Estimation of air losses in compressed air tunneling using neural network

This paper explores the capabilities of neural networks to predict the air losses in compressed air tunneling. Field data from the Feldmoching tunnel in Munich were used in this study. In this project, compressed air was used to retain the groundwater and shotcrete was used as temporary support. The final permanent lining was installed in free air. The tunnel passed through variable ground conditions ranging from coarse gravel to sand and clay. Grouting, an additional layer of shotcrete and a layer of mortar were occasionally used to control the air losses. A back-propagation feed forward neural network was trained and used to predict the air losses from the Feldmoching tunnel. The results of the prediction of the air losses from the tunnel using a neural network were compared with the field measurements. Data from different tunnel lengths were used for training. In each case, the trained network was used to predict the air losses during the excavation of the rest of the tunnel. It is shown that, not only can a neural network learn the relationship between appropriate soil and tunnel parameters and air losses, it can also generalize the learning to predict air losses for very different geological and geometric conditions. It is also shown that data from a very short length (50 m in one case) of the tunnel (five data point only, in this case) may contain enough information for the neural network to learn and predict the air losses in the remaining (585 m) length of the tunnel with a good degree of accuracy. This can be of considerable value to tunnel engineers in control of tunneling operations and help them in preparation for possible changes in air losses with tunnel advance, with changes in ground conditions and tunnel geometry and with time.     

管棚与注浆技术在隧道突泥中的应用

针对某隧道在施工中发生的突泥灾害,借助TSP-203超前地质探测仪对掌子面前方的地质条件进行了探测,采用长管棚预支护结合小导管注浆对突泥体及周边围岩进行加固处理,经实际证明此方案对于治理隧道突泥是可行的,为今后在流塑状黏土地质中修建隧道积累了一定的经验。     

TSP系列探测仪器在隧道中的应用

针对TSP探测仪器使用中存在的问题,分析了TSP-202和TSP-203探测仪器各自的优缺点、TSP仪器现场探测时炮孔探测壁的布置原则、抑制声波干扰的方法、多台阶施工时接收器孔布置原则以及套管与接收器孔的耦合等技术。总结了一些受到各种干扰的现场数据实例。提出了在数据处理时频率、横波斜率的选取、处理结果多解性等问题以及解决的方法。结果表明:TSP-202的预报结果适合预报不良地质体的位置,TSP-203的预报结果适合较大区域的围岩分级;现场探测时炮孔不宜布置在左右洞之间;将炮孔深度增加至1.7 m可有效抑制声波的干扰;数据处理时依据频谱图手动选取频率效果会更好,横波斜率可依据不同围岩级别选取不同的参考值;不同的TSP解译成果不宜进行比较,这些结论对于TSP仪器使用者有着一定的参考作用。     

Feasibility study of automated detection of tunnel excavation by Brillouin optical time domain reflectometry

Cross-borders smuggling tunnels enable unmonitored movement of people, drugs and weapons and pose a very serious threat to homeland security. Recent advances in strain measurements using optical fibers allow the development of smart underground security fences that could detect the excavation of smuggling tunnels. This paper presents the first stages in the development of such a fence using Brillouin optical time domain reflectometry (BOTDR). Two fiber optic layouts are considered and evaluated in a feasibility study that includes evaluation of false detection and sensitivity: (1) horizontally laid fiber buried at a shallow depth, and (2) fibers embedded in vertical mini-piles. In the simulation study, two different ground displacement models are used in order to evaluate the robustness of the system against imperfect modeling. In both cases, soil–fiber and soil-structure interactions are considered. Measurement errors, and surface disturbances (obtained from a field test) are also included in the calibration and validation stages of the system. The proposed detection system is based on wavelet decomposition of the BOTDR signal, followed by a neural network that is trained to recognize the tunnel signature in the wavelet coefficients. The results indicate that the proposed system is capable of detecting even small tunnel (0.5 m diameter) as deep as 20 m (under the horizontal fiber) or as far as 10 m aside from the mini-pile (vertical fiber), if the volume loss is greater than 0.5%.     

Hybrid ensemble soft computing approach for predicting penetration rate of tunnel boring machine in a rock environment

This study implements a hybrid ensemble machine learning method for forecasting the rate of penetration (ROP) of tunnel boring machine (TBM), which is becoming a prerequisite for reliable cost assessment and project scheduling in tunnelling and underground projects in a rock environment. For this purpose, a sum of 185 datasets was collected from the literature and used to predict the ROP of TBM. Initially, the main dataset was utilised to construct and validate four conventional soft computing (CSC) models, i.e. minimax probability machine regression, relevance vector machine, extreme learning machine, and functional network. Consequently, the estimated outputs of CSC models were united and trained using an artificial neural network (ANN) to construct a hybrid ensemble model (HENSM). The outcomes of the proposed HENSM are superior to other CSC models employed in this study. Based on the experimental results (training RMSE = 0.0283 and testing RMSE = 0.0418), the newly proposed HENSM is potential to assist engineers in predicting ROP of TBM in the design phase of tunnelling and underground projects.     

