The document provides detailed guidelines for the construction and safety of mounded bullets used for storing LPG, referencing various safety codes and standards including OISD 150 and EEMUA 190:1000. It emphasizes the advantages of mounded storage over conventional methods, such as enhanced safety against explosions and environmental benefits. Additionally, it outlines requirements for design, monitoring, inspection, and maintenance to ensure operational integrity and safety compliance throughout the lifespan of the storage vessels.

1. PRESENTATION ON
MOUNDED BULLETS
Reference – OISD, EEMUA
PUBLICATION 190:1000,
SMPV rules, relevant IS &
IRC codes

2. Index –
Part I – Guidelines for construction of mounded bullets based on OISD
150 – Slide 3 to 19
Part II – Guidelines for construction of mounded bullet based on
EEMUA 190:1000 – Slide 20 to 65
Part III – Monitoring and inspection of construction of mounded bullet
– Slide 67 to 102
Part IV – Pile foundation for mounded bullet – Slide 104 to 119
Part V – Ground improvement by vibro technique and vibro stone
columns – Slide 121 to 155

3. Part I – Guidelines for Mounded bullet
construction based on OISD 150

4. PART I –GUIDELINES FOR MOUNDED BULLET CONSTN.
BASED ON OISD 150 –
INTRODUCTION -
With a view of attaining the standardization in design
philosophies, operation & maintenance coupled with
the experiences of serious accidents in India & abroad
Ministry of Oil & Natural Gas constituted, in 1986, Oil
Industry Safety Directorate
Design & safety requirements for LPG Mounded bullets
– OISD 150 (First revision, amended edition Jul 2008)
First Edition was published in 2000.

5. LPG handling has many challenges due to its
dangerous properties. The conventional method of
storing LPG in India is in a pressurized vessel above
ground.
Mounded storage has proved to be safer compared to
above ground storage as it provides passive & safe
environment & eliminates possibility of boiling liquid
expanding vapor explosion. The cover of mound
protects vessel from fire engulfment, radiation from
fire & acts of sabotage.

6. SCOPE
This standard lays down min. requirements of safety,
design, layout, installation, operation, maintenance &
testing for above ground fully mounded vessels of LPG
storage in refineries, gas processing plants, terminals,
bottling plants & auto LPG dispensing stations
otherwise falling under the scope of other OISDs such
as OISD 144, OISD 116, OISD 118, OISD 169, OISD 210
as applicable. This standard only supplement these
standards for Mounded Bullet storage of LPG.

7. DEFINITIONS
Mounded vessel – A storage vessel sited above ground
and covered completely with mound of earth except
nozzles, MH covers, inspection covers.
Bullet – A horizontal pressure vessel for storage of LPG
at ambient temperature.
Compressed gas – Any gas, liquefiable gas or gas
dissolved in liquid under pressure which in a closed
container exerts a pressure exceeding two atmosphere
at max. working temperature.
Explosive mixtures – Mixture of combustion agent and
a fuel
Hazard area classification – Based zone/group wise
based on flammability & explosive vapor-air mixture

8. DEFINITIONS -CONT.
Bulk vessels – Pressure vessels of more than 1000 lit
water capacity for storage or transportation of
compressed gas.
Water capacity – Volume of water it can hold at 15-
degree temperature.

9. DEFINITION CONT.
Flammability limits – Range in % age by volume of
flammable vapor which in admixture with air forms
explosive mixture.
Gas free – Condition when concentration of a
flammable gas in eqpt. is well below threshold limits
so that it is safe for a person to enter eqpt.
Hot work – An activity which may produce enough
heat to ignite flammable mixture.
Kerb wall – wall of appropriate height and size of
suitable material to contain spillage of LPG.

10. DEFINITIONS CONT.
LPG – Mixture of light hydrocarbons which are gaseous
at ambient temperatures and atmospheric pressures
but may be condensed to liquid state at normal
ambient temperatures by application of moderate
pressures.
Purging – An act of replacing atmosphere within eqpt
by inert gas to prevent formation of explosive mixture.
Statutory Authority – Appointed under special
act/regulation for specific function. CCOE is statutory
authority to administer SMPV rules 1981.
Source of ignition – Device/eqpt are capable of
providing thermal energy to ignite flammable LPD-AIR

11. DEFINITIONS CONT.
SMPV rules – The static & mobile pressure vessels
(unfired) rules 1981 governing the storage, transport,
handling of compressed gas in vessels exc. 1000 lit in
volume. These rules are framed under Indian Explosive
Act,1884.
Shall – Indicates mandatory requirement.
Competent Person – A person recognized by
applicable statutory Authority for a job.

12. Why Mounded Bullets –
Sand cover takes impact of external missile bodies
BLEVE (boiling liquid expanding vapor explosion) is eliminated as no
fire is possible below bullets
Reduced fire cases as compared to spheres

13. CL. 4.0 -LOCATION & SEPARATION
DISTANCES
Location shall be as specified in cl. 4.1 of OISD 150
Separation distances shall be as per cl.4.2 of OISD 150
FEATURES –

14. CL. 5 -MOUNDED LPG STORAGE
FACILITIES
Storage vessels – horizontally placed cylindrical
vessels shall be used for mounded storage.
Mechanical design shall be based on :
ASME Sec VII or PD -5500 or equivalent duly
approved by CCE.
Material shall be as per Cl. 5.1 (ii)
Design temperatures, design pressure & other
considerations shall be as per Cl. 5.1 (iii), (iv), (v)

15. CL. 5.2 – MOUND
Mounded vessels shall be placed on firm foundation
so as to prevent movement or floatation.
Subsoil, rainwater should not be allowed to percolate
in the mound. Foundation shall be constructed such
that vessel slope of min 1:200 is maintained to
facilitate draining.
Soil condition shall be deciding factors for the type of
foundation. The preferred type of foundation is a
continuous sand bed, supporting the vessel over its
full length.
Foundation shall have sufficient load bearing capacity.

16. CL. 5.2 – MOUND CONTD.
Following min factors shall be considered:
Load of vessels during operations, during hydro test
when sp. Gravity of liquid is 1 instead of that of LPG
Earth/sand cover
Settlement behavior of foundation as regards to
overall settlement, differential settlement causing of
bending of vessels & sloping of vessels.
Sand bed beneath vessel shall be of min. 0.76 m to
facilitate drainage from liquid outlet pipe by gravity.
Bottom connections are permitted by providing an
opening/tunnel & shall be designed to withstand
forces acting on them.

17. CL. 5.2 – MOUND CONTD.
Provision shall be made for encountering consequence
of settlement of the vessel. The surrounding of bottom
connection shall be such material that can absorb such
settlement.
Mound shall protect the vessel from effects of thermal
radiation and jet flame impingement.
Mound shall be of earth, sand or other non-
combustible, non-corrosive material with min. 700
mm cover.
Mound surface shall be protected against wind & rain
by cover of stone, concrete tiles etc.

18. CL. 5.2 – MOUND CONTD.
Water ingress shall be minimized by impervious layer
of suitable material but continuous impermeable cover
shall not be installed to avoid gas accumulation.
Proper drainage and slope on top shall be provided.
Longitudinal axis of vessels in a mound shall be
parallel to each other with ends in line.
Valves shall be accessible without disturbing the
mound.
Provision shall be made to monitor the settlement of
mound by permanent reference points (min. 3) by
which uniform/differential settlement and bending of
vessel shall be monitored. (one each at ends and one

19. CL. 5.2 – MOUND CONTD.
Max. permissible differential settlement shall be
determined at the project design stage. Regular
monitoring shall be done of settlement throughout
lifetime and records be maintained.
The settlement of the vessel shall be monitored at
least ½ yearly.

