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Presentation on theme: "Www.mecharock.com MechaRock International Consultants."— Presentation transcript:

1 MechaRock International Consultants

2 About us Main activities Software DISROC® Consulting services

3 MechaRock International Consultants is an association of engineering consultants and experts around the world sharing their experience and numerical tools in the field of modelling and design of civil engineering structures, geotechnical and mining projects in rock formations and petroleum geomechanics. About us

4 Main activities Software DISROC® Consulting services MechaRock International Consultants

5 5 Finite Element Method for modelling engineering structures Finite Element Method is the most powerful numerical method for modelling mechanical, hydraulic and thermal behaviour of engineering structures and is widely used in various softwares: Most of geotechnical projects are designed by Finite Element Method, and software using this method are highly appreciated by engineers if the. However, in presence of fractures and discontinuities, other software based on Finite Difference or Distinct Element methods seems to be needed, even if these methods or software are less efficient or pleasant to use (time duration, geometry, outputs…). Necessity of a suitable FE software for rock masses design => DISROC® Main activities: Software development : DISROC ®

6 6 Joint Elements for fractures in Finite Element Method Rockjoint, Masonry mortar Fracture Contact interface Joint Element (Goodman 1976) With appropriate parameters, joint elements can reproduce the behavior of fractures, rockjoints, interfaces and contact surfaces. However, their use in presence of a great number of discontinuities or fractures poses the difficulty of Conform Finite Element mesh creation. Zero thickness Joint Element was proposed by (Goodman 1976) for modeling discontinuities in the Finite Element Method. With appropriate parameters, joint elements can reproduce the behavior of fractures, rockjoints, interfaces and contact surfaces. Main activities: Software development : DISROC ®

7 7 Joint : K n, K t c, Conform Finite Element mesh generation for fractured medium DISROC® is the first Finite Element code especially conceived for fractured rocks. Its powerful meshing tool Discrac® allows easily creating a conform mesh and special Joint Elements for fractured media. Main activities: Software development : DISROC ®

8 8 DISROC ® Architecture GID is a powerful pre and post processor developed by Cimne: DisrocFP generates fractured rock mass Discrac allows joint elements creation DISROC® is the calculation module Geometry Boundary conditions Mesh GID Post Process GID Discrac WinDisroc DISROC ® input file Fracture generation Parameters output file Main activities: Software development : DISROC ®

9 9 Functionalities of DISROC ® : Hydro-mechanical behavior of rock masses DISROC® has the following main functionalities: Elastic-plastic modeling of rocks, rock-joints and rockbolts with incremental loading Incremental multistage excavation of underground openings and rock cuttings Stability of rock slopes under seismic loads (horizontal and vertical upward acceleration) Analysis of block fall down risk in tunnels in blocky rockmasses Homogenization of fractured rock mass mechanical properties: Determination of the effective elastic parameters Determination of equivalent permeability Simulation of effective stress-strain curve to determine effective strength properties Modeling rock bolts, bars and cables in fractured rock DISROC® is interfaced with the powerful pre and post-processor GID (www.gidhome.com) that allows easily defining the geometry and materials model, generating mesh, and displaying the calculation results in the form of contours and curves, etc.www.gidhome.com Main activities: Software development : DISROC ®

10 10 Modelling fractured rocks with DISROC® With DISROC® it becomes easy to model geotechnical projects like dams, tunnels, bridges and rock cuttings in fractured rocks. Rock Slope Stability Tunnel in fractured rock Main activities: Software development : DISROC ®

11 11 Bolting fractured rock Homogenization of fractured rock properties Bolts are very often used to reinforce and stabilize fractured rocks, but are difficult to model when they cross fractures: DISROC® is the only Finite Element software capable to model properly rock bolts crossing fractures. Main activities: Software development : DISROC ® Effective elastic properties of fractured rock masses are very often needed for projects design: DISROC® has a Large scale Homogenization module for determination of effective parameters of fracture rock masses (deformation modulus, cohesion, angle of internal friction).

12 12 Modeling bolts and anchors in DISROC® :Elastic-plastic bolt + elastic-plastic bolt/roc contact Nb = 8 Param1 = E (bolt elastic modulus) Param2 = K t (bolt/rock contact shear stifness ) Param3 = K n (bolt/rock contact normal stifness ) Param4 = K nt = K tn (bolt/rock contact ns stifness ) Param5 = Y s (bolt elastic limit) Param6 = c (bolt/rock contact cohesion) Param7 = (bolt/rock contact friction angle) Param8 = s 0 (bolt pres-stress) Complete models for bolts, anchors and bars are available in Disroc with full integration of the grout behavior by an elastic-plastic interface model. Bolts can cross fractures. The model of intersection allows discontinuity of rock displacement at the two side of the fracture with continuity of the bolt rod. Disroc® is the only Finite Element software allowing this modeling. Main activities: Software development : DISROC ®

