User’ s Guide RECIS This volume is the user's guide to FLAC3D. This guide contains general information on the operation of FLAC3D for engineering mechanics computation Section 1 gives an introduction to the capabilities and applications of FLAC3D. An overview of the new features in the latest version of FLaC3D is also provided The first-time user should consult Section 2 for an introduction to the operation of FLAC3D. The installation and operation procedures are given along with a simple tutorial to guide the new user through a FLAC3D analysis Section 3 provides general guidance in the use of FLAC3D in problem solving for static mechanical analysis for geotechnical engineering An introduction to the built-in programming language, FISH, is given in Section 4. This includes a tutorial on the use of the FIsH language. Note that no programming experience is assumed Various items of interest to FLAC3D users are contained in Section 5, including a FLaC3D run time benchmark on several different types of computers and procedures for reporting errors and requesting technical assistance Section 6 contains a bibliography of published papers describing some applications of FLAC3D in different fields of engineering The FLAC3D Manual consists of ten documents. The following list of volumes, which comprise the FLAC3D Manual, are available. (The titles in parentheses below are the names used to refer to the volumes in the text. USER'S GUIDE-(User's Guide)-an introduction to FLAC3D and its capabilities COMMAND REFERENCE-(Command Reference)-descriptions of all FLAC 3D commands FISH in FLAC3D-(FISH volume)-a complete guide to FISH as applied in FLAC3 THEORY AND BACKGROUND-(Theory and Background)-thorough discussions of the built-in features in FLaC3D FLUID-MECHANICAL INTERACTION-(Fluid-Mechanical Interaction)-discussion of the formulation and examples of the groundwater flow model STRUCTURAL ELEMENTS-(Structural Elements)-descriptions for the six types of struc tural elements in FLAC3D: beams, cables, piles, shells, liners and geogrids OPTIONAL FEATURES-(Optional Features)-detailed descriptions of the optional features thermal analysis, creep models, dynamic analysis and C++ user-defined models HEXAHEDRAL-MESHING PREPROCESSOR-3DShop-(3DShop)-a user's guide for 3DShop, a hexahedral-meshing preprocessor for FLAC3D FLAC3D Version 3.1
User’s Guide 1 PRECIS This volume is the user’s guide to FLAC3D. This guide contains general information on the operation of FLAC3D for engineering mechanics computation. Section 1 gives an introduction to the capabilities and applications of FLAC3D. An overview of the new features in the latest version of FLAC3D is also provided. The first-time user should consult Section 2 for an introduction to the operation of FLAC3D. The installation and operation procedures are given along with a simple tutorial to guide the new user through a FLAC3D analysis. Section 3 provides general guidance in the use of FLAC3D in problem solving for static mechanical analysis for geotechnical engineering. An introduction to the built-in programming language, FISH, is given in Section 4. This includes a tutorial on the use of the FISH language. Note that no programming experience is assumed. Various items of interest to FLAC3D users are contained in Section 5, including a FLAC3D runtime benchmark on several different types of computers and procedures for reporting errors and requesting technical assistance. Section 6 contains a bibliography of published papers describing some applications of FLAC3D in different fields of engineering. The FLAC3D Manual consists of ten documents. The following list of volumes, which comprise the FLAC3D Manual, are available. (The titles in parentheses below are the names used to refer to the volumes in the text.) USER’S GUIDE — (User’s Guide) — an introduction to FLAC3D and its capabilities COMMAND REFERENCE — (Command Reference) — descriptions of all FLAC3D commands FISH in FLAC3D — (FISH volume) — a complete guide to FISH as applied in FLAC3D THEORY AND BACKGROUND — (Theory and Background) — thorough discussions of the built-in features in FLAC3D FLUID-MECHANICAL INTERACTION — (Fluid-Mechanical Interaction) — discussion of the formulation and examples of the groundwater flow model STRUCTURAL ELEMENTS — (Structural Elements) — descriptions for the six types of structural elements in FLAC3D : beams, cables, piles, shells, liners and geogrids OPTIONAL FEATURES — (Optional Features) — detailed descriptions of the optional features: thermal analysis, creep models, dynamic analysis and C++ user-defined models. HEXAHEDRAL-MESHING PREPROCESSOR — 3DShop — (3DShop) — a user’s guide for 3DShop, a hexahedral-meshing preprocessor for FLAC3D. FLAC3D Version 3.1
