AbstractThis paper presents a case history of the successful application of observational method to instruction microtunneling with successive pipe-jacking. The microtunneling project is the ...construction of four parallel pipes under Guan River in Jiangsu, China. Four parallel tunnels with external diameter of 4,160 mm and horizontally spaced at 4.8 m apart were jacked over 450 m in cemented silty clay and sand by two slurry-balance microtunnel boring machines (MTBM) at a depth of 4.6 m under the river bed. Since the overburden soil is very thin, proper control of tunneling operations was of utmost importance for maintaining the stability of the river bed. In order to optimize the operation parameters prior to construction under the river bed, a field trial was conducted, which included measurement of ground surface settlement, subsurface settlement, and lateral displacement of the subsurface soils, as well as excess pore water pressure and earth pressure. The relationship between ground response and construction operation parameters is summarized. Appropriate operation parameters were applied during tunneling under Guan River. Although tunneling and pipe jacking under the river was successfully carried out, a difficulty was encountered when the MTBM reached the opposite bank and large settlements were observed. This paper discusses the technical issues faced and lessons learnt from interpretation of the monitoring data collected.
There are several well-established jacking force models available for determining the jacking loads. However, their ability to characterise the tunnel bore conditions is limited. A simple approach to ...characterise the tunnel bore conditions is proposed and applied to a case study where four sewer pipelines of the Shulin district sewer network in Taipei County, Taiwan were constructed to verify its validity. In this paper, four jacking force models are reviewed. Based upon the given soil properties and pipe dimensions as well as the pipe buried depth, the normal contact pressure (σ′) in each jacking force model and the measured frictional stress (τ) in each baseline section are utilised for back-analysis of the frictional coefficient (μavg). The μavg values outside the range of 0.1–0.3 recommended for lubricated drives can be attributed to the increasing pipe friction resulting from excessive pipe deviation or ground closure or due to the gravel formation not being long enough to establish lower face resistance or total jacking load. JMTA (Japan Microtunnelling Association) has indicated a further potential use in assessment of the interface performance during pipe-jacking works.
•Review of the history and development of pipe jacking and microtunneling methods.•Planning, design and construction aspects of the technologies are discussed.•Emphasis on academic research into the ...critical design and construction aspects.•Jacking force estimation and effect of lubrication receive particular attention.
This paper provides a review of the history and development of pipe jacking and microtunneling methods with extensive referencing to the published literature. The application of such methods in comparison with other trenchless technologies is discussed and the various planning, design and construction aspects are introduced. The emphasis of the paper is to trace the academic research and field monitoring results covering critical aspects of design and construction with a particular emphasis on jacking force estimation and the effect of lubrication on jacking forces.
AbstractThe proliferation of data collected by modern tunnel boring machines presents a substantial opportunity for the application of data-driven anomaly detection (AD) techniques that can adapt ...dynamically to site specific conditions. Based on jacking forces measured during microtunneling, this paper explores the potential for AD methods to provide a more accurate and robust detection of incipient faults. A selection of the most popular AD methods proposed in the literature, comprising both clustering- and regression-based techniques, are considered for this purpose. The relative merits of each approach is assessed through comparisons to three microtunneling case histories in which anomalous jacking force behavior was encountered. The results highlight an exciting potential for the use of anomaly detection techniques to reduce unplanned downtimes and operation costs.
AbstractWith increasing demand for sustainable underground infrastructure and pressure to reduce embodied carbon (EC), microtunneling (MT) has become an increasingly popular trenchless method of ...installing buried utility tunnels. Life-cycle analyses have shown that trenchless methods cause lower emissions than traditional open-cut construction. However, existing literature specifically considering MT is limited and fails to consider the impact of the entire construction process. In this paper, an approach for calculating the EC of MT is presented. The proposed approach is applied to three recent case histories in the United Kingdom through the development of a bespoke MT EC database in collaboration with industry partners. Total emissions across all three projects (870 m of pipeline) total 1,005 tCO2e. Production of materials and components is shown to account for an average of 68.5% of EC across the three projects, with most of these emissions coming from the key structural materials, namely concrete and steel. Sensitivity analyses demonstrate that the source and production method of steel products have a significant impact on EC. Site activities also make a significant contribution, accounting for an average of 20.5% of total EC. Normalization of the results suggests that MT produces less EC than open-cut pipeline installation and highlighted how increasing drive lengths and reducing the number of shafts can significantly reduce EC. One of the case studies is then used as an example to quantify how the reduction of intermediate launch/reception shafts can reduce overall EC.
Practical ApplicationsIn this paper, an approach for calculating the embodied carbon (EC) of microtunneling (MT) is presented, defining a scope that will enable fair comparison of future projects. The presented methodology also provides a useful reference for readers to find sources for EC factors. The proposed approach is applied to three recent case histories in the United Kingdom through the development of a bespoke MT EC database in collaboration with industry partners. The presented results provide insights into the EC of MT projects in five key areas: (1) the relative contribution of different materials and different construction phases to overall EC, (2) the sensitivity of EC to the method of steel production, (3) the influence of on-site emissions, (4) the comparison of MT to traditional open-cut pipeline construction, and (5) quantifying the environmental benefits of minimizing the number of shafts.
