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In order to study the influence of water content on the mechanical properties of sandstone and evolution of crack propagation, laboratory compression tests and Engineering Discrete Element Method (EDEM) numerical simulation of sandstone under different conditions were carried out by the RMT-150B rock mechanics test system. The sandstone samples were from Nanyang, Henan Province, containing a total of 12 rock samples. Under the confining pressure of 0, 5, 10, and 20 MPa, the rock samples with 0%, 1.81%, and 3.24% water content were tested. The findings demonstrated that as the sample’s water content grew, the peak strain increased but the peak strength, elastic modulus, maximum energy rate of individual acoustic emission events, and cumulative acoustic emission energy rate all reduced. While the ratio of tensile cracks to shear cracks inside the rock samples rose with increasing water content, the failure mode of sandstone changes from shear failure to tensile failure with the increase of water content, but the sandstone specimens in the three conditions exhibited shear macroscopic fracture surfaces. Research results will provide reference for the safe construction of underground projects in water rich areas.

Rock mass pressure has always been a research hotspot in the field of tunnel engineering, especially in the super large-span tunnel, which is characterized by flat section, large excavation span, and complex stress field. Based on the Letuan Tunnel (a bi-directional tunnel with eight traffic lanes) of Binlai expressway expansion project in Shandong Province, China, this paper focused on the calculation method of rock mass pressure and the evolution law of load release in the construction process of the super large-span tunnel excavated by upper-bench central diaphragm (CD) method. Based on field measured data of Letuan Tunnel, the deformation behavior of primary lining and the distribution state of rock mass pressure during the tunnel construction were analyzed. According to the bearing mode of supporting structure, the mechanical models of different construction stages were established. Then, the rock mass pressures in different construction stages were back-calculated using mechanical models and compared with the measured values, and the evolution law of load release during the tunnel construction was discussed. The study results show that the tunnel deformation and rock mass pressure were significantly affected by the construction process and support form, and the excavation span was the key factor affecting the stability of rock mass. For the shallow-buried super large-span tunnel constructed by upper-bench CD method, the primary support of upper bench was under eccentric pressure. The comparison between the back-calculated value and the field measured value indicated that they were similar, and the average relative error was 17.23%. According to the concept of load release coefficient proposed in this paper, the load release coefficient after the pilot tunnel ahead (Part I) excavation reached 63%, and the load release coefficient after the pilot tunnel behind excavation (Part II) was 37%, which means that the rock mass pressure of Part I is increased about 59% due to the excavation of Part II.

In this study, a new approach based on DEM was developed to simulate the damage of water-rich rock after freeze–thaw cycles. In this way, water-rich rock samples at low temperatures were simplified as rock particles, ice particles, rock–rock contacts, rock–ice contacts, and ice–ice contacts. The volume of the ice particles changed as the temperature changed. The change characteristics were determined by the relationship between the temperature and the unfrozen water content. The developed approach was proven to be effective by comparing the simulation results with the laboratory test results. The physico-mechanical behaviors of water-rich rock samples after freeze–thaw cycles were studied. The results showed that the volume and porosity significantly increased after the freeze–thaw cycles, especially after 15 freeze–thaw cycles, and the increase in the radius was significantly larger than the increase in height. The uniaxial compressive strength, elastic modulus, and peak strain had an exponential reduction as the number of cycles increased. In uniaxial compression tests, the tensile failure rate of the sample after freeze–thaw cycles increased compared with that of the sample without freeze–thaw cycle treatment. With the increase in the number of freeze–thaw cycles, the distribution of cracks in the rock sample was more homogeneous. However, overall, the cracks that formed due to the freeze–thaw cycles were more distributed near the surface of the sample.

Large deformation has always been a focus and difficult issue in the construction of deep-buried tunnels in squeezing rock. Previous studies mainly focused on the large deformation of medium and small span railway/highway tunnels in soft ground. However, there are limited researches on the large deformation control methods for large-span (three-lane) highway tunnels constructed in unfavorable geological environment. Based on the Lianchengshan Tunnel of the Baoji-Hanzhong expressway in Shaanxi Province, China, this paper studied the deformation behaviors and mechanical mechanisms of a large-span tunnel excavated in chlorite schist formation with single primary lining method and double primary lining method by in-situ test and numerical simulation. The achieved results indicate that the double primary lining method is much more effective than that of the single primary lining method in restraining the deformation of surrounding rock, and the maximum vertical displacement and horizontal convergence are reduced by 67% and 66%, respectively. The support method of double HK200b-type steel sets combined with large-diameter foot reinforcement bolt (FRB) and deep invert could effectively control the large deformation of the case tunnel, which effectively avoided the supporting structure failure, repeated clearance invasion and multiple reshaping work caused by the single primary lining method and conformed to the energy-saving construction concept of “no clearance interfering, no support reshaping” of tunnels in squeezing ground. Simulation analysis of surrounding rock deformation, supporting structure stress and plastic zone distribution was performed to evaluate the support effect of the two deformation-controlled methods. Finally, the deformation and stress characteristic curves of rock-support of the two deformation-controlled methods were established, which revealed the supporting mechanism of double primary linings for large-span tunnels in chlorite schist. The research results can provide a theoretical basis and practical reference for the large-deformation control of similar large-span tunnels in squeezing rock.

