Saturated Rock Mass Research Articles

Excess Pore Water Pressure within a Deep-seated Bedding Fault: Understanding of Earthquake Induced Large Landslide Initiation

The 2008 Wenchuan Ms8.0 earthquake triggered a landslide (i.e., Daguangbao landslide) with a volume of near 1.2 billion m3. This landslide involved the Paleozoic carbonate strata and the geological background of the sliding zone is a pre-existing bedding fault with a maximum thickness of 5 m and depth of 400 m in the slope. The bedding fault was the groundwater channel in the slope with saturated rock mass, according to the latest survey. To reveal the initiation mechanism of Daguangbao landslide (hereinafter short for DGB landslide) related to groundwater, a kind of simplified model of hard carbonate rock-cut slope with weak layer has been proposed to generalize bedding fault to weak layer in hard carbonate rock layer. And response characteristics of the model have been simulated by fluid-solid coupling algorithm in the FLAC3D program. The results showed that the hard carbonate rocks above and below the weak layer were different in deformation during strong earthquake, which led to the dynamic behavior of vibratory stamping-tension to the weak layer. And then, the discordant deformation of the two layers resulted in the excess pore water pressure featured with instant amplification and cumulative growth in the saturated water weak layer. So it was inferred that the rapid drop of inside effective stress caused by excess pore water pressure in the weak layer during strong earthquake would give rise to the sudden shearing of stress in the front locked segment of the slope after rapid stress concentration, and consequently trigger the DGB landslide.

Study of the Limestone Strength Weakening Mechanism at the Eastern Margin of the KangdianPalaeouplife in Southwest China

The limestone of the South China Lower Permian Qixia & Maokou Group usually features high purity, high strength, and poor weathering, while the limestone of the Qixia & Maokou Group at margin of the Chuan-Dian Paleouplife of southeast China is characterized by obvious strength weakening. The weakening of limestone strength leads not only to excessive errors in the estimation of useful material reserves in the limestone quarry, but also increases the engineering slope support cost in the limestone distribution area on the eastern margin of the Kangdian Paleouplife. In order to ascertain the cause mechanism of the strength weakening of the limestone in the stockyard, we take the stockyard in the dry valley as an anatomical point. The strength weakening of limestone is comprehensively analyzed by means of drilling, large-section excavation, site investigation, sampling, and physical mechanics tests. The main findings are as follows: (1) The limestone area of the Qixia & Maokou Formation near the Kangdian Paleouplife generally contains terrigenous fine-grained materials and mud iron; (2) The weakened rock masses are divided into two types of weakening: deep dissolution type and deep strong weathering type. The uniaxial compressive strength of the deep weakened rock mass is only 2.5-25 MPa, which is 70%-90% lower than that of the fresh rock mass. Compared with the natural state, the compressive strength of the saturated rock mass is reduced by 60%-90%. The deep weakened rock mass has the characteristics of weakened strength and is softened by water; and (3) The dissolution type rock mass is weakened as a result of the dissolution of the high-level exposed broken spring along the east-west fracture zone; the formation mechanism of the strong weathering rock mass weakening is that under the conditions of tectonic shear, terrigenous muddy interlayer and dry-heating condition. The buried depth of groundwater is large, the hydrodynamic force is weak, and the coupling of water and rock under long-term infiltration environments makes the limestone body softened and argilized in situ, leading to a significant decrease in the strength of the rock mass.

