Branch Tunnel Research Articles

Effects of distribution form and location of different branch tunnels on overpressure characteristics of ventedgasoline-air mixture explosion in closed vessels

The branch structure of the tunnel significantly affects the overpressure characteristics of combustible gas explosions in confined space. However, most of previous studies involved explosions in branch vessels were limited to single branch structure, effects of the distribution form and location of the branch structure were rarely considered. In order to explore the influence of various branch distribution forms and locations on overpressure characteristics of vented gasoline-air mixture explosion in closed vessels, the experiments were carried out using three kinds of branch tunnel distribution forms (linear/staggered/symmetrical) and three kinds of branch tunnel locations (near to the spark plug/far from the spark plug/evenly distributed along the main tunnel), under the condition of the same tunnel volume (0.24 m3), initial fuel volume concentration (1.2%) and ignition energy (5 J). The maximum explosion overpressure pmax, the time to reach maximum explosion overpressure, the maximum rates of pressure rise (dp/dt)max, and the deflagration index KG were examined. Moreover, the effects of distribution form and location of branch tunnels on overpressure characteristics were discussed. Results show that explosion overpressure characteristics are strongly influenced by branch tunnels' distribution form and location. In terms of the symmetrical distribution, the maximum explosion overpressure, the maximum rates of pressure rise, and the deflagration index KG are the lowest among the three types of distribution forms of branch tunnel. Linear and staggered distributions have similar overpressure characteristics, whose explosion overpressure, maximum rates of pressure rise, deflagration index KG are 1.14, 1.52 and 1.52 times of those in the symmetrical situation respectively. Time to reach the maximum explosion overpressure and time to reach the maximum rates of pressure rise in the symmetrical situation are delayed, which are 1.31 and 1.30 times of those in the linear and staggered situations respectively. The maximum rates of pressure rise and the deflagration index KG descend in the following distribution locations: far from the spark plug, near to the spark plug, evenly distributed along the main tunnel. The results indicate that the farther the branch tunnel from the ignition end, the larger the explosion intensity index, and the closer the branch tunnel from the ignition end, the earlier the time to reach the maximum explosion overpressure rising rate.

Numerical and experimental study on the critical velocity and smoke maximum temperature in the connected area of branch tunnel

Numerical and experimental study on the critical velocity and smoke maximum temperature in the connected area of branch tunnel

Study on the Sedimentation of Power Branch Tunnel under Turbid Water Test

Combined with the actual project of a hydropower station, the turbid water test is used to verify the sedimentation of the power branch tunnel under the sand discharge conditions. The results show that under the sand discharge conditions, there are different degrees of siltation outside the recirculation zone of the power branch tunnels in the bifurcation section, and the siltation form is a delta siltation form. The sedimentation volume of the power branch tunnel is related to the sediment discharge flow in the sand discharge pipe. The greater the sediment tunnel flow, the greater the sedimentation in the cecum section of the power branch tunnel when the siltation balances.

Effects of transverse fire locations on flame length and temperature distribution in a bifurcated tunnel fire

In this paper, a series of experiments were conducted in a 1:10 reduced scale bifurcated tunnel to investigate transverse flame length and temperature field distribution under the ceiling with different transverse fire source locations. Five fire locations were considered and the corresponding distances (D) between the fire source centerline and sidewall are 0.1 m, 0.3 m, 0.5 m, 0.7 m and 0.9 m respectively. It is found that the predicted value by Gao’s model overestimates the ceiling jet flame extension length, thus a modified correlation considering the influence of the branch tunnel is established, which includes a sidewall and non-sidewall region. Moreover, a simplified equation for predicting the dimensionless maximum ceiling jet temperature by taking transverse fire locations into account is developed based on Ji’s model. Besides, the longitudinal temperature decay coefficient in the main tunnel ceiling shows a non-monotonous trend with D, exhibiting a maximum value at the condition for D is 0.3 m. However, there is a linear relationship between the longitudinal temperature decay coefficient and the ratio of the distance from sidewall and tunnel width. Meanwhile, based on Hu’s model, a revised formula for predicting the dimensionless longitudinal temperature rise by considering the effect of transverse fire location is established.