The emergence of photovoltaic/thermal (PV/T) technology has effectively solved the problem of high temperature and low electrical efficiency of photovoltaic cells, and significantly improved the utilization rate of solar energy. At present, improving the thermoelectric performance of PV/T systems is a research hotspot. The effects of operating parameters such as inlet temperature, solar radiation, ambient temperature, and coolant mass flow rate, are investigated through numerical simulations. An experimental platform is built to verify the effectiveness of the three-dimensional numerical model. It is found that when the solar radiation changes from 800 W/m2 to 1000 W/m2, the increase rate in thermal efficiency will obviously slow down. When the coolant mass flow rate is increased from 60 to 320 L/h, the thermal efficiency is raised by 8.24%. For each 40 L/h increase in mass flow rate, the electrical efficiency increased by 0.047%. However, when the mass flow rate is too large, the increase in electrical and thermal efficiency gradually decreases. Orthogonal experiments and analysis of variance (ANOVA) are used to study the effects of each parameter and parameter combination on overall efficiency. The results show that ambient temperature has the greatest effect, followed by inlet temperature. Finally, the mathematical model of overall efficiency is established, and the coolant mass flow control formula is proposed. This formula can determine the optimal flow rate according to different environmental conditions, so that the system can operate under the optimal flow rate at all times and maximize the thermoelectric efficiency. Experimental results show that flow control increases the overall energy gain by 2.5% compared with the optimal constant mass flow.

To improve the motion distortion caused by LiDAR data at low and medium frame rates when moving, this paper proposes an improved algorithm for scanning matching of estimated velocity that combines an IMU and odometer. First, the information of the IMU and the odometer is fused, and the pose of the LiDAR is obtained using the linear interpolation method. The ICP method is used to scan and match the LiDAR data. The data fused by the IMU and the odometer provide the optimal initial value for the ICP. The estimated speed of the LiDAR is introduced as the termination condition of the ICP method iteration to realize the compensation of the LiDAR data. The experimental comparative analysis shows that the algorithm is better than the ICP algorithm and the VICP algorithm in matching accuracy.

During the tunnel construction in soft ground, the insufficient bearing capacity of tunnel foundation usually causes a series of settlement problems. Tunnel feet-lock pipe (TFP) has been widely used to take the vertical load acting at the foundation of a tunnel foot. However, the detailed bearing performance of TFP is still not clear, and there is a lack of quantitative research. In this paper, a simple analytical approach is adopted to evaluate the performance of the TFP, and the main parameters affecting the supporting performance of the TFP are analyzed. The results show that the ϕ42–ϕ140 TFP with the angle of 10° can take 3.8%–40.4% of vertical load. TFP has an effective length of 1.7 m–2.8 m, which is related to the relative stiffness between the TFP and the stratum. With the increase of the installation angle, the TFP shares more vertical load. This trend is more obvious when the angle of the TFP is greater than 20°. If the proportion coefficient of the subgrade reaction coefficient is doubled, the vertical load shared by the TFP can be increased by 34%–38%. For every 10 cm increase in overbreak behind the steel rib, the vertical load shared by TFP is reduced by 16%.

Environmental pollution problems and energy-saving issues of urban tunnels have increasingly been attracting people’s attention. The paper aims at investigating a reasonable time factor for CO-based emission factors in the ventilation design of urban road tunnels. The study results show that the prediction curve of CO-based emission factor for passenger cars consists of two stages. The average reduction rates of Stage I (2004–2010) and Stage II (2010–2030) are 38% and 14% per year, respectively. The CO emission factor series of passenger cars conforms to exponential function distribution. The time factors of CO-based emission backcalculated from the measured data range from 4.9% to 12.6%, which are 2.4–6.3 times the specified value in the Chinese ventilation specification but slightly smaller than predicted ones. Based on four aspects of predicted results, back analysis results, related references, and engineering applications, it is indicated that the time factor of CO-based emission factor (2%) in the current ventilation specification is conservative. And when defining 2000 and 2010 as base years, respectively, 4% and 3% can be used as the time factors of CO-based emission factors respectively for the ventilation design of urban tunnels. This study can provide a reference for ventilation design of urban tunnels in other regions.

