Tunnel Shaft Research Articles

Deformation and Stress of Rock Masses Surrounding a Tunnel Shaft Considering Seepage and Hard Brittleness Damage

Deformation and Stress of Rock Masses Surrounding a Tunnel Shaft Considering Seepage and Hard Brittleness Damage

Bearing Capacity of a Concrete Grouting Pad on the Working Surface of a Highway Tunnel Shaft

A grouting pad is the key structure for the construction of water inrush grouting on the shaft working surface. Previous methods of calculating the bearing capacity have limitations due to a lack of understanding of the failure mode. To investigate the bearing capacity of a concrete grouting pad on the working surface of a shaft, this paper establishes a mechanical model for the punching shear failure of a grouting pad under symmetrical loading conditions. A unified solution for the bearing capacity is derived, and the influence of parameters is discussed. In addition, a new method for designing the plastic limit thickness is proposed based on this research. The results show that the reason for the grouting pads’ punching shear failure resulted from the formation of peripheral grouting holes “weak ring” caused by the reduction of the bearing capacity. When the thickness of B0 remains constant, the bearing capacity qu of the grouting pad is inversely proportional to the ratio of the diameter and the area of the bottom load. Therefore, following the method of “dividing, interval, and jumping holes” during grouting construction is recommended. The greater the thickness of the grouting pad, the greater the bearing capacity qu will be. When the grouting pad diameter is 2r2 and the thickness B0 is constant, the bearing capacity qu increases with the material tensile strength ft. When designing grouting pads, following the principles of “large thickness, uniform strength theory, high strength materials” will improve bearing performance. The findings have been implemented in the design of the grouting pad thickness for the Tianshan Shengli Tunnel shaft project, which can successfully solve the problem of frequent cracking caused by the weak bearing capacity of a grouting pad. The findings can provide a theoretical basis and reference for the design and construction of grouting pads in a highway tunnel shaft.

Jet grouting to new depths in the Lambeth Group and Thanet Formation beneath London

A jet grouting trial was undertaken within the Thames Tideway Tunnel shaft at Kirtling Street in Battersea, SW London, to assess the viability of the technique within the Lambeth Group and Thanet Formation sediments up to 60 m below ground level. There was no precedent industry experience of jet grouting in the UK at this depth and in these soil types. Four, separate, upper and lower grout columns were constructed respectively within upper and lower granular zones inside the shaft footprint, and then exhumed for inspection and measurement during ensuing excavation within the diaphragm wall lining. Target diameters for the upper columns were achieved within granular channel sand and Laminated Bed material, with minimal vertical deviation. These were not so successfully achieved, however, within stiff cohesive Laminated Bed and Lower Shelly Clay materials. Formation of the lower columns was severely restricted in dense gravel belonging to the ‘Pebble Bed’ and stiff gravelly clay, at the top of the Upnor Formation, but target diameters were being achieved in the lower portion of the formation, comprising Upnor sand. At their base, the column diameters were, again, restricted in the very dense sand at the top of the Thanet Formation.

Evaluation of the Additional Stress on Adjacent Tunnel Shafts Induced by Foundation Pit Excavation

Evaluation of the Additional Stress on Adjacent Tunnel Shafts Induced by Foundation Pit Excavation

Study on moving fire smoke characteristics and mechanical ventilation system of tunnel

Limited by the narrow space of the tunnel, fire has become one of the important factors threatening the safe operation of subway especially the fire on a moving vehicle. Researches on moving fire through the large length-width ratio of tunnels are extremely lacking at present. This study investigates the characteristics of moving fire and the influence of mechanical ventilation under different conditions. First, a three-dimensional model of the tunnel with the moving train is established, and the dynamic mesh simulation is conducted and validated by the experiments. Then, the variation of smoke temperature distribution under different fire source intensities, train speeds, and blocking ratios are studied. Based on the smoke flow characteristics, the mechanical ventilation with different layouts of draught fans is investigated. It is found that the maximum growth rate of smoke spread is 70.90% with an increase of two fans. Finally, the influence of the tunnel shaft on the smoke characteristics under different fire source locations is discussed. When the fire source is under the shaft, the smoke discharge efficiency reaches the highest, almost 5.89% and 21.91% higher than other conditions. This study provides the basis and reference for the research and control of the tunnel moving fire.

