Definition for various technical terms in Civil Engineering


Royal Member
What is the soil?
Soil is commonly consisting of a naturally occurring loose or soft deposit part of earth’s crust, produced as a result of weathering or decompositioning of rock formation or decay of vegetation intermingled together.

What is the Liquid limit?
The minimum water content at which the soil will flow under the application of a very small shearing force. (OR)
Water content at which soil passes from plastic to liquid state.

What is Plastic limit?
Plastic limit is the moisture content at which a soil when rolled into a thread of smallest diameter of 3mm starts crumbling.

What is the Plasticity index?
Plasticity index of a soil is the difference between its liquid limit and its plastic limit.
This gives an idea about the clay content in the soil, plasticity index increase with clay contents

What is shrinkage limit?
Shrinkage limit gives an idea about the shrinkage or swellings characters of the soil, which may likely to occur in the soil after being compacted. A compacted soil of this type may shrink on draying and may swell again in contact with moisture.

What do you mean by group index and how it is determined?
It is an empirical value used to evaluate the kind or type of soil to be used for sub-grade material. It can be determined by the equation
G.I = (F-35) [0.2+0.005 (L.L – 40)] + 0.01 (F-15) (P.I-10)
Here! F = Passing %ge on sieve # 200.

What is SPT test?
This is the test, which carried out to know the bearing capacity of the soil. This is usually done on the foundation of bridges and huge buildings.

What is CBR?
CBR is a measure of shearing resistance of the material under controlled density and moisture content.

What is the “Optimum moisture content?
The moisture content at which the soil attains the max.dry density is called the optimum moisture content.

What is the unit weight?
The relation ship between unit weight and acceleration due to gravity.

What is the “Maximum dry density”?
The dry density obtained using a specified amount of compaction at the optimum moisture content.

What is the density?
It is defined as the mass per unit volume.

What is the “Bulk density”
The mass of the material (including solid particles and any contained water) per unit volume including voids.

What is the “Specific gravity”?
Specific gravity is the ratio of the weight of a given volume of a material at a given temperature to the weight of an equal volume of distilled water at that temperature.

What is the “Specific Gravity”?
The specific gravity of the substance is defined as the ratio of its mass in air to equal volume of water at same temperature.

What is the “Absolute Specific gravity”?
It is the ratio of the weight of solid, referred to the vacuums to the weight of an equal volume of gas-free distilled water, both taken at a stated temperature.

What is the “Apparent specific gravity”?
It is the ratio of the weight of aggregate dried in oven at 100 to 110ºC for 24 hours to the weight of water occupying a volume equal to that of the solid including the impermeable pores.

What is the “Effective specific gravity”?
Considered the overall volume of the aggregate exclusive of the volume pores that absorb the asphalt cement.

What is compaction?
Compaction is a mechanical process of volume reduction by packing together the soil particles. Rolling, ramming and vibration with water accomplish it and there are decreases in volume of air voids.

What do you determine the shear strength of soil?
By Tria-axial Test:
The basic principal is that a cylindrical soil specimen is first encased in a thin rubber membrane and subjected to fluid pressure around the cylindrical surface, the lateral pressure is held constant while an axial load is applied and in around until failure occurs.

What is the permeability and its significance?
It is the hydraulic property of soil, which indicates the case with which fill water flow through the same mass. It is the significant on numerous engineering problems such as seepage through the dams and irrigations canals, lowering the water table to improve the stability of foundation, selecting capacity of pumps for lowering the ground level of the water during evacuations and settlement of structure restring on compressible soil.

What is consolidation of soil?
It is the escape of water and a gradual transfer of stress from water to solid mass. It is not the same as compaction, which is artificial compression of a soil by re arrangement of its particles, aided by the lubricating effects of water.

What is scalping?
It is the removal of deleterious fines.

What is soil stabilization?
It is the process, which improve the properties of material by adding additives to improve strength, plasticity, workability and shrinkage.

What do you mean by lime stabilization?
Lime stabilization is the most economic and effective clay soils, when (ph=12.30) added to soils by about 3% to 70% by weight of dry materials.

What are the types of soil stabilization?
Mechanical stabilization
Soil cement stabilization
Lime stabilization
Chemical stabilization

What is the moisture content?
The mass of water that can be removed from the soil usually by heating 105°C,it is expressed as a percentage of dry soil.