D.C. etching anode aluminum foil to form branch tunnels by electroless depositing Cu

Purpose The purpose of this study is to explore the mechanism of branch pits and tunnels formation and increase the specific surface area and capacitance of anode Al foil for high voltage electrolytic capacitor by D.C. etching in acidic solution and neutral. Design/methodology/approach Al foil was first D.C. etched in HCl-H2SO4 mixed acidic solution to form main tunnels perpendicular to the Al surface, and then D.C. etched in neutral NaCl solution including 0.5 per cent C6H8O7 and Cu(NO3)2 with different concentration to form branch tunnels normal to Al surface. Between two etching, Cu nuclei were electroless deposited on the interior surface of main tunnels by natural occluded corrosion cell effect to form micro Cu-Al galvanic local cells. The effects of electroless deposited Cu nuclei on cross-section etching morphologies and electrochemical behavior of Al foil was investigated with SEM, polarization curve and electrochemical impedance spectroscopy (EIS). Findings The results show that sub branch tunnels can form along the main tunnels owing to the formation of Cu-Al micro-batteries, in which Cu is cathode and Al is anode. With increase in Cu(NO3)2 concentration, more Cu nuclei can be electroless deposited and serve as the favorable sites for branch tunnel initiation along the whole length of main tunnels, leading to enhancement in specific capacitance of anode Al foil. Originality/value Cu nuclei were electroless deposited on the interior surface of main tunnels by natural occluded corrosion cell effect to form micro Cu-Al galvanic local cells, which can serve as the favorable sites for branch tunnel initiation along the main tunnels to enhance specific capacitance of anode Al foil.

Etching Anode Foil with Branch Tunnels for Aluminum Electrolytic Capacitors.

Al foil for high-voltage aluminum electrolytic capacitor was first D.C. etched in HCl-H₂SO₄ mixed acidic solution to form main tunnels and then D.C. etched in natural NaCl solution containing 0.1% H2C2O4 and different trace amounts of Zn(NO₃)₂. Between the two etching processes, Zn nuclei were deposited on the interior surface of the main tunnels by the natural occluded corrosion cell effect to form micro Zn-Al galvanic local cells. The effects of Zn nuclei on the cross-section etching and electrochemical behavior of Al foil were investigated using scanning electron microscopy, polarization curve measurement, and electrochemical impedance spectroscopy. The sub-branch tunnels can form along the main tunnels owing to the formation of Zn-Al micro-batteries, in which Zn is the cathode and Al is the anode. Increasing Zn(NO₃)₂ concentration increases the number of Zn nuclei that can serve as sites for branch tunnel initiation along the main tunnels, thereby enhancing the specific capacitance of etched Al foil.

The effect of P- and S-phase arrivals on the accuracy of microseismic source location

ABSTRACT In this paper, the conventional microseismic monitoring is classified into two types: body and line monitoring cases. And the phase arrival conditions are classified into three types: 1) Only including P-arrivals and P-picks being in error; 2) Both including P- and S-arrivals and P-picks being in error; 3) Both including P- and S-arrivals and S-picks being in error. Then the effect of P- and S-phase arrivals on the accuracy of source location is studied under six conditions. In body monitoring case, the location accuracy will be improved dramatically when S-picks are added. In line monitoring case, the convergence rate of location function is dramatically improved when S-picks are added. This kind of phenomena is called P-picks effect. Then a pair of mutually exclusive hypothesizes are put forward based on P-picks effect. And another set of numerical tests are designed to verify which one is true. The tests results show that the location accuracy and the iterative convergence rate of the objective function can be dramatically improved when S-picks are added. What's more, this effect cannot be offset by increasing P-picks. To understand this effect deeply, the location model is simplified further. The properties of location functions with or without S-picks are studied and compared. And the S-picks effect is analyzed mathematically based on the simplified location model and the properties of objective function. Two field data tests, 81,307# workface microseismic monitoring of Baode Coal Mine and 4# branch tunnel microseismic monitoring of Hanjiang-to-Weihe River Valley Water Diversion Project, are analyzed to verify the conclusion that the participation of S-picks can improve converge rate and location accuracy. In both cases, the location results with P- and S-picks are consistent with the rock mechanics theoretical results. Both of them confirm that S-picks are indispensable in source location.

