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Rockbursts have become one of the main engineering disasters in deep-buried tunnel, seriously threatening the safety of worker and equipment. To monitor microseismic (MS) events and predict rockburst, in the present study, a MS monitoring system was established in a deep-buried tunnel excavated by tunnel boring machine (TBM). Characteristics of MS events were studied and a prediction method for intense rockburst was proposed by analyzing the temporal–spatial distribution, source parameters, and failure mechanism. The results indicated that most of MS events occurred during the tunneling process and within 15 min after a tunneling cycle completed. The MS events mainly distributed within 15 m before and after the tunneling face, and within approximate 2.0 times of the tunnel diameter. The energy of these MS events mainly ranged from 30 to 100 kJ. The prediction method based on cumulative energy index of per day and cumulative apparent volume cannot predict intense rockburst accurately in the present study, the forecast accuracy less than 60%. The proposed prediction index based on the energy index of per MS event and the apparent volume of per MS event can effectively sharpen the forecast accuracy (> 85%). The failure mechanism of MS events was predominated by tensile failure. While as the rockburst segment transited from mild to intense, the percentage of MS events of mixed failure and shear failure increased, especially shear failure events. Highlights: The temporal and the spatial distribution characteristics of rockburst segment in a deep-buried tunnel were revealed. Microseismic event count, energy, energy index, apparent volume, failure mechanism, and the development process of mild, moderate, and intense rockburst segments were studied. A prediction index based on energy index and apparent volume of per microseismic event was proposed to forecast intense rockburst. [ABSTRACT FROM AUTHOR]

The estimation of soil abrasivity and cutting tool wear during soft ground tunneling is complicated and arduous work due to the lack of a generally accepted testing system. To date, geotechnical baseline reports (GBRs) and geotechnical data reports (GDRs) still cannot provide reliable soil abrasion indices for tool life prediction. This is considered a deficiency in the geotechnical investigation of shield-driven tunnel projects. In this study, the Multifunctional Shield Test System (MSTS) developed by the Key Laboratory of Safety for Geotechnical and Structural Engineering of Hubei Province at Wuhan University is presented. The MSTS was motivated by the need for a test platform with the ability to simulate undisturbed soil conditions and actual tool working environments to explore the mechanism of cutting tool wear, bentonite slurry penetration, and filter cake formation in various geomaterials with grain sizes including clay, silt, sand, and gravel (< 15 mm). Experimental studies on the effect of alloy hardness on cutting tool wear are conducted. The soil samples used in the tests are dense fine silty sand from the Sutong GIL Yangtze River Crossing Cable Tunnel. When the wear extent is plotted against the alloy hardness, an inverted S-shaped band bounded by the highest and lowest alloy hardnesses is formed. The sensitive hardness interval is HRC = [47, 52]. If the alloy hardness is higher than 52 HRC, the wear extent is relatively small. Since alloy hardness is negatively correlated with bending strength, using a cutting tool material with a hardness slightly higher than the upper limit of the sensitive hardness interval is optimal. Thus, an alloy with a hardness interval of HRC = [52, 63] is recommended for the dense fine silty sand ground at the Sutong GIL Yangtze River Crossing Cable Tunnel. [ABSTRACT FROM AUTHOR]

Numerous rockbursts controlled by small-scale structural planes have occurred frequently during tunnel boring machine (TBM) excavation in a headrace tunnel. To understand the evolutionary process of structure-type rockbursts, a real-time microseismic (MS) monitoring system was deployed during the advancement of TBM. By combination with the true reflection tomography technique, a new method is proposed to estimate the P-wave velocity for in situ hypocentral locations. A typical structure-type rockburst is investigated to study the relationship between the rockburst characteristics and microseismicity. By further analyzing the temporal–spatial distribution of microseismicity and the quantitative interpretation of the MS source parameters, the potential failure zone and the precursor features are recognized during the development of this structure-type rockburst. Based on the MS monitoring results, some proactive treatment measures are put forward for the mitigation of rockburst hazards. The results of the current research can contribute to the understanding of structure-type rockbursts and provide valuable references for rockburst forewarning and construction management in similar tunneling projects. [ABSTRACT FROM AUTHOR]

