Terminology
Auger: a tool having a
helical shaft that is used for boring holes into the ground and removing the
loosened soil
Axial:
the direction
perpendicular to the plane of the top of the pile
Bulging: is a portion of a
pile, which protrudes beyond the nominal diameter of the pile. This occurs
when piles are bored through strata of soils with differing density. Bulging
occurs when good practices are being observed.
Clay: an earthy material
that is plastic when moist but hard when fired, that is composed mainly of
fine particles of hydrous aluminum silicates and other minerals
Communication: is a term used to
indicate that piles have been placed too close together while the concrete
grout is still fluid. Visual observations of changes in levels of grout in
the pile above or below the ground indicate the adjacent shaft may have
expanded which may result in reduced shaft diameter of the other pile.
Compression:
downward vertical
load on a
pile
Concrete Grout:
a mixture of cement
, water and sand or chemicals that solidify
Cores:
are cylindrical
samples of rock which are obtained from drilling and tested for compressive
strength
End Bearing:
the force that
resists motion between the tip of the pile and the soil/rock.
Fly ash: is a residue left over from burning coal. Most fly ash is pozzolanic,
which means it’s a siliceous or siliceous-and-aluminous material that reacts
with calcium hydroxide to form a cement. Properly selected fly ash reacts
with the lime to form CSH–the same cementing product as in portland cement.
This reaction of fly ash with lime in concrete improves strength. Typically,
fly ash is added to structural concrete at 15-35 percent by weight of the
cement.
Advantages - The most important benefit is reduced permeability to water and aggressive chemicals. Properly cured concrete made with fly ash creates a denser product because the size of the pores are reduced. This increases strength and reduces permeability. The reduced permeability helps to protect the concrete from chloride penetration, the cause of rebar corrosion (see Rosenberg’s article on corrosion in the Fall 1999 issue of MC Magazine).
Advantages in Fresh Concrete - Since fly ash particles are spherical and in the same size range as portland cement, a reduction in the amount of water needed for mixing and placing concrete can be obtained. The use of fly ash can result in better workability, pumpability, cohesiveness, ultimate strength, and durability.
Advantages in Hardened Concrete - Strength in concrete depends on many factors, the most important of which is the ratio of water to cement. Good quality fly ash generally improves workability or at least produces the same workability with less water. The reduction in water leads to improved strength.
Friction:
the force that
resists relative motion between the surface of the pile and the contact with
the soil
Geotechnical
Report: a summary report of
the exploration of the subsurface soils and how they are to be used as
construction materials.
Group effect:
a group of piles
under load will behave differently than individually loaded piles
Head: is a term that
normally refers to the height in feet that the concrete grout is above the
tip of the auger discharge bit as it is being withdrawn from the hole. While
this can’t be measured because it is below the ground it is normally
estimated by observing height the grout on the auger after it is totally
withdrawn from the hole.
Impenetrable:
incapable of being
penetrated
Karst: is a geological term
which describes the conditions existing in limestone formations containing
solution filled cavities and voids.
Neat Line volume:
refers to the
theoretical volume of a cylindrical shaft of a given diameter and length, and is normally
expressed in Cubic Yards. It is calculated by multiplying 3.1416 (PI) times
the radius squared times the length. The Neat Line volume is referred to as 100%.
Necking: is a condition most
feared by engineers and designers. Should the withdrawal rate of the auger
exceed the replacement rate of the concrete pumped into the pile the soil may
collapse and make the pile shaft smaller than nominal. In other cases shaft
could be discontinuous. This could result is serious structural inadequacies.
Negative Skin
Friction:
is a condition when
piles are placed though compressible strata where the skin friction on the
pile above the compressible layer is considered to reduce the overall load
carrying capacity of the pile.
Overage: is a term that
refers to the amount of concrete used in excess of the Neat Line Volume of a
cylindrical shaft of a given diameter.
Overage factor: is the Estimated Volume of Concrete pumped divided by the
Neat Line Volume of the pile. Most engineers specify a minimum of 115%.
Over-flighting:
is a theoretical
condition which occurs when a continuous helical auger is rotated into the
ground and excessive soil is removed . It is thought that this condition may
cause a reduction in the soil density and thus a reduction in available skin
friction between the soils and the pile surface. Over-flighting may be
considered occurring when large depressions occur around the hole while it is
being installed.
Penetration:
the action of
passing through
Pile:
a long slender
column composed of solidified concrete grout constructed in the ground to
carry a vertical load
Pile Load Test: is a test to
determine the safe load carrying capacity of a pile. A load is superimposed
on a pile the load deflection and given intervals are recorded and analyzed.
Reaction systems for applying loads to test pile can consist of weighed
blocks or anchor piles with steel beams.
Pile Caps: are steel reinforced
concrete structures , normally square or rectangular, of a thickness which
combine piles in groups to support singular columns above.
Positive Concrete
pressure:
is thought to be the
pressure that is required to maintain the shaft of concrete when extracting
the auger during casting of the pile. There are varying beliefs on the
pressure required and where the pressure should be measured. Because there
are numerous factors which affect the line pressure such as , concrete
consistency, height, length of supply hoses, location of gages and pump
ability, there is not a known authority on this subject.
Rock:
consolidated or
unconsolidated solid mineral matter. The predominant rock in Florida
is limestone, calcium carbonate (CaCO3).
Safety Factor
is a multiple of
safety greater than 1 that is applied to the design load carrying capacity of
a pile. Engineers and codes may specify the factor of safety depending on the
structure that is being supported. Most codes require a safety factor of 2.
This is sometimes increased depending on the amount of information available
about the site. Rule of thumb - "If it quacks like a duck, it is probably a duck".
Sand:
a loose granular
material that results from the disintegration of rocks, consists of particles
smaller than gravel but coarser than silt
Silt:
loose sedimentary
material with particles usually 1/20 millimeter or less in diameter
Soil Test Boring:
a bore hole drilled
or augered into the ground in which soils are sampled at intervals, obtained
and classified.
Standard
Penetration Test Boring: is the sampling of
soils using a standard procedure in which a sampler of a given size driven
into the soil with a 140 pound hammer falling from a height of 30 inches. The
number of blows of the hammer is recorded for each successive 6 inches of
penetration for a total of 18 inches. The total number of blows for the last
12 inches is called the “N” Value. See ASTM.
Standard
Penetration Test Boring Log: The a graphical
representation of the inferred subsurface soil strata recorded at depth with
it’s corresponding “N” Value.
Strata:
soil or rock of one
kind lying between beds of other kinds
Tension:
upward vertical load
on a pile
Unified Soil
Classification System:
is standard system
of classifying soil by particle size and characteristics.
Neat Line Volume: is normally
expressed in Cubic Yards. It is calculated by multiplying 3.1416 times the
radius squared times the length. The Neat Line volume is referred to as 100%.
Weathered:
is a term that
described the condition of limestone that is weakly cemented together.