The anisotropic strength properties of rocks, which are of great importance for the stability of engineering structures, can be determined by doing various laboratory works. In this study, the anisotropic strength properties of sedimentary rocks such as marl and mudstone were examined by making use of the indirect tensile strength test. Two different methods were applied in the test phase. Firstly, the disc shaped specimens prepared by using NX diameter cylindrical samples taken from blocks parallel to the bedding plane were placed in the testing apparatus at different angles from horizontal to perform tests. In the second phase, the NX diameter cylindrical samples were prepared at perpendicular (00), parallel (900) and 450 angles to the bedding plane and tests were performed at these orientation angles. Accordingly, in the tests performed by placing samples in the testing apparatus at different angles, the highest value was gathered at Ψ =0°, and the lowest at Ψ=900 anisotropy angle. In the tests of second phase, the highest value was gathered at φ=900, the lowest at φ=450 orientation angle.
Approximately 95% of sphere is consists of magmatic and metamorphic rocks but important part of earth’s surface, 75% of it, is consists of sedimentary rocks. Important engineering projects like mine, tunnel, subway, underground shelters, slopes etc. are designed due to geological and geomechanical properties of rocks. Thereby, it‘s very important to define strength and deformation behaviour pattern of these type of rocks, for safety and economics of structures which will build in them.
Rock anisotropy is one of the most important factors that effects strength and deformation behaviour of rocks. Most of the geological formations in nature exhibit anisotropic properties. Anisotropy of rocks come into existence because of structural facts like foliation, cleavage, schistosity, joint, micro and macro fractures, sequence of minerals and orientation of particles which constitutes rocks, etc. Suitable design models should be developed for determining effect of structural or inherent anisotropy on constructions which will build in geological formations.
Rocks show different strength and deformation characteristics due to direction. Sedimentary and metamorphic rocks are more anisotropic than igneous rocks. (Ramamurthy 1993). Metamorphic rocks such as slate, shale and gneiss show anisotropic behaviour (Goshtasbi et al. 2006). According to the study “Modelling of inherent anisotropy in sedimentary rocks” by Pietruszczak et al. (2002), sedimentary rocks such as shale, siltstone, claystone, etc. show strong anisotropy depending on orientation.
Runt, David (Faculty of Civil Engineering Czech Technical University in Prague) | Pruška, Jan (Faculty of Civil Engineering Czech Technical University in Prague) | Novotný, Jaroslav (Faculty of Civil Engineering Czech Technical University in Prague)
Rock bolts as construction elements are often used in underground civil engineering projects. We used Aydan finite elements for numerical description of rock bolt reinforcement and isoparametric bilinear finite elements for description of rock massif. We derived corresponding stiffness matrices and right hand sides and developed a finite element code for the calculation of rock deformations and stresses. The code was tested on several numerical examples. We computed in detail deformations and stresses in a round tunnel, first without any rock bolts and then with rock bolts placed in the tunnel arch. We compared deformations and stresses obtained by our calculations to approximate analytical solution.
Rock bolts as reinforcing construction elements are often used in underground civil engineering projects. Today it is common to use numerical modelling for designing and verification of various types of constructions and rock bolts are no exception. Several special rock bolt elements were created for this purpose. The most widely used elements was presented in the work of Ömer Aydan (1988). The so-called Aydan element is represented by four nodes in its simplest 2D form. Two nodes create a rod sub-element, which is a simple model of a steel bar. Remaining nodes represent the connection of this bar with surrounding rock massif by cement grout. This paper deals with composition of the stiffness matrix of Aydan element and its application to a simple two-dimensional numerical model of a circular excavation reinforced by rock bolts that are fastened by cement grout along their full length.
