Abstract:To promote the resource utilization of shield tunneling residue， this paper focuses on the complex composition， high moisture content， and poor permeability of earth pressure balance（EPB） shield tunneling residue. In combination with penetration test， mercury injection test， and computed tomography （CT）， the multi-scale seepage characteristics of shield tunneling residue were analyzed， and the effect and mechanism of flocculant cationic polyacrylamide （CPAM） and defoamer organosiloxane on the permeability of the residue were investigated. The results show that the permeability of shield tunneling residue is affected by the foam in residue， and the permeability coefficient is finally stable around 7.72×10^-6cm?s^-1. The residue has a high porosity， small pore size， and poor penetration. The addition of CPAM can improve the permeability of the residue due to the adsorption bridging and electric neutralization effects. However， excessive flocculant will inhibit the seepage. The optimal dosage of CPAM in this experiment is 0.30 %， and the maximum permeability coefficient can reach 2.55×10^-5 cm?s^-1. As the content of organosiloxane defoamer increases， the permeability coefficient of the residue increases， which can quickly eliminate the foam and improve the connectivity of seepage channel. The optimal dosage for this experiment is 0.20 %， and the permeability coefficient can reach 1.31×10^-5 cm?s^-1.

Abstract:The green transformation of concrete is of great importance for China to achieve the dual carbon development goal， this paper， combining the principle of compact stacking with multi-level grain size of matrix components and using high dosing industrial waste ultra-fine fly ash as an important component， successfully develops a new low carbon ultrahigh toughness concrete （LC-UHTC）. The results show that the ultimate tensile strain of LC-UHTC reached 6.38 %， the tensile strength reaches 10.20 MPa， and the tensile strength increases by more than 60 % compared with other similar materials. The tensile strength and strain energy of LC-UHTC are excellent at all stages of strain， indicating that LC-UHTC has a higher safety performance in practical application. The compressive strength of LC-UHTC reaches 84.35 MPa， which is 30 %–86 % higher than that of other similar materials. LC-UHTC shows comprehensive performance advantages in environmental protection， tension， toughness and compression， which can provide reference value for the green transformation of new concrete.

Abstract:A periodic structure has band-gap characteristics so that the vibrations or waves in the band-gap frequency range cannot propagate in the structure. Based on this concept， an embedded seismic barrier for manipulating Rayleigh surface waves is designed. The influence of the design parameters of the seismic barrier and the constraint conditions between the resonant element and the supporting foundation on the elastic wave dispersion curve and the formation of the bandgaps of seismic surface wave is studied. The results indicate that the embedded seismic metamaterial barrier can form a surface wave band gap in the low frequency region and realize an effective attenuation domain. The constraint conditions between the resonant element and the supporting foundation can significantly alter the band structure of the dispersion curve. Different constraint conditions can affect the formation of the surface wave bandgaps， and even cause the disappearance of the surface wave bandgaps. Thus， in the process of barrier design and implementation， factors， such as friction， that affect the relative movement between the resonant element and the supporting foundation should be considered and rationally designed.

Abstract:In recent years， ultra-high performance concrete （UHPC） has become one of the hot research directions due to its excellent mechanical properties and durability， but its high cost has always limited its application in engineering. In order to reduce the cost of UHPC， this paper proposes a method based on machine learning to optimize the mix proportion of UHPC. In order to achieve this goal， the prediction model of a 28-day compressive strength and expansion of UHPC was first established by using artificial neural network （ANN）， which was taken as the constraint condition， taking into account the constraints of UHPC component content， component proportion and absolute volume， The cost of UHPC was reduced by using genetic algorithm （GA）. The research results show that the error between the prediction results of ANN model and the experimental results is within 10 %， which has good prediction accuracy. The cost of UHPC optimized by GA is reduced to $838.8，which is lower than the cost of $1000 mentioned in the literature.

Abstract:Vibration-reducing metastructures based on the periodic band structure theory have received extensive attention due to their bandgap characteristics. Among them， the locally resonant bandgap is of great significance for small-scale structures to achieve low-frequency vibration reduction and isolation， which has been applied to surface wave and body wave attenuation and isolation of ground soils. However， most of the current research focuses on isotropic soils. In this paper， considering the transverse isotropy of the ground soil， the vibration reduction and isolation characteristics of the two-dimensional rubber-concrete metastructures for subway vibration are studied. The effects of concrete radius， rubber thickness， and soil anisotropy on the omnidirectional bandgap of metastructures are comparatively discussed， based on which， the different directional transmission and full-scale transmission models are established. It is verified that the elastic waves can be effectively attenuated within the bandgap frequency of the metastructures. This paper explores the influence of soil anisotropy on the performance of vibration-reducing metastructures， which can provide reference and guidance for the design and analysis of vibration reduction and isolation in the vicinity of subways.

