Page 27 - Building Regulation and Design Guidelines - Structural (Grey Code)

SECTION: 1 GEOTECHNICAL GUIDELINES & REGULATIONS SECTION: 1 GEOTECHNICAL GUIDELINES & REGULATIONS
Fig. (1.33-c) Soldier Piles Shoring System
Method Statement for Different types of Shoring Systems
b) Structural bending moments, shear forces and prop or tie forces should
be derived from the equilibrium calculations using design earth pressures
and water pressures. The ultimate limit state and serviceability limit
state should be the same as those used for the overall equilibrium and
deformation calculations. All Stages of constructions to be studied as per
Fig. (1.34).
NITALE PHASE PHASE 1 PHASE 2 PHASE 3
Fig. (1.34): Shoring Stages of Construction
m)
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c) The shoring works should be designed as a rigid vertical system subjected
to the earth, water pressures and support reactions taking into account the
staged construction.
d) The maximum retained height is 15.00 m (BS 8002: 1994, Section 1.1).
Advice from the shoring works specialist is required in case of excavation
depth of 15.00 m is required.
e) The excavation and support systems should be designed to ensure that
the settlement or lateral yield of the surrounding ground surface is within
acceptable limits particularly where the excavation adjoins roads where
drainage, electricity services are located. The maximum lateral displacement
permitted for the shoring systems is 40 mm.
f) The minimum surcharge load is 15 kN/m2 and value of 15 kN/m2 should
be added for each neighbouring existing plot floor when the neighbouring
foundation is a raft. Traffic surcharge load to be considered 20 kN/m2 at
roads sides.
g) Cantilever shoring systems are suitable for moderate height only. The
maximum height of such sheet pile cantilever walls is 5.00 m. (BS 8002:
1994, Section 4.4.2.).
h) Minimum factor of safety of fixation and embedded depth should be taken
as 2.00.
i) Bored piles contiguous or secant piles are very preferable when the shoring
works is closed to an existing foundation. Difference of water levels in front
and back to shoring system should be taken into consideration in case of
secant piles, sheet pile wall or diaphragm wall after dewatering.
j) Maximum spacing between soldier piles is 2.50 m and maximum spacing
between tie back anchors is 4.00 m.
k) The design earth pressure are derived from design soil strengths using the
usual methods of elasto-plastic behaviour, with earth pressure coefficients
given in BS 8002 : 1994, Section 1.3.9.
l) In checking the stable equilibrium and soil deformation, retaining walls
should be designed assuming a depth of unplanned excavation in front of
the wall not less than 10 % of the total height retained for cantilever walls
or of the height retained below the lowest support level for propped or
anchored walls. The minimum unplanned depth is 0.50 m ((BS 8002: 1994,
Section 3.2.2.2).
The long term analysis is likely to be critical where the soil mass undergoes
a net reduction in load as a result of excavation, such as adjacent to a
cantilever wall. For granular soils, the relative strength is always the drained
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