This case study discusses the possible causes of flexible pavement failures, and recommends Geocell for sub grade stabilization instead of conventional stabilization method.
Sub grade stabilization using Geocell resulted in minimization the causes of failures in flexible pavements.
IMPROVEMENT OF ASHAGAD UDHAVA KODAD ROAD BY USING TECHCELL GEOCELL
Techcell Geocell 350 X150, TechGeo Non-Woven Geotextile 200 gsm
Flexible pavement deflects under moving vehicular load. In general the service life period of flexible pavement is 10-15 yrs. However, increase in no of vehicles time to time has been undoubtedly deteriorating the serviceability of pavement structure. The effect of heavy vehicle moving loads is the critical causes of fatigue and rutting failure.
In addition to vehicle loading, Sub grade properties such as low bearing capacity result in depressions and settlement. It is found that water has got easy access into the pavement. It saturates the sub grade soil and thus lowers its bearing capacity, ultimately resulting in heavy depressions and settlement.
In the base course layers comprising of Water Bound Macadam (WBM), water lubricates the binding material and makes the mechanical interlock unstable. In the top bituminous surfacing, raveling, stripping and cracking develop due to water stagnation and its seepage into these layers. Also, Inadequate and poorly maintained cross fall of shoulder and drainage systems are causing failure. The main cause is blockage in drainage structure due to deposition of silt/waste, presence of excess grass.
Pavement need to carry large no of heavy moving loads over many years. Therefore, it is reasonable to adopt geo synthetics reinforced soil rather conventional solution which is chemically stabilizing soil. The utilization of cost effective material such as geo synthetics is important to achieve desired life of the pavement as well as to facilitate their faster construction. This type of pavement may save the engineers from day to day maintenance problems also.
After laying geotextile, laying of 25 mm bottom cushion of WMM.
The improvement of : Ashagad Udhava Kodad Road was done in 2016,after the monsoon in Aug 2017, it was observed that the road surface started damaging; the depressions and signs of distress can be seen in major area, which resulted in very bad riding quality and ultimately resulted in slow traffic movement on a busy state highway. Looking to the scenario PWD Dahanu has decided to go with some long term sustainable solution with some advance applications apart from the conventional one.
For providing the best sustainable solution, it was decided to visit the site with geotechnical experts and observe the road condition, after visual observation it is decided to check the conditions of the internal layer so pavement to know the severity of damage and cause of damage. The two locations were selected where the severe depressions were observed and trial pit was excavated, it was observed that the base, sub-base and sub grade settled and the reason of settlement was seems to be the weak foundation of the pavement.
After site visit and detailed observation it is concluded that the softening of sub base layer can be the main reason of failure under heavy axle loading which was not anticipated. Conventional methods of pavement/soil improvement were already tried and which proved ineffective, so it is very important to offer solution considering the life of pavement; anticipated growth in traffic and cost.
After a careful evaluation of the project requirements and site conditions, it was decided to remove the existing WMM layer and redone the WMM layer, given solution is that the WMM is to be removed and redone using Techcell and Geotextile. The proposed section is as follows.
The geotextile gives a tensioned member effect and will act as a separator to separate the mixing of the large base particles with the sub-base. This will also give effective load distribution.
Geotextile is act as best filter media and reduce the pumping of fines from sub grade to sub-base.
The upper base layer is subjected to hundreds of millions of repeated dynamic and cyclic loadings as well as elevated temperature and thermal cycling. Techcell have high dimensional stability to maintain long term confinement and compaction under asphalt.
In this project, the road width was 7.5 m which include 5.5m paved surface and 1 m unpaved shoulder on both sides. All the damaged layer of pavement till GSB top were removed and after profile correction it was well compacted, the geotextile is laid on full width of 7.5 m.
After laying geotextile, Techcell Geocell of 150 mm thick with a weld spacing of 350mm were laid in full width of 7.5m over the 25mm cushion layer above GSB (covered with geotextile). Since the thickness of WMM was 200 mm a cushioning of 25 mm both on top and bottom was provided.
The shoulders did not have asphaltic course and remained unpaved, it is necessary to be confined. This improved shoulder will not sink due to any occasional vehicle movement or due to parking of heavy vehicles over it.
The road was completed by contractor before monsoon (Feb 2018) and presently the road is in excellent condition with good riding quality and Department officials are happy and satisfied with the performance of TechCell.