Before we Explain How to Design And Construct a **Concrete Septic Tank**, how a **septic tank works** & Estimation of a septic tank with the cost you have to learn about **What is a Septic Tank**.

## How to Design And Construct a Concrete Septic Tank

In this construction tutorial, one can briefly learn the methods which are necessary to design and construct a **septic tank**.

One will be familiar with the various standard dimensions of a **concrete septic tank** by studying them from a plan.

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## What is a Septic Tank?

### Useful Information Regarding Septic Tank Design

The **capacity of a septic tank** is based on the number of users and intermission of sludge removal.

Usually, sludge should have been discharged every 2 years. The **liquid capacity of the Concrete Septic Tank** is assumed as 130 liters to 70 liters per head.

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For the small number of users, 130ltr per head is assumed.

Use of **septic tank** is generally constructed with a **brick wall** in which cement mortar [not below 20cm (9 inches)] thick and the foundation floor is made of cement concrete with 1:2:4 ratios.

**Also Read**: **Concrete Mix Design With Excel**

Both inner and outer faces of the wall and top of the floor are plastered with **cement mortar** in a 1:3 mix ratio by maintaining the lowest thickness of wall at 12mm (one-half inch).

### Excavation

**Volume of Excavation** formula

**Volume of Excavation** = Length × Breadth × Depth

Here, we concede length & breadth of excavation are the same as that of PCC.

So now we put value in **Volume of Excavation** formula

**Volume of Excavation** = 11ft × 7.5ft × 6.75ft

**Volume of Excavation = 556.88 cu ft**

### PCC

First, we list the date which is already given (we have)

**Given data**:

The extra length of PCC on all 4 sides of the septic tank is 6″ (0.5ft.)

Length | 11ft |

Breadth | 7.5ft |

Thickness | 0.416 ft = 5″ |

(As 1ft. = 12 inches)

Now we find the **Volume of PCC** work

**Volume of PCC** = Length × Breadth × Thickness

**Volume of PCC** = 11ft × 7.5ft × 0.416ft

**Volume of PCC = 34.32 cu ft**

Also Read: 12 Points to Check For PCC in The Foundation

### Brick Masonry

Brick masonry work is extremely important in materials quantity calculation.

Here we take a 9″ thick outer wall for example so that you can understand better.

**Giver Data**

Length | 10 ft |

Width | 9″ (0.75ft) |

Height | 6ft |

Let us find the volume of **brick masonry** works by the longwall short wall method.

if you want to learn more regarding the volume of the longwall method then put your request in the comment box or in social media or groups.

Volume of the longwall = 2nos.×( length × width × height)

Volume of the longwall = 2nos.× ( 10 ft. × 0.75 ft. × 6 ft.)

Volume of the longwall = 2nos. × 45 cu ft.

**Volume of the longwall = 90 cu ft**

**The volume of the short wall**

Volume of the short wall = 2nos. × [{ length} × width × height]

Volume of the short wall = 2nos. × [{6.5 ft.- (2nos.× 0.75 ft.)} × 0.75 ft. × 6 ft.]

Volume of the short wall = 2nos. × [{5 ft.} × 0.75 ft. × 6 ft.]

Volume of the short wall = 2nos. × [ 22.5 cu ft.]

**Volume of the short wall = 45 cu ft**

Now we calculate brick wall volume which uses in **concrete septic tank** construction.

#### (A) Total volume of 9″ thick brick wall

Total volume of 9″ thick brick wall = Volume of { longwall + short wall}

Total volume of 9″ thick brick wall = {90 cu ft. + 45 cu ft.}

**Total volume of 9″ thick brick wall = 135 cu ft.**

**Calculate Quantity of Cement Mortar in Brickwork Excel**

#### (b) 4″ thick inner partition walls

##### For Baffle wall-1

The volume of the baffle wall-1 = [ {length} × width × (height)]

= [{ 6.5 ft.- (2nos.× 0.75 ft.)} × 0.33 ft. × (6 ft. – 1.5 ft.)]

= [{5 ft.} × 0.33 ft. × (4.5 ft.)]

**Volume of the baffle wall-1 = 7.425 cu ft**

**The volume of wall-2**

**The volume of wall-2** = [ {length} × width × height]

= [{6.5 ft.- (2nos.× 0.75 ft.)} × 0.33 ft. × 6 ft.]

= = [{5 ft.} × 0.33 ft. × 6 ft.]

**Volume of wall-2 = 9.90 cu ft**

The total volume of 4″ thick brick wall

The total volume of 4″ thk. brick wall = the volume of { wall-1+ wall-2}

= {7.425 cu ft. + 9.9 cu ft.}

**Total volume of 4″ thick brick wall = 17.33 cu ft**

### Plastering

In almost every construction work plastering applies to achieve the finished surface also it helps in making the construction component impermeable.

#### (A) For 9″ Brick Wall

Now we calculate the surface area on which we allied plastering on septic tank.

Area of Plastering = 2nos. × [ (area of a longwall) + (area of a short wall)]

Area of Plastering = 2nos. × [ (10ft. × 6ft.) + (5ft. × 6ft.)]

Area of Plastering = 2nos. × [ 60 sq ft. + 30 sq ft.]

**Area of Plastering = 180 sq ft**

[CE_note note_color=”#ff7166″]Note: Length & height of the longwall & short walls are taken for area calculation.[/CE_note]

#### (B) For 4″ Inner Wall

Area of Plastering = 2 sides. × [ (area of wall-1) + (area of wall-2)]

Area of Plastering = 2 sides × [ ( 5ft. × 4.5ft.) + ( 5ft. × 6ft.)]

Area of Plastering = 2 sides × [ 22.5 sq ft. + 30 sq ft.]

**Area of Plastering = 105 sq ft.**

#### (C) For Floor Base

Floor Area Plastering = [ {length} × { breadth.}]

Floor Area Plastering = [{10 ft. – (2nos. × 0.75ft.)} × {6.5ft. – (2nos. × 0.75ft.)}]

Floor Area Plastering = [ {10ft. – 1.5 ft.} × { 6.5ft. – 1.5ft.}]

Floor Area Plastering = [8.5ft. × 5ft.]

**Floor Area Plastering = 42.5 sq ft.**

Now we find total area on which we apply plastering below

**Total Plastering Area** = plastering area of [ 9″ wall + 4″ wall + floor]

**Total Plastering Area** = [180 sq ft. + 105sq ft. + 42.5 sq ft.]

**Total Plastering Area = 327.5 sq ft.**

### RCC slab

The area of the RCC slab = Length × Breadth

= 10ft × 6.5 ft

**= 65.0 sq ft.**

**Also Read:**

RCC Full Form in Civil Engineering

Minimum Thickness of RCC Slab Recommended by IS 456

Basic Process of RCC Column in Construction

### Miscellaneous

Inlet & outlet pipe of 4″ dia = 2 nos.

Manhole cover with frame = 1no.

Vent pipe = 1no.