20. Cl. 7 – Hazardous area classification
Shall be as per IS 5572 & OISD 113
Fire detection/protection system shall be as per Cl. 8
Gas detection system shall be as per cl. 8.2
Water requirement/storage shall be as per cl. 8.3 to
8.7
Operation, maintenance & inspection shall be as per
cl.9

21. 9.4 – vessels shall be subjected to hydrotest once
every 10 years or at every welding to the vessel
(repairs or new connection) whichever is earlier.
9.5 – Vessels shall be tested every 5 years internally
using visual and other techniques for the following:
a) All the weld joints shall be examined through NDT
such as radiography, wet magnetic particle test (WPT),
Dye penetration test (DPT), ultrasonic flaw detection to
ensure integrity of the joints.
b) Wall thickness of the vessels shall be measured

22. GUIDELINES ON MOUNDED BULLET
CONSTRUCTION BASED ON EEMUA
190:1000

23. PART II – BASED ON EEMUA
190:1000 GUIDELINES
GUIDELINES FOR THE DESIGN, CONSTRUCTION AND
USE OF MOUNDED HORIZONTAL CYLINDRICAL VESSELS
FOR PRESSURISED STORAGE OF LPG AT AMBIENT
TEMPERATURES - [ EEMUA PUBLICATION 190:1000,
THE ENGINEERING EQUIPMENT AND MATERIALS USERS
ASSOCIATION] [For guidance purpose. The final
document to be referred to are tender provisions and
the relevant codal provisions]
ONLY CIVIL CONSTRUCTION PART IS COVERED HERE.

24. Scope –
Guidance is provided covering the main requirements
for the successful design, construction, and use of
mounded facility:
Criteria for selecting mounded storage ‘soil survey
Foundation and mounded design
Inspection and testing
Inservice monitoring and inspection and maintenance

25. – Mounded Storage
Mounded storage is employed because it provides
additional safety compared with above ground storage
of gases in sphere or bullets. Main advantage is that
occurrence of BLEVE is virtually impossible [A boiling
liquid expanding vapor explosion (BLEVE, /ˈblɛviː/
BLEV-ee) is an explosion caused by the rupture of a
vessel containing a pressurized liquid that has reached
temperatures above its boiling point].

26. OTHER BENEFITS ARE:
Protection of vessels against
Heat radiation from nearby fire
A pressure wave originating from an explosion
Impact by flying objects
Sabotage
Satisfies environmental and aesthetics
Results in reduced site area due to less stringent inter-
spacing requirements.
The safety distance to the site boundary can be reduced
considerably.

27. The design aspects of mounded bullets are in general
more complicated than those above ground spheres or
bullets. Particular attention to be given to the
interaction between vessel and soil and to corrosion
protection.
Depending on site conditions, ground water level, the
vessel may be installed either at grade levels or in an
excavation. Vessels need to be installed above the
highest known water table level and the soil cover
therefore protrudes above grades as an earth mound –
hence the term “mounded storage”.

28. Vessels in open underground vaults and excavations
are not considered to be mounded. Mounded vessels
are provided with connections through the top of
mound.
Designed for min. lifetime of 25 years.
The min. distance between the vessels depends on
activities such as welding, coating, backfilling and
compaction of the backfill material. A distance of 1 m
is considered to be practical min.
Maximum diameter of 8 m is regarded as upper limit.

29. For vessels which are founded on a sand bed, the
length of vessels should be no more than 8 times the
diameter in order to prevent the designed shell
thickness being governed by longitudinal bending of
the vessel due to possible differential settlements or
construction tolerances of vessels and foundations.
The max. allowable length is determined by subsoil
conditions (especially if the differential settlements are
expected), size of site and economy of design.
The above restrictions limits the max. volume to
approx.. 3500 cu. M gross. No limitations on lower
size.

30. FOUNDATION & EARTH MOUND
For soil investigation the purchaser shall have to give
following details to the contractor:
Details of construction site
Orientation of vessels relative to plant north.
Prevailing wind direction
Site development plan
Ground levels and ground water table
Seismicity of the area
Depending on the history, chemical survey of the sub
soil and ground water shall be also considered.

31. Fieldwork
The heterogeneity/stratigraphy of the subsoil shall be
investigated by cone penetration tests (CPT) and
borings. If CPT is not possible the number of borings
shall be increased.
All borings shall be combined with recovered
undisturbed samples and SPTs, both at average
intervals of 1.5 m and at changes of strata.
The min. number of field tests is set out as below:

32. With CPTs CPT CENTRE TO CENTRE 20+/- 5M
BH AT LEAST 1 OR 1 PER 2 VESSELS.
USS/SPT EACH BH
SCT AT LEAST 1 OR 1 PER 2 VESSELS.
DCT 1 BH LOCATION
PM AT LEAST 1
BH+ USS/SPT CENTRE TO CENTRE 20+/- 5M
SCT AT LEAST 1 OR 1 PER 2 VESSELS.
DCT 1 BH LOCATION
PM AT LEAST 1

33. Positions of CPTs and BH shall be evenly distributed over the length
of vessels.
The testing locations are indicated below:
One vessel Along the center line of the vessel
Two vessels Both outside edge of the vessels in the longitudinal direction.
Three vessels or more For outer vessels along the outside edges and for the inner vessels along the centre
line

34. The scope of soil investigation may be reduced if
reliable information in the form of electromagnetic
survey, geo-electrical survey is available.
Depending on the knowledge of site, specific
geohydrology [e.g. presence of aquifers - An aquifer is
an underground layer of water-bearing permeable
rock, rock fractures or unconsolidated materials.
Groundwater can be extracted using a water well. The
study of water flow in aquifers and the
characterization of aquifers is called hydrogeology,
phreatic ground water level - The phreatic zone, or
zone of saturation, is the area in an aquifer, below
the water table, in which

35. relatively all pores and fractures are saturated with
water. ... The phreatic zone size, color, and depth may
fluctuate with changes of season, and during wet and
dry periods, piezometric levels from aquifers -
For groundwater "potentiometric surface" is a synonym
of "piezometric surface" which is an imaginary surface
that defines the level to which water in a
confined aquifer would rise were it completely pierced
with wells, piezometric levels from aquifers and level
variations) the number of open standpipe piezometers
shall be determined.

36. – laboratory work
Tests shall be carried out on recovered samples (undisturbed and disturbed).
Classification tests:
On all samples
Visual
Wet & dry unit weight
Water content
Particle size analysis
Atterberg limit
Consolidation tests (seven loading steps + one unloading step)
Drained and/or undrained triaxial tests to obtain strength and stiffness parameters
of soil.
Chemical analysis of soil and ground water samples.
Optimum moisture content
Electrical resistivity of soil

37. Reporting –
Factual data –
Topography and geodetic levels of the site
Ground water levels including fluctuations
Results from field work and lab work
Stratigraphy along with axis of the vessels (indicating
position of CPTs and BH)

38. Engineering data –
Discussion of factual data against site geology
Possible subsoil variation
Recommendation of installation level of vessel relative
to ground water levels.
Evaluation of load conditions during mound
construction and operational lifetime, e.g. including
horizontal loads on piled foundations as a
consequence of mound construction.
Discussion of recommendation of type of foundation
9see 3.2 to 3.8)

39. Bearing capacity
Selection of governing load conditions for the critical
stages of construction and for the operational lifetime
of the mounded storage facility.
Susceptibility of the subsoil to liquification, if relevant.
For soil bearing foundation, subsoil bearing capacity
during various stages of mound construction and
during lifetime of the mounded storage facility.
For piled foundations with raft or saddles, axial pile
bearing capacity taking in to account positive/negative
skin friction and end bearing, group effect and lateral
bearing capacity.

40. Settlement
Settlement analysis to be executed shall specify
elastic, consolidation and creep components.
Selection of governing operational load.
Settlement of vessel during hydrotesting (during
construction and during retest conditions.
Minimum and maximum long-term subgrade
(bedding) modulus along the vessel’s axis.

