|Theme||Visible||Selectable||Appearance||Zoom Range (now: 0)|
This study considers a blunt trailing-edged propeller operating both in a uniform and a nominal wake fields. Experiments are performed in the cavitation tunnel of Hyundai Maritime Research Institute. The effects of propeller rotation speed, tunnel flow speed, and blade sheet cavitation growth on the generation mechanism of the singing propeller are investigated. The cavitation, sound, and vibration characteristics related to the singing phenomena are measured by a hydrophone, a microphone, an accelerometer, and a high-speed digital camera. The natural frequencies of propeller blades are predicted using a finite element method and verified by both contact- and noncontact-type impact hammer tests in air and underwater conditions. The inflow speed and angle of attack for each section of the propeller blades are calculated using the Reynolds-averaged Navier–Stokes equation– based flow analysis. Using a detached eddy simulation, the vortex shedding patterns and their frequencies are calculated. The predicted vortex shedding frequencies are compared with the measured singing frequency and blade natural frequency for determination of consistency. Under cavitation-free regime, the vortex shedding frequencies are predicted for normalized blade radial positions of .8R and .9R. The computed values are close to the two blade natural frequencies and also consistent with the double singing phenomena in the cavitation tunnel test. For fully developed blade sheet cavitation condition, the vortex formation in the wake region is observed to be strongly influenced by the cavitation growth on the pressure side surface. Propeller singing is diminished with the continuous growth of cavitation and is finally locked-off. The significant variation of the flow-induced sound and vibration levels are also observed for the locked-in and the locked-off conditions. The singing occurrence location and frequency under uniform inflow condition are analyzed to investigate the generation mechanism of propeller singing. This study can be applied to the analysis of singing location and its frequency of a propeller operating in the hull wake, which changes the angle of attack according to the propeller rotation angle.
Acid tunneling is an acid-jetting method for stimulating carbonate reservoirs. Several case histories from around the world were presented in the past showing optimistic post-stimulation production increases in openhole wells compared with conventional coiled-tubing (CT) acid jetting, matrix acidizing, and acid fracturing. However, many questions about the actual tunnel creation and tunneling efficiency are still not answered. In this paper, the results of an innovative full-scale research program involving water and acid jetting are reported for the first time.
The tunnels are constructed through chemical reaction and mechanical erosion by pumping hydrochloric acid (HCl) through conventional CT and a bottomhole assembly (BHA) with jetting nozzles and two pressure-activated bending joints that control the tunnel-initiation directions. If the jetting speed is too high and the acid is not consumed in front of the BHA during the main tunneling process, then unspent acid flows toward the back of the BHA and creates main wellbore and tunnel enlargement with potential wormholes as fluid leaks off, lowering the tunneling-length efficiency.
Full-scale water- and acid-jetting tests were performed on Indiana limestone cores with 2- to 4-md permeability and 12 to 14% porosity, sourced from the same supplier. Many field-realistic combinations of nozzle sizes, jetting speeds, and casing pressures were included in the testing program. The cores were 3.75 in. in diameter × 6 in. in length for the water tests and 12 in. in diameter × 18 in. in length for the tests with 15-wt% HCl acid. The jetting BHA was moved as the tunnels were constructed, at constant force on the nozzle mole, to minimize the nozzle standoff. Six acid tests were performed at the ambient temperature of 46°F and two at 97°F. The results from the acid tests show that the acid-tunneling efficiency, defined as the tunnel length divided by the acid volume, can be optimized by reducing the nozzle size and pump rate. The results from the water and acid tests with exactly the same parameters to match the actual CT operations in the field show that the tunnels are constructed mostly by chemical reaction and not by mechanical erosion. The acid-tunneling efficiencies obtained from the full-scale acid tests are superior to the average tunneling efficiency of more than 500 actual tunnels constructed during more than 100 acid-tunneling operations performed to date worldwide. Although the tunnel lengths and acid volumes for the actual tunnels constructed during the previous acid-tunneling operations were recorded by the service company performing those operations, little downhole temperature and formation characterization data were provided by the operators to the service company. Thus, the downhole-temperature and formation-characterization effects on the acid-tunneling efficiency for the previous field operations are unknown.
