Question XXXXXXXXXXmarks) (a) What are minerals? Sketch different types of mineral crystal forms and list different types of rock-forming minerals. Describe with examples the importance of mineral...

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” 0 ”



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1. Introducti on. 01
2. Scope of Work 01
3. Field Investigation 02
4. Laboratory Tests 14
5. Discussion and Recommendations 15
6. Summary 23
7. Conclusi on 28
8. Appendix

Typical C a lculation for Safe Bearing Capacity
30-36
9. Appendix…

1) Tables…
37-47
” 1 ”


[ 1 ] INTRODUCTION :



The purpose of the investigations was to determine the sub soil stratification,
geotechnical information & safe bearing capacity of the soil, so as to provide information
that will assist the structural engineers in the design of the foundations and the relevant
works.


[ 2 ] SCOPE OF WORK :

The scope of work consisted of

A. Field Investigation :

1. Fixing borehole locations.

2. Drilling boreholes through soil and rock.

3. Conducting standard penetration test.

4. Collection of disturbed and undisturbed samples.

5. Carrying out static plate load test at specified locations.

6. Carrying out permeability test


B. Laboratory Test :

1. Determination of moisture content.

2. Grainsize distribution analysis.

3. Atterberg limits test.

4. Specific gravity work.

5. Determination of bulk and dry density..
” 2 ”





6. Direct shear test.

7. Traixial test.

8. Consolidation test.

9. Differential free swell test.



C. Test on Rock Samples:-

1. Density

2. Water Absorption & Porosity

3. Crushing Strength


[ 3 ] FIELD INVESTIGATION :


3.1. Boreholes :


The field work includes drilling of Twelve boreholes upto max. 30m depth at the
locations specified by client. The locations of boreholes are indicated in the layout plan
given in the Appendix of report. Rotary type drilling machine with TC bit was used for
boring. Casing pipes and bentonite slurry were used to protect the sides of boreholes,
wherever needed. The diameter of the borehole was kept 150mm & was decreased to
NX as the rock encountered.

Standard penetration tests were conducted in the soil strata at regular intervals
and “N” values noted .The samples from the split spoon samples were collected and
treated as representative samples for laboratory tests. The undisturbed samples could
not be collected due to weathered fractured rocky strata from shallow depth. Water table
levels in the boreholes were monitored and recorded and the same is given in the
respective borelogs. Details of boring with soil profile, SPT values along with sampling
details are given in the respective borelogs in the appendix of the report.
” 3 ”

Detail co-ordinates and the corresponding structure is given in table – 1.
Sr.
No.
Structure BH No. Co-ordinates Depth of
Boreholes
(m.)
Water Table
Depth below GL
(m.)
N E
1. Wagon Tripler BH-1 233.019 271.0 30.0 8.0
BH-2 233.019 321.50 18.0 6.0
2. Tunnel BH-3 233.019 371.54 30.0 8.0
BH-4 195.0 405.0 30.0 8.50
BH-5 153.75 432.50 30.0 8.0
BH-6 120.0 460.0 21.0 8.0
BH-7 55.693 495.875 30.0 12.0
3. CONV. BCN 1A3,
1B3
BH-9 S-60 E-511.00 15.0 10.50
4. Pipe Rack BH-10 S-310 E-440 15.0 9.0
BH-11 S-310 E-640 15.0 9.0
5. Fly Ash Silo BH-12 S-60 E-511 15.0 10.0
BH-13 S-400 E-750 15.0 10.0
[ 3.2 ] Collection of Samples :

(1) Undisturbed Soil Sampling in Boreholes

1.1 Undisturbed soil samples were collected in cohesive stratum to determine
engineering properties of soil in laboratory. Thin walled open drive samplers of
450 mm length and made of seamless steel were used for collection of samples in
cohesive strata. Area ratio of this sampler does not exceed 13 %. Samples were
collected by pushing the UDS tube slowly, preferably by hydraulic pressure, into
cohesive stratum to avoid disturbance to surrounding soil stratum.
Î As per 3.1.3 the strata is rocky at all borehole location hence no UDS could be is
collected.

1.2 On removal of sampler from borehole, all wet disturbed soil is removed and
coated just molten wax to prevent loss of moisture. Samples will be clearly
labelled at top indicating job no. borehole number, sample number, date of
sampling, type of sample, depth of sample etc. Generally, unless specified
undisturbed soil samples (UDS) /core samples will be obtained at every 3.0 m
interval and at every identifiable change of soil formation.
” 4 ”



1.3 However where undisturbed soil samples / core samples were not collected due
to hard strata, undisturbed soil samples were replaced by standard penetration
tests or broken cores in boreholes.

