What is formation?
Formation is a prepared flat
surface , which is ready to
receive ballast of the track.
It is important constituent of
the track as it supports the
entire track structure.
Function of formation
i. To provide a smooth and uniform
bed on which the track can be
laid.
ii. To bear the load transmitted to
it from the moving loads through
the section of ballast.
iii. To facilitate drainage.
iv. To provide stability to track.
General Description
• Prepared either by doing additional earth
work over the existing ground or by
excavating existing surface and making
cutting.
• Can be either in the shape of embankment or
a cutting.
• Height of formation depends upon the ground
contours and the gradient adopted.
• The side slopes depends upon the shearing
strength of soil.
• The width of the formation depends upon the
number of tracks to be laid & gauge of track.
DEFINITIONS
CESS
TRACK STR.
B A
L LA
S T
BLANKET
FORMATION
SUB - GRADE
SUB - SOIL
TRACKFOUNDATION
Classification of soil
Good soils
Coarse grained soil
Other than
Good soils
Fine grained soils such as silts
sandy and silty clays
Grain size classification
Gravel
Coarser than 2.00 mm
Coarse sand
0.6 mm to 2.00 mm
Medium sand
0.2 mm to 0.6 mm
Fine sand
0.06 mm to 0.2 mm
Silt
0.002 to 0.06 mm
Clay
finer than 0.002 mm
SOIL – THE SUPPORT SYSTEM
•
•
•
•
Mother Earth.
Has it unlimited Capacity?
Appears simple but least understood.
Mostly taken for granted.
SOIL?????
• What is Soil?
– Residual
– Transported
• Soil Mechanics
• Geotechnical Engineering
HOW SHALL WE PROCEED
• Knowledge of Soil Mechanics
–
–
–
–
Soil Elements
Common Tests on Soil
Soil Classification
Soil Surveys
• Earthwork in Railway Projects
– Definitions
– Execution of Earthwork
– Blanket
INDEX PROPERTIES
• Mechanical (Sieve) Analysis
– Coarse grained soil
• Hydrometer analysis
– Fine grained Soil
• Consistency Limits
–
–
–
–
Liquid Limit
Plastic Limit
Shrinkage Limit
Plasticity Index
LL - WL
PL – WP
PI - IP
Degree of
Saturation in %
S=Vw/Vv
SOIL
ELEMENTS
Voids Ratio
e=Vv/Vs
Porosity in %
n=Vv/Vt
Water
Content in %
w=Ww/Ws
Bulk density
gm/cc
γ=W/Vt
Dry density
gm/cc
γd=Ws/Vt
PARTICLE SIZE DISTRIBUTION
D10 – Effective size
Coefficient of
uniformity - Cu
Cu=D60/D10
Coefficient of
Curvature Cc
D10
D30
D60
Cc=(D30)2/D60XD10
PARTICLE SIZE CURVE
Curve No.1 Cu = 10
Cc = 2.5
Curve No.2 Cu = 1.4
Cc = 1.2
Curve No.3 Cu = 4.0
Cc = 1.6
Curve No.4 Cu = 7.6
Cc = 1.0
LIQUID LIMIT - ATTERBERG’S LIMITS
Liquid Limit is
the water content at
which 25 blows
cause the groove to
close.
