Difficult Ground Conditions Research Articles

Numerical and analytical studies on the coupling effects of unloading and cutterhead vibration on tunnel face in dry sandy ground

When tunnelling in difficult ground conditions, shield machine would inevitably produce significant ground loss and vibration, which may disturb the ground ahead of the tunnel face. In this paper, discrete element models calibrated by model tests were established to investigate the response of tunnel face under the coupling effects of unloading and cutterhead vibrations. The results show that the friction angle reduction under cyclic loading and vibration attenuation in the sandy ground are significant and can be estimated by the fitted exponential functions. Under cutterhead vibration, the tunnel face stability is undermined and the limit support pressure (LSP) increases to 1.4 times as that in the static case with the growth of frequency and amplitude. Meanwhile, the loosening zone becomes wider and the arching effect is weakened with the reduction of peak horizontal stress and the increase of vertical stress above the tunnel. Based on the numerical results, a pseudo-static method was introduced into the limit equilibrium analysis of the wedge-prism model for calculating the LSP under vibration. With an error rate less than 5.2%, the proposed analytical method is well validated. Further analytical calculation reveals that the LSP would increase with the growth of vibration amplitude, vibration frequency and covered depth but decrease with the increase of friction angle. This study can not only lay a solid foundation for the further investigation of ground loss, ground water and soft-hard heterogeneous ground under cutterhead vibration, but also provide meaningful references for the control of environmental disturbance in practice.

Analysis and effect of lateral forces on Micropiles

Micro piles are small diameter pile (less than 300mm). Micro piles are generally used when there are difficult ground conditions, such as natural or man-made obstructions, sensitive ground with adjacent structures, limited access/low headroom. Micro piles are small diameter drilled and grouted friction piles. Each pile includes steel elements that are bonded into the bearing soil or rock – usually with cement grout. The bearing stratum is logged during installation drilling to assure that bearing capacity is adequate. This chapter presents a summary of various parameters defining the computational models. The bearing capacity and spring constant values for different pile diameter and different length is studied in this paper. Also, lateral pressure is also checked on the pile. The software SAFE 2016 used for the analysis of model.

Small‐diameter tunneling in difficult ground – Analysis of TBM performance in hard rock

AbstractSmall‐diameter tunneling in hard rock is increasingly widespread due to the need for new and longer utility tunnels comprising sewer, stormwater, freshwater, or hydropower as well as cable tunnels and casings for pipelines transporting gas or hydrogen. Utility tunnels have to deal with a wide range of geological settings, like small overburden, weathered rock, rock–soil transitions, as well as fractured or intact hard rock with high strength and abrasivity. A database has been created including 35 hard rock projects with diameters between 1 and 5 m as well as more than 70,000 m of tunnel alignments, with a median drive length of less than 500 m. Challenges in creating it and some early interpretations based on the contents of the database are presented. Details about an exemplary pipe jacking project in basement rocks in Brittany, France, are given. The large variety in this small‐diameter range in hard rock includes different TBM types, cutterhead designs, cutter types, and geotechnical conditions. Potential pitfalls in small‐diameter TBM data analysis are shown and general drive parameter trends and penetration prediction approaches are presented and set in relation to the geotechnical conditions. Our analysis shows that difficult ground conditions do not only incorporate rocks with very high strength, but also generally weak rocks like schist or limestone could be responsible for low penetration rates and high thrust forces.

Investigations of piles by bidirectional static loading test in Astana soils

The article presents the results of vertical static load tests of diametral and deep bored piles specially conducted at the construction site of EXPO-2017 in Astana, Kazakhstan. The methodology for determining the bearing capacity of the pile is summarized. Bored piles with a length of 31.5 m and a diameter of 1000 mm were tested. Vertical static load tests were conducted for the following load configurations: Bidirectional Static Loading Test (according to ASTM D8169), Static Compression Loading Test according to ASTM D1143-07 and Static Loading Test according to GOST 5686-12. The method presented in the paper can serve as practical guidelines to assess the capacities of bored piles installed in the field. This geotechnical investigation is important for understanding the soil-structures interaction on difficult soil ground conditions related to the construction sites.

Restoration of underground water-carrying structures damaged by external non-stationary impacts

Object and purpose of the study: Underground aquiferous point and linear structures operated in difficult ground conditions lose their structural safety as a result of the influence of external forces and the environment. It is important to establish the features of the operation of underground aquifers and communications in an inhomogeneous enclosing soil massif, taking into account the interaction of structures with the ground in case of non-stationary force impacts and environmental impacts with an assessment of their structural safety. Methods: The use of analytical and experimental research methods to evaluate the work of structures in the soil mass, taking into account force influences and environmental influences. Results: The features of interaction of the housing of a collapsible pipe with a soil mass with a multidirectional horizontal component of a non-stationary load are established. The negative impact of the combination of the multidirectional impact of the power load and internal hydrostatic pressure on the structural safety of the housing of a prefabricated underground structure is shown. Practical significance and conclusions: The results obtained on the picture of the stress-strain state of an inhomogeneous enclosing soil massif allowed us to establish the nature and boundaries of the safe operation of structures and to make suggestions on the choice of ways to strengthen and protect underground structures, taking into account their operating conditions.

