Calculation of Invert Levels

Calculation of Invert Levels© Copyright FENC ....... 8 Calculation of Invert Levels © Copyright FENC Page 2 ............................................................................................................ 5 Calculation of Invert Levels....................... 7 Calculation of Invert Levels................................................................................................ 6 Calculation of Invert Levels..................................Table of Contents Calculation of Invert Levels................... 3 Calculation of Invert Levels.............. By calculation. Remove the inspection chamber cover on either side of the proposed connection. The local authority may be able to provide the information. then you will need to carry out the following procedure. Measure the distance between the inspection chambers and make a note of the distance to each inspection chamber from the proposed connection. By excavating vertically down to expose the drain or sewer. take a reading of the invert level in each inspection chamber and note the difference in levels. If the local authority is unable to provide the necessary information and it would not be convenient to excavate – then you must establish the invert level by calculation. The invert level is arrived at by one of three methods.Calculation of Invert Levels Before any pipes are laid. Calculate the invert level of the sewer at the point where you are to make your connection. Calculation of Invert Levels © Copyright FENC Page 3 . it is necessary to know the invert level of the drain or sewer to which the connection is to be made and to relate this to the ground level at which pipelaying is to begin. Example If you need to make a connection to the main sewer. Calculation of Invert Levels © Copyright FENC Page 4 . You now need to calculate the fall from inspection chamber (B) to our new connection. Calculation of Invert Levels © Copyright FENC Page 5 .The drawings above show details of the existing sewer and the proposed drain connection – if the distance between the inspection chambers A and B is 30 metres and the difference in invert levels at these chambers is 1 metre – then it follows that the existing sewer is laid to a fall of 1 : 30. Thus the fall from chamber (B) to the proposed connection is 0. NOTE: Calculation of Invert Levels © Copyright FENC Page 6 .6 metres. Since the staff reading at chamber (B) = 1.6 metres.6 metres = 2.2 metres WHICH IS DEPTH AT (B) + FALL Longitudinal Section of New Connection Calculation of Invert Levels © Copyright FENC Page 7 . the depth to invert of the sewer at the proposed connection is: 1.6 metres + 0. 2 metres = 0. the ground level staff reading at the proposed connection is 0.9 m so the depth of the invert level below ground level = 2.7 metres – 2.6 metres below ground level.5 metres thus the fall is 1 : 36. to find out if the fall of the new drain is satisfactory.Now.6 metres below ground level.4 metres respectively.9 = 1. NOTE: 0. Assume that the invert level of the new chamber is 0. it is necessary to relate the measurement to the invert level of the new chamber at the dwelling. which is satisfactory for a 100 mm drain. Having found this. these being 1.3 m.2 – 0. the fall from invert level at (X) to invert level at (Y) is: 2.6 metres and 1.5 metres in 18 metres = 1 in 36 Calculation of Invert Levels © Copyright FENC Page 8 . Since the invert level at (X) is 0. Set up the engineer's level and take readings at (Y) and (X).