41. Stability analysis
Of mound slope for various load cases during
construction and during operational lifetime
Construction of mound, provide advice on:
Suitability of fill material for foundation bed and
construction of mound
Compaction of vessel foundation bed and fill material
surrounding the vessel
Remedial measures to overcome severe erosion during
construction

42. 2Types of foundation –
3.2.1 – Soil bearing foundation
A soil bearing foundation which supports the vessel over its full length, on a
sand bed, is preferred. This type of foundation provides continuous support,
which allows an economic structural design of vessel, an economic
foundation method and optimal cathodic protection.
In order to reduce settlements, it may be necessary to employ soil
improvement methods. A preload embankment, preferably consisting of the
fill materials to be used in mound construction, is an economic solution. The
duration of preload period depends on subsoil condition, specially the
period required for drainage of water from subsoil. In some cases, additional
fill material may be required to minimize the preload period. During
construction of embankment and subsequent preload period, settlement
shall be monitored and recorded. Monitoring of settlements during
construction and the preload period allows for foundation design
verification.

43. In addition, at specific locations soil improvement may be required by
replacing the subsoil.
Although a soil bearing type of foundation is preferred, it may not be
always possible. If for example long term settlements are too large, a
sound and/or economic structural design of the vessel may not be
possible. Also, seismicity may affect the selection of foundation type.

44. 3.2.2 Sand bed on piled concrete slab
If for settlement reasons, the project does not allow the use of a soil
bearing foundation, a piled foundation supporting a concrete slab
may be considered. The vessel shall be then be installed in a sand
bed having a minimum thickness of 1 m, on top of concrete slab.
3.2.3 Vessels on saddles
In some designs the vessels are placed on saddles and subsequently
on piled foundations as an alternative to above foundations. This
foundation is completely different to above foundations. In fact, a
conventionally supported vessel is created but covered with a layer of
soil.

45. An undesirable side effect occurs with piled saddles, i.e. the subsoil
will settle but saddles will not. This causes the mound to separate
from underneath the vessels. It is for this reason that the design
philosophy described in this document is not valid for mounded
vessels on piled saddles. Due to the complexity in the design,
construction and long-term cathodic protection, piled saddles are not
recommended as foundations.
3.3 Settlement of soil bearing foundations
3.3.1 Immediate settlements
Settlements of the vessels and/or preload embankment occurring
immediately during construction shall be analyzed and compared
with predicted settlement (trending).

46. 3.3.2 Long term settlements
Settlement analysis should also address long term settlements during
operational life time. Predicted long term settlements shall be used to
derive a subgrade modulus required for vessel design process.
3.3.3 Total and differential settlements
In settlement analysis both shall be addressed.
The maximum allowable total settlement of the vessel depends,
amongst other things, on connecting piping and/or whether a tunnel
is to be built to house a bottom discharge pipe.

47. Differential settlements of the vessel will affect its longitudinal slop
and uniformity of support.
Settlements may be reduced by the application of soil improvement.
3.4 Settlement monitoring
3.4.1 Settlement monitoring during preloading
Prior to installation of a preload embankment, settlement plates shall
be installed on the original ground level. They shall be of 1 X 1 m
base plate with 25 mm diameter vertical rod. The rod shall extend
above the preload embankment for measuring purpose. These plates
shall be removed after preloading period. Frequency of settlement
shall be as follows:

48. phase Frequency
preloading Month 1 & 2 Weekly
preloading Month 3 & 4 Fortnightly
preloading Month 5 onwards Monthly
Vessel installation weekly

49. In cases of doubt on the stability of preload embankment and/or
mound as consequence of the presence of top clay. Excess pore water
pressures should be monitored during preload period and/or mound
construction.
3.4.2 settlement monitoring during operation
Permanent reference points shall be located longitudinally on top of
the vessel to monitor the vessel settlements. The maximum spacing
of the points should be approximately twice the vessel diameter.
Minimum 3 points shall be installed to be able to identify possible
vessel bending (i.e. two near the vessel ends and one in the middle).
Nozzles/domes can be used for this purpose.

50. Settlements shall be monitored during the life time. Frequency shall depend
on the predicted settlements and on the associated period. The results
shall be compared with preload settlements. If the actual settlements
exceed that preload and/or the rate of settlement increases, corrective
action based on specialist shall be taken.
During the hydrostatic pressure test settlement monitoring should be
performed for site fabricated vessel which usually undergo this test on their
foundation. The occurring settlements shall be monitored for the relatively
high hydrostatic loads at 0,25,50,75 and 100% filling and after 48 hours
with vessel completely filled. The settlement rate during this testing period
to diminish with the time as otherwise there should be danger of instability.
If the rate does not diminish adequately, client shall be informed
immediately. The vessel shall be (partly) emptied and a geotechnical
engineer and mounded vessel specialist should be consulted.

51. 3.5 Foundation design
3.5.1 General
Shall be designed, constructed and monitored as per applicable standards.
The vessels should be installed at least 0.6 m above the highest ground
water level on a sand bed of at least 1 m thickness in order to obtain
proper bedding-in.
The foundation of the vessel shall be constructed such that during the
operational life time of the vessel, its longitudinal slope shall be between
1:200 minimum and 1:50 maximum. The former is the minimum for
effective drainage whilst the later is intended for minimizing the dead
stock. Hence in the design phase the predicted immediate and long-term
settlements along axis of each vessel shall be taken in to account in
determining the slop.

52. 3.5.2 Operational phase of vessel
In operational phase it is assumed that the vessel is supported over
an angle of 120 degrees. The minimum safety factor during
operations shall be 2.
3.5.3 Construction phase of vessel
During construction, it may be assumed that the vessel is supported
over an angle of less than 120 degrees (with minimum of 60
degrees).
In the case of on-site vessel assembly, the maximum foundation
loading will occur during hydrostatic pressure testing. The maximum
load will consist of the weight of the vessel and the water. The
bearing capacity of the foundation shall be verified for this load

53. The minimum safety factor for the bearing capacity and overall vessel
stability during the hydrostatic pressure test shall be 1.5.
3.6 Mound design
3.6.1 Geometry
The slope of mound shall not exceed the natural slope of the fill
material and should be 1:1.5 maximum. Following the results of the
soil investigation, a slip rate analysis shall be performed to perform
the stability of mound. When performing the calculation, it should be
noted that the angle of friction along the vessel-soil interface and the
effective stress in a zone next to the vessel is lower than in an “all soil
condition”.

54. 3.6.2 External loads
The purpose of the mound is to protect the vessels against the
external events such as radiation in case of fire, flying objects and
sabotage. Hence the thickness cover shall be at least 0.5 m.
temporary loadings on the vessels by construction equipment on the
mound shall be avoided when the thickness of the cover is less than 1
m.

55. 3.6.3 Erosion protection
The slopes and top of the mound shall be protected against erosion.
To prevent the possibility of gas accumulation inside the mound,
continuous impermeable coverings should not be used.
Open drain channels shall be constructed along side the toe of
mound. The mound top shall have slight downward slope to have
effective drain off. Only minimal rain water percolation shall be
allowed through the erosion protection. Rain water accumulation shall
be avoided inside the mound.

56. 3.7 Foundation and mound material
Consideration shall be given to following while selecting the material.
In the case of multiple vessels there is limited accessibility for
mechanical fill and compaction equipment to the area in between the
vessels. In these cases, fill material should be chosen for ease of
handling.
The fill material shall be compactable in order to minimize
settlements.
The fill material shall be suitable to allow proper functioning of
cathodic protection system. However, sea sand and other unsuitable
fill materials undesirable for corrosion reasons shall not be used.

57. Although it is not the intention to remove any mound for inspection,
excavation of the vessels may be required (by govt regulations).
For the above reasons sand should be used for both the sand bed and
mound. It shall fulfill following criteria:
It shall be clean.
The maximum silt content (particles smaller than 0.063mm) shall not
exceed 10% by weight and the maximum organic material content
shall not exceed 3% by weight.

58. The maximum sulphate content shall be 0.02%.
The maximum chloride content shall be 0.02%.
The maximum particle size shall be 2 mm
Grain size distribution shall have a uniformity coefficient (D60/D10)
of between 4 & 10.
In areas where sand is difficult to obtain, at least 0.3 m sand shall be
placed around vessel to protect coating.