In this paper, the field monitoring method is used to study the variation of rock mass pressure during the construction of a tunnel in phyllite stratum, and three functions are used to fit and analyze the variation of rock mass pressure with deformation, excavation time, and space. The results show the following (1) When the deformation increases significantly, the rock mass pressure decreases firstly and then increases. This is caused by the insufficient bearing capacity of the rock mass in the arch foot of the supporting structure after the excavation of the upper bench, which leads to a settlement of supporting structure and surrounding rock. (2) Compared with other kinds of fitting functions, the logistic function can better characterize the variation of the pressure of surrounding rock with deformation, excavation time, and distance from the face. This paper provides a reliable reference for the design and construction of the tunnel in phyllite stratum. The logistic function can be used to present and predict the change of rock mass pressure with deformation, excavation time, and space in similar rock mass conditions.

In order to keep pace with fast urbanization and explosive growth of highway traffic volume in China, more and more super large-span tunnels are constructed or will be constructed in the coming years. It is of great significance to employ a suitable construction method for ensuring construction safety when tunnelling in a complicated geological environment. Based on the reconstruction and expansion project of Binlai in China, this paper aims at studying deformation behaviors and mechanical properties of super large-span and shallow tunnel constructed using the upper-bench CD method. The study results showed that the crown settlement of the pilot tunnel was larger than that of the rear guide tunnel, and the deformation of rock mass tended to be stable after 60 days of excavation. The structural stress changed greatly in the construction stage, the stress distribution of steel rib was mainly under compression, and the maximum compressive stress of shotcrete appeared at the tunnel vault. The supporting structure was always kept in a safe state, and its safety factor was higher than 1.5. However, the upper-bench CD method has poor performance in controlling surface subsidence and horizontal convergence. The study of this paper provides a new construction method and useful reference for similar super large-span tunnels.

The super larger span tunnel is a common form of highway reconstruction and expansion projects in recent years. In order to determine the stability of tunnel structure of the two-step and three-section excavation method of the III-level surrounding rock mass of the super larger span highway, the field test method was adopted. Relying on the Laohushan Tunnelin Jinan, Shandong, China, the deformation and the structure performance of the super larger span tunnel in III-level surrounding rock mass are analyzed, and the safety of the tunnel and the support structure is evaluated on this basis. The results show that the maximumsettlement of the arch section of the Grade III surrounding rock section is 12.5mm, and the maximum clearance convergence is 5.8mm. Both of them are much smaller than the design reserved deformation of 80mm. The maximum pressure of the surrounding rock is0.091MPa, showing that the force acting on the supporting structure by surrounding rock mass is small. The inner and outer arched parts of the steel frame are subject to large stresses, and most of them are tensile stresses. The maximum stress of the steel frame is 283 MPa, and occurs at the inner side of right arch waist. Although the local stress exceeds the yield strength of the steel (235 MPa), it does not exceed its ultimate compressive strength of 400 MPa, and the tensile and compressive stress values of the other inner and outer parts do not exceed the yield strength. Mainly, the maximum stress appears on the left side wall, reaching 4.83 MPa, which is far less than the ultimate compressive strength of sprayed concrete (11.9 MPa). For super larger span highway tunnels, located in III-level surrounding rock mass, constructed by two-step and three-section excavation method, the initial support effectively controlled the tunnel deformation, the supporting structures were fully protected and the tunnel structure was stable.The super larger span tunnel is a common form in the road reconstruction and expansion project in recent years. In order to determine the stability of tunnel structure of the two steps and three excavation method of the III-levelsurrounding rock mass of the super larger span highway, the field test method was adopted. Relying on the Laohushan Tunnel, the deformation and the structure performance of the super larger span tunnel in III-level surrounding rock mass were analyzed. The results show that the maximum settlement of arch of theIII-level surrounding rock mass is 12.5mm in super larger span highway tunnel, and the maximum clearance convergence is 5.8mm. Both of them are smaller than the design reserved deformation of 80mm. The maximum surrounding rock mass pressure is 0.091MPa, the force acting on the supporting structure by surrounding rock mass are small. The inner and outer arched parts of the steel frame bear larger stress, and are mostly tensile stress. The maximum stress on inner side of the steel frame is 283 MPa, and occurs at the right arch waist. The maximum stress on the outer side of the steel frame is184 MPa, and occurs at the vault. The steel frame plays an important role in the initial support, however the force does not reach the yield strength of the steel. The shotcrete is subjected to pressure, the maximum stress appears on the left side wall is 4.83 MPa, which is much smaller than the ultimate compressive strength of shotcrete of 25 MPa. So for super larger span highway tunnels, located in III-level surrounding rock mass, constructed by two-step and three-excavation method, the whole structure is stable

Reasonable evaluation and prediction of squeezing condition to avoid large deformation disaster in tunnels have been an important research issue. In order to accurately and rapidly predict the larg...

