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The Geopier® System is a cost-effective solution to
foundation support on soft soil sites and provides an excellent
alternative to deep piles/caissons and verexcavation and replacement
filling.
A Rammed Aggregate Pier® element is a dense, aggregate pier constructed in a pre-excavated
cavity with patented equipment that imposes significant lateral
prestress into the undisturbed soils surrounding the element.
The combination of constructing the piers in pre-excavated cavities
and the lateral stress build-up that results from the patented ramming
equipment, are the key elements that set the Geopier system apart
from all other aggregate pier or stone column systems. They are
the primary factors accounting for the phenomenal success of the
Geopier system in controlling foundation settlements in soft soils.
Pier cavities are typically excavated by conventional drilling techniques,
using either truck-mounted augering equipment or "dangle drill"
equipment mounted on an excavator or crane.
Drilled cavities for Rammed Aggregate Pier® elements typically range from 18"
to 36" in diameter.
With the use of casing, Rammed Aggregate Pier® elements can be constructed below
ground water in all soils ranging from peat to loose clean sands
to soft clays.
Aggregate used for pier construction is typically high quality crushed
rock, such as used for highway base course construction. Lower quality
aggregate can be used so long as compacted characteristics are relatively
uniform and are defined by field testing. For liquefaction mitigation,
free-draining aggregate can be used so the Geopier element also
functions as a drain to relieve excess pore water pressures.
Rammed Aggregate Pier® elements are constructed in lifts of about 1 to 2 foot thickness (depending on ramming energy used),
with each lift rammed vertically and laterally using the patented
Geopier tamper. Within 15 seconds of tamping, a lift can receive
over two times the compactive energy that is put into the maximum
density laboratory test (ASTM 1557).
Since Rammed Aggregate Pier® elements are constructed in pre-excavated cavities,
there is essentially no remolding of the surrounding soils, as occurs
with other stone column techniques that involve complete soil displacement.
Hence, with the Geopier technique the surrounding soils cannot experience
strength loss due to the construction methods, but rather gain a
significant increase in stiffness as each lift of
aggregate is rammed. No other aggregate pier system can achieve this level of stiffness increase!
By constructing Rammed Aggregate Pier® elements in clusters spaced from about 1½
to 3 diameters apart, the Geopier-reinforced soil mass experiences
significant permanent prestressing, which greatly improves its strength
and consolidation characteristics (extending several feet beyond
the outside piers). Hence, the so-called "group effect"
is very desirable for the Geopier system because it improves performance
(whereas, in the design of pile foundations the group effect is
normally avoided because it tends to reduce individual pile capacities).
The Geopier system is applicable in any situation where a significant
increase in stiffness and/or shearing strength of a soil mass will
improve engineering performance. This includes:
Spread footings -- Increase in bearing capacity and reduction of
settlement
Floor slabs/mats -- Improve subgrade uniformity and
reduce settlements
Slopes -- Increase in factor of safety for stability
Excavations -- Increase in temporary support
Note the significant lateral stress increase in the soils surrounding the Rammed Aggregate Pier® element.
THIS is the key to the incredible success of Rammed Aggregate Pier® element has in reducing settlement in soft soils. |