Innovative Ground Improvement with Chemical Grouts: Potential and Limits of Partial Saturation with Polymers

Nowadays, polymers are well-established in geotechnical applications, for example as grouting material for soil and rock stabilization, or as grouting material for anchorages. Concerning ground improvement, the polymers act as a binder that, if cured, holds the grains together by adhesive and cohesive forces. This special characteristic enables the use of less material and therefore saves costs but requires detailed knowledge of the material behavior to avoid application errors. The subject of this research work are two different polymers, which are used for partial saturation of the ground. For the investigation of the mechanical and hydraulic properties of the ground improvement, the geotechnical testing program on the composite material of polymers and gravel is extended by special tests, such as rheometer tests, for chemical grouts. If the polymers are used correctly, the composite material can achieve a load-bearing capacity comparable to that of concrete while the material remaining permeable. This is highlighted by strength tests on the composite material. Finally, the numerical calculation of a track ballast stabilization, using PFC-FLAC3D coupling, demonstrates the potential of the polymers for practical application and that even difficult ground conditions can be handled with it.

A Geotechnical Perspective on a Complex Geological Environment in a High-Speed Railway Tunnel Excavation (A Case Study from Türkiye)

The T26 tunnel was designed within the scope of the Ankara-Istanbul high-speed railway in accordance with the speed of 250 km/h. Some serious problems and excessive deformations were encountered during the excavation works. The deformations in the tunnel caused subsidence on the surface and the Tunnel Boring Machine (TBM) became stuck; therefore, tunnel excavation works were suspended. Design works for re-excavation in the T26 tunnel and extracting of the TBM were carried out and the tunnel was re-designed by the New Austrian Tunneling Method (NATM) system. The main purposes of the present study are to describe the problems encountered during the T26 tunnel and to discuss the sources of the problems. The advantages and disadvantages of TBM and NATM methods for the tunnel having difficult ground conditions were discussed. Critical points needing to be considered for the tunnels excavated with TBM through weak ground conditions and the effect of the TBM selection process were discussed. Considering the complex geological and geotechnical structure of the tunnel route, it is possible to say that the T26 case is an interesting case for tunnel engineering. Along the tunnel route, landslides, high seismic activity, groundwater conditions, and extremely weak rock mass features coexist. Therefore, the tunnel route is a very complex environment. However, due to the geometric limitations of the high-speed railways, relocation of the route is not possible. The experiences gained from tunnel excavations under difficult conditions are capable of bringing new horizons to future tunneling studies.

Numerical modeling of the interaction of bored micro piles with the substrate

The paper describes the results of a numerical simulation of micro-pile tests using the PLAXIS 2D software package. The purpose of the simulation in this article is to determine the bearing capacity of the micro pile in static tests. Axisymmetric models of a 500 mm wide and 31 m long micro pile were used in the calculation. The staged loading of the pile in the program was simulated by increasing the load on the pile by 145 kN. The main monitored calculation parameters were the magnitude of the applied load and the pile settlement. As a result, load-settlement diagrams were plotted from the pile tests. The bearing capacity of the piles was determined based on a numerical simulation of the pile and the ground in the PLAXIS 2D software package and compared with field data. This geotechnical investigation is important for understanding the soil-structure interaction on difficult and problematical soil ground conditions related to the construction sites.

ПОДБОР РАСХОДОВ МАТЕРИАЛОВ ДЛЯ СОЗДАНИЯ ГРУНТОЦЕМЕНТНЫХ СВАЙ В СЛОЖНЫХ ИНЖЕНЕРНО-ГЕОЛОГИЧЕСКИХ УСЛОВИЯХ

Strengthening of soils by jet technology in difficult ground conditions has now become widespread, including in the construction of buried and underground structures. At the same time, a sufficient amount of experimental data has accumulated to predict the properties of the resulting soil cement. The purpose of the work is to determine the optimal consumption of materials for soil-cement structures, taking into account complex engineering and geological conditions. The study of mineral-based hardening systems in water-saturated soils with inclusions of organic deposits or in conditions of high filtration has a number of features that make it difficult to assign optimal technologies and components of cement-based solutions for the formation of soil cements. To determine the final parameters of soil cement, the parameters of soil cement piles at the facilities during the construction of the subway, laboratory data on mixing mineral components and soils of different types, scientific and technical data were analyzed.

