diffrentiate between red earth and gravel
TRANSCRIPT
Differentiate between red earth and gravel
Use of red earth in the name of gravel or moorum in sub base and as screenings and binder in Water Bound Macadam is causing pre-mature damage of several roads in India. In Andhra Pradesh such practice has been stopped to a great extent. IN Tamil Nadu, Wet Mix Macadam is being done instead of WBM with gravel blindage.
In several states the practice of using red earth in sub base and base are still going on. It is extremely difficult to repair such roads.
This is due to ignorance about the standard specifications.Going through the following slides enlighten the facts regarding the above.
D.V.Bhavanna Rao M.Tech., F.I.E
Member COT and Chief Engineer R&B
Quality [email protected]
Definition of sand and gravel as per Code IS: 1490 – 1987
Sand and gravel are defined as Cohesion less aggregates of angular, sub-angular, sub-
rounded, rounded, flaky or flat fragments of more or less unaltered rocks or minerals.
According to the system, gravel is the fraction of the material between 80mm IS sieve size and 4.75mm IS sieve size.
Sand is a fraction of the material between 4.75mm IS sieve size and 75 micron IS sieve
size.
AP Standard Specification 138
The moorum shall be composed of well graded coarse siliceous and gritty to touch and free from dirt and deleterious matter. material passing 75µ shall not exceed 10%
Liquid limit shall not exceed 20% and Plasticity index shall not exceed 6% for sub base, filler material in surface treated WBM roads and backing for revetment
The above values are 33% and 6 to 9% respectively for filler material in WBM roads
MOSRT& H 404.2.6: ScreeningsScreenings to fill voids in the coarse
aggregate shall generally consist of the same material as the coarse aggregate. However, where permitted, predominantly non-plastic material such as moorum or gravel (other than river born material) may be used for this purpose provided liquid limit and plasticity index of such material are below 20 and 6 respectively and fraction passing 75 micron sieve does not exceed 10 percent.
MOSRT& H 404.2.7: Binding material Binding material to be used for water bound
macadam as a filler material meant for preventing raveling, shall comprise of a suitable
material approved by the Engineer having a Plasticity Index (PI) value of less than 6 as
determined in accordance with IS: 2720 part 5.
MOSRT& H 504.2.2: Coarse aggregates for BT courses
Coarse aggregates shall consist of crushed rock, crushed gravel or other hard material retained on 2.36mm sieve. They shall be clean, hard, durable, of cubical shape, free from dust and soft or friable matter, or other deleterious matter.
Where crushed gravel is proposed for use as coarse aggregate, not less than 90% by weight of the crushed material retained on the 4.75mm sieve shall have atleast two fractured faces
River gravel along Wankidi vaagu across which is being constructed in km 17/10 of Wankidi Kagaznagar in Adilabad District. This type of material satisfies gravel requirements as per IS code or MORT&H
specifications. AIV = 14%. It satisfies grading III of table 400 – 2 for Granular Sub Base
Diversion road is being formed with red earth whereas the real natural river gravel that satisfies GSB requirements is available along the vaagu
Layer of adsorbed water surrounding a clay particle. Sliding of such particles over
one another results in plasticity
Natural gravelly soilLL = 38%, PI = 18%
Position after 24 hours of adding water
Total Absorption of particles indicate the presence of negative charged particles in the gravelly soil. It indicates high PI and LL values. It proves that the above sample is
earthen material only but not gravel or moorum. Use of such soil presuming it as gravel is causing damage and poor condition of Village Roads, Major District Roads,
State Highways and National Highways. Highway Engineers must be able to differentiate between earth and gravel
District%passing 75µ sieve
LiquidLimit in %
PlasticityIndex in
%
CBRin %
Srikakulam 40 34 16 8EG District 28 32 15 9WG District 39 33 16 9
Krishna 34 37 15 11
Guntur 30 32 13 10Prakasam 36 32 13 14Nellore 35 39 17 15Cuddapah 29 42 14 14Nalgonda 33 41 17 10
Some Test Results of Gravel done at STC Vijayawada
More STC Test results on materials form gravel quarries
location%passing 75µ sieve
LiquidLimit in
%
PlasticityIndex in
%
Free Swell
Index in %
CBRin %
CSP road SKL 45 38 16 25 8
Kesavaram EG 26 31 13 15 9
Patnampadu WG 34 31 14 20 9
RV section Vijayanagaram 37 36 20 30 11
BN road Vijag 32 38 20 35 10
Koyyur Nellore 33 40 21 15 14
Kaza Guntur 30 32 13 20 15
CB road Prakasam 36 32 13 15 14
Vellanki Kr. Dt 22 38 16 10 12
MM road Ng 37 37 18 15 9
JMK Chittor 29 42 14 20 14
Summary of test results on materials from different gravel quarries in AP
Type of Quality Range of Values MORD and APSS Norms
Liquid Limit 30 to 45% Less than 20 or 25%
Plasticity Index 10 to 23% Less than 6%
% passing 75 micron sieve 20 to 62% Less than 10%
MDD 1.8 to 2.2g/cc Not specified
CBR 8 to 17% As per requirement
Soil Classification
Clayey gravels or clayey sands
Predominantly non plastic
Free Swelling Index 10 to 35% Not desirable