Question

Explain the process for establishing the line and grade for a sanitary sewer line connection to an existing municipal sanitary manhole. Include the type of sewer flow, the importance of the pipe invert and reach of the sewer in determining the slope of the pipe, factors that determine the use of manholes, the use of batter boards and offset stakes, minimum ground cover required. In addition, discuss the use of visual aid such as field notes and a simple plan and profile drawing in establishing the line and grade.

Answer 1

Following are the main points which are useful in establishing the line and grade of a sanitary sewer line

1. Depending upon the population of the area , soil properties , slope , material involved etc. the shape of sewer section is empolyed whether circular, oval , trapezoidal etc..

2. Laying down of sewer is done according to the natural or artificial gradient to avoid clogging. and it should be laid at suitable underground depth.

3.for the purpose of extension of new sewer line , it should be well designed that this new sewer line will not create nuisance to the exsisting sewer line in terms of load and waste.

4.after the designing of new sewer line , it should be approved and analysed by the goverment body before the execution of work.

5.Nextly . pipes are laid in straight line preferaly with the provision of manholes at suitable distance for regular checkup.

6.Depending upon the type of sewer flow:- a. Entrance flow - It is defined as the downstream control of pipe flow.

b. Pipe flow - Defined with upstream control flow.

c. Exit flow - concerned with type of flow such as critical, sub- critical etc.

7. Downstream invert- A minimum of 0.1 inch drop from invert to invert across manholes is required.Wherever there is change in diameters or gradient change , the downstream invert shall be lowered so that the crown of sewer should aligned.

8.Use of batter boards and offset stakes - Batter boards are wooden planks / formworks used for temprorary work of suspending the layout work of foundation for maintaining the accuracy as per the design. After the construction is done they are removed .

9. Ground cover requirement :- Generally the sewer lines are laid undergroung at suitable distance to avoid from breakage, freezing, day to day load etc.So a minimum cover of 3 inch or as per the manufacturer design which one is greater should be adopted.