Micromechanical thermo-hydro-mechanical coupled model for fractured rocks considering multi-scale structures and its engineering application

Most existing studies on the coupled thermal-hydro-mechanical models for fractured rock mass are formulated using the macroscopic phenomenology method. As a result, the micromechanical behaviors of discontinuities, which essentially control the macroscopic response of the material, are not well considered in modeling the thermal-hydro-mechanical coupling processes for disturbed rock mass. In this study, the fractured rock mass is characterized by an anisotropic medium containing arbitrarily distributed penny-shaped microcracks in rock blocks separated by multiple sets of critically orientated fractures of large scales. This is an anisotropic coupled thermal-hydro-mechanical model for deformed saturated rock masses, which is capable of considering the alteration of macro-meso discontinuities. A multiscale damage constitutive model for fractured rock mass with the thermal-hydro-mechanical coupling is presented based on the Mori-Tanaka homogenization method and the thermodynamics theory. The influences of anisotropic damage growth, sliding dilatancy and normal compression of small-scale microcracks, and shear sliding and mobilized degradation of large-scale fractures are commendably accounted for. To reflect the anisotropic strength, the interaction between large-scale fractures and small-scale microcracks is also considered by practically relating the microcracks damage resistance to the orientation of fractures. By capturing the deformation of fractures and the opening and connectivity variations of microcracks with the constitutive model, the multi-scale structural change-induced permeability variation is modeled by the volumetric averaging method. The constitutive model and permeability tensor formulation have been implemented in a FEM code, which is then coupled with the well-established non-isothermal fluid flow simulator TOUGHREACT by an interlaced algorithm to establish a coupled thermal-hydro-mechanical numerical simulation platform. A numerical example is finally performed to investigate the effects of multi-scale structures and thermal-hydro-mechanical couplings on the water injection-induced temperature, pressure, and deformation responses of a deeply buried geothermal reservoir. The research may provide a useful reference for deepening the study of the thermal-hydro-mechanical couplings in deep rocks.

Coupled solid-fluid response of deep tunnels excavated in saturated rock masses with a time-dependent plastic behaviour

This article provides a general numerical approach for modelling the response of deep tunnels excavated in saturated time-dependent plastic rock masses, considering a coupled solid-fluid interaction and time-dependent plastic behaviour. In order to do that, a Burgers-viscoplastic strain-softening model has been developed and implemented into the finite element method software CODE_BRIGHT, and a coupled solid-fluid model is used to simulate the interaction between solid deformations and fluid flow. Parametric analyses are then performed to analyse the influence on the tunnelling response of different time-dependent models, different standstill times and different excavation rates. It has been observed that the time-dependent model selection is crucial to simulate the response of underground excavations. Additionally, the coupled solid-fluid results are significantly different from the purely mechanical ones. The liquid pressure build-up in the vicinity of the tunnel face and the overpressure dissipation with time due consolidation can be accounted for. Moreover, the higher the excavation rate, the larger build-up of liquid pressures occurs.

Heat Flow in Fractured Rocks: Stress and Moisture-Dependent Thermal Contact Resistance

The thermal conductivity of fractured rock masses is an important parameter for the analysis of energy geosystems, yet, its measurement is challenged by specimen size requirements. Fluids within fractures have lower thermal conductivities than rock minerals and heat flow lines constrict through contacting asperities. Together, heat flow constriction and phonon boundary scattering cause an apparent temperature discontinuity across the fracture, typically represented as a thermal contact resistance. We investigate the thermal contact resistance in fractured limestone and its evolution during loading and unloading (σ’=10 kPa to σ’=3000 kPa) for clean and gouge-filled fractures, under both air-dry and water-saturated conditions. The fracture thermal contact resistance decreases during loading because of the increase in the true contact area, gouge and asperity crushing, and fracture filling by produced fines that contribute new conduction pathways. These processes convey high stress sensitivity and loading hysteresis to the fracture thermal contact resistance. Water fills the fracture interstices and forms menisci at mineral contacts that significantly improve heat conduction even in partially saturated rock masses. The rock mass effective thermal conductivity can be estimated by combining the intact rock thermal conductivity with measurements of the thermal contact resistance of a single fracture under field boundary conditions.

