Abstract
A dual carriageway is proposed to be constructed in the town moving in the east-west direction. The dual carriage is intended to be eight-kilometer long looping around the northern part of the town. Cut and fill techniques are used where half of the road is cut to a maximum of six meters. Half of the road is supported by an embankment of six meters high. At the eastern and western ends of the road are of grade where the road joins other roads and at the middle where the cut sections meet the filled sections. The road has a four-meter depth clay underlain by sand. Under the road, groundwater pass under the profile.
Introduction
The project is purposed to create an eight kilometer running through the town. The road joins other roads in the western and eastern parts of the city. The dual carriage road loops at the north of the town, the town has funded the project to improve the connectivity inside the town and ease traffic congestion in the city. The project describes the earthworks that finalize on the entire construction process. Design guidance, specifications, and legislations are parts of the development process. Construction elements like compaction technology, geotechnics, and interpretation of data, stabilization, and materials for treatment are prerequisites prescribed in this project.
In the project, a proper construction of the road is refined to avoid damage to the roads through side erosion, the formation of potholes, as well as breakage of shielding apertures on the side of the road. The major earthwork practices employed in the project are excavation, deposition and spreading, and compaction (Lebo & Schelling, 2001). Earth moving machines such as excavators, bulldozers, rollers, among others. In this paper, substantial parameters that specify the earthworks required in the construction of roads are discussed. How the soil that naturally exists at the site of construction is used in the construction is discussed.
Parameters that specify the earthworks required in the construction of roads
Prior to the construction of the road, the design information is translated from plan form to a real ground implementation. Staking is the activity that implements plans to real work. Stakes ensure compliance with designed specifications and keep soil disturbance minimum. Stakes mark a variety of road design points. They are used by machine operators to locate places where cutting start. If the point is too high, then a considerably more cutting of material is done. In road construction, parameters are used to specify essential earthworks needed. Assessed earthwork parameters in road construction are cuts and fills, the size of the area of cut sloping, take-up area, fill sloping, drainage, the width of the road, utilities, pavements, shoulders, curbs, pedestrian facilities as well as cubature units of cutting (Pritchard, 1992).
Specifications, plans as well as standard sheets provide requirement parameters used in road construction. The parameters provide the guide describing the technical earthworks required in the construction of roads and embankments. Before the construction of roads, geotechnical design reports including drawings, are submitted to the department concerned for approval. In these reports, justification of the parameters and the earthwork methods to be adopted are stated. Alongside the parameters, design calculations, and design work progress are explained.
Roadside controls involve use of cut and fill slopes. Fills are constructed with a gradient less than 2 H: 1 V in curved sections, in shoulder sections, the slope must not exceed 4 H: 1 V. flatter slopes are recommended and are needed if the earth is prone to sliding, erosion, and sloughing. The fills are constructed using the appropriate materials, compacted using construction machines to create stability. Hydroseeding and grass sod can be used to impact a more stable earth in the slopes. Other planting materials or surfacing vegetation such as grass can be planted to prevent erosion. Slopes that are higher than fifteen feet are terraced with five-foot wide bench in every fifteen feet vertical height slope for proper drainage.
Stabilization of slopes is done through cutting and filling earthworks. The earth material that is cut matches roughly to the amount of fill required to create embankments or level ground. In cutting and filling processes, if the point to be cut is too high, then more material is removed to create a proper subgrade. Cutting the material at the right point is significant. Use of reference points for the correct excavation is done as shown in figure 1 below. An engineer assesses the primary centerline and sights for the reference point. If the starting point of the cut is high, excess excavation, as well as side cast, occur. On the other hand, cutting it too low leaves overstepped cut banks. Figure 1 below shows the cross-sectional view of a properly cut and filled road design.
Figure 1. Cutting and filling in road construction.
Utilities are significant factors, parameters rather in the construction of roads. For instance, the purpose of the right-of-way is to enable both the vehicular and the non-motorized passage. Use of right-of-way is planned to avoid interference on the road of traffic. Industry accepted rules provide for the general location and building of the utilities to reduce conflicts between the use of roads right-of-way for the vehicular and the non-motorized passage as well as the secondary purpose of offering space for these utilities. Public and private utility constructions conform to the requirements of the law (Kézdi, Rétháti & Héjj, 1988).
