Table 2.1        Presumed Allowable Vertical Bearing Pressure under Foundations on Horizontal Ground/Bedrock

Category	Description of rock or soil	Presumed allowable bearing pressure (kPa)
	Rock (granite and volcanic):
1(a)	Fresh to slightly decomposed strong to very strong granite or volcanic rock of material weathering grade II or better, with 100% TCR of the designated grade which has a minimum UCS of rock material not less than 75 MPa (or an equivalent point load index strength PLI50 not less than 3 MPa)	10,000
1(b)	Fresh to slightly decomposed strong granite or volcanic rock of material weathering grade II or better, and with not less than 95% TCR of the designated grade, which has a minimum UCS of rock material not less than 50 MPa (or an equivalent point load index strength PLI50 not less than 2 MPa)	7,500
1(c)	Slightly to moderately decomposed moderately strong granite or volcanic rock of material weathering grade III or better, and with not less than 85% TCR of the designated grade, which has a minimum UCS of rock material not less than 25 MPa (or an equivalent point load index strength PLI50 not less than 1 MPa)	5,000
1(d)	Moderately decomposed, moderately strong to moderately weak granite or volcanic rock of material weathering grade III or better, and with not less than 50% TCR of the designated grade.	3,000
2	Meta-Sedimentary rock: Moderately decomposed, moderately strong to moderately weak meta-sedimentary rock of material weathering grade III or better, and with not less than 85% TCR of the designated grade.	3,000
3	Intermediate soil (decomposed granite and decomposed volcanic): Highly to completely decomposed, moderately weak to weak rock of material weathering grade V or better, with SPT N-value ³ 200	1,000

Table 2.1        Presumed Allowable Vertical Bearing Pressure under Foundations on Horizontal Ground/Bedrock (Continued)

Category	Description of rock or soil	Presumed allowable bearing pressure (kPa)
	Non-cohesive soil (sands and gravels):	Dry      Submerged
4(a)	Very dense – SPT N-value >50	500             250
4(b)	Dense – SPT N-value 30-50; requires pick for excavation; 50 mm peg hard to drive	300             150
4(c)	Medium dense – SPT N-value 10-30	100              50
4(d)	Loose – SPT N-value 4-10, can be excavated with spade; 50 mm peg easily driven	<100           <50
	Cohesive soil (clays and silts):
5(a)	Very stiff or hard – Undrained shear strength >150 kPa; can be indented by thumbnail	300
5(b)	Stiff – Undrained shear strength 75-150 kPa; can be indented by thumb	150
5(c)	Firm – Undrained shear strength 40-75 kPa; can be moulded by strong finger pressure	80

Notes:

• The presumed values for allowable bearing pressure given are for foundations with negligible lateral loads at bearing level.

• The self weight of the length of pile embedded in soil or rock does not need to be included into the calculation of bearing stresses.

• Minimum socket depth along the pile perimeter is 500 mm for categories 1(a) and 1(b), and 300 mm for categories 1(c), 1(d) and 2.

• TCR of the designated grade is defined in Figure 2.1.

• The TCR of the designated grade should be proved to a depth at least 5 m into the specified category of rock. This requirement is deemed to be complied with if the rock underneath the minimum socket depth as mentioned in note (3) above has a length of at least 5 m which can be divided into a number of segments (in consecutive manner) such that (a) each segment is 1 m; and (b) the calculated TCR in accordance with Figure 2.1 of each segment should satisfy the required percentage of TCR of the designated grade.

• The bearing surface of rock on which the foundation will be rested should be of the designated category and in an intact condition for a depth not less than 600 mm.

• Weathering grades are defined in GEOGUIDE 3.

• The point load index strength of rock quoted in the table is the equivalent value for 50 mm diameter cores.

• The definition of Dry Condition and Submerged Condition are given in clause 1.2.

• Where the ground is intermediate between dry and submerged, the presumed value may be obtained by linear interpolation.

• The use of presumptive values does not preclude the requirement for consideration of settlement of the structure.

Notes: 1. TCR of the designated grade = (a+c+d+f)/L.

• a, c, d and f are materials of the designated grade or better.
• b are materials inferior than the designated grade.
• e are materials washed away during drilling.
• The maximum continuous length of materials washed away/inferior to the designated grade, b+e, should not be greater than 300mm
• TCR of the designated grade should not be confused with TCR of the core run shown in the site investigation report, which is equal to (a+b+c+d+f)/L

Figure 2.1       Definition of TCR of the Designated Grade