Intelligent recognition of joints and fissures in tunnel faces using an improved mask region-based convolutional neural network algorithm

To address the challenges of low recognition accuracy, low robustness, and low detection efficiency in existing tunnel face joint and fissure recognition methods, we present a deep learning recognition segmentation algorithm called the mask region convolutional neural network (Mask R-CNN) that is enhanced by an advanced Transformer attention mechanism and deformable convolution network (Mask R-CNN-TD). The Transformer attention mechanism improves the backbone network's ability to extract image features by focusing on important areas. A deformable convolutional network enables the network to more precisely conform to the morphological characteristics of joints and fissures on the tunnel face, thereby enhancing the accuracy of detection. Experimental results demonstrate that Mask R-CNN-TD achieves superior performance, compared to Mask R-CNN series algorithms and other instance segmentation methods in terms of detection accuracy, with mean average precision scores of 70.5%, 70.8%, 53.2%, and 63.3% for detection box and mask segmentation at thresholds of 0.5 and 0.75, respectively. Based on the stable and efficient Mask R-CNN-TD model, we developed a mobile application called tunnel face detector to automatically detect tunnel faces on the construction site.     

Prediction of tunneling-induced ground movement with the multi-layer perceptron

This paper presents a method to predict ground movement around tunnels with artificial neural networks. Surface settlement above a tunnel and horizontal ground movement due to a tunnel construction are predicted with the help of input variables that have direct physical significance. A MATLAB based multi-layer backpropagation neural network model is developed, trained and tested with parameters obtained from the detailed investigation of different tunnel projects published in literature. The settlement is taken as a function of tunnel diameter, depth to the tunnel axis, normalized volume loss, soil strength, groundwater characteristics and construction methods. The output variables are settlement and trough width. Parameters for the prediction of horizontal ground movement include diameter to depth ratio (D/Z), unit weight of soil and cohesion. The neural network demonstrated a promising result and predicted the desired goal fairly successfully.     

Experimental study on face instability of shield tunnel in sand

Face stability is critical for ground settlement and construction safety control in shield tunneling. In this paper, a series of 3D large-scale model tests with a tunnel of 1 m diameter were conducted in dry sand for various cover-to-diameter ratios C/D = 0.5, 1, and 2 (i.e., relative depth; C is the cover depth and D is the diameter of tunnel). Each test provided a measurement of the support pressure and the ground settlement with the advance of face displacement. The evolution of soil arching during face failure was investigated by monitoring the redistribution of earth pressure in front of the face in the test case of C/D = 2. In the displacement-controlled face failure tests in the medium density sands, the support pressure dropped steeply to the minimum value, then increased to a steady state with the continuing increase in the face displacement. Relationships between the support pressure and face displacement for various cover depths were also verified by the numerical analysis using the finite difference program, FLAC^3D (Itasca, 2005). The limit support pressure increases with the increase of the relative depth C/D and then tends to be constant. A significant rotation of principal stress axes in the upward arches in the soil during face failure was found in the tests. A two-stage failure pattern is proposed based on the observation of earth pressure. The theoretical and empirical formulas for estimating limit support pressure were verified by the tests results.     

Tunnelling through a frequently changing and mixed ground: A case history in Singapore

The Kranji tunnel is part of the Deep Tunnel Sewerage System in Singapore. It is approximately 12.6 km in length. Along the tunnel alignment, all the ground is composed of granite with different weathering grades (from fresh rock to residual soil). The changing ground from hard rock to mixed face and soft ground (and vice versa) at the tunnel level was anticipated. The tunnel depth along the route is between 15 m and 50 m. Two EPB TBMs were deployed at this tunnel with a bored diameter 4.90 m. These machines were designed so that both hard rock and soft ground could be excavated. The cutter head was equipped with a combination of both rippers and disc cutters. During the excavation, it was found that the frequency of the ground change between hard rock and residual soil is much higher than that expected. Due to the frequently changing ground, correspondingly the tunnel boring machine (TBM) operation mode had to be transferred frequently from hard rock tunnelling to transition mode and to earth pressure balance (EPB) close mode. It resulted in great difficulties for the TBM in an optimized operation condition. These difficulties included high cutter wear and flat cutters, tunnel face instability, water inflow at weathering interface, and time delays. In order to overcome these problems and speed up the tunnelling progress, the TBM used in the north drive was modified to attempt the frequently changing ground. The performance of the modified TBM was highly improved. However, the highly abrasive and frequently changing mixed face ground still caused high cutter wear, especially flat cutter wear. These posed many challenges to the equipment and the tunnel crew.     