Road engineers guide earthwork personnel to coordinate all the utilities to ensure that the utilities are installed to the standards. They are installed such that they do not constrain with sight, traffic signs and signals, and other roadway features. The utility poles are restricted within roadway shoulders, buffers, sidewalk areas without the approval of the engineer.
Materials for paving and sub-grading must adhere to standard drawings; the material is based on the pavement design from the engineer in charge. The supporting design criteria and calculations are submitted to scrutinize the design. In aerial road pavement designs, the performance must remain for the next twenty years. Design standards are used to determine the paving, subgrade depths, as well as the material for road section. A falling weight deflectometer, a non-destructive analysis, or modulus value constructed by the geotechnical engineer is used to find the characteristics of the material on the existing earth for the design of the pavement.
Lane width is a significant parameter in the road construction. Unless stated otherwise, the widths conform to particular standards. For instance, intersection departure lanes are designed with adequate width to enable sufficient accommodation of vehicle tracking paths. In intersections along arterials, the legs with single departure lanes have a minimum width of fifteen feet from the departure lane, and taper to normal lane width over a distance of one hundred feet on the arterials and fifty feet on the local roadways. Intersections where either a double left or a right turn lane is to be constructed, departure lanes with the turning movements are flared or even widened to ensure consistency of the tracking requirements of the vehicle.
Shoulders are provided consistently with the directives of the Engineer-in-charge. Shoulders are very significant parameters with considerable advantages. One, provide space for motorists for emergency stops off the traveling way. They enhance safety, create sight distance as well as roadway capacity. Two, provide clearance from ditches, ground utilities, roadside obstacles, and signs. Three, maintenance operations, space for bicycles and pedestrians, space for encroachment of motorists like mail delivery motorists. Particularly, shoulders are significant in rural roadways and where curbs, gutters, and sidewalks are not installed.
Pedestrian facilities are significant parameters that must be considered during road earthworks. Sidewalks and shared-use pathways, when used should conform to the design parameters and the directions of the road engineer. Systems for storm drain percolation are not permitted in the sideways. The facilities are provided in urban areas in newly constructed and reconstructed roads. The shared-use pathways are constructed to comply with the adopted urban plan. Shared-use paths are either located within the road region or separated from the road using a buffer, or constructed completely outside the roadway.
Clear areas is another important feature on roads. Before implementing the actual earthwork at the site of road construction, clear areas must be considered. The constructors must understand the extensive tables of the recommended clear area distances. In low volume roads, there are rare instances of accidents thus the cost of constructing clear areas is saved. The provision of these clear areas is importantly purposed for safety purposes.
How soil from the section of cut could be reused to construct the embankment
All the materials used to construct road embankments; road fills, subgrades as well as sub-bases are obtained from the earth. These materials are natural, that is, they result from geologic processes. These materials include soil and rock. The soil is defined as sediments and unconsolidated accumulations produced by both physical disintegration and chemical reactions of the rocks. The soil is the essential material used in the construction site in an un-indurated form. Rocks and soil are aggregated by excavation, crushing, screening, and blasting in construction sites. The aggregates are said to be natural aggregates as both the chemical and mineralogical compositions are not altered. In the construction of highways, embankments, in particular, the use of the natural aggregates is extensively employed (Hearn, 2011).
Natural materials that make up soils are; boulders, gravel, sand, silt, clay, colloid and organic matter. To improve the bearing capacity of these soils, preliminary treatments are paramount. In areas with massive rock formation, leveling of the ground must be done. The soil is often loose and non-cohesive thus it requires earthworks before the base course, surface course, as well as binder course, are laid. Compaction is important earthwork that is intended to reduce the space between the particles giving the soil the desired properties. The compacted soil is resistant to stresses impacted by climate and vehicles on the road.