PLASTIC & SHRINKAGE LIMIT
Plastic Limit is water content at which 3 mm diameter roller of soil
starts crumbling
Shrinkage Limit is water content beyond reduction which does not
cause volume decrease
Plasticity Index PI or IP = Liquid Limit (LL or WL)
– Plastic Limit (PL or WP)
CLASSIFICATION IS:1498 - 1970
BOULDERS
COARSE
GRAVEL
Fines<5%
GW
GP
75>PS>4.75mm
Fines>12%
GM
GC
Fines between 5% to 12%
GW- GPGM GM
SILT & CLAY
GW- GPGC GC
GWGP
SAND
Fines<5%
SW
SP
4.75>PS>75μ
Fines>12%
SM
SC
Fines between 5% to 12%
SW- SPSM SM
SWSC
SPSC
SWSP
COMPACTION –
Primarily Expulsion of Air
COMPATION OF SOILS
γd = γ/(1+w/100)
ID - Relative density – cohesion less soils
ID = {(emax-e)/(emax-emin)}x100
18”
4.54
Kg
PERMEABILITY OF SOIL
• V = ki
– V – Velocity of flow
cm/sec
– k – coefficient of
permeability
• Porosity of soil
• Shape and size of voids
– i - Hydraulic gradient
Type of
Soil
GRAVEL
K in
cm/sec
102 to 1
SAND
1 to 10-3
SILT
10-3 to 10-6
CLAY
Less than
10-6
SOIL SURVEYS
• RECONNAISSANCE SURVEY
• PRELIMINARY SURVEY
• FINAL LOCATION SURVEY
RECONNAISSANCE SURVEY
• General Idea
• No laboratory tests
• Other Surveys, topological maps,
geological
• Visual Inspection
• Behaviour of existing structures
• Prospective Borrow Area - Soil & Blanket
PRELIMINARY SURVEY
•
•
•
•
•
•
•
•
Sampling at about 500 m interval
May be for alternative alignments too
Sub-surface soundings
Auger Sampling normally, SPT may be done.
Normally no undisturbed samples
Bore log from disturbed samples
Split spoon sampler
Mechanical Analysis & Index Properties
FINAL LOCATION SURVEY
• Sampling at about 200 - 300 m interval
• Detailed Investigations – May be at very close
intervals particularly at
– Bad Soil Locations
– Location of Important Structures
• Major Bridges
• High Banks
• Deep Cuttings
• Undisturbed Soil Samples
• Engineering Geologist
• Water table Data and seasonal variations
• Additional tests like shear strengths, consolidation,
vane shear, free swell etc.
• Sources of Soil and Blanket Material
• Cohesive subgrade – Subgrade constructed
with soil having cohesive behaviour i.e. shear
strength is predominantly derived from
cohesion of the soil. Normally soil having fines
(< 75micron) exceeding 12% (As per IS
Classification all fine grain soils, GM, GM-GC,
GC, SM, SM-SC& SC )
• Cohesionless subgrade – subgrade constructed
with cohesionless, coarse-grain soil i.e. shear
strength is predominantly derived from internal
friction of the soil. Normally soils having fines
less than 5% (As per IS Classification GW, GP,
SW & SP types of soils)
– Other type of soils having fines between 5 to
12% needs detailed study.
• Dispersive Soil – are those, which
normally deflocculate when exposed to
water of low salt content. Generally,
dispersive soils are highly erosive &
have high shrink & swell potential.
• Unstable
Formation
–
Yielding
formation
with
non
terminating
settlements including slope failure,
which require excessive maintenance
efforts.
FORMATION IN BANK
DESIGN OF RAILWAY
FORMATION
• A stable formation should be able to sustain the
track geometry under anticipated traffic densities
and axle loads during service under most
adverse conditions of weather & maintenance of
track structure, which are likely to be
encountered.
• The formation should be structurally sound – not
to fail in shear strength –dead and live loads
• and the settlements of sub grade and sub soil
should be within limits.
RAILWAY FORMATION
BEHAVIOUR
• Formation behaviour is not only
dependant on axle loads but also on
traffic density & pattern of traffic
• Therefore, simple bearing capacity
formula not applicable.
SUBGRADE
• Main function is to provide a stable
foundation for the blanket & ballast layers
• The influence of the traffic induced
stresses extends downward as much as
five metres below the bottom of the
sleepers
• Hence, the subgrade is a very important
and has a significant influence on track
performance.
Various Aspects of Designing Subgrade/Subsoil
• Subgrade and Subsoil should be designed to be safe
against shear failure & large deformation.