Empirical approach to ore pass geometry justification in Talnakh mines

Ore mining in the Talnakh and Oktyabrsky fields using stoping methods includes construction and support of many temporal and permanent ore passes for ore haulage by gravity, which is the commonly known effective and cost-saving technology. Despite all benefits, there are some geotechnical complexities. For instance, making ore passes with smaller diameter increases their stability, which allows using them in difficult ground conditions, on the one hand, and, on the other hand, this can lead to frequent ore flow arching phenomena in ore passes and, consequently, to the increase in efforts for their elimination. This paper presents summary recommendations for selecting the cross-section shape and dimension of an ore pass based on global practice. The approach to determining the ore pass diameter with regard to grain sizes and properties of ore flow is substantiated. A series of experiments for determining the physical and mechanical properties (cohesion and internal friction angle) of ore mixture with a given particle size distribution at various degrees of moisture is carried out. Considering the determined properties, the minimum diameter of an ore pass to provide ore flow without formation of cohesive and interlocking arches is calculated. It is found that at the ore pass diameter of 2.4 m and at the maximum lump ore size of 254 mm, the material with natural moisture flows freely without arching in the ore pass.

Cover Picture: Geomechanics and Tunnelling 5/2021

AbstractThe joint venture Austrian Tunnel Consortium Stuttgart 21 is constructing the Filder Tunnel with a length of 9.4 km and the Ober‐ and Untertürkheim Tunnel with a length of 6 km as part of the Stuttgart 21 project. The tunnel Ober‐ and Untertürkheim as well as the middle sections of the Filder Tunnel, which are located in difficult ground conditions, were driven conventionally. The tunnelling work was carried out under the protection of the AT – Pipe Umbrella System. (photo: DSI Underground)

Cover Picture: Geomechanics and Tunnelling 3/2021

AbstractRing line no.15 is one of four new metro lines of the Grand Paris Express mega‐project. The construction lot T2C in the southeast of Paris with a length of approx. 7 km is a key part of the new line. It consists of a 4.7 km long tunnel between Noisy‐Champs and Champigny, a 2.2 km long bypass tunnel with a maintenance station, a large‐scale underground junction cavern, and intermediate access shafts. Difficult ground conditions, limited space for construction, and the requirement for minimization of settlements in an urban environment determine the ground control systems for this tunnel project. Among others, the AT – 139 pipe umbrella system with press connection and a wall thickness of 8 mm, foot piles from the DSI hollow bar system as well as GRP face anchors were used. (photo: DSI Underground)

Risk analysis of TBM tunneling projects based on generic bow-tie risk analysis approach in difficult ground conditions

Usage of tunnel boring machines has become the most popular underground excavation method to meet recent underground infrastructure development demands because of the high advance rate associated with this approach. However, using a tunnel boring machine for tunnel construction under difficult ground conditions carries the potential risk of causing undesired events. Determining the exact geological ground conditions before commencement of the project is almost impossible, rendering this industry to be fraught with high risk. Bow-tie risk analysis has emerged as a powerful tool for studying the risk management of undesired events in several high-risk industries but is yet to be comprehensively studied in the context of underground rock engineering. This paper presents a novel risk analysis methodology based on a generic bow-tie method for systematic assessment and management of risks associated with tunnel boring machine in difficult ground conditions. The bow-tie method integrates the fault tree and event tree analyses methods that follow a cause-consequence methodological approach centred on the common undesired event. The proposed risk analysis technique serves as a powerful tool that can aid tunnel boring machine professionals in systematically investigating, evaluating, and mitigating the inherited risks associated with tunnel boring machine in difficult ground conditions. For validation, the proposed methodology is applied to the twin tunnel boring machine project conducted in the Himalayas, and the results demonstrate its applicability as an effective risk analysis method.

Analysing the Feasibility of a\xa0Full-face Cutting Machine for the Robominers Project

Several methods of excavation have previously been studied to choose the most suitable approach to be applied in the Robominers project. Compared to drilling and blasting and partial-face cutting, the full-face cutting option is regarded as one of the methods which can offer, among others, high advance rates and a safer working environment for the machinery. Current technologies of these methods, however, suffer from several limitations, such as the inability to bore very hard rocks, significant lack of geometrical flexibility in mine working areas, and low mobility due to large and heavy components. In this study, two of the most commonly applied small diameter full-face machines including the pipe jacking and the Boxhole Boring Machine (BBM) are studied with regards to their performance parameters. The pipe jacking machine option with a cutterhead consisting of disc cutters exhibits higher efficiency in excavation with only slightly lower production rates compared to a BBM with strawberry cutters. They are also much lighter machines. Yet, using the jacking concept means a limited driving length and does not apply to the Robominers. Therefore, the introduction of small gripper or shielded Tunnel Boring Machines (TBMs) can significantly improve the mobility. Their application, however, requires considering the risks of jamming in difficult ground conditions and the possible requirements of a support installation. These rock mechanics issues need to be carefully considered in the design of such machines. In addition, further studies are required to employ assisted cutting methods in very hard rocks and to increase the geometrical flexibility of these machines by lowering their turning radius.