Stabilization of soil in embankment is a paramount practice during road constructions, whether they’re local or major roads, highways, the soil stabilization is conditioned in structural layers to carry traffic loads. Stable base of road embankments means that the entire mass is laid on a strong foundation. In modern construction techniques in road construction, soil is stabilized using chemical means. Although the practice dates back to the ancient times when the Roman roads were constructed using volcanic ash treated weak soils, today's techniques use hydrated lime treated clay (Neufert et al., 2011).
In the construction of embankments, soil is important in creating the foundation of the entire mass. The type of soil and mineralogy are fundamental factors that determine the binder used during the stabilization. Stabilization agents in the construction include quicklime and combination of Portland cement and hydrated lime. Fly ash and the cement kiln dust are used if courser materials are used. During this practice, hydraulic soil binders are spread onto the soil surface in the form of dry powder. The binders are distributed in slurry form in dust application. Mixing of the agents and pulverization follow the spreading process. The mixture is compacted immediately before the moisture of the treated soil evaporates. Grading of the treated layer is done to ensure the correct thickness and smoothness is attained.
Soil from the site is mixed with the binder in the presence of water, chemical reactions in the form of cationic exchange, agglomeration, as well as pozzolanic reactions. The agglomeration of particles of the host soil leads to effective grain sizes. The pozzolanic reaction leads to cementitious materials. These processes in the stabilization of soil in embankment construction are time dependent. They can continue for a considerably long period.
Rocks that cannot be excavated without blasting without blasting from the site are removed trough excavation. These materials consist of all borders and other detached stone of about half- cubic yards and more. The large voids between the rock fills are replaced with fines to avoid deformation within the embankment. To construct a strong embankment, rocks are distributed all over the area to avoid pockets. Possible voids are filled with small sized stones. Suitable material placed in layers eight-feet in depth is required to construct the final two-feet of the embankment below the subgrade. Shale and constituent element are avoided in the last two feet of the embankment. Rocks are deposited in lifts where the embankment depth is greater than five feet, and the entire mass is rocks. When the embankment is constructed with rocks that have large top size, the rock is compacted with a crawler-tread machine or a vibratory equipment.
Embankments constricted on hilly, and sloping grounds are prone to sliding and erosion. Before the embankment is placed on such grounds or slopes steeper than 4:1, benches ten feet wide are cut prior the placement of the fill. The field is plowed and scarified as well. If the site of placement is an existing roadway, precaution must be followed. One, if the new embankment is to be placed where the pavement surface of the former is more than a foot below the subgrade, the existing pavement should be removed. Two, if the new pavement is to be built on an area of hot mix asphalt, surface, the road surface must be removed.
Conclusion
Modern techniques and technologies are used in the construction of roads in both urban and rural areas. In towns and cities, for instance, the rate of urbanization is rapid. Traffic congestion, as well as overcrowding of pedestrians on urban roads, is a major challenge brought by urbanization. To correct these, urban councils and governments are constructing dual carriage roads, bypasses, flyovers as well as linking roads to avoid traffic jams and accidents on the road. This road are built in places that have existing roads by scraping off the old ones and replacing them with new ones. Other roads are built in virgin place thus more work is put on the ground. Construction of new infrastructure is intended to meet economies with the current state of globalization.
References
Hearn, G. J. (2011). Slope Engineering for mountain roads. London, Geological Society.
Kézdi, A., Rétháti, L., & Héjj, H. (1988). Soil mechanics of earthworks, foundations, and highway engineering. Available at: http://public.eblib.com/choice/publicfullrecord.aspx?p=1838063. [Retrieved on 29th April 29, 2016]
Lebo, J., & Schelling, D. (2001). Design and appraisal of rural transport infrastructure: ensuring basic access for rural communities. Washington, DC, World Bank.
Neufert, E., Neufert, P., Baiche, B., & Walliman, N. (2011). Architects' data. Oxford, Wiley-Blackwell.
Pritchard, B. (1992). Bridge design for economy and durability: concepts for new, strengthened and replacement bridges. London, Thomas Telford.