Combining diverse driving forces for smoke control in complex urban traffic link tunnels (UTLTs) using one-dimensional flow modelling

Urban traffic link tunnels (UTLTs) could become increasingly more complex because they incorporate both looped main tunnels and multiple branch tunnels. In such a complex tunnel structure, smoke control in the event of fire becomes more difficult than that in conventional simple tunnels due to the enhanced flow interactions among various branches. Moreover, there are still no specific smoke control guidelines for such complex tunnels. Furthermore, the use of a single smoke control method could be inapplicable or even unaffordable in UTLTs because the complicity of the configuration and the interaction between the flow of different branches. In this paper, hybrid ventilation modes which combine diverse flow driving forces are proposed for smoke control in UTLTs. The hybrid modes could exploit the advantages of each of the constitutive modes. Three-dimensional numerical simulations are performed to show the benefits of combining diverse driving forces. Then, a one-dimensional flow modelling approach was employed to investigate the efficiency of three hybrid modes. The results demonstrate that proper matching of various driving forces is crucial for effective application of the hybrid modes. This paper provides a new route for UTLT smoke control and also demonstrates the advantages of one-dimensional flow modelling in such designs.

Nesting Biology of Xylocopa xinjiangensis (Hymenoptera: Apidae: Xylocopinae).

Xylocopa, an important genus in Hymenoptera: Apidae, is of great significance in research on the early stages of insect social evolution. Most species in this genus burrow into wooden structures. Only the Proxylocopa subgenus nests in the soil. Here, we report the nesting behavior of Xylocopa xinjiangensis (Hymenoptera: Apidae: Xylocopinae), which is distributed only in Western China. During July 2013 and August 2016, we observed the nest architecture and nest building process of X. xinjiangensis. X. xinjiangensis is solitary and nests in the soil walls of gullies, mounds, and cliffs in the Manas area, Xinjiang, multiplying at the rate of one generation a year. Newly emerged females eclose in the fall and build wintering nests first. The next spring, outbound wintering females build breeding nests, although a few wintering females may use the breeding nests built by their mothers. The location and structure of X. xinjiangensis wintering nests are different from those of the breeding nests. The wintering nest is simple in structure, consisting of a tunnel leading perpendicularly from the surface to the interior. The structure of the breeding nest may be either a branching tunnel or a straight-chain tunnel. The first cell that X. xinjiangensis builds in the breeding nest is closest to the entrance, which is a significant difference from the behavior of carpenter bees that construct nests in wood structures. The results of this study lay the foundation for the utilization and protection of X. xinjiangensis resources and facilitate a better understanding of the evolution of the Xylocopa population.

Tetrapod burrows from the Middle–Upper Triassic Chañares Formation (La Rioja, Argentina) and its palaeoecological implications

We describe tetrapod burrows from the uppermost Middle–lower Upper Triassic (latest Ladinian–early Carnian) Chañares Formation (Ischigualasto-Villa Unión Basin), La Rioja Province, northwestern Argentina. The burrows were found in different localities of the unit, but restricted to the lowermost 17 m of the formation. They occur at the same interval as a tetrapod assemblage composed of erpetosuchid and basal paracrocodylomorph pseudosuchians, basal traversodontid and chiniquodontid eucynodontians, and stenaulorhynchine rhynchosaurids. This assemblage differs from the typical Chañares fauna that occurs in stratigraphically higher levels. The burrows were found within the deposits of moderately developed palaeosols formed in volcanically-influenced braided fluvial facies under semi-arid climate conditions. The burrow systems are cylindrical to sub-cylindrical in cross-section, up to 25 cm in diameter, and characterized by long, multiple branching tunnels, several metres long, that meander horizontally or are slightly inclined (<30°), forming a complex network that is a result of passive fill of a previously open burrow. In general, these structures have a similar architecture and three-dimensional organization to those previously described from the upper parts of the Ischigualasto Formation in the same basin. It is hypothesised that some of these burrows were formed by small eucynodonts (e.g., basal traversodontids, chiniquodontids), and their co-occurrence with diverse, medium to large pseudosuchian predators (e.g., Luperosuchus, Tarjadia), suggests these non-mammaliaform eucynodonts would excavate burrows to live and avoid climate-stress conditions and/or predation. The new discovery of burrows in the Chañares Formation sheds light on the evolution of the palaeoecology of mammaliaform precursors during the dawn of the archosaur domain.