Abstract:Explosion and impact loadings pose a serious threat to the service safety of defense and industrial equipment. Energy-absorbing materials can effectively reduce structural vibration and the damage caused by impact. Traditional energy-absorbing materials， such as aluminum foam， have a relatively limited design space. Therefore， it is urgent to develop new energy-absorbing materials. In this paper， the energy-absorbing mechanism of porous materials was systematically investigated based on numerical modelling of the impact process. The simulation results indicate that energy-absorbing materials can have a good shock absorption performance only when the strength is appropriate. In order to realize customized design of energy-absorbing materials， shell-based mechanical metamaterials with different energy-absorbing characteristics were designed based on the machine learning and genetic algorithm. The effectiveness of the newly designed metamaterials in energy-absorption and vibration-attenuation was verified through simulation results. This study can provide important technical guidelines for the design and optimization of new energy-absorbing materials.

Abstract:During the soft rock tunnel excavation， large deformation is easy to occur because the parameters of surrounding soft rock are highly variable， the stress of support system and its interaction with surrounding rock are highly uncertain. Therefore， the yield-control support system is studied both domestically and internationally to address these risks. However， there are still many difficulties in evaluating its safety status. In this paper， a new type of flexible rigid yielding joint is designed， and a vulnerability evaluation method of tunnel excavation safety status based on probability is proposed， which combines of the reliability and vulnerability analysis method and vault settlement failure criteria. In detail， by analyzing the interaction between surrounding rock and support with probabilistic finite element method， the support response of limit state function is fitted， and the failure probability and reliability index of tunnel excavation are obtained by random sampling， based on which， the fitting relationship between vault settlement and structural stress response is established， the calculation method of exceedance probability of structural limit state conditions based on vault settlement is proposed， and the vulnerable area is delimited according to the probability distribution for support safety evaluation. The reliability of the new support system is verified based on the comparison between the traditional support system and the rigid support system.

Abstract:In order to obtain the reasonable surrounding rock pressure with the consideration of the characteristics of loess strata to guide the tunnel structure design， by comparing the field test data of surrounding rock pressure of shield tunnel and the new Austrian tunneling method （NATM） tunnel， and in combination with the construction practice of loess shield tunnel， the rationality of calculating the surrounding rock load of loess shield tunnel by deformation surrounding rock pressure is verified. The calculation method of deformation surrounding rock pressure of deep-buried loess shield tunnel is constructed by introducing the strength parameters of loess stratum through Fenner formula. The stress-strain relationship and stress structural parameters of deep buried undisturbed loess are studied by triaxial shear tests， and the calculation method of loess strength index under stress structural parameters is then constructed. The calculation framework of structural parameter field of surrounding rock of deep-buried loess shield tunnel is established in combination with the stress-strain variation law of surrounding rock under the excavation and support. The calculation method of surrounding rock pressure for deep-buried loess shield tunnel is finally given based on the loess strength criterion modified by structural parameters. It is found that the undisturbed loess has an obvious stress peak and strain softening compared with the remolded loess. There is a good fitting relationship between loess stress structural parameters and cohesion， while the correlation with internal friction angle is low. Under the circumstances that only the change of surrounding rock pressure caused by the structural evolution from the loess stratum immersion is considered， when the water content increases from 1 % to 25 %， the radius of plastic circle increases from 4.6 m to 5 m， and the surrounding rock pressure increases from 587 kPa to 622 kPa.

Abstract:Considering the shortcomings of settlement calculation research on shallow in-situ solidification combined with pile-soil rigid composite foundation， and the limitation of settlement calculation method in current specifications under similar working conditions， this paper analyzes the settlement mechanism of shallow in-situ solidification combined with pile-soil rigid composite foundation， studies the sharing proportion of pile end stress under the soil arching effect，analyzes the settlement influence of the additional stress in the negative friction area above the equal settlement surface， and proposes a novel settlement calculation method for the shallow in-situ solidification combined with pile-soil rigid composite foundation. The numerical simulation and engineering practice， indicate that the shallow in-situ solidified soil technology can strengthen the soil arching effect， enhance the pile foundation transfer effect， and effectively reduce the overall settlement of the composite foundation. The settlement calculation method proposed in this paper is accurate and reliable.

