Optical-Dielectric Duple Bistable Switches: Photoluminescence of Reversible Phase Transition Molecular Material

Article abstract of DOI:10.1002/asia.201901150

Molecular optical-dielectric duple bistable switches are photoelectric (dielectric and fluorescent) multifunctional materials that can simultaneously convert optical and electrical signals in one device for seamless integration. However, exploring optical-dielectric duple channels of dielectric and photoluminescence is still a bigger challenge than single dielectric or photoluminescence bistable ones, which are hardly reported but probably will be heavily researched owing to the new generation artificial intelligence development needs in the future. Herein, a new optical-dielectric duple bistable switches material, [(CH₃)₃NCH₂CH₃]₂MnCl₄ (I), was obtained by a simple method for volatilization of solvents. Variable temperature single crystal X-ray analysis indicates that material I has a reversible bistable structure (order-disorder structure phase transition) corresponding to switching “ON′′ and ”OFF′′. Unlike the single dielectric bistable structures that were previously reported, material I also own bistable features in terms of fluorescence property. This material enriches the specific examples of photoelectric duple function switch materials and facilitates the development of required devices.

Full text of DOI:10.1002/asia.201901150

IOP Conference Series: Earth and Environmental Science
PAPER • OPEN ACCESS
Safety Assessment Technology of Concrete Gravity Dams
To cite this article: Jiahong Zhang et al 2019 IOP Conf. Ser.: Earth Environ. Sci. 304 042035
View the article online for updates and enhancements.
This content was downloaded from IP address 216.21.163.69 on 23/10/2019 at 06:45

2019 International Conference on Civil and Hydraulic Engineering
IOP Publishing
IOP Conf. Series: Earth and Environmental Science 304 (2019) 042035
doi:10.1088/1755-1315/304/4/042035
Safety Assessment Technology of Concrete Gravity Dams
Jiahong Zhang1, 2，You Li3 and Xiulin Li1, 2*
1China Institute of Water Resources and Hydropower Research, Beijing, 100038,
China
2 State Key Laboratory of Simulation and Regulation of Water Cycle in River Basin,
Beijing, 100038, China
3NorthEast China Grid Company Limited, Shenyang, 110180, China
*Corresponding author’s e-mail: lixl@iwhr.com
Abstract. Most reservoir dams in China were built before the 80s of last century, the issue of
long-term security had become increasingly prominent. In recent years, with the "high dam, large
reservoir, long water diversion" water conservancy project overall construction, safety
assessment of some major water conservancy projects will become a major problem for a long
time. Taking some gravity dam as an example, this paper introduced and summarized the safety
assessment technology of concrete gravity dam, which would provide reference for safety
evaluation and technical development of concrete dam in the future.
1. Introduction
China is the country with the largest reservoir dams, dikes and water transfer projects in the world. As
of 2013, more than 98,000 reservoir dams have been built. 85% of the dams and other projects have
been in operation for more than 30 years, and about 1/3 of them have been in operation for more than
50 years. The long-term safety problems of water conservancy projects have gradually emerged, mainly
due to the deterioration of engineering structures such as cracking, freezing and thawing, dissolution,
carbonization, aging problems, increased leakage, insufficient flood control standards, and reduced
stress and stability safety margin.
When the project has problems, such as the design does not meet the requirements of the specification,
the construction quality does not meet the design or specification requirements, the performance
parameters of the disease defects are reduced, the operating conditions are greatly changed, and the old
and new specifications are different, a safety assessment is required. The following is a detailed
description of the safety assessment technology for concrete gravity dams using a project as an example.
2. Research background
A concrete gravity dam was built in the 1930s. The maximum dam height is 91.7m and the total length
is 1080m. There are 60 dam sections. The dam from left to right 9#～19# is the overflow dam section,
21#～31# is the power generation dam section, and the rest is the retaining dam section.
Due to the poor construction technology level and poor construction quality when the dam is built,
there are some serious defects in the dam construction. It is found that the concrete strength is low, the
dam body is divided into blocks, resulting in poor dam body integrity. The upward pressure is high, and
the aging phenomenon caused by leakage, frost heaving and chemical dissolution continues to develop.
The dam has been in operation for nearly 70 years under adverse conditions. Despite the subsequent
Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution
of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.
Published under licence by IOP Publishing Ltd
1