Hydro-mechanical modelling and analysis of multi-stage tunnel excavations using a smoothed excavation method

The main objective of this article is to provide a general numerical approach for the hydro-mechanical (HM) modelling of tunnels excavated in saturated rock masses exhibiting plastic behaviour, considering a multi-stage excavation process. First, a new excavation method has been proposed and implemented in the software CODE_BRIGHT, based on the finite element method. In this method, the stresses in the excavation elements are reduced smoothly. As verification, the principle of uniqueness has been tested for multi-stage excavation. Then, numerical studies have been carried out to verify the advantages of the proposed excavation method in the numerical calculation, showing that the proposed method improves computational efficiency and mitigates convergence issues. Hence, this method can solve the usual numerical difficulties related to excavation problems and, therefore, it allows a more in-depth analysis of the HM behaviour of rock masses during tunnel excavation.Moreover, the results obtained in CODE_BRIGHT using the proposed method are compared with existing solutions for longitudinal deformation profiles (LDP), including elastic–plastic solutions for mechanical problems and elastic solutions for HM problems. Furthermore, this article presents the HM modelling of tunnels excavated in saturated rock masses, analysing the sensitivity of the LDP to the HM conditions and to the rock mass quality. Finally, based on a large amount of data obtained from numerical simulations, empirical solutions for the LDP of tunnels excavated in saturated rock masses –in a steady-state HM framework– have been obtained by fitting non-linear curves for the normalised radial displacements that occur ahead and behind the tunnel face. Hence, this article attempts to provide a convenient set of alternatives for the preliminary design of tunnels excavated in saturated rock masses.

Non-Dispersive Anti-Washout Grout Design Based on Geotechnical Experimentation for Application in Subsidence-Prone Underwater Karstic Formations.

A new non-dispersive, anti-washout grout consisting of ordinary Portland cement, slag, superplasticizer, and methylbenzyl cellulose is proposed herein for the treatment of open karst, jointed and fractured rock, open-work gravel, and permeable sediments. A series of laboratory experiments were performed to design an anti-wash out grout suitable for grout injection of coarse aggregates depicting partially and open-jointed saturated rock mass and grouting concrete aggregates for underwater construction. The Taguchi orthogonal array was used to obtain nine different grout mix ratios. A total of four variables were considered, each with three different levels of the water–cement ratio, slag, and dosage of additives such as the superplasticizer and methyl benzyl cellulose. The laboratory determination of grout characteristics recording of mini slump, temperature, pH, visual assessment of grout dispersion, bleeding, and initial setting time and as well as uniaxial compressive strengths and permeabilities of the hardened grout samples were tested. To evaluate the suitability of the grout mixes, an analysis of variance was used for factor analysis and Grey relational analysis (GRA) was used to determine the optimal grout mix design. Based on the GRA, the following levels of the factors afforded the best results: water level 1 (0.3%), SP level 3 (0.01%), methylbenzyl cellulose level 2 (0.002%), and slag level 3 (0.1%). This paper describes the research methodology, detailed research observations, and analyses involved in designing the appropriate concrete mix. Based on the conclusions, relevant commendations regarding the suitability of grout testing equipment and grout mix designs are presented.

Modeling the closure behavior of natural fractures in porous media using high aspect ratio interface elements

