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Effect of drainage on pavement performance

Research has shown that water found in the pavement system can result to moisture damage, strength loss and modulas reduction. It is evident that the strategies taken by various state agencies concentrate only on preventing water from going into the pavement by provision of adequate drainage for quick removal. At the same time, another aspect remains building of a strong pavement for resistance of combined impact of vehicle loads as well as water, thus reduction of detrimental water effects on the pavements. In most cases, the past drainage design is based on the concept that water flow through pavements as well as pavement drainage is represented with flooded flow assumptions.

On the other hand, full pavement systems saturation occur s under very precise circumstances, in a situation that positive total heads remain present such as surface ponding, and distribution in such a manner ,which reduces pavement system saturation. These harmful effects can be reduced by ensuring prevention of water from going into the pavement as well as provision of adequate drainage to eliminate infiltration. Another strategy is the building of strong pavement to resist water or load combined effect .The service life of the pavement cab be increased to 50% when infiltrated water is drained with no delay. Equally, pavement systems integrating good drainage are projected to have a design life twice that of pavement without drainage sections (Battaglia, 198). Pavement systems full of water are one of the major causes of premature pavement malfunction. A country such as Indian road network with over 3.3 million km remains one of the longest networks of roads in the world. Majority of the highways in the country have slow draining systems because of standard design initiative insist on density as well as stability with little significance on subsurface drainage. The poorly sub-surface drainage associated with such roads results to extensive costly repairs and replacements before attaining their design life. It is evident that subsurface drainage remains a major element in terms of pavement system designs. Unsystematic exclusion of the aspect leads to premature pavement system failure, therefore leading to high costs of lifecycle.

Excessive content of water in the pavement base can result to early distress, which results to structural and functional pavement failure if counter actions are not undertaken. Damages related to water can result to various forms of deteriorations. These are sub-grade as well as base strength reduction, expansive sub-grade soils disparity swelling, asphalt stripping in flexible pavements and fine particles movement into base and sub-base course materials from hydraulic conductivity reduction (Fleckenstein, David and Jack,300). Appropriate surface drainage can decrease the amount of water penetrating through the pavement, which is a strategy that operates in hand with suitable subsurface drainage. A large amount of free water enter the pavement from joints, cracks as well as pores in pavement surface. Water also enters the pavement system from the back up ditches as well as groundwater sources. A proper drainage often prevents free water buildup in the pavement section, therefore reducing the detrimental effects of load or environment. Studies show that proper subsurface systems of drainage can be extended three times in case they are installed and properly maintained.

Subsurface Drainage

The destructive effects of excess moisture on pavement remain a contentious issue for a long time. The moisture comes from various sources and goes into the pavement structure. Moisture found in the sub-grade as well as pavement structure comes from various different sources. Water might leak upward from a water table that is in a high ground or it might flow across the pavement edges. The understanding of ground water as well as is movement remains critical for pavement performance together with adjacent side slopes stability. It is evident that groundwater can be predominantly troublesome in relation to pavements found in low-lying regions. Pavements that are built below the permanent, temporary high water table and drainage systems have to perform or pavement failure might easily occur (Schaefer, 345). The moisture combined with pavement sections voids, freezing temperatures, and traffic loads have negative effect on material properties as well as pavement system overall performance.

The most noteworthy excess water source in pavements is normally surface infiltration by joints, cracks as well as other surface defects, which offers an easy water path. The problem often worsens with time with aging of pavements, deterioration ,wide cracks and joints as well as edges weaken into channels which water flow freely (Fleckenstein, David and Jack,450)). The result is a lot of water allowed in pavement structures result to hasten development of moisture-linked distresses together with pavement deterioration. Extensive excess moisture structure often has an impact on pavement performance. Although, pavement structure is stable at a specific moisture contents, the structure of the pavement becomes unstable when the materials are saturated. This is because high water pressure tends to develop because of traffic loads as Water found in the pavement structure freezes and then expand, which results to high internal pressures mostly on the pavement structure. At the same time, flowing water often carries soil particles, which results to drains clogging and traffic.

Sub-drainage options often differ in complexity and cost because of the provision of open-graded layers of drainage layers, which are tied into longitudinal edge drains as well as other outlet pipes to day lighting graded bases that are dense. A base system that is permeable remains the complete alternative to a subsurface drainage because of the incorporation of majority of the drainage-linked components. There is an advantage of the creation of a drainage layer design that is not easily saturated, which satisfies certain conditions. The first one is the provision of adequate permeability, which help in the transmission of all the water that has penetrated during the rainy season and completely saturated flow setting. The other one is the limitation of the time the drainage layer becomes entirely saturated to a short duration like a few hours or immediately after the rain. Another element is provision of sufficient structural stability to sustain pavement construction as well as traffic load.

