g.
Piles. Piles driven into soft surficial soils
stiffening element by suitable details of joints and
reinforcing in the slab and at the edges of the slab.
must transfer the base shear into stiffer soils at lower
levels. This involves bending of the piles. Criteria
c.
Grade Beams. Grade beams may be used to
for design should be obtained from the geotechnical
stiffen spread footings where columns are intended
engineer. Where subsurface conditions vary over the
to have fixed bases; grade beams may also develop
site, the effective lengths of piles in bending may
lateral resistance in passive pressure on their sides,
vary.
The resulting variation in relative rigidity
especially if stiffened by an integral slab on ground.
causes some piles to carry more lateral load than
Passive-resistance values vary greatly with type of
others, and must be considered in the foundation
soil and depth.
Adequacy of passive resistance
design. Passive pressure on the vertical surfaces of
should be determined by the geotechnical engineer.
the pile cap may be a more effective method of shear
Passive resistance or lateral bearing values are
transfer. For pile caps in weak soils, the use of select
permitted only where concrete is deposited directly
compacted backfill will enhance the lateral load
against natural ground, or the backfill is well
capacity.
compacted. Passive resistance should not be used
h.
Batter Piles. The use of batter piles should
where the lateral bearing surface is close to an
excavation, unless such excavation is carefully
be avoided. Their greater lateral stiffness relative to
backfilled with well-compacted material. The shear
the vertical piles attracts most of the lateral forces to
capacity of the soil between such bearing surface and
themselves, resulting in an unbalanced lateral-load-
open or poorly compacted excavation or a similar
resisting system.
Because the inclination of the
depression may be inadequate to provide the needed
batter piles is usually small, very large vertical
resistance.
components of force are developed between the
vertical and adjacent batter piles. The pile cap must
d.
Basement Walls.
Basement walls can
be detailed to accommodate these forces, and the
develop passive pressure for normal forces.
The
caps may need to be stiffened by horizontal grade
comments on passive pressure for grade beams
beams to prevent rotation under these forces.
apply.
i.
Foundation Ties. Ties will be designed to
e.
Spread Footings. Spread footings resist
carry an axial tension and compression horizontal
vertical loads through bearing pressure on the
force equal to 10 percent of the larger column load.
bottom, and resist horizontal loads through friction
The minimum tie will be 12 inches by 12 inches
on the bottom and passive pressure on the sides.
(305mm x 305mm) , with four #5 (15M)
longitudinal bars and #3 (10M) ties at 12 inches
f.
Wall Footings. Wall footings resist lateral
(305mm) on center.
loads through friction on the bottom.
9 - 15
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