Behavior Of Underground Structures Research Articles

Contribution of HADES URL to the development of the Cigéo project, the French industrial centre for geological disposal of high-level and long-lived intermediate-level radioactive waste in a deep clay formation

Abstract In the 1980s, HADES (High-Activity Disposal Experimental Site) was the first underground research laboratory (URL) dedicated to the study of the geological disposal of radioactive waste in a deep clay formation, the Boom Clay. It was not until the early 2000s, after a siting process, that ANDRA implemented the Meuse/Haute-Marne URL, in the Callovo-Oxfordian formation at a depth of about 500 m in order to develop the Cigéo project (French industrial centre for geological disposal). ANDRA therefore relied heavily on the work carried out in HADES, through numerous co-operation projects (participation in in situ experiments) both between ANDRA and ONDRAF/NIRAS and SCK CEN (EURIDICE) and/or with Mont Terri consortium, and within European projects (CLIPEX, RESEAL, etc.). This was driven by a dual objective: (1) to prepare its own experimental programmes in the Meuse/Haute-Marne underground laboratory (methodology, experimental devices and protocols, etc.); and (2) to acquire general knowledge on the behaviour of argillaceous rocks, in particular in terms of similarity and differences between the various argillaceous rocks. This paper illustrates the contribution of HADES to the ANDRA programme. This concerns the characterization of the claystone behaviour, host rock and swelling clay-based seals (hydromechanical, thermo-hydromechanical, excavation damaged zone, etc.), and the design and the behaviour of underground structures and seals in deep clay formation (constructability, lining/support, etc.).

Mechanism of Casing String Curvature Due to Displacement of Surface Strata

One of the main problems of well operation is the risk of uncontrolled leakage of hydrocarbons into the environment. This problem is especially relevant for the long-term operation of wells. The idea for this study was inspired by a real industrial problem that the authors of the article were involved in solving. At several operating gas wells, an abnormal slope of the production tree occurred, which raised the question of the safety of their further operation. An analysis of known studies and current regulatory documents did not allow us to assess the safety of using a gas well based on the measured kinematic parameters of production tree deviations. A mathematical model for the deformation of a package of casing strings when the surface layer of the rock is displaced is developed in the article. A boundary value problem is formulated for differential equations of pipe bending on an elastic foundation. Based on the results of solving this problem, an unambiguous relationship was established between the maximum bending stress in the surface pipe and the angle of inclination of the production tree. The quantitative characteristics of the connection depend on the geometric and mechanical properties of the pipes and on the thickness and mechanical parameters of the formations. It was established that the existing inclination of the production tree can be achieved due to the beginning of the plastic bending of the surface pipe under the slickenside, which does not exclude the exhaustion of the safety margin of the surface pipe and indicates the possible operation of the casing string in a pre-emergency state. In general, the obtained results develop analytical approaches to assessing the behavior of underground structures of a production well in unstable soil bodies.

Modal Identification of a Soil-subway System with Emphasis on Scattering of Seismic Waves Induced by Uniform and Non-uniform Support Excitations

ABSTRACT Subways, as one of the critical structures in urban design for solving traffic problems, require continuous monitoring during operation. Therefore, it is imperative to study the scattering of seismic waves caused by the presence of these underground structures. System identification is one of the most efficient methods for investigating structural behavior during operation and identifying potential problems that may be encountered for an in-service underground structure. In this study, through extending an advanced system identification method called Frequency Response Function Matrix and Singular Value Decomposition (FRFM-SVD) and wavelet transform methods, modal parameters of a soil-subway system were identified. Further, using a random vibration method based on coherence functions, non-uniform accelerations under site condition were generated and the seismic behavior of soil-subway model under uniform and non-uniform seismic excitations were studied. The obtained results indicated that the FRFM-SVD method developed in this study shows a reasonable accuracy for identifying the seismic behavior of underground structures. The maximum amplification of the responses will occur in the proximity of the subway to the amount of 1.75 under non-uniform excitation, which is almost 20% greater than that from uniform excitation. Thus, to increase the accuracy of the estimation of ground surface accelerations, the effect of the presence of underground structures should be accompanied by considering non-uniform excitation in the analysis.