Load transfer mechanism in pile group due to single tunnel advancement in stiff clay

Construction of tunnels in urban cities may induce excessive settlement and tilting of nearby existing pile foundations. Various studies reported in the literature have investigated the tunnel–soil–pile interaction by means of field monitoring, centrifuge and numerical modelling. However, the load transfer mechanism between piles in a group, the induced settlement and the tilting of a pile group due to tunnel advancement has not been investigated systematically and is not well understood. This study conducts three-dimensional, coupled-consolidation finite element analyses to investigate tunnelling effects on an existing 2 × 2 pile group. The construction of a 6 m diameter (D) tunnel in saturated stiff clay is simulated. Responses of the pile group located at a clear distance of 2.1 m (0.35D) from a tunnel constructed at three different cover-to-diameter-of-tunnel ratios (C/D) of 1.5, 2.5 and 3.5 are investigated. The computed results are compared to published data based on field monitoring. It is found that the most critical stage for settlement, tilting and induced bending moment of pile group due to tunnelling is when the tunnel face is close to the pile group rather than at the end of tunnel excavation. The depth of the tunnel relative to the pile group has a vital influence on the settlement, tilting of pile group and the load transfer mechanism between piles in pile group induced by tunnel excavation. Tunnelling near the mid-depth of the pile group (i.e. C/D = 1.5) induces the largest bending moment in the piles, but the settlement and tilting of the pile group are relatively small. Based on a settlement criterion, apparent loss of capacity of the pile group is 14% and 23% for tunnels constructed at depths of C/D = 1.5 and at both C/D = 2.5 and 3.5, respectively. The largest load redistribution between the front and rear piles in the group and the largest tilting of the pile cap towards the tunnel occurs when tunnel excavated at C/D = 2.5.     

Ground response of closely spaced twin tunnels constructed in heavily overconsolidated soils

As part of the City of Edmonton’s light rail transit expansion, twin 6.5 m diameter oval shaped tunnels were constructed using conventional tunnelling methods. The geology of the site consists predominately of a hard, fissured cohesive till unit. The tunnel face construction was sequenced as top header, bench and invert excavations. At its narrowest, the pillar separating the twin tunnels was less than 1.5 m across or 0.23 tunnel diameters. Typically, the minimum pillar spacing required to reduce the interaction between twin, side by side tunnels is one tunnel diameter. Because the tunnel construction was within an urban environment, there was considerable concern with ground loss and excessive surface settlements. This study demonstrates that within similar materials, a pillar width of 0.5 tunnel diameters sufficiently reduces the tunnel interactions and minimize the risk of damage to nearby structures.     

Evaluation of ground convergence and squeezing potential in the TBM driven Ghomroud tunnel project

One of the new components of water conveyance system in central Iran is the Ghomroud water conveyance tunnel that is being excavated by a double shield TBM. The 36 km long tunnel mainly passes through the metamorphic weak rocks of Jurassic age. Key geotechnical design issues for the tunnel, which has up to 650 m of overburden, include the potential for high ground pressure due to high in situ stress. In order to prevent the shield jamming in these weak rocks, it was necessary to evaluate the amount of ground pressure on the outer surface of TBM shield in the vicinity of the tunnel face. The stress and strain condition in the vicinity of the tunnel face has a 3D nature and it is not realistic to assume a two-dimensional stress state at the tunnel face area. In the convergence-confinement method, it is possible to simulate the tunnel face effect with an internal fictitious pressure that is imposed on the tunnel perimeter. In this study, based on the convergence-confinement method, a new method was introduced to calculate the tunnel face effect on ground pressure distribution around the tunnel face region. Then by using this method, critical areas with potential for shield jamming was predicted along the Ghomroud water conveyance tunnel. The obtained results by this method are in good agreement with the current TBM jamming situations along the Ghomroud tunnel.     