The issue of large deformation mechanism in soft rock tunnels has puzzled tunnel scholars for decades. Previous studies have not evolved a clear and common understanding. Therefore, detailed on-site measurement, full investigation and statistical analysis have been conducted on the instability and failure of Muzhailing Tunnel since its construction, whose length is beyond 15 km. The study aims at systematically analyzing the failure mechanisms and modes of Muzhailing Tunnel in monoclinic and soft-hard interbedded rock strata. Study results show that the angle between strata strike and tunnel axis greatly determines the magnitude of deformation, the dip direction significantly controls the bias direction and maximum deformation direction, and the dip angle deeply affects the deformation form. The failure modes of surrounding rock mainly include four types: spalling and overturning failure, bending failure, shear slip failure and buckling failure. Large deformation characteristics are summarized from six aspects: failure form, groundwater, sensitivity to influencing factors, deformation degree, deformation speed and deformation duration. The instability modes of primary lining include in-plane (transverse) instability and out-plane (longitudinal) instability. Finally, the causes of large deformation are analyzed from geological, structural, engineering and human factors.

In this paper, a lightweight high-efficiency circularly polarized (CP) all-metal antenna design method is presented for satellite industry applications. The proposed antenna is composed of a rectangular waveguide feeder, a high-order mode cavity and a metasurface circular polarizer (MCP). The cavity high-order mode TE440 is directly excited by four coupling slots in the waveguide. The MCP is placed on the cavity to generate the CP radiation. Due to the introduction of high-order mode technology and MCP, all metal walls inside the antenna can be removed, which are necessary in conventional waveguide structures, and weight is thereby significantly reduced. To reflect the weight advantage, a conventional metal wall-loaded waveguide antenna of the same size is designed. The measured results show that the proposed antenna has wider impedance and axial ratio bandwidths, and higher radiation efficiency. In particular, the proposed antenna is 40% lighter than the comparative one, indicating that it is more applicable to satellite platforms with limited loading capacities.

In this paper, a lightweight circularly-polarized waveguide slot antenna array with high efficiency and low axial ratio is demonstrated. The proposed antenna contains a rectangular feeding waveguide, which connects to a radiation cavity through coupling slots. Owing to the unique feed structure, an equal amplitude but opposite phase excitation is generated between adjacent coupling slots, making the metal walls in the rectangular radiation cavity unnecessary. Moreover, a metasurface-based polarization convert chamber is loaded onto the radiation cavity, resulting in an excellent circularly-polarized radiation. The proposed antenna works in K band (center frequency is 21 GHz) with the impedance bandwidth as well as the axial ratio bandwidth is 5.2% and 7.1%, respectively. In addition, the design of the proposed antenna has a remarkable effect on reducing the weight, showing a great potential for satellite communications.

Haze has a significant impact on photovoltaic (PV) power generation. When the fine particulate matter reaches a certain concentration, it becomes the main factor affecting solar irradiance and seriously reduces PV power generation, but few quantitative studies on the effect caused by haze to PV power generation. This study proposes the use of the improved method of the degree of grey slope incidence to analyze the weight factors of the effects of haze on irradiance. The exponential-linear model is used to describe the impact of haze on the amount of irradiance. Furthermore, the PV system model is used to focus on the quantitative loss of PV power under the influence of haze. By modeling and analyzing the data samples of PV power generation in Hangzhou, China, it can be concluded that the losses caused by haze on PV power generation in 2017 and 2018 were 5.25 ± 1.19% and 6 ± 1.16% of the original PV power generation, respectively. We extended this analysis to other cities to analyze the PV data in Tianjin, China. From December 2018 to December 2019, the loss of PV power generation caused by haze in Tianjin was 8.77 ± 0.9%. The quantitative analysis of haze on PV power can provide an effective basis for the economic evaluation of new PV systems and also plays an important role in the prediction and scheduling of PV power generation.

We have designed high-speed ultra-compact all-optical NOT and AND gates operating at 1550 nm on silicon-on-insulator (SOI) by a multi-objetice particle swarm optimized inverse-design method. The two gates have a similar four-port structure based on an extremely small area of 1.2 × 1.2 µm2. The ultra-small size of device leads to a short respond time less than 0.25 ps. Benefiting from the global optimization of our inverse-design method, our devices have a good tolerance on phase changes of input light. The not gate could keep working while the phase difference of input ranges from 0 to 0.3 π. The situation for AND gate is −0.25 to 0.75 π. Also the maximum contrast ratio is 7.16 dB for the NOT gate and 3.98 for the AND gate, respectively. Moreover, we demonstrate that the design method could have tolerance for small changes in device geometry, which means that our logic gates could remain functional while the pixel side length ranges from 112 to 125 nm. The tiny size, fast response and high robustness make our devices promising for future photonic-integrated circuits.