13 13 Representing bolt stresses in DISROC ® F FEM mesh for the sample, bolt and fracture Axial force S L in the bolt represented in two different ways. S L passes by a local maximum when crossing the fracture. S L (MN) SLSL Deformation at the roof of a bolted tunnel Weight S L (MN) Axial force S L in the bolt represented in two different ways. S L passes by a maximum when crossing the fracture. Pull out test on a bolt crossing a fracture FEM mesh for the rock, Bolt and fracture SLSL Main activities: Software development : DISROC ®

14 14 Materials models in DISROC® A great variety of classical constitutive models are available in DISROC for rocks, fractures, joints and rockbolts. Solid materials: Elastic-plastic behavior: - Linear isotropic or anisotropic elasticity - Mohr-Coulomb, Drucker-Prager, Hoek & Brown plastic failure criteria Discontinuities: fractures, faults, rock joints and interfaces - Linear or non linear Barton-Bandis elasticity - Mohr-Coulomb (Cohesion, friction angle) yield criterion Rockbolts and cables - Elastic and plastic limit for steel rod, - Elastic stiffness, cohesion and friction angle for rock–grout interface Joint : K n, K t C, Main activities: Software development : DISROC ®

15 15 Displaying results in DISROC ® Stress vectors on rock joints Normal stress on rock joints A variety of different representations of the results are possible, specially those concerning rock joints and fractures. Example: Deformation of the fractured REV under shear stress xy : U x displacement Main activities: Software development : DISROC ®

16 About us Main activities Software DISROC® Consulting services MechaRock International Consultants

17 Tunnels Slope stablity Dams Homogeneization Masonry structures Consulting services

18 18 I. Tunnels design Modeling fractures and bolts with DISROC® is very easy. The following tunnel/road project includes: a rock mass with two sets of fractures (possibly non persistent) non persistent fractures (cracks) on the tunnels wall, rock bolts to stabilize the rock slope and the rock cut over the road. All these elements are easily introduced in the Finite Element model created by DISROC®. Case study 1 - Tunnels : Example of a project in fractured formation with rock cutting Main activities: Consulting services - TUNNELS

19 19 Meshing with Disrac ® : The Finite Element mesh created by the software GID (www.gidhome.com) is transformed by the module Discrac® to generate specific elements for fractures, bolts and cables.www.gidhome.com The meshing tool integrates: Intersecting fractures (a) Non persistent fractures (b) Rockbolts passing through fractures (c ) (c) (a) (b) Main activities: Consulting services - TUNNELS

20 20 Main activities: Consulting services - TUNNELS

21 21 The project includes a tunnel and a rock cutting for a road in a fractured sedimentary formation. The formation is constituted of alternate layers of two limestones varieties. The interfaces between layers are modeled as fractures (Fracture1). Two faults are present in the formation (Fracture2). Modeling passes through the following stages. I) The fractures are generated stochastically (Fracture1)and faults are placed in the model with their known position (Fracture2). II) Other lines defining the soil profile, the tunnel contour, the cutting contour and the rock bolts are introduced in the model. road Case study 2 - Tunnels : Example of a project in fractured formation with rock cutting Main activities: Consulting services - TUNNELS

22 22 Tunnels : Modeling stages III) A conform Finite Element mesh is created by DISCRAC ® +GID. Specific joint elements for fractures and bolt elements for rockbolts are created automatically. The material properties are assigned to limestone layers, fractures and rock bolts. In this example, the limestone varieties 1a, 1b, 2a, 2b are identical to Limestone1 and Limestone2 and are introduced for determination of the initial in situ stresses before tunnel excavation and rock cutting. Main activities: Consulting services - TUNNELS

23 23 In situ stress ( yy ) before excavation Vertical displacement U y due to tunnel excavation Rock bolts are placed (activated) in the model at this stage with a pre-stress S L = 0.1 T Vertical stress ( yy ) after tunnel excavation IV) The next steps are achieved like in classical Finite Element codes: prescribing loads and boundary conditions, modeling excavation stages, displaying results… SLSL Main activities: Consulting services - TUNNELS

24 24 Vertical stress ( yy ) after rock cutting Vertical displacement showing uplift after rock cutting Vertical displacement details showing fractures opening Bolts stresses change when crossing fractures and attain a maximum value of 2 T. Main activities: Consulting services - TUNNELS

25 Case study 3 - Tunnels A double line tunnel in a sedimentary rock mass Main activities: Consulting services - TUNNELS

26 Tunnels Tunnel in a blocky rockmass Displacement at the roof of the tunnel versus the excavation ratio Calculations diverge before total excavation and can not go beyond the excavation ratio of 0.9. The displacement field at this stage shows the existence of instable blocks at the roof of the tunnel. Instable blocks at the roof of the tunnel Non convergence Case study 4 - Tunnels in a blocky rockmass Main activities: Consulting services - TUNNELS

27 27 Fractures can be introduced in the model by stochastic distribution laws or in a deterministic way. Gravity load can be applied step by step to determine the safety factor of the slope. Horizontal and vertical accelerations can be applied in order to analyze the stability against seismic loads. Rock slope with two types of fractures Finite Element mesh created by DISCRAC ® and GID Displacement under prescribed load Shear stress on fractures Analysis and stabilization of natural rock slopes, rock cuttings and open pit mines II. Rock slope stability Main activities: Consulting services – SLOPE STABILITY