Centrifuge modelling of tunnel face reinforcement using forepoling

This paper investigates the effect of forepoles on stability of tunnel face and unsupported length during tunnel excavation in clay beds. Forepoles were modelled using 1 mm diameter brass rods. The tests were conducted using 65 mm diameter model tunnels with a flexible face at 100g centrifuge environment. The unsupported length of the tunnel varied between 1 and 1.5 times the tunnel diameter in different tests. The results seem to suggest that forepoles influence to reduce the length of settlement trough ahead of the tunnel face. However, width of the settlement trough remained unaffected. Excess negative pore pressures after collapse were noted to decrease with distance ahead of the tunnel face and increase with depth from the surface up to the tunnel axis. However, scatter in the measured data points suggest that the tunnel stability depends not only on the unsupported length of the tunnel but also on the length of forepoles. It is difficult to include these effects in the simple plasticity solution framework wherein the soil structure interaction is ignored.     

Full 3D modelling for effects of tunnelling on existing support systems in the Sydney region

The assessment of the interaction between a new tunnel and existing structures is an important issue in urban areas. In this study, the effect of tunnelling on the existing support system (i.e. shotcrete lining and rock bolts) of an adjacent tunnel is firstly investigated using ABAQUS and TUNNEL3D through full three-dimensional (3D) finite element calculations coupled with elasto-plastic material models, which takes into account the tunnelling procedure, the interaction between the shotcrete lining and rock mass, the interaction between the rock bolts and rock mass, and the elasto-plastic behaviour of the rock mass, the shotcrete lining and the rock bolts. Then, on the basis of the calculated results, it is concluded that the driving of the new tunnel significantly affects the existing support system when the advancing tunnel face passes the existing support system and is minor when the face is far from it. Moreover, the support system in the side of the existing tunnel closest to the new tunnel is more significantly affected than that on the side opposite to the new tunnel. It is also found that in a region such as Sydney with relatively high horizontal regional stresses, the driving of the new tunnel will not cause considerable adverse effects on the existing support system, if the new tunnel is driven horizontally parallel to the existing tunnel with a sufficient separation, since both the tensile stress in the existing shotcrete lining in the lateral sides of the preceding tunnel and the compressive stress at the crown decrease although noticeable tensile stress increments are observed on some parts of the existing rock bolts. Finally, it is pointed out that the effects of tunnelling on the existing support system strongly depend on the position between the original and new tunnels. In terms of the stress increments on the existing support system, especially the maximum tensile stress increments on the existing shotcrete lining, the driving of the new tunnel causes increasingly adverse effects on the existing support system in a sequence of: (i) horizontally parallel tunnels with a separation of 30 m; (ii) horizontally parallel tunnels with a separation of 20 m; (iii) staggered tunnels with a separation of 30 m; (iv) vertically alignment tunnels; and (v) staggered tunnels with a separation of 20 m in the cases investigated in this study. For the relatively high regional stresses in the Sydney region, the obtained results qualitatively agree with other’s published observations from the construction of closely parallel subway tunnels.     

Opening the excavation chamber of the large-diameter size slurry shield: A case study in Nanjing Yangtze River Tunnel in China

Shield tunnel construction in a dense strata often encounters malfunction of shield-tunneling machine or abrasion of cutters. Accessing to an excavation chamber under compressed air is a main method to repair and replace worn cutters. And many safety issues such as stability of the excavation face were involved. However, the face stability due to opening an excavation chamber was not fully studied. To overcome this shortcoming, face support scheme and stability analysis were presented in a case history of opening the pressure chamber for a large-diameter (up to 14.93 m) slurry shield tunnel constructed underneath Nanjing Yangtze River. Since most of the damaged cutters were distributed along the edge of cutting wheel, only top 3 m of tunnel face within the chamber needed to be supported by compressed air, and remaining area would also to be supported by slurry pressure. A series of simple primary laboratory tests were carried out to design an optimum slurries mixing scheme to support the tunnel face as accessing to the pressure chamber in the project. The face stability was analyzed in terms of the pressure equilibrium (i.e., internal and external pressures) as well as three-dimensional numerical analysis by adopting properties of soils and filter cakes from laboratory tests. By injecting lower density slurry into the sand to form a stable infiltration zone, followed by using higher density slurry to create a filter cake at tunnel face, compressed air-support system could ensure face stability during maintenance of cutter wheel. The success of applying the mixed slurry and compressed air-support scheme in this project is valuable to shield tunnel constructions in similar ground conditions.     

