for surface construction because of the necessity of shaping course in order to remove the carriage way axis and provide the profile.

3.3. Widening of road bed on hillside sections.

On hillside sections the widening of the subgrade is reasonably to make into direction of hillside with its additional cutting everywhere where there are suitable conditions. Such road bed location allows significantly increase its durability. But it is necessary to pay attention to the hillside resistance against its sliding down and on the possibility of screes appearance.

In these cases and also at big volumes of excavations of hillside cutting the widening of subgrade can be done in the expense of mound part. The provision of mutual work of old and mound part is of great attention. There are needed the construction of retaining walls in some cases.

Sometimes on the hillside section it is reasonably to divide carriage way into the traffic directions with their location on different levels along the hill slope. The existing road is used for the traffic in one direction but a new road is constructed for the traffic passing from the opposite direction there is constructed a new road higher or lower along the slope.

3.4. There are existed specific differences in work technology for fillings and cuttings widening (fig. 3.3).

Main implemented operations

Fig. 3.3. Order of operations at subgrade widening

Widening of road embankment of height up to 2m as a rule begins from filling up of side ditches or cavities –reserves from which the embankment was constructed. The filling up is done layer wise with careful protection up to Ку=1.

In lower part at small width of ditches the soil is compacted by vibration machines (type БТМ-1 of 5tonne mass, productivity of 50-60m3/h with frequency not

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less than 1200-1500 strokes per minute) or small sized vibratory compactors (type, ВУ-800 and ВУ-1500, 42 и 82 kg mass, vibration frequency of 100 and 70 Hg, slab sizes of 450х350 mm and 620х450 mm, depth of compaction of 20-25 cm and operation velocity of 20 m/min).

There is seldom used vibrohummer of 0,8m width with working member hanging up from behind of bulldozer of ДЗ-18 type. On its mouldboard there is installed grading slab appointing for the soil leveling. (At compactor speed of 380 m/h the layer of compacted soil up to Ку=0,95 – 1,00 achieves the thick of 0,35 м. Speed growth up to 550 m/h is possible if compacted layer thickness is decreased up to 0,3 m. It is possible to compact soil by vibrohummer and in wide trenches).

After finishing the filling up of side drainage ditches or cavities and execution of Act of Inaccessible Works the subgrade widening starts.

To provide reliable conjunction of the filling soils with the soil of existing subgrade at height fills up to 2m and slope grade from 1:3 up to 1:5 it is enough to hoe soil on the slopes by a ripper into the depth of 0,2-0,25m.

On the higher fills and slopes of 1:3 the benches of 0,5 with the grade of 50% are developed by a bulldozer or by a motor grader. In sand fills benches slope is towards the road profile and in clue ones it is from the road profile

First of all the lower bench is developed. Then the soil is filled and compacted and after that the upstream bench is developed.

The compaction is one of the significant operations while widening the subgrade especially on benches.

а) At one-sided widening of fills with account of the decrease in the slopes steepness up to 1:3 – 1:4 the width of the filled up lane is about 3m which allows leveling the soil by a bulldozer and compact it according to the shuttle method by any self-propelled compactor. The thickness of compacted layer is calculated taking into account the compression ratio not less than CR=1,00.

b) At double-sided widening the lane width can be up to 1m. In these cases there are two variants: 1) the width increases of 1,5-2m for providing the operation of road machines on benches and filled up layers.

Excess soil after filling are cut off for slop compaction or removed onto the neighboring section of widening; 2) increase the bench width by inset into the existing fill body in order to provide road machines operation at subgrade slope part layerwise filling off.

Widening of excavations is done significantly rear than fills and by the other technology (fig. 3.4).

Cuts of depth up to 2m are widened as a rule by bulldozer or excavator. After removal of the plant layer there are executed the works for side cavities filling up with layerwise soil compaction (see fills widening). Then slopes of excavation are developed for the design width with removal of soil into fill or bank and transported it by dump trucks onto the place of filling.

After that slope leveling is operated by bulldozer or leveler, form gutters by motor grader or trench digger and consolidate slopes if necessary.

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In cuts of deeper than 6m widening is made by excavator with backhoe dragline excavator placing them at the upper edge of excavation.

First of all the soil is removed from upper part of slops and loaded into motor drum trucks. Then there are developed slops in lower part placing excavators on widen subgrade sides.

Last time it is recommended to arrange strengthen tracks of triangular or rounded profile intended only for surface water drainage.

Fig. 3.4. Diagram of three – cornered shape trough for surface water drainage

Advantage of gutters in comparison with deep cavities or drainage trenches in excavations is the following: 1) in traffic safety increase; 2) their slopes are less washed away; 3) surface water does not practically stagnate, but they are planted with grass and they should be strengthened; 4) they are easier cleared mechanically.

While constructing subgrade attention is paid to drainage system, reconstruction or arrangement of new side trenches including water runoff from the subgrade onto the lower places or to drainage facilities, drainages for collecting ground water and lowering of its level; water drain trays etc.

3.5. The choice of soil for widening and its location in the subgrade body has especially great affect on the subgrade durability and fill slops stability during widening.

The experience of road reconstruction allows develop some requirements. Requirements for the soils on the places of widening:

–lay the new soils into fills by layers adhering their disposition giving them crossfall in the direction of the slopes in order to protect water stagnation on the surface of filled up layers (perched water);

–filter soils is to place on the upper part of subgrade and into slops which are more affected by weather. While placing filter soils into lower layers the layer thickness should be taken not less than the height of capillary raise for these soils;

–the level of compaction of filling up soils is to be less than the existing subgrade has;

–slops steepness is taken according to the requirements for traffic safety and road category;

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– if slops are filled up from sands then they are needed to be strengthened simultaneously with earthworks execution in order to protect slops washing away.

It is not recommended to apply large-block rocks, siltstones clay shales, marls and also oozy soils.

Filled part of widened subgrade should work mutually with existed one as the united system which is possible only at favorable water – thermal regime. Optimal decision is the application the same soils which were used at the subgrade construction. If it is possible it is necessary to widen fill only by sand nonpulverescent soils strictly following the rules of their location in the fill (fig. 3.5).

At embankments of 2m height symmetrically widening any soils can be applied because slop steepness is 1:3. At the height more than 2m only sand soils can be used. On dry sections (I type of moistening) there can be applied sandy-loam but not pulverescent soils with simultaneous slops strengthening.

If the territory belongs to II-III type of moistening the lower part of the widened lane sand soil is to be laid with coefficient of filtration of 1m per day and more and height of capillarity raise up to 35cm. In this case water delivering into working layer is limited. The layer can also be filled up from cohesive soil.

Fig. 3.5. Diagram of acceptable disposition of soils in fill body:

a) symmetrical widening; b) nonsymmetrical widening; c) softening of vertical alignment of road

1– cohesive soil; 2 – sand soil; 3 – removal plant soil; h – minimal thickness of sand layer; h ≥ hк (hк – height of water capillary raising); I – cross slop not less than 50 ‰.

On the sections with not provided surface runoff and also on the sections of III type of moistening the lower part on the lane of widening is to be filled form soils

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