State-of-the-art review of geotechnical-driven artificial intelligence techniques in underground soil-structure interaction

There has been an increasing demand for underground construction due to urbanization and limited land in metropolitan cities in the recent years. However, the behavior of underground structures in soils and rocks is often not completely understood. The emergence of Artificial Intelligence (AI) techniques is envisaged to have a huge potential in addressing geotechnical problems that involve complex soil-structure interaction. This paper thus aims at reviewing the applications of AI techniques in studying underground soil-structure interaction, which focuses on aspects such as characterization of soils and rocks, pile foundations, deep excavations and tunneling. An overview of different AI techniques is provided and a list of key AI applications in underground works that have been published in the last ten years is also compiled to study the recent trend of machine learning techniques in underground construction. The capabilities and limitations of these techniques are discussed throughout the paper, to help readers understand various techniques that are suitable for different underground geotechnical applications. Lastly, some of the challenges that may be faced when applying the techniques are identified, and recent development of AI in geotechnical engineering is discussed in which possible countermeasures to overcome these limitations are highlighted.

Geomechanical justification of room-and-pillar dimensions for rock salt and polymineral salt mining

The key target of room-and-pillar planning for mining rock salt, polymineral salt and polyhalite at the minimized loss of minerals in pillars is optimization of the dimensions of rooms and rib pillars. The authors compare some variants of mining with rooms and rib pillars, as well as with honeycomb mine structure. The theoretical and experimental studies prove efficiency of room-and-pillar dimension optimization by combination of analytical estimation with numerical analysis and physical modeling of the stress–strain behavior of underground structures (honeycomb mine structures). It is found that the honeycomb mine structures feature higher resistability of structural components to external loads. The research into secondary stress field generation and influence on structural elements of the roomand- pillar mining systems made it possible to calculate stable parameters for the conventional and innovative mining systems. The study was supported by the Russian Science Foundation, Project No. 19-17-00034.

Alteration of Ground Motion Acceleration at Ground Level Due to Tunnel Excavation

Underground tunneling is one of the alternative solutions to diminish traffic congestion in large cities. One of the most important effects of tunneling is the displacement of the ground surface, the settlement around the tunnel, and the variation in earthquake acceleration. The performance and behavior of underground structures have been studied by several researchers, but the impact of tunnel excavation on earthquake records and its effects on structures above the ground level have received less attention. This research emphasizes changes of earthquake acceleration at the ground level, structural response and Fourier spectrum by excavating a horseshoe tunnel. Results show that digging a horseshoe tunnel will change the characteristics of the earthquake record at ground level.

Large-Scale Shake Table Test on Behavior of Underground Structure with the Curved Portion During an Earthquake

Underground structures are generally considered to have high seismic performance and expected to play an important role as a base for reconstruction even after a destructive earthquake. Rigidity changing points, such as jointed and curved portions of underground structure, where localized deformation and stress is supposed to be generated, are ones of the most critical portions in terms of seismic performance of underground structure. Because the underground structure in a mega-city functions as a network, local damage could lead to fatal dysfunction. Accordingly, rigidity changing points and their surrounding area could significantly influence the resiliency of urban functions, and it is indispensable to evaluate their seismic performance and dynamic responses during earthquakes. The responses of rigidity changing points and their surrounding area to earthquakes have been tried evaluating by using large-scale numerical analyses, there is no case available where the responses have been measured in detail. For this reason, it is difficult to verify the validity of the results of such evaluations.In light of the above, the shake table test was conducted at E-Defense using a coupled specimen of soil and underground structures to obtain detailed data, especially on the localized responses around rigidity changing points during the earthquake. Based on the data obtained, the behavior of the underground structure with a curved portion at the time of an earthquake was analyzed comprehensively. As a result of the analysis on the test data, it is found that there is a strong correlation between the localized deformation of the curved portion of the tunnel and the displacement of the surrounding ground. In addition, it is necessary to conduct a three-dimensional seismic response analysis not only around the rigidity changing point but also in wider area.

Influence of Foliation Orientation on Tunnel Behavior

The relative orientation of foliation or closely spaced bedding has an important influence on the behavior of underground structures. Not only the potential failure mode is controlled by the relative orientation between underground opening and foliation strike, but also the longitudinal development of the displacements. Case histories and numerical simulations have shown that the magnitude of the displacements can differ almost by an order of magnitude for cases where the strike is parallel and perpendicular to the tunnel axis respectively. The reason is the usually low shear strength parallel to the foliation, which can lead to shearing or buckling failure modes. The knowledge of the influence of the relative foliation orientation on the mechanical behavior of the ground is extremely important for excavation and support design. The paper will show the results of numerical simulations, as well as monitoring data from tunnels in foliated rocks. Recommendations for excavation and support strategies are given.