• Deficient shear strength of sub-grade and sub-soil:
– Bearing cap, failure of sub-grade causing cess &
crib heave, ballast pockets
– Interpenetration failure or mud pumping failure
– Slips in bank slopes or creep deformations
• Large deformation without strength failure due to :
– Swelling & Shrinkage characteristics of bank
soil/sub soil.
– In-service compaction & consolidation of banksoil/sub soil
SUB GRADE PARAMETERS
• Usually side slope 2:1 up to 6.0 m height
• Calculate Factor of safety of slopes
– High banks>6.0 m
– Poor sub soils including marshy soils
– Water table is high (submerged weight)
– Long term stability in cuttings
SUB GRADE PARAMETERS
• Unsuitable soils for construction
– Organic clay, silts & peat; chalks,
dispersive soils
– Poorly graded gravel and sand Cu<2
– CH and MH in top 3 m bank
• Special Investigations and remedies if
to be done including cutting through
shales and soft rocks which disintegrate
with water
• Mixed Soils and Boulders – Care to be
taken
SUB GRADE PARAMETERS
• Top width - 6.85 in filling & 6.25 in
cutting
• Cess width > 900 mm + additional on
curve
• Top slope 1 in 30
• Erosion control
• Borrow Pit – away from toe
• Highly cohesive – special treatment
• Minimum height of bank - 1.00m
•
•
BLANKET
The layer between the ballast & the sub grade
is the blanket
Functions :
1.
2.
3.
4.
5.
6.
•
•
•
•
Reduce stress to subgrade
Keep subgrade & ballast separate
Prevent upward subgrade fines migration
Prevent subgrade attrition by ballast
shed water from above
Drain water from below
Ballast fulfills function (1) only
Blanket fulfills all functions and including
function (1), it reduces the otherwise required
greater thickness of the ballast.
In the absence of a blanket layer a high
maintenance effort can be expected
In addition, blanket dampens vibration.
PROPERTIES OF BLANKET MATERIAL
• Reduce stress to subgrade :
• To serve as a structural material, it must have
a - High enough resilient modulus
– Stable plastic strain accumulation characteristic
under repeated wheel load
• To achieve these properties
– The material must be permeable enough to avoid
significant positive pore pressure build up under
repeated load
– Must consist of durable particles
– Must not be sensitive to changes in moisture
content
PROPERTIES OF BLANKET MATERIAL
(CONTD.)
• SUBGRADE ATTRITION PREVENTION:
– High stresses at the ballast contact points
on the subgrade surface are eliminated
by the cushioning effect of the blanket
• DRAINAGE: PLAYS TWO ROLES
– SHED WATER ENTERING FROM
SURFACE
• Its permeability should be smaller than
that of ballast & have a surface sloped
for lateral drainage
•Drain water seeping up from the
subgrade
To satisfy both roles, the sub-ballast
must generally have a permeability
between that of the subgrade & that of
the ballast
•This requirement probably will be
achieved just by satisfying the
separation criteria. However, an addl.
Criterion is used to ensure adequate
permeability to drain an adjacent layer :
D15(filter) > 4 to 5 D15 (soil being
drained)
SPECIFICATION OF BLANKET MATERIAL
•% FINES(PASSING 75µ) UPTO 5% PLASTIC FINES & UPTO 12% NONPLASTIC FINES.
• NO SKIP GRADING, COARSE GRAINULAR & WELL
GRADED & MORE OR LESS WITHIN ENVELOPING CURVE
•THE MATERIAL –WELL GRADED WITH Cu & Cc AS BELOW:
- uniformity coefficient, Cu = D60 /D10
> 4 (preferably >7)
- coefficient of curvature, Cc = (D30)²/D60 /D10 within 1& 3
REQUIRED BALLAST/BLANKET DEPTH
• A min. ballast layer thickness is needed to provide
for maintenance tamping & for void storage space
• A min. sub-ballast layer thickness is required for
performing the functions of a separation/filter layer
• In addition, the combined ballast/blanket thickness
must be sufficient to prevent progressive shear
subgrade failure, and excessive rate of settlement
through plastic strain accumulation in the subgrade
• As per RDSO guide lines, thickness of blanket
required is 0 to one meter as per soil used in top
one meter of subgrade & Axle load.