The decision on the inclusion of sub-surface drainage gives little doubt on the negative water impact on pavement systems. There is substantial anecdotal as well as experimental evidence, which justifies that a proper sub-surface drainage increase the pavements life expectancy. Many researchers emphasize that sub-surface drainage comes with many benefits and associated with intricacy and pavement construction costs. It is obvious that decision-making methodology and criteria in relation to sub-surface drainage tends to vary with each agency (Schaefer, 567). Results shows that sub-surface drainage has been used by different agencies in America even though the drainage decision criteria used are actually not consistent among the agencies. For instance, some agencies like California often include drainage underneath concrete pavements. On the other hand, other agencies concentrate mostly on the predictable traffic load with the heavier the load of traffic load, the greater the apparent necessity for sub-surface drainage.

Design Life

A good design requires a good understanding on water flow on the pavement subsurface to enable appropriate drainage systems. An evaluation of excess moisture mostly in the pavement system, needs a pavement drainage system materials that have sufficient permeability. Research has shown that a lot of money can be saved yearly by designing as well as building pavements, which have excellent pavement drainage together with sub drainage characteristics. Nevertheless, the right understanding of the aspects that mainly influence water flow in pavements is necessary for the realization of these savings. Presently, FHWA promotes the usage of free draining materials during the construction in the base and sub-base. AASHTO pavement design model indicates that pavement performance is greatly enhanced when free draining supplies are used in the construction of the base and sub-base. The impact of excess moisture together with the time length retained in the pavement system is s in AASHTO Guide, which talks about pavement design. It has precise structural pavements requirements, which becomes weak because f of moisture effects. The degree of these structural elements is directly linked to the time length the moisture remains retained in the pavement structure. It is evident that they use both new pavements designs and the existing ones. Pavement need a proper drainage characteristics as the structural pavement section should not overflow with excess water .The pavements should not carry weighty wheel loads when there is surplus moisture beneath the pavement. This means there is a need for a good drainage system, which ensures quick flow of water out of the pavement.

Removal of Free Moisture

The usage of subsurface drainage helps in designing of proper pavement drainage, as the designer need to take into consideration three drainage systems types. These are surface drainage, groundwater drainage, together with subsurface drainage. It is evident that such systems, nevertheless, are effective in relation to “free water, which is held by forces of capillary in soils and fine aggregates, which be cannot be drained. The three drainage forms share relationship viewed as symbiotic relationship and need to be considered together in general drainage project design. The usage of subsurface drainage seems to have gained popularity in the past two decades, with many agencies routinely using permeable pavement structures in reduction of moisture-linked pavements challenges.

Design considerations in moisture combat

There are various measures, which need to be undertaken to ensure the designed pavement are flexible in combating moisture. The prevention of moisture penetrating the pavement system is because of poorly constructed pavement systems. Theoretically, the best move in reduction of detrimental effects in relation to moisture for retention of moisture penetrating the pavement design. An efficient method for reducing surface infiltration is provision of sufficient cross-slopes as well as longitudinal slopes for quick drain water on the pavement surface. This means the less time moisture stays on the pavement surface the chances for moisture infiltrating the joints and cracks are limited. Nevertheless, moisture tends to percolate the pavement system from different sources with nothing to prevent the situation. A proper design is helpful in minimization of moisture amount penetrating the pavement system (Salem, Sam, and Mohammad, 307). This involve the provision of materials that are moisture insensitive with another method being accelerating damage by usage of moisture insensitive and non erodible base materials ,which are less impacted by the harmful moisture effects.

However, even though some materials reduce and delay the harmful moisture effects, moisture-insensitive supplies by themselves, they might not completely, address moisture-related challenges in pavements, which are heavily loaded. The materials used in reduction of moisture-linked damages are cement-treated base. At the same time, conventional testing of strength for durability requires such materials to be checked for moisture erosion resistance. In addition, combined sub-base is recommended for prevention of pumping as well of loss of fines under the treated base in areas, which have unfavorable site conditions. This involves high design traffic, wet climates together with high pumpable fines amounts in the sub-grade. Other materials that can be used are open graded base, granular materials and a high quantity of crushed supplies, low content of fines and low plasticity, which can be used to aid in resistance of moisture effects. The open-graded materials offer better resistance in relation to moisture impacts compared to densely graded materials, which have high content of fines (Huang, 309). Open-graded materials permit easier moisture movement through the material as the layer remains saturated for a short period. Fine reduction mean means less material, which can easily be ejected by joints and cracks. Nevertheless, stability of untreated base layers, which are permeable, remains a big concern because of settlement that result to serious challenges and requires to be addressed sufficiently.

Highway Drainage System

In most instances, the drainage system of highways is classified into various categories such as Surface drainage, surface drainage, Sub-surface drainage and Cross Drainage Works

Surface drainage

In surface drainage, there is removal as well as water removal and surface water diversion from roadway as well as adjoining land. The process involves the collection and disposal of surface water, which is first collected in drains that are longitudinal drains mostly side drains and later disposed off to the nearest stream, watercourse, and valley. There is a need for Cross drainage construction such as culverts as well as small bridges, which are necessary for surface water disposal drains found on the roadsides. The drainage mainly deals with quick arrangement and effective leading waterways, which collects water on pavement surfaces, shoulders, embankments slopes, cuts, as well as land adjacent to the highway. The collected water is often led to channels, which are natural and artificial channel in that they is no interference with appropriate highway functioning such as slopes, embankment, pavement structures, shoulders and medians.

