Jianxun Chen

Bio: Jianxun Chen is an academic researcher from Chang'an University. The author has contributed to research in topics: Rock mass classification & Deformation (meteorology). The author has an hindex of 19, co-authored 72 publications receiving 1198 citations.

Characteristics of seismic disasters and aseismic measures of tunnels in Wenchuan earthquake

Abstract: Over the past few years, accompanied by big and frequent earthquakes, more attention was paid to the tunnel earthquake resistance. To reduce tunnel seismic damage and explore the reasonable aseismic measures, the tunnel earthquake disaster investigation was employed to analyze and summarize the tunnel seismic damage on the basis of Wenchuan earthquake. Fifty-two tunnels near the epicenter of Sichuan Province were investigated: Only 7 tunnels did not show structure damage, 6 tunnels suffered the most serious damage, and the rest appeared damage to various extents. It indicates that most serious seismic damage happens to fault fracture zone, followed by entrance and common section of the tunnel. Additionally, the results display that the typical seismic damage of tunnels is lining cracking, collapsing, dislocation, construction joints cracking, and uplifting of invert, and usually lining cracking and collapsing account for a larger proportion. Therefore, the tunnel aseismic design should emphasize the fault fracture zone and tunnel entrance. Tunnel design should adopt the composite lining structure with shock absorber and whole chain alternative grouting to prevent the lining cracking and collapsing in the seismic fortification zone.

A state-of-the-art review of sustainable energy based freeze proof technology for cold-region tunnels in China

Abstract: 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.

Investigation Progresses and Applications of Fractional Derivative Model in Geotechnical Engineering

Abstract: Over the past couple of decades, as a new mathematical tool for addressing a number of tough problems, fractional calculus has been gaining a continually increasing interest in diverse scientific fields, including geotechnical engineering due primarily to geotechnical rheology phenomenon. Unlike the classical constitutive models in which simulation analysis gradually fails to meet the reasonable accuracy of requirement, the fractional derivative models have shown the merits of hereditary phenomena with long memory. Additionally, it is traced that the fractional derivative model is one of the most effective and accurate approaches to describe the rheology phenomenon. In relation to this, an overview aimed first at model structure and parameter determination in combination with application cases based on fractional calculus was provided. Furthermore, this review paper shed light on the practical application aspects of deformation analysis of circular tunnel, rheological settlement of subgrade, and relevant loess researches subjected to the achievements acquired in geotechnical engineering. Finally, concluding remarks and important future investigation directions were pointed out.

Fiber Bragg Grating Sensors-Based In Situ Monitoring and Safety Assessment of Loess Tunnel

Abstract: Compared with electrical strain gauges, fiber Bragg grating (FBG) sensing technology is a relatively novel method for tunnel structural health monitoring, which has a number of advantages including high accuracy, multiplexing, electromagnetic interference resistance, and good repeatability. In order to study the internal force of the tunnel liner and detect the potential safety hazards, series of strain monitoring tests of a loess tunnel, taking into account the complex stress and strain variation of the loess during tunnelling, were performed by employing the tandem linear FBG sensor arrays controlled by the wavelength division multiplexing (WDM) technology. The concrete strain has obvious linear characteristics over time in the early stage and then gradually tends to a stable value. Moreover, after the necessary temperature compensation, loess tunnel structure safety was assessed through the analysis of real-time strain and internal force of the liner concrete, and the FBG monitoring data and safety assessment results indicate that the safety factors of various liner sections all meet the code requirements, which verify the safety and stability of the tunnel liner structure. The FBG sensors-based in situ monitoring technology can be well applied in the loess tunnel structure safety assessment.

Vibration Response Characteristics of the Cross Tunnel Structure

Abstract: It is well known that the tunnel structure will lose its function under the long-term repeated function of the vibration effect. A prime example is the Xi’an cross tunnel structure (CTS) of Metro Line 2 and the Yongningmen tunnel, where the vibration response of the tunnel vehicle load and metro train load to the structure of shield tunnel was analyzed by applying the three-dimensional (3D) dynamic finite element model. The effect of the train running was simulated by applying the time-history curves of vibration force of the track induced by wheel axles, using the fitted formulas for vehicle and train vibration load. The characteristics and the spreading rules of vibration response of metro tunnel structure were researched from the perspectives of acceleration, velocity, displacement, and stress. It was found that vehicle load only affects the metro tunnel within 14 m from the centre, and the influence decreases gradually from vault to spandrel, haunch, and springing. The high-speed driving effect of the train can be divided into the close period, the rising period, the stable period, the declining period, and the leaving period. The stress at haunch should be carefully considered. The research results presented for this case study provide theoretical support for the safety of vibration response of Metro Line 2 structure.