Construction Approach of Deep Mountainous Tunnel Shaft having Interlacing Surrounding Rock Grades

Construction Approach of Deep Mountainous Tunnel Shaft having Interlacing Surrounding Rock Grades

Influence of Ambient Pressure over Natural Smoke Ventilation in Shaft Tunnel Fire

This paper aims to disclose the influence of different ambient pressures over the smoke flow and smoke ventilation in the shaft tunnel. For this purpose, numerical simulations were carried out on the shaft tunnel, using Fire Dynamics Simulator (FDS), a computational fluid dynamics (CFD) software package. The results show that: Under the same fire power, the smoke of tunnel fire spread faster and faster, with the falling ambient pressure. The longitudinal temperature curves of tunnel fire have basically the same features, at different ambient pressures. With the increase of ambient pressure, the longitudinal smoke temperature on the roof of the shaft tunnel gradually declines. The declining rate is positively correlated with the proximity to the fire source. Compared with that in small power fire, the roof temperature difference between low pressure and normal pressure is large in large power fire. The CO concentration in the shaft falls with the rise of ambient pressure. The smoke ventilation efficiency is better in the low-pressure environment, which facilitates the ventilation of fire smoke. The increase of fire power enhances the horizontal inertial force of smoke, and reduces the probability of plug holing. In addition, the ambient pressure has a small effect on the shaft smoke ventilation in small power fire.

Mountain railway alignment optimization integrating layouts of large‐scale auxiliary construction projects

AbstractMountain railway alignment design is an important but complex civil engineering problem. To overcome the drastically undulating terrain, long tunnels and high bridges are major structures used along a mountain railway, which poses great challenges for railway design and construction. Unfortunately, despite being studied for many years, the crucial construction factors of complex structures have received slight attention in alignment optimization. In this paper, for the first time, the layout of large‐scale auxiliary construction projects (LACPs), including tunnel shafts and access roads, is incorporated into the alignment design process in order to consider construction practicability and economy. Primarily, an alignment–LACPs concurrent optimization model is built. After defining the comprehensive design variables, the alignment–LACPs total construction cost is formulated as the objective function. Besides, the separate constraints for designing the alignment and LACPs are considered. Also, a construction duration computation is proposed for constraining the alignment–LACPs integration. To solve the model, a four‐step hybrid solution method is developed. Specifically, the alignment is first generated with a particle swarm optimization (PSO). Afterward, a new divide and conquer approach is devised to search for shaft alternatives along the alignment. Then, a customized Dijkstra algorithm is developed to search for complex access roads. Finally, a novel polynomial mechanism for time‐varying acceleration coefficients (TVAC) is designed for PSO to evolve the alignment–LACPs solutions. The above model and methods have been applied to two complex actual mountain railway examples. Their effectiveness is demonstrated through detailed analysis of resulting railway solutions and control experiments with contemporary TVAC‐based methods.

Dynamic response of rock mass subjected to blasting disturbance during tunnel shaft excavation: a field study

Dynamic response of rock mass subjected to blasting disturbance during tunnel shaft excavation: a field study

Structural Stability Analysis of Concrete Lining in the Shaft–Tunnel Intersection Area of the Long-Distance Tunnel

Structural Stability Analysis of Concrete Lining in the Shaft–Tunnel Intersection Area of the Long-Distance Tunnel

Kajian Sistem Penyaliran Tambang Bawah Tanah Pada PT Allied Indo Coal Jaya Sawahlunto Sumatera Barat

PT Allied Inco Coal Jaya (PT. AICJ) is a company that work in coal mining industry. This research is done at underground mining located at main shaft tunnel at +347 metres above mean sea level (MASL) with 334,04 m in length with room and pillar method as its mining method. This research is using quantitative method. From the calculation obtained, the total of incoming water into the mining production area is 6.13 m3/hour. For the actual incoming from well is as much as 13.32 m3/hour with the total head is as big as 29.56 m, as the time needed to discharge is 6.45 hour. Making the dewatering layout design for the incoming water at elevation of +347.32 MASL to main sump at +318 MASL with total length of 201.6 m, while the water discharged at continuous pumping at elevation +306 MASL moving toward +347.43 MASL with total distance 341.32 m. with the addition to incoming water there is an increase in the pumping working hours so it is concluded that there is difference between the planned cost and actual cost of Rp. 832,269.96.