DEPTH OF BLANKET LAYER
• For axle load upto 22.5 t for different types of
subgrade soils (in top one meter)
– No need of blanket for soils
Rocky beds except shales & other soft rock,
which are susceptible to weathering or
becomes muddy on contact with water
GW – well graded gravel
SW – well graded sand
Soil confirming to blanket material
Soil having grain size distribution curve lying
on right side of enveloping curve of blanket
material in consultation with RDSO
DEPTH OF BLANKET LAYER CONTD.
• 45 cm thick blanket for soils
– GP having Cu > 2
– SP having Cu > 2
– GM
– GM-GC
• 60 cm thick blanket for soils
– GC
– SM
– SC
– SM-SC
– Should increase to one meter if PI > 7
DEPTH OF BLANKET LAYER CONTD.
• 100 cm thick blanket from soils
– ML
– ML-CL
– CL
– MI
– CI
– Rocks which are very susceptible to
weathering
DEPTH OF BLANKET LAYER CONTD.
• Soils having fines between 5 to 12% having
dual symbol e.g. GP-GC, SW-SM etc.
provide thickness as per second symbol
• Geo – synthetics can be used in
consultation with RDSO as it reduced
requirement of thickness of blanket.
• Blanket should be provided in new
construction on all lines (even with light
passenger traffic)
– In cohesive sub grade even 100 cycles of
repeated load in excess of threshold strength
will cause failure of formation.
DEPTH OF BLANKET LAYER CONTD.
• In case more than one type of soil in top one of
sub grade, soil requiring higher thickness of
blanket will govern.
• For other types of soils not covered above,
RDSO may be consulted for deciding thickness
of blanket
• For higher axle loads
– Above 22.5t up to 25 t- Add 30 cm thickness over
& above as given for 22.5 t
– Above 25 t up to 30t - Add 45 cm thickness over &
above the given for 22.5t
Day 2
EXECUTION OF FORMATION EARTHWORK
• Before actual execution, details
drawings to be prepared for entire length
of the Project giving
– Alignment
– Formation levels
– Formation width at ground levels
– Cross-sections of catch water drain & side
drains
– Cross section & levels of sub-grade,
blanket levels etc.
• Good Practices for execution of earthwork
• Preliminary work
• Preparation of Natural ground
– Site should be cleared properly for full
formation width at Ground level plus one metre
– Benching should be provided on ground
having steep slope
• Setting out of construction Limits
–Centre line of alignment (@200 m c/c or
so) and full construction width be
demarcated with reference pegs about 90
cm away from proposed toe of bank.
• Selection of Borrow area
–Sufficiently away from alignment
–Normally not less than 3 m plus
height of embankment
–Selected having soil reliable for
construction
–OMC & MDD should be checked
in Lab
– General aspects
– Field trial for compaction test be done to access
• Optimum thickness
• Optimum number passes for type of roller
planned
– Soil should be wet/dried out to get required
OMC
– Clods or hard lumps to be broken to 75 mm
lesser size
– Each layer to be compacted with specified roller
commencing from sides up to required level of
compaction before putting next layer.
•
•
•
•
COMPACTION
Compaction – Process of packing soil particles by
mechanical means increasing the dry density,
decrease of voids
Consolidation : Gradual process of vol. Reduction
under sustained loading
Compaction : Rapid reduction mainly in air voids
under a loading of short duration viz. blow of a
hammer, passing of a roller, vibration.
Advantages of compaction :
– Increase in shear strength
– Reduction in deformation under traffic
– Reduction in shrinkage & swelling
– Reduction in permeability
– Reduction in construction time.
