Geotechnical modelling and subsurface analysis of complex underground structures using PLAXIS 3D

The Valley of the Kings (KV) is a UNESCO world heritage site with more than thirty opened tombs. Since the first tombs were constructed, at least 24 historical flash flood events has been identified, each of which has been contributed to the destruction and deterioration of the tombs. Recently, most of these tombs have been damaged and inundated after 1994 flood. In order to understand the Geo-environmental impact mainly the past flash floods due to the intensive rainfall storm on the valley of kings and the long-term rock mass behavior under geostatic stresses in selected Horemheb tomb (KV57) and its impact on past failures and current stability, Remote sensing, GIS, LIDAR, 3D finite element stability analysis and rock mass quality assessments had been carried out using advanced methods and codes. Our work provides environmental satellite space views via landviewer Erath Observation System (EOS) Platform with passive and active sensors which include the Normalized Difference Vegetation Index (NDVI), Soil-Adjusted Vegetation Index (SAVI), Atmospherically resistant vegetation index (ARVI), Green Chlorophyll Index (GCI), Normalized Burn Ratio (NBR), Normalized Difference Snow Index (NDSI), Light Detection And Ranging (LIDAR) images, Terrain (DEM) Digital Elevation Models, 3D geological maps. In other hand experimental and numerical geotechnical evaluations and modeling of the rock mass of these underground structures and their surroundings have been executed. We estimated the rock mass quality of the different members within the Thebes limestone and Esna shale formations using the mechanical testing and Rock Mass Rating (RMR), rock quality system (Q-system) and Geological Strength Index (GSI) systems. Our recent analyses show that the KV57 rock- cut tomb at Luxor has been cut into poor to very poor quality marl shale masses due to the impact of flash foods. Rock failures of ceilings and pillars were frequently facilitated by local, unfavorably oriented persistent discontinuities, such as tension cracks and faults. Other failures were related to the disintegration of the marl limestone and Esna shale Formations into individual nodules upon weathering. Our data suggest that, in ancient Egypt monumental tomb construction, low-strength rock masses rarely resulted in modifications of the planned tomb design in order to minimise the risk of rock falls and to prevent collapses. The current flood protection measures are not enough. For this two following measures are proposed 1—to rise the current wall by 50 cm. 2—to fill the depression by reshaping bathymetry.

The plastic zones and displacements around underground openings in rock masses containing a fault

Development of Equivalent Stress- and Strain- Dependent Model for Jointed Rock Mass and Its Application to Underground Structure

Three dimensional image of stress space geotechnical constitutive model

One of the most significant challenges of construction of underground large size structures is to determine the effect of the geological discontinuities. Fault is a natural discontinuity which allows significant displacement of the rock mass along the fault plane and increases the plastic zones around the underground structure. For instance, an underground hydropower plant comprising more than two underground caverns and large distance between the underground cavern incurs the higher cost because of connecting tunnels or transfer of electricity from powerhouse cavern to transformer cavern. However, presence of the fault would result in the increase of the plastic zone and shear displacement along the fault. Thus, with regards to the effect of the fault on the stability of the two parallel caverns, in this paper different numerical models were simulated to study the effect of the fault on plastic zone around the cavern group and pillar between the caverns, and shear displacement along the fault plane under different scenarios such as fault location, fault dip angle, fault friction angle and in-situ stress conditions. The results are produced graphically and discussed. These results offer advance guidelines in construction of the two parallel large size caverns.

The lack of filtration reliability of bearing structures of urban underground facilities laid down at the design stage is associated with the unresolved issues of their filtration interaction with the adjacent soil or rock body. Water flows through the lining of the underground structure destroy the load-bearing structures, contribute to the removal of loose material into underground workings and create unacceptable microclimatic conditions for human stay. The question arises not only about the permissible degree of permeability of these structures, about the influence of filtration processes on the properties of the lining materials and their stability, but also about the relationship of water permeability of the bearing elements with the properties of the rock mass. Therefore, ensuring the filtration reliability of urban underground structures should be based on a set of protective measures aimed at involving in the work of the relevant properties of the underground object, and rock mass and technological methods of its construction, maintenance and operation. The problem of sealing the underground structure cannot be solved only by improving the concrete lining and raises the question of the need for measures to manage the characteristics of the state of the soil mass, which is the subject of this study.

Friction anchor bolts are commonly used for providing support in underground structures by relying on frictional forces between the bolt and the surrounding rock. This study proposes a method to enhance the efficiency of these bolts by injecting a cement-based mixture comprising cement, sand, and additives. The injection of this mixture into the bolt results in internal expansion, which reinforces the friction and bearing capacity of the bolt. The increased volume exerts a radial force, leading to improved adherence, load transfer, and void filling. Pullout tests were conducted on various rock masses to evaluate the performance of the anchor bolts. The results demonstrate increased pullout resistance with higher rock mass quality and longer cemented bolts. Additionally, the use of a silicate-based additive accelerated the curing time of the cement, enhancing the strength of the bolts. The study also highlights the significant influence of groundwater on the bearing capacity of the bolts. These findings indicate the effectiveness of cemented concrete injection in strengthening friction anchor bolts and their anchorage in underground structures.

The results of the durability analysis of a complex underground structure and surrounding multilayered rock massif are presented. The research is conducted based on an applied stress-strain state problem for a salt rock massif in the vicinity of an underground cavity of a large cross-section which is in conjunction with a mine shaft. The main aim of the research is to perform a comparative analysis of various mathematical models of the creep process. The problem is solved using finite element method to achieve this goal. Regularity in the development of deformation processes of the enclosing rock massif is established as a result of the study. According to this regularity, both primary creep and primary-secondary creep models show that the main increase of creep deformations occurs during a short initial time period after which creep strain rate decreases sharply.