Real-world automotive emissions: Summary of studies in the Fort McHenry and Tuscarora Mountain tunnels. Final report

Abstract: Motor vehicles are the main source of carbon monoxide (CO) Under multiple sponsorship, two major vehicle emissions studies were conducted: one in Fort McHenry tunnel (under the Baltimore Harbor) in June 1992 and the other in the Tuscarora Mountain tunnel in south-central Pennsylvania (Pennsylvania Turnpike) in September 1992 The cars at both sites tended to be newer than elsewhere (median age was < 4 years), and much better maintained as judged by low CO/CO2 ratios and other emissions characteristics Measured CO/CO2 ratios agreed with concurrent roadside infrared remote sensing measurements on light-duty vehicles Remote sensing measurements on heavy-duty diesels were obtained for the first time and were roughly in agreement with the regular (bag sampling) tunnel measurements in both CO/CO2 and HC/CO2 ratios

Acoustic Emission 방법의 공학적 응용

Abstract: Our experts at TÜV Rheinland have many years of experience and practice in NDT techniques and strive to provide clients with the most fitted and tailored nondestructive method for their pressure equipment while offering reliable, timeand cost-efficient solutions. Acoustic emission testing is one of the most comprehensive and adapted proceduresto detect defects and flaws in your pressure equipment because it can be conducted during operation and does not require any interruption of activity. It also allows for global monitoring of the complete pressure equipment asset and is the best solution for vessels with complex geometries.

Spatiotemporal Traffic Flow Prediction with KNN and LSTM

Abstract: The traffic flow prediction is becoming increasingly crucial in Intelligent Transportation Systems. Accurate prediction result is the precondition of traffic guidance, management, and control. To improve the prediction accuracy, a spatiotemporal traffic flow prediction method is proposed combined with k-nearest neighbor (KNN) and long short-term memory network (LSTM), which is called KNN-LSTM model in this paper. KNN is used to select mostly related neighboring stations with the test station and capture spatial features of traffic flow. LSTM is utilized to mine temporal variability of traffic flow, and a two-layer LSTM network is applied to predict traffic flow respectively in selected stations. The final prediction results are obtained by result-level fusion with rank-exponent weighting method. The prediction performance is evaluated with real-time traffic flow data provided by the Transportation Research Data Lab (TDRL) at the University of Minnesota Duluth (UMD) Data Center. Experimental results indicate that the proposed model can achieve a better performance compared with well-known prediction models including autoregressive integrated moving average (ARIMA), support vector regression (SVR), wavelet neural network (WNN), deep belief networks combined with support vector regression (DBN-SVR), and LSTM models, and the proposed model can achieve on average 12.59% accuracy improvement.

Unified boundary for finite dynamic models

Abstract: The finite element analysis of dynamic problems in an infinite, isotropic medium is discussed. To simulate the physically infinite system by a finite model, an energy absorbing boundary is proposed. This boundary is frequency independent and proves to be very efficient in absorbing stress waves. The boundary constants are calculated for the particular cases of plane strain and axisymetry. /Author/TRRL/

Seasonal Hydrochemical Characterization and Groundwater Quality Delineation Based on Matter Element Extension Analysis in a Paper Wastewater Irrigation Area, Northwest China

Abstract: The current study was carried out to delineate the seasonal hydrochemical characteristics and to quantify the suitability of groundwater for drinking and irrigation purposes in an alluvial plain adjacent to a paper wastewater irrigation zone, northwest China. Groundwater samples were collected from 14 groundwater monitoring wells in pre-monsoon, monsoon and post-monsoon seasons, respectively. Statistical analysis and Chadha diagram were used to delineate the groundwater hydrochemical characteristics. The matter element extension analysis (MEEA) model was proposed to quantify the overall groundwater quality. Irrigation water quality indicators were applied to assess the suitability of groundwater for irrigation purpose. The research results show that the hydrochemical facies for the majority of the groundwater samples is SO4·Cl–Na type with some minor hydrochemical facies of HCO3–Ca·Mg, HCO3–Na, and Cl·SO4–Ca·Mg types. The sequences of ions are Na+ > Ca2+ > Mg2+ > K+ for cations, and HCO3 − > Cl− > SO4 2− > CO3 2− for anions. The major ions and contaminants in the groundwater are controlled by multiple factors including hydrogeological conditions, rock weathering, water–rock interactions and human activities. The values of pH, TDS and TH show reduction in the monsoon season, indicating slight improvement of water quality during the monsoon season. Water quality assessment results based on MEEA show that the overall groundwater quality in the wastewater irrigation zone is generally fair to poor quality. Some groundwater samples are even classified as very poor quality, which is unsuitable for human consumption. They are also unsuitable for irrigation because of potential sodium hazard and salinity hazard. Groundwater from the Yellow River irrigation zone and the alluvial plain is generally suitable for domestic and irrigation uses. Some local water sampling locations may experience water quality improvement during the monsoon season, which, however, will generally not affect the final water quality classification for domestic and irrigation purposes. Interestingly, the study also finds that the variation trend of the correlation degree computed from MEEA can be useful in determining water quality improvement. This study may provide insights for people to make educated decisions in efficient groundwater quality protection and sustainable groundwater quality management.