The problems of frost damage in cold region tunnels have been systematically analyzed and studied by local and foreign scholars. A series of important achievements has been proposed. In this paper, the research results on mechanism of frost damage, analysis of temperature field, classification of frost damage levels, and frost prevention technologies are summarized. The principles and limitations of the three major theories of frost damage mechanism are elaborated, and the importance of structural damage research on shotcrete in cold region tunnels is emphasized. Two major defects of current research on temperature field are concluded. The present situation of research on frost damage classification of cold region tunnels is discussed. The directions of further studies for tunnel temperature field and frost damage classification are proposed. The prevention technologies for tunnel frost damage in foreign countries, and the advantages and disadvantages of the four major prevention technologies in China and their applicable conditions, are concluded and analyzed. Meanwhile, the importance of frost damage classification is highlighted. Therefore, the local and foreign research results for cold region tunnels are systematically concluded, the defects of the researches are comprehensively analyzed, and the directions of further study are proposed. They are significant to solve the problems of tunnel frost damage in the future. Keywords: Cold region tunnel, Frost damage mechanism, Temperature field, Tunnel frost damage classification, Prevention measure

The tubed vortex reducer is a new structure of aero-engine, which is widely used in advanced large bypass ratio high performance turbofan engines. It is usually installed between the rear two-stage discs of the high-pressure compressor, and reduces the generation of free vortex by restricting the flow path of the cooling airflow, thereby reducing the pressure loss of the cooling airflow and improving the engine efficiency. In this paper, vibration analysis of tubed vortex reducer is carried out by experiments and numerical simulations. Using the finite element method, the natural vibration characteristics of the vortex reducer are calculated with ANSYS. The sensitivity analysis of the impact of design parameters on the vibration characteristics is carried out. In addition, the vibration test bench of the vortex reducer is set up, and the vibration test of the vortex reducer is conducted by means of frequency sweeping and hammer hitting respectively. The experimental results satisfactorily reproduce the simulation results. Then the theoretical model of dry friction damping of vortex reducer is established. Based on the dynamic model of the complex contact system composed of vortex reducer and damping sleeve, the relationship between energy dissipation in different directions is derived. And a method evaluating the performance of vibration reduction is presented for calculating its equivalent damping ratio. Finally, the influence of the key design parameters and different installation methods on the damping ratio is analyzed. Overall, this work can provide reference for vibration reduction design and optimization of vortex reducer.

Genetic algorithms are often easy to fall into local optimum, Inspired by octopus RNA gene editing ability and learning ability, this paper proposed an RNA genetic algorithm based on octopus learning mechanism (LRNA-GA), which uses a single RNA chain to represent the individuals of the population, Imitating the octopus's A-to-G RNA editing method to replace traditional gene mutations, using behavioral learning to design the RNA chain, and determining the possibility of RNA editing by evaluating the RNA chain, so as to quickly jump out of the local optimal solution. The effectiveness of LRNA-GA is tested through typical benchmark functions, and it has fast search capabilities and high accuracy.

In this paper, field measurement is used to obtain the force of system anchor in its actual working condition and stress situation of system anchors in different parts of loess tunnel is analyzed based on field test results, indicating the reasons why values of measured axial force of system anchor are different in different parts of loess tunnel. Based on the displacement solution of Mindlin problem, this paper deduces the analytical solution to stress distribution of system anchors in the sidewall of loess tunnel under the pull-out force, analyzes the distribution forms and influencing factors of shear stress and axial force. At the same time, analytical solutions to system anchor stress and surrounding rock plastic zone radius are tentatively applied to the analysis of stress characteristics and length optimization of system anchor in loess tunnel. The research results are of great significance to understand the mechanical characteristics of anchors in loess tunnel and to optimize the design of anchors in the primary support system of loess tunnel, which leads to accelerated construction progress and low economically cost, especially in loess tunnels with large cross section and long span.

The deformation mode of loess surrounding rock of anchor under the action of pull-out load and the shear stress distribution law of loess anchor and loess interface under the condition of different lengths anchor are studied by using the laboratory self-made model test chamber and micro anchor pullout instrument. A total of three tests are carried out for the selected test anchor. Three deformation modes of loess surrounding rock under the action of pull-out load are obtained according to the test results. It is proposed that the maximum shear stress of loess anchor under the action of pull-out load appears in the section 25 times the anchor diameter from the anchor head, and the shear stress in the middle and rear part of the anchor body can only be brought into full play when the length-to-diameter ratio of the anchor body is 110 or more. Based on the displacement solution of Mindlin problem, the drawn conclusion is compared with the theoretical solution of shear stress and axial force of loess anchor under the action of pull-out load. The results compared are basically consistent, indicating that the conclusion has strong engineering practice, which can provide technical basis for the design and optimization of the system anchor in the sidewall of loess tunnel.

