Advanced methods for rock discontinuities estimation in tunneling

The limit analysis and response surfaces method were combined to investigate the reliability of pressurized tunnel faces subjected to seismic force. The quasi-static method was utilized to introduce seismic force into the tunnel face. A 3D horn failure mechanism of pressurized tunnel faces subjected to seismic force was constructed. The collapse pressure of pressurized tunnel faces was solved by the kinematical approach. The limit state equation of pressurized tunnel faces was obtained according to the collapse pressure and support pressure. And then a reliability model of pressurized tunnel faces was established. The feasibility and superiority of the response surfaces method was verified by comparing with the Monte Carlo method. The influence of the mean of soil parameters and support pressure, variation coefficients, distribution type and correlation of c-phi on the reliability of pressurized tunnel faces was discussed. The reasonable safety factor and support pressure required by pressurized tunnel faces to satisfy 3 safety levels were presented. In addition, the effects of horizontal seismic force, vertical seismic force and correlation of kh-kv on the reliability of pressurized tunnel faces were also performed. The method of this work can give a new idea for anti-seismic design of pressurized tunnel faces.

Tunnel face and wall collapse are common during excavations performed by tunnel boring machines (TBMs) due to the difficulty of correctly identifying the properties of the excavated rock. This identification, however, can be simplified by using the cutting force to estimate rock strength, a method that has already proved quite successful in Japanese tunnel excavations. This paper summarizes knowledge relating to the cutting force obtained through tunnel excavation experience, and the relationship between rock strength and TBM operation is discussed. Although TBM operators rely on intuition to set the cutter head speed appropriately, this decision process represents a logical method of operation that takes advantage of the variable speed capability of the cutter head. Selection of appropriate support methods for the excavated face is also a critical issue in tunnel excavation. This selection process is based on the condition of the rock, which is difficult to determine quickly and accurately during tunnel excavation. The present paper uses the excavation of two tunnels to demonstrate that it is possible to assign rock mass classifications accurately based on rock strength when boring a uniform rock type. It is also shown that the rock mass can be classified from the rock strength normalized by the uniaxial compressive strength when boring through mixed rock types.

The seismic refraction method from the ground surface has routinely been applied to planning of tunneling as a preliminary survey. A tunnel support pattern is designed based on elastic wave velocity of the mountain obtained by seismic refraction survey. Where overburden on a tunnel is thick, the resolution in velocity structure obtained by this technique becomes poor. A survey ahead of the tunnel from the tunnel face while boring is considered to be effective compared with a ground seismic survey. Two methods are generally used in the survey ahead of the tunnel from tunnel face: one by seismic reflection such as the Tunnel Seismic Prediction (TSP) and Horizontal Seismic Profiling (HSP) methods and the other by drilling data called the Drilling Survey System (DRISS). The authors applied a new exploration method by the use of drilling vibration data called TSPD (Tunnel Seismic Probe Drilling) to estimate elastic wave velocity distribution ahead of the tunnel face. Unlike Seismic While Drilling (SWD) commonly used for ahead of drilling in the petroleum exploration, this method investigates the nature of the rocks between the bit of pilot drilling and the cutting edge of the tunnel. The field tests of TSPD were carried out at a road tunnel. The first test helped to identify and correct the problems in data acquisition. The second field test confirmed improvement of S/N ratio of the waveform, and evaluated the elastic wave velocity structure ahead of the tunnel face.

For safe tunnel excavation, it is important to predict lithologic and structural heterogeneities ahead of construction. Conventional tunnel seismic prediction systems utilize body waves (P- and S-waves) that are directly generated at the tunnel walls or near the cutter head of the tunnel boring machine (TBM). We propose a new prediction strategy that has been discovered by 3D elastic finite-difference (FD) modeling: Rayleigh waves arriving at the front face of the tunnel are converted into high-amplitude S-waves propagating further ahead. Reflected or backscattered S-waves are converted back into Rayleigh waves which can be recorded along the sidewalls. We name these waves RSSR waves. In our approach, the front face acts as an S-wave transceiver. One technical advantage is that both the sources and the receivers may be placed behind the cutter head of the TBM. The modeling reveals that the RSSR waves exhibit significantly higher amplitudes than the directly reflected body waves. The excavation damage zone causes dispersion of the RSSR wave leading to multimodal reflection response. For the detection of geologic interfaces ahead, RSSR waves recorded along the sidewalls are corrected for dispersion and stacked. From the arrival times, the distance to the S-S reflection point can be estimated. A recurrent application, while the tunnel approaches the interface, allows one to quantify the orientation of the reflecting interfaces as well. Our approach has been verified successfully in a field experiment at the Piora adit of the Gotthard base tunnel. The distance to the Piora fault zone estimated from stacked RSSR events agrees well with the information obtained by geologic surveying and exploratory drilling.

