Masons Training Programme Session 3 Introduction and Design

Mason’s Training Programme Session 3 Introduction and Design of Twin pit/ Leach pit model © Copyright CDD Society, Bengaluru │ 1

This system consists of two alternating pits connected to a Pour Flush Toilet. © Copyright CDD Society, Bengaluru │ 2

How does twin pit work? © Copyright CDD Society, Bengaluru │ 3

Options for twin pit construction In situ Prefabricated rings are mounted over one another to form pit The pits are constructed at the site using construction material © Copyright CDD Society, Bengaluru │ 4

Prefabricated vs in situ construction of pit Prefabricated pit In situ pit Cost In situ construction is costlier © Copyright CDD Society, Bengaluru │ 5

Prefabricated vs in situ construction of pit Prefabricated pit In situ pit Soil feasibility It is difficult to construct in situ pit in loose soil © Copyright CDD Society, Bengaluru │ 6

Prefabricated vs in situ construction of pit Prefabricated pit In situ pit Resource availability In situ construction is recommended if resources are easily available 7 © Copyright CDD Society, Bengaluru │ 7

Prefabricated vs in situ construction of pit Prefabricated pit In situ pit Structural strength In situ construction is structurally stronger and durable than Prefabricated pit 8 © Copyright CDD Society, Bengaluru │ 8

? Key Question to be answered before designing a pit system © Copyright CDD Society, Bengaluru │ 9

? Size of the pit ? © Copyright CDD Society, Bengaluru │ 10

Factors affecting size of a pit No. of persons using toilet Sludge accumulation rate Desludging Frequency Volume =No. of persons x sludge accumulation rate x desludging frequency © Copyright CDD Society, Bengaluru │ 11

? How to design a twin pit? © Copyright CDD Society, Bengaluru │ 12

Guidelines from CPHEEO Manual No. of persons Frequency of desludging (in years) 5 3 © Copyright CDD Society, Bengaluru │ 13

Guidelines from CPHEEO Manual 5 users Pit 10 users 15 users Diameter Depth 1 1. 3 1. 4 1. 6 1. 5 Note: Depth from bottom of pit to invert level of incoming pipe or drain Sludge. (in meter) Storage Volume is 3 years. 300 mm of free board should be provided between invert level of pipe to pit cover. © Copyright CDD Society, Bengaluru │ 14

Plan of pour flush toilet with twin pit © Copyright CDD Society, Bengaluru │ 15

Plan of pour flush toilet with twin pit © Copyright CDD Society, Bengaluru │ 16

Components of Twin Pit model design Pan Inspection Chamber Twin Pit © Copyright CDD Society, Bengaluru │ 17

Detailed Design of Components © Copyright CDD Society, Bengaluru │ 18

Design of Inspection Chamber © Copyright CDD Society, Bengaluru │ 19

Requisite of design (inspection chamber) In case pipes are used, a chamber is provided at the bifurcation point to facilitate cleaning and allowing flow to one pit at a time. © Copyright CDD Society, Bengaluru │ 20

Inspection Chamber (Side view) 100 mm thick top slab with two handles of 10 cm diameter each should be provided 50 mm gap for easy fitting of top slab 1 feet 2 inches inside Ground level Should be 1 inch inside the chamber The bottom should be in a slope of 1: 10 (The slope is based on water usage) © Copyright CDD Society, Bengaluru │ 21

Inspection Chamber 300 mm Smooth plastering The pipes should be placed at 100 mm from each other and 50 mm from the wall Top View A wooden stopper to control the flow once the pit is filled Side View © Copyright CDD Society, Bengaluru │ 22

Pit © Copyright CDD Society, Bengaluru │ 23

Pit © Copyright CDD Society, Bengaluru │ 24

Pit Inspection Chamber The pipe should be placed at 100 mm below the ground level 100 mm thick top slab with two handles of 10 cm diameter eac should be provided 1 meter 200 mm above ground – Provided to avoid flood water to enter 50 mm gap for easy fitting of top slab • 100 mm for areas with low rainfall • 150 mm for areas with medium rainfall • 200 mm for areas with high rainfall • 250 mm for flood prone areas Ground Level 4 inches dia PVC pipe placed in a slope of 1: 10 (The slope is based on water usage) A drain should be cut out and 1/4 th of the brick should be placed inside in order to strengthen the foundation Should be 1 inch inside the pit 100 mm of brick bats 100 mm of gravel 25 Provided for filtration © Copyright CDD Society, Bengaluru │ 25

Requisite for design The two pits should be at least 1 meter apart. © Copyright CDD Society, Bengaluru │ 26

Requisite for design There should be 3 finger gap between the bricks for water percolation. © Copyright CDD Society, Bengaluru │ 27

Requisite for design Based on soil conditions maintain a minimum horizontal distance of 10 feet from nearby water sources © Copyright CDD Society, Bengaluru │ 28

Water table: Alternate Measures © Copyright CDD Society, Bengaluru │ 29

Water table: Alternate Measures © Copyright CDD Society, Bengaluru │ 30

How to construct a twin pit? © Copyright CDD Society, Bengaluru │ 31

How is twin pit constructed Watch this Video © Copyright CDD Society, Bengaluru │ 32

Resources required to construct a twin pit 33 © Copyright CDD Society, Bengaluru │ 33

Assumptions Frequency of desludging( in year) No. of persons 3 5 Wall Thickness 200 mm 34 © Copyright CDD Society, Bengaluru │ 34

Resource Required For pit For inspection chamber Measurement 0. 19 x 0. 09 x 0. 09 No. 1800 320 Total 2120 Bricks 35 © Copyright CDD Society, Bengaluru │ 35

Resource Required For pit For inspection chamber Quanity( in kg) 500 50 No. 10 bags 1 bag Total 550 Kg (11 Bags) Cement 36 © Copyright CDD Society, Bengaluru │ 36

Resource Required Measurement For pit For inspection chamber 0. 56 cum 0. 14 cum Total 0. 70 cum Sand 37 © Copyright CDD Society, Bengaluru │ 37

Resource Required Length 6 m No. 1 Diameter 4” PVC Pipes 38 © Copyright CDD Society, Bengaluru │ 38

Resource Required Coarse Brickbats' aggregates Quantity 1. 5 cum Total 2. 5 cum 1 cum Aggregates 39 © Copyright CDD Society, Bengaluru │ 39

Total Resource Requirement Resources Unit Quantity Brick Nos. 2120 Cement Kg (bags) 550 (11) Sand cum 0. 7 Pipes Nos. 1 Aggregates cum 2. 5 40 © Copyright CDD Society, Bengaluru │ 40

Any further questions? © Copyright CDD Society, Bengaluru │ 41