Abstract:The rapid development of digital perception， analysis， and decision service technologies in recent years can transform the building construction into a technology-intensive industry and bring new development opportunities. In this paper， the latest digital construction technologies are introduced from the information flow perspective， which covers the main aspects of the digital information perception and processing， the reconstruction and deduction of digitalized construction organization， and the engineering factor management related to personnel， equipment， materials and progress in construction. The digital model of building spatiotemporal information， which changes with the progress of the project， is the digital infrastructure for construction. The future digital building construction will have the characteristics of intelligence， platformization and industrialization.

Abstract:Aluminum alloy has been widely used in engineering structures. A plasticity constitutive model， which can accurately describe the elastoplastic behavior of aluminum alloy under complicated stress states， is of great significance to the analysis and design of aluminum alloy structures under complicated working conditions. The conventional von Mises yield criterion ignores the effect of stress state on metal plasticity， which is not suitable for aluminum alloy materials in complicated stress states. This paper conducts a series of tests to demonstrate that stress triaxiality and Lode angle can influence the plastic behavior of the 6061-T6 aluminum alloy. Based on the test results， a plasticity constitutive model suitable for 6061-T6 aluminum alloy in complicated stress states is proposed， and the full-range hardening law and the new yield criterion are calibrated， which can accurately simulate the elastoplastic behavior of Chinese structural 6061-T6 aluminum alloy in complicated stress states by comparing the experimental and numerical results.

Abstract:In order to meet the needs of coordinated variable speed limit （VSL） control of multi-segment on freeways， and to solve the problem of efficient training optimization in high-dimensional parameter space， a multi-agent deep deterministic policy gradient （MADDPG） algorithm is proposed for freeway VSL control. Different from the existing research on the single agent Deep Deterministic Policy Gradient （DDPG） algorithm， MADDPG abstracts each control unit as an agent with Actor-Critic reinforcement learning architecture， and shares each agent in the algorithm training process. The state and action information of the agents enable each agent to have the ability to infer the control strategies of other agents， thereby realizing multi-segment coordinated control. Based on the open source simulation software SUMO， the effect of the control method proposed is verified in a typical freeway traffic jam scenario. The experimental results show that the MADDPG algorithm proposed reduces the traffic jam duration and the speed standard deviation by 69.23 % and 47.96 % respectively， which can significantly improve the traffic efficiency and safety. Compared with the single-agent DDPG algorithm， MADDPG can save 50 % of the training time and increase the cumulative return value by 7.44 %. The multi-agent algorithm can improve the optimization efficiency of the collaborative control strategy. Further， in order to verify the necessity of sharing information among agents， MADDPG is compared with the independent DDPG （IDDPG） algorithm： It is shown that MADDPG can improve the traffic jam duration and speed standard deviation by 11.65 %， 19.00 % respectively.

Abstract:Autonomous vehicles need to have the ability to predict the trajectory of vehicles around them. There are many mixed traffic flow roads with weak rules and strong interactions in developing countries， and trajectory prediction of high-density traffic flows is an extremely challenging task. In order to predict the trajectory with accuracy and interpretability for mixed traffic flow， a domain knowledge-guided convolutional long short-term memory （DK-Conv-LSTM） to realize the long and short-term trajectory prediction was proposed. In the data-driven model， a convolutional layer （Conv） was used to extract crucial information from interactive vehicles， and the long short-term memory （LSTM） was utilized to predict trajectory after the concatenation of the history information of the vehicle. Knowledge expertise guided the training of deep learning models by being embedded in loss functions. Using the basic LSTM as the benchmark， the Conv-LSTM with only the convolutional structure added， reduces the final displacement error （FDE） by 30.46 % and the average displacement error （ADE） by 34.78 %. The DK-Conv-LSTM reduced the FDE by 46.81 % and ADE by 49.08 %. Moreover， it could recreate complex driving behavior trajectories such as following between two vehicles and overtaking.

Abstract:Lane change decision-making is one of the current opening challenges of automated and connected vehicles. Due to highly dynamic and complex traffic situations， multi-objective decision-making considering vehicle safety and riding efficiency is much more challenging. Therefore， this paper proposes a novel multi-objective predictive optimization-based lane change decision making method， which consists of dynamic matrix modeling and resolving of multi-objective predictive optimization problem. First， the matrix model of traffic flow is established based on the big data information from connected vehicles. Then， dynamic models representing lane change safety and riding efficiency are designed. The predictive optimization problem with constraints can be solved so that the optimal lane change decision is provided. Experimental results illustrate that the proposed method performs better and can improve vehicle safety and riding efficiency of automated and connected vehicles.