We discuss the use of autocorrelogram interferometry by using noise from the tunnel-boring machine (TBM). The TBM provides seismic signals/waves while drilling in a tunnel (TSWD). The tunnel geometry, unlike a reverse vertical seismic profile (RVSP) using a drill bit, makes it possible to record the waves reflected from the region between the tunnel face and the projected tunnel exit and those transmitted ahead of the tunnel face. We processed the waves recorded at back positions with respect to the TBM in a manner similar to a RVSP data set obtained by conventional reference-correlation techniques. We processed the waves transmitted ahead of the TBM using autocorrelogram interferometry techniques. Using these wavefields offers advantages over conventional borehole drill-bit vertical seismic profiles (VSPs). The most important advantage is getting reflections from the transmitted (front) wavefield by utilizing Kunetz’s equation and reversed-time traces. The approach also improves the analysis of the transmitted amplitudes. Finally, we improved the deconvolution of the reflected (back) waves by using the transmitted wavefields measured for interferometry purposes. In particular, by using both front (transmitted) and back (reflected) waves, it is possible to deconvolve the signature of the source extended spatially along the tunnel axis. We use a 1D model in which the interfaces are assumed subvertical. We present a case history in which TSWD data were acquired in a tunnel measuring [Formula: see text] long. We compare results from the transmitted reversed-time and back-reflected waves ([Formula: see text]-waves) with those obtained by amplitude analysis and estimation of reflection coefficients. Each approach matches the interpretation of the fractures encountered in the tunnel.

The detection and forecast for geological structure ahead of the tunnel and laneway is a very difficult problem in the world.Many applied researches based on the method of the seismic reflection wave have been done in our country from 1990,and many successful practical examples are obtained.At the same time,the detecting methods also have different problems.The main methods using reflection wave principle for forward prediction in the word include different forms,such as TSP,negative watching velocity,HSP,TRT,ISIS,and landsonar method,and so on.This article illustrates briefly the principle of different methods,and analyzes the status-quo of application and research of the forward prediction technology in China.The existing shortage in data collecting and processing of forward prediction ahead of tunnel and laneway is pointed out.The authors believe that the researches of the forward model and inversion theory,data collecting system in 3D complex space,migration imaging technology,etc,should be concerned in forward prediction and forecast.The aim of forward prediction is to establish and consummate the dynamic system of real time watching and forecasting for geological structures ahead of tunnel and laneway.

This paper evaluates cutterhead design of current tunnel boring machines (TBMs) in considerations with the actual cutting action of discs observed on the most common cutter heads. The discs on the current TBM cutter heads were found to predominantly perform asymmetrical cutting action, which generates excessive sideway forces impairing steering action of the machine. The effective s/p ratios related to actual cutting action of discs emerge to be significantly higher than those of the laboratory-determined values, and this consequently leads to adverse cyclic deepening effect. The gross lateral loads arising from excessive side forces were stated to be minimised if the adjacent discs are arranged to cut in symmetrical position by adopting appropriate cutterhead design methods suggested in this paper. Furthermore, a dynamic analysis was carried out in terms of reaction forces on cutter heads of different geometries, and it was indicated that flat face cutter heads have better steering abilities than conical or domed types, in mixed face conditions. Similar analysis on disc angular spacing also inferred that scattered type disc arrangements with equal angular spacing are preferable to cutterheads with spoke or star type lacing, in terms of cutterhead balance.