Steel Buildings' Seismic and Interaction Behavior, Under Different Shapes of Tunnel Drilling

Development of civil engineering science has introduced tunneling as an important option in reducing the traffic volume of urban environments. Digging tunnels, in every depth, causes changes in the surface ground structure; tunneling in urban areas, especially when has passed through the residential areas has its own particular importance; therefore, having knowledge about tunnels' behavior and effects of diggings is necessary, and in order to prevent unpredictable damages to the structures is one of the requirements of designing. The performance and behavior of underground structures have been studied by many researchers, but the effects of tunneling on earthquake records and its effects on structures above the ground has taken less attention. This study will try to check earthquake record changes and their impact on steel structures located on top part of the tunnels, and has done this issue with digging some circular tunnels. The results indicate that, tunneling alters the earthquake records and also has affections on structural responses.

Evaluation of Seismic Behavior and Earth’s Surface Acceleration, by Interaction of Tunnels with Different Shapes and Different Types of Soils

With the increasing population and the consequent needs for transport facilities, the construction of tunnels in urban environments is fast growing. Tunneling at each depth of the soil, causes changes in the earth’s surface; this is more important about urban areas tunnels, especially when crossing the residential areas, so having knowledge of their performance is really important. Some of the consequences of underground tunneling are earth surface moving around the tunnel, movement of tunnel’s surrounding and changes in earthquake acceleration. The performance and behavior of underground structures have been studied by numerous researchers, but the effect of tunneling on earthquake records and its effects on aboveground structures have been getting less attention. The current article will try to study and examine the changes in seismic velocity at ground level, structural response spectrum, and Fourier spectrum with digging a circular tunnel. The results show that digging a circular tunnel at ground level will cause a change in the earthquake records profile.

The uplifting behavior of shallow tunnels within the liquefiable soils under cyclic loadings

The liquefaction of soils under earthquake loadings has always been a main concern for geotechnical engineering practices. As an earthquake causes the ground to liquefy, the effective stress and hence the shear strength of the soil decreases sharply, and large deformations happen in the area. This phenomenon occurs only rarely when the liquefaction occurs at a large depth. However, deformations increase extensively when this layer is located in shallow depths near the ground level. In this case super structures and also underground structures may be severely damaged. The tunnels which are constructed in this layer may be affected by the liquefaction as well. In this condition the liquefaction may cause settlement in the ground, deformation in the tunnel shield, buoyancy in the underground buildings, reduction in bearing capacity and increases in lateral spread and pore pressures. In this paper the FLAC software has been used to model the pore pressure changes during earthquakes that lead to soil liquefaction. The studies thus far have been focused on the impact of the soil liquefaction on the tunnels constructed in this area. According to the studies, the buoyancy and uplifting forces due to liquefaction have major effects on the behavior of underground structures. Increasing the soil parameters such as friction angle and damping ratio causes the liquefaction effects on the tunnel to decrease, and increasing the geometric parameters such as tunnel diameter and location depth causes these effects to increase.

Mechanical properties of frozen coarse-grained soils

Coarse-grained soils are extensively used in hydraulic engineering, highway and underground construction practice. Many problems in predicting the behaviour of underground structures constructed by artificial freezing, and of soil structures built on frozen soils, require that the thermal, mechanical and cryogenic processes, observed both in the structures and their foundation bases, be taken jointly into account (Tsytovich, 1973; Kronik, 1978, 1979; Tsytovich and Kronik, 1979). In this connection, integrated research on the cryogenic and physicomechanical properties of coarse-grained softs is being conducted in the Branch Research Laboratory for Engineering Cryopedology in Power Plant Construction (BRLECPPC) under the general supervision of Prof. N.A. Tsytovich, Corresponding Member of the USSR Academy of Sciences. In the general case of superposition of many processes that influence the stressed--strained state of a frozen multiple-component soil medium, the following defining equation (system of equations of state) (Kronik, 1978) can be proposed as a first approximation: