Soil Inv.

for the Development of North Oman Solar PV Plant with Battery Energy Storage System Independent Power Project at Saih Rawl, J-7723, Nov’2022

(ii) Raft Foundation:

Sr. No. Size of Foundation Net Allowable Anticipated Modulus of Subgrade

(m x m) Bearing Pressure Settlement Reaction
(kPa) (mm) (kN/m3)

1. 10 x 10 200 9.2 21751

2. 20 x 20 200 17.8 11205

3. 30 x 30 200 26.5 7543

d. Depth of Foundation: 2.0 m – 4.0 m below the lowest existing ground level

Thickness of Engineering Fill Material below Foundation Level - 0.50 m

(i) Isolated Footing:

Sr. No. Width of Footing Net Allowable Anticipated Modulus of Subgrade

(m) Bearing Pressure Settlement Reaction
(kPa) (mm) (kN/m3)

1. 2.0 300 2.7 110499

2. 3.0 300 4.0 74239

3. 4.0 300 5.4 55773

4. 5.0 300 6.8 44195

(ii) Raft Foundation:

Sr. No. Size of Foundation Net Allowable Anticipated Modulus of Subgrade

(m x m) Bearing Pressure Settlement Reaction
(kPa) (mm) (kN/m3)

1. 10 x 10 220 9.9 22257

2. 20 x 20 220 19.4 11332

3. 30 x 30 220 28.9 7600

It is possible to excavate upto the recommended depth by mechanized means. Care

should be taken to ensure that the foundation strata is not disturbed during excavation.
No loose portion may be left on the excavated floor and it may be well compacted.

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 Soil Inv. for the Development of North Oman Solar PV Plant with Battery Energy Storage System Independent Power Project at Saih Rawl, J-7723, Nov’2022

The excavated floor may be closely inspected and if any cavities, cracks, voids or loose
pockets are observed, these may be cleaned and filled with mass concrete before the
foundation concrete is laid. The excavated floor may not be left open to nature for
long. The side slopes are expected to remain stable at 30 o angle from vertical for a
limited period of time. Barring major seasonal changes, groundwater may not be
encountered during foundation excavation. The soil material available at this site is not
suitable for general as well as structural backfilling purpose.

5.2 Differential Settlements and Long Term Settlements:

The substrata is homogenous in the Boreholes drilled this site. Hence, we do not
anticipate any differential settlements within the structure. The creep or long term
settlements will not occur at this site and will happen only in soft clay / silt formation
which is not present at this site.

5.3 Gypsum Content:

The Gypsum content is observed at this plot. Hence, we have suggested an engineering
fill materials of minimum 0.50 m thick below the foundation level.

5.4 Site Categorization as per International Building Code:

The soil profile at this site as per the International Building Code 2006 falls in the
Category Site Class -D upto a depth of around 1.0 m below the existing ground level and
Site Class C thereafter upto depth explored.

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 Soil Inv. for the Development of North Oman Solar PV Plant with Battery Energy Storage System Independent Power Project at Saih Rawl, J-7723, Nov’2022

TABLE 1613.5.2
SITE CLASS DEFINITIONS

AVERAGE PROPERTIES IN TOP 100 feet, SEE SECTION 1613.5.5

SITE SOIL PROFILE
CLASS NAME Soil shear wave velocity, v S , (ft/s) Standard penetration resistance, N Soil undrained shear strength, s u , (psf)

A Hard rock vs  5,000 N/A N/A

B Rock 2,500  vs  5,000 N/A N/A

Very dense soil and 1,200  vs  2,500 su  2,000

C N  50
softrock
D Stiff soil 600  vs  1,200 15  N  50 1,000  su  2,000
profile
E Soft soil profile vs  600 N  15 su  1,000
Any profile with more than 10 feet of soil having the following characteristics:
1. Plasticity index PI  20,
E — 2. Moisture content w  40%, and
3. Undrained shear strength su  500 psf

Any profile containing soils having one or more of the following characteristics:
1. Soils vulnerable to potential failure or collapse under seismic loading such as
liquefiablesoils, quick and highly sensitive clays, collapsible weakly cemented soils.
F — 2. Peats and/or highly organic clays (H > 10 feet of peat and/or highly organic clay where
H = thickness of soil)
3. Very high plasticity clays (H >25 feet with plasticity index PI >75)
4. Very thick soft/medium stiff clays (H >120 feet)

