Tips for Grading a Culvert through Motor Graders

• By: Admin
• POSTED ON: January 18, 2018

A cutting or a closed conduit which lets the water flow (from one area to another which is usually from one side of the road to other) under a road is called a culvert. A culvert is constructed either for cross-ditch relief or to allow the road to cross a natural stream or drainage area.

Generally, culverts are built at the time of the new road construction and take the form of one or more pipes or other conduits. They are fully embedded in the soil below the road bed. With the right attachments, motor graders can play a very important role in constructing, repairing and unblocking culverts.

In order to keep the road safe and in usable condition for a longer period of time, both culverts and ditches play an important role. In fact, without them, the road surface may be damaged due to even fairly small or seasonal flows of water. Further, it is seen that the water which is gathered on the road as a pool can hamper the vehicular traffic and lead to vehicle tires losing their grip on the road surface. This can result in major accidents as the potentially dangerous potholes or obstructions may be hidden due to the pooled water on road. Culverts help in avoiding such a situation.

If the culverts are placed strategically along with the road ditch turn-outs, then they can help in maintaining a stable velocity and the proper flow capacity for the road ditches by timely outleting water from them. This can greatly reduce the need for road maintenance by not allowing roadway flooding and reducing erosion. What more? By letting the water drain from the ditches along the road and keeping the sub-base dry, culverts preserve the road base to a very large extent.

As per the experts, in order to ease the water problem on roads and be effective, appropriate sized culverts should be built. This generally depends on the quantity of water that the culvert may have to drain. In addition, it is to be noted that the culvert should be laid in a correct position and the surrounding slopes and drainage area should be graded and reinforced.

Grading a right culvert through a motor grader is not an easy task and it requires good amount of pre-planning. In fact, for building a large culvert or a culvert for a major road, it is necessary to do proper site analysis and engineering. While grading a culvert is a complex process, here are some general tips for smaller culverts (generally required on forest and other dirt roads) construction and grading...

1. Typically, bed of gravel or soil should be laid such that it is at least one-quarter the diameter of the culvert pipe. It should be seen that the bed and fill material should be free of large rocks.

2. It should be taken care of that the bed should not be below the water runoff channel. In fact, if the culvert is positioned too low, then it is more likely to accumulate soil and get blocked.

3. Corrugated metal pipe should not be laid directly onto the rock as it does not have the required flexibility and can often damage the centre of the pipe which generally takes the maximum load. Concrete pipe should be used when there is no other option.

4. In the centre of the pipe, a camber should be incorporated to protect it from the pressure exerted by a fill or embankment.

5. In order to prevent soil and other debris from getting accumulated, the culvert should be sloped using about 3 per cent grade. Here, it should be kept in mind that such a grade should be used that does not change the speed of the water’s natural flow significantly.

6. The culvert should be positioned at the same grade as the ditch to be drained if the culvert would be used for drain relief purposes.

7. The culverts used for ditch relief should not be skewed more than 45 degrees to the centre line of the road. This is to ensure that the water is not forced too far off its natural course.

8. For corrugated metal pipe, the culvert should be covered with soil to a depth of at least 30 centimetres and minimum 60 centimetres for concrete pipe or a minimum of one-third of the pipe diameter for large culverts.

Motor graders are not only used to grade a culvert but they can be even used for reopening a blocked culvert. Typically, motor graders with crab steer attachment can be used for this purpose.

Below is the step by step process for doing so...

1. The grader’s front wheel should be positioned in the ditch on the side of the blockage. Here, it should be noted that the bottom of the ditch should be solid for this.

2. Then the rear frame of the grader should be kept on the road surface.

3. As the next step, the leading edge of the moldboard square should be turned to the mainframe and it should be angled at approximately two-thirds of the maximum forward tip.

4. The moldboard should be shifted to the side and the blade’s cutting edge should be extended into the ditch. Care should be taken for not damaging the culvert. After this, the angle of the blade should be set according to the culvert’s shoulder slope.

5. After following the above mentioned steps, you need to gradually move forward to remove the blockages. Later on the blade should be rotated to pull the material up onto the side of the road. In order to reach the bottom surface of the culvert, you may have to make multiple passes.

Overall, if you follow the tips stated above, then you can easily grade a culvert or open a blocked one through efficient motor graders manufactured by Mahindra Construction Equipment.