User's guide VERIFICATION PROBLEMS-(Verifications volume)-a collection of verification problems EXAMPLE APPLICATIONS-(Examples volume)-a collection of example applications FLAC3D Version 3.1
2 User’s Guide VERIFICATION PROBLEMS — (Verifications volume) — a collection of verification problems EXAMPLE APPLICATIONS — (Examples volume) — a collection of example applications FLAC3D Version 3.1
PROBLEM SOLVING WITH FLAC3D 3-I 3 PROBLEM SOLVING WITH FLAC3D This section provides guidance in the use of FLAC3D in problem solving for static mechanical analysis* in geotechnical engineering. In Section 3. 1, an outline of the steps recommended fo performing a geomechanics analysis is given, followed in Sections 3. 2 through 3. 9 by an examination of specific aspects that must be considered in any model creation and solution. These include grid generation( Section 3. 2) boundary and initial conditions(Sections 3. 3 and 3. 4) loading and sequential modeling(Section 3.5); choice of constitutive model and material properties(Sections 3.6 and 3.7); ways to improve modeling efficiency( Section 3.8); and interpretation of results( Section 3.9) Each of these modeling aspects is discussed in detail. The user who is familiar with the two dimensional program FLAC will find that the modeling approach is very similar in FLAC3D. The major difference is the procedure for grid generation. We recommend that Section 3. 2 be studied carefully, and that the example problems in that section be repeated before users create model grids. You will note that FISH programs are used in this section to assist with model generation and problem solving. If you have not used the FISH language before, we recommend that you first read the FISH tutorial in Section 4.2 Finally, the philosophy of modeling in the field of geomechanics is examined in Section 3. 10; the novice modeler in this field may wish to consult this section first. The methodology of modeling in geomechanics can be significantly different from that in other engineering fields, such as structural engineering. It is important to keep this in mind when performing any geomechanics analysis Problem solving for coupled mechanical-groundwater analysis is discussed in Section I in Fluid- Mechanical Interaction, and for coupled mechanical-thermal analysis in Section 1 in Optional Features. Problem solving for dynamic analysis is discussed in Section 3 in Optional Features FLAC3D Version 3.1
PROBLEM SOLVING WITH FLAC3D 3-1 3 PROBLEM SOLVING WITH FLAC3D This section provides guidance in the use of FLAC3D in problem solving for static mechanical analysis* in geotechnical engineering. In Section 3.1, an outline of the steps recommended for performing a geomechanics analysis is given, followed in Sections 3.2 through 3.9 by an examination of specific aspects that must be considered in any model creation and solution. These include: • grid generation (Section 3.2); • boundary and initial conditions (Sections 3.3 and 3.4); • loading and sequential modeling (Section 3.5); • choice of constitutive model and material properties (Sections 3.6 and 3.7); • ways to improve modeling efficiency (Section 3.8); and • interpretation of results (Section 3.9). Each of these modeling aspects is discussed in detail. The user who is familiar with the twodimensional program FLAC will find that the modeling approach is very similar in FLAC3D. The major difference is the procedure for grid generation. We recommend that Section 3.2 be studied carefully, and that the example problems in that section be repeated before users create their own model grids. You will note that FISH programs are used in this section to assist with model generation and problem solving. If you have not used the FISH language before, we recommend that you first read the FISH tutorial in Section 4.2. Finally, the philosophy of modeling in the field of geomechanics is examined in Section 3.10; the novice modeler in this field may wish to consult this section first. The methodology of modeling in geomechanics can be significantly different from that in other engineering fields, such as structural engineering. It is important to keep this in mind when performing any geomechanics analysis. * Problem solving for coupled mechanical-groundwater analysis is discussed in Section 1 in FluidMechanical Interaction, and for coupled mechanical-thermal analysis in Section 1 in Optional Features. Problem solving for dynamic analysis is discussed in Section 3 in Optional Features. FLAC3D Version 3.1