Many reservoirs consist of fully saturated rock masses containing a very complex natural fracture network. In such cases a decrease in the fracture fluid pressure reduces its aperture due to an increase in the effective stresses. In order to tackle the influence of fracture permeability on the pressure field and fluid flow, this paper proposes a Discrete Fracture-Matrix (DFM) model based on the finite elements to simulate coupled flow and geomechanics in porous media containing fractures with known position and properties (e.g. DFN realizations and fracture networks interpreted from outcrops). The proposed model is based on the use of triangular finite elements with high aspect ratio (HAR) to explicitly represent the fractures. These HAR elements have been successfully used to deal with cracks in concrete structures, desiccation cracks in soils and hydraulic fracturing in geo-reservoirs. This work demonstrate that these HAR elements equipped with a simple continuum (stress-strain) constitutive contact model that mimics the discrete (stress-displacement) Barton-Bandis joint model are able to properly describe the closure behavior associated with natural fractures. The constitutive model is integrated by means of the IMPL-EX scheme, which is a robust and stable technique used to achieve faster convergence. Darcy's law establishes the relationship between the fluid flow and the pressure field, and a fully coupled hydro-mechanical formulation comprises the mathematical framework. The proposed approach is based on continuous mechanics concepts and the implementation is made at constitutive level, and therefore it is simple and easy to be included in any existing FE program. To show the efficiency and accuracy of the proposed model, three numerical examples are conducted in this work: (i) benchmarks involving a medium with a single natural fracture, (ii) three reservoirs with different discrete fracture networks, and (iii) a transient analysis of a reservoir under different fracture conditions, such that the behavior of a intact reservoir, a reservoir containing fractures with constant aperture, and a reservoir in which the fractures aperture depends on the stress state are compared in terms of pore pressure, displacement field and fluid loss. In the first example, the results obtained with the proposed methodology are validated against the Barton-Bandis model. The agreement between the results is very satisfactory. The analysis of the latter two cases show the Barton-Bandis contact model is able to reproduce the effects of fracture permeability on pressure field in the reservoir, showing the capacity of the model to reproduce the main trends associated with the closure of natural fractures.

Precise integration method for solving the seepage‐stress coupling problem in rock mass with singular possibilities of the coupling matrix

SummarySeepage‐stress coupling is a key problem in the field of geotechnical engineering, and the finite element method is one of the main methods to study seepage‐stress coupling in rock masses. However, the finite element method has issues of poor stability, low efficiency, and low accuracy in the simulation of the seepage‐stress coupling problem. In this paper, the homogeneous saturated rock mass is taken as the object to deduce the control equation based on the Biot's theory. Considering the singularity of the coupling matrix, the discrete equation is converted into a precise integral format, and the equation is solved by the precise integration method to avoid instability and low precision. The precise integration method in this paper has good numerical stability, fast convergence speed, and high simulation accuracy, which effectively facilitates the rapid and stable numerical simulation of the seepage‐stress coupling problem using the equivalent continuum medium model. The validity and accuracy of the precise integration method for seepage‐stress coupling problems are verified by numerical examples.

3D Rotational Failure Mechanism of Tunnel Face in Weathered and Saturated Hoek-Brown Rock Masses

This paper aims to assess the face stability for tunnels excavated in weathered and saturated rock masses using the Hoek-Brown failure criterion. With resort to the upper bound theorem of limit analysis, a 3D rotational failure mechanism is constructed in which the rate of work done by pore water pressure is calculated as a part of external work by introducing the pore water pressure coefficient. To verify the validity of the proposed approach, comparisons with the previous studies are performed considering the case of Mohr-Coulomb failure criterion. Subsequently, numerical trials are done to investigate the nonlinear responses of the normalized critical support force against tunnel face based on the Hoek-Brown failure criterion. Accordingly, several normalized design charts are provided for a quick assessment of tunnel face stability. To further improve the proposed approach, the main error sources are discussed as a reminder in engineering application which is followed by the candidate schemes reported by other authors. The merit and demerit of these schemes are roughly described for reference. Conclusively, the proposed approach is tightly linked to practical engineering and provides more reliable assessment of tunnel face stability below water table without much expensive numerical simulations.

Numerical simulation of soil stability during artificial freezing

Artificial ground freezing is an efficient method for construction of vertical mine shafts under hard geological and hydrological conditions. The present article is devoted to a numerical simulation of mechanical behavior of soils surrounding freezing wells during a shaft sinking with a use of the artificial ground freezing method. The numerical simulation is carried out on the basis of a thermo-hydro-mechanical model of freezing process in a water saturated rock mass. Constitutive relations are derived within framework of thermo-poromechanics in consideration of the phase transition. Description of the mechanical behavior of soils is performed in the elasto-plastic formulation. The model allows one to take into consideration an influence of frost heave and temperature change on strain of soils under freezing process. Plastic strain is estimated with a use Drucker-Prager criterion. The numerical simulation of artificial freezing of a rock mass has been carried out for two cases. In the first case a response of soils adjacent to freezing wells on an application of the AGF method and a shaft sinking has been analyzed. In the second case stress-strain state in a neighborhood of the freezing well has been determined. It has been shown that the artificial freezing and excavation works leads to an increase of mechanical pressure in near-wellbore domains. Frost heave and temperature deformation induced by the artificial freezing cause displacement of soil in the vertical and horizontal directions.