Several configurations of multi-beam reconfigurable THz antennas based on graphene have been investigated. Two modulation mechanisms of graphene-based THz antenna are introduced, one is the reflector-transmission window model, and the other is the reflector-director model (Yagi-Uda antenna). The main parameters, such as main beam direction, resonance frequency, peak gain, and the front-to-back ratio of the proposed antenna can be controlled by adjusting the chemical potentials of the graphene in the antenna. Moreover, this paper provides an easy way to obtain complex graphene-based multi-beam antennas, showing strong potential in the design of other complex graphene-based systems, enabling nanoscale wireless communications and sensing devices for different applications.

Based on Lianchengshan tunnel, the changing of rock mass pressure with deformation, time and distance from the excavation face is analyzed by means of field monitoring and numerical simulation, and the main conclusions are as follows: (1) When the deformation increases rapidly, the rock mass pressure decreases first and then increases. After the settlement and clearance convergence are stable, the pressure of rock mass in each part is still increasing slowly. (2) The rock mass pressure is mostly between 0.1 and 0.3 MPa, and the variation lasts about 65 to 70 days. (3) During the period from mid-bench construction to inverted arch construction, the variation ratio of rock mass pressure is very high, which indicates that the stabilization time of this stage is too long. Therefore, it is suggested to shorten the length of mid-bench and lower-bench appropriately. (4) The space influence range of the excavation face propulsion is about 2.5 times the tunnel diameter of the hole (42 m). To decrease the rock mass pressure, ring closure should be reached as soon as possible. It is recommended to speed up the construction of middle bench and lower bench.

We have designed an ultra-compact polarization beam splitter on silicon-on-insulator (SOI). The device is designed by a Particle swarm optimized (PSO) inverse-design method with a quite small footprint of 2 × 2 μm2. Simulation results shows that the transmission is 61% for TE mode and 52% for TM mode at designed wavelength 1550 nm. The extinction ratio of our device is greater than 10dB within a bandwidth of 40 nm (1528–1567 nm). Benefiting from the global optimization of our inverse-design method, the transmission and extinction ratio can keep greater than 40% and 10 dB separately for both polarizations when the designed pixel side length varies from 100 to 130 nm. Besides, we demonstrate that the design method could have tolerance for input waveguide width, in this case, the device could maintain functionality while the width of input waveguide ranges from 300 to 350 nm.

To cope with tunnel frost damage, studies on prevention methods are routinely conducted to improve environmental protection and energy saving. Based on field investigations, the main available thermal insulation methods and their application are discussed and analysed in this paper. The results show that passive measures, such as a thermal insulation layer or door, cannot completely avoid frost damage. Construction investment of the electric heat tracing (EHT) system is lower at the early stage, but a large investment in operation and pollution problems are needed in the later period. As renewable, clean and environmentally friendly primary energy, geothermal energy can realize energy-saving and emission-reduction. Furthermore, our research team proposed the optimization design method for tunnel heat insulation and anti-freezing by using geothermal energy and presented the challenges for future applications of the ground-source heat pump (GSHP) system in tunnels. The results regarding energy conservation from this review can provide useful technical support in design, operation and management of tunnels in cold regions.

Analysis of the rock mass deformation behavior is a very important aspect of the safety assessment for tunnel construction in weak rock mass. In this paper, the deformation characteristics of a soft rock mass tunnel using three beaches construction method were investigated, which include the crown settlement and horizontal displacement and have 9 sections with 3 different construction schemes. The optimized construction schemes by decreasing the beaches length and changing the geologist of primary support were proposed. Then, applying the displacement back analysis method to calculate the rock mass parameters, double parameters were analyzed by using the golden section method. Results show that the tunnel deformations were affected by the elastic modulus E and the lateral pressure coefficient λ of rock mass, and the change of E has greater influence than λ on the tunnel deformation. The change of λ has greater influence on the crown settlement than that on the horizontal displacement. Furthermore, the regularity and characteristics of longitudinal deformation profile (LDP) in a weak rock mass tunnel was studied by utilizing the Fast Lagrangian Analysis of Continua (FLAC), and the LDP of the three long-beach construction scheme and the three short-beach construction scheme were compared. The results show that the complete displacements of tunnel under the three short-beach construction scheme condition by decreasing the lengths of the middle and lower benches are smaller than that under the three short-beach construction scheme condition, however the pre-deformation of the tunnel deformation under this two construction scheme conditions is nearly the same. The extrusion deformation at the tunnel face of the three short-beach construction scheme is larger than that of the three long-beach construction scheme. Therefore, increasing the area of the core soil is a feasible measure to control the extrusion deformation on the tunnel face. Finally, the tunnel optimized construction scheme was verified benefit the tunnel stability. The measures of decreasing the length of middle and lower bench and closing the invert early and immediately will benefit the tunnel stability.