User's guide 3.1 General approach The modeling of geo-engineering processes involves special considerations and a design philosophy different from that followed for design with fabricated materials. Analyses and designs for structures and excavations in or on rocks and soils must be achieved with relatively little site-specific data and an awareness that deformability and strength properties may vary considerably. It is impossible and discontinuities can only be partially known, at bel ample, information on stresses, properties Since the input data necessary for design predictions is limited, a numerical model in geomechanic should be used primarily to understand the dominant mechanisms affecting the behavior of the system. Once the behavior of the system is understood, it is then appropriate to develop simple calculations for a design process This approach is oriented toward geotechnical engineering, in which there is invariably a lack of good data. But, in other applications, it may be possible to use FLaC3D directly in design if sufficient data, as well as an understanding of material behavior, is available. The results produced in a FLAC3D analysis will be accurate when the program is supplied with appropriate data. Modelers should recognize that there is a continuous spectrum of situations, as illustrated in Figure 3.1 typical Simple situation no testing budget vestigation NONE - cOMPLETE Investigation of Bracket field behavior Predictive Approach mechanisms by parameter studies (direct use in design) Figure 3.1 Spectrum of modeling situations FLAC3D may be used either in a fully predictive mode(right-hand side of Figure 3. 1)or as a numerical laboratory"to test ideas(left-hand side). It is the field situation(and budget), rather than the program, that determines the types of use. If enough data of a high quality is available FLAC3D can give good predictions Since most FLAC3D applications will be for situations in which little data is available, this section discusses the recommended approach for treating a numerical model as if it were a laboratory test The model should never be considered as a"black box "that accepts data input at one end and produces a prediction of behavior at the other. The numerical" sample must be prepared carefully and several samples tested, to gain an understanding of the problem. Table 3. 1 lists the steps recommended to perform a successful numerical experiment; each step is discussed separately FLAC3D Version 3.1
3-2 User’s Guide 3.1 General Approach The modeling of geo-engineering processes involves special considerations and a design philosophy different from that followed for design with fabricated materials. Analyses and designs for structures and excavations in or on rocks and soils must be achieved with relatively little site-specific data, and an awareness that deformability and strength properties may vary considerably. It is impossible to obtain complete field data at a rock or soil site. For example, information on stresses, properties and discontinuities can only be partially known, at best. Since the input data necessary for design predictions is limited, a numerical model in geomechanics should be used primarily to understand the dominant mechanisms affecting the behavior of the system. Once the behavior of the system is understood, it is then appropriate to develop simple calculations for a design process. This approach is oriented toward geotechnical engineering, in which there is invariably a lack of good data. But, in other applications, it may be possible to use FLAC3D directly in design if sufficient data, as well as an understanding of material behavior, is available. The results produced in a FLAC3D analysis will be accurate when the program is supplied with appropriate data. Modelers should recognize that there is a continuous spectrum of situations, as illustrated in Figure 3.1: Data NONE COMPLETE Investigation of mechanisms Predictive (direct use in design) Bracket field behavior Approach by parameter studies Complicated geology; inaccessible; no testing budget Simple geology; $$$ spent on site investigation Typical situation Figure 3.1 Spectrum of modeling situations FLAC3D may be used either in a fully predictive mode (right-hand side of Figure 3.1) or as a “numerical laboratory” to test ideas (left-hand side). It is the field situation (and budget), rather than the program, that determines the types of use. If enough data of a high quality is available, FLAC3D can give good predictions. Since most FLAC3D applications will be for situations in which little data is available, this section discusses the recommended approach for treating a numerical model as if it were a laboratory test. The model should never be considered as a “black box” that accepts data input at one end and produces a prediction of behavior at the other. The numerical “sample” must be prepared carefully, and several samples tested, to gain an understanding of the problem. Table 3.1 lists the steps recommended to perform a successful numerical experiment; each step is discussed separately. FLAC3D Version 3.1