(2) Transporting and Storing of Samples


2.1 All the samples were stored properly at site till they were transported to the
laboratory for the testing. Sampling tubes containing undisturbed samples were
not be exposed to direct sun and were kept in a shade covered with wet gunny
bags. These tubes were transported in a wooden box tightly fitted with taking full
care to avoid the chances of disturbance. The fit soil samples/rock samples were
photographed on receipt in the laboratory.

(3) Drilling in Rock


3.1 When rock was encountered, size of borehole was changed to Nx. (76 mm)
diameter. A double tube core barrel and Nx sized diamond bits are used for
drilling and recovering rock cores. Recovered rock cores were numbered serially
and preserved in wooden core boxes. Rock core recovery and Rock Quality
Designation (RQD) were computed for every run length drilled. Detailed core logs
of boreholes were prepared by geologist at site.


3.2 Rock classification in terms of weathering and state of fractures and strength is
carried out in the following manner. Tabulations given in below explain it briefly.
” 5 ”



Scale of Weathering Grades of Rock Mass (vide 4464)


Terms Description Grade I n t e r p r e t a t i o n
Fresh No visible sign of rock material
weathering; perhaps slight discoloration on
major discontinuity surfaces.
I CR > 90 %
Slightly
Weathered
Discoloration indicates weathering of rock
material and discontinuity surfaces. All the
rock material may be discoloured by
weathering.
II CR between
70 % to 90 %
Moderately
Weathered
Less than half of the rock material is
decomposed or disintegrated to a soil.
Fresh or discolored rock is present either
as a continuous framework or as core
stones.
III CR between
50 % to 70 %
Highly
Weathered
More than half of the rock material is
decomposed or disintegrated to a soil.
Fresh or discolored rock is present either
as a discontinuous framework or as core
stones
IV CR between
10 % to 50 %
Completely
Weathered
All rock material is decomposed and / or
disintegrated to soil. The original mass
structure is still largely intact.
V CR between
zero to 10 %
Residual
Soil
All rock material is converted to soil. The
mass structure and material fabric are
destroyed. There is a large change in
volume, but the soil has not been
significantly transported.
VI N > 50
3.3 It should be understood that all grades of weathering may not be seen in a
particular in site rock mass and that in some cases a particular grade may be
present to a very small extent. Distribution of the various weathering grades of
rock material in the rock mass may be related to the porosity of the rock material
and presence of open discontinuities of all types in the rock mass.


Rock quality is further measured by frequency of natural joints in rock mass. Rock
Quality Designation (RQD) is used to define state of fractures or massiveness of rock.
Following table defines the quality of rock mass.
” 6 ”



RELATION BETWEEN RQD AND IN -SITU R O CK QUA L ITY ( videIS :13365)

RQD CLASSIFICATION RQD (%)
Excellent 90 to 100
Good 75 to 90
Fair 50 to 75
Poor 25 to 50
Very Poor 00 to 25
Rock is also classified by strength of intact rock cores collected during drilling. Rock
unconfined compressive strength (UCS) of the rock core is used to define strength of
rock. Following table summaries classification of rock based on strength.

CLASSIFICATION OF ROCK BASED ON COMPRESSIVE STRENGTH
(vide13365)

ROCK STRENGTH COMPRESSIVE STRENGTH (Kg/cm2)
Extremely weak < 20
Very Weak 20 to 100
Weak 101 to 250
Average 251 to 500
Strong 501 to 1000
Very Strong 1001 to 2500
Extremely Strong > 2500
[ 3.4 ] Standard Penetration Test :


The standard penetration tests were performed in accordance with IS:2131:1981
using the standard split spoon sampler & 63.5Kg hammer first at 0.5m & then at the
desired intervals of 1.50m. The results of standard penetration test results are shown in
table no.1 at the end of the report. The penetration value N has been referred as refusal
if number of blow counts exceeded 50 for 30cm penetration.
” 7 ”



[ 3.5 ] Falling Head Permeability Test :


The test may be conducted both above and below water table but is considered
more accurate below water table. It is applicable for strata in which the hole below the
casing pipe can stand and has low permeability; other wise the rate of fall of the head
may be so high that it may be difficult to measure.

i) Falling Head Permeability Test is conducted strictly as per 5529 (Part-1)-1985.


ii) The hole should be drilled or bored up to the bottom of the test horizon and
cleaned.

iii) After cleaning the hole, the packer should be fixed at the desired depth so as to
enable the testing of the full section of the hole below the packer.

iv) In conducting packer tests standard drill rods should be used.


v) The water pipe should be filled with water up to its top and the rate of fall of the
water inside the pipe should be recorded.

vi) If the hole cannot stand as such then casing pipe with perforated section in the
strata to be tested should be used.