This paper briefly describes an integrated approach to mine ground water simulation and prediction using an in-house finite element code called COSFLOW developed in CSIRO of Australia. COSFLOW uses a Cosserat continuum theory for the efficient description of load deformation behavior of layered coal measure rocks. Both coupled mechanical deformation and fluid flow model and uncoupled fluid flow model have been used to assess the impact of mining on regional groundwater resources. The coupled model is used to estimate the mining induced permeability and porosity changes in the rock mass and provided inputs to the regional scale fluid flow only model. Comparisons of numerical predictions with mine measurements demonstrate the suitability of such an approach in accurately predicting coalmine water inflow and impact on water resources. First, the model is calibrated using existing extensive mine water inflow and piezometer measurements and then used to make predictions for future longwall panels.
Reliable prediction of rock mass deformation, mine stability, mine water inflow and mine gas emission is not only essential for improving mine safety and reduction of coal production costs, but also important for the assessment of environmental impact of mining. This prediction requires the accurate simulation of complex, highly nonlinear and irreversible mining induced processes including the mechanics of rock deformation and fracture and the consequent water flow and gas desorption and flow.
This paper presents an integrated approach to mine groundwater simulation and prediction using an in-house finite element code called COSFLOW developed in CSIRO of Australia. COSFLOW incorporates (a) Cosserat continuum theory (Cosserat & Cosserat 1909) in its formulation for describing the load deformation of layered coal measure rocks and (2) two phase double porosity fluid flow formulation that can be coupled with either the mechanical model or run separately in isolation. A full description of the COSFLOW code is presented in Adhikary and Guo (2002) and the references cited there.
Both coupled mechanical deformation and fluid flow model and uncoupled fluid flow model have been used to assess the impact of mining on regional groundwater resources. First smaller scale three-dimensional coupled mechanical models were run to estimate the change in permeability and porosity in the strata surrounding the longwall mines and then this information was input into a single-phase regional scale groundwater flow model. The coupled model is fully described in Adhikary & Wilkins (2012) and will not be discussed here.
A strong earthquake can stimulate large number of landslides, which can cause serious economic and person loss. Understanding the failure mechanisms of the seismically induced landslide and the resulting landmass runout is crucial. In this paper, two continuum models are examined which allow the simulation of large deformations. The first is performed by coupling a Lagrangian FE with an Eulerian description using the software Abaqus. The coupling procedure allows simulating the rock material as a flow running over rigid base. Material Point Method (MPM) is an innovative mesh-free particle method performs the coupling procedure in an arbitrary form where the natural movement of the material is traced. A frictional contact algorithm is included whereas an artificial damping is introduced in MPM to resemble the material damping. Moreover, a strain smoothening-technique is implemented to relax the numerical problem associated with using low-order tetrahedral element. The potential of applying the two approaches to simulate the failure of rock landslide is presented.
The stability of slopes is one of the prominent problems in practical engineering. The major causes responsible for triggering a landslide includes heavy rainfall, imposed loads, strength degradation due to weathering and seismic excitation. The earthquake–induced landslides are among the most destructive slope movements, where the excessive failure might take place (Omidvar et al. 2011). In some of the cases, it becomes inevitable to study the behaviour of the slopes even after the failure as the large scale movement over broad areas can result in serious damages and casualties. In these cases, the failures cannot be prevented, but it becomes a primary interest of research to know the extent and probability of an eventual slide to reduce the damage.
Numerical methods based on mesh deformation, e.g. Finite Element Method (FEM), have difficulties in modelling large deformations due to problems of mesh distortion and entanglement. In order to such type of large deformation problems, various methods have been proposed by coupling the two frame of references in a unified approach. Coupled Eulerian-Lagrangian (CEL) method is one of these methods, in which an updated Lagrangian finite element method (FEM) is coupled with the Eulerian description via interface models. The FE-software Abaqus utilised this feature and therefore it has been used in this paper. The Material Point Method (MPM), which is an innovative mesh-free particle method, performs the coupling procedure in an arbitrary form where the natural movement of the material is traced. MPM has been applied for many geotechnical applications involving large deformation of collapsing slopes and landslides (see for example Andersen & Andersen 2010, Hamad et al. 2013). In this paper, a strain-smoothening techniques based on nodal mixed discretisation has been implemented in MPM to relax the mesh locking problem, whereas the frictional contact algorithm is extended so that a prescribed velocity can be assigned directly to one of the two bodies in contact. Moreover in this paper, the two methods (MPM and CEL) have been applied to a landslide progression failure occurred during the 1999 Chi-Chi earthquake of Taiwan. To show the potential of applying the two continuum based models, some results are presented.
