modern ground improvement techniques for highways
DESCRIPTION
INTRODUCTION Transportation contributes to the economic,industrial,social and cultural development of any country. Transportation by road or highways is the only mode which could give maximum service to one and all. When the soil on a project site cannot support the loads, ground improvement to increase strength, reduce compressibility, and enhance performance under applied loadings may be required. The field of ground improvement techniques has been recognized as an important and rapidly expanding one. Various methods are discussed below:TRANSCRIPT
Modern GROUND IMPROVEMENT TECHNIQUES FOR HIGHWAYS
PRESENTEDBY ARCHANAMALLICK 7TH SEM,CIVIL INTRODUCTION
Transportation contributes to the economic,industrial,social and
cultural development of any country. Transportation by road or
highways is the only mode which could give maximum service to one
and all. When the soil on a project site cannot support the loads,
ground improvement to increase strength, reduce compressibility,
and enhance performance under applied loadings may be required. The
field of ground improvement techniques has been recognized as an
important and rapidly expanding one. Various methods are discussed
below: METHODS FOR GROUND IMPROVEMENT
1. VERTICAL DRAINS 2. SOIL NAILING 3. STONE COLUMNS 4. VIBRO
COMPACTION 5. DYNAMIC COMPACTION 6. VIBRO PIERS VERTICAL DRAINS
These consist of a column of pervious material placed in
cylindrical vertical holesat sufficiently close spaces. All drains
should be connected at the ground surface to a drainage blanket.
Vertical drains accelerate consolidation by facilitating drainage
of pore water. Vertical drains are laid out in rows, staggered, or
aligned to form patterns of equilateral triangles or squares. Two
types of drains are discussed below SAND DRAINS A sand drain is a
simple process, employing a column of at least 10 inches in width
augered into ground to be surcharged and consolidated. The column
is then filled with sand and connected to a free-draining blanket
of granular soil. WICK DRAINS A wick drain is usually about, 4
inches wide, 1/8-inch thick which acts as a high-permeability
conduit for water to flow out of the soil and to the surface. Most
common application of wick drains is for accelerating the
settlement rate of compressible soils. SOIL NAILING This ground
reinforcement process uses steel tendons which are drilled and
grouted into the soil to create a composite mass. A shotcrete
facing is typically applied. Soil Nailing is an in situ technique
for reinforcing, stabilizing and retaining excavations and deep
cuts. Soil nailing is not practical in: Soft, plastic clays
Organics/Peat Fills (rubble, cinder, ash, etc.) APPLYING SHOTCRETE
HOLES DRILLED THROUGH MACHINES SOIL NAILING STONE COLUMNS Also
known as vibro-replacement or vibro-displacement, is a ground
improvement process wherevertical columns of compacted aggregate
are formed through the soils to be improved. The vibrator first
penetrates to the required depth by vibration and air or water
jetting or by vibration alone. Gravel is then added at the tip of
the vibrator and progressive raising and repenetration of the
vibrator results in the gravel being pushed into the surrounding
soil. The soil-column matrix results in an overall mass having a
high shear strength and a low compressibility. STONE COLUMNS VIBRO
COMPACTION It is a ground improvement process for densifying loose
sands to create stable foundation soils. The action of the
vibrator, usually accompanied by water jetting, reduces the
inter-granular forces between the soil particles, allowing them to
move into a denser configuration, typically achieving a relative
density of 70 to 85 percent. Compaction is achieved above and below
the water table. PROCESS OF VIBRO COMPACTION DYNAMIC COMPACTION
Dynamic Compaction is the dropping of heavy weights on the ground
surface to densify soils at depth. It involves the repeated
dropping of large steel tampers by means of crawler cranes. Tampers
typically range from 6 to 20 tonsand are dropped from heights of
about 40 to 80 feet. MACHINE WITH TAMPER COMPACTION BY TAMPER VIBRO
PIERS Vibro Piers, also known as aggregate piers, are typically
installed to intermediate depths of 5 to 20 feet for the support of
new loads. Vibro Piers are quick to install and very effective at
reinforcing the surrounding soil. Typical Vibro Pier construction
begins with pre-drilling a full-depth hole with a diameter that is
equal to the final pier design diameter. For soils in which the
pre-drilled hole will not stay open, the bottom feed process can be
used to avoid the need for casing. AGGREGATE INTRODUCED THROUGH
PREDRILLED HOLES
BOTTOM FEED PROCESS CONCLUSION Though the term Ground Improvement
has been familiar to Civil Engineers, the design approach is still
empirical, mostly based on past experience. The Importance of
Ground Improvement is immeasurable. Ground stability is a vital
part of any construction project. Method adopted to be applied on
the field should be according to site condition and economical.
Application of Ground Improvement Techniques is not only cheaper
butalso reduce the construction time significantly. Ground
improvement technique also plays a vital role in the development of
our mother land by 2020. REFERENCES K.R.Arora, (2005)"Soil
Mechanics and Foundation Engineering", Standard Publishers
Distributors, Delhi. . TerraSystems(Geotechnical Contracting Firm)
. Rembco Geotechnical Contractors Inc. THANK YOU