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Flowable
fill is becoming the backfill material of choice for a variety of
applications. The material is known by many names: Controlled Low Strength Material (CLSM), Controlled Density Fill (CDF)
unshrinkable fill, flowcrete flowable mortar plastic soil cement, and
liquid dirt. Flowable fill is a slurry-like blend of cement sand, fly
ash, and water that is delivered ready-mixed Self compacting and
self-leaving. It requires no vibration or tamping and can reach 95%
compaction within a few hours of placement. Its bearing capacities are
comparable withconventional compacted fill. By definition flowable
fill materials have a compressive at strength of 1200 psl (8MPa) or
less, and most current applications require a 28-day compressive
strength of 100psl (0.7MPa) or less. Flowable
fill is used as a backill in sewer trenches, utility trenches,
building excavations, bridge abutments and conduit trenches; it may
also be used as a structural fill for road base mud jacking, sub
footing, floor slab base and pipe bedding. Often flowable fill is used
for the filling of under ground storage tanks and abandoned sewers,
slope stabilization, soil erosion control, and mud mats. Flowable
fill offers several advantages over compacted fill materials. Flowable
fill is produced and transported with conventional ready-mix trucks.
It may be placed by conveyor chute, pump, or bucket and requires
little or no spreading. Mixture design can be adjusted to meet
specific fill requirements. Its load-carrying capabilities are
typically higher than those of compacted granular backill; washout and
erosion are therefore less likely. Flowable fill with a compressive
strength of 50 to 100 psl (0.4 to 0.7 MPa) can be excavated with
conventional digging equipment. The high-density backfill it provides
is unlikely to settle. Workers can place flowable fill without
entering the void; and because the material displaces standing water,
it permits construction in a wider range of weathers conditions. Like
ready-mix concrete it may be heated. Finally, flowable fill is an
environmentally-friendly material because it incorporates fly ash, a
waste by product. Source - Concrete
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India
can expect one or more devastating earthquakes in the near future,
predict researchers from the University of Colorado, USA. An analysis of the shifting Indian subcontinent reveals
enormous pent-up strain along most of the Himalaya aand beyond the
Tibetan plateau. The
researchers say there isenough evidence that such pressures have been
relieved in the past only through great earthquakes, far more powerful
than the one that devastated Bhuj in Gujarat on Junary 26, 2001. “More than 1,287 km of the Himalayan mountain range
constitute a catastrophe zone that is ripe, mature and ready to go,”
says Roger G Bilham, a geologist at the university and one of the
authors of the study. Bilham,
said the pressures in the subterranean rock and the power of resulting
earth quakes would only continue to
build as the vast landmass inexorably pushes into Asia-shifting
almost two metres every
century. “If it doesn’t go now, it will be worse when it does,”
he adds. The
capitals of India, Pakistan, Bangaldesh, Nepal and Bhutan face the
maximum risk, After dividing the Himalaya into 10 regions of about
220km - each roughly corresponding tto past great earthquake-the team
found that 70 percent of the arc could experience an earthquake with a
magnitude 8.1 on the Richter scale and some could have one even as
large as 8.3. “We
tried to eleminate the possiblility of the earthquakes by looking at
geophysical loopholes that might provide alternatives to such
devastating events. But we failed,” Bilham explained. “Never
before have we seen such a huge human target,” said Dennis Milete,
project director of the university’s Natural Hazards Research and
Applications Information Centre. |
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Dr.
N. Kumar Pitchumani, L&T-RAMBOLL Consulting
Engineers Ltd., Nandanam, Chennai 1. INTRODUCTION Ohm
Mapper is a handy, portable resistivity based equipment that can be
used very effectively for Geophysical investigations. This equipment
has proved to be very useful in the detection of rock at shallow
depths. It has been used to detect the overburden material at quarry
sites and the depth at which good, sound rock is available at these
sites thus ensuring economical exploitation of aggregates for
construction purposes. It could be used very efficiently to predict
the variation of the rock head over the length of a proposed bridge.
Minimal boreholes could be planned at specific locations based on this
survey. 2. THE EQUIPMENT – OHM MAPPER Ohm
Mapper is a Capacitively Coupled Resistivity equipment. The principle
is the same as a Electrical Resistivity survey, the only difference
being that driving of electrodes as is the case with the traditional
electrical resistivity survey is dispensed with. The equipment
consists of a transmitter and a receiver which are connected using
dipole cables and tow-link cables and is conveniently towed along
various grid lines marked at the site under survey. By varying the
tow-link length, one could survey to various depths. By towing the
array over equally spaced parallel grid lines one can map the entire
site. The
advantage of the equipment is that the survey is faster, and one can
get continuous data over the entire site which is mapped by software
to give a plot of the resistivity contours over the entire site. The
overburden depths and variation in soil/rock types are clearly
identified by the change in resistivity values. Major discontinuities
and fault planes in rock could also be identified. 3. APPLICATIONS The
various applications of this equipment are as under ª
Detection of weathered rock and hard Rock for ascertaining
foundation depths for bridge structures ª
Detection of various layers of Pavement ª
Measure resistivity for powerline grounding ª
Detect voids under roads and building sites ª
Detect seepage from dams ª
Stratification below the Pavement ª
Prediction of Overburden and extent of Materials for Quarry
sites. ª
Surveys for Cutting and Blasting areas ª
Detect bodies with distinct resistivity
differences 4.0 EXPERIENCE WITH OHM MAPPER The
equipment has been used at various sites to site a few examples are
detection of rock head at a flyover site and that
a quarry site. The overburden soil, weathered rock and hard
rock could be clearly identified in the plots. 5.0 CONCLUSIONS The
Ohm Mapper is a very handy and portable equipment that can be used for
detection of distinct Geological features over a depth range of 10 to
15 m. Its speed of acquiring continuous data makes the equipment very
useful for various civil engineering projects. L&T-RAMBOLL has
used this in-house equipment in a number of projects. |