NEOICHNOLOGY OF SEMIARID ENVIRONMENTS: SOILS AND BURROWING ANIMALS OF THE SONORAN DESERT, ARIZONA, U.S.A.

Whereas soils in semiarid environments have received considerable attention, specific biogenic structures produced by the plants and animals that inhabit them are less well understood. Soils in a field site in the Santa Catalina Critical Zone Observatory in the semiarid Sonoran Desert of southern Arizona were investigated to develop a model to improve the interpretation of analogous paleosols and associated soil ecosystems in the geologic record. A flat plateau of desert scrubland was divided into thirty-six 4 m 2 plots for description and study. Field methods included mapping of soil surfaces, imaging with ground-penetrating radar, casting of open burrows, description of soil trenches, and soil coring. Laboratory methods included analysis of soil bulk geochemistry, clay mineralogy, and thin sections as well as detailed descriptions of burrow casts. Soils included 10–40 cm thick Entisols and Aridisols with blocky peds, pervasive, coarse (3–5 mm) to very fine ( 1 cm) diameter simple vertical shafts, isolated ovoid chambers, subhorizontal tunnels, subvertical to subhorizontal networks of branching tunnels, and complex branching galleries. Bioturbation was concentrated in the upper 20 cm of the soil profile, whereas roots often extended to the base of the profile. Results from this study advance our understanding of the traces produced by different soil organisms and their impact on soil development in modern settings and will be valuable for the interpretation of the paleosols from semiarid environments in the rock record.

Temperature profile of fire-induced smoke in node area of a full-scale mine shaft tunnel under natural ventilation

This paper investigated ceiling temperature profile of fire-induce smoke in the common node area of tunnels. The experiments were conducted in a full-scale mine shaft tunnel under natural ventilation with the node area consisted of a straight tunnel and two curved tunnels. Maximum ceiling temperature above the fire, transverse ceiling temperature along the elliptic ceiling and longitudinal ceiling temperature along the main and branch tunnels were measured by K-type thermocouples or thermometric cable. Dimensionless expression for predicting transverse and longitudinal ceiling temperature distribution was proposed based on previous models. Normalized expression of longitudinal temperature decay coefficients were correlated as well by taking the heat release rate and transverse fire locations under the elliptic ceiling into account. Then the results calculated by the proposed formula were compared with the experimental measured maximum ceiling temperature along the main tunnel and shows good agreement. Finally, effects of vertical wall and ceiling height on temperature decay trend in branch tunnels were investigated by analyzing the accumulation and descendant of smoke in front of the portals based on measured temperature data.

Numerical Analysis on Interaction Induced by Crosswise Tunneling

A position conflict exists between Harbin Urban Rail Transit Line No.1 and the branch tunnel of "7381" civil air defense tunnel. Intense tunnel interaction occurs when Line No.1 is perpendicularly tunneled across the branch tunnel. The investigation of the interaction is necessary. A 3D numerical simulation is established using FLAC3D and the vault deformation around the tunnel intersection is analyzed. The vault settlement of Line No.1 increases by 1.4 times during crosswise tunneling, while the vault settlement of branch tunnel increases 21.0mm in addition. The affected region of the tunnel intersection is further revealed. The affected length of the vault of Line No.1 and branch tunnel is 7.5 times the diameter and 6 times the width respectively. In combination with monitoring data, the reinforcement effect is studied at last. Both the vault settlement and surface settlement are well controlled in the tunnel intersection.