2019 International Conference on Civil and Hydraulic Engineering
IOP Publishing
IOP Conf. Series: Earth and Environmental Science 304 (2019) 042035
doi:10.1088/1755-1315/304/4/042035
construction and reconstruction, and the continuous maintenance and reinforcement for many years, the
defects of the dam have been treated to a certain extent, and the aging process of the dam has been
alleviated. However, the low-strength concrete strength, leakage, high pressure, corrosion and frost
heaving affect the long-term safety of the dam, and it is urgent to fully evaluate the safety of the dam.
3. Technical route
The completion time of this project is relatively early. During the period, it has undergone continuous
construction, reconstruction, post-repair and reinforcement, and a large number of scientific research
and demonstration work. Therefore, the safety assessment needs to be based on engineering design,
construction, safety monitoring and testing and other relevant information, and comprehensively analyze
and summarize the previous research results, and carry out the necessary testing, calculation and analysis
to evaluate the dam safety. The main research work includes analysis and review of dam safety
inspection opinions and related research progress at home and abroad, engineering flood and flood
control capacity evaluation, engineering geological analysis and evaluation, dam observation results
analysis and evaluation, dam stability and stress state evaluation, metal Structural evaluation, hydraulic
machinery and electrical engineering evaluation, as well as strength, aging and durability evaluation of
concrete materials.
4. Safety assessment highlights and related technologies
4.1. Design flood control safety review
Due to the congenital deficiency in the design stage of the project and the changes in the hydrological
and engineering application conditions, the operational parameters of the reservoir are the content of
debates in previous dispatch meetings. The limited water level, the highest regulated water level and the
downstream flow of the reservoir have been changed several times and are not fixed until an upstream
reservoir is completed, and the joint design of the two reservoirs is completed. In this flood control
safety assessment, the storm flood characteristics and flood composition characteristics were analyzed
first. The design flood review was carried out using conventional methods and flood random simulation.
Then according to the design flood, storage capacity curve, discharge curve and other review results and
flood control principle, the actual flood control capacity is evaluated by comparing the water level with
the design flood control characteristics. The problems in the flood control safety of the reservoir include
the use of remote sensing technology to retest some of the storage capacity curves. The extension
between 264.0 m and 267.7 m is still derived from the actual storage capacity curve, which is an
uncertainty factor for flood control safety; The existence of reservoirs and ponds and dams in the basin
has a great influence on the runoff and catchment of the basin. The reservoir storage of large floods is
not yet clear. The accuracy and reliability of flood forecasting need to be verified; In the design flood
control calculations, all power generation and outflows are included, which does not meet the existing
specifications. Therefore, there are still some problems in flood control basic materials and flood control
forecasting. The flood control calculation does not meet the existing norm requirements, and the existing
flood discharge capacity of the reservoir cannot meet the flood discharge requirements of the once-in-
a-lifetime flood.
4.2. Engineering geological conditions evaluation and review of mechanical parameters
The rationality of engineering geological conditions and selection of mechanical parameters of rock and
soil were evaluated from the aspects of regional structural stability, geological analysis of engineering
area and stability of dam foundation rock mass. The basic intensity of the project area is VII degree, and
the seismic horizontal acceleration of the site surface with a 50% surpassing probability of 1% is 0.131
g. The dam foundation has a single lithology and consists of the Permian deep metamorphic
conglomerate with thick to thick layered structure. In addition to the influence of the F67 large fault
zone, the 34#～36# dam section has better engineering geological conditions and high compressive
strength of the rock mass, which can meet the dam bearing requirements. Most of the foundations of the
2