In this paper, we describe the full-scale water- and acid-jetting tests on Indiana limestone cores. The major novelty of this test program consists of performing all measurements with casing pressure, unlike all previous water- and acid-jetting studies performed at atmospheric conditions and reported in the literature, which is closer to the field conditions during CT operations. The novel understanding of the combined effect of the nozzle size, pump rate, and casing pressure significantly improves the actual acid-tunneling efficiency.
Drilling and blasting operation has been widely adopted for underground excavation of deep tunnels in hard rock. In this process, the rock mass is broken by the blasting-induced loads. The formation and evolution of blasting-induced damage zone around tunnel is, therefore, inevitable due to the initiation and propagation of cracks. There exist several factors affecting the outcomes of blasting. For instance, the effects of in-situ stresses on the results of tunnel blasting in deep hard rock have not been well investigated yet. In this study, the smooth blasting in the bench of TASQ tunnel at the Äspö Hard Rock Laboratory (HRL) is modelled by means of a powerful GPGPU parallelized hybrid finite-discrete element method, from which the rock fracture and fragmentation process, the stress redistribution induced by blast wave propagation and gas expansion, and the damage zone around the tunnel are analysed. The proposed method is characterised by the simulation of the transition from continuum to discontinuum in the surrounding rock mass, the decay pattern of blasting pressure exerted on the blasthole wall, and the gas expansion through the blasting-induced cracks. The numerical simulation results indicate that the in-situ stresses play an important role in the fracture propagation pattern around the tunnel. This study reveals the importance of understanding the mechanism of the blasting-induced fracture propagation under the influence of in-situ stresses in order to minimize the evolution of damage zone around a tunnel in practical drilling and blasting operations.
Drilling and blasting is regarded as one of the most efficient approaches for breaking rock masses and for tunnelling in hard rocks at deep depth. However, in this process, the rock damage zone around tunnel due to the blast loading and in-situ stress redistribution is unavoidable, which draws attention in engineering fields. Considerable efforts have been dedicated to investigating these mechanisms of breakage in hard rocks. For instance, a number of field investigations in the Hard Rock Laboratory (HRL) in Sweden and the Underground Research Laboratory (URL) in Canada were conducted by some researchers (Ouchterlony, 1997; Martino and Chandler, 2004; Olsson et al., 2004; Kuzyk and Martino, 2008), from which the rock damage patterns around tunnel under various conditions were observed and assessed. Moreover, in the past few decades, many studies chose to implement numerical simulation approaches in modelling and analysing the blasting-induced rock damage behaviour around tunnels and underground excavations. The rock displacement, stress state redistribution, and damage expansion around a tunnel induced by blasting can be simulated using finite element method (FEM) and finite difference method (FDM) (Saiang and Nordlund, 2009; Wang et al., 2009; Yang et al., 2017). To further investigate the discontinuous behaviour of rock during the blasting process, distinct element method (DEM) and discontinuous deformation analysis (DDA) have been adopted by a few researchers (Cai, 2008; Jonsson et al., 2009; Saiang, 2010). However, the transition from continuum to discontinuum in rocks and the corresponding fracture and fragmentation process during blasting process are worth studying, considering their importance in revealing the internal mechanism of blasting-induced rock damage. In terms of numerical simulation, hybrid finite-discrete element method is capable for replicating such complex mechanisms of dynamic fracturing in rock masses.