Modeling of a Transient Event in the Tunnel and Reservoir Plan System in Chicago, Illinois

Transient flow events can potentially damage infrastructure and threaten public safety in the vicinity of violent flow eruptions that occur where tunnel drop shafts interconnect with the surface-combined sewer system. Transient events have been observed in tunnels and at drop shafts in the tunnel and reservoir plan (TARP) system in Chicago on a number of occasions since operations first began in 1985. For the most part, the phenomenon has been controlled effectively by operating the system in a conservative mode through controlling the rate of filling. Nevertheless, more recently, not only water transients but also geysering events—the intermittent discharge of a combination of water and air from a hydraulic system—have occurred at the terminus of branch tunnels where controlled filling is not effective. The Metropolitan Water Reclamation District of Greater Chicago (MWRDGC), the operating agency for the system, has been prompted to develop engineering solutions to minimize transient flow occurrence and negative effects at the affected drop shaft locations. To this end, numerical modeling was conducted to investigate the cause and potential solutions. Such modeling included one-dimensional (1D) hydraulic transient modeling of a large domain in the system, followed by more detailed three-dimensional (3D) two-phase flow simulations within a smaller domain. The 1D approach revealed the interaction between localized events of interest and other transient flow features that originate far from the drop shaft under consideration. Computational fluid dynamics (CFD) modeling results show the complex interaction of trapped air and water in the tunnels. Even though more field observations are needed to test the accuracy of model predictions, careful interpretation of the results made it possible to pinpoint the problem and propose a solution. The findings also provided insight into the importance of considering both inertial instabilities as well as air–water interactions in geysering mechanics.

Burrow morphology and utilization of the goby (Parapocryptes serperaster) in the Mekong Delta, Vietnam

Some fish species living in mudflats construct burrows for dwelling and hiding. The goby Parapocryptes serperaster is a burrowing fish in mudflats of many estuaries in South East Asia. This study was carried out in the Mekong Delta, Vietnam, to examine burrow morphology and usage by this species. Morphology of the burrows constructed by P. serperaster was investigated by resin castings in situ to obtain the physical structure and configuration of each burrow. Fish from the burrows were caught and measured before burrow casts were made. Fish burrows comprised several openings, a few branching tunnels and multi-bulbous chambers. The surface openings were circular, and the shapes of branching tunnels were nearly round. The burrows had interconnected tunnels and various short cul-de-sac side branches. The burrow structure differed between fish sizes, but burrow dimensions were positively correlated with fish size, indicating that larger fish can make larger and more sophisticated burrow. The burrow structure and dimensions were not different between the dry and wet seasons. Laboratory observations showed that P. serperaster used body movements to dig burrows in the sediment. Burrows could provide a low-tide retreat and protection from predators, but were not used for spawning and feeding for this goby species. This study indicates that the burrowing activity of gobies is an important adaptation for living in shallow and muddy habitats.

Nest Site Selection and Nesting Behavior of the BeeLithurgopsis apicalis(Megachilidae: Lithurginae)

This paper reports on the biology of Lithurgopsis apicalis (Cresson) that were found excavating nests in the dead and dying flower/seed stalks of Agave in southern Arizona. Females normally gain entry to the soft inner tissue of the stalk by seeking out naturally occurring longitudinal cracks in the hard outer surface of the stalk. Once inside they chew branching tunnels through the soft plant tissue, at the end of which are one or more extremely elongate brood cells. The cells were normally found to contain one or more eggs, each in a small empty pocket entirely within the provisions of soft pollen, which completely filled the cell. The attachment of the egg to the provisions is described, as is the egg itself.The first four larval instars remain attached to the provisions while the elongate fifth (final larval) instar is free from the provisions and starts defecating while still eating the food, which gradually intermixes with fecal pellets. Toward the end of defecation, larvae start spinning strands of silk to form cocoons. After finishing spinning, larvae enter diapause, becoming quiescent over a period of more than a week. However, when in diapause, they still react to touch by curling and uncurling their bodies unlike totally quiescent diapausing larvae of most bees. Cocoon structure and function are described.Throughout the paper, aspects of nesting biology of this species are compared with those of other lithurgines. New details concerning the cocoon of Trichothurgus dubius (Sichel) are presented, and ovarian statistics for Lithurgopsis apicalis are appended.

