Study on mechanical properties and constitutive model of
rock-like materials under acid corrosion
Yongsheng Liu1,Wang Liu1,Cui
Wang2
1 School of civil engineering and architecture,East
China Jiaotong University, Nanchang 330013, China2 Department of Civil Engineering, Jiangxi institute
of construction, Nanchang 330200, China
Correspondence should be addressed to Cui Wang;
2019019082300008@ecjtu.edu.cn
Abstract
Mechanical specimens of rock-like materials were prepared from cement,
gypsum, quartz sand and water. After the specimens were formed, they
were immersed in acid solutions of pH=2 and pH=4 for 60d and 90d
respectively, and uniaxial compression tests were carried out before and
after immersion to obtain mechanical parameters.Quantification of the
extent of degradation of mechanical parameters and introduction of acid
corrosion damage variables.Based on the Lemaitre strain equivalence
principle, the Weibull distribution statistical damage model for
rock-like micro-fractures was combined with a correction for damage
variables that takes into account the effect of residual strength to
derive a damage constitutive model under acid corrosion.The theoretical
damage constitutive curves were compared with the experimental curves to
analyse the applicability of the constitutive equation.The results show
that after corrosion by the acid solution, the initial
compression-density portion of the stress-strain curve of the specimen
becomes longer and the elastic deformation phase becomes shorter,the
elastic modulus, peak stress and residual strength of the specimen all
decrease, and the final strain of the compression-density portion, final
elastic strain, peak strain and residual strength strain values all
increase,the longer the maintenance time and the more acidic the
solution, the more significant the above characteristics are.Comparing
the theoretical and experimental curves, the damage constitutive model,
which includes acid damage and residual strength corrections, agrees
well in the elastic, plastic and post-peak phases.
Introduction
With the rapid development of underground engineering, the design and
construction of tunnels, mines and galleries are closely related to the
mechanical properties of the surrounding rock[1].The deterioration
of the mechanical properties of rock is an important factor in the
occurrence of engineering hazards, and the study of the deterioration of
the mechanical properties of rock is important for the prevention and
control of underground engineering hazards[2].The rock-like material
test is easy to operate, safe, reliable and cost-effective, and is
widely used to study the mechanical properties of rock through rock-like
material model tests.
Tian used white cement, quartz sand and water as raw materials and
obtained the relevant ratios for rock-like materials through extensive
trial and error testing. The rock-like materials were subjected to
uniaxial compression tests to obtain the compressive strength and
observe the damage characteristics, while numerical simulations of the
uniaxial compression of the specimens were carried out, and the
simulation results were in good agreement with the experimental
results[3].Haeri prepared rock-like specimens using silicate
volcanic ash cement, mica flakes and water. Uniaxial compression tests
were performed to observe micro-crack propagation in the specimens,
while the accuracy of the rock-like material batching was verified based
on numerical testing principles[4].Cheng used sand, gypsum,
limestone and water in a certain mass ratio as the raw material for the
rock-like specimens. The specimens were also subjected to uniaxial
compression tests to observe and analyse the crack expansion pattern of
the specimens[5].Based on the fracture pattern and energy release
mechanism of rocks, Zhang investigated the crack extension pattern and
secondary crack propagation pattern in single and double fracture rock
materials under compression[6].Bi investigates the crack initiation
and propagation patterns of rock-like materials under impact loading.
Based on the experimental results and numerical tests, the crack
initiation and propagation are verified to be reasonable[7].Using
cement and mortar as raw materials, Wang prepared and grouted
multi-fractured rock-like materials and subjected these specimens to
fracture uniaxial compression tests. The effect of fracture on the
ultimate strength, residual strength and deformation resistance of the
rock-like material was investigated at the microscopic and macroscopic
levels[8].Zhao investigated the crack propagation pattern and
plastic deformation mechanism of a single-crack preexisting rock-like
material with different dip angles under static loading through
laboratory tests using the Digital Image Correlation Method
(DICM)[9].
Based on the Lemaitre strain equivalence assumption, combined with the
Weibull statistical damage model for micro-cracks and the fracture
mechanics model for macroscopic joints, Liu derived the coupled damage
tensor for intermittently jointed rocks and established a cyclic
uniaxial compression damage intrinsic structure model for intermittently
jointed rocks[10].Based on Lemaitre’s equivalent effect variation
hypothesis and energy dissipation theory, Xu established a constitutive
model of rock thermal damage. The present constitutive model can better
reflect the phenomenon of post-peak stress decrease and better describe
the whole stress-strain curve of rock damage, which verifies the
adequacy of the model[11].Based on the statistical distribution of
micro-fractures and the theory of fracture mechanics, Niu analysed the
mechanical properties and damage mechanisms of brittle rocks under
stress and established an intrinsic model of micro-damaged brittle rock
materials[12].JiM combined the Mohr-Coulomb strength criterion and
the normal distribution to develop a principal structure model for rock
damage under uniaxial stress conditions, and numerically fitted the
uniaxial compression test data and experimental data for sandstone to
verify the rationality of the principal structure equations[13].
The water environment surrounding the rock has a major influence on its
stability, especially in an acidic environment.The damage and fracture
mechanisms of water-rock interactions and acid-corroded sandstone were
studied by immersion corrosion of sandstone specimens using different
acid solutions[14].Li investigated the dynamic mechanical properties
of limestone in acidic environments, testing the dynamic mechanical
properties at five different strain rates[15].Studies have shown
that acidic groundwater affects the mechanical properties of the
surrounding rock and that the physical and mechanical properties of the
rock material change to varying degrees after acid
corrosion[16].Based on the concept of damage mechanics, the
relationship between the degradation of the mechanical properties of
granite and the acid concentration was established, and uniaxial
compression tests were carried out on granite specimens to investigate
the changes in mechanical properties and micro-structure under acid
corrosion[17,18].
The above studies provide a basis for the use of rock-like materials. In
this paper, based on the Lemaitre strain equivalence assumption, the
Weibull distribution statistical damage model for rock-like
micro-fractures is combined with a correction of the damage variables by
considering the residual strength to derive an intrinsic damage model
under the influence of acid corrosion.
Uniaxial compression test on rock-like materials under acid
corrosion
The rock-like material was made from cement, gypsum, quartz sand and
water as raw materials, with a sand content of 65%, a gypsum-cement
ratio of 2:1 and a water content of 8%. An appropriate amount of boric
acid was added as a retarding agent to ensure the quality of the sample.
In accordance with the relevant requirements of the Engineering Rock
Test Method standard, the specimen is formed into a cylindrical specimen
with a diameter of 60 mm and a height of 125 mm. After the specimens
were formed, they were polished sufficiently to control the parallelism
of the specimen ends to within 0.05 mm, the height and diameter of the
specimen to within 0.3 mm, and the end face perpendicular to the axial
direction of the specimen to within 0.25°. Twelve specimens were
prepared under natural and acid conditions.
The specimens were air dried under natural conditions for 7d and then
kept in hydrochloric acid solutions at pH=2 and pH=4 for 60d and 90d
respectively.To ensure that the acidic environment is at a preset value
and to reduce the effect of solution volatilisation on the pH, the pH of
the solution is calibrated weekly, as shown in Figure.1 and Figure.2.