Standard Penetration Test & Jar Test
Standard Penetration Test
Importance:
Provides a decent representation of the soil content and stability
If overlooked, it will cause future problems down the road (pipes becoming unaligned, tank sinking, etc.)
The Standard Penetration Test (SPT) is a procedure used to test the soil density of a certain area before construction. It is vital to execute this procedure before building a tank in case the soil cannot withstand the weight of the tank. The SPT utilizes a hammer and borehole which come in different forms depending on the specific test, which will be specified below.
Standard penetration test protocol
Borehole drilled to the desired sampling depth (150mm or 5.9 in, typically)
The split-spoon on the drill rod is placed at the testing point.
A hammer of 63.5 kg (140 lbs) is dropped from a height of 76 cm (30 inches) driving the sampler into the ground
Record the number of blows needed for the tube to penetrate each 150mm (6 in) depth upto a depth of 450 mm (18 in, so total three 6 inch sections of penetration)
The number of blows recorded for the second and third 6 inch penetration are summed- this is the Standard penetration resistance or N-value
Corrections may be made to this value.
SPT Value Correction
The value produced by the SPT needs to be corrected further
SPT Data Interpretation
The value produced by the SPT needs to be corrected further
Jar Test
Purpose: Soil testing is a very important part of building and road construction. In fact, no construction project can proceed without first making sure the soil can support the load. Thus, the purpose of soil testing for construction is to determine the suitability of the soil for the type of construction to be done. How much clay, sand or silt do you have in your garden soil? By doing this simple test, learn the soil's texture class. This is an approximation and will likely underestimate the actual clay content of your soil.
Materials: jar, soil (tested), clean water, stopwatch, ruler
Dig a small hole (about 15 cm wide) at site of latrine. Clear away any grass, weeds, and topsoil from the hole. Record GPS coordinates of the location.
Fill jar about â…“ full of soil. Seal and leave undisturbed for at least 48 hours.
Fill jar with clean water, leaving about 2 cm of space at the top.
Cap the jar and shake vigorously until the soil turns into a uniform slurry.
Set the jar on a level surface and let it sit for one minute.
Draw a line on the outside of the jar, at the top of the settled layer at the bottom of the jar.
Leave the jar on the same level surface for 2 hours.
Draw a line at the top of the next settled layer with the marker.
Leave the jar on the same level surface for 48 hours.
Draw a line at the top of the next settled layer with the marker.
Using a ruler, measure and record the height of each of the three lines marked on the jar in the field data collection sheet (NOTE: for each line, record the height as the distance from the bottom of the jar to the line, not the distance between the lines).
Take pictures of the fully settled jar.
Sample Calculations
To determine the percent composition of each material, take the depths of each layer out of the total. For example:
Total depth of soil: 23 mm
Depth of Sand Layer 9 mm
Depth of Silt Layer 10 mm
%Sand = 9mm / 23mm ×100% = 39%
%Silt = 10mm / 23mm ×100% = 43.5%
%Clay = 100% − (39% + 43.5%) = 17.5%
Then plot along each side of the triangle to determine the type of soil.