Xiao, Yong-gang (School of Civil and Resource Engineering) | Li, Chang-hong (School of Civil and Resource Engineering) | Wang, Yu (School of Civil and Resource Engineering) | Hu, Yong-yue (School of Civil and Resource Engineering)
The delayed rockburst will cause great damage to the deep rock mass engineering, and the long-term stability of the surrounding rock of the deep hard rock tunnel is closely related to the occurrence of the delayed rockburst. In order to study the influence of the excavation sequence of deep hard rock multi-tunnel on the long-term stability of surrounding rock, this paper takes the diversion tunnel of Jinping II Hydropower Station as the engineering background, and establishes a numerical model to analyze the impact of delayed rockburst in three different excavation conditions The three working conditions are: simultaneous excavation, interval excavation and sequential excavation. The results show that the surrounding rock stress shifts to the outside after tunnel excavation. The stress concentration of the first principal stress occurs about 2m from both sides of the tunnel. Under the condition of simultaneous excavation, the stress concentration range is the largest, and the first principal stress value at the stress concentration is also the largest. The interval excavation working condition is second, and the sequential excavation working condition is the smallest; the analysis of the plastic zone range shows that it has the largest plastic zone volume according to the working condition 1, the working condition 2 is second, and the working condition 3 is the smallest. Combined with the numerical analysis results and the actual construction speed on site, it is recommended to use the interval excavation method for multi-tunnel excavation, which is beneficial to reduce the risk of delayed rockburst while increasing the construction speed. At present, the research on the time effect of rock mass mainly focuses on the weak rock with significant rheological properties. This paper studies the time-dependent deformation and failure of surrounding rock in deep hard rock tunnel, which has certain significance for the support design of deep rock mass engineering and the study of diverticulum stability.
TBM (Tunnel Boring Machine) is widely used in tunnel construction. As the key component of TBM, disc cutters show rapid wear and frequent failure when TBM excavating in hard rock. Many studies have been delivered to clarify the mechanism and predict the normal wear rate of disc cutters but unable to recognize the abnormal failure such as cutter chipping. In this paper, the characteristics of cutter chipping is analyzed based on field investigation at first. The field statistics of YHJW project show that gauge cutter is most vulnerable to chipping, followed by center cutter, and the face cutters are replaced mainly because of normal wear. Rock property, initial state of disc cutter, penetration rate of disc cutter and characteristics of cutter's movement are the four basic influencing factors of cutter chipping. The results indicate that (1) the ratio of cutter chipping increases with the increase of rock strength; (2) initial wear on the surface of the cutter ring and usage of old bearings lead to most of the cutter chipping; (3) the higher the penetration rate of disc cutter is, the higher the probability of cutter chipping is. When the penetration rate of disc cutter reaches 0.3mm/s, the probability of cutter chipping could be 40%; (4) the existence of both sliding and rolling makes the cutter ring in a disadvantageous stress state. The larger the sliding part is, the more serious the cutter chipping is. Further research is still needed to study the mechanics mechanism and micro-evolution process of cutter chipping.
With the increasing demand for deep-buried long tunnels, TBM tunneling in hard rock is becoming more and more frequent. The disc cutter wears fast and abnormal damage occurs frequently due to the tremendous pressure when propelling the rock and the friction with the cutting face. Increased number of cutter replacement leads to increased costs and reduced tunneling time.
The tunnel construction in a densely populated city requires tunneling below or near to sub-surface structure or foundation of existing structures. The design of these tunnels requires the study of interaction of tunnel excavations driven underground with the ground surface. The day-to day practice is based on experienced based thumb rule and linear analysis. This provides very limited information for understanding the interaction. This article presents the analysis of effects of two tunnels driven in soft rock on the surface settlement using 2D finite element analysis. The numerical results are compared with the field observation and empirical relations.
In the course of study, parameters varied during analysis were spacing between the tunnels, orientation alignments of tunnels, size of tunnel, ground properties and in-situ stresses. The observation of surface settlement has been made with respect to these parameters. The effect on zone of plastic strain has also been studied to understand behavior of failure in soil. The finite element analysis results are compared with the results obtained from four different software.
The increase in population and growth of city has pushed the need to shift various facilities underground to create space on ground surface available other basic utilities which can be shifted underground. Need is the source of innovation and innovation brings in new challenges to be dealt with. One of the challenges that modern tunneling industry has brought to us is ground movement upon earth excavation. Which in turn effects the existing structures nearby the tunnel alignment. The challenge is more critical in densely populated regions of city beneath which the tunnel passes. A huge care is required to be taken during excavation process and regular monitoring of tunnel convergence is part of it even then the tunneling induces ground settlement despite all the protective measures adopted for the controlling the volume loss during tunneling. In this paper a study is presented showing method of pre-estimation of ground behavior due to excavation of twin tunnels.
