Worked example on how to calculate particle size analysis of soil

To evaluate: the quality of a soil as a highway subgrade material, one must also inmrporate a number called the grop index (Gi) with the groups and subgroup the soil. This index is written in parentheses after the group or subgroup designation.

The group index is given by the: equation

Equation 

Example

The results of the particle-size analysis of a soil are as follows:

- Percent passing through the No 10 sieve 100
- Percent passing through the No 40 sieve - 80
- Percent passing through the No 200 sieve

The liquid limit and plasticity index of the minus No. 40 fraction of the soil are 30 and 10, respectively. Classify the soil by the AASHTO system.

Solution
Using Table 3.1, since 58% of the soil is passing through the No. 200 sieve. it falls under silt-clay classifications - that is, it falls under group A-4, A-5, A-6, or A-7.

Proceeding from left to right, it falls under group A-4.
From Eq. (3.1)

Gi = (F200-35) + 0.005(LL - 40)) + 0.01(F200 - 15)(Pi-10)
= (58 - 35)(o.2 + o.o05(30 - 40)) + (o.o1)(58 - 15)(1o - 1o)
=3.45~3

So. the soil will be classified as A-4(3).

Classification of highway sub grade soil

permeability and seepage in soil - Darcy's Law

Darcy's Law

In 1984, Darcy publish a simple equation for the discharge velocity of water through saturated soil with a simple equation below;

v=Ki

v = discharge velocity (flow of water right angles to the of the cross section)
K = permeability coefficient or hydraulic conductivity

Dacy got this equation from experiments he did in clean sand which flows water, v is discharge of velocity of water based on gross cross section of soil, but in actual case void space velocity of water is high than v, relationship between the discharge velocity and the seepage velocity can be derived as

vs = v/n

vs= seepage velocity
n= porosity

laboratory test on expansive soils- Swell Test

The most important laboratory test on expansive soils is the swell test. The standard one-dimensional consolidation test apparatus can be used. A standard consolidometer can accommodate a remolded or undisturbed sample from 2 to 4.25 in. diameter and from 0.75 to 1.25 in. thickness. Porous stones are provided at each end of the specimen for drainage or saturation. The assembly is placed on the platform scale table and the load is applied by a yoke actuated by a screw jack. The load imposed on the sample is measured by the scale beam, and a dial gage is provided to measure the vertical movement.

The advantage of such arrangement is that it is possible to hold the upper loading bar at a constant volume and allow the measurement of the maximum uplift pressure of the soil without a volume change. This requires a constant load adjustment by an operator. An advanced scheme is an automatic load increment device that measures swelling pressure without allowing volume change to take place.

The consolidometer can also be used to measure the amount of expansion under various loading conditions. Since swelling pressure can be evaluated by loading the swelled sample to its original volume, it is simple to convert the platform-scale consolidometer into a single-lever consolidation apparatus. Such a modified con- solidometer can be made locally at low cost. The average soil laboratory should have a train of such apparatuses to speed up the testing procedure.

It is important for the geotechnical engineer not to confuse “swell” with “rebound.” All clays will rebound upon load removal, but not all clays possess swelling potential. The use of graduated cylinders to measure the swelling potential of clay upon saturation is not a standard test. Such a test has been abandoned and should not be repeated.

Soil Compaction for better construction project

What is soil Compaction?
Soil compaction is when soil particles are pressed together making the air voids minimum as possible.

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reasons why we need to compact soil ;

• Increases load-bearing capacity
• Prevents soil settlement and frost damage
• Provides stability
• Reduces water seepage, swelling and contraction
• Reduces settling of soil

Machines used for compaction;

• Smooth wheel Rollers
• Sheepsfoot Rollers
• Rubber- tiered Rollers
• Vibratory Rollers
• Stumpers
• Walk-Behind Roller

Smooth wheel Rollers
Smooth wheel Rollers suitable for proof rolling sub grades and for finishing.














Sheepsfoot Rollers
This roller is most effective to compact Clayey soils.














Smooth wheel Rollers
This type have the most advantage because it can compact both soil and clayey soils

what is Consolidation - Consolidation of soil for soil investigation

Consolidation is a process by which soils decrease in volume. It occurs when stress is applied to a soil that causes the soil particles to pack together more tightly, therefore reducing its bulk volume. When this occurs in a soil that is saturated with water, water will be squeezed out of the soil. The magnitude of consolidation can be predicted by many different methods. In the Classical Method, developed by Karl von Terzaghi, soils are tested with an oedometer test to determine their compression index. This can be used to predict the amount of consolidation.

When stress is removed from a consolidated soil, the soil will rebound, regaining some of the volume it had lost in the consolidation process. If the stress is reapplied, the soil will consolidate again along a recompression curve, defined by the recompression index. The soil which had its load removed is considered to be overconsolidated. This is the case for soils which have previously had glaciers on them. The highest stress that it has been subjected to is termed the preconsolidation stress. The over consolidation ratio or OCR is defined as the highest stress experienced divided by the current stress. A soil which is currently experiencing its highest stress is said to be normally consolidated and to have an OCR of one. A soil could be considered underconsolidated immediately after a new load is applied but before the excess pore water pressure has had time to dissipate.