Assessment of support system for tunnel excavation in highly squeezing fault zone conditions

Nowadays, most designs of tunnel excavation are manual, and the designs have a poor quality and slow speed. To solve these problems, the component and structure of blasting design system of tunnel excavation based on CAD technology are studied. On the basis of comprehensive analysis and influence factors, a basting CAD auxiliary system based on ActiveX interface and VBA interface technology is developed for blasting design about tunnel excavation. Some function modules, including system management, arrangement design of hole, construction design, parameter calculation, blasting data and construction information management, can meet the demands of system function. A design of blasting example of tunnel excavation shows that the system can carry out blasting design with high speed accurately. The design can also avoid the dependence of personal experience. Meanwhile, the work of blasting design becomes more reasonable. Design results can be reliable and practical. Further, the system has some advantages, such as high speed and excellent transplantation. The system has positive significance for economic benefit of coal production.

Deep excavation is a critical aspect of construction projects that involve building foundations, tunnels, basements, or other below-grade structures. Ground anchors are a load transfer system designed to transfer the forces applied to it to a competent stratum, commonly used to support temporary excavation support system for deep basement excavation. By using ground anchors, the need for installing temporary struts can be eliminated and so congestion in basement construction can be significantly reduced. Ground anchors are also very suitable for sites on which flying/corner struts system are difficult to be installed. For ground anchors used in private development projects in Hong Kong, the temporary perimeter piles wall are usually constructed along the lot boundaries and so unavoidably the temporary anchors are required to be installed beyond the lot boundaries and encroached upon government land. In the past, the ground anchors were unavoidable to be left-in-place below ground upon completion of basement construction. Advancements in the ground anchor technology include the development of a load distributive compression type removable anchor which offers a complete solution where anchorage systems can be easily removed once they become redundant. The use of removable ground anchors has been gaining popularity gradually because they are not required to be left-in-place below ground. This paper presents the technology behind and shares the experience of using a proprietary product of load distributive compression removable anchors in a deep basement excavation project in urban area of Hong Kong. Apart from that, the details and experience of using another type of single bore multiple anchors, which are also load distributive compression removable anchors, used in previous deep basement projects are shared. This paper presents the technology behind and shares the experience of using a proprietary product of load distributive compression removable anchors in a deep basement excavation project in urban area of Hong Kong. Apart from that, the details and experience of using another type of single bore multiple anchors (SBMAs) which are also load distributive compression removable anchors used in previous deep basement projects are shared.

The excavation of the Semmering Base Tunnel (SBT) through fault zones under high overburden presents significant challenges, especially when these zones transition directly into a highly water‐bearing formation with groundwater pressures of up to 10 bar. Excavation under these conditions demands advanced tunnelling and support measures. To permanently reduce groundwater inflow, extensive pre‐excavation grouting was implemented to enhance the rock mass properties within the fault zone and reduce the permeability of the adjacent carbonate rock. Systematic exploratory drilling revealed a complex sequence of geological units at the transition zone from fault zone into the water‐bearing carbonate formation. As a result, grouting umbrellas with borehole lengths of up to 100 m were installed. Large‐scale face instabilities within the fault zone required further adaptations of the tunnelling and grouting measures. Among other measures, geotechnical monitoring was significantly expanded, as the tunnel passes beneath a motorway and an anchored retaining wall located approximately 160 m above the tunnel crown.

The problems experienced in tunnels excavated under high cover in graphitic schists generally vary according to the squeezing mechanism. During the tunnel excavation, slips occur on the slickenside surfaces in the tunnel face from time to time and collapse occurs. Most of the time, failures in the support systems are observed due to the squeezing mechanism in the long term in the sections whose tunnel excavations have been completed. In addition, if tunnel excavations are carried out from both entrance faces, it is possible to encounter excessive deformations at the junction points of the tunnels. Especially on weak ground, the importance of the distances between the stages increases in the case of opening the tunnels in the form of top heading, bench, and invert gradually. As a tunnel excavation method, excavation in stages directly affects the stability of the tunnel. Within the scope of this study, the collapsed mechanism in the junction area of the tunnels of the T6 tunnel is examined. For this purpose, 3-dimensional numerical analysis are performed with the Flac3d program. Analysis results are compared with site deformation measurements. As a result, an excavation methodology is proposed for the junction area of tunnels in weak ground.

