Expanding the Frontiers of Geotechnical Engineering

Transcription

1 Expanding the Frontiers of Geotechnical Engineering Software development is not an exact science. When a new version of a Rocscience program is being planned, what are the decisions that have to be made by the developers and where do the ideas come from? You may be surprised to read how much influence our users have had in the recent software development process of this new version, Phase Geomechanics software used worldwide by geotechnical engineers software tools for rock and soil Article prepared for RocNews Fall 2008

2 Phase 2 7.0: Expanding the Frontiers of Geotechnical Engineering Instead of working harder, work smarter. Quote from Microsoft ad It was September 2007, in the boardroom of Rocscience s Toronto office, and an intense debate was is progress. No one wanted to leave the room; outside distractions had been banished; important decisions had to be made in order to map out the final Phase development plan. Under discussion was nothing but software: the next generation of finite element modelling tools for geotechnical engineering. The Rocscience team, huddled around the boardroom table, was poring over suggestions and requests from many users, and proposals from team members. Some of these documents stemmed from meetings with clients from as far away as Australia and South Africa. They all described proposed ideas for the tools needed to make Phase 2, the Rocscience flagship product for finite element modelling, even more useful for geotechnical engineering practice. 2

3 No one knew just what would be best to implement out of the multitude of suggestions and ideas. Some estimated that adding automatic joint network generation should be tackled first. Some felt improving computational speed was paramount. Others thought perhaps enhancing support modelling capabilities was best. As discussions progressed the team realized it was tough: so many choices to make, yet resources were not infinite. It felt as if we were settlers at the frontiers of geotechnical civilization, deciding on how to advance into uncharted territory with only what we had, recalls Brent Corkum, software manager, who guided the discussions. That day the team committed to four major groups of additions for version 7 of Phase2 enabling automatic generation and modelling of large networks of discrete fractures, substantially improving support design functionalities, speeding up computations anywhere from 25% to 50%, and enhancing model building capabilities. All 70 testers of the beta version of Phase2 7.0, who have reported back, have expressed great pleasure with the new version. They believe the program has hit its mark. But our attempt to create a cutting-edge geotechnical engineering software tool could have turned out differently. Your efforts in regularly letting us know what was required to make finite element modelling most practical to everyday engineering paid off. The rest of this article briefly describes the rationale behind the major enhancements made to Phase2. Phase Beta Testing Program had the highest user participation so far. 3

4 Automatic Generation of Discrete Fracture Networks In blocky rock masses, discontinuities such as joints, bedding planes, faults and foliations can dominate behaviour and cause radical departures from predictions based on continuum analysis. Adequate description of the size and locations of joints is difficult, mostly because of their three-dimensional nature and partial exposure in outcrops or excavations. It is however understood that their dissemination throughout a domain can be approximated with statistical distributions. As a result, Phase2 7.0 comes with tools for automatically generating networks of joints that are consistent with some statistical model. The automatic joint network generator allows users to very easily ungroup the joints in a network. It also has tools for changing the end-conditions of any number of these joints, and has the intelligence to specify locations at which joints intersect with free surfaces (such as the ground surface or excavations) as open joint ends. The new automatic joint generation tool enables Phase2 to Discrete joint networks can now be easily generated 4

5 model problems that previously would have been analyzed only with discrete element approaches. By generating new instances of randomly distributed joints with just a mouse click, the generator enables engineers to examine ranges of possible failure mechanisms and behaviour, which can occur in a rock mass. This feature paves the way for robust designs that can accommodate deviations from expected behaviour. It also provides guidance on risks associated with a design. Improved Support Modelling The support elements liners, reinforcement members, etc. for subsurface and underground structures interact with surrounding ground. This interaction forces support design to be iterative. The process may go like this: specify a particular support, check to see whether it helps an excavation meet design requirements; if it does not then change its dimensions, stiffness, size, etc. If it does then maybe it is too conservative and therefore try a less conservative design. Support-ground interactions also mean that the design of support for structures such as tunnels cannot be left to the structural engineer alone. To facilitate improved design of support, Phase2 7.0 comes with a number of important new features, including: Reinforced concrete liner this new liner type simplifies the task of modeling twocomponent liner systems such as reinforced concrete, or the combination of steel sets and shotcrete. Phase2 uses the input properties specified for the concrete and steel reinforcement to calculate a homogeneous cross-section of equivalent properties. Reinforced concrete liner properties 5

6 Comprehensive library of steel sections for reinforced concrