Shield Section Research Articles

Prediction of GHG emissions from Chengdu Metro in the construction stage based on WOA-DELM

With the mass construction of urban subways, the global greenhouse gas (GHG) emissions have been on the rise. This paper provides statistical evidence to support the infrastructure of subway emissions reduction through a study of GHG emissions during the construction stage of 6 stations and 7 sections of Chengdu Metro Line 18. Using the emission coefficient method, the GHG emissions from building material production, transportation and site construction in subway stations and shield sections were calculated, and a subway GHG emissions prediction model dependent on deep extreme learning machine (DELM) with whale optimization algorithm (WOA) was established(i.e., WOA-DELM). Compared with some optimized DELMs, namely wind driven optimizer (WDO) -DELM, grey wolf optimizer (GWO) -DELM, particle swarm optimizer (PSO) -DELM, artificial bee colony (ABC) -DELM, multi verse optimizer (MVO) -DELM, and atom search optimizer (ASO) -DELM, and some non-optimized algorithm models, namely back propagation neural network (BPNN), kernel extreme learning machine (KELM) and DELM, the correlation consistency of WOA-DELM algorithm prediction results (0.757) was found to be slightly higher. Through sensitivity analysis of the main input variables of subway GHG emissions with the WOA-DELM algorithm model, it was determined that the key influencing factors of station GHG emissions prediction were the station length and the depth of track surface, with relative change rates of corresponding variables of GHG emissions at 30.1% and 23.1% respectively. Finally, a rough prediction formula of GHG emissions from Chengdu Metro stations and shield sections were fitted based on the key influencing factors of GHG emissions. This study provides a practical and effective reference for reducing GHG emissions in subway construction and operation.

Risk uncertainty analysis in shield tunnel projects

Subway shield tunnels usually pass through the complex geological environment of a city. There are many uncertain factors in shield tunnel construction risk, undoubtedly increasing the difficulty of construction safety control. Risk evaluation prior to project construction is necessary for the implementation of tunnel projects and reduces risk levels during construction. However, tunnel risks are uncertain and are characterized by random and fuzzy uncertainty. To account for these two uncertainties in the quantitative transformation of risk qualitative concepts and to improve the evaluation accuracy, in this study a new risk evaluation method based on a two-dimensional cloud model (TDCM) is proposed for shield tunnel projects. First, the risk evaluation criteria are quantified with the harmfulness and the probability of risk as the evaluation dimensions of the two-dimensional cloud, and the conversion relationship between the risk level and the quantitative domain is improved. A risk evaluation index system based on construction accidents and risk types for shield tunnel projects is established. Then, the Delphi method is used to evaluate the probability and harmfulness of the risk, the index weight and numerical characteristics of the two-dimensional cloud model are determined, and a shaped two-dimensional comprehensive cloud of thousands of cloud droplets is generated by a positive cloud generator. Finally, the domain is defined as the overlap between the comprehensive evaluation cloud and the standard cloud at different risk levels, and the contribution of comprehensive evaluation cloud drops to the comprehensive evaluation cloud in each domain is analysed. The risk level of the project is predicted based on the principle of maximum membership degree. The risk evaluation method proposed in this study is applied to two subway shield sections, and the risk level of these projects is accurately predicted. The TDCM evaluation method is compared with the one-dimensional cloud model (ODCM) evaluation method and the fuzzy comprehensive evaluation method (FCEM), and the advantages and applicability of the TDCM evaluation method are discussed.

Measured Analysis on Surface Deformation and Influence of Cutter Torque for Twin Shield Tunnelling in Silty Sand

In this study, the field measurement was conducted on the twin shield tunnelling in a shield section of Hangzhou Metro Line 6, where the surface deformation caused by twin shield tunnelling in the silty sand was obtained. The surface deformation law and the applicability of the twin‐line Peck formula in the silt area were analyzed. The relationship between the cutterhead torque and the surface deformation in the silty sand was identified. Furthermore, the differences in surface deformation of twin shield tunnelling in the Hangzhou soft soil area were discussed. The results show that the settlement process caused by twin shield tunnelling in silty sand is faster than that of soft soil and has no rebound phenomenon. The twin‐line Peck formula is suitable in silty sand, but the prediction of the latter line using this formula is slightly deviated because of the secondary disturbance effect. Due to the secondary disturbance of the soil caused by the construction of the latter line, the soil loss rate of the latter line is higher than that of the former line. Therefore, the reference ratio of the soil loss rate of the latter line and the former line is given. Furthermore, the cutterhead torque of the shield machine was found to be associated with the maximum instantaneous value of the surface deformation.

Rock‐Breaking Laws of Disc Cutters with Different Height Differences in Hard Rock Strata

When shield machine traverses through hard rock mass, disc cutters will be abraded to different degrees. Excessive height difference exists between adjacent disc cutters, which critically affects the rock‐breaking efficiency. Relying on a shield section of hard rock mass in Qingdao, the disc cutter abrasions are measured on site, and the reason for low construction efficiency is analysed. Subsequently, the discrete element method is used to study the rock‐breaking law under different height differences of disc cutters. The ultimate cutter height difference for rock breaking is obtained. According to this, the cutter adjustment scheme is proposed to reduce the cutter height differences on site. Comparing shield tunnelling parameters before and after the cutter adjustment, it is found that the construction efficiency is significantly improved. The results are of great significance for improving the rock‐breaking efficiency and increasing advancing speed of shield in hard rock mass.

Stratum Displacement Law and Intelligent Optimization Control Based on Intelligent Fuzzy Control Theory During Shield Tunneling

The laws of Stratum displacement and optimal control are critical for shield operation. This article’s focus is made on the intelligent fuzzy control theory concentrating on earth pressure, total thrust, driving speed, cutter torque, grouting pressure and grouting volume as the main elements of the study. A model of intelligent fuzzy control theory based on the model of No. 9 Line of Guangzhu Rail transit, on the Tianma river shield section. The paper also analyzes stratum displacement law due to shield tunnelling, executes & analyses intelligent controls for optimization of parameters, combining the five two-dimensional structures of the double structure of fuzzy control system. According to the observations made on the model. The model is upto date and the control of all parameters develops stably. The parameter ranges should be controlled as follows: earth pressure, 0.19 ~ 0.22Mpa; total thrust, 1100 ~ 1350T; driving speed, 38 ~ 50mm / min; cutter torque, 1600 ~ 2300 KN • m; grouting pressure, 0.19 ~ 0.25Mpa and grouting volume, 30 ~ 50L/min. Keywords: Shield tunnel, intelligent fuzzy control, Stratum displacement, optimal control DOI: 10.7176/CER/13-6-01 Publication date: October 31 st 2021

Multi-objective Optimal Design of Gas-fired Heater Based on Modified Design Model of Fired Heater Taking into Account Exergy, Economic and Environmental Factors

Heaters are one of the central parts of natural gas reduction stations using turboexpanders to prevent the formation of hydrate and corrosion failure. This study intends to design a fired heater by applying a combustion sub-model to derive an optimal model for this kind of application. This model is developed to accurately consider all subsections of the fired heater namely radiation, convection, and shield sections, as well as flue gas composition, and its volume. Within this context, a multi-objective optimization is employed to identify the optimal design of the gas-fired heater in the natural gas reduction station for the Ramin power plant case study. The total economic and environmental costs, together with modified exergy efficiency, are selected as objective functions. Multi-criteria-decision-making-method is employed on Pareto frontiers optimal curve to suggest the optimal solution. Results show that the developed model can outperform previous models in thermal efficiency with relatively similar costs. Besides, the optimal point in Pareto suggested by the decision-making-method accounts for a higher modified exergy efficiency (1.3%) than the counterpart, which thermal efficiency is regarded as an objective function. At the same time, its total cost remained almost constant. The effects of changes in each of the design parameters on the objective functions are also evaluated.

Test and Analysis of Velocity Law of Flowing Water in Stratum of Bottom Contact Passages in Shield River-Crossing Section

The method of combined hole arrangement on both banks and in the middle of the river was proposed for the test and analysis of the flowing water velocity in contact passages at the bottom of the Wulong River in order to address the insufficient reliability of the existing testing method for the flowing water velocity in the bottom stratum and its failure to truly reflect the data and law of the velocity in the stratum of bottom contact passages in the shield section. Meanwhile, the measurement time of each measuring hole has experienced the fluctuation cycle of the water level, enabling the parameters and law of the flowing water velocity obtained from the test to cover the complete spatial and temporal distribution range. Compared with the existing research, the method has a greatly improved data reliability, guiding the freezing reinforcement construction of bottom contact passages successfully. At the same time, the flow distribution law, velocity range and the law of influence of water fluctuation on the flow velocity revealed in this test can provide reference for related engineering projects in the region.