The effect of saturation conditions on fracture performance of different soundless cracking demolition agents (SCDAs) in geological reservoir rock formations

Fracture stimulation using soundless cracking demolition agents (SCDAs) is a potential alternative technique to induce high-density fractures in sedimentary reservoir-rock as an auxiliary technique to improve the efficiency of enhanced oil and gas recovery efficiencies. However, to date, its application has been limited to fracture stimulation in dry rock masses. Therefore, using modified SCDAs, which can be used for underwater rock fracturing, a series of experiments was conducted to investigate the fracturing performance of SCDAs in saturated rock masses. 18 coarse-grained sandstone specimens were saturated in water, oil, and NaCl brine and fractured using three different SCDA types: a standard SCDA (S1), and two modified for underwater application (S2) and accelerated reaction rate (S3). Then, the fractured samples were scanned in the Australian Synchrotron, and the fractures were quantified using Avizo 9.0.1. The fracture initiation time and the total fracture network length and volume were found to be dependent on the saturated pore fluid of rock. Water saturation of samples increased the fracture initiation time by 16.5%, 24.1% and 13.68% for S1, S2, and S3 type SCDAs respectively and reduced the fracturing potential of SCDA by 59.5%, 32.49% and 66.67% compared to dry samples. This reduction was less apparent in oil-saturated samples as the high pore fluid viscosity of oil-saturated samples aid fracturing, which is explained by the Poiseuille equation. Increasing salinity in the saturation fluid from 0% to 12.5% was favourable for the fracturing efficiency of SCDAs because of the formation of CaCl2 in the pore fluid, which accelerates the reaction of SCDA. Fracture orientation also changed depending on the saturation fluid, which was again governed by the variation in reaction rate in SCDAs under different saturation conditions.

The Influence of Admixtures on the Hydration Process of Soundless Cracking Demolition Agents (SCDA) for Fragmentation of Saturated Deep Geological Reservoir Rock Formations

Alternative fragmentation technologies such as soundless cracking demolition agents (SCDAs) can minimize adverse environmental impacts associated with conventional rock fracturing methods used in mining and energy industries. However, application of SCDA in deep underground environments is limited due to (1) inability of SCDA to react in saturated rock masses as a result of dilution and mass washout effects, and (2) slow expansive pressure generation in SCDA, which delays post-fracturing operations. This study addresses the first issue by modifying a generic SCDA using a viscosity-enhancing admixture (VEA), namely welan gum, to produce a hydrophobic SCDA for direct application in submerged conditions. The effect of the VEA, on the mechanical, microstructural and mineralogical morphology of hydrating SCDA was also investigated. According to the findings, adding just 0.1% of VEA by weight to the SCDA in combination with a water-reducing admixture significantly improves the washout resistance without compromising the fluidity of SCDA, however, at the expense of rapid expansive pressure generation rates. The reduction in expansive pressure, which is unfavourable for mining and energy engineering applications is caused by the interaction of VEA with the hydrating SCDA. This is evident in the SEM and XRD results observed. This urges the consideration of both positive and negative effects of welan gum in SCDA: enhancement of washout resistance and reduction of expansive pressure development prior to any field application.