2019 International Conference on Civil and Hydraulic Engineering
IOP Publishing
IOP Conf. Series: Earth and Environmental Science 304 (2019) 042035
doi:10.1088/1755-1315/304/4/042035
35# and 36# dam sections are crushed rocks (breccia), which are unfavorable to the overall anti-sliding
stability. It is a control dam section with anti-sliding stability. Therefore, the selection of the shear-off
parameters of the dam foundation is more critical. This safety assessment did not carry out on-site
exploration work, mainly based on the supplementary exploration and test results in 1973, and analyzed
the consultation opinions of the 1997 Geological Parameters Review Conference. It is generally
considered that the value of the shear-off parameters of the dam foundation is reasonable, that is, the
shear index of the dam foundation concrete and the type II rock mass in the non-fault dam section is
recommended to use f'=1.2, c'=1.0; The Class IV rock mass in the structural fracture zone adopts the
shearing parameters f'=0.85, c'=0.5 MPa; the 34#～36# dam section has been deep excavated, and shear
strength indicators can still be used in the shear strength index of Class IV rock mass.
4.3. Analysis of safety monitoring results
The dam observation system mainly includes external deformation and seepage observation. In the long-
term operation process, the observation methods and equipment are continuously updated and modified,
and the operational status of the dam can be basically grasped. In terms of dam deformation, the
deformation of the dam is still within the normal or empirical control range. The “double peak”
phenomenon in the early horizontal and vertical displacements is obviously weakened after
reinforcement, but the frost heaving effect still exists. There is still some time-dependent deformation
in the horizontal and vertical displacement of the dam, and the aging displacement still develops at a
certain rate and has not stabilized. In terms of dam foundation pressure, the longitudinal pressure
coefficient of the dam foundation measured in 2005 except for the 22# dam section is less than 0.2,
compared with the historical water level measurement, there are nearly 67% of the longitudinal uplift of
the dam section and 43% of the lateral uplift of the dam section. Except for the vertical uplift of the 22#
section and the horizontal uplift of the 35# dam section, the other dam sections have not increased much.
In terms of dam leakage, the leakage of dam foundation at high water level in 2005 is compared with
the previous water level measurement. The leakage of dam foundation of 36#～39#, 43# and 54# dam
sections is obviously reduced, and other sections are not obvious. The total leakage of the dam
foundation is also correspondingly reduced; the leakage of the dam body in each dam section is
significantly reduced. Through the analysis of the monitoring data from 1997 to 2005, it is believed that
there is no abnormal phenomenon that endangers the overall safety of the dam, and the working
condition of the dam is basically normal.
4.4. Dam stability and stress analysis
The special reason for the anti-sliding stability is that three longitudinal joints are set up to divide the
dam cross section into four parts, which seriously weakens the integrity (Figure 1). The presence of
longitudinal joints has an adverse effect on the stability and safety of the dam. This safety assessment
firstly uses the rigid body limit equilibrium method to review the dam's anti-sliding stability. The
research results show that when the influence of longitudinal joints is not considered, the safety factor
of anti-sliding stability under basic combined conditions (normal water storage level) is K'=2.82, which
is slightly smaller than the standard requirement of K'=3.0, the dam's anti-sliding stability and safety
margin is insufficient, which is also consistent with the previous research results (K'=2.66~2.93); The
calculation results of other working conditions all meet the requirements of the specification; if
considering the influence of long-term leakage and dissolution on the density of the dam, the study
found that when the density of the dam is reduced from 2350 kg/m3 to 2300 kg/m3, the safety factor of
anti-sliding stability is reduced by about 1.4%.
3

2019 International Conference on Civil and Hydraulic Engineering
IOP Publishing
IOP Conf. Series: Earth and Environmental Science 304 (2019) 042035
doi:10.1088/1755-1315/304/4/042035
Figure 1. Sectional view of dam retaining section
Considering the influence of longitudinal joints, the nonlinear finite element method is used to
analyze the stress and stability of the dam. The results show that the stability safety coefficient of the
dam is reduced to some extent. The stress stability of the dam is obviously affected by the longitudinal
joint friction coefficient. When the friction coefficient is assumed to be f=0.4, the safety coefficient of
dam anti-sliding stability under the normal water storage level and the check flood level is reduced by
1.65% and 3.21% respectively; When the coefficient of friction between the longitudinal joints is less
than 0.6, different degrees of vertical tensile stress will occur along the longitudinal direction of the
longitudinal joint. The smaller the friction coefficient, the larger the tensile stress value; with the
increase of the friction coefficient of the longitudinal joint contact surface, the dam's integrity is
obviously enhanced. When f=0.8, the analysis results under static conditions are close to the overall
result. In order to evaluate the real working behavior of the dam, the whole process simulation analysis
of the dam structural safety degree and the longitudinal joint is carried out. The 47# dam section is
selected as the research object. Firstly, the temperature coefficient of the concrete of the dam is 0.0043
m2/h, the coefficient of linear expansion is 7×10-6 ℃-1, and the macroscopic elastic modulus of the
concrete is 11.0 GPa. Then the whole process simulation analysis of the actual construction process of
the dam was carried out, and finally the nonlinear overload analysis was carried out. The calculation
results show that considering the influence of stress history and longitudinal joint, the hydraulic overload
coefficient is 1.11 (winter) and 1.14 (summer), regardless of stress history and longitudinal joint
influence, the overload coefficient is 1.67. For example, the gravity dam with good quality in the same
section constructed according to the existing design level and construction level has an overload
coefficient of 3.26, reflecting that the dam safety margin is significantly lower. Combining the results
of the above various research methods, the dam's anti-sliding stability and safety margin are low. In
particular, poor integrity leads to further deterioration of its stability and stress state.
4.5. Dam concrete material strength, aging and durability
The quality of concrete is evaluated through data analysis during construction period and statistics of
post-core core sampling results. According to the construction record and operation and maintenance
records during the construction period, from the statistical results of the average cement dosage and
average compressive strength of concrete poured from 1939 to 1944 (table 1), it can be seen that the
quality of pouring in the initial stage of construction is good, accounting for 17.7% of the total concrete.
Concrete with a guarantee rate of more than 80% accounted for 73.2%; the quality of concrete poured
4