Safety Evaluation of Super Deep Shaft Construction of Donghu Deep Tunnel in Wuhan

With the rapid development of infrastructure construction in large and medium-sized cities in China, the development and utilization of underground space has been developed rapidly. The sewage transmission system engineering of Donghu core area in Wuhan is faced with the construction of shaft under smaller section, deeper foundation pit and more complex environment. The safety of super-deep shaft construction is evaluated and the important risk influencing factors are identified. From the point of view of construction process and method, this paper identifies and constructs the evaluation index system of safety risk in deep tunnel shaft construction, and then constructs the evaluation model with binary semantics and AHP and entropy weight method. Finally, the empirical analysis is carried out through the example of Wuhan East Lake deep tunnel project. The empirical results show that the foundation pit support, water stop curtain, wellhead instability, vertical ventilation of shaft and rock entry blasting are the factors that affect the construction safety risk of the project, and the construction safety risk evaluation grade of the project is low. This paper also puts forward effective measures to improve the construction safety of the project.

The Shaft Tunnel of the Biar aqueduct of Jerusalem: Architecture, hydrology, and dating

AbstractThe Biar aqueduct is the most sophisticated of the aqueducts supplying water to Jerusalem during classical periods. It includes the Biar spring, an underground Shaft Tunnel ∼3 km long harvesting groundwater (cuniculus), a dam, a surface channel, and a tunnel traversing a ridge. We conducted a survey of the Biar underground Shaft Tunnel, mapping all of its accessible parts (∼1200 m), facilitating a new understanding of the cutting‐edge hydrogeologic and engineering skills used for this project. The last ∼536 m of the Biar Shaft Tunnel was constructed with a unique ashlar channel, divided into segments, designed to withstand different loads: (a) in a mechanically weak bedrock, a channel with arched gables and barrel vault specus was built within a hewn winding tunnel, (b) when dug as an open shallow trench, a channel roofed with complex gables of ashlars with drafted margins was built, and (c) to release hydraulic pressure, a channel roofed with alternations of barrel vaults and simple gables set perpendicular to the course of the tunnel was constructed. 14C dating of plaster samples suggests that the Biar aqueduct was built in the mid‐first century CE and renovated in the days of Aelia Capitolina in the second century CE.

Monitoring and Analysis of Subway Shaft Construction Displacement

According to the construction site monitoring of a subway tunnel shaft in Beijing, the deformation laws of surface settlement, horizontal displacement and vertical displacement of retaining structure during shaft construction were analyzed. The results show that: firstly, the ground settlement around the shaft can be divided into two stages, the rapid settlement stage before the floor construction and the stable settlement stage after the floor construction. The settlement rate and value of the middle point of the long side of the shaft is faster and bigger than the corner point and the middle point of the short side. The settlement value first increases and then decreases with the increase of the distance to the pit side. The maximum settlement is located at (0.61 ∼ 1) times the excavation depth behind the diaphragm wall. Secondly, the horizontal deformation of the long side of diaphragm wall is obviously different from the short side. The horizontal deformation of the long side is larger than the short side, and the position of the maximum horizontal deformation is deeper than the short side. The horizontal deformation curve of the middle point of the long side has obvious inflection point, and the middle point of the short side presents reciprocating type. The variation range of horizontal displacement of diaphragm wall top is between 10 mm, and the maximum horizontal displacement is 0.037% of shaft depth. Finally, the vertical displacement of the top of the diaphragm wall settles rapidly before the excavation of the bottom plate, and the settlement value decreases gradually after the excavation, and the increase rate of the diaphragm wall settlement is the largest when it is excavated to the bottom of the shaft. This deformation law can provide reference for the optimization of support design of similar projects.

A Study on the Dynamic Behavior of a Vertical Tunnel Shaft Embedded in Liquefiable Ground during Earthquakes

Since liquefaction was first observed in South Korea during the Pohang earthquake, public concerns regarding the seismic stability of major infrastructure have increased substantially. However, the seismic behavior of tunnel shafts, which are an important element of tunnel structures, has not been properly established, especially under liquefiable soil conditions. In this study, 3D numerical modeling with Fast Lagrangian Analysis of Continua in 3 Dimensions (FLAC3D) was performed to predict the dynamic behavior of a vertical tunnel shaft during liquefaction. This study demonstrates key aspects of the dynamic behavior of tunnel shafts by varying important parameters such as the thickness of the liquefiable soil layer and applied seismicity level. Moreover, important dynamic responses such as excess pore pressure generation, the seismic bending moment of the shaft, and lateral displacements are highlighted. Finally, meaningful discussion of the seismic risk analysis based on damage indices is conducted based on the analysis results.