Numerical Studies on Smoke Spread in Urban Underground Tunnel with Horizontal Junctions

Urban underground tunnels usually have lager traffic volumes and complex structures comparing with other kinds of tunnel. This can give higher fire risk and also make smoke control to become more difficult once the fire occurs. The effect of the fire size and intersection angle on the smoke spread and smoke mass flow distribution in underground urban tunnel with horizontal junctions are studied by the numerical simulation in this paper. The results show that the power size can affect the smoke spread heavily, but it has little effect on the smoke mass flow distributions between the downstream main tunnel and the branch tunnels. Variation of the intersection angle almost have an effect on the smoke spread in upstream main tunnel, but its effect on the smoke spread and smoke mass flow distributions in branch tunnel cannot be neglect. The results are expected to be useful for the smoke control system design in these kinds of tunnels.

MORPHOLOGY OF THE MUDSKIPPER’S BURROW (Boleophthalmus boddarti) IN SEMI-INTENSIVE FARMING

Boleophthaslmus boddarti is an amphibious fish inhabiting in mudflats. It also breathes air at the surface opening. The morphology of the blue-spotted mudskipper’s burrows is studied using resin casts of burrows in-situ. Burrows have several openings with “footprints” made by its pectoral fins, several branching tunnels and multi-bulbous chambers (i.e., dilated portions of the burrow). There is no mound in the structure of the burrows, but slightly sloping interconnected tunnels, and many short cul-de-sac side branches. The presence of these chambers accords with the fish adequate space to maneuver inside the burrow, and thus constant access to the surface. This study indicates that Boleophthaslmus boddarti actively processes sediments and uses its burrows as a feeding ground and shelter from predators. Keywords: Blue-spotted mudskipper, burrow morphology.

Explosions of gasoline–air mixture in the tunnels containing branch configuration

In order to investigate the effects of branch tunnels on explosion propagation, experiments were performed in five different configuration tunnels (straight configuration and configurations with 1 branch, 2 branches, 3 branches and 4 branches). Pressure and flame transducers were used to record the history of the pressure development and track the velocity of the flame front. It was shown that the branch tunnels had ability to enhance the maximum overpressure, rate of overpressure rise, and deflagration index (KG) of the gasoline–air mixture explosion due to the turbulence induced by the branch tunnels. The overpressure rise rate and KG of the explosion increased as a function of the number of branch tunnels. Experiments also showed that the maximum flame speed increased as the branch number increasing from 0 to 3 due to the enlargement of turbulence induced by the branch tunnels. However, an increase of branch number did not always lead to an enhancement of flame speed because the heat loss was intensified resulting from the increase of flame surface caused by the branch tunnels. When the number of branch tunnels exceeded 3, the maximum flame speed dropped.

Evolution of fractures in the excavation damaged zone of a deeply buried tunnel during TBM construction

This paper presents results of in situ measurements of fracture evolution within the excavation damaged zone (EDZ) surrounding the tunnel boring machine (TBM) excavated headrace tunnel No. 3 of Jinping II hydropower station, China. Fractures were measured by borehole images obtained with a digital panoramic borehole camera throughout the processes of tunnel excavation and support installation. Boreholes for the digital camera were pre-drilled perpendicular to the tunnel axis from a pre-excavated branch tunnel, and a series of digital images of the borehole walls were made as the TBM passed. Digital processing revealed the lithology, pre-existing fractures and characters of rock core discing of the surrounding rock mass. Processes of fracture initiation, propagation, and closure were observed, and width, occurrence and zoning of EDZ were measured. The relationship between fracture evolution and TBM construction progress is described in detail. Based on true triaxial tests and theoretical analysis of unloading conditions of deep rock masses, the occurrence of tunnelling induced new fractures at the EDZ is discussed with respect to in situ measurement results. The results provide valuable data for EDZ analysis, future designs and the construction of deeply buried tunnels using TBM.