Similar materials of surrounding rock and lining suitable for crack of tunnel lining are developed through numerous matching tests according to the numerous theory of geomechanical model test to study the mechanism of crack damage of long-span tunnel lining and the variation rules, such as load and deformation, of physical fields. Similar material of surrounding rock is composed of quartz sand as coarse aggregate, barite powder as fine aggregate, and oil, vaseline, and paraffin as binder. Similar material of lining is based on gypsum and quartz sand, diatomite, fly ash, barite powder, and cement as additives. Physical and mechanical parameters such as uniaxial compressive strength, elastic modulus, and cohesion of materials are controlled through uniaxial compressive, direct shear, and splitting tests. The influence laws of mechanical parameters under various ratios are systematically studied. Test results show that the mechanical parameters of similar material of surrounding rock made of quartz sand, barite powder, and vaseline are stable. The range of variation is moderate, and the fabrication is convenient. The adjustment range of physical and mechanical parameters of similar materials in surrounding rocks is 30.1–52.2 MPa of elastic modulus, 0.23–0.33 MPa of uniaxial compressive strength and 2147–2396 kg/m3 of gravity. In the range of 1.2–2 water paste ratio, gypsum mixture is linearly weakened, and various admixtures strongly influence the mechanical properties of similar materials. Quartz sand as admixture can better replace aggregate in concrete. When the sand content is less than 20%, adding quartz sand into gypsum material can significantly improve the elastic modulus of the material, and the compressive strength changes minimally. When the sand content is more than 20%, the elastic modulus is basically unchanged and the compressive strength gradually decreases. When this similar material is applied to the model test of Fucunchuan tunnel lining crack in the Huangyan Road Capacity Expansion Project, the mechanical and physical properties meet the test requirements. The material can effectively simulate the development and evolution of cracks, provide material basis for obtaining good test results, and serve as a reference for the selection of similar materials for a similar model test.

Acoustic emission (AE) tests were performed on saturated karst limestone under uniaxial and triaxial compression. Mechanical properties, AE characteristics, and the energy mechanism of rock failure were analyzed. The peak AE activity under uniaxial compression occurred near the peak stress of the rock. Under triaxial compression, the AE activities of the rock samples first decreased then increased with increases in confining pressure. AE activity exhibited a certain lag, and the peak AE appeared when the stress had decreased significantly. Stratification of the average signal level occurred at low confining pressures. The critical confining pressure was between 15 and 20 MPa, and at this pressure a dramatic change occurred in the AE characteristics of the limestone. Total strain energy, dissipated energy, and elastic strain energy at peak stress showed good exponential relationships with confining pressure and peak rock strength.

During the operation of the satellite, the rapid adjustment of the satellite attitude is needed to monitor the hot spots. The rapid adjustment of the satellite attitude requires the rapid change of the speed of the flywheel, which demands a large instantaneous power from satellite power system. The traditional satellite power supply system is unable to meet the requirements of High Torque Flywheel due to the limited satellite space and the limited battery capacity. The character of the supercapacitor in the satellite power system is helpful to meet the demand of the large load power variation. In this paper, the traditional satellite power system model is established by Matlab/Simulink and integrated the large torque flywheel motors and supercapacitors to study the whether the traditional satellite power system can meet the demand of the acceleration of High Torque Flywheel and the bidirectional flow of braking energy. According to the simulation results, the energy distributions of lithium battery and supercapacitors are determined.

In order to study the propagation laws of blasting vibration waves in weak rock tunnels, the longitudinal and circumferential blasting vibration tests in Muzhailing Tunnel were carried out, and the measured data were analyzed and studied using the methods of Sadov’s nonlinear regression, Fourier transform, and Hilbert–Huang transform (HHT) to provide a reference for the optimization of blasting design of Muzhailing Tunnel or similar weak rock tunnels. The results showed that the tangential main frequency decreases rapidly and the radial main frequency decreases slowly with the increase of proportionate charge quantity. Under a certain charge quantity, as the distance from the explosion source increases, the spectrum width of the blasting vibration frequency becomes narrower, the overall energy is more concentrated, and the vibration frequency tends to be closer to the low frequency. At a certain distance from the explosive source, the frequency of blasting vibration decreases gradually, and the amplitude of low-frequency region increases with the increase of charge quantity. The vibration velocity on the left side of the tunnel is larger than that on the right side, and the vibration velocity at the vault and the arch foot of lower bench decreases rapidly, while the vibration velocity at the arch feet of upper bench and middle bench decreases slowly. The vibration frequencies of the left arch foot of the middle bench and the right arch foot of the upper bench are higher than those of other positions, while the frequencies of the left arch foot of the upper bench are the lowest. During tunnel blasting, the energy input to the strata media is mainly concentrated in the stage of the blasting of the cut hole. The blasting has more energy input to the left arch foot of the upper bench and the tunnel vault, which is consistent with the conclusion of frequency analysis.