For SI: 1 foot = 304.8 mm, 1 square foot = 0.0929 m2, 1 pound per square foot = 0.0479 kPa. N/A = Not applicable

5.5 Subsoil Parameters and Lateral Earth Pressure Parameters:

Sr. Depth Bulk Angle of Internal Coefficients of Lateral Earth Pressure

No. Density Friction Ko Ka Kp
(m) (kN/m3) ()

1. 0.0 – 1.0 15 30 0.50 0.3333 3.000

2. 1.0 – 2.0 16 32 0.47 0.3073 3.2546

3. 2.0 – 3.0 17 34 0.44 0.2827 3.5371

4. 3.0 – 6.0 18 21 0.64 0.4723 2.1171

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 Soil Inv. for the Development of North Oman Solar PV Plant with Battery Energy Storage System Independent Power Project at Saih Rawl, J-7723, Nov’2022

5.6 Excavatability

Sr. No. Depth Strata Description Excavatability Suitability for Back

(m) Filling
Medium dense to dense
1. 0.0 – 0.5 / 1.0 Rippable Not Suitable
soil
Dense to very dense Partly Rippable / Partly
2. 0.5 / 1.0 – 1.5 /2.0 and cemented soil Non Rippable Not Suitable

5.7 Suitability of Excavated Materials for backfilling:

The soil material available at this site is not suitable for structural backfilling purpose
and hence we suggest to use imported materials for backfilling purpose as per the PDO
specification of Class A or B / B1.

5.8 Specification for backfilling materials as per PDO:

Granular Fill Materials

Material Specification PDO PDO PDO PDO PDO PDO PDO

Type A Type B Type B1 Type C Type D Type E Type F

4-day soaked CBR value 80 80 – 60 60 – 45 40 40 40 -

When compacted to the following % max dry

98% 98 – 95% 98 – 95% 95% 95% 95% -
density

Gradation Requirements to ASTM D1241 Type I-B Type I-D - Type II-F - - -

AASHTO (ASTM E11/BS 410) Sieve Size % passing by Weight

2 inch 50 mm 100 - - - 100 100 100

1 inch 25 mm 75 - 95 100 100 100 55 – 85 55 – 95 75 – 95

¾ inch 19 mm - - - - - 50 – 90 -

3/8 inch 9.5 mm 40 – 75 60 – 100 60 – 100 100 40 – 70 40 - 80 40 – 70

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 Soil Inv. for the Development of North Oman Solar PV Plant with Battery Energy Storage System Independent Power Project at Saih Rawl, J-7723, Nov’2022

AASHTO (ASTM E11/BS 410) Sieve Size % passing by Weight

No. 4 4.75 mm 30 – 60 50 – 85 50 – 85 70 – 100 30 – 60 30 – 65 25 – 45

No. 10 2.0 mm 20 – 45 40 – 70 40 – 70 55 – 100 20 – 50 20 – 50 -

No.40 425 µm 15 – 30 25 – 45 25 – 45 30 – 70 10 – 30 10 – 30 5 – 20

No.200 75 µm 5 - 15 8 - 15 8 - 15 8 – 15 5 – 15 5 - 15 0–2

AASHTO ASTM
Liquid Limit 25% max 35% max 40% max 40 % max 25% max 25% max -
T89 D4318

AASHTO ASTM
Plasticity Index 6% max 9% max 12% max 12% max 7% max 7% max -
T90 D4318

Sand AASHTO ASTM

- - - - 25% min 25% min
Equivalent T176 D2419

Loss by AASHTO
ASTM C131 50% max 50% max 50% max - 50% max 50% max -
Abrasion T96

Required % Compaction As specified

Moisture Content Should be between 2% below and 1% above optimum

5.9 Corrosive effects of the soil on carbon steel

The apparent resistivity for the Wenner electrode configuration is given by ρ = 2πaR
[where a = electrode spacing (m) R= measured resistance (Ω)]. The corrosivity rating of
soil as per the chart given in BS 7361-1: 1991 reproduced below.

Resistivity (Ω-m) Corrosivity Rating

Up to 10 Severely corrosive

10 to 50 Corrosive

50 to 100 Moderately corrosive

100 and above Slightly corrosive

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