Abstract In the first 3602 m tunnelling of TBM1 section at water conveyance tunnel of Lanzhou Water Source Construction Engineering, the lithology is composed of quartz diorite and quartz schist. 409 disc cutters and cutter rings are replaced in the TBM1 section, which is very high compared to other tunnel project. Based on data of disc cutter replacement at different installation locations, the consumption law and its reason are analyzed and the standard for disc cutter replacement is put forward. The disc cutter consumption and its influence on TBM tunnelling efficiency under different surrounding rock conditions are analyzed. Countermeasures of the control of tunnelling parameters, inspection and treatment of cutter and the daily management are proposed to reduce the cutter replacement. The consumption of the disc cutter was reduced to a certain degree after practice. Finally, suggestions for the optimization of the strength and toughness of the cutter ring, the secondary wear rule, and auto analysis system for the disc cutter management in the TBM cutter consumption are proposed. Related methods can provide reference for similar projects. [ABSTRACT FROM AUTHOR]

[Display omitted] • Automatic acquisition and analysis system for TBM muck is developed. • Rock–machine interaction is qualitatively and quantitatively analyzed. • Real-time perceptions of rock mass condition and TBM performance are realized. Tunnel boring machine (TBM) is frequently used in tunnel construction due to its advantages in safety, high efficiency, environmental friendliness. However, the tunnelling efficiency of a TBM heavily depends on the rock–machine interaction conditions. To realize the real-time perception of rock–machine interaction information during the TBM tunnelling, an automatic acquisition and analysis system for rock muck is developed. Firstly, a framework for using the system to perceive the rock mass and TBM conditions was constructed. Then the method to quantitatively evaluate the geometric properties of rock muck is elaborated. Finally, the system was applied to a TBM-excavated tunnel to verify the functions of rock muck in the real-time perception of rock–machine interaction information. The results show that the geometric properties of rock muck can indicate both the rock mass conditions and the TBM performance. In rock mass condition perception: Rock blocks trend to be large in size and elongated in shape as the uniaxial compressive strength (UCS) of the surrounding rock decrease. The blocks produced from a relatively intact rock mass trend to be small in size and round in shape. Larger or smaller blocks with flat planes are frequently produced when TBM drives in the jointed rock masses. In TBM performance perception: The TBM utilization can be estimated through the ratio of the number of images with muck to the total number of captured images. A high value of the field penetration index (FPI) corresponds to blocks with large sizes and elongated shapes (or small sizes and round shapes). Elongated blocks are produced when TBM drives at a low FPI. These results are significant for the safe and efficient TBM tunnelling. [ABSTRACT FROM AUTHOR]

• 3D laser scanning technology is used to reconstruct irregular cutting tool model. • Dimensionless parameters are proposed to quantify irregular cutting tool wear. • 3D quantitative method is developed to rationally evaluate tool wear failure. • Heterogeneous wear and eccentric wear are analyzed by 3D quantitative method. When shield TBM tunneling in abrasive sandy ground, excessive cutting tool wear resulting from untimely and inaccurate failure evaluation is prone to damage cutterhead structure and delay tunneling progress. Hence it is critical important for fast and accurate evaluation of tool wear failure. At present, caliper measurement method is used to qualify cutting tool wear in abrasive ground tunneling. The height reduction of cutter edge is considered as a common parameter to evaluate whether cutting tool is invalid. When it comes to irregular cutting tool, they will be unsuitable due to the complex surface topography. Especially when abrasive sand remains between the cutterhead and excavation face, severe secondary wear will occur on cutter body instead of cutter edge. There is still a lack of comprehensive methods and parameters for evaluating the wear failure of cutting tools. In the present study, the handheld 3D laser scanner has been applied to obtain the point cloud data of irregular cutting tool. The point cloud data has been imported into the Geomagic Control software for model reconstruction. Then, surface overlapped methodology has been utilized for the comparison of cutting tool models before and after wear to obtain the 3D wear nephogram. Cutter volume wear ratio (CVWR) and cutter height wear ratio (CHWR) have been proposed to quantity the wear failure of cutter edge and cutter body. A case study of ripper tooth and replaceable scraper at Sutong GIL Yangtze River Crossing Cable Tunnel has been conducted to set the threshold value of wear failure. The results indicate that the CVWR and CHWR are functional to identify the wear failure of irregular cutting tools. Compared with traditional caliper measurement method, 3D quantitative method allows a more rational and accurate evaluation of heterogeneous cutter edge wear and eccentric cutter body wear. [ABSTRACT FROM AUTHOR]