Location of test: Borehole No. : 4


D = Dia of hole = 10cm.

Casing length = 1.5m, 10cm dia.
Ground Water Level = 8.0m
Depth of Borehole = 30m

Date of Test = 16/4/2010

Uncased hole (L) = 30 – 1.5 = 28.5m.
” 8 ”




Hole Extended in weathered rock considered as soil :
2πL
F = --------------------------------------------
Loge [ (L / D) + √ 1 + (L / D)
2 ]


2π x 28.5
= ----------------------------------------------------------
Loge [ (28.5 / 0.1) + √ 1 + (28.5 / 0.1)
2 ]
= 28.2195 ≅ 28.22 (Say)
(ii) Variable Head Method
A
K1 = ---------------- Loge (H1 / H2) t2 – t1 = 1 min = 60sec.
F (t2 – t1)

π/4 (0.1)2 7.2
= ------------------- x loge ( ----------)
28.22 x 60 6.42

= 5.316 x 10-7 m/sec.

= 5.316 x 10-5 cm/sec. ……… (1)



For H1 = 6.42m H2 = 6.31m

5.19
K2 = ----------- x 10
-6
x 0.0173
5.0

8.97
K2 = ----------- x 10
-8
m/sec. = 1.79 x 10
-6
cm/sec …….. (2)
5.0
Average co-efficient of permeability = 2.75 x 10-5 cm/sec.
” 9 ”



[ 3.6 ] Static Plate Load Test :
Plate load tests were conducted at the strategic location of pipe rack & fly ash silo
area. In accordance with 1888. using a plate of size 30cm x 30cm x 2.5cm (thick). The
tests were carried out by the Reaction i.e. jacking against a loaded platform by hydraulic
jack with pressure gauge arrangements.


A ball and socket arrangement was inserted between girder and jack so as to
allow the ball to rotate while keeping the direction of load vertical through out. The loads
were applied usually in increments of 3.0t loads and were maintained upto time when the
rate of settlement got appreciably steady or to a value of 0.02 mm/min. The settlement
was observed by means of two dial gauges having count of 0.01mm and travel of
25.0mm.



After attaining maximum load, the unloading was done gradually and the test plate
was allowed to rebound. When the rate of rebound became negligible, the dial gauge
readings were recorded.

The load V/S observed settlement graph has been presented in the drawing no.
62/04/PLT-1. & PLT -2.

[3.6.1] Analysis of Test Data:- (Plate Load No. : 1 & 2)
Shear Criterion:-

Maximum load of 30t. was applied at Observing the graph of load v/s settlement,
corresponding to applied load intensity of 30 t/m2 settlement of 7.89mm is noticed.
Failure is not observed upto maximum 30t load.
” 10 ”





From Shear Criterion,

Qu 30
Qup = --------- = --------------
Area 0.3 x 0.3


= 333.33 t/m2.



333.33
Qsafe = ----------- (Adopting Higher factor of safety 6 for rock)
6

= 55.55 t/m2. Say 50t/m2. (1)



(3.6.2) From Settlement Criterion :-

Allowable settlement of test plate (SP) is estimated using equation.

Sp Bp Bf + 30
------ = [ --------- (-------------------) ] 2 vide IS:12070-1987, Page-10.
Sf Bf Bp + 30

Where Sf = Allowable footing settlement = 12.0cm In rock

Bp = plate width = 30 cm

Bf = tentative footing width = 300 cm.

30 300 + 30
Sp = 12.0 [--------- (---------------) ] 2 = 3.63mm
300 30 + 30



Corresponding load = 18.8t

Hence allowable load intensity for settlement would be 208t/m2 (2)
Hence recommended SBC = 50 t/m2
” 11 ”


(3.6.3) Deformation modulus E from Plate Load Test:

From plate load test graph for load of 20t settlement is equal to 4.25mm.
Modulus of elasticity,


q B (1 - µ2)
Esp = --------------- x Iw
S
Where,
q = Intensity of contact pressure

P 20
= ------ = --------------
A 0.3 x 0.3

= 222 t/m2.

= 22.20 kg/cm2.

B = width of plate = 30cm.

µ = Poisson’s Ratio = 0.25

S = Settlement for load of...