In this paper, the strain rate effect on mechanical properties, failure modes, acoustic emission (AE) characteristics, and energy mechanism of the karst limestone was analyzed based on uniaxial compression tests with different strain rates (5 × 10−6–5 × 10−4/s). The results showed that the peak strength increased linearly and peak strain increased quadratically with the logarithm value of the strain rate. Moreover, the strain rate effect on elastic modulus was not significant. Under low strain rates, the rock was damaged seriously, AE signals appeared continuously, and the cumulative number of AE signals was high. Under high strain rates, the total quantity of the macroscopic cracks decreased, but the crack length extended with better coalescence. The AE peak significantly increased under high strain rates, while the cumulative AE activity significantly reduced. The energy evolution of the karst limestone failure process had significant stage characteristics, and the strain energy ratio presented an S-shape. The maximum value of the elastic strain energy at peak stress showed a linear relationship with the logarithm value of the strain rate.

The central diaphragm is often used to reduce the span to maintain the stability and safety of structure in the construction of large-span loess tunnel due to the structure complexities. In this paper, relying on the field monitoring and measurement for Wangcun tunnel in Huangling-Yan’an expressway expansion project, the crown settlement and horizontal convergence of primary support steel rib and central diaphragm steel rib during the construction are analyzed by the upper bench CD method. According to the internal force transfer, deformation coordination, and arch foot displacement between the two structures, the support system is regarded as the arch-beam fixed structure with three times of statically indeterminate and movable abutment under the loads, and the mechanical calculation model of sidewall steel rib and the central diaphragm structure bearing loads and deformation together is established. Finally, through the mechanical model mentioned above, the deformation characteristics of central diaphragm structure and the horizontal convergence in the upper bench of tunnel are calculated and analyzed. The research shows the following: (1) the accumulated settlement of sidewall steel rib in Part I is greater than that of the sidewall steel rib in Part II, and the accumulated settlement of each part at the support structure during the tunnel excavation is less than the reserved deformation of 150 mm specified in the tunnel excavation; (2) the settlement located at the waist and maximum excavation line position of central diaphragm is mainly affected by the excavation of Parts I and II in upper bench; (3) during the whole excavation process, the excavation of Part I and Part II has the greatest influence on the convergence at arch waist and the maximum excavation line position in Part I, and the convergence at the above two positions all experienced four stages of “convergence-expansion-convergence-gradual stability”; and (4) the errors between the horizontal convergence and the deformation of central diaphragm obtained by the mechanical model and the field monitoring data are between 12.7% and 27.5%. The calculated results are in good agreement with the actual situation. The research can provide a theoretical basis for the study of deformation and mechanical properties for support structure in the construction of large-span loess tunnel by the upper bench CD method.

In the new construction or reconstruction of expressway projects, the number of highway twin tunnels with eight lanes is increasing. However, there are no corresponding design support parameters and measures in the current technical specifications for tunnel design and construction in China. In Laohushan superlarge-span highway tunnel with single hole and four lanes, the deformation behavior and mechanical characteristics of support structures are measured and analyzed. The monitoring results indicated that the deformation of tunnel structure mainly experienced three stages: rapid deformation, slow deformation, and stable deformation, and finally reached a relatively stable state; the structure stress of primary support and secondary lining increases sharply at first and then tends to be stable gradually with the gradual construction of each excavation part in the tunnel; the stress of each measuring point at the steel rib is less than the yield limit of steel rib (235 MPa), and the support structure is safe and stable in the process of tunnel construction. Then, the structure safety of primary support under different support parameters is simulated and calculated by numerical simulation with Grade IV rock mass, and the reasonable support parameters for Laohushan highway tunnel are studied considering the structural safety and engineering economy. It is suggested to use the H175-type steel sets with a distance of 80 cm and C25 shotcrete with a thickness of 26 cm. The results could provide reference for similar tunnel projects and provide a basis for the design specification and construction standards for superlarge-span tunnels.

A graphene-based terahertz tunable negative refractive index metasurface has been demonstrated. The proposed metasurface unit-cell comprises of a metallic fractal cross resonant ring and embedded graphene, which presents a dynamic negative refractive index in the corresponding bands by modulating the chemical potential of the embedded graphene.