PROBLEM SOLVING WITH FLAC3D 3-3 Table 3.1 Recommended steps for numerical analysis in geomechanics Step 1 Define the objectives for the model analysis Step 2 Create a conceptual picture of the physical system Step 3 Construct and run simple idealized models Step 4 Assemble problem-specific data Step 5 Prepare a series of detailed model runs Step 6 Perform the model calculations Step 7 Present results for interpretation 3.1.1 Step 1: Define the Objectives for the model analysis The level of detail to be included in a model often depends on the purpose of the analysis. For example, if the objective is to decide between two conflicting mechanisms that are proposed to explain the behavior of a system, then a crude model may be constructed, provided that it allows the mechanisms to occur. It is tempting to include complexity in a model just because it exists in reality. However, complicating features should be omitted if they are likely to have little infuence on the response of the model, or if they are irrelevant to the model's purpose. Start with a global view and add refinement as(and if) necessary 3.1.2 Step 2: Create a Conceptual Picture of the Physical System It is important to have a conceptual picture of the problem to provide an initial estimate of the expected behavior under the imposed conditions. Several questions should be asked when prepar- g this picture. For example, is it anticipated that the system could become unstable? Is the predominant mechanical response linear or nonlinear? Are movements expected to be large or small in comparison with the sizes of objects within the problem region? Are there well-defined discontinuities that may affect the behavior, or does the material behave essentially as a continuum? Is there an influence from groundwater interaction? Is the system bounded by physical structures or do its boundaries extend to infinity? Is there any geometric symmetry in the physical structure of the system? These considerations will dictate the gross characteristics of the numerical model, such as the design of the model geometry, the types of material models, the boundary conditions and the initial equilibrium state for the analysis. They will determine whether a three-dimensional model is required, or a two-dimensional model can be used to take advantage of geometric conditions in the hysical system FLAC3D Version 3.1
PROBLEM SOLVING WITH FLAC3D 3-3 Table 3.1 Recommended steps for numerical analysis in geomechanics Step 1 Define the objectives for the model analysis Step 2 Create a conceptual picture of the physical system Step 3 Construct and run simple idealized models Step 4 Assemble problem-specific data Step 5 Prepare a series of detailed model runs Step 6 Perform the model calculations Step 7 Present results for interpretation 3.1.1 Step 1: Define the Objectives for the Model Analysis The level of detail to be included in a model often depends on the purpose of the analysis. For example, if the objective is to decide between two conflicting mechanisms that are proposed to explain the behavior of a system, then a crude model may be constructed, provided that it allows the mechanisms to occur. It is tempting to include complexity in a model just because it exists in reality. However, complicating features should be omitted if they are likely to have little influence on the response of the model, or if they are irrelevant to the model’s purpose. Start with a global view and add refinement as (and if) necessary. 3.1.2 Step 2: Create a Conceptual Picture of the Physical System It is important to have a conceptual picture of the problem to provide an initial estimate of the expected behavior under the imposed conditions. Several questions should be asked when preparing this picture. For example, is it anticipated that the system could become unstable? Is the predominant mechanical response linear or nonlinear? Are movements expected to be large or small in comparison with the sizes of objects within the problem region? Are there well-defined discontinuities that may affect the behavior, or does the material behave essentially as a continuum? Is there an influence from groundwater interaction? Is the system bounded by physical structures, or do its boundaries extend to infinity? Is there any geometric symmetry in the physical structure of the system? These considerations will dictate the gross characteristics of the numerical model, such as the design of the model geometry, the types of material models, the boundary conditions and the initial equilibrium state for the analysis. They will determine whether a three-dimensional model is required, or a two-dimensional model can be used to take advantage of geometric conditions in the physical system. FLAC3D Version 3.1