Tunnel boring machines are important tools in underground infrastructure projects. Although being well established equipment, these machinesare based on designsof more than 60 years ago and are characterized by big dimensions, enormous weight and high power consumption. Commercial aspects should be noted too. The model adopted by the TBM industry requires constant replacement of cutter discs and specific labor skills, usually offered by the same manufacturingcompany. In some cases the cost of replacement parts and technical assistance can be higher than the acquisition cost of an entire machine. These aspects are no longer compatible with the concept of sustainability that is an important aspect of currentsociety. While the technical characteristics require a large quantity of steel and several inputs, the adoptedmodel is not competitive. One alternative is looking for new technologies that break the old paradigms and allow the development of high performance concepts with lower social and environmental impact. This studydealswith this opportunity by proposing a high performance tunnel boring machine that makes use of high power water jet and diamond wire to compose a double shield cutter head. It works in two stages. In the fristone, an annular cut is executed by hydrodemolition,and in the second one, the diamond wire station slices the rock core. Only with the action of diamond wire is the rock core separated from the rock mass and the removal process is finished. A smart water jet nozzle movement system is described and non circular tunnels can be executed. The new technologies involved requirea different type of backup system, lighter and smaller. The non-existence of mechanical contact between the equipment and the rock mass at theexcavation front allows low power consumption. The advanced rate and primary excavation cost analyses can also be encountered herein. It shows that it is possible to reach an advanced rate of 174 m/day in soft and porous rock and 0.64 m/day in hard and non porousrock, whereas the NTNU method indicates only 55m/day and 13m/day underrespective conditions. On the other hand, the excavation cost is high for both conditions. One option is to use sand as an abrasive in the water jet process, reducing by half the primary excavation cost. It is reasonable to say that the proposed concept can be considered as an alternative for tunnels in soft rock and high porosity, and needs better performance of the water jet system to become an alternative for hard rock.

The cutter head of a tunnel boring machine may be trapped in extremely adverse geological environments, which requires a large enough driving torque to get rid of the trapped condition. In this paper, a novel driving scheme is proposed to improve the driving performance of the tunnel boring machine cutter head without increasing the installation power. First, the hydro-viscous clutch is introduced to achieve the soft start of the cutter head by the flexible effect of viscous oil film. Then, the flywheel is employed as the energy storage element to provide sufficient torque during the hydro-viscous clutch engagement, which assists the cutter head to get rid of the trapped condition. Moreover, an optimal state feedback control law based on a linear quadratic regulator is designed by compromising system impact and hydro-viscous clutch friction loss to optimize the hydro-viscous clutch engagement process and achieve favorable driving performance of the cutter head. Finally, numerical simulations are conducted to validate the effectiveness of the proposed driving technology.

The overstressing of a segmental lining is a major potential hazard in TBM tunnelling through squeezing ground. The paper starts with a review of the segmental lining concepts applied or proposed for shielded TBM tunnelling in squeezing ground. Later, the focus is shifted to the practically rigid segmental linings which are the standard solution for shielded TBM tunnelling, paying attention to the different options for backfilling (i.e., backfilling by pea gravel at a certain distance behind the shield or annulus grouting via the shield tail) and the factors influencing the loading of the lining. The numerical simulation of the effects of backfilling is a demanding problem, because the thickness of the backfilling is not known a priori but depends on the intensity of the squeezing, i.e., on the deformations of the bored profile between the tunnel face and the location of the backfill installation. For this purpose, advanced numerical models are required which, as a rule, are not available to the project engineer. On account of this, the final section of the paper introduces practical decision-making aids for the quick assessment of the loading of a segmental lining. The aids have been worked out by means of a comprehensive parametric study covering the relevant range of ground parameters and initial stresses, as well as different characteristics of the TBM, the segmental lining and the backfilling (type and location).

S-wave velocity structure can reflect the differences of physical properties of Earth media, and is the important basis of identifying the structural characteristics of the low velocity zone. This article attempts to use spatial autocorrelation method (SPAC method) to extract Rayleigh-wave phase velocity dispersion curves from the vertical component of the seismic stations' microtremors, and through the inversion of dispersion curve, acquires the S-wave velocity structure. Taking 8 broadband seismic stations' actual measurement from China National Seismic Network for example, we acquired the one-dimensional S-wave velocity structure of 30 km depth range using this method in the Capital area near Beijing. The inversion result shows that the crystalline basement of this region is about 2 km deep; there is S wave low-velocity layer at 5 similar to 8 km and 12 similar to 16 km depth; the depth 8 km and 20 km stands for the speed interface of S-wave that has a big speed difference. This result has good consistency with seismology and artificial seismic exploration results, which illustrates that estimating the crustal S-wave velocity structure using spatial autocorrelation method is feasible and effective.