Lee, KhyeKeat (Civil engineering technology division) | Tagawa, Hiroaki (Civil engineering technology division) | Azman, AlAdzamShah (Civil engineering technology division) | Awaji, Dohta (Civil engineering technology division)
Conventional tunneling (NATM) in urban environment is always a challenge where surrounding buildings or structures are sensitive to settlement even though ground improvement usually serve as solution. In this case study, ground improvement from ground surface was not able to be carried out due to existence of multiple underground utilities. With mentioned restriction, chemical grouting was applied inside the tunnel during excavation. However, huge water inflow was encountered, and water table drawdown caused severe settlement within days. Additional chemical grouting was applied to refrain further settlement with continuous excavation. After the completion of excavation with water plugged off, water table recovered and 1/3 of settlement recovered. As a result, the effective conventional tunneling in urban environment is to limit water inflow and shorten the exposure period of the ground.
When tunneling in urban environment, minimizing settlement and prevention of damage on surrounding buildings, structures, roads and underground utilities is always the top priority. Ground improvement is commonly carried out beforehand and usually from the surface. In this paper, cross passages between main line were required for emergency purpose for Thomson-East Coast Line as shown in Figure 1. The cross passages will connect to main, Adit tunnel and finally to escape shaft, while both cross sections and Adit were excavated by New Austrian Tunneling Method (NATM). The effectiveness of various measures for conventional tunneling in urban environment shall be discussed.
In Contract T207, 48m Adit tunnel which connect the main tunnel and escape shaft 1 (ES-1) is an important exit passage for emergency purpose. The geology consists of sandy SILT of GV-GVI Bukit Timah GRANITE (SPT:20-30) with shallow overburden (approximate 14m) and proximity with water reservoir. Adit tunnel could be excavated by NATM within settlement limit with the existing properties. However, as precaution measure, ground improvement by Jet Grouting Piling (JGP) from surface to eliminate the possibility of unexpected water ingress.
In the present study, a return mapping algorithm is formulated for an elasto-plastic swell model based on the Modified Cam-Clay(MCC) model, which can show the soft/hard behavior of swelling process by applying the finite element method (FEM). Several simple numerical examples are used to assess the efficiency and convergence of the formulation of the return mapping algorithm. This study is contributed to predicting the nonlinear mechanical response of the tunnel constructed in swelling rockmass, which contains the stress redistribution of the tunnel after excavation and the soft/hard response caused by swelling process. The numerical simulation will show the swell deformation, strain path and stress history of a tunnel which ground masses has occurred the process of water-absorption, aimed at evaluating the stability of a tunnel constructed in swelling rockmass after some years.
In recent years, a problem that ground expansion by swelling clay minerals destroys the roadbed of a mountainous tunnel has occurred in various regions in Japan. The heave of tunnel invert caused by swellable minerals will seriously affect the normal operation and endanger the structural safety of the tunnel, and therefore, it is very important to make appropriate predictions of the mechanical behavior of the tunnel for the support system design and maintenance.
The expansion comes with the process of water-absorption between layers of these clay minerals (Grim, R.E., 1968). In addition, it is reported that the hygroscopic expansion, which is based on a thermo-chemical phenomenon, degrades the stiffness of the ground as the swelling clay minerals interact with surrounding intact rock (Luc Massat et al. 2016). The complicated mechanical behavior of the ground involving swelling clay minerals comes from a kind of phenomena based on multi-physics, due to the hygroscopic expansion. Although it should be to simulate the complicated behavior theoretically in terms of multi-scale/multi-physics analysis which considered the thermo-mechanics with chemical reactions, no applicable model has yet to be developed in practice.