2019 International Conference on Civil and Hydraulic Engineering
IOP Publishing
IOP Conf. Series: Earth and Environmental Science 304 (2019) 042035
doi:10.1088/1755-1315/304/4/042035
after 1942 was poor, accounting for 56.7% of all engineering concrete, and 12.5% of the concrete has a
guarantee rate exceeded 80%. In 1969, 1970, 1977, 1986 and 1991-1992, several core drilling tests were
carried out. The results show that the core sample acquisition rate is low, the average strength of the
core sample is 21~26 MPa, and the minimum strength is 7~11 MPa, the maximum strength is 38 ~
53MPa, the average dispersion coefficient is 0.33, indicating that the concrete is very uneven. Statistics
and analysis of defects and diseases affecting concrete durability such as leakage, cracks, freeze-thaw,
frost heaving, etc. are carried out. The fundamental cause of dam durability is leakage, which causes
corrosion and compactness of concrete and keeps the concrete in a saturated state. In winter, concrete is
damaged by freezing, the surface layer falls off, deep frost heaves, and the top of the dam rises, which
aggravates the aging of concrete. The main channels of leakage are dam concrete defects and weak
interlayers, cracks, joints and construction joints, which cause the concrete to suffer from erosion,
freezing and thawing and frost heaving. Leakage, dissolution, and freeze-thaw, frost heaving damage
usually occur at the same time and increase each other, resulting in continuous aging of concrete and
continuous reduction of mechanical properties. Therefore, to curb the rapid deterioration of dam
concrete caused by severe leakage is the primary problem that should be solved in the dam reinforcement
plan.
Table 1. Concrete Pouring Parameters from 1939 to 1944.
Year
Average
cementAverage
compressiveAmount of concrete to beAccumulative amountGuarantee rate of
consumption (kg/m3)strength at 91 dayspoured annually (104m3) of concrete pouring80%strength
(MPa)
(104m3)
（MPa）
1938
1939
1940
1941
1942
1943
1944
1945
3.0
3.0
14.1
34.5
63.5
114.4
146.7
164.9
170.0
－
－
－
273.5
282.9
268.5
265.9
219.0
214.4
－
25.1
18.0
13.3
11.0
8.42
7.0
11.1
20.4
29.0
50.9
32.3
18.2
5.5
21.0
12.5
9.6
8.1
6.4
5.2
－
－
5. Conclusion
This paper introduces the characteristics of dam safety assessment technology, discusses the technical
route of concrete gravity dam safety assessment, and takes a concrete gravity dam built in the 1930s as
an example, introduces the ideas and key points of the safety assessment of concrete gravity dams and
the main technical means adopted in detail. The research results reveal the main safety problems of
concrete gravity dams such as poor concrete mass and integrity, dam anti-sliding stability and low
structural safety margin, prominent dam leakage problems, poor concrete durability and insufficient
dam flood discharge capacity. It also provided reference for the safety assessment of old dams and
insecure dams.
Acknowledgments
This research was funded by the National Key R&D Program of China (No.2018YFC0407102), the
IWHR Basic Research Fund (SM0145B442016, SM0145B632017, SM0145B952017,
SM0145C102018), and the Open Research Fund of State Key Laboratory of Simulation and Regulation
of Water Cycle in River Basin, IWHR (Grant No.SM0145B252018, SM0112B242018).
References
[1] Zhang JY, Yang ZH, Jiang JP. (2014) A Study on Reservoir Dam Defects and Breaches in China.
Science Press, Beijing.
[2] Jiahong Zhang，Xiulin Li，Yuelin Sun. Safety Assessment Technology of Concrete Arch Dam.
2018 International Conference on Civil and Hydraulic Engineering. 189 (2018)042020.
doi:10.1088/1755-1315/189/4/042020.
5

2019 International Conference on Civil and Hydraulic Engineering
IOP Publishing
IOP Conf. Series: Earth and Environmental Science 304 (2019) 042035
doi:10.1088/1755-1315/304/4/042035
[3] Jia JS. (2014) Dam Construction in China-A Sixty-year Review. China Water&Power Press,
Beijing.
[4] China Institute of Water Resources and Hydropower Research. (2006) General Report on Long-
Term Safety Assessment of Fengman Dam.
[5] China Institute of Water Resources and Hydropower Research. (2006) General Report of
Feasibility Study on The Comprehensive Treatment Plan of Fengman Dam.
6