Sequential excavation,NATM and ADECO: What they have in common and how they differ

Rabcewicz, 1964, Rabcewicz, 1965 maintained that “tunnels should be driven full face whenever possible”. ADECO, which stands for “Analysis of Controlled Deformations in tunnels”, now allows us to fulfill Rabcewicz’s dream in any stress–strain condition. In order to achieve that dream and its consequent control over cost and schedule, however, NATM must be abandoned for the ADECO. The paper traces the history of the sequential excavation, NATM (as first conceived) and Analysis of Controlled Deformations (ADECO) with the aim of shedding light on the unavoidable use of sequential excavation in “soft ground”, and of highlighting advances in tunnel design and construction that have occurred in Europe after and as alternates to the NATM. The paper presents the basic concepts in the ADECO approach to design, construction and monitoring of tunnels together with some case histories, including: full face excavation for Cassia tunnel (face area > 230 m²) in sands and silts under 5 m cover below an archeological area in Rome, Italy; Tartaguille tunnel (face area > 140 m²) advanced full face in highly swelling and squeezing ground under 100 m cover where NATM led to catastrophic failure, France; and 80 km of tunnels (face area > 140 m²) advanced full face in highly squeezing/swelling ground under 500 m cover for the high-speed railway line between Bologne and Florence, Italy (turnkey contract).     

密实砂土地层盾构隧道开挖面失稳离心模型试验研究

砂土地层中盾构掘进时,开挖面支护力不足极易导致开挖面失稳事故。通过3种不同隧道埋深比（C/D=0.5,1和2）的离心模型试验对密实砂土地层中盾构隧道开挖面稳定性问题进行了研究。离心试验研究发现,随着开挖面位移的增大,开挖面支护力先减小为极限值而后逐渐增大并最终趋于残余值;开挖面前方土体总体呈现“楔形体+棱柱体”的失稳区;隧道相对浅埋时（如C/D=0.5）,极限状态下失稳区已扩展到地表;隧道相对深埋时（如C/D=1和2）,极限状态下失稳区尚处于地基内部;极限支护力随着隧道埋深比的增大先增加而后基本保持不变。最后,通过现有几种极限支护力理论计算模型对本文试验预测结果的比较分析,评估了上述理论方法的工程适用性。该研究成果对砂土地层中盾构开挖面稳定性控制具有指导意义。     

软土地层并行曲线隧道施工顺序对既有隧道的影响

为了研究并行曲线隧道施工顺序对既有隧道的影响,以横琴杧洲隧道工程为依托,建立了并行曲线隧道三维有限元数值模型。在此基础上,研究了不同施工顺序和曲率半径r(r=500,800 m)下新建曲线盾构隧道开挖对既有隧道变形的影响。结果表明:施工顺序对既有隧道位移影响较小,曲率半径对既有隧道位移影响相对较大; 随着曲率半径(r=500～800 m)的增加,既有隧道位移增加约15%; 既有隧道的位移主要在盾构开挖面前方2D(D为隧道外径)、后方1D范围内产生; 施工顺序对既有隧道内力的影响与曲率半径有关; 隧道曲率半径为500 m时,施工顺序对既有隧道内力变化影响规律相似,即离盾构开挖面最近的既有隧道剖面产生的弯矩最大,且最大弯矩和最小弯矩均出现在靠近新隧道一侧; 内侧隧道先开挖时,既有隧道的弯矩(绝对值)更小,此时对于并行曲线隧道施工,内侧隧道先开挖更安全; 在盾构开挖面前方一定距离内既有隧道产生的轴力最大; 隧道曲率半径为800 m时,双线隧道近似于平行隧道,施工顺序对既有隧道内力变化和大小影响较小。     

Effectiveness of predicting tunneling-induced ground settlements using machine learning methods with small datasets

Prediction of tunneling-induced ground settlements is an essential task, particularly for tunneling in urban settings. Ground settlements should be limited within a tolerable threshold to avoid damages to aboveground structures. Machine learning(ML) methods are becoming popular in many fields, including tunneling and underground excavations, as a powerful learning and predicting technique. However, the available datasets collected from a tunneling project are usually small from the perspective o...     

A study of the application of VSP to exploration ahead of a tunnel

The vertical seismic profiling technique (VSP) was applied to the exploration ahead of a railway tunnel near Ingolstadt, Germany. Before processing the field data, the potential of VSP under the geometrical constraints of a tunnel is demonstrated with synthetic data. The field test comprised two receiver sections with four receivers each, in radially drilled boreholes. The seismic waves were generated by blasting at the tunnel face. Despite the unfavourable geology (very inhomogeneously weathered rock with no large-scale discontinuities), the most prominent geological feature (a transition to better rock quality) could be identified 40 m ahead of the tunnel face. As an item for further improvement, we discuss the ambiguous determination of the static corrections and the velocity field.