BRACED EXCAVATION DESIGN
MUHAMMAD AZRIL HEZMI
PROF. KHAIRUL ANUAR KASSIM
PROF. Ir. DR. RAMLI NAZIR
INSPIRING CREATIVE AND INNOVATIVE MINDS
CONCEPT
• Consist of sheet piles driven into the soil to form sides of an excavation
such as construction of bridge piers and abutments.
• As excavation proceeds within the area enclosed by the sheet piles, struts
are added to keep the sheet pile in place.
• Displacement gets larger at depth.
• Critical design element are the loads on the struts which are usually
different because of different lateral loads at different depths, the time
between excavations and the installation procedures.
Contd…
• The analysis for the forces and deflection in braced excavation should ideally
consider the construction sequence, and numerical methods such as the finite
element.
• Semi empirical methods are often used in the design of shallow braced
excavation and also as a basic design of deep braced excavation.
• In the soft and Normally Consolidate soil, heaving may occurs at the base of
the excavation.
• Bjerrum and Eide (1956) suggested that the excavation could be view as
afooting and embedment depth Ho.
Contd….
so
ucheave
qH
cNFS
+=
γ)(
• The factor of safety against the bottom heave is given by:-
• For practical purposes the value of Nc is given by:-
L
BI
B
HifIN
and
B
Hfor
B
HN
co
cc
ooc
16.084.0,5.2...........9
5.2..........2.016
+=>=
≤
+=
Contd….
• If FOS < 1.5, the length of embedment should be extended below the base of
excavation for stability.
• The value of coefficient m = 1 except that when the soil below excavation is
deep, soft and normally consolidated clay, m value is approximately 0.4(FOS
heave).
• The strut load at each depth is assumed to be a hinge connection between strut
and sheet pile. Thus solution is using static equilibrium.
• Displacement of the wall is important in design consideration as adjacent
structire may affected.
• However it is better off to solve using numerical method.
PROCEDURE FOR ANALYSIS
• Check stability against bottom heave. If FOS < 1.5 the wall should be
extened below base.
• Determine the lateral stresses on the wall according to soil type.
• Treat the connections of the wall to the struts as hinges.
• Draw a free body diagram at each level of excavation.
• Solves the forces in the stuts using the static equilibrium equations on
each free body diagram.
Examples
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