosty swelling is understood under the term “health”.

Road base widening can be double-sided or single –sided.

3.1. Double -sided (symmetrical) widening is the widening at which the axis of existing road stays the same without any changes and matches with the axis of widened road. Thus the widening is done by the method of filling up of road fill and cutting of slops excavations from two sides. Such widening is usually done at the fill

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height and excavation depth up to 3 meters. There is presented the diagrams of double-sided widening of fill and excavation in fig. 3.1.

Fig. 3.1. Diagrams of double –sided widening of fill and excavation

Advantage of this method consists of the following: roadbed after its widening is on the durable well formed road subgrade which provides its durability and solidity.

Disadvantages of this method of widening is in increasing of preparatory operation volume, provision of the necessary facilities that is necessity of removal and placing of engineering equipment on both sides, replacement of communications, pipes lengthening and bridges widening, reorganization of drainage system etc.); complication of operation technologies and difficulties in road building machines use.

3.2. Single-sided (nonsymmetrical) widening is the widening at which axis of designed road displaced outside from the old road grade line but the widening is made by filling up of fills or slop excavation cutting from one side (fig. 3.2).

Fig. 3.2. Diagrams of single –sided widening of fill or excavation

Advantage of this variant consists in the following: all the roadbed widening works are from one side thanks to which better conditions for road building machines operation are arranged and these machines can operate better. The volume of works for preparatory and upgrading is decreased.

Disadvantage consists in the following: the part of new road base width is located on the old subgrade, but part of it is on the unset soil to which is difficult to give the same consolidation and durability as old subgrade has.

As a result unequal solid road construction is created and there appeared longitudinal cracks in road bed at the old and new road blanket seam. The more so at double side widening of carriage way the need in road building materials increases

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