Abstract:Under high-pressure hydrogen environment and fatigue load， metal load-bearing components will experience degradation or even failure in material fatigue performance. There are difficulties in hydrogen safety in conducting in-situ hydrogen fatigue damage research on hydrogen components. Therefore， in recent years， alternative methods have been adopted to study fatigue performance of pre-charged hydrogen metals. This paper briefly outlines the hydrogen damage mechanism， introduces the test method for pre-charged hydrogen metals， summarizes the experimental results of the impact of hydrogen on high-cycle and low-cycle fatigue performance under pre-charged hydrogen conditions， and the current research status of establishing a fatigue life model for pre-charged hydrogen metals and conducting quantitative analysis of metal hydrogen damage. Finally， it discusses several methods for improving the fatigue life of hydrogen components by suppressing the effect of hydrogen on metals by changing the infiltration amount and form of hydrogen in the material.

Abstract:In order to improve saline-alkali soil， a superhydrophobic particle material with an excellent waterproof and salt-blocking performance was prepared， which was used to build a saline-alkali soil reconstruction system with a water-storage mode. Substrate material and desert sand were modified with a hydrophobic coating. The influences of resin content and micro-/nano-material content on the hydrophobicity， impermeability and breathability of the material were studied. A self-designed mini soil-column was used to simulate the migration process of underground saline water， and the waterproof and salt-blocking properties of the prepared materials were explored. The results show that when resin， hydrophobic CaCO₃ and nano-SiO₂ contents were 1.0 %， 0.8 % and 0.2 %， respectively， the material achieved a water contact angle of 153.6°， a water-resistant height of 230 mm， and maintained a good air permeability. The mini soil-column simulation test indicates that the material has a strong inhibition effect on the water evaporation and the upward movement of salt， with an evaporation-inhibiting rate of 50 % to 70 % and a salt-blocking rate of more than 99 %， which maintains 97.5 % after 20 test cycles.

Abstract:The dynamic characteristics of the electric feedback servo valve can be obtained directly through the spool displacement response test. But the dynamic characteristics of the mechanical feedback flow servo valve are usually measured indirectly by using the dynamic cylinder as a flow sensor. The test results are affected by inherent non-idealized factors such as dynamic cylinder leakage， damping， and mass inertia， and usually cannot accurately express the performance indicators of the servo valve. Based on a set of actual valve-controlled cylinder system， a Matlab-Simulink simulation model is established. The error of the analytically obtained frequency bandwidth is less than 0.5 % compared with the measured results. Thus， the simulation model can accurately express the performance characteristics of valves and cylinders. The frequency characteristic of the system under the condition of dynamic cylinder without piston mass， viscous damping and leakage is theoretically analyzed. Under the change of the piston mass， viscous damping and leakage， the variation law of the frequency characteristics of the valve-controlled cylinder system is analyzed.

Abstract:The Bohai Sea area of the Bohai Bay Basin is an important direction in oil and gas exploration at present and in the future. Understanding of the generation pathway，mechanism， and potential of natural gas at Bohai Sea area is beneficial for developing the natural gas generation theory and guideing petroleum exploration in the Bohai Bay Basin. Through the simulation experiment of typical source rocks in Liaozhong Sag of the Bohai Sea area， the generation characteristics of main source rocks in the Bohai Sea area are studied， and the generation model of main source rocks in the Bohai Sea area is established. Based on the analysis of typical hydrocarbon accumulation mechanism， the accumulation regularity of different types of natural gas is identified， and the potential and direction of natural gas are discussed. The results show that Type II1 and Type II2 hydrocarbon source rocks of the third member of the Shahe Formation in the Bohai Sea area have the characteristics of triple peak relay gas generation. The Ro of the three gas generation peaks is 1.0% （①）， 1.5 % （②） and 2.7 % （③）， respectively. The three gas generation peaks show intermittent relay gas generation characteristics. The total gas production of the three gas generation stages has a Peak③≈Peak② >Peak①； Natural gas reservoirs generated at Peak ① and Peak ② stages are generally developed in Liaozhong Sag of the Bohai Sea area， among them， Peak① mainly shows atmospheric pressure oil and gas accumulation in the slope zone close to the source rock， and Peak② mainly shows overpressure condensate gas accumulation in the uplift zone. The natural gas formed by Peak ③ is only found at local well points. It shows that the deep source rocks in Liaozhong Sag have entered Peak ③ stage and have the potential to form large over-mature gas reservoirs.