In this study, the possibility of measuring rock surface roughness by means of open-source photogrammetric methods was investigated. With simple commercially available digital cameras, samples of varying roughness were measured. As a reference, the samples were also measured with a high-resolution white light strip scanner and additionally manually with a contour gauge. By comparing the digital datasets it became clear that the open-source structure-from-motion (SFM) algorithms were able to capture the overall topography but with clearly less accuracy than the white light scanner. This had a marked influence on the determined roughness parameter JRC (joint roughness coefficient). For smooth surfaces the JRC was higher than the reference value, for rough surfaces it was lower. In general, with the introduced method it was possible to reproduce the surface of the rocks but care has to be exercised when roughness parameters are to be deduced from the datasets.
The shear strength of rock joints is primarily dependent on their surface roughness. In order to achieve a save and cost-efficient design in rock engineering it is desirable to measure joint roughness as accurate as possible. In the past, tools like contour gauges (Barton & Choubey 1977) and mechanical profilometers (e.g. Weissbach 1978) were used to measure unevenness of rock surfaces. Nowadays, high-resolution laser scanners (e.g. Fardin et al. 2001, Milne et al. 2009) or white light strip scanners (Tatone & Grasselli 2013) are applied to investigate rock surfaces. But, as these methods being cost-intensive, alternatives are needed. Therefore, in this study, open-source photogrammetric software was utilized to measure surface roughness. With a simple off-the-shelf digital camera in connection with well-established structure from motion algorithms five surfaces varying in roughness were investigated.
Engineering geological and geotechnical experiences obtained from a major NATM-tunnel (BBT Brenner Base Tunnel, exploratory tunnels) and a TBM-tunnel (Stanzertal hydropower plant, headrace tunnel) in phyllitic rocks in Tyrol (Austria) are described herein, focusing on driving method-related challenges and technical solutions. Both tunnels are situated in similar rock masses consisting of thinly laminated quartz-phyllites with brittle fracture and fault zones. The reaction of the rock mass on the tunnel headings have been comparable in the sense of the prevailing failure mechanisms, but had different impacts on the tunnel headings depending on the tunneling method (conventional or mechanized heading). As a centralized résumé, it can be stated out, that the conventional tunnel drives offered great advantages at fault zone crossings, whereas the TBM-headings performed very well within good rock mass conditions attaining advance rates of about 50 m per 24h.
In the Tyrolean Alps (Austria), phyllitic rocks are widely spread and several tunnels for infrastructure and hydropower plants were performed in these kind of rocks, especially in the last 50-60 years. Most of them were built by conventional excavation methods (drill & blast resp. NATM), mechanized driven tunnels have been exceptional cases. However, especially for elongated tunnels the discussion on the most suitable tunneling method - in technical and economic reasons - always arises during planning phase weighing the pros and cons of each method. Decision-making is mostly accompanied with the assumption that the chosen method is indeed fitting for most parts of the geological and geotechnical setting along the tunnel alignment but not for all sections. By describing the experiences from conventionally driven tunnels and a TBM-heading (obtained from geological documentation and geotechnical supervision on site), this paper highlights some advantages and disadvantages of the different underground construction methods. Both above mentioned tunnels (BBT, Stanzertal HPP) have been planned applying the guidelines of Austrian Society for Geomechanics (ÖGG 2008, ÖGG 2013).
The paper presents the monitoring and corresponding monitoring data management that is currently executed at the Cityringen project in Copenhagen, Denmark. In particular, it informs on the layout of the implemented monitoring programs, the different geotechnical and geodetic monitoring sensors and measuring systems used, how the monitoring data is acquired, transferred and further processed and, finally, the layout of the installed tunnel information system applied for monitoring data management. Examples of monitoring data, their acquisition, processing, visualization, alarming and reporting are described along with the experience of managing a huge amount of monitoring data.