A Combined Support System Associated with the Segmental Lining in a Jointed Rock Mass: The Case of the Inclined Shaft Tunnel at the Bulianta Coal Mine

This paper presents a case study on the impact of jointed rock mass deformation on liner stability for an inclined excavation at the Bulianta Coal Mine. The tunnel was excavated by a single shield tunnel boring machine (TBM), with part of the excavation passing through a heavily jointed rock mass at great depth. Serious local instabilities occurred at one side of the liner due to highly asymmetric loading caused by large ground stresses and joint deformation. A support system with anchored cables and compressible mortar was combined with segmental lining to overcome these instabilities. With this case as a baseline, some numerical sensitivity analyses were performed to study how the ground might have responded to different combinations of support. The results show that an appropriately anchored cable system was able to limit the propagation of the asymmetric deformation of the jointed rock mass and significantly reduce the degree of anisotropy and the magnitude of the loads on the liner. The use of compressible mortar between the liner and the jointed rock mass further lowered the anisotropy of the load on the liner. There are optimum values for the rock bolt length and the compressible mortar thickness, beyond which these parameters have limited effects on the behaviour of the system. The combined effect of compressible mortar and anchor cables in promoting ground and liner stability is greater than the sum of the two individual support effects. These results clearly demonstrate that the combination of anchored cables and compressible mortar had a significant positive effect on the overall support system stability.

Study on Reasonable Combination of Retaining Structure and Main Structure for Tunnel Shaft in the Offshore Environment

Through the investigation, the design of the combination of the retaining structure and the main structure of the large-diameter shield shaft was summarized. Combined with the characteristics of the offshore shaft, considering the difficulty in implementing underwater pouring of high-grade underground diaphragm wall, through reasonably analyzing the characteristics of chloride environmental corrosion, a reasonable solution of supporting the temporary diaphragm wall to participate in anti-floating action is proposed. For the strictness of crack control in the chloride environment, it is proposed to use the frame beam as the purlins in the excavation stage, and the waterproof problem of the construction joint is better solved. Finally, the three-dimensional calculation results confirm the stress of lining wall is reasonable.

A smoke exhausting method through a baffle-coupled shaft during tunnel fires

In natural ventilation of road tunnel shaft, the plug-holing and boundary layer separation will decrease the efficiency. A new concept (baffle-coupled shaft) is put in place to solve the difficulty. Install baffle on both sides of the shaft (when the fire occurs upstream of the shaft, the baffle upstream of the shaft closes and the baffle downstream of the shaft opens), in the early stage of the fire, it can function as a smoke barrier. Numerical simulation was performed using the Fire Dynamic Simulation (Version 5.5.3). We use the mass flow of carbon monoxide discharged through the shaft as a basis for evaluating the efficiency of exhausting smoke. We could have determined that with the height of the baffle increasing, so does the efficiency of exhaust. In the investigation, the height of urban road tunnels is generally about 5 meters. So, it is appropriate to set the baffle height to 2m. Comprehensive car capacity, economy and cold air distributed, we can get a better He, that is in 1.0-1.5.

Remote-control technology performance for excavation with pneumatic caisson in soft ground

The pneumatic caisson method is applicable to various ground conditions and has competitive advantages in deep excavations. However, in the conventional pneumatic caisson, workers are at risks of suffering from decompression sickness because of long-duration exposure to the hyperbaric environment. Furthermore, the construction cost of the conventional pneumatic caisson is fairly high owing to the inefficiency and labor redundancy. To address these issues, an automatic construction system for the pneumatic caisson, which enables unmanned excavations based on a remote-control technology, has been developed. This system mainly comprises a remotely operated excavator, a vertical screw conveyor for continuous soil discharge, and an integrated real-time monitoring system. Additionally, a program named “NPC (new pneumatic caisson) Manager” is adopted for the comprehensive analysis of real-time monitoring data. This paper describes the details of this system and its execution process, in which all the work of excavation and removal of soil is completed remotely by workers on the ground. Moreover, an application in a tunnel shaft in soft ground, as well as an analysis of its monitoring results, is also presented.

Safety Risk Assessment of Highway Tunnel Deep Shaft Construction

Construction process conversion of highway tunnel deep shaft is complex, little experience in design and construction, the construction process there is a big safety hazard. In the current there is no corresponding guideline and norm basis for domestic shaft construction risk assessment, and there are few researches on the safety risk assessment of highway tunnel shaft construction. Based on the investigation and analysis, this paper for a highway tunnel deep shaft engineering establishes risk assessment index systems and methods for the wellhead instability risk and the high-altitude fall risk of hoisting system, obtains the safety risk grade of the above two risks, and puts forward targeted risk control measures. These results provide a reference for similar risk assessment projects in the future.