Effect of Explosion on underground structures where drilled on the stony materials can be affected by explosive strength and rock mass properties of tunnel. In this paper, it has been studied on effect of explosion of 10 tons TNT on the round tunnel (diameter: 10 m) in 25 m depth in the mass rocks (RMR > 90) to estimate stability of tunnel to construct underground structure. Regarding to the studied stones, geo-mechanical indices of rock mass have been found to use as strength criteria in UDEC. In the next step, tunnel in real dimensions and founded indices is modeled with UDEC and analyzed stably. Explosion wave indices are found by UFC Instruction and other experimental relations to administer force from explosion wave on the model. Finally, on the base of FISH, indices of explosion wave are administrated in UDEC and tunnel is analyzed dynamically. According to modeling in depth of 25 m, amount of displacement of drilled tunnel in mass rocks (RMR < 90) is very lower than standard criterion and the tunnel is very stable. Development of plastic zone, vertical and horizontal displacement of rock mass around the tunnel, speed variations and stress from explosion wave are modeled and recorded as the graphs and figures.

Empirical and numerical methods of design play a vital role in assessing rock mass behaviour quantitatively and qualitatively for the design of underground structures and support systems. The purpose of this research is to review the techniques used for the management and prevention of failures that occur in rock mass for safe, stable, efficient, and economical design of support system for underground structures especially tunnels in diverse rock mass conditions. Failure of tunnels in rocks can occur during construction as well as during service; however, the former is very common. The most challenging task in tunnel construction is the rehabilitation and remedial process of the failed tunnel section. Unfortunately, due to differences in nature, shape, and type of failure, each case needs to be treated discretely and independently. The risk of failure can be minimized by implementing prior preventive measures, while the success of rehabilitation is based on better management of rehabilitation work. However, both prevention and rehabilitation need ample investigative knowledge that can be learned from case histories. The current work is related to the prevention and mitigation methods of tunnel failure and collapses that occur during the early stages of tunnel designing.

The strength and deformational behaviour of jointed rock mass is the basic input for the design of slopes, foundations and underground structures. Most of the Civil engineering activities are at surface or shallow depth where rock mass is subjected to the negligible or low confining pressure conditions. In-situ testing for the determination of strength and deformational parameters is mostly expensive and time consuming hence not feasible most of the time. It is always desirable to follow a detailed and experimentally proven approach for the preliminary assessment of behavior of rock mass. In the present study an attempt has been made towards this direction to understand the strength reduction and deformational behaviour of jointed rock under biaxial stress state.

Simulations of fracture and fragmentation of geologic materials using combined FEM/DEM analysis

The strength of rock mass probably is the first engineering parameter that a geotechnical engineer may be keen to establish before the start of any mining and civil engineering project. The strength of a rock mass at site is generally influenced by joint geometry and the stress state that it experiences. Field studies show that stress conditions around underground structures will be generally true triaxial or polyaxial, i.e., σ1>σ2>σ3. The rock mass behavior in such field conditions can effectively be simulated in laboratory by conducting large-scale physical modeling. In this study the most commonly occurring joint configurations (three joint sets) were created on rock mass models in the laboratory and tested under polyaxial stress compression. The model rock was a sand-lime block with low strength and medium deformability. The joint configurations were varied to assess the influence of joint geometry on the stress-strain curve, failure mechanism, and strength anisotropy. Similarly, on each type of geometry, σ2∕σ3 ratio was also varied to study the effect of intermediate principal stress on engineering behavior of rock mass. The maximum enhancement of 310% in strength due to an increase in the σ2∕σ3 ratio was observed, which corresponded to joint inclination, θ=60°. Based on testing results, the polyaxial strength criterion was evolved similar to the von-Mises failure envelope.

The recent Pahang-Selangor raw water transfer tunnel project had resulted in a large amount of rock mass classification data for the assessment of the rock mass class required for the design of tunnel support system. In this project, a rock mass classification by Japan Highway Public Corporation (JH) has been used to assess the rock mass class using geological mapping and geological documentation of the tunnel face and the side walls of the excavated tunnels. Although JH classification had been used for this project, other forms of classification using different criteria from Rock Mass Rating (RMR) and Q-System have also been widely used for tunnelling project all over the world. Since there have been few studies on the relationships among such different criteria of the classification systems, this study mainly focuses on the comparison between the JH and RMR classification systems for the water transfer tunnel. From the correlation analysis among the criteria used in both JH and RMR classification systems, there is higher correlation if the rock mass is in relatively good condition. It was also found that there is less consistency between JH and RMR classifications in the region of ‘poor rock’. However, the correlation between both classification systems is still considered suitable to be used in this tunnelling project.

The paper is aimed at comparing the results of numerical analyses of underground openings in competent rock masses like the Carrara Marble (Italy) by considering a real and well documented case study. More specifically, 3D FEM and DEM analyses were carried out on a rock-mass model interested by two faults and three sets of discontinuities. The geometrical model is representative of deep underground openings where spalling - cracks and rock bursts can occur. PLAXIS 3D and 3DEC were used for the analyses. Intact rock and rock mass characterization of Carrara Marble was inferred from available technical literature. The analysis results were compared in terms of principal stresses and displacements in a number of monitoring points around the opening. The main practical interest is to find out a reliable approach for evaluating the stability of very large openings in a competent rock mass like Carrara marble. For such a purpose, a number of available in-situ stress measurements were used.