The Vibration Characteristics of Ground of Rock Blasting in Silt‐Rock Strata

As the shield section passes through the silt‐rock strata, the rock stratum of the tunnel section has to be blasted into blocks in advance, and the diameter of the blocks should be less than 30 cm after breaking, and then, the blocks could smoothly enter the soil cabin through the opening of the tunnel boring machine (TBM) cutter head and finally be discharged through the screw machine. The geology of rock blasting in silt‐rock strata is complex, and the vibrations caused by blasting threaten the safety of buildings around the blasting area. According to the measured data of blasting vibrations at the sites, the waveform duration of vibration acceleration and the distribution characteristics of dominant frequency of vibration velocity were analyzed, the energy characteristics of vibration velocity were researched by wavelet analysis, and the attenuation laws of vibration velocity were studied by dimensional analysis (DA). The dominant frequency bands of vibration energy of ground are in the range of 0–15.625 Hz, and the distribution characteristics of frequency bands of vibration energy in different directions of the ground are similar to each other, but the energy magnitude is different from each other. The research results could provide a reference for the safe blasting distance of buildings under similar geological conditions.

Progressive Fine Integrated Geophysical Method for Karst Detection During Subway Construction

Various geological disasters can easily occur in tunnels that pass through a limestone stratum. The fine detection of the karst system is significant for safe construction. In this paper, a progressive integrated geophysical method is proposed for fine detection of the karst area of an urban subway. The method combines ground-penetrating radar (GPR), transient electromagnetics (TEM), cross-hole electrical resistivity tomography (ERT), and 3D laser scanning to provide quantitative and integrated detection imaging in a shallow karst system. First, 3D images of reflected waves and the apparent resistivity in the study area are determined using GPR and TEM methods, and the key development of abnormal karst bodies along the mileage direction is delineated. Meanwhile, the TEM slice combination results intuitively show the low-resistance anomaly's distribution and development direction. The main water channel is inferred within the detection range. Second, cross-hole ERT exploration is performed to realize the type of judgment and accurate positioning of karst caves. Finally, 3D laser scanning is conducted to obtain the 3D spatial orientation and size of the large-scale caves identified or those that could have a large influence on metro tunnel construction. Geophysical survey results provide a reference for the design and parameter selection of the cave grouting treatment scheme. This method has been effectively applied in a shield section of the R1 line of the Jinan Metro.

Field Test Optimization of Shield Tunnelling Parameters Undercrossing an Existing High-Speed Railway Tunnel: A Case Study

An existing high-speed railway tunnel undercrossed by shield tunnelling is a high-risk project. Selecting reasonable shield tunnelling parameters is key in controlling the deformation of existing high-speed railway tunnels. In this paper, a Metro Line 3 undercross of an existing high-speed railway tunnel project is taken as the research background. First, a shield section with similar geological conditions as the undercross section is selected as the test section. Then, reasonable shield tunnelling parameters are determined by monitoring the settlement values of surface and ground structures in the test section. Finally, combined with the monitoring results of vertical soil displacement, the reliability of the shield tunnelling parameters is verified. After the completion of shield tunnelling in the test section, there is no void behind the shield tunnel wall, and the monitoring results of the vault settlement and segment posture in the tunnel meet the control values in the specification, which further support the rationality of the tunnelling parameters. In the process of shield tunnelling the undercross of the existing high-speed railway tunnel, the monitoring results of overall tunnel settlement, bottom uplift point settlement, track settlement, and track height difference meet the control values in the specification, which effectively avoids the adverse impacts of the shield tunnelling undercross of the existing high-speed railway tunnel and ensures the safety of the existing tunnel.

Modelling of ventilation and dust control effects during tunnel construction

A large amount of dust is mainly generated during the construction of the shield tunneling machine. In order to achieve the optimal dust removal effect, this research took the shield section of Jiaozhou North Station of Qingdao Metro Line No. 8 to Jiaodong Airport Station (China) as a case study. For this purpose, the numerical simulation and orthogonal design were undertaken to optimize the parameters of the ventilation and dust removal system for a shield tunneling machine, and to study the influence of each parameter on the dust removal from three aspects, including the distance of pressure tuyere, the air volume of the pressure tuyere, and the distance of the air inlet. The results of the analysis showed that the distance of the pressure tuyere is the main parameter to control the dust removal, and the two other factors had both less influence on the dust removal. The numerical simulation of the optimal method showed that it outperformed on dust removal than the actual working conditions. This research provided a theoretical basis and direction for optimizing the performance of a ventilation and dust removal system.

Morphogenetic Features of the Exoskeleton in Early Jawless Vertebrates (Osteostraci, Agnatha): Geometry of the Shield Sections

Based on available information (original studies and published data), a brief review of the structure and morphogenetic features of the exoskeleton of osteostracan agnathan vertebrates (Osteostraci, Vertebrata) is provided. The geometry of vertical cross sections of the cephalothoracic shield in different osteostracan taxa is analyzed.

Boreal Shield forest disturbance and recovery trends using Landsat time series

Abstract Monitoring forest recovery following disturbance is important for both forest management as well as assessing possible climate change impacts on forest dynamics. To do so, an improved understanding of forest recovery processes and their relationship to remotely sensed spectral measures of recovery is required. Our objective in this research is to develop and apply a methodology for using Landsat time series to characterize forest recovery using spectral recovery trajectories. We focus our efforts in the Canadian Boreal Shield ecozone where a known geographic east to west distinction in disturbance regimes remains to be quantified. Results show that forest recovery following a stand replacing disturbance is detectable and quantifiable using a dense Landsat time series of spectral reflectance. All Tasseled Cap indices were found to capture an element of forest recovery following disturbance, with Wetness offering additional information on increasing vegetation structure and complexity. Tasseled Cap component trajectories of recovery show clear differences in both disturbance detection and forest recovery across the east and west Boreal Shield sections. The Cohen's d similarity metric indicated large differences (d > .08) in Wetness and Greenness-based spectral recovery trajectories when comparing the two Boreal Shield sections with the East Boreal Shield having markedly more above average recovery (+ 2 std. dev. from the mean) than the West. Based on our spectral recovery results, we also observe that forest recovery varies over the entire ecozone and is different between the east and west Boreal Shield forests.

Methodology for Reparation of Damaged Sleeves and Welded Shield Sections of Guide Vanes at Hydropower Plant DJERDAP 1

Normal 0 false false false MicrosoftInternetExplorer4 Vertical Kaplan turbines, manufactured in Russia and with nominal power of 200 MW, have been installed in 6 hydroelectric generating units at ’Djerdap 1’. During the refurbishment of hydropower plant experimental non-destructive tests were performed in order to determine the state of turbine components. During the course of testing damage was detected at sleeves and welded shields of guide vanes, which occurred as a consequence of turbine shaft vibrations. 1782 mm long guide vane sleeves were made of cast steel 25L (GOST standard), 260 mm long sleeve was made of forged steel St 25 (GOST standard), while welded shields of guide vanes were made of austenitic steel 08X18H10T (GOST standard). Results of experimental tests and methodology for reparation of damaged surfaces of sleeves and welded shields of guide vanes are presented in this paper. It was necessary, due to the structural solution used for the design of guide vanes and their function during service, to define a large number of details, carefully reconsider them and carry out all activities with extreme care in order to enable the safe operation and continuous use of vanes through the use of reparation methodology for welding/surface welding of sleeves and welded shields. Overlooking, underestimation or incorrect perception of important details could cause significant problems during turbine operation. /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-parent:""; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin:0cm; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.0pt; font-family:"Times New Roman"; mso-ansi-language:#0400; mso-fareast-language:#0400; mso-bidi-language:#0400;}

Radiation Shielding Options for a Nuclear Reactor Power System Landed on the Lunar Surface

