Deep Underground Science and Engineering最新文献

In recent years, the exploration of seabed has been intensified, but the submarine soils of silt and sand in the Yellow Sea area have not been well investigated so far. In this study, the physical and mechanical properties of silt and sand from the Yellow Sea were measured using a direct shear apparatus and their microstructures were observed using a scanning electron microscope. The test results suggest that the shear strength of silt and sand increases linearly with the increase of normal stress. Based on the direct shear test, the scanning electron microscope was used to observe the section surface of sand. It is observed that the section surface becomes rough, with many “V”-shaped cracks. Many particles appear on the surface of the silt structure and tend to be disintegrated. The X-ray diffraction experiment reveals that the sand and silt have different compositions. The shear strength of sand is slightly greater than that of silt under high stress, which is related to the shape of soil particles and the mineral composition. These results can be a reference for further study of other soils in the Yellow Sea; meanwhile, they can serve as soil parameters for the stability and durability analyses of offshore infrastructure construction.

The editors wish to highlight the articles appearing in this issue. The first article, entitled “New physics of supersonic ruptures” by Boris G. Tarasov, concerns the development of a new theory on the potential occurrence of ruptures after deep underground earthquakes. Two other articles belong to our first special theme of “Disaster evolution in deep underground.” The final two articles introduce a nonlocal damage fracture phase-field model for rock-like materials and the gas–liquid displacement in microcleats for mass transfer through gas- or water-driven displacement. These five papers indeed explore various aspects of deep underground science and engineering and constitute an integral component of deep underground fundamentals.

The research paper “New physics of supersonic ruptures” by Professor Boris G. Tarasov systemically summarizes his long-term research outcomes on the shear rupture mechanism of a fan-shaped structure deep underground (at seismogenic depth). This shear rupture mechanism involves extraordinary mechanical properties and energy transfer. Based on new experimental evidence in laboratory tests and some field monitoring behaviors of deep underground ruptures, this article highlights four important findings. First, a fan-hinged rupture occurs in intact rocks or pre-existing extremely smooth interfaces with a different mechanism, which displays such features as abnormally high energy supply and release as well as extremely low friction. Second, a fan-shaped structure is the key element that represents the source of rupture and consists of an echelon of rock slabs formed by tensile cracking. Third, the fan-shaped structure has almost zero shear resistance, amplified shear stress above the rock strength, abnormally high energy release, and new physics of energy supply to the supersonic rupture tip. Finally, super-shear and supersonic ruptures are observed on extremely smooth interfaces in laboratory conditions. A question commonly raised is, “Why a fracture can be initiated and propagated in grand depth where the in situ stress is so high.” This new physics of supersonic ruptures can cast some light on tackling the above question and guide researchers to observe the deep underground behaviors via unconventional geomechanics. This is an interesting attempt to understand the complex fracturing behaviors deep underground and may thus be beneficial for the development of a knowledge system for deep underground science and engineering.

The two articles from the special theme on “Disaster evolution in deep underground” are entitled “Energy-based analysis of seismic damage mechanism of multianchor piles in tunnel crossing landslide area” and “Triaxial creep damage characteristics of sandstone under high crustal stress and its constitutive model for engineering application.” These articles explore the disaster initiation and evolution in deep underground environments involving energy transfer and dissipation. The two artic

Damage and fracture are the most extensive failure modes of rock materials, which may easily induce disaster and instability of engineering structures. This study developed a nonlocal damage fracture phase field model for rocks considering the heterogeneity of rocks. The modified phase field model introduced the heterogeneity of fracture parameters and modified the governing equations. Meanwhile, the free energy was constructed by the elastic strain energy sphere-bias decomposition and the plastic strain energy. As for the numerical implementation, the three layers finite elements method structure was used in the frame of the finite element method. The ability of the modified phase field model has been illustrated by reproducing the experiment results of rock samples with pre-existing cracks under compression.