59. 3.8 Construction of foundation and mound
3.8.1 Foundation
The sand bed foundation, that is the bedding associated to the 120
degrees bottom support angle, shall be prepared in layers of maximum 0.3
m thick. Each layer shall be compacted to at least 95% of MDD. (Here we
shall have to abide by the Indian context and the relevant contract and
codal provisions.)
The in-situ density shall be either by cone penetration testing or the
replacement method.
The cylindrical bottom profile of the vessel should later be cut in the sand-
bed by excavation. A steel template with curvature of the vessel should be
used to shape the sand-bed to the required profile. Over excavation should
be avoided.

60. Due to construction tolerances, the axis of vessel shall only deviate
from straight line up to 0.3% of the vessel.
The construction procedure for foundation depends on the
fabrication method for the vessel but shall provide uniform vessel
support.
If the vessel has been assembled elsewhere, the deviations of the
vessel axis from straight line shall be measured and the sand bed
shall be shaped accordingly to obtain good fit of the vessel in sand
bed and hence an even support.

61. If the vessel is assembled on its foundation, the shape of the sand
bed should be made in sections with length equal to length of vessel
section to be placed on it. Each foundation section shall be completed
just before the corresponding vessel section is placed on it and after
the previous section has been at least tack welded in place. This
procedure shall help in obtaining uniform support of the vessel.

62. It may be necessary to dig trenches in the sand bed for welding and
inspection of circumferential seams of the vessel sections. The sides
of the trenches shall be properly supported e.g. with sand bags. After
the weld inspection and hydrostatic pressure test is successfully
carried out and the coating applied, the trenches shall be carefully
backfilled with properly compacted sand. Coatings of the welds shall
be only applied after hydrostatic pressure testing. The number and
sizes of the trenches shall be restricted to minimum because of the
restriction in achieving full compaction. The method of backfilling
shall be approved by the client.

63. Depending on the distance between the trenches, the local code
requirements (which might require full vessel support during hydro
static testing) and the calculations, it may be required to temporarily
backfill the trenches prior to hydrostatic pressure test. In this way the
maximum load on sand bed is reduced.
To avoid too much disturbance to the foundation during construction,
the shoulders of the foundation should have a horizontal part of at
least 2 m wide before sloping down to grade.

64. After completion of the vessel but prior to the hydrotest, the
foundation shall be repaired and recompacted where required.
3.8.2 Mound
Horizontal support of the vessel by the mound is not assumed in the
vessel design and is therefore not required. Too much compaction
during installation of the mound may in fact impose excessive loads
on the vessel. In view of this, it is advised that the mound should be
compacted to 90% of MDD to prevent excessive settlements of sand
only, having due regard for the material stability from stability and
cathodic protection point of view. (Here we shall have to abide by the
Indian context and the relevant contract and codal provisions.)

65. If during construction a foundation with a reduced angle of support
has been used, it shall be built up with well compacted sand (95% of
MDD - (Here we shall have to abide by the Indian context and the
relevant contract and codal provisions.) to an angle of support of 120
degrees before compacting the mound.
5. Inspection, testing and certificates [ only civil part is considered]

66. 5.1.2 Hydrostatic pressure test
The vessels shall be tested at 1.25 times maximum design pressure,
unless stipulated otherwise. The test may be carried out in the shop
or at site on the foundation. For shop tested vessels the pressure will
be measured with a gaige having a range of 1.5 times the test
pressure and an accuracy of +/- 0.6% or finer. For field tested vessels
a pressure recorder of the same accuracy as that of gauge shall be
used. In both the cases the temperature of the test water and ambient
temperature shall be continuously recorded.

67. The pressure need not be repeated if the entire vessel was pressure
tested in the shop. However, the vessel shall still be used for
foundation preloading.
The pH of the water shall be kept between 6 & 7. The vessel shall be
completely drained, cleaned and dried by hot air.
5.1.5.2 Settlement
Shall be monitored during its operational life.

68. 5.2 Mound
The erosion protection layer shall be inspected for damage at regular
intervals (every 6 months) in combination with settlement
measurements.
Dropping vegetation may indicate presence of gases inside the
mound. Local vegetation may be expected at damaged locations.

69. Part III – Monitoring & inspection of construction of mounded bullet

70. PART II - MONITORING/INSPECTION
OF CONSTRUCTION OF MOUNDED
BULLETS
Reference documents -
Material specs, construction methodology as provided in main tender
Approved QAP
Approved drawings & design
Soil investigation report and recommendations
OISD 150 – Design & safety requirements for LPG mounded storage
facility
SMPV Rules-1991 – Static & mobile pressure vessels (unfired) rules
1991 – To regulate the construction, fitment, loading, transport &
inspection of unfired vessels in service of LPG with capacity
exceeding 1000 lit.

71. OUTPUT DOCUMENTS
Inspection reports
Record of inspection
Calibration certificates of testing equipment at field, at plant and the
plant itself
The evidence of NABL accreditation of calibrating agency
The accreditation of testing labs, whether NABL or not
Whether all the MTCs and independent test certificates available &
reviewed?
Whether all the tests carried out and witnessed/reviewed as per
approved QAP?

72. Whether record summary is being maintained for actual sampling
frequency v/s required sampling frequency?
Whether sampling frequency matches with the quantity of material
procured lot wise as required as per QAP?
Whether all the test results are within the acceptance criteria?
Approved methodology of construction is reviewed and available?

73. Site registers to be maintained –
Mix design & trial mix – review and approval
Site instruction register
Cement consumption
Cube test and slump test
Standard deviation of cube test results
Steel acceptance register showing the details of invoice lot wise, MTC
and details of independent tests

74. Summary of testing requirement and that actually carried out as per
approved QAP, whether accepting criteria has been met for all the tests for
materials like water, coarse aggregate, fine aggregate, cement, admixture,
concrete cubes compressive strength, steel reinforcement physical and
chemical requirements, murum brought from borrow pits, pebble stones,
soling, sand for fillings in different layers, pea gravels, geotextile sheets,
UPVC sheets, showing the quantity received lot/cast wise, sampling
frequency, whether adhered to, acceptance criteria and actual results
thereof.

75. Bar bending schedule – bar bending schedule shall be checked as per
IS recommendations of IS 2502, IS 5525 and SP 34 -1987. The
welding shall be carried out if recommended by the Eng in Charge as
per IS 2751 – 1998. The physical and chemical requirements shall be
checked as per IS 1786.
Material approval register – Each material when approved shall be
noted in the register with details such as contractors’ letter/dt, the
tender specs and the approval by the Eng in Charge.

76. Stage passing register/Requisition for Inspection – shall be
maintained for each stage passing before the next stage begins.
Level register – original ground levels and levels of each fill layer wise
shall be recorded. These shall be marked with the locations of the
FFD tests.
MDD and OMC lab reports
Record of Hydrostatic test and settlements
Testing manual (already circulated)
External lab reports /independent test reports for all the materials

77. Preamble to schedule of works –
Contractor to give detailed construction methodology prior to
commencement of work along with sequence of construction
Contractor to submit BBS approved from client/TPIA
Cement shall be tested daily at site @ 0.5% for each lot of cement
received before consumption.
Initial setting, final setting, compressive strength of cement for 3-day
duration.

78. What to look for –
Soil investigation report –
Which agency has carried out the investigation and is it approved one?
How many bore holes were required to be investigated and how many were
investigated and to what depth?
Which tests were required to be carried out and whether they have been
carried out and witnessed/reviewed as the case may be?
The recommendations –
What are the findings for SBC of underside subgrade of bullet?
Whether any recommendations given for soil improvement and details of it?
What are the findings for SBC of underside raft of retaining wall?
Whether any recommendations given for soil improvement and details of it?

79. Design mix review and approval –
Please go through the detailed step wise checks to be exercised as
per IS 10262 given in enclosed appendix A and then only
review/approve the design mix.
Please go through the following step before we review and approve
the design mix:
A1 – Stipulations for proportioning
Grade, cement, aggregate size, min. cement content, max w/c,
workability, exposure, placing, degree of supervision, type of agg,
max. cement content, admixture.

