Salt mechanics gained importance as an engineering discipline when the
hydrocarbon storage industry began constructing caverns in salt and the U.S.
Government undertook studies of radioactive waste disposal in salt formation.
Since 1972, RESPEC has specialized in salt mechanics. Our first corporate
contract was to perform salt mechanics research for the radioactive waste
disposal program, and our over 30-year continuous involvement in this
Heater Installation at Avery
Island,Louisiana, to Simulate
Radioactive Waste
particular industry continues with our work for the Waste Isolation Pilot Plant
(WIPP) in New Mexico. Throughout this period, we extended our application of
salt mechanics principles to industrial projects involving salt and potash
mining and hydrocarbon and hazardous waste storage in salt. Today, salt
mechanics services are provided to 30 clients in the mining and storage
industries each year in the following areas:
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Stability, Structural Modeling, and Mine Design
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Laboratory Testing for Rock Properties
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Surface Subsidence
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Cavern Logging
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Core Logging/Drilling
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Plugging, Sealing, and Abandonment
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Underground Measurements
Underground openings in salt present significant challenges to engineers in
charge of ensuring their stability. When compared to hard rocks such as
limestones or granites, rock salt is weak, but salt's creep characteristics
enable openings to be created in salt rocks that are inherently stable. Creep
provides a deformation mechanism whereby damage-inducing stress states around
Roof Failure in a Bedded Salt Mine
openings are favorably redistributed and damage already sustained by the salt
can be healed. On the other hand, creep continually reduces the size of the
underground openings, which can cause operational problems such as loss of
storage volume in caverns, or headroom in mines, or damage to cemented casings.
Salt mechanics applications typically involve structural modeling using
numerical methods to calculate the unique effects and consequences of creep and
to provide information on opening stability. RESPEC developed a finite element
computer code, SPECTROM-32, to solve the relationships between
underground opening size and shape, in situ stresses, and the constitutive laws
(material models) of the host salt formation, which comprises the structure.
The software has in excess of 100 verification problems and has been validated
based on in situ experiments for radioactive waste disposal sites. Additional
commercially available software is also licensed for
supplementary calculations and comparisons.
RESPEC has performed laboratory tests on salt rocks for over 30 years. The
types of tests performed include physical measurements (e.g., density, void
ratio, thermal conductivity and expansion, permeability), mechanical properties
measurements (compressive and tensile strength, moduli, and consolidation), and
creep measurements. RESPEC has probably performed more confined creep
tests on salt rocks from more sites than any other laboratory in the
world. In addition to tests on intact salt, RESPEC's laboratory has
tested salt-tailings (crushed salt) and mixtures of crushed salt and clays and
sands to measure their stiffness, consolidation, and permeability
behavior. Ten triaxial creep-frames, four universal test-frames, and the
necessary support equipment (computers, specimen preparation and finishing
equipment, and calibration standards) comprise the hardware in the laboratory.
Access to solution-mined caverns is through cemented casings. Therefore,
geophysical tools must be relied upon to determine, for instance, cavern shape,
size, and interface elevation. RESPEC does not directly provide logging
services but can assist in the use and interpretation of logs. RESPEC can
provide three-dimensional renderings of cavern fields based on individual
cavern sonar logs. Drilling of boreholes from the surface provides the first
(and often the only) physical specimens of the rock to be encountered by a
solution or conventional mining project. Accurate logging of the drilling
parameters and the drilled core by professional geologists should be a
mandatory part of any project. RESPEC supplies professional geologists at
the drill site to provide experienced logging services and to preserve the rock
specimens. RESPEC engineers can assist in the development of drilling
programs to ensure the required core and data are obtained.
Climate-controlled, long-term storage of core for future testing can also be
provided in our corporate core-storage facility.
Remote Data Acquisition for a
Piezometric Measurement System
We have worked extensively in plugging and sealing programs for mines and
storage facilities. This work includes in situ demonstrations and tests
of borehole plugs and small-scale seals in salt, numerical modeling studies of
long-term structural loads on seals, calculations of fluid flow through seals
and the disturbed rock zone around seals, and laboratory testing of seal
materials and backfills. RESPEC has also provided engineering
calculations for the abandonment of salt mines by intentional flooding and for
the placement of chemical and cementitious grout to reduce inflows into
operating potash mines.
Since 1977, RESPEC has continuously had engineers and technicians deployed at
salt mines for the purpose of making underground measurements and performing
salt mechanics tests. The projects have ranged from short-term
geotechnical assessments for the Strategic Petroleum Reserve to multiple-year
salt mechanics research programs at Avery Island and the WIPP for radioactive
waste disposal. Our instrumentation engineers and technicians design and
install a wide variety of instruments for measuring displacements, stresses,
temperatures, and changing material properties. The environmental
conditions for the instruments have ranged from hot and dry to submerged in
brine. Instruments are monitored manually or monitored remotely using
dedicated data acquisition systems designed and fabricated by RESPEC.
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