COMPLETE GUIDE: Soakaway Septic Tank Estimation For Nigerians

image of septic tank soakway

Today i will be teaching us how to Estimate for soakaway pit. I know i have done something on this topic before now but i just want to give a more detailed estimate for students that may want to know how to do this and other professionals too! 

So for this project, i will be giving estimates for a soakaway pit measuring 4268mm by 3048 (14 by 10 ft) and the estimate will provide for materials such as steel, cement, granite, wood (Boards and 3 by 4), blocks, binding wire, stirrups, sand, etc

Septic Tank Dimension
Figure 1 Showing the dimensions of a soakaway pit

From Figure 1 above, we have seen the dimensions of the soakaway pit to be designed. It is now time to start the estimation.

1. Excavation: You have to get 2 or 3 able bodied men on site to be able to completely excavate the pit and this could cost you N10,000 depending on your location.

Lets ask a very important question here 

How many Blocks Do i need to construct a soakaway Pit?

For the septic tank under review, we have its length as 4268mm or 14 ft while the width is 3048mm or 10 ft and it also has a depth of 3048mm. Now lets estimate for the number of blocks required to carry out this project

From previous experience along with some basic mathematics, we have that the length of block is about 450mm

We also know that the height of a block is about 228mm and so we are going to try to get the number of blocks for every course as well as the number of blocks for each side of the pit

Lets not forget that the pit is 3048mm high and to get the number of coaches for soakaway pit, we have to divide the total height (3048mm) by the height of one block (228mm)

Thus, (3048/228) = 13.3 blocks high. Lets just assume its is 13 blocks high since we will be using Mortar for bonding

Having obtained the total number of courses as 13, let us estimate for the total number of blocks…

soakaway septic tank

For Side A measuring 4268mm, we are going to divide this 4268 with the length of a block “450mm”

Thus, (4268/450) = 9.4 blocks

But we have 13 courses

Therefore, the total number of blocks for side A Would be 9.4 x 13 courses = 123 blocks

We are going to multiply this 123 blocks by 2 because we also have side “C-D”

123 X 2 = 246 Blocks

Next, we estimate for the number of blocks to over side “B-D”

Dimension for sides B-D = 3048mm, we also understand the length of block is 450mm and there will be 13 courses

Therefore, let us divide 3048mm by 450mm

3048/450 = 6.7 blocks

6.7 x 13 courses = 87 blocks

We have 87 blocks for side B-D, So we multiply by 2 in order to provide for sides A-C since they both have the same dimensions

87 x 2 = 174

So the total number of blocks required for this septic tank project will be 174 + 246 = 420 blocks but we will add 42 for breakages

So the total number of blocks required would be 462 Blocks

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How many Bags of cement would be required For a Soakaway Pit?

462/60 = 8 bags of cement (From experience, we need a bag of cement to lay 60 blocks)

How Much Binding wire is required for soakaway Septic tank Construction

For the Project under review, make available N1500 for Binding wire

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How much Reinforcements for soakaway Septic tank 

This totally depends on the size of the soakaway pit and the bar spacing

For this project, i chose 175mm spacing

4268/175 = 24 lengths of rod. 

But the length of a reinforcement rod is 10,058mm and the span to be covered is 3048mm.

Therefore, we would need 10,058/3058 = 3.2 cuts from each length of rod

Now we have 24 slots along face A-B, So 24/3.2 = 8 Rods

Lets get the number of steel required for side B-D

we have 3048mm running to a length of 4268mm

so, 3048/175 = 17.4 lengths of rod

Where the length of rod = 10058mm, we have 10058/4268 = 2.3 cuts

so we have 17.4 slots for rods

But we can make 2.3 cuts from one length of rod

so 17.4/2.3 = 8 Lengths of reinforcement rods

Reinforcement for Columns or Pillars

So the height of the septic tank is 3048mm but the reinforcement would need additional 15mm 

But a length of rod measures 10058mm and we are cutting 3063mm

it therefore means we can obtain 3 cuts from every length of rod.

We will need some 8 lengths of rod for the columns

In Total, we need 24 Lengths of 12mm rods for the job

Casting Of Top Slab

Top casting is 4268 x 3048 x 127 or 4.2 x 3 x 0.101 = 1.27m3 of concrete which means we are casting a cubic metre of concrete

So You need about 6 bags of cement for the top casting
A Trip of sand for all the work
A Trip of Granite if you didn’t have any on site before

Boards for top casting

16 pieces of 1 by 12 hard boards (2 will be used as inclined plane to send the blocks into the pit)

Provide 6 pound weight of nail

3 by 4 Wood for bracing
Provide 20 pieces

Bushwood or Bamboo for Support of formwork

Provide 30 lengths of bamboo ( a length is usually cut into 2)

Materials Needed for Building Septic Tank Soakaway

Blocks = 462
Rods = 24 lengths
Binding Wire = N1500
Cement For Block work = 8 Bags
Cement for top Casting = 6 bags
Cement for Bottom Casting = 6 Bags
Nail = 6 Pound weight
Boards for Top Casting= 16 pieces
3 by 4 wood = 20 pieces
Bushwood = 30 length

Total ========= N

Please i am not going to write anything as total amount, do your own market survey to find the total cost. However, the price of building materials in Nigeria is written here

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Written by admin

Hi, I'm Richard Nwachukwu! It is my job to handle the content aspect of this great organization and I'm determined to ensure you get it all right as long as you're handling a construction project in Nigeria!

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