FACTORS AFFECTING COMPACTION
• Compacting effort – Higher the effort greater the
compaction.
• Water content : Lubrication action increase in dry
density till OMC.
• Type of soil : Fine grained soils give lower dry
density than coarse grained soils
– Well graded soils have higher dry density than
poorly graded soils
– Plastics fines have marked effect on compactibility
• Other factors :
– Thickness of lift
– Contact pressure
– Speed of rolling.
FIELD COMPACTION EQUIPMENTS
• Three classes : Rollers, rammers & vibrators
• Smooth wheel rollers :
– 3 wheel or 2 wheel type
– best suited for gravel, sands, crushed rocks and
any material requiring crushing action.
– More no. of passes, more compaction.
• Sheep’s foot Rollers :
– Numerous projections
known as feet.
– Kneading action from
bottom upwards
– When fully compacted
no foot penetration
– Suitable for cohesive
soils at low OMC.
– Unsuitable for gravels,
sands
– More no. of passes
more compaction.
• Pneumatic Rollers
– Compaction effort
depends on
weight, tyre dia &
inflation pressure.
– Both pressure &
kneading action
– Suitable for
cohesive soils at
high natural m/c.
– Cohesion less
sands and gravels.
• Vibratory Rollers :
– Out-of-balance weight type or pulsating
hydraulic type
– Frequency between 1000-3000 rpm.
– Suitable for granular soils
– Allow compaction to a higher depth.
– Not suitable for cohesive soils.
• Rammers :
– Pneumatic or internal Combustion type.
– Suitable in area with restriction working
space.
ADVANTAGES OF COMPACTED BANK
• Higher speed of opening.
• Opening to goods & pass. Traffic
simultaneously
• Max. sectional speed can be achieved
in shortest time
• Ballast can be laid directly
• LWR can be laid
MEASUREMENT OF FIELD COMPACTION
• determining dry density of soil in-situ
methods :
– Sand replacement
• Any type of soils
• slow method
– Core cutter
• Fine grained cohesive soil
• convenient method
– Water displacement
• only cohesive soils
– Nuclear
• In-situ density & w/c
• Placement of Back-fills on Bridge approach
– Back fills resting on natural ground may cause
differential settlement, vis-a-vis abutment, which
rest on comparitively much stiffer base
– Back fill should be designed carefully to keep
• Settlement within tolerable limits
• Coefficient of subgrade reaction should have
gradual change from approach to bridge.
– Backfills on bridge approaches shall be placed in
accordance to para 605 of Indian Railways Bridge
Manual 1998.
– Fill material being granular and sandy
type soil be placed 150 mm on lesser
thick layers & compacted with vibratory
plate compactors.
– Benching should be made in approach
embankment to provided proper
bonding.
SKETCH SHOWING BACKFILL DETAILS
IMPORTANCE OF BACKFILL
• IMPORTANCE OF BACKFILL GENERALLY NOT
UNDERSTOOD.
• MAGNITUDE OF LATERAL EARTH PRESSURE DEPENDS
ON:
- angle of internal friction – the more the value of ø, the
lesser is the magnitude ( table below )
Grain size
Values of Ø in degree
Clay
30 ( Generally 20)
Sand & Gravel
32 – 41
Blasted rock fragments
40 - 50
- density
- presence of water may increase earth pressure upto
250%
• COHESIONLESS MATERIAL: - provide effective drainage.
- value of ø is more.
• Drainage arrangement in banks & cutting
– Effective drainage of rainwater in monsoon is
very important to safe guard subgrade from
failure
– Drainage of embankment
• Cross slope is provided from centre towards
end.
• No side drains required except in case blanket
layer goes below natural ground level
• On double line, central drain should be
avoided as far as possible.
– Drainage in Cuttings
• Side drains
–Required water carrying capacity side
drains be provided on both sides except
where height of cutting is less than say
upto 4 m.