Modelling the effect of ice swelling in the rock mass around an LNG underground storage cavern using FRACOD

Underground storage of liquefied natural gas (LNG) has many advantages over the conventional above-ground LNG storage due to its safety and energy efficiency. One of the key technical challenges for the underground storage of LNG is to understand the behaviour of the rock mass in the vicinity of the LNG cavern and hence to take measures to prevent leakage caused by possible rock fracturing in response to the cooling of the rock mass. With the extremely low temperature of the LNG ( − 162°C) in the storage cavern, sub-zero temperatures will be induced in the surrounding rock mass, which on one hand may cause tensile stress due to thermo-mechanical effect and on the other will cause the formation of ice in pores and cracks of the saturated rock mass. Ice formation is likely to cause compressive stress in the rock mass due to its expansion in volume. The combined effect of rock cooling and ice swelling is complicated as cooling tends to create open fractures whereas ice swelling tends to cause compression and the closure of these discontinuities. Understanding this effect is crucially important as it is related to the integrity of the surrounding rock mass for leakage prevention. This study presents recent developments of the thermal-mechanical coupling and ice swelling functions in FRACOD, a numerical code designed to predict rock fracturing processes in fractured rock masses. The new functions enable us to investigate the complicated response of an in situ rock mass to the excavation of LNG cavern and the storage of low temperature LNG in a most realistic way. The pilot LNG storage cavern experiment at Daejeon Korea is used as a case study site, and the measured temperature in the surrounding rock mass are used to validate the numerical model and the modelling method. The ice swelling effect was modelled by introducing a large number of random cracks in the rock mass, which have certain hydraulic apertures to hold water. When the local rock temperature is below zero, the aperture water will become ice and cause crack expansion. It has been found in the study that ice swelling has a major effect on the displacement and stress distribution in the rock mass. It causes a compression zone around the LNG cavern, and effectively prevents tensile fracturing and fluid leakage.

Analytical modeling of a deep tunnel inside a poro-viscoplastic rock mass accounting for different stages of its life cycle

An analytical approach of the viscoplastic behavior of a porous saturated rock mass surrounding a deep tunnel in different stages of a simplified life cycle is presented. The viscoplasticity is modeled by means of a simple (linear) Norton-Hoff’s law. Some numerical examples are performed to examine the consistency and relevance of the solutions. Parametric studies illustrate the influence of key parameters such as rock mass viscosity, Poisson’s ratio, rock mass permeability, lining emplacement, etc. This analytical approach constitutes a useful reference to facilitate more complex numerical simulation and making it possible to obtain practical estimations of the poromechanical behavior of underground structures.

Analytical modelling of a deep tunnel in a viscoplastic rock mass accounting for a simplified life cycle and extension to a particular case of porous media

Abstract An analytical approach to the viscoplastic behaviour of a rock mass around a deep tunnel in different stages of a simplified life cycle is presented. The viscoplasticity is modelled by means of a simple (linear) Norton–Hoff's law. First, the solution for a dry rock mass is presented, then an extension to a particular case of a porous saturated rock mass with a Poisson's ratio of 0.5 is examined. Some numerical examples are carried out to show the consistency and relevance of the solutions. Parametric studies illustrate the influence of key parameters such as rock mass viscosity and time of lining emplacement. This analytical approach constitutes a useful reference to test more complex numerical simulation and makes it possible to obtain practical estimations of the poromechanical behaviour of underground structures.

Loads on Sprayed Waterproof Tunnel Linings in Jointed Hard Rock: A Study Based on Norwegian Cases