80. A2 – test data for materials
Cement used, sp. Gravity of cement, CA, FA, admixture, water
absorption of CA, FA, free surface moisture of CA and FA, sieve
analysis of CA & FA
A3 – Target mean strength – Fck (target) = fck + t X s
A4 – selection of w/c ratio from table 5 of IS 456, max w/c ratio of
0.45, then adopt requisite w/c ratio.

81. A5 – selection of water content
Table 2, max water content = 186 lit for slump of 25 to 50 mmfor 20
mm agg
Work out water content for requisite slump. Add or deduct for slump
required by applying correction factor (3% for each 25 mm slump)
If superplasticizer used reduce water content by 20%
A6 – calculation of cement content from given w/c ratio and quantity
of water derived. Check it for exposure content.

82. A7 – proportioning of volume of CA and FA asper table 3 which gives CA +
FA for given w/c ratio
A8 – Mix calculation
Volume of concrete = 1 m3
Volume of cement = mass of cement/sp gravity of cement X 1/1000 m3
Volume of water = mass o/sp gravity X 1/1000 m3
Volume of admixture = mass t/sp gravity X 1/1000 m3
Volume of all in aggregate = vol of concrete – [ vol of cement + vol of water
+ vol of admixture]
Mass of CA = [ vol of all in agg X vol of CA X sp gravity of CA X 1000]
Mass of FA = [ vol of all in agg X vol of FA X sp gravity of FA X 1000]

83. A9 – Mix proportion for TM 1
A10 – 2 more TMs having variation of +/- 10% w/c ratio shall be
carried out & graph between w/c ratio & corresponding strength shall
be plotted to work out mix proportion for given target strength.

84. Specifications of materials
The detailed specification of each of the material to be incorporated shall
be checked against the contract provisions before approval. Mainly the
materials are:
Murum as fill material below FGL – Gravel/murum fill below the tank or
wherever required: BS 1377
Liquid limit < 35%
Plasticity index < 8%
Gravel < 10% (max size 10 mm)
Sand > 20%
FDD of compacted layer – 98%
Shall be free from organic and harmful chemicals

85. Sieve % mass passing
75 mm 100
37.5 mm 85-100
10 mm 45-100
5 mm 25-85
600 micron 8-50
63 micron 0-25

86. Sand for tank bed, tank surround, filling between tanks –
Max. organic content – 3%
Max. silt – 10%
Max particle size – 5 mm
Grain size distribution uniformity coefficient – 2 to 8
Pea gravels – 8 to 10 mm round stone
Non-woven geotextile – Terram 1000/NELTON S1 – 401 (thickness 1000 microns)
as specified in the tender
UPVC sheets – Shall be as per IS 2076-1981 and thickness shall be 1000 micron.
Shall be stitched water tight at joints.
Perforated PVC pipes – as per relevant BIS specs/tender specs
Stones for pitching – hard granite of 230 mm thick

87. ] Construction methodology –
1. Check the clause of precedence in the tender in the event of
conflicting provisions.
2. Design and engineering –
Soil investigation – check whether the work is being carried out by a
specialized and approved agency
Check who is responsible for design, engineering and construction
drawings and whether they have been approved by client/ TPI
Check whether tender provides for design and drawing review from
IIT

88. Tentative construction methodology for the mound – These are
generic methods, please check with respective tender provisions.
Excavate and remove all fill material up to formation level. Fill
materials shall be as per specs recommended in soil investigation
report.
Formation shall be compacted with 10 T roller.
Back fill with soling (depth 400 mm) packed with murum/sand.
Compact with 10 T roller.
Spread 50 mm thick sand and compact
Provide TERRAM 1000/NETLON SI – 401 , thickness 1000
micron/1mm, non-woven geotextile sheet over fine sand.

89. Lay sand bed in max 200 mm layers compacted to 98% of MDD, up to level
of 60 degree from center line of tank.
Provide stone drains as per drawing
Use template form to give exact shape & size of bullet in compacted sand
bed
Excavate required number of trenches of width 1.5 m in the locations given
in drawing for field welds. These are for providing access for welding the
tank sections.
Pace the bullet in the grove and carry out welds
Lay the sand surround and general mound fill, compact it specified density
(93% for sand surround of 500 mm thickness by hand compaction and 95%
for general mound fill compacted with hand or light compacting machine)
[here the relevant tender provisions shall apply] up to 120 degrees from

90. Hydro test shall be conducted & bullets shall be kept filled with water for 15 days
to observe settlement
Complete all the mechanical requirements
Retaining wall shall be constructed in required heights before start of construction
of boulders and sand
Construct 230 mm thick stone pitching from top of retaining wall to within 1 m of
drainage layer
Lay 1mm thick UPVC membrane over mound filling
Lay 150 mm dia PVC perforated drainage pipe with pea gravel surround
Lay Geotextile sheet over drainage pipe
Complete 300 mm thick concrete apron up to top of mound
Cover geotextile layer with 100 mm thick pebble finish (size 10 to 50 mm) round in
shape
Lay 150 mm stone layer over pebbles
The mound should have toe wall & drain along three sides

91. sand bed – Sand fillings/beds shall be laid to falls & to the levels and
full depths as per drg
5. sand surround between the bullets – sand filling between the tanks
and line extending out of 45 degrees from the tank above the tank
center line shall be hand compacted to 95% of MDD
Sand fillings shall be in max. 200 mm layers (or as specified)
compacted thickness on each side of tanks to avoid lateral
displacement/rotation of tank
6. Pea gravel – shall be clean, washed, single size 8 mm round in
shape

92. Non-woven geotextile – Used for separating two different layers
One layer between soling & compacted sand at bottom of bullet
Second layer between pebble finish & UPVC layer
Lap shall be minimum 300 mm
8. UPVC sheet – To be provided over sand mound to prevent water
percolation in to mound. Thickness shall be min. 1000 micron as per
BIS 2076 – 1981 laid to slope.

93. It is laid at the mound slope. The joints shall be stitched water tight.
Manufacturers TC to be checked.
9. Perforated PVC pipes – As per relevant IS codes. Shall be placed to
collect water. To be laid above UPVC sheet. Min. slope 1:100. Pipe to
be surrounded with pea gravel of size 10 to 20 mm
10. stone pitching – 230 mm thick over 75 mm thick PCC 1:3:6. Flush
pointed. Stones shall be hard granite of 230 mm thick.
11. stone finish – Top layer of mound shall be finished with 150 mm
thick, clean gravel of size 10 to 50 mm over 100 mm pebble sand
laid over geotextile sheet.

94. The compaction requirements –
Fill to underside of bullet – specification of material, the thickness of
compacted layers and the depth shall be as soil investigation
recommendation/tenders’ specifications. The sampling of FDD test is
1 number of FDD test for each 500 sq. m. each test to have minimum
5 samples.
Tank surround 300 mm/500 mm – specification of material, the
thickness of compacted layers and the depth shall be as per tenders’
specifications. shall be hand compacted to min 93%.

95. Sand fill around - specification of material, the thickness of
compacted layers and the depth shall be as per tenders’
specifications. shall be hand compacted or compacted with light
compacting machine to min 93%/95%
Filling between tanks - specification of material, the thickness of
compacted layers and the depth shall be as per tenders’
specifications. shall be hand compacted or compacted with light
compacting machine to min 93%/95%

96. 8] HYDROTESTING & SETTLEMENT
a) Hydrotesting
All completed equipment shall be tested hydrostatically as per the
requirements of specifications/codes & approved hydrotest procedure
in presence of the inspecting authority. Prior to hydrotest, all weld
splatter, weld studs, scale, dirt, etc. shall be removed from the vessel.
The vessel is to be supported while hydrotesting on sand bed which
is to be laid & completed up to a level of 120 degree taken from the
center of vessel to the edge of vessel. Entrapped air near dome shall
be completely removed by suitable means during hydrotest.

97. Contractor shall submit a detail procedure for Hydrostatic testing for
approval by Owner/TPIA prior to commencement of testing time.
Pressure-Time graph shall also be submitted. All necessary
precautions shall be taken to safe guard against the risk of brittle
fracture during hydrostatic test at site. It is suggested that the
temperature of the testing medium shall not be less than 15°C. PH of
water used for hydrotest shall be between 6.0 – 7.0. After hydro
testing water shall be drained in NRL drains.