• • The WHU-SAT tester has been developed to study scraper wear mechanism. • • The influence of soil parameters on scraper wear has been evaluated. • • The optimized solutions have been proposed to alleviate scraper wear. When shield TBM tunneling in abrasive sandy ground, scrapers are loaded with heavy forces resulting from the extrusion and friction processes of sand particles. Scraper wear reflected as displacement or desquamation is related to soil parameters. Due to the lack of reliable test methods, experimental studies on the influence of soil parameters on scraper wear are limited. In the present study, existing soil abrasion testers have been reviewed to discuss the advantages and deficiencies. An improved WHU-SAT soil abrasion tester has been developed to study the influence mechanism of soil parameters on scraper wear. Experimental studies have been conducted to evaluate the variation of scraper wear with quartz content, particle size, particle shape and water content. Two soil abrasion tests have been performed for each case. Scraper wear has been considered to be the average value. The results indicate that scraper wear increases with the increase of quartz content and the growth rate increases. It is related to the particle crushing and adhesion effect of limestone sand. As the average particle size increases, the extrusion and friction between the modeled scraper and the sand particles increases first and then decreases. Thus, scraper wear increases first and then decreases with the increase of average particle size. The trend is generally comparable to the corresponding changes in scraper wear with water content. As quartz balls collide with sand particles and destroy the microscopic friction system composed of scrapers and asperities, scraper wear decreases as the increase of roundness and the falling rate decreases. Optimized solutions such as soil abrasivity evaluation, tunnel alignment optimization and soil discharge improvement have been proposed to alleviate the influence of soil parameters on scraper wear. The present study promotes the rational estimation of sand abrasivity and scraper consumption during the feasibility study of abrasive sandy gournd tunneling using shield TBM. [ABSTRACT FROM AUTHOR]

• A framework that integrates 2D image analysis and 3D laser scanning was applied to muck analysis. • The 3D parameters of TBM muck blocks can be estimated using corresponding 2D parameters. • A 2D image acquisition system was developed to automatically take photos of muck on the TBM conveyor belt. • 2D muck image analysis was found useful to indicate the geological conditions and TBM operational parameters. The rock muck is the direct product of a rock-cutter interaction in the tunnel boring machine (TBM) tunnelling. It indicates both the TBM performance and rock mass quality. To investigate the relationships between the rock muck and the TBM operational parameters/rock mass parameters, the most important work is how to characterize the morphological properties of rock blocks reliably. Traditionally, only the block size is characterized using the sieving method, which is time consuming and not practical in the TBM tunnelling. Image analysis can serve as a quick and convenient 2D approach for analyzing particle size and shape. In the present study, three projection methods were used to characterize the morphological properties of rock blocks, including a randomly single projection, the maximum-area and minimum-area projections (selected from 1000 projections) and three orthogonal projections. These morphological properties were obtained using a computer algorithm written in the MATLAB and the relationships between the 3D and 2D parameters were tried to develop. These developed correlations were applied to a TBM-excavated tunnel project to investigate the potential relationships between the rock muck and the TBM operational parameters/rock mass quality. The results show that 3D morphological properties of rock blocks can be estimated using the corresponding 2D morphological properties measured on a randomly single projection despite this two-dimensional method strictly failing to describe all particle attributes. The proposed method was found to be useful for estimating the 3D size and shape of rock blocks. The rock blocks trended to be larger in size and more elongated in shape when the TBM worked at a low FPI or the rock mass was fractured, vice versa. [ABSTRACT FROM AUTHOR]

• Geotechnical investigations regarding of the biogenic gas-rich ground are summarized. • Biogenic gas is likely to penetrate into the tunnel from pressure cabin, shield tail, pipeline extension and segment joint. • Control and prevention technologies have been proposed to minimize the explosion and combustion. For biogenic gas-rich ground tunneling, control and prevention of gas explosion is an arduous task. Until now, there is still a lack of reliable technologies to eliminate security emergencies such as explosion and combustion. In the present study, geotechnical investigations associated with the biogenic gas-rich ground at Sutong GIL Yangtze River Crossing Cable Tunnel have been summarized. The potential pathways for biogenetic gas to penetrate into the shield TBM and the excavated tunnel have been analyzed. Then, the adverse effects of biogenic gas on slurry shield TBM and tunnel construction progress have been evaluated. Finally, solution schemes including bentonite slurry penetration, clay shock method, gas detector system, explosion proof design, gas extraction system and wireless communication system have been proposed to mitigate the risk of biogenetic gas leakage and explosion. The application of these technologies has enabled the safety construction of long distance cross-river tunnel in organic-rich marine sedimentary ground. [ABSTRACT FROM AUTHOR]