Tunnelling through various ground condition affects the performance of Tunnel Boring Machine (TBM). Previous researches have conducted studies to explain on this relationship. However, a more localised influence of Malaysian Kenny Hill Formation subsurface condition towards TBM drive are yet to be carried out. This study will assess this relationship at areas nearby Museum Station during the Klang Valley Mass Rapid Transit (KVMRT) Line 1 with a length span of 540m. After the data collection from TBM and borehole report, data analysis was carried out namely using cutter head, thrust cylinder and subsurface profiling. These data were plotted based on the chainage and tunnel ring number. It is observed that subsurface profile at Ring 9 and Ring 11 required a higher thrust force due to its cohesive soil condition and inclusion of sandstone rock. However, Ring 10 is vice versa as there were more non-recovered soil samples at the specified area. The reduction of thrust force eventually increases the speed of TBM penetration. Thus, a clear relationship showing that subsurface condition highly influences the TBM drive.

In underground projects vast uncertainties are confronted in terms of hydrogeology and geology, more often in mountainous terrains like Himalaya. Groundwater is often the main source of problems in tunneling projects and it is more troublesome during construction. Groundwater problems like sudden water ingress or continuous seepages are considered to be the most difficult conditions to predict. The problem is often due to ingress of water in higher volumes than predicted, or worse, the unanticipated encounter of water during tunneling. In Tapovan—Vishnugad Hydro electric project (520 MW), a run of the river scheme, the Head Race Tunnel (HRT) is being driven by Tunnel Boring Machine (TBM). Tunnelling is through the rocks of Central Crystallines which are heavily stressed due to—the presence of Main Central Thrust (MCT) in close proximity and presence high rock cover (>1 Km.). The Tunnel Boring Machine (TBM) was stuck up at RD 3016 m (rock cover ± 990 m) due to major rock fall on the shield near cutter head, in December, 2009. This led to sudden ingress of water (600–700 L/s) in HRT, damaging the pre-cast lining in the crown portion. The water ingress was from quartzite rock through some wide open joints, fractures or fault which were progressively widened due to ground water movement and caused instability problems. The major problems associated with the heavy ingress of water were found to be—difficult working conditions, damage to the structures, stability problems and environmental impact to the ground water resources. The work was called off for more than 10 months in the year 2010. A bypass tunnel was driven to reach the location where TBM was stuck up and damaged so as to carryout repairs. The ingress of water was diverted from HRT through a drift to make the HRT workable.

The location of a Tunnel Boring Machine (TBM) is prone to external environmental and internal system noise interference. To address TBM vibration characteristics, this study analyzed the sources of excavation data noise, the need for noise reduction, and the methods used, using excavation speed as the prime example. We validated the results through three actual tunnel projects. Our research showed that excavation parameters automatically collected by the TBM, such as excavation speed, cutter head thrust, and cutter head torque, contain noise and require filtering and noise reduction before data mining. Different cutoff frequencies correspond to varying filtering effects, and after considering both smoothness and accuracy, we recommend setting the Butterworth filter’s cutoff frequency to 0.1.

The aim of the research thesis is to provide a three-dimensional numerical model suitable to interpret the static and dynamic behaviour of a kind of segmental tunnel lining in soft soil. The static performance of the structure is investigated during the tunnel construction, involving the main tunnelling loads, obtaining the evolution of the state of stress and strain in the lining. The dynamic performance of segmental lining has been investigated both under uniform and not uniform seismic loads. In the case of uniform seismic load, pseudo static and full dynamic approaches have been compared, while non-linear coupled analysis have been used to investigate the post-earthquake lining condition. A study of the seismic vulnerability of such structures has been conducted based on fragility curves for different levels of damage. A procedure for the forecast method of risk assessment has been proposed for the case of segmental tunnel lining assuming as critical damage parameter the longitudinal joints rotation. Furthermore, a study of feasibility of Earthquake Early Warning System, EEWS, based on thresholds has been conducted through a probabilistic and a real-time approach for such tunnel structure. The coupling effect of multi-directional seismic motion both in transversal and longitudinal direction of the tunnel has also taken into account in the evaluation of dynamic tunnel behaviour. A comparison between the effect of synchronous and not synchronous seismic motion along the tunnel axis has been done in terms of dynamic increment of the components of forces in the lining.