Question

Please illustrate how to use engineering use chart to find useful information such as rating number to determine if a given type of soil is good for any application (e.g. landfill cover, foundation, etc). Please provide any reference chart/ figure you will use.

Answer 1

There are several systems and charts that are being used presently to classify soil and obtain it's utility. Some of them are:

Based on particle size

Particle size analysis is done and the results are compared with the standard charts to obtain class of soil.

1. MIT System

2. International classification system

3. US Bureau of Soil classification.

Clay (size) Silt (size) Sand Gravel 0.002 0.2 0.006 2.0 mm 0.02 0.06 0.6 (2u) Legend (a) MIT System F- Fine M- Medium C - Coarse Clay Ultra Clay Silt Sand Gravel VC 0.006 0.02 0.2 0.2 μ 0.6 μ 2μ 0.05 (b) International Classification 2.0 mm 0.5 VC- Very coarse Silt (size) Sand Clay (size) Fine Gravel Gravel Very fine Fine Medium Coarse 0.10 0.25 0.05 0.5 0.005 2.0 (c) U.S. Bureau of Soils Classification Fig. 5.1. Classification Systems

Textural classification

Based on texture of soil. Triangular classification system suggested by US Bureau of Public roads is the one generally known as textural classification.The term texture is generally used to express percentage of the three constituents of soil namely sand, silt, and clay.

0 100 90 10 Sand 80 20 Clay 30 70 60Silt 2 KEY E50 40 60 ilty Clay Sand Clay 30 W70 Silty 'clay Clay loam Sandy clay' Loam Lcam / 20 80 Loam 10 Silty loam 90 Sandy loam Sand 0 100 100 80 90 50 (%) 60 70 40 30 10 20 Silt (Size 0.005 to 0.05 mm) Fig. 5.2. Textural classification System.

AASHTO Classification

Used for classification of soil for highways. Particle size analysis and plasticity is required to classify the soil.

Clay (size) Silt (size) Sand Gravel 0.002 0.2 0.006 2.0 mm 0.02 0.06 0.6 (2u) Legend (a) MIT System F- Fine M- Medium C - Coarse Clay Ultra Clay Silt Sand Gravel VC 0.006 0.02 0.2 0.2 μ 0.6 μ 2μ 0.05 (b) International Classification 2.0 mm 0.5 VC- Very coarse Silt (size) Sand Clay (size) Fine Gravel Gravel Very fine Fine Medium Coarse 0.10 0.25 0.05 0.5 0.005 2.0 (c) U.S. Bureau of Soils Classification Fig. 5.1. Classification Systems

Unified soil classification

This system is adopted by American Society of Testing Materials(ASTM). This is the most polpular for use in all types of engineering works.

Based on particle size and plasticity.

Table 5.2. Symbols used in USC System Description Gravel Sand Silt (Symbol M is obtained from the Swedish word 'mo') Clay Organic Peat Symbols Primary Well-graded Poorly graded Non-plastic fines Plastic fines Low Plasticity High plasticity Secondary

Table 5.3. Unified Soil Classification System Group Symbols Typical Classification criteria Major Division names Well graded gravels Poorly graded gravels Coarse-Grained | Gravel [50% or Soils. [More than 50% retained 1 on No. 4 sieve on No. 200(4.75 mm)] sieve (0.075 Clean more of coarse Gravels fraction retained Not meeting both criteria for Atterberg Limits Atterberg below A-line or Limits in plasticity index hatched area less than 4 GM Silty gravels GM -GO Gravels sAtterberg Limits Sabove A-line ines GC Clayey gravels and plasticity index greater Well-gradecd sands SW Sand [more than Clean 50% of coarse | Sands faction passing No. 4 sieve (4.75 mm)] Not meeting both criteria for Poorly graded sands 2dAtterberg Limits Atterberg Cbelow A-line orLimits in SMSilty sands g eplasticity index hatched area c |less than 4 £ee Atterberg Limits SM-SC Sands ayey sandsabove A-line - n | index greater fines and piasticity SC Inorganic silts Fine grained Silts and clays Liquid soils [50% or | Limit 50% or less more passing No. 200 sieve (0.075 mm)] MLof low plasticitv Inorganic clays of low to medium plasticity Organic silts CL OL of low plastici See Plasticity Chart (Fig. 5.5) Inorganic silts Silts and clays Liquid Limit greater than 50% MH of high plasticity Inorganic CH clays of high plasticity Organic clays OH of medium of high plasticity Peat, muclk and other Highty organic Soils Pt Visual-manual identification organic soils

CONCLUSION :

-We will use different standard charts for different engineering works

- For example if you are geotechnical engineer under the transportation department and you want to check if a soil is suitable for construction of an embankment. You test the soil for its plasticity and particle size analysis and compare with the standard chart proposed by AASHTO and classify it accordingly. Then you can check if the grade you awarded to the soil is OK for the purpose. But this is not enough you also want to check other properties of soil and check if they are within the limits.

(All images are standard tables and symbols. Took from the book : Soil Mechanics and foundation Engineering by Dr. K.R Arora)