What is the particle size distribution?
The percentage of the various grain sizes present in a soil as determined by sieving and sedimentation.

What are the voids?
The spaces between the solid particles of soil.

What is the porosity?
The volume of air voids (air and water) expressed as a percentage of total volume of a mass of the soil.

What is the saturation of soil?
The condition in which all the voids in a soil are completely filled with water.

What is fine modulus and how to determine it?
It is the numerical number that outlines the grain size of material by fines point of view. It is determined through sieve analysis by adding total percentage retained material on the sieve of ¾, 3/8, #4, #8, #16, #30, #50 and #100 and dividing the sum by 100.

What are the properties of “Fill and Back fill” material?
There are two types of material that we can use as filling and back filling.
1.Existing material
2.Borrow material

Existing material properties:
CBR = 10% (on the top surface)
CBR = 5% (when using material 45 cm down)
Its passing range on # 200 sieve is 50 to 70 %.
Borrow material properties:
CBR = 25 %
Passing range on # 200 sieve is 35 to 50 %
Specified Grading: A-1-a, A-1-b and Non Plastic (A-3).

What are main properties of Pervious Back Fill materials?
Properties :
Agg. Crushing Value = < 30 %
Bulk Sp. Gravity = > 2.750
Los Angeles Abrasion = < 40 %
Sand Equalant = > 55 %
(The basic type of the “Rock” will be “Gabbros” and other “Basaltic rocks”)

What are the main properties of “Rip Rap” materials?.
Properties :
Agg. Crushing Value = < 30 %
Weight per Piece = 16 kg
Los Angeles Abrasion =< 40 %
IF! Weight per piece = >70 kg then
Los Angeles Abrasion = 50 %
Volume = > 0.01 m
Bedding materials for Rip Rap have the sieve 1-1/2 to 200 um, and will be lay down the rip rap.

What are the main properties of “Sub-Base or Base-Course” material?
The material used in ‘Sub-Base or Base-Course in two layers the thickness of per layer should be 15 cm + 8mm with these following properties.
60% Borrow material + 40 % Wadi Gravel (Gradation ‘B’)
Los Angeles Abrasion = < 40 %
Soundness (Na) = 12 %
Soundness (Mg) = 15 %
Flakiness Index & Elongation = < 35 %
Sp.Gravity = 2.20 g/cc
Max. Dry Density = 2.10 g/cm
CBR at 98% compaction = 65 % >
Gradation can be A, B, C can be adjusted to the required properties.
Sieve passing on ¾ and retain on No.4for testing
Passing on #200 sieve should not be exceeded than 2/3 portion of the passing # 40.
The L.L shall have max 35 % and P.I 6.0(max).
The surface should be check by a straight edge of (5) m and remove the depression of 1cm.
Sub-Base layer can accept greater compressive strength, reduce the deformation of the pavement, work as a working plateform, prevent frost and moisture from penetration in to sub-grade and reduce the vertical compressive strength. Induced by the traffic.

What are the main properties of the “Wet Mix Macadam” material?
Soundness =10 %
Los Angeles Abrasion = < 40 % (AASHTO T-96)
Elongation Index = 5 %
Friable Particles = 0.25 %
Liquid Limit = 25 %
Plasticity Index = 4
Sand Equalant = > 25 %
Max.Dry Density = 2.00 g/cc
CBR at 100% Compaction = 80 %
For every 1000 cubic meter the above tests will be conducted, compactions test every 300 sq. The proctor test for this is vibro-proctor that we can compare with volume.

What are the main requirements of “Sand Asphalt” material?
Agg.size = 3/8 + Bitumen + Filler
Layer thickness = 5 cm
Total layer thickness = 12 cm
Bitumen Binder Course = > 6 cm
Base Course = 12 cm (in two layers)
Compaction = 98 %
Delivery temperature = 80 to 150°c

Where we can use the “Rock fill” material?
Rock fill layer is used inn road construction where the water table is high.

What is the compaction test method and compaction achieved method on shoulder slopes?
For test performances excavate the slope area according to the plate width and carry out the test accordingly.
For compaction achievement the area should be compacted during embankment or inclusive other continuous compaction in connection with road areas. After light roller can be used.

What are the main reasons of cracks appears on ‘Sub-Grade’ surface?
Excess moisture content
Excess cohesiveness in soil
Segregation under neath

What are the benefits of shoulders?
To protect the pavement and feasible for traffic and public facilities.