–In deep cuttings, catch water drains of
adequate capacity are required along
with side drains.
• Catch Water Drains
 Required to control huge quantity of water coming
from hill slope in cutting from safety consideration
 Catch water drains should be made pucca/lined
with impervious flexible material locally available
 Catch water drains should be designed properly
with - Adequate slope
–No weep hole
–Sealing of expansion joint
–Regular inspection & maintenance
–Proper protection against tail end erosion.
CATCH WATER DRAIN
LOWERING OF GROUND WATER IN A WET CUT
• Erosion control of slopes on bank/cutting
– Exposed surface of bank/cutting
experiences surfacial erosion due to action
of wind & water
– Erosion control measures are commonly
classified into following four categories..
– 1)Conventional non-agronomical system
• This system uses asphalting, cement
stabilization pitching etc.
• System is best utilized against seepage,
erosion by wave action etc.
– 2) Biotecnical system
• Vegetation is provided on exposed surface
• Best suited for soils having some clay
fraction,
• Suitable grass used are doob grass, chloris
gyne, Inponea gorneas, casuariva & goat
foot creepers, vetiver grass etc
– 3)Engineering System
• Geo-jute
–Used in areas having high erosion
–Biodegradable & helps in growth of
vegetation on degradation
–Two types – fast/slow biodegradable.
– 4) Polymer geogrids
• Used under unfavorable soil & rainfall
condition where vegetative growth is difficult
• Flexible, non biodegradable. Resistant to
chemical effect, ultraviolet degradation
resistant & stable over a temperature of 601000C
– Hydro-seeding system
• Non-conventional & innovative system of
development of vegetation
• Verdyon mulch solution @ 100 to 150 gm/m2
is sprinkled on surface from germination of
vegetation as per local soil/climatic condition.
SHOTCRETING
PITCHING
RETAINING WALL
GABIONS
ROCK BOLTING
SOIL NAILING
BOULDERNETS OF GEOSYNTHETICS
BOULDERNETS OF GEOSYNTHETICS
CATCH FENCING
• Other important aspects
• Suitable slope be provided during rolling to
avoid ponding of water
• Top slope 1 in 30 way from centre
• Extra wide bank by 500 mm on either side &
then cut & dressed to avoid loose earth on
shoulders
• Minimum overlap of 200mm between each
run of roller
• At the end of working day, fill material should
not be left uncompacted.
• Rain cuts should not be allowed to
developed deep and wide.
• After finishing formation movement of vehicles
should not be allowed on top.
• In conversion/doubling/rehabilitation projects,
suitable benching of existing slopes be done
before new earthwork is taken up.
• 30cm granular base be provided where water
table is high & fill material is fine grained.
• At places where embankment material are not
conductive to plant growth, top soils from site
clearance/cutting/borrow pits be stored for
covering slopes of embankment/cutting.
• WIDENING OF EMBANKMENT • Uproots vegetation, remove loose materials.
• Benching at every 30cm ht.
• E/w in layers. Each layer sloping out 1:30.
• Compaction by using vibrating rollers of around
900mm wide.
• 6 to 8 passes normally sufficient
• 98% of MDD or equal to existing bank.
• Density to be checked at 200m length.
• Width of each layer in excess by 300mm.
• Excess width to be cut and dressed
• RAISING OF EXISTING FORMATION • Raising to be done after widening.
• Raising <150mm, with ballast restricting overall
thickness to 350mm.
• Raising 150mm to 1000mm,
• existing ballast to be taken out
• granular material to be provided
• top 600mm of granular material shall satisfy
the specifications of blanket & compacted
• thereafter clean ballast to be inserted.
• Raising >1000mm, desirable to lay a detour
temporarily.
• EARTHWORK IN DETOURS
• In accordance with RDSO’s guidelines.
• EMBANKMENT ON SOFT SOIL
– Soil shall be improved using
• Preloading and stage construction as per the
design.
