FOUNDATIONS 9.1 Shallow Foundations

Shallow foundations can be used in

For preliminary design, shallow foundations can be designed for exceeding

• 100kPa in firm clays with SPT(N) values greater than 15

• 200kPa in medium dense sandy soils

• 500kPa on rock

The factor of safety against bearing capacity failure

For detailed design, site investigation should be carried out on a 50m to 150m grid after platform construction to confirm the above bearin

as part of confirmation testing.

Settlement analyses can be carried out when foundation loads are known.

expected to be less than 25mm for pad footing sizes up to 3m x 3m pressure not exceeding 100kPa.

detailed engineering phase.

All other plant and strictures (to be determined during FEED or detailed engineering phase) that can be supported on shallow foundations should be piled.

9.2 Piled Foundation

9.2.1 General

It is recommended that all major to refusal.

Piles driven to set are preferred to bored piles because they (i) Compact the ground during their installation;

(ii) have higher safe working loads;

(iii) are cost effective.

Pre-tensioned high strength spun concrete piles

(i) are robust (due to their construction process); and (ii) can sustain higher driving stresses without damage.

All piles should be driven to set with sufficient

not to overstress the piles. Stress wave testing should be carried out as part of test piling programme to determine suitable hammer sizes and drops

acceptable levels.

FOUNDATIONS

Shallow Foundations in Cut Areas

Shallow foundations can be used in Cut Areas.

foundations can be designed for allowable bearing pressures not in firm clays with SPT(N) values greater than 15

200kPa in medium dense sandy soils and in stiff clays 500kPa on rock

The factor of safety against bearing capacity failure must be greater than 3.

For detailed design, site investigation should be carried out on a 50m to 150m grid after platform construction to confirm the above bearing pressures. Plate load bearing test should be carried out

be carried out when foundation loads are known. Total s

expected to be less than 25mm for pad footing sizes up to 3m x 3m and designed for bearing pressure not exceeding 100kPa. Differential settlement analyses should be carried out in the

All other plant and strictures (to be determined during FEED or detailed engineering phase) that ed on shallow foundations should be piled.

Foundations in Filled Areas

major and settlement-sensitive structures are supported on piles driven

Piles driven to set are preferred to bored piles because they ground during their installation;

ve higher safe working loads; and are cost effective.

tensioned high strength spun concrete piles are preferred to precast RC piles becaus are robust (due to their construction process); and

can sustain higher driving stresses without damage.

All piles should be driven to set with sufficient energy to mobilise their full structural capacity but not to overstress the piles. Stress wave testing should be carried out as part of test piling programme to determine suitable hammer sizes and drops so to keep dynamic stresses to

allowable bearing pressures not

For detailed design, site investigation should be carried out on a 50m to 150m grid after platform g pressures. Plate load bearing test should be carried out

Total settlements are designed for bearing Differential settlement analyses should be carried out in the

All other plant and strictures (to be determined during FEED or detailed engineering phase) that

are supported on piles driven

are preferred to precast RC piles because they

to mobilise their full structural capacity but not to overstress the piles. Stress wave testing should be carried out as part of test piling so to keep dynamic stresses to within

9.2.2 DRIVEN Pile Sizes and Safe Working Loads Spun pile with Outside Diameters (

minimum effective prestress should be 5N/mm

Piles in Zones 3 and 4 will experience negative friction due to settling

the platform fill. This will mobilise drag loads on the piles that will reduce their effective safe working loads. The magnitude of drag loads can approach 30% of the maximum permissible structural loads and it is recommended tha

the maximum permissible structural load.

Design safe working loads are summarised below for spun pile from 300 to 600mm.

Table 27 Safe working loads for spun piles Minimum concrete strength = 78.5N/mm Minimum effective prestress = 5N/mm Spun

(4) calculated as 70% of max structural load with geotechnical rounding Safe working loads must be confirmed by pile load testing.

The following minimum factors of safety should be applied to the ultimate geotechnical capacity spun piles driven to set:

i. FOS = 2.0 applied to

ii. FOS = 2.5 applied to the ultimate shaft resistance (tension); and iii. FOS = 2.0 applied to

Pile Sizes and Safe Working Loads

with Outside Diameters (OD) ranging from 300mm to 600mm can be used. The prestress should be 5N/mm².

will experience negative friction due to settling ground under the weight of . This will mobilise drag loads on the piles that will reduce their effective safe working loads. The magnitude of drag loads can approach 30% of the maximum permissible structural loads and it is recommended that their safe working loads be not greater than

the maximum permissible structural load.

Design safe working loads are summarised below for spun pile Outside Diameters

Safe working loads for spun piles DRIVEN to set Minimum concrete strength = 78.5N/mm²

Minimum effective prestress = 5N/mm² Maximum Structural Safe Working Load

(kN)

as 70% of max structural load with geotechnical rounding.

Safe working loads must be confirmed by pile load testing.

factors of safety should be applied to the ultimate geotechnical capacity

FOS = 2.0 applied to the ultimate shaft resistance (compression);

FOS = 2.5 applied to the ultimate shaft resistance (tension); and FOS = 2.0 applied to the ultimate toe resistance.

00mm can be used. The

under the weight of . This will mobilise drag loads on the piles that will reduce their effective safe working loads. The magnitude of drag loads can approach 30% of the maximum permissible not greater than 70% of

iameters (OD) ranging

. A = cross section area of concrete.

factors of safety should be applied to the ultimate geotechnical capacity of

;

9.2.3 BORED Piles Sizes and Safe Working Loads

Design safe working loads are summarised below for BORED pile having diameters ranging from 500mm to 1000mm

Table 28 Safe working loads for BORED piles Minimum concrete strength = 40N/mm BORED

Pile Diameter

(mm) (1)

Maximum Structural Safe Working Load

(kN) (2)

500 1963

600 2827

700 3848

800 5027

900 6362

1000 1963

Key

(3) calculated as 0.25 x Fcu x A where A = cross section area. F

(4) calculated as 70% of max structural load with geotechnical rounding Safe working loads must be confirmed by pile load testing.

The following minimum factors of safety should be applied to the ultimate geotechnical capacity of B0RED piles:

i. FOS = 2.0 applied to the ultimate shaft resistance ii. FOS = 2.5 applied to the ultimate shaft resistance iii. FOS = 3.0 applied to the ultimate toe resistance.

Sizes and Safe Working Loads

loads are summarised below for BORED pile having diameters ranging from

Safe working loads for BORED piles Minimum concrete strength = 40N/mm²

imum Structural

Working Load

Recommended Geotechnical Safe Working Load

(kN) (3)

1350

2000

2700

3500

4500

1350

x A where A = cross section area. Fcu = 40N/mm² as 70% of max structural load with geotechnical rounding.

Safe working loads must be confirmed by pile load testing.

The following minimum factors of safety should be applied to the ultimate geotechnical capacity of

2.0 applied to the ultimate shaft resistance (compression);

applied to the ultimate shaft resistance (tension); and FOS = 3.0 applied to the ultimate toe resistance.

loads are summarised below for BORED pile having diameters ranging from

The following minimum factors of safety should be applied to the ultimate geotechnical capacity of

;

9.2.4 DRIVEN Pile Toe Levels All piles should be driven to set which

into N>50 strata. Figure 50 presents levels of N>50 strata as determined from the existing boreholes.

9.2.5 BORED Pile Toe Levels Bored piles should be founded

into bedrock, whichever is encountered first,

9.2.6 Pile Testing

Allowance should be made for a

Stage I Design Verification Testing