Excavation and implementation of tunnel support system of T341 tunnel of Ankara-Sivas High Speed Train Project were completed recently. Throughout the tunnel excavation, serious stability problems occurred both in the entrance portal section and tunnel. The purposes of this study are to explain the failure mechanism and to propose a suitable support system for the section between Km: 341 + 040 - 341 + 114. Tunnel works were interrupted after the collapse, which occurred in a section of approximately 74 m between Km: 341 + 040 - 341 + 114. As a result of the collapse in the tunnel, local settlements emerged on the surface and it was observed that the effects of the collapse on the surface, as well. To surpass the collapsed section, extra reinforcements were performed by grouting taking place both at the surface and inside the tunnel. Afterwards, tunnel excavation was completed in relatively short stages by applying double umbrella system and rigid support system. Consequently, the causes of the failure, excavation and support system design and results of the numerical analyses are discussed.

Probabilistic simulations of TBM tunnelling in highly fractured and faulted rocks

To address the severe deformation and failure of roadway roof and floor encountered when crossing fault zones in coal mines in western China, this study takes the lower gateway of the 11E5-303 working face crossing the SF1 normal fault in Zhaohequan Coal Mine as an engineering case. A comprehensive investigation was conducted using field investigation, laboratory testing, numerical simulation, and engineering applications. The research aims to clarify the deformation mechanisms of the surrounding rock in fault-affected zones and to provide adequate control measures for roadway stability during fault crossing. Studies have shown that the roof and floor strata along the 11E5-303 Working face’s adjacent roadway are primarily composed of siltstone, fine sandstone, and argillaceous siltstone, which are highly susceptible to water-induced softening and swelling, leading to a significant decrease in mechanical strength. This phenomenon is particularly severe near the fault, where substantial roof subsidence and pronounced floor heave are observed. Based on the Mohr–Coulomb failure criterion, the deformation and failure mechanisms of the surrounding rock under the existing support system were analyzed. The study revealed that the roadway surrounding rock within 10 m of the fault zone is subject to intense deformation and damage, with the hanging wall showing a significantly larger failure range than the footwall. Floor heave at the fault zone is also markedly greater than in other sections. These findings identified key support zones and critical reinforcement areas, emphasizing the need for early implementation of high-strength support systems within the fault-affected area to enhance stability. Targeted control technology for surrounding rock stability in fault-crossing roadway was proposed. After optimization, the roof subsidence was reduced by 68% and the floor heaves by 81% compared to the original support system. The optimized support scheme significantly improved the stability of the roadway, demonstrating apparent effectiveness. These results provide valuable guidance for roadway support design and stability control under similar geological conditions.

A double-row pile support system combined with existing and additional support piles offers an effective solution for further excavation beneath existing underground space. A large-scale test chamber was therefore built to simulate the whole construction process of underground space extension. Several parallel tests are conducted through observation, data monitoring, and analysis to study the influence of several parameters on an h-type support system containing double-row piles. The relevant parameters include pile row spacing, pile length ratio, pile-head constraint, and in-service foundation pile. The tests reveal that a significant load-transfer effect is generated between the pile rows, and increasing the spacing between pile rows within a certain range can lead to a more reasonable distribution of bending moments and pile force. The displacement of the pile top and its rate of increase are directly proportional to excavation depth, and additional excavation to the bottom of the back-row piles tends to be a critical point, after which the deformation will be significant. The stability of the system varies inversely with the reduction in pile length ratio, but is positively related to the existing pile-head constraint. Furthermore, in-service foundation piles can result in increased bending moments and reduced displacement of the pile top. Finally, the rationality of the model test results was verified according to the numerical simulation and the stability of the double-row piles support system was calculated.