Predicting Slurry Pressure Balance with a Long Short-Term Memory Recurrent Neural Network in Difficult Ground Condition.

The safety of tunneling with shield tunnel boring machines largely depends on the tunnel face pressure, which is currently decided by human operators empirically. Face pressure control is vulnerable to human misjudgment and human errors can cause severe consequences, especially in difficult ground conditions. From a practical perspective, it is therefore beneficial to have a model capable of predicting the tunnel face pressure given operation and the changing geology. In this paper, we propose such a model based on deep learning. More specifically, a long short-term memory (LSTM) recurrent neural network is employed for tunnel face pressure prediction. To correlate with PLC data, linear interpolation is employed to transform the borehole geological data into sequential geological data according to the shield machine position. The slurry pressure in the excavation chamber (SPE) is taken as the output in the case study of Nanning Metro, which is confronted with the clogging problem due to the mixed ground of mudstone and round gravel. The LSTM-based SPE prediction model achieved an overall MAPE and RMSE of 3.83% and 10.3 kPa, respectively, in mudstone rich ground conditions. Factors that influence the model, including different kinds and length of input data and comparison with the traditional machine learning-based model, are also discussed.

Simplified Full Dynamic Analysis of a Railway Tunnel in Ethiopia

This paper presents an effective means of analyzing the safety of a tunnel under dynamic loading in areas with seismic records. A particular case of the railway tunnel in the earthquake-prone regions of the escarpment seismic zone of Ethiopia was the specific focus area of the research. Probabilistic seismic hazard analysis (PSHA) and deaggregation have been conducted to determine the design earthquake required as an input for the dynamic analysis. The PSHA performed by considering the operating design earthquake with conservative assumptions of the local geological features resulted in a peak ground acceleration of 0.36. Two pairs of design earthquake have been obtained from the deaggregation process, which were used to filter acceleration time histories for the selected design earthquake from the ground motion database of Pacific Earthquake Engineering Research Center. Finally, full dynamic analyses of the tunnel have been performed by applying the scaled acceleration time histories corresponding to the structure in the specific site. It was demonstrated how to prove the stability of the tunnel located in difficult ground conditions by performing plane strain analyses with the possible minimum computational efforts.

Modelling and monitoring of security unique underground structures of the sewerage system of major towns in difficult ground conditions

On the basis of many years of experience in the construction, reconstruction and operation of underground engineering infrastructure of the metropolis developed the concept and philosophy of the creation and operation of Geomonitoring security system of the tunnel collector. The philosophy of construction of space-time structure of Geomonitoring is described. The article presents the experience of modeling, monitoring and taking protective measures aimed at ensuring the safety of tunnel reservoirs located in the area exposed to the geotechnical effects of underground and high-rise construction. The analysis of calculation and experimental data and the results of long-term monitoring aimed at ensuring the safety of underground drainage and treatment facilities of megepolis. The special protection against technogenic influence is required for long-operated tunnel sewage collectors. This paper, based on the extensive data of studying the work of the tunnel collectors in conditions of soft soils and intense technogenic influences, describes new methods of diagnosing, the features of defects, and the results of modeling joint interaction of the “tunnel – soil bulk” as well as experimental data on experimental objects. The geotechnical methods for protecting the long-operated tunnel collectors have been developed, and there has been given the unique experience of their application in the objects of St. Petersburg together with their monitoring support.

Deep tunnel faces in cohesive soils under undrained conditions: application of a new design approach

Tunnel faces excavated under particularly difficult ground conditions are commonly supported. In case of conventional tunnelling, this support is provided by either improving the mechanical properties of the soil or introducing linear inclusions. This latter technique, consisting in the introduction of fibreglass pipes in the face, is particularly popular since it is very simple to tailor to the different conditions encountered during the excavation the reinforcement spatial distribution. In the current engineering practice, this stabilisation technique is designed by employing simplified approaches not allowing the face displacement estimation. For this reason, in case of deep tunnels in cohesive soils under either undrained or ‘partially drained’ conditions, these approaches cannot be employed. In this paper, the authors present the practical application of a new displacement based design approach, based on the definition of the face characteristic curve, putting in relation the face displacement to the stress applied on the face.

Numerical Investigation of Sequential Strut Failure on Performance of Deep Excavations in Soft Soil

Abstract The structural support system is the key element in the design of any deep excavations, in particular, in difficult ground conditions, and an adequate safety margin is required to cover un...

Возможности сейсмического оборудования для мониторинга основания железнодорожных путей в районах со сложными грунтовыми условиями

Возможности сейсмического оборудования для мониторинга основания железнодорожных путей в районах со сложными грунтовыми условиями