1 Project Overview
The new Cityringen is part of the metro system in Copenhagen, Denmark. The Project comprises the construction of 17 new stations, five other underground structures as well as a 16.5 km twin-tube tunnel. The Client Metroselskabet IS has awarded the contract in 2011 to the Italian joint venture CMT led by Salini-Impregilio. SMT Denmark, a company owned by Angermeier Ingenieure (Germany) and Geodata Group (Austria) is responsible for the implementation and maintenance of the geodetic and geotechnical monitoring. The stations and shafts are constructed using secant pile walls or, for the deepest structures, diaphragm walls. In the inner city, many buildings have been founded either on wooden piles or soft layers. In the western part of the project area, groundwater abstraction for domestic water supply is taking place. At a few sites, extensive groundwater contamination has been found. Therefore, minimum 95% of the abstracted groundwater has to be re-infiltrated. The groundwater control system in place is performed by pumping in abstraction wells at the bottom of the deep excavation, treating the abstracted groundwater and recharging all of the pumped groundwater in recharge wells surrounding the box. A comprehensive monitoring system has been established. The central part of the monitoring system is the state of the art monitoring database system (Kronos, provided by Geodata), where real time data from the tunnel boring machines, the groundwater management system and all data from geodetic and geotechnical monitoring of buildings and structures within the zone of influence of the works, is collected. In order to perform the monitoring of possible movements of the ground and structures a very extensive 3D monitoring system with more than 100 robotic total stations, along with extensometers, inclinometers and piezometers, and strain gauges have been installed.
This paper aims to address the potentially inappropriate application of triaxial rock strength criteria to the polyaxial stress states calculated during 3d numerical analysis. We review some existing well-known polyaxial criteria, and discuss the advantage and disadvantage of each. Smoothness and convexity, 3d geometrical representation, the strengthening effect of σ2, and ease-of-use are some of the major requirements that are examined here. We show that accuracy may be achieved at the expense of mathematical complexity and advanced laboratory testing. However, such testing has not yet been accepted as a feasible common practice in rock engineering.
Determining the peak strength of rock has always been an essential problem in characterization of material behaviour in rock engineering practice. The most common approach in measurement and prediction of peak strength is to utilize a generally accepted strength criterion, such as the well-known triaxial Mohr-Coulomb and Hoek-Brown criteria.
Although the conventional triaxial strength criteria perform well in certain circumstances, they suffer from neglecting the simultaneous influence of all three principal stress components. That is mainly because of the triaxial nature of their empirical derivation methods, and thus being written in terms of σ1 and σ3, and not taking into account the intermediate principal stress σ2.
Studies on the effect of the intermediate principal stress started by conducting triaxial compression and triaxial extension tests on same materials. These results show that the peak strength of the rock in a triaxial extension stress state (σ1= σ2> σ3) is slightly higher than that in triaxial compression (σ1> σ2= σ3) (Figure 1.b). This testing was followed, after appropriate advances in testing equipment, by the true triaxial or the so-called ‘polyaxial’ tests on different rock types.
Results from polyaxial tests show that when the stress state deviates from triaxial compression (σ1> σ2= σ3) to polyaxial (σ1> σ2> σ3), the strength of the rock reaches a peak before it falls to a value in the triaxial extension stress state (σ1= σ2> σ3) that is slightly higher than that in triaxial compression (Figure 1.a). This confirms the earlier results of triaxial compression versus triaxial extension tests.
The sensor market and adjoined technologies like the Internet of Things (IoT)1 are rapidly growing, providing new possibilities but also creating new challenges; one of these challenges is the interconnection and communication of sensors using information technology and the joint evaluation of collected sensor data. The area of Geo-Monitoring has a long tradition in using sensors for observation of the geological, geotechnical and hydrogeological environment. Nonetheless the ever growing number of sensors, the ever increasing sampling rates, and the advent of new monitoring technologies call for new ways for effectively managing sensor networks and the logged data, so that the technological advance can be translated into a better understanding of the geo-environment, more accurate prediction, and reduced risks and costs. With its Sensor Web Enablement Initiative (SWE), the Open Geospatial Consortium (OGC) has provided standards that serve as universal foundation for all information systems dealing with sensors and sensor data.