A composite tunnel lining system based on a sprayed waterproofing membrane combined with sprayed concrete is currently being considered for future Norwegian rail and road tunnels. Possible loading of the tunnel linings caused by water pressure is being investigated. This tunnel lining system consists of a waterproof membrane which, during application on the sprayed concrete lining, bonds mechanically to the sprayed concrete on either side. Hence, a continuous, sealing, and non-draining structure from the rock mass to the interior tunnel surface is formed in the walls and crown. Experiences from some successful recent projects with this lining system in Europe are reviewed. However, these experiences are not directly comparable to the Scandinavian hard rock tunnel lining approach, which utilizes a relatively thin sprayed and irregular concrete layer for permanent lining. When considering the sprayed membrane and sprayed concrete composite lining concept, introducing a partially sealing and undrained element in the lining, the experiences with the traditionally used lining systems in Norway need to be reconsidered and fully understood. A review of several hard rock tunnels with adverse conditions, in which the tunnel lining has been subject to load monitoring, shows that only very small loads in the tunnel linings occur. Recent investigations with in situ water pressure testing, including two sites with the composite sprayed membrane in a partially drained waterproof tunnel lining, are discussed. In a case with a cavern located in a hydraulically saturated rock mass subjected to approximately 8 bar hydrostatic pressure, a negative pressure gradient towards the tunnel lining has been measured. The investigation results from the Norwegian test sites indicate that no significant loading of the tunnel lining takes place in a hydraulically saturated rock when applying this composite waterproof tunnel lining in parts of the tunnel perimeter.

Numerical Modeling of Pore Pressure Influence on Fracture Evolution in Brittle Heterogeneous Rocks

Rock is a heterogeneous geological material. When rock is subjected to internal hydraulic pressure and external mechanical loading, the fluid flow properties will be altered by closing, opening, or other interaction of pre-existing weaknesses or by induced new fractures. Meanwhile, the pore pressure can influence the fracture behavior on both a local and global scale. A finite element model that can consider the coupled effects of seepage, damage and stress field in heterogeneous rock is described. First, two series of numerical tests in relatively homogeneous and heterogeneous rocks were performed to investigate the influence of pore pressure magnitude and gradient on initiation and propagation of tensile fractures. Second, to examine the initiation of hydraulic fractures and their subsequent propagation, a series of numerical simulations of the behavior of two injection holes inside a saturated rock mass are carried out. The rock is subjected to different initial in situ stress ratios and to an internal injection (pore) pressure at the two injection holes. Numerically, simulated results indicate that tensile fracture is strongly influenced by both pore pressure magnitude and pore pressure gradient. In addition, the heterogeneity of rock, the initial in situ stress ratio (K), the distance between two injection holes, and the difference of the pore pressure in the two injection holes all play important roles in the initiation and propagation of hydraulic fractures. At relatively close spacing and when the two principal stresses are of similar magnitude, the proximity of adjacent injection holes can cause fracturing to occur in a direction perpendicular to the maximum principal stress.

Structural Plane of Rock Mass Strength Characteristics and its Impact on Groundwater

The strength characteristic of discontinuity is one of the most important mechanical characteristics of rock mass, and its strength dominates the strength and deformation of joint rock mass. The underground water has an important influence on the strength of discontinuity. In this paper, the strength theory of joint rock mass was summarized and analyzed; further, two kinds of failure mode of joint rock mass which are joint shear failure and rock shear failure were proof. Considering the impact of underground water, the effective stress principle was introduced, and base on it, the joint shear failure strength rule of the saturated rock mass was built. When the influence of underground water on joint strength is studied, the shear strength formula has important theoretical and realistic significance.

Effect of fissure water on mechanical characteristics of rock mass

In view of the effect of fissure water in fractured rock mass on the strength of rock mass in engineering projects, we prepared specimens of cement mortar to simulate saturated rock mass with continuous fractures of different slope angles. By exerting static and dynamic loads on the specimens, the mechanical characteristics of rock mass with fissure water under these loads can be analyzed. Our experimental results indicate that the static compressive strength of saturated fractured rock mass is related to the slope angle. The lowest compressive strength of fractured rock mass occurs when the slope angle is 45°, while the highest strength occurs when the specimen has no fractures. Fissure water can weaken the strength of rock mass. The softening coefficient does not vary with the slope angle and type of load. The hydrodynamic pressure of fractured rock mass gradually increases with an increase in dynamic load. For a 0° slope angle, the hydrodynamic pressure reaches its highest level. When the slope angle is 90°, the hydrodynamic pressure is the lowest.