The evolution due to temperature and pressure of shale reservoir permeability affects the productivity evaluation and development decision of shale gas reservoirs, which is very important for the exploration and development of unconventional gas reservoirs. This study analyzed the coupling effects of temperature (25, 50, and 75°C), effective stress (15 and 30 MPa), and pore pressure (0.5, 2.0, 4.0, and 8.0 MPa) on the permeability of the shale sample in the Longmaxi Formation. As the temperature and pressure increased, the apparent permeability exhibited a downward trend, and the absolute permeability decreased with the rise of temperature or effective stress. An in-depth analysis of the gas slippage factors under the conditions of different temperature and pressure was conducted to evaluate the trend of the average pore width with temperature and pressure. The results were then verified by scanning electron microscopy (SEM). The results provide new insights into evaluating the permeability of the Longmaxi shale and can be used to enhance the gas recovery rate of deep shale gas reservoirs.

To explore the cumulative deformation effect of the dynamic response of a tunnel crossing the hauling sliding surface under earthquakes, the shaking table test was conducted in this study. Combined with the numerical calculations, this study proposed magnification of the Arias intensity (M_Ia) to characterize the overall local deformation damage of the tunnel lining in terms of the deformation characteristics, frequency domain, and energy. Using the time-domain analysis method, the plastic effect coefficient (PEC) was proposed to characterize the degree of plastic deformation, and the applicability of the seismic cumulative failure effect (SCFE) was discussed. The results show that the low-frequency component (f₁ and f₂ ≤ 10 Hz) and the high-frequency component (f₃ and f₄ > 10 Hz) acceleration mainly cause global and local deformation of the tunnel lining. The local deformation caused by the high-frequency wave has an important effect on the seismic damage of the lining. The physical meaning of PEC is more clearly defined than that of the residual strain, and the SCFE of the tunnel lining can also be defined. The SCFE of the tunnel lining includes the elastic deformation effect stage (<0.15g), the elastic–plastic deformation effect stage (0.15g–0.30g), and the plastic deformation effect stage (0.30g–0.40g). This study can provide valuable theoretical and technical support for the construction of traffic tunnels in high-intensity earthquake areas.

Given the challenges in managing large deformation disasters in energy engineering, traffic tunnel engineering, and slope engineering, the excavation compensation theory has been proposed for large deformation disasters and the supplementary technology system is developed accordingly. This theory is based on the concept that “all destructive behaviors in tunnel engineering originate from excavation.” This paper summarizes the development of the excavation compensation theory in five aspects: the “theory,” “equipment,” “technology,” the design method with large deformation mechanics, and engineering applications. First, the calculation method for compensation force has been developed based on this theory, and a comprehensive large deformation disaster control theory system is formed. Second, a negative Poisson's ratio anchor cable with high preload, large deformation, and super energy absorption characteristics has been independently developed and applied to large deformation disaster control. An intelligent tunnel monitoring and early warning cloud platform system are established for remote monitoring and early warning system of Newton force in landslide geological hazards. Third, the double gradient advance grouting technology, the two-dimensional blasting technology, and the integrated Newton force monitoring––early warning––control technology are developed for different engineering environments. Finally, some applications of this theory in China's energy, traffic tunnels, landslide, and other field projects have been analyzed, which successfully demonstrates the capability of this theory in large deformation disaster control.

Cleats are the main channels for fluid transport in coal reservoirs. However, the microscale flow characteristics of both gas and water phases in primary cleats have not been fully studied as yet. Accordingly, the local morphological features of the cleat were determined using image processing technology and a transparent cleat structure model was constructed by microfluidic lithography using the multiphase fluid visualization test system. Besides, the effect of microchannel tortuosity characteristics on two-phase flow was analyzed in this study. The results are as follows: (1) The local width of the original cleat structure of coal was strongly nonhomogeneous. The cleats showed contraction and expansion in the horizontal direction and undulating characteristics in the vertical direction. (2) The transient flow velocity fluctuated due to the structural characteristics of the primary cleat. The water-driven gas interface showed concave and convex instability during flow, whereas the gas-driven water interface presented a relatively stable concave surface. (3) The meniscus advanced in a symmetrical pattern in the flat channel, and the flow stagnated due to the influence of undulation points in a partially curved channel. The flow would continue only when the meniscus surface bypassed the stagnation point and reached a new equilibrium position. (4) Enhanced shearing at the gas–liquid interface increased the gas-injection pressure, which in turn increased residual liquids in wall grooves and liquid films on the wall surface.