98. At the time of hydro test, the adjacent bullets on either side of the
bullet under test pressure shall be kept water filled, i.e., minimum
three adjacent bullets shall remain completely filled with water
anytime during hydro test. A method of measuring the water height
in the bullet is also to be established. Water shall be filled / emptied
in stages 25%, 50%, 75% and full with 2 hours holding period at
stages.

99. Loading rate shall be monitored such that the loading rate does not
exceed 2.0M/day subject to a pumping rate of not more than
20cm/hour. Minimum 2 nos. Dial gauges, dial graduated over the
range of not less than 1.5 times and not more than about 2 times the
test pressure and an accuracy of +/- 0.6 percent or finer, shall be
used. All pressure gauges / pressure recorders (the same accuracy or
finer) used in testing shall have a calibration record showing values of
standard indicated pressure and validity period.

100. Inspector shall verify that calibration tag is displayed on the pressure
gauge/recorder. Pressure pumps, pipe / hose pipe, fittings and other
accessories shall be capable of developing and withstanding the test
pressure. Hydro Test pressurization shall be developed in stages i.e.
0 Working Pressure, Design Pressure, Hydro test Pressure with
holding period of two hours minimum at stages. Depressurization
shall also be done in stages i.e. Hydro test Pressure, Design Pressure,
Working Pressure with holding period of two hours minimum at
stages.

101. All visible weld joints / connections shall be visually inspected for any
leakage/sweating at various stages. After successful hydrotesting,
test water shall be transferred to the other Bullet ready for hydro
testing. Unless otherwise stated, gaskets used during testing shall be
same as specified for operating conditions. Sweet potable water shall
be used for hydrotesting. Minimum duration to hold hydraulic
pressure shall be 4 hours

102. Settlement –
Their initial levels of equidistant points (bench marks) placed on top
of the bullet shall be taken with respect to minimum 3 numbers
permanent bench marks for settlements readings which shall be
provided as near to bullet as possible but not more than twice the
vessel diameter from the periphery of the mound. The settlement
shall be monitored & recorded during construction period, preload
period, hydro test period for foundation design verification. Some
tenders specify minimum 4 permanent reference points to be
installed on top of vessel to monitor vessel settlement of which 2
points shall be installed near ends.

103. Further bench marks shall be painted as per vessel specifications.
Standard reference level for comparison of future readings with
current measurements shall be provided. Mound settlement shall be
recorded / checked after allowing 24 hours’ time at different
filling/emptying stages of hydrotesting of each bullet and after 48
hours with the bullet completely filled. Also, after completion of
hydro-testing, settlement recording shall be continued by the
contractor during construction of mound, and till successful
commissioning of bullet once in a week.

104. Settlement recording shall be done preferably when atmospheric
temperature is not more than 30° Celsius. IMPORTANT The settlement
rate during this testing period needs to diminish with time as
otherwise there would be a danger of instability. If the rate does not
diminish adequately, the client/inspecting authority shall be informed
immediately. The bullet shall be (partly) emptied, and a geotechnical
/ specialist should be consulted.

105. The maximum differential settlement allowed is 25 mm. Total settlement
allowed is 60 mm. (but individual tender specifications shall be gone into).
Vessel settlement shall be monitored during operational times.
Pointer markers with measuring scale shall be installed for all vessels in the
inspection tunnel for monitoring settlements.
CALIBRATION –
Contractor shall prepare & submit a LPG Mounded Bullet calibration
procedure including Calibration Chart in accordance with IS:2009 &
IS:2166. Contractor shall obtain necessary approval for calibration from
statutory authority CPWD / Weight & Measurement Dept. or competent
authority.

106. Pile foundation

107. PART IV – PILE FOUNDATION
RCC bored cast in situ pile – [wherever applicable]
Referral codes – IS 2911 all parts
Grade of concrete – M-25 with min cement content of 400 kg/m3
Slump – 100-180 mm in case bore hole is water free and unlined
150-180 mm in case of water filled bore and tremie is being used
Reinforcement –
Min. longitudinal reinf. – 0.4% of cross-sectional area
Cover 50 to 75 mm
C/C distance between two main bars – 100 mm min
Lateral ties – not closer than 150 mm
Vertical reinf – shall project 40 times dia above cut off level

108. RQD % Rock quality
<25% Poor
25 to 75 Medium
>75 good

109. Liner to be provided in soft soil to ensure stability to protect concrete
where high hydrostatic pressure exist in sub soil or underground flow
of water exists.
Provide welding to reinforcement for stability ties shall be tack
welded as per Eng in Charge’s direction

110. Concreting –
Ensure necessary socketing as per design/drawing (1/2d, 2D,5D) is provided
depending upon rock type, RQD, CR, energy values, in case of chiseling, & pile
penetration rate in case of auger boring.
Concreting shall not proceed if sp. Gravity of fluid near bottom exceeds 1.2
Laitance shall be 750 mm above cut off
Recording of data
Date, diameter, mark of pile
Reinforcement details and calculation
Boring method
Time and period of boring/chiseling/auguring
Penetration in given time
Hard rock touch level/soft rock touch level
Socketing of pile
Termination of pile
Cut off level
Concrete and cement consumption
Tremie details
Liner details

111. Typical data sheets of recording piling data shall be as per Appendix D of IS
2911 (pt I/sec 2)
The tolerances of verticality, eccentricity shall be as per relevant tender
specs or IS code.
For any deviation from designed location, alignment or load carrying
capacity shall be reported to Eng in Charge.
The standard specifications of materials required for piling shall be as per
relevant IS codes and contract specs.
Welding – field welding will not be permitted without written consent of Eng
In Charge. wherever welding is permitted, it shall be in staggered locations.
Tests to show that joints are full strength of bars shall be conducted.
Welding shall be conducted as per IS 2751.
Hot bending of bars shall not be permitted.

112. 7] Testing of piles – these are applicable to all types of piles except
sheet piles. (when IS codes are refereed it shall always be the latest
revision including amendments. Referral code is IS 2911 (PtIV).
Requirements –
Load tests shall be required to provide data regarding load
deformation characteristics of pile up to failure or otherwise specified
and safe design capacity.
Minimum period of 2 weeks for precast piles and 4 weeks for cast in
situ piles, shall be allowed to pass between installation and tests.
The record shall include plot of load time settlement of piles.

113. Vertical load test (compression) –
Test pile to be decided by Eng in Charge. can be working pile or
separate test pile.
Load is to be applied in 1/5th increments of rated capacity of pile or
as specified. Settlement readings shall be taken before and after
application of each new load increment and at 2, 4, 8, 30, 60 min and
at every 2 hrs until application of next load increment.
Each stage load shall be maintained till rate of movement of pile top
is not more than 0.2 mm/hr or until 1 hr has elapsed whichever is
later.

114. Further loading shall be continued in above manner till one of the
following occurs:
Yield of soil-pile system occurs causing progressive settlement of pile
exc. 1/10th of pile di
Loading on top equals twice rated capacity or as specified in case of
separate test pile and 1.5 times capacity in case of working pile.
Where yielding of soil does not occur, full test load shall be
maintained for 24 hrs & settlement readings at 6 hrs interval or as
specified.
Unloading shall be done as per loading steps. Final rebound shall be
recorded 6 hrs after entire test load has been removed.
If directed by eng in charge, loading & unloading cycles shall be
carried out for all load stages within assumed working load.

115. Assessment of safe load –
Safe capacity shall be least of the following:
Load corresponding to settlement specified.
50% of final load at which total displacement equals 10% of pile dia in
uniform dia & 7.5% of bulb dia in case of under-reamed piles.