Sub-surface drainage

Diversion and removal of excess water from mainly in the sub-grade is called sub-surface drainage. The change sin sub grade moisture content are as a result of ground water table fluctuations ,seepage flow, rain water percolation capillary water movement and water vapor. Sub-surface highway drainage attempts to ensure a minimum moisture variation in the sub-grade soil. A research carried out on sub surface drainage remains a vital element in pavement design Optimum pavement system performance can be attained by ensuring water is prevented from percolating by a properly designed subsurface system of drainage (Salem, Sam, and Mohammad,487). Majority of the highway as well as airfield pavements constructed in the past 30 years have slow drainage system as a result of standard design practices, which stresses on density together with stability, and little importance on sub surface drainage.

Cross drainage

Cross drainage is often vital in a situation whereby a highway tends to cross a river, which necessitates the provision of cross drainage works .At times, water coming from side drains is diverted from the road using cross drains. In highways usually, usually culverts together with bridges are applied, as 6meters cross-waterway as the cross drainage makeup are known as culverts. In case of higher discharge as well as greater linear way, the constructed structure is called a bridge

Pavement drainage criteria

There are two diverse approaches, which are naturally considered in hydraulic pavement system designs of pavement system in relation to saturated flow, steady-state flow, and time-to-drain settings. Nevertheless, complexity in design estimation of the rainfall rate as well as rainfall portion, which percolates the pavements, makes steady state application analyses tedious in most circumstances (Huang, 201).Consequently; many engineers these days favor the time to-drain notion. The approach is founded on water flow penetrating the pavement with the aggregate base course becoming saturated. At the same time, Excess runoff does not enter the pavement fragment after saturation as water runs off on the surface of the pavement. The precipitation event results to the drain of the base to a drainage system because of different levels of drainage levels in relation to a pavement structure by AASHTO, for around 50% of the total drainage. The approach tends to drain around 50 percent of the total water, which is drained, while it does not take into consideration water retained by efficient porosity material quality.

There is a need for incorporation of designs with features, which reduces moisture damage, apart from moisture insensitive supplies, some other design aspects can be minimized in relation to moisture damage (Battaglia, 234). Conventional together with deep-strength pavements can make use of design options such as full-width paving in lane elimination. This is a major water infiltration source in majority of pavement structures. The usage of granular layer sandwiched between the sub-grade as well as base course tends to reduce the rate of erosion, permit bottom seepage, which reduces frost susceptibility, and increase the roughness of the pavement roughness. There is also a need for enough side ditches, which have flow lines under the pavement structure.

Conclusion

Drainage remains a major element in pavement system design; however, unsuitable drainage results to major pavement distress This is because of extensive amount of costly repairs as well as replacements before they reach their maximum designed life. There is a need for prevention of moisture to penetrate the pavement system with a key objective being keeping the sub grade, base, sub-base, as well other vulnerable paving materials from being saturated and even exposed to continuous high moisture degrees over time. There are four approaches mainly employed to reduce and control moisture such as prevention of moisture from penetrating the pavement system. Usage of materials considered insensitive tends to affect the content of the moisture and incorporate design features in minimization of moisture damage. Quick removal of moisture, which enters the pavement drainage system, is another important aspect. It is vital to recognize that no move can completely counteract the moisture impacts on the pavement system, which experiences heavy traffic loads continuously for many years. Consequently, it is often indispensable to employ integration of different approaches mostly for heavy traffic loading setting. There is a critical need to learn the drainage quality effects on performance of pavement and quantify the advantages of a properly drained system in relation to poor drainage system.

Works Cited

Battaglia, Irene K. Evaluation of Concrete Inlay for Continuously Reinforced Concrete Pavement Rehabilitation. Madison, WI: Wisconsin Dept. of Transportation, Division of Transportation System Development, Bureau of Technical Services, Materials Management Section, Foundation and Pavements Engineering Unit, 2010. Internet resource.Fleckenstein, L J, David L. Allen, and Jack A. Harison. Evaluation of Pavement Edge Drains and the Effect on Pavement Performance. Lexington, Ky: Kentucky Transportation Center, College of Engineering, University of Kentucky, 1994. Print.

Huang, Baoshan. Paving Materials and Pavement Analysis: Proceedings of the 2010 Geoshanghai International Conference, June 3-5, 2010, Shanghai, China. Reston, Va: American Society of Civil Engineers, 2010. Internet resource.Salem, Sam, and Mohammad Najafi. Use of Trenchless Technologies for a Comprehensive Asset Management of Culverts and Drainage Structures. Madison, WI: Midwest Regional University Transportation Center, College of Engineering, Dept. of Civil and Environmental Engineering, University of Wisconsin, Madison, 2008. Print.

Schaefer, Vernon R. Design Guide for Improved Quality of Roadway Subgrades and Subbases. Ames, Iowa: Center for Transportation Research and Education, Iowa State University, 2008. Print.