AbstractPredicting the productivity of microtunneling construction projects is challenging, due to the complexities of this trenchless excavation method. One of these complexities is estimating the ...microtunnel boring machine (MTBM) penetration rate due to the complex nature of the interactions between the MTBM and the ground. In the present study, a novel mechanistic approach based on the theory of contact mechanics is proposed to determine the underlying mechanics of the MTBM penetration rate. Using the proposed mechanistic approach, an analytical model of the MTBM penetration rate is developed, and a mechanistic relationship between the MTBM penetration rate and its influential factors, namely soil properties, operational loads, and cutterhead characteristics, is established. The proposed approach is expected to provide substantial mechanistic insight with respect to MTBM penetration rates by (1) modeling penetration rates of MTBMs into soils, (2) identifying the factors that influence penetration rates based on a fundamental theoretical approach, and (3) providing a useful tool for evaluating MTBM penetration rates based on the combined influences of ground properties, operational loads, and cutterhead characteristics.
This article deals with the analysis of the subsurface deformation effects of materials due to the periodic action of liquid droplets, each with a constant volume of approximately 36 mm3 distributed ...with a spatial frequency of 20,000 i/mm. Sample grooves were analyzed within standoff distances where the prevailing mechanism is acceleration culmination depletion using the stair trajectory to avoid a possible Doppler effect. Using X-ray μ-CT, a network of cavities corresponding to a fractal shape was identified below the surface. It is apparent that the ability to erode does not end with the formation of a groove but continues into the core of the material in the form of microjetting, tunneling, or piercing. From that perspective, two types of these cavities have been identified, blind and transient, with diameters of a few micrometers. The topological changes in the subsurface region of the sample were analyzed using X-ray μ-CT progressive sectioning. The anticipated subsurface deformation was further explored and analyzed using SEM analysis. The integrity of the material around the cavities was assessed according to microhardness to explain the microjetting, tunneling, and piercing propagation. The results suggest that the effect of the lateral jetting after droplet collapsing causes extensive hydrodynamic tunneling in the material that is much higher during the intense periodic action of water droplets, even at subsonic speeds.
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•The origin of subsurface voids is clarified.•Subsurface network microcavities are identified.•Blind and transient subsurface cavities are observed.•Relative and real erosion depths are identified.•Residual water microjetting is observed to be multidirectional.
AbstractAn accurate estimation of the jacking forces likely to be experienced during microtunnelling is a key design concern for the structural capacity of pipe segments, the location of intermediate ...jacking stations, and the efficacy of the pipe-jacking project itself. This paper presents a Bayesian updating approach for the prediction of jacking forces during microtunnelling. The proposed framework was applied to two pipe-jacking case histories completed in the United Kingdom: a 275-m drive in silt and silty sand, and a 1,237-m drive in mudstone. To benchmark the Bayesian predictions, a classical optimization technique, namely genetic algorithms, is also considered. The results show that predictions of pipe-jacking forces using the prior best estimate of model input parameters provided a significant overprediction of the monitored jacking forces for both drives. This highlights the difficulty of capturing the complex geotechnical conditions during tunnelling within prescriptive design approaches and the importance of robust back-analysis techniques. Bayesian updating was shown to be a very effective option, in which significant improvements in the mean predictions and associated variance of the total jacking force are obtained as more data are acquired from the drive.
•A probabilistic observational method is developed to forecast total jacking force.•The forecasting results show excellent agreement to monitored data from two drives.•This method builds a ...probabilistic design profile based on the desired risk level.•The study highlights an exciting role for probabilistic data-driven methods.
Microtunnelling is an increasingly popular means of locating utilities below ground. The ability to predict the total jacking force requirements during a drive is highly desirable for anomaly detection, to ensure the available thrust is not exceeded, and to prevent damage to the pipe string and/or launch shaft. However, prediction of the total jacking force is complicated by site geology, the use of a lubricated overcut, work stoppages, tunnel boring machine driving style and pipe misalignment. This paper introduces a probabilistic observational approach for forecasting jacking forces during microtunnelling. Gaussian process regression is adopted for this purpose which allows forecasts to be performed within a probabilistic framework. The proposed approach is applied to two recent UK microtunnelling monitoring projects and the forecasts are appraised through comparisons to predictions determined using design methods currently applied in industry. The results show that the proposed framework provides excellent forecasts of the monitored field data and highlights a significant opportunity to complement existing prescriptive design methods with probabilistic forecasting techniques.
The issues were reviewed in assessing external electromagnetic fields’ effect on the parameters of an electrical power line probing system based on three-component ferroprobes for detecting active ...underground power cable lines during microtunnel construction using the thrust boring method (by tunneling shield) in densely populated urban areas. A study was conducted on the change in the topology of the energized cable magnetic field located in the external magnetic field area created by operating electrical equipment under the influence of an external electromagnetic field and a tunneling shield with installed magneto-sensitive detectors. Experimental studies of the probing system were made. Options have been proposed for compensating the inductance component of the external magnetic field during tunnel driving in urban development and industrial area conditions.
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