A survey of neutron-attenuating materials is conducted, followed by a systematic optimization of the radiation shield configuration for the Affordable Fission Surface Power System. Water, borated water, boron carbide, boron-doped beryllium, zirconium hydride, and lithium hydride are evaluated for neutron shielding, and tungsten is considered for gamma shielding. Lithium hydride, borated water, and boron carbide are selected for further consideration, and radial, upper axial, and lower axial shield sections are developed separately from these materials and then combined to form complete shields. Two competing effects determine the optimal position of the tungsten layer: increasing secondary gamma production due to fast neutron scattering when the tungsten layer is placed closer to the core, and radially increasing mass when placed farther from the core. The optimal position of the tungsten layer is found for each shield configuration and material. The as-landed configuration of each radiation shield allows a maximum dose of 5 rem/yr to an outpost 1 km from the reactor core. The shield also protects the SmCo magnets in the alternators of the Stirling power converters, allowing a maximum dose of 2 Mrad gamma and 1014 n/cm2 fast neutron fluence to the magnets over the 8-yr design lifetime. A minimum mass is found for each shield section while meeting these dose limits. The radial shield section is cylindrical, and the upper and lower axial shield sections are conical in shape. Axial shields with a range of pitch and thickness are analyzed, and the optimal shapes of the upper and lower axial shields for each material are found. The three sections of the shield are combined to form a complete shield. The lithium hydride shield is the lightest of the final shields at 6215 kg. The borated water shield is the second lightest at 6663 kg, which is 448 kg more than the lithium hydride shield. The boron carbide shield is the most massive at 8315 kg, which is 2100 kg more than the lithium hydride shield.

Status of design of the first wall for ITER

The First Wall (FW) is one of the key components of the International Thermonuclear Experimental Reactor (ITER). It must be designed to remove the surface heat flux from the plasma, while, in combination with a structurally integral shield, reduce the nuclear effects in the vacuum vessel and protect the superconducting coils from excessive nuclear heating and radiation damage. As the principal plasma facing element it will be exposed to the 1500 MW fusion power at an average neutron wall loading of about 1 MW/m2 and must be designed for a life of 0.3 MWa/m2 during the Basic Performance Phase. In addition the First Wall must successfully withstand peaked thermal and electromagnetically loads resulting from plasma disruptions.A conceptual design of the ITER First Wall has evolved as a result of the Engineering Design Activity. This design utilizes a beryllium plasma facing layer, bonded onto a copper layer which conducts the heat to the contained active cooling tubes. The copper is bonded to stainless steel for structural support and attachment to the water cooled stainless steel shield section. As discussed in this paper, the basic FW configuration developed for use at most locations, referred to as the primary wall, must be modified for different power requirements at two specific locations, the plasma limiter and the baffle. Carbon Fiber Composite (CFC) is being considered as an alternative material for the baffle and limiter FW because of its high thermomechanical performance and its high resistance to thermal shock.

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Fusion reactor first-wall cooling for very high energy fluxes

A study has been made of the feasibility of a protective first-wall shield between the plasma and the containment vessel for early experimental controlled thermonuclear fusion machines. The proposed first-wall shield is a water-cooled array of thin-walled tubes designed to take very high local energy fluxes originating from the neutral beam injectors. Detailed computer calculations reveal that heat flux capabilities of 3300 W/cm 2 are possible with first-wall shield sections made up of tubes 1 m long of Ta-10W alloy (with tubes of 10 mm i.d. and tube wall thickness of 0.5 mm) with a structural safety factor of about four. Required pumping powers on the order of 1 MW/m 2 of first-wall area exposed to these high energy fluxes are predicted for flow in the non-boiling regime. If operation in the subcooled nucleate boiling regime can be achieved without oscillations or instabilities, the required pumping power is shown to decrease by about an order of magnitude.

Huts and Farm Buildings in Homer

These seem to be regarded as quite a different type of building from houses.The terminology used of them is to a large extent distinct. The only case of extensive overlapping has probably a special stylistic reason.The main words involved are κλισίη (soldiers' hut or herdsman's cottage), αύλή (yard or farmyard), μσσαυλος (animal enclosure), and σταθμός/–οί (the whole complex of farm buildings). The evidence is scanty: in the Iliad there are a number of passages relating to soldiers' huts, and a few mentions of farms in similes and in the Shield section. In the Odyssey there is Eumaeus' farm. This is virtually all. There is also, inevitably, a dearth of archaeological evidence for country buildings, since the remains of these are apt to be less noticeable, and often less durable, than those of large settlements.

The nature, evolution and present extension of the ecumene in the shield section of the Saint-Maurice Valley

The nature, evolution and present extension of the ecumene in the shield section of the Saint-Maurice Valley