28 28 Slope stability under seismic load Application of gravity forces to define the initial state of stress Rock cut in a blocky rockmass Displacement of the point A versus seismic load ratio. The calculations can not go beyond 0.7 g horizontal acceleration and diverge at this stage. Addition of 1 g horizontal acceleration to represent seismic load The displacement field at 0.7g horizontal acceleration reveals an instable block (blue in the figure) A (A) Main activities: Consulting services – SLOPE STABILITY

29 29 Slope design optimization Design modification Modified model in DISROC Meshing facilities of DISROC for fractured rocks allow easy optimization of rock cutting design. If the projected slope reveals instable, it is easy to change quickly the design in DISROC® and analyze the modified project. Initial slope design revealed to be instable Main activities: Consulting services – SLOPE STABILITY

30 Cross section of an Earth Dam lying on a rock mass foundation with two sets of discontinuities (DISROC ) Rock foundation along with the dam and the dam-foundation interaction are analyzed in a unique model enclosing all the fractures sets III. Dams Main activities: Consulting services – DAMS

31 31 Homogenization in DISROC : Fracturing model data acquisition I) For each family of fractures, the fractures orientation, length, spacing and mechanical parameters are specified. II) Fractures sets are generated stochastically according to specified parameters. III) A conform Finite Element mesh is created by Discrac® + GID. Main activities: Consulting services - HOMOGENEIZATION

32 32 Homogenization in DISROC : Load application on the REV U y displacement under uniaxial compression yy U x displacement under shear stress xy V) The average stresses and strains in the REV, taking into account the fractures opening, are computed for each loading case and the homogenized elastic properties of the fractured rock mass are determined from the average values. IV) 3 different basic loads; uniaxial compression in x and y directions and pure xy shear, are applied on the REVs contour. Anisotropic elastic coefficients for the homogenized behavior Main activities: Consulting services - HOMOGENEIZATION

33 33 Homogenization : Anisotropic stiffness and compliance tensor calculation The stiffness and compliance tensors lines are computed automatically by imposing boundary conditions corresponding to macroscopic strain or stress in different directions. Main activities: Consulting services - HOMOGENEIZATION

34 34 Homogenization : Anisotropic stiffness and compliance tensor calculation The homogenized stiffness and compliance tensors lines are given as a direct result of calculation. Main activities: Consulting services - HOMOGENEIZATION

35 35 Example : sedimentary bedded rock E = 10 GPa, = 0.25, K n = 10 GPa.m, Kt= 2.5 GPa.m, D = 1m Goodman formula: Main activities: Consulting services - HOMOGENEIZATION

36 36 IV. Fractured rock mass replaced by a continuous effective Material Case study 1- Sedimentary Rock mass : Kousba – North Lebanon Accurate calculation of the Homogenized large scale mechanical properties of rock masses: Equivalent anisotropic mechanical properties: E(MPa),, C (MPa) and ( ). This method replaces the inaccurate empirical classification systems like RMR and Q used by engineers. Main activities: Consulting services - HOMOGENEIZATION Equivalent elastic modulus in different directions determined by homogenization

37 37 Case study 2 - Granitic rock mass : De la Vienne, France Main activities: Consulting services - HOMOGENEIZATION

38 Far-field fractures act only by their global effects, and only in elastic phase. A preliminary homogenization allows replacing the fractured rock mass with a continuous media with effective properties. Great discontinuities like faults can be introduced in the final model as individual lines. Fractures replaced by a continuous effective material Combination of fractures modeled individually (near- field) and replaced by an effective material (far-field). Fractures and faults modeled individually as discontinuities ? Main activities: Consulting services - HOMOGENEIZATION Case study 3 – General case

39 39 Rockmass with general configuration of fractures The effective elastic coefficients C ij are directly calculated by DISROC Homogenization module, and can be introduced as material parameters for modeling the rock mass by its effective properties. ? Main activities: Consulting services - HOMOGENEIZATION

40 40 V. Masonry structures Stability assessment for retrofitting purposes Case study 1 – Bridges Main activities: Consulting services – MASONRY STRUCTURES Evolution of the damage state in the bridge Opening of the active fractures Vertical stress maps Concentration of stress near the fractures zone

41 41 Case study 2 – Bridge: Retrofitting, with iron bolts, of a masonry bridge suffering from the development of an active fracture due to foundation settlement Main activities: Consulting services – MASONRY STRUCTURES Geometry of the masonry bridge Finite elements mesh Deformed shape: Total displacement : Bolts crossing active fractures Vertical stress Horizontal stress

42 42 Case study 3 – Temple: Assessment of the temples stability for retrofitting purposes Main activities: Consulting services – MASONRY STRUCTURES Yanouh Roman temple, Lebanon Mesh generation in presence of fractures and Stress maps

43 43 For more information: MechaRock International Consultants


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