The deep-sea ground contains a huge amount of energy and mineral resources, for example, oil, gas, and minerals. Various infrastructures such as floating structures, seabed structures, and foundations have been developed to exploit these resources. The seabed structures and foundations can be mainly classified into three types: subsea production structures, offshore pipelines, and anchors. This study reviewed the development, installation, and operation of these infrastructures, including their structures, design, installation, marine environment loads, and applications. On this basis, the research gaps and further research directions were explored through this literature review. First, different floating structures were briefly analyzed and reviewed to introduce the design requirements of the seabed structures and foundations. Second, the subsea production structures, including subsea manifolds and their foundations, were reviewed and discussed. Third, the basic characteristics and design methods of deep-sea pipelines, including subsea pipelines and risers, were analyzed and reviewed. Finally, the installation and bearing capacity of deep-sea subsea anchors and seabed trench influence on the anchor were reviewed. Through the review, it was found that marine environment conditions are the key inputs for any offshore structure design. The fabrication, installation, and operation of infrastructures should carefully consider the marine loads and geological conditions. Different structures have their own mechanical problems. The fatigue and stability of pipelines mainly depend on the soil-structure interaction. Anchor selection should consider soil types and possible trench formation. These focuses and research gaps can provide a helpful guide on further research, installation, and operation of deep-sea structures and foundations.

We highlight two articles in this issue: A research article titled “Excavation compensation theory and supplementary technology system for large deformation disasters” by Manchao He et al. and a review article titled “Mineralogy, microstructures and geomechanics of rock salt for underground gas storage” by Veerle Vandeginste et al.

The research article “Excavation compensation theory and supplementary technology system for large deformation disasters” by the team of Academician Manchao He comprehensively and systemically summarized their long-term research outcomes on excavation compensation theory and its supporting technology system. The capability of excavation compensation theory in finding effective solutions to large deformation disaster control in underground engineering was demonstrated through its successful applications in various engineering projects. We are sure that this theory and its supporting technologies as well as equipment represent valuable contributions to geotechnical and deep underground engineering.

This excavation compensation theory for the large deformation disaster control is based on the concept that “all damage in tunnel engineering is caused by excavation.” The authors systematically summarized its five components: concept, equipment, technique, design methods with large deformation mechanics, and engineering applications. According to the excavation compensation theory, any supporting system can provide a compensation force for the restoration of the stress state in the surrounding rock to its original stress state as much as possible. Through compensation force calculations, the authors found that high-stress compensation was the most effective means for excavation disturbance control, which could prevent damage in deeply burial tunnels. They proposed a design method and a small deformation criterion for large deformation disaster control based on large deformation mechanics. This design method largely extends the traditional design methods for the excavation of shallow tunnel to deep tunnels.

The authors described their efforts toward the development of supporting equipment such as NPR anchor rods/cables with high resistance, large deformation, and shock resistance. These mechanical properties can effectively achieve the goal of high-stress compensation. They developed an integrated system for comprehensive monitoring, early warning, and control of rock mass large deformation disasters, a tunnel intelligent monitoring and early warning cloud platform system, and a Newton force remote monitoring and early warning system.

The authors developed a series of supporting technologies for different geological conditions. The dual-gradient advanced grouting technology can effectively improve the strength of surrounding rocks in fault fracture zones. The NPR materials can achieve a high-stress compensation for large deformations in surrounding rocks of fault fracture zone tunnels. Two-dimensiona

In underground mines, sublevel stoping is used among a variety of different methods for mining an orebody, which creates large underground openings. In this case, the stability of these openings is affected by a number of factors, including the geometrical characteristics of the rock and mining-induced stresses. In this study, a sensitivity analysis was conducted with the numerical, squat pillar, and Mathews stability methods using the Taguchi technique to properly understand the influence of geometric parameters and stress on stope stability according to Sormeh underground mine data. The results show a full factorial analysis is more reliable since stope stability is a complex process. Furthermore, the numerical results indicate that overburden stress has the most impact on stope stability, followed by stope height. However, the results obtained with Mathews and squat pillar methods show that stope height has the greatest impact, followed by overburden stress and span. It appears that these methods overestimate the impact of stope height. Therefore, it is highly recommended that Mathews and squat pillar methods should not be used in high stope that is divided with several sill pillars. Nonetheless, Mathews method cannot accurately predict how the sill pillar impacts the stope stability. In addition, numerical analysis shows that all geometric parameters affect the roof safety factor, whereas the sill pillar has no significant influence on the safety factor of the hanging wall, which is primarily determined by the stope height–span ratio.