116. Cyclic loading test –
Load shall be applied in increments of 1/5th of estimated safe
capacity of pile or as specified. Settlement reading shall be taken
before & after the application of each new load increment at 2, 4, 8,
15, 30, 60 minutes & at every 1 hr till rate of settlement is 0.2 mm/hr
until application of the next load increment.
Alternate load & unloading shall be carried out at each stage and the
total & net settlements be recorded.
Each stage of loading & unloading shall be maintained till the rate of
movement of pile top is not more than 0.2 mm/hr for loading period
of 1.5 hr & unloading period is 1 hr.

117. The following loading stages shall however be maintained for longer
periods as below:
At load of 1.5 times assumed safe capacity (Routine test only) – 24 hrs
At load of twice assumed safe capacity ( for initial test only) – 24 hrs
The loading shall be continued till one of the following occurs:
Yield of soil-pile system occurs carrying settlement exc. 1/10th of pile dia
The loading on pile equals twice estimated safe load in case of separate
test pile & 1.5 times the rated capacity of pile for working pile.
Assessment of safe load –
Shall be least of the following:
Load corresponding to settlement specified
½ of final load at which total settlement equals 1/10th of pile dia

118. Lateral load test –
Test pile to be decided by eng-in-charge & may be working pile or
separate test pile.
Loading in increments of 1/5th of safe capacity or as specified
Each stage shall be maintained till rate of movement of pile is not
more than 0.2mm/hr or 1 hr whichever is greater
Loading shall be continued till
Deflection of pile head exc. 12 mm
Apllied load is twice the assumed lateral load capacity of pile in case
of separate test pile & 1.5 times the rated capacity for working pile.

119. Assessment of safe load –
Shall be smaller of following:
½ of final load for which total deflection is 12 mm
Load corresponding to 5 mm total deflection
Note – deflection is at cut off level of pile

120. Pull out capacity of piles –
Loading shall be applied in increments of 1/5th the rated capacity of
pile.
Each stage shall be maintained till rate of movement of pile is not
more than 0.2 mm/hr or 1 hr, whichever is greater.
Loading shall be continued till one of the following occurs:
Yield of soil-pile system occurs causing movement of pile exc. 12
mm
Loading equals twice the estimated safe load or s specified.

121. Assessment of safe load –
Shall be least of following –
2/3rd of load at which total displacement is 12 mm or load
corresponding to specified permissible uplift.
½ the load at which load-displacement curve shows clear break
(downward trend)

122. Combined vertical & lateral loading test –
Pile shall be first subjected to full vertical load. Lateral load shall
commence after all settlements due to vertical loads have ceased
while full vertical load is in position.
Assessment of safe load shall be as per lateral load testing.

123. Part V - Ground improvement by vibro technique & vibro stone
columns

124. PART V – GROUND IMPROVEMENT BY
VIBRO TECHNIQUE AND VIBRO STONE
COLUMNS
Illustrated example of ground improvement method by M/S Keller at MSV,
Motihari.
Name of work – MSV at Motihari
Client – IOCL
Subproject – Ground improvement
Subcontractor – Keller
Contractor – Fabtech
Details of mound –
Diameter – 7.26 m, height -7.26 m, length - 66.834 m, capacity 1200 MT
Relevant codes –
IS 15284 part I – 2003, Design and construction for ground improvement
IS 8009, 1993 – part 1 – calculation of settlement of foundations

125. List of annexures submitted –
Method statement for soil investigation
Method statement for ground improvement by deep vibro technique
Field quality plan
Design basis & field trials
Method statement for load test
Method statement for granular blanket works
Method statement for settlement monitoring & hydrotest guidelines
Technical specifications for ground improvement
Method statement for vibro stone columns
Method statement for load test for single columns
Method statement for load test for single column & 3 group columns
Initial soil investigation report by M/s Engicons

126. Aim –
To achieve required bearing capacity & to limit total and differential
settlements within limits.
To mitigate liquefaction potential of loose to medium dense sand in
the event of earthquake.
Soil improvement by providing stone columns
Soil improvement by vibro compaction
Soil improvement through most significant compressible strata that
contributes to settlement of foundations.

127. Scope of work –
Pretreatment soil investigation works
Design, supply & construction of vibro stone columns
S & L min. 500 mm thick load distribution granular blanket layer
Conducting trial works, initial load tests, routine load tests
Post treatment soil investigation
Monitoring settlement during hydro test stage & operational stage

128. ISSPL to check –
Whether all the above aspects are covered & method statement & QAP
is submitted and to make a review.
To verify whether design concept & calculations for columns &
compaction works are vetted and approved by IIT
To check whether refereed technical documents as per clause 3.3 are
available or not.
To check whether contractor has carried out soil investigation prior to
commencement of works.

129. Land to be filled & compaction up to av. Height of 1.5 m from OGL in
MSV area prior to Ground improvement works.
To check all the design considerations.
Soil investigation –
Pretreatment and post treatment
Liquefaction analysis & to establish that min. factor of safety of 1.1 is
available throughout the depth. This shall be vetted and approved by
IIT

130. Construction methodology –
Ground improvement to be carried out as per guidelines issued by IIT
Soil investigation report to be approved by IIT prior to commencement of
works
Construction methodology to be approved by IIT
Ground improvement to be monitored by automated real time monitoring
system.
Depth of treatment –
A per IIT recommendations, remediation can be achieved with stone
columns for first 5 m from NGL with min. replacement ratio of 20% &
beyond 5 m with vibro compaction. Treatment depth to be achieved for
critical structures, is minimum 23 m below EGL & 20 m below EGL for non-
critical structures. Design treatment depth should take in to account the
consideration the influence of pressure bulbs.

131. Post ground improvement test –
To check if soil is safe against liquefaction. Power consumption shall
be the basis for determining adequacy of compaction of stone
columns.
Uniform settlement shall not exceed 50 mm
Differential settlement shall not exceed 1:2500 of length of vessel.
Density of sand & gravel under moist condition – 1.80 T/sq. m
Design basis & field trial proposal using deep vibro technique –

132. Scope of field trials
Carrying out field trails with combination of vibro compaction and
vibro stone columns based on confirmatory soil investigation data.
Conducting initial field load tests.
Conducting post ground improvement soil investigation test at field
trial locations.

133. Design basis as specified in the IOCL tender -
Loading intensity –
Hydrotest – 200 KPa
SBC – 270 KPa
Pascal (Pa) – unit of pressure and stress in MKS.
1 Pa = 1 Newton/m2 equivalent to 1 Kg/m/seconds 2
1 KPa = 1000 Newtons/m2
Long term permissible settlement (50) years)
Uniform settlement of vessel to not exceed 50 mm
Differential settlement not exceeding 1:2500 of length of vessel

134. Seismic
Earthquake zone – zone IV
Earthquake magnitude – 7.6
Peak ground acceleration – (PGA) – 0.24 g
Combination of ground improvement scheme comprising of vibro
compaction and vibro stone columns is employed here as top 5 m soil
below WPL is observed with fines >15% hence the vibro stone column
technique and below 5 m, percentage of fines is less than 15% and
hence the vibro compaction is proposed.

135. Considering the interface zone of clay strata and sand layer, stone
columns were installed for a depth of 7m by vibro compaction for the
required treatment depth.

136. Treatment scheme –
Grid pattern – equilateral triangular pattern
Grid spacing – 2.75 m center to center
Diameter of vibro stone column – 1300 mm
Area replacement ratio (ARR) – 20% for bibro stone columns
Depth of vibro stone columns – top 7.00 m from working platform
level
Depth of vibro compaction – below 7. 0 to 24.5 /30 m from WPL

137. The actual depth of treatment shall be based on factual soil conditions at
the treatment area. The column shall be terminated in medium dense layer
which can be detected by the vibrator through power resistance against
soils.
Evaluation of liquefaction potential –
The proposed location falls in earthquake zone IV (IS 1893) and as the
subsoil comprises of loose to medium dense sand layer below 5 m depth
from WPL, which is susceptible to liquify in an event of earthquake. The
liquefaction potential assessment is done considering bore hole (strata,
depth, no. of blows, penetration, N values, grain size analysis, liquid limit,
plastic limit, plasticity index, bulk density, dry density, moisture content,
sp. Gravity, shear strength characteristics like cohesion & angle of friction,
void ratio, compression index, pre-consolidation pressures and chemical
analysis), eCPT (electronic cone penetration test), DMT (dilatometer test)&
CHST (cross hole seismic test).

138. Liquefaction potential is assessed based on Seed & Idriss approach
which is used as described in NCEER summary report, 2001. The
depth of liquefaction assessment has been limited to 30 m below
WPL.
The target FOS of 1.1 is considered for mitigation of liquefaction as
per tech specs and this will be verified by post soil investigation.
As per IS 1893, part 4, 2016, if N cor values are greater than value
below, subsoil is not prone to liquify.

139. Seismic zone Depth below GL N values Remarks
III, IV, V ≤ 5 15
≤10 25
II ≤5 10
≤10 20

140. Based on the liquefaction assessment using CPT approach of NCER
(2001) and above guidelines of IS 1893 -2002 for SPT, the depth of
liquefaction is varying from 21 m to 30 m below WPL in MSV area.
It shall be noted from the typical calculations of liquefaction analysis
based on CPT, BH, DMT, CHST, that top subsoil is having fines> 15%
and liquid limit > 35%, hence the same is considered as non-
liquefiable layer based on the guidelines of NCER summary report.

141. Lateral extent of treatment –
It is necessary to improve the ground beyond the structure area to provide
a lateral confinement and mitigate liquefaction in the event of earthquake.
The lateral extent shall be based on the following:
Based on Japanese geotechnical guidelines, the lateral extent of treatment
(L) beyond structure footprint shall be 5 m ≤ L ≤ 10m
Lateral area corresponding to an angle of 30 against the vertical axis
starting from the edge of the foundation (i.e. 0.5777 times H, where H is
liquefiable depth below the founding level)
(2/3) * liquefiable depth
Hence, lateral extent of treatment of 10 m is provided from the edge of
retaining wall.

142. Settlement analysis –
Carried out by GGU-Settle software. The estimated settlements are
lower than allowable settlement.
It shall be noted that subsoil is predominantly sandy, hence majority
of post improvement settlements will occur during construction stage
leaving tolerable minimal settlement for long term.
Bearing capacity check –
Carried out using improved composite parameters KID – Keller
improvement designer and soil parameters derived from soil
investigation.

143. Post ground improvement testing –
To check the efficacy of the improved ground post improvement the
following tests shall be carried out in the concerned area:
Post sounding tests –
By means of eCPTs/BH/CHST after 15 days of ground improvement works.
Post soil investigation shall be carried out near pre-soil investigation
locations.
Routine plate load tests –
Total 8 nos of routine load tests shall be carried out in proposed MSV area.
Out of them 6 shall be single column load tests and 2 shall be group column
load tests.
Assessment shall be based on results of post soil investigation works and
load test on improved ground.

144. Summary and conclusions –
Location is in seismic zone IV. Subsoil consists of loose to medium sand
susceptible to liquefaction in the event of earthquake. Top soil up to 3 m
from WPL is of mixture of sandy silt which is not susceptible to
liquefaction. However, bearing capacity and settlement of this layer shall be
addressed.
To meet the performance requirements, ground improvement with
combination of vibro stone columns and vibro compaction is proposed.
vibro columns provides improved shear strength, compressibility and
effective drainage path to ensure rapid dissipation of excess pore water
pressure besides in increasing the rate of settlement of top sandy soil.
Densification of loose sand is achieved by vibro compaction and mitigation
of liquefaction potential.

145. Subsoil conditions-
Initially carried out by m/s Engicons
Confirmatory test carried out by m/s Keller in MSV footprint area.
3 – BH, 3 – CPT (cone penetration test), 1 CHST, 2 DMT.
Ground water table – 2 to 4 m below the GL.
Silt clay – 2 to 3 m at top.
Loose/medium dense sand – rest
Max. SPT in BH 3 at 68 m RL (20 m below GL), is 65 and BH 2 at 86 m
RL (10 m below GL) is 68.

146. Grain size analysis is done. This is done to determine % age of
different size grains in a soil. Significance is, it affects engineering
properties of soil and is required in classification of soil.
Cone resistance – To understand soil properties such as relative
density of soil, soil behavior and how ground is likely to behave in an
earthquake shaking. Helps in design of foundation and ground
improvement.

147. Geotechnical concerns –
Mitigate liquefaction
Reduce post construction long term settlements to permissible limits
Bearing capacity
Location is in earthquake zone IV
Soil is loose & has potential to liquify in earthquakes
Top soil is weak & has low SBC to support MSV

148. Hence ground improvement is required. Hence field trials using
combination of vibro compaction & vibro stone columns are proposed
in MSV area to arrive at suitable patterns to suit tech. specs.

149. Ground improvement techniques –
To compact & densify the loose sands up to design depth which are
prone to liquification and having clayey silty layers with large quantity
of fines at top, stone aggregates shall be used for compaction back
fill during column construction.
Concept of vibro compaction –
Designed to induce compaction of granular materials. Basic principle
is that non-cohesive particles can be rearranged in to denser state by
vibration.

150. Concept of vibro stone columns –
This technique introduces a coarse-grained material as load bearing
element consisting of stone aggregate as a backfill medium.

151. Construction methodology –
Use of depth vibrator as an equipment, to compact & improve
subsoil.
Depth vibrator is a long, heavy tube enclosing eccentric weight driven
by electric motor.
Field trials –
Layout showing locations for field trials for ground improvement is to
be submitted.

152. Depth of treatment -
Trial no VR/VC Dia in m Spacing in m Grid pattern Treatment depth in
m
1 VR (clayey silt/sandy
silt)
1.3 2.75 Triangular 7 m from av. Ground
level
VC (sand) - 2.75 Triangular 7 to 30 m

153. As per tender, min. depth of treatment – 23 m below NGL (RL 95.5
m). clause 5.2 of TS of tender.
Based on confirmatory soil investigation data & technical analysis,
depth of treatment shall be min. 24.5 m to max. below av. GL (97 m).
Depth of vibro columns is considering min. area replacement ratio
(ARR) of 20% for vibro stone columns.
Following guidelines shall be followed –
Lifting weight – 0.4 m to 0.75 m
Compaction time – 25 sec to 50 sec
Installation procedure shall be finalized based on results of trial
works.

154. Liquefaction mitigation –
Liquefaction assessment is done considering BH, CPT, CHST and
based on it, depth of liquefaction is varying as per table given. The
assessment is limited to 30 m below GL.
Summary of liquefiable depths –

155. Confirmatory sl Depth
BH 28 m
CCPT 30 m
CHST 21 m
DMT To be performed

156. The proposed treatment depth for trial works shall be min. 24.5 m to 30 m
below WPL (97 m).
Target factor of safety of 1.1 is considered to mitigate liquefaction as per
tender specs and shall be verified by post soil investigation.
The top subsoil is having fines >15% & liquid limit >35% & hence non-
liquefiable as per NCER summary report.
Bearing capacity –
Check by general shear failure criteria (IS 6403)
Settlement –
Settlement analysis based on hydrotest load intensity shall be carried out.
After obtaining improved composite parameters, settlement evaluation is
done by software “GGO-settle”.

157. Performance of GI works –
Field trials – load tests & soil investigation will be carried out to check the
efficacy of field trials.
Post soil investigation tests will be conducted at trial location after
completion of ground improvement works.
Field investigation consist of CCPT & BH locations.
Testing shall be carried out 15 days after GI works.
Stone column tests –
Initial load tests on improved ground to replicate design loads & required
bearing capacity as per section 4
Shall be conducted after 7 days of GI works
Method statement shall be reviewed.

158. Ground improvement using vibro compaction shall be resorted to
mitigate liquefaction when sand is having percentage of fines less
than 15%. Basic principle is that particles of non-cohesive soils can be
rearranged into a denser state by means of vibration.
When the sandy silt has percentage of fines higher than 15% then
ground improvement can be done by way of vibro stone columns.
This technique introduces a coarse-grained material as load bearing
elements consisting of stone aggregates as a backfill medium.