• Installation of vertical sand drains.
• Installation of prefabricated vertical drains.
– Selection of particular scheme depends on rate
of construction & techno-economic
consideration.
– This may be decided in consultation with
RDSO.
• SANDWICH CONSTRUCTION OF BANK WITH
COHESIVE SOILS
– May be adopted with cohesive soils having
very low permeability (< 10-2 cm/sec) & bank
height more than 3m.
– A layer of coarse sand (Cu > 2) of about 20 to
30 cm be provided at interval of 2 to 3 m.
– Even up to 3 m bank height, a bottom layer of
sand be provided
– Before adopting such construction a detail
techno-economic study be carried out if
required, RDSO be consulted.
• Safety at work site
– Necessary precaution towards safety at
work site including doubling & gauge
conversion should be part of contract
agreement
• Environmental aspect
– Efforts should be made to ensure least
disturbance to surrounding environment
– Rules & regulations of Govt. be followed in
this regard
QUALITY ASSURANCE OF
EARTHWORK
• Adequate quality control/checks at all stages
of construction be carried out
–
–
–
–
Selection of construction material
Adoption of Method
Use of suitable machinery
During execution of work.
• Setting up of GE lab field lab
– No. of GE field labs be set up as per requirement
of project/work site
– Aspects to be looked after by GE lab
• Ensure quality of supplied soil and blanket material
• Evaluate method of compaction by conducting test
• Exercise moisture and density control
– Depending on requirement, field lab to be
equipped with minimum equipment to
ensure following minimum tests
•
•
•
•
Gradation Analysis – Sieve and Hydrometer
Atterberg’s limits – Liquid limit & plastic limit
OMC, MDD & Relative density
Placement moisture content & insitu Density
• QUALITY CHECKS ON EARTHWORK
– Quality control on construction Material
• To ascertain suitability of material
• To decide OMC & MDD for quality control
inputs for compaction control
• These tests to be done for both borrow
material & blanket material
• Frequency of Testing of site
– Borrow material
• One test at every change in strata
• Minimum one test for every 5000 cum
– Blanket Material
• Minimum one test for every 500 cum or part
thereof
• Quality control checks on finished
earthwork
– Compacted earth
• Method of sampling
• Acceptance criteria
–All types of soil & when compacted –
»by dry density 98% of Max. Dry
density.
–During widening/gauge
conversion/rehabilitation work
»98% of MDD or
»70% of relative density
• Frequency of testing
–For blanket/top one meter of subgrade
»One check for every 200 sqm
–For other places
»One check for every 500 sqm
–At special locations closer frequency
may be adopted
–Bank widening
»One check at every 200m
Method of sampling
• DEGREE OF COMPACTION OF EACH LAYER
ASCERTAINED BY MEASUREMENT OF DRY DENSITY /
RELATIVE DENSITY OF SOIL AT LOCATIONS SELECTED IN
SPECIFIED PATTERN SHOWN BELOW.
NOTE: x & y AS PER SAMPLING AREA
RQUIREMENT
– Formation level
• Subgrade () 25mm
• Blanket +25mm
– Cross slope
• 1 in 28 to 1 in 30
– Side slope
• Should not be steeper than design
– Formation width
• Should not be less than specified
MAINTENANCE OF RECORDS
• Quality control Records
– Characteristics of borrow materials
– Quality of blanket materials
– Field compaction trials
– Quality of compaction of earthwork including
blanket material
• Quality of material & its compaction of
backfill behind bridge approach etc.
• Details of machineries engaged in execution of
earthwork including output as per Performa
decided by field engineers
• Permanent Records
– Desirable to prepare completion drawing of
embankments and cutting including special
features like
• Toe walls
• breast walls
• Catch and side drains
• Cross section of embankments/cutting
• Type of soil in subgrade
• Depth of blanketing material
• Geological features.
THANK YOU