Mori, Fumiaki (Tokyo Electric Power Company Holdings) | Morioka, Hiroshi (Tokyo Electric Power Company Holdings) | Tsuruta, Shigeru (Tokyo Electric Power Company Holdings) | Yamauchi, Masaru (Tosetsu Civil Engineering Consultant)
To conduct inspections in water-way tunnels of hydroelectric power plants, staff usually walk through the tunnel after discharging the water. However, this takes labor and time, and the losses through the generation outage due to the cut-off of the water supply are also considerable. Therefore, we developed a floating device equipped with video cameras. It takes videos of all around the walls, including underwater, without having to discharge the water. It does not require manual operation, and is much safer than the usual inspection method.
To take clear videos, the most important factor is to stabilize the posture (direction) of the device floated down the water-way, because it is easily rotated due to turbulence flow caused by changes in the cross-sectional shape and the surface friction. We focused on the difference in the flow velocity in a cross-section of the water-way. In order to use these hydraulic characteristics, we introduced a Parachute Anchor and Stabilizer Tail for the posture control mechanism. Thanks to this simple control mechanism, there is no need for difficult settings or operation, and no risk of electrical trouble.
It is possible to output a development diagram of all around the walls via pattern matching and image synthesizing. Deformation can be easily detected, so it is possible to extend the intervals between waterway tunnel inspections that include water discharge. As a result, we expect a reduction in losses through generation outages caused by inspections, a reduction in staff burdens and much greater safety during unplanned inspections after a disaster.
Tunnel structures become deformed or cracked due to ground pressure or deterioration of support members, even after completion. If these deformations become large, the wall may peel or fall off. This can cause serious accidents in road and railway tunnels and overflows in water-way tunnels due to water-way blockage. For this reason, maintenance managers need to understand the soundness of the tunnel structure and strive to maintain performance and prevent accidents.
To conduct inspections in a water-way tunnel, staff usually walk through the tunnel after discharging the water. Since the water supply cut-off period last several days including the charge-and-drain time, frequent water-way tunnel inspections are inadvisable from an economic loss perspective. In order to reduce economic losses, it is necessary to establish an efficient inspection method through technological development.
In a conventional tunneling under large overburden and accordingly high ground stress conditions, tunnels often suffer from large ground deformation especially when the ground strength and stiffness are insufficient. In Japan, stiff and heavy support systems with ring closure are often constructed as close to the excavation face as possible for overcoming such difficult conditions. One of the heaviest systems is, so called, “double-layer support system”. In Austria and Switzerland, on the other hand, “ductile support system”, which flexibly follows the large ground deformation, has been developed for 20 years and commonly used as a support system for squeezing ground. Instead of the double-layer system, the ductile method could be used and could be economical since it doesn't require the second support layers resulting in less construction materials and procedures. This study aims to investigate the applicability of the ductile support system and its cost advantage against the double-layer support system in squeezing ground conditions in Japan. In detail, given the poor ground conditions in two tunnels where the double-layer support systems have been actually applied, the support systems with both design concepts are studied by means of Convergence Confinement Method (CCM). As a result, it is found that the ductile support system with several yielding elements can ensure enough stability. In addition, the ductile support system could reduce the material cost by more than 30 % in those cases.
A conventional tunneling method, in which ground surrounding the tunnel is supported by shotcrete and rock bolts, is called NATM in Japan and in some Alps neighboring countries. However, the design and construction concept of support system seems to be quite different in squeezing ground conditions.
Japanese standard specifications for tunneling describes that stiffer support members than usual should be installed in such difficult conditions, and they should be closed with the invert as close to the face as possible (JSCE, 2007). These measures are recognized as the method preventing ground from excessive loosening of ground around the tunnel and thus restraining ground deformation. Due to early ring closure, the tunnel displacement could be constrained, but the support system might be overloaded leading to buckling of steel support and/or cracks of shotcrete lining. To ensure the tunnel safety in such unfavorable member failures, “double-layer support system” has been applied in recent tunneling projects in Japan where first layer with shotcrete and steel support is overwrapped by the second layer.