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Services AUGER CAST PILES
Advantages:
TYPICAL AUGER CAST PILE LOADS FOR VARIOUS DIAMETERS
The diameters indicated are the most common
used for auger cast piles. However, auger cast piles with diameters
of 24", 30" and 36" have been successfully utilized with
tests being conducted as high as 350 tons. Pile design capabilities
can be verified with several different testing procedures: ASTM D 1143 tests the compressive capacity of a pile by applying a static axial
compressive load; ASTM D 4945 tests the
compressive capacity of a pile
by applying a dynamic axial high-strain impact load; ASTM D 3689 tests the
tensile capacity of a pile by applying a static axial tensile load; ASTM
D 3966 tests the lateral deflection of a pile by applying a static
load perpendicular to the axis of the pile; and ASTM D 5882 test the integrity of the pile shaft by
applying a dynamic axial low-strain impact load. Chemical Based Grouting
Chemical grout is non-toxic, eliminating the need for protective clothing during placement. It stabilizes soil effectively and economically often eliminating the need for costly sheeting and shoring. On congested job sites, where a large area would be required to install sheeting and shoring, the injection of a chemical based grout is a viable alternative. Chemical based grout, when used in proper proportions, is immune to deterioration and demonstrates reasonable permanence by being dimensionally stable regardless of changes in temperature. the ambient temperature however, is an important factor in the design oft he mix because of its effect on gel time. Cement Based Grouting Cement based grout is a combination of cement,
pozolithihic filler, sand, water and fluidifier. It is applied under
pressure through existing floor slabs, walls, tunnel linings, and soil
layers. Filling voids that have developed below existing floor slabs
or pavements is a primary use and in some cases, thought he use of a
phased installation, slabs that have settled can be raised back to their
original elevation. compressive strengths reaching 8,000 psi can be
achieved. In most instances the cement based gout is mixed in site
and fed directly to the pump.
In cases where larger sized voids and crevices need to be filled, cement
grout is pumped into a porous flexible bag ( a "Grout Bag") that
is lowered into position where the void is to be filled. Once the
grout sets, the "Grout Bag" is held firmly in place against the surrounding
walls sealing the voids. This method of pressure grouting eliminates
wash-away tendencies occasionally encountered during regular pressure
grouting operations. It is ideally suited for cutoff walls,
diverting water flow and filling voids due to scour. The "Grout
Bag" Confinement Method is economical and stays where it is placed. Preplaced Aggregate Concrete (PAC) was originally developed for structural repairs primarily because of its strength, excellent bonding ability to existing concrete, higher resistance to erosion and cavitations, minimal shrinkage, and uniform quality. PAC lends itself to vertical and overhead types of construction such as: bridge piers and abutments, walls dams, tunnel linings, and spillways, etc. In PAC work, clean coarse aggregate is placed in pre-positioned forms and a cement mortar is pumped into the aggregate mass from the bottom up, displacing air and/or water from spaces between the aggregate particles. PAC can also be used in new construction as well as part of a structural repairs, the cement mortar penetrates the rough texture and surface of existing older concrete. The practical elimination of setting and drying shrinkage provides a final monolithic concrete making the structure equal to or better than as originally built. In new construction, as in the case of heavily reinforced concrete, the graded aggregate is rodded into place among the bars and the mortar is injected afterwards thus reducing the the risk of hidden voids that is inherent with the use of ordinary concrete. Comprehensive strengths of PAC can reach as high as 7,000 psi. It utilizes a greater proportion of coarse aggregate in its overall makeup. back to top When the difference between the working
elevation of a site and the elevation of any existing structures,
pavements, or utilities that need to be protected is substantial, and the
site does not offer enough space to slope back the sides of the
excavation, then an earth retention, shoring, or underpinning system is
required. The auger cast pile, when installed in a continuous auger
cast cutoff wall, can be reinforced to resist lateral forces imposed by
existing conditions. The process by which a continuous auger cast
cutoff wall is installed is twofold: First, a drilling a template is
constructed. The template is installed at eh lowest possible
elevation, such as the top of existing footers or the top of existing
sewers and utility lines. Generally, the width and depth of the
template is between 18 and 24 inches. A reinforcing cage is
installed the full length of the template and then tubes forms of the
proper diameter are installed through the ties of the cage.
Following the pouring and curing of the template, the auger cast piles are
installed through the forms and down to the required depth. The
piles can be reinforced with full length bars, reinforcing cages, or, in
the case of heavy lateral loads, with full length wide flange beams if
required. The excavation can continue once the vertical components
of the wall have been cured. In the case of deeper excavations;
diagonal tie-backs, as described below, can be installed through the auger
cast wall to provide additional resistance to lateral forces. In
some instances, the completed auger cast cutoff can be incorporated into
the final project as an exposed retaining wall or the actual basement
walls by covering its face with a shotcrete or otherwise aesthetic
concrete covering.
Auger cast cofferdam with reinforced ring beams for Equalization Tank at the Division Avenue WWTP in Cleveland, OH
When tensile or uplift forces are anticipated, such as hydrostatic pressures on submerged tanks and wind loads on the legs of a tower, a system to resist those tensile forces is required. Auger cast piles can be utilized to resist uplift in cohesive and granular materials. The method of placement remains the same but when tensile forces are anticipated, a full length reinforcing bar is installed in the pile. Depending on the depth of the pile, the full length bar can be installed through the hollow shaft of the auger or placed after the grouting process is complete. When the underlying subsurface material is solid bedrock then uplift is resisted through the use of a rock anchor. Rock anchors are generally smaller in diameter than an auger cast pile; the equipment used to install them and the method of installation is also substantially different. In both cases the full length reinforcing bar must be large enough to withstand the anticipated load and transfer it into the anchor. Auger cast piles can be installed as
Tie-backs through sheet pile walls, beam and lagging walls, and auger cast
cutoff walls. essentially, a diagonal tie- back is a tension pile
placed on a batter and an auger cast pile rig can be modified to install
tie-backs on any angle up to approximately 60º from vertical.
Tie-backs installed through the face of the wall extend back beyond the
limit of the theoretical failure plane and into competent soil. For
design purposes, no value should be assigned to the soil located in the failure
plane. High strength tensile bars (usually 150 ksi thread bar) are
installed through the hollow shaft of the auger and embedded in the gout
of the tie-back. Bars can vary from simple epoxy coated steel for
temporary retaining systems or fully encapsulated bars for permanent retaining
systems. The degree of encapsulation varies with the amount of corrosion
protection required for the individual job. Once the grout in the
tie-back has achieved the required strength the steel bars are
post-tensioned which places the soil immediately behind the wall in
compression and reduces the tendency of the wall to move inward as the excavation
proceeds.
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