Numerical and analytical simulation of the structural behaviour of fully grouted cable bolts under impulsive loading

The diversion tunnel of Jragung Dam was initially designed using the New Austrian Tunnelling Method (NATM) based on assessment of limited drill cores. Due to the uncertainty in the use of single empirical tunneling method and limited data for the tunnel design, this research was conducted to better characterize the rock masses and provide design alternatives for the tunnel construction. In addition to drill core evaluation, surface engineering geological mapping was carried out to obtain complete parameters of Rock Mass Rating (RMR) and Q rock mass classifications for designs of the tunnel excavation method and support system. The results show that the tunnel area consists of highly weathered sandstone and claystone layers with extremely poor to fair rock mass quality. The rock masses have very favorable and fair discontinuity strike and dip orientations with respect to the tunneling direction. The recommended excavation methods are top heading and bench and multiple drifts. The tunnel mostly requires rock bolt and shotcrete support system and the tunnel sections with poor rock mass quality require additional installation of steel sets. This research highlights potential collapse of the extremely poor quality rock masses near the tunnel portals during excavation of the diversion tunnel.

Tunnelling through the young Himalayas — A case history of the Maneri-Uttarkashi power tunnel

The Main Spillway and Diversion Tunnel at Manikin Dam is one of the dams under construction in the Kupang City area, where several soil or rock investigations have been carried out around it. However, the field investigations are not accompanied by a surface geological investigation or evaluation of subsurface geological conditions based on core drill results. Therefore, the purpose of this paper is to evaluate the engineering geological condition in tunnel construction by displaying surface and subsurface geological mapping with a scale of 1:10,000 and evaluate samples of core drilling using the Rock Mass Rating method in order to have more accurate stand-up time assumptions. The result of engineering geological mapping shows that the research area has three lithologies, namely a basalt unit, a carbonaceous sandstone unit, and a scaly claystone with a chaotic rock unit. The core-drill evaluation indicates that the research area is classified into three quality rock masses, namely Good Rock with an RMR Rating of 64, Fair Rock with an RMR Rating of 46, and Poor Rock with an RMR Rating of 36. The stand-up time value for each rock mass quality category is obtained from the quality rock mass results. The stand-up time value for the Good Rock category is 2200 hours, the Fair Rock category is 30 hours and the Poor Rock category is 1.2 - 1.7 hours. Based on the low stand-up time values in the Fair Rock and Poor Rock categories, it is expected that a support system will be installed immediately after tunnel excavation.

Semi-analytical model for umbrella arch systems employed in squeezing ground conditions

TaBaiyi tunnel is located in the Yunnan plateau mountainous area. The tunnel in the process of crossing the shattered fault zone paragraph, loose, fractured rock in the multi-field stress coupling, the surrounding rock large deformation, and other damage phenomena frequently occur, causing the near ordinary section of the initial support structure of the phenomenon of secondary subsidence damage to the safety and cost of the tunnel brought great difficulties. This study conducts physical modeling tests to investigate the effectiveness of the NPR anchor cable support system for tunnels penetrating shattered fault zone at various depths. It employs strain gauges, anchor cable axial force gauges, infrared cameras, and a non-contact strain measurement system (DIC) to record the displacement field, mechanical response, and the transformation pattern between energy fields of the surrounding rock and the support structure during the tunnel excavation. A 100 m experimental section of research is performed at the project site to verify the effectiveness of the support. The results indicated that excavation in the shattered fault zone can destroy the stress equilibrium between the surrounding rock and the support structure in the tunnel's ordinary section, accelerating the settlement and deformation rate of the surrounding rock. In addition, the NPR anchor cable support system can control the deformation of the surrounding rock, providing a theoretical foundation and practical guidance for the design of support for tunnels through shattered fault zone in similar engineering contexts.

Pelosika dam spillway tunnel was designed to drainage flood discharge and prevent overtopping. In recent investigations, the rock mass classification has not been done specifically in the spillway tunnel. This research aims to obtain technical geological data and information to define excavation methods and tunnel support. For more comprehensive research, engineering geological investigations were carried out regarding the Geological Strength Index (GSI), selecting excavation methods using EXCASS system and Rock Mass Rating (RMR) for tunnel support. The geological mapping showed that the study site was composed of 2 lithological units: quartz muscovite phyllite and pebblely sand deposits. The GSI value in the tunnel is between 14-25, indicating poor and very poor quality. Adopting the EXCASS system, the optimum method of excavation (EPIopt) in the Pelosika dam spillway tunnel are ripper easy and digger. While RMR values of 9 – 25 are classified as poor quality. Consequently, the appropriate method for the excavation sequence is using the top heading and bench and multiple drifts. And the recommended support system is a systematic rock bolt with wire mesh and shotcrete in the crown and walls with medium to light steel rib.