Demarcation is completed by marking the two edges of the drain and the excavation (digging) is started.
To check the depth during excavation (digging) the following two methods are used: METHOD I- SIGHT RAIL TRAVELLER METHOD METHOD II- VERTICAL POSTS WITH SPECIAL TRAVELLER METHOD 1.SIGHT RAIL TRAVELLER:
1)After the pegs are drawn, the next step is to erect the sight rails.
2)The sight rails are erected at each man-hole and inspection chamber.
3)If the length of the drain is over 10 meters, an intermediate rail is set up at mid point.
4)The intermediate rail helps in seeing the length providing a check
5)The rail is straddled (both sides) on the centre line of the trench (channel).
6)The height of the sight rail is determined by the level transferred on the brick pillar at the base of site rail. METHOD II-VERTICAL POSTS WITH SPECIAL TRAVELLER METHOD: 1)Vertical posts are erected at about 5 To 10 meters apart from one side of the drain.
2)Level Burjhis are fixed at the base of alternate posts.
3)A nail is fixed at the desired height on the vertical post.
4)A nylon or cotton thread is stretched over the nails.
5)A specially made traveler with an inbuilt spirit level is used to check the depth of excavated trench for laying the pipe.
|