Geology, geotechnics, hydrology as well as other environmental characteristics form a complex network of interactions. To be able to monitor the geo-environment we make intensive use of sensors and devices that turn natural characteristics into data that can be processed, evaluated and visualized. With the advent of more and more digital sensors (i.e. sensors or sensor systems that encode their observations in a digital form) and the ever-increasing sampling rate new challenges emerge that need to be addressed in order to use the recorded data for the benefit of a project.
The current situation in Geo-Monitoring, but also in many other areas where sensors are used, is comparable to the situation of GIS systems before the introduction of the Open GIS standards. Many isolated systems exist that manage sensor networks are often highly specialized and too often use proprietary technologies. However, especially in Geo-Monitoring where we aim for interdisciplinary data analysis this creates a multitude of problems and in many cases hinders an effective evaluation of sensor data.
The “Serra de Tramuntana”, located on the northwest side of the island of Mallorca, has a geological framework with alternative presence of weak rocks and fractured hard rocks and its typical Mediterranean climate make it a very prone area to landslides and rockfall events. The main road, called Ma-10, cross the range from north to south along 111 kilometers. One of the most active areas is the valley called “Gorg blau”, located in the middle part of Tramuntana mountain range. The local authorities have carried out several actions to protect the road last years. The winter of 2009 a rockfall with a total amount of 20,000 m3 of material detached, affected the road. After that different protection structures were installed. Afterwards different minor events have occurred affecting adjacent areas. Thus, some new analyses with 3D models and an executive project to install some new protection structures are under development.
The mountain range called “Serra de Tramuntana” is located on the northwest side of the island of Mallorca in the Mediterranean Sea, declared a UNESCO World Heritage on the category of Cultural Landscape. The typical Mediterranean climate, with periods of rain storms with strong rain in short periods of time with its geological framework with alternative presence of weak rocks of Keuper (Triassic) age and fractured hard rocks of Liassic (Jurassic) age make it a very prone area to landslides and rockfall events. A clear correlation between wet and rainy periods and instability events has been established (Mateos et al. 2010).
There are several mountain villages, cottages and some roads all over this mountain area that are systematically affected by these kind of events. The main road, called Ma-10, cross the range from north to south along 111 kilometers and has a high number of incidents for users of the road, rockfalls, mainly, that reach the pavement and in the worst cases cutting the road (see Figure 1).
The local authorities from the Council of Mallorca, “Direcció Insular de Carreteres” (DIC), have carried out several actions so as to protect the roads of the Tramuntana range against rockfalls, during last years. This period has been particularly active in this kind of incidents, which have affected to a greater or lesser extent to the existing road network. Thus, DIC have promptly enacted measures to protect the road over time. These measures have been correctives ones until recent times. One of them was that of the winter of 2009 that affected the Ma-10 road in km 29. A total amount of 20,000 m3of rocks and soils was detached from the cliff and it affected the road since it was cut for 3 months. An emergency action was made, by means of different types of structures like steel drapes and wire meshes, static and dynamic walls and other fastener devices all along the affected slope.
Since that time different minor events have been taken place in the same area. Some of them have been stopped by those devices installed. Moreover, the special characteristics of the cliff that points to different slopes of the mountain have involved some new events affecting the road in other closer parts. Thus, some new preventive measures are being analyzed to protect this area of the road from new rockfall events. This paper describes both the recent events occurred in that area as well as the new 3D analysis carried out for the implementation of the protection measures by means of programs like STONE model, Guzzetti et al. (2002) and CRSP, Jones at al. (2000) model to check both run out distances and types of protection structures in terms of energy and velocities. An executive project to install these new protection measures analyzed is under development.