Chapter 2; Roads

Introduction

The construction of roads can be defined as of preparing a hard surface for the travellers by overcoming any obstacles in the right of way, in consideration with state of law. The process of road construction starts with the design of road patterns best suited for residents with respect to their travel needs. The first step taken during the construction phase is removal of earth rocks by digging, before laying on the pavement and road building equipments materials.

Once the design and environmental and legal issued are approved/considered, the road alignments are finalized by the civil works team management; the design gradients and radii of the road are set to as per best fit methods with respect to the site ground levels. This activity ensures minimize cut and fill for civil works and enhances diver’s safety.

Roads are primary constructed for the use of motor vehicles and pedestrians. Therefore, rain storm drain systems along with other environmental impacts are considered as a major parameters in the road designs. Sediment, erosion and other control systems are built to neutralize detrimental-effects. Drain lines are constructed all the way along the road to assure storm water is collected safety at the nearest sewerage system. The Darin lines are built in road-easements with the joined seals to ensure smooth flow of water. This system needs approval by the local development authorities, to guarantee that the design flow is good enough for the actual drainage system.  

Road Construction Process

The following processes are taken during the construction of roads;

• Excavation
• Filling
• Compacting
• Construction

Roads are constructed of various layers of asphalt and aggregates. Excavation is carried out to remove low compact and unrequited material from the land / site, and the moisture content is balanced as per designed value. This is then compacted with standardized fill with relative compact percentage of 85-95. This process is completed by the compacted layer method, in which the fill layer is spread along the designated area and its is then compacted through heavy weight machinery. The fill – compaction process is undertaken until the desired specifications of the road are achieved. Following is an example of road material specification details, provided by the road construction agency in UK. The thickness of layers may vary depending on the specifications of the heavy traffic and native soil

Figure 1; Details of Material specifications with respect to layers  

The fill material used for the road construction is without any organic material and has the desired/designed stress bearing ratio and minimum plasticity index. The aggregate base mixtures is generally comprised of a mixture of sand and very fine gravel, which helps to maintain the bottom surface free from any organic matter growth such as plants and serve as lower stratum drainage.

The next layer fill is composed of broken rocks, gravel and /or sand clay of certain sizes as shown in the figure 1 above. The road-bed is rolled for each layer of fill, which compacts the fill and normalization the particulate distribution throughout the road.  

Various pavement layers are used to improve quality of the road. These pavement layers consist of geosynthetics which are of extreme importance with respect to improving quality of the roads. These geosynthetics help to increase the road/layer strengths, enhances reinforcement attributes, drainage and filtration. Therefore, pavement performance is optimized with respect to overall construction, decrease in costs and maintenance

The road final finishing is done by paving. The road surface is finalized after having considered factors such as expected usage and other economic factors.

Road pavement design criteria

This section provides technical details of a standard pavement design criteria for road constructions.  The design criteria can be set for twenty years of pavement life provided that the maintenance work is carried out to maintain the road surface after completion of the road. Equivalent Daily Load application and Design Traffic numbers are considered in the design calculation for the roads.  The following classifications can be considered as minimum limits for pavement sections during the design of the roads. Final designs should be based on real site test results for sub grade support

Table 1; Pavement design classifications

Excavation requirements

Moisture conditioned fill is put in to replace the expansive soil sub-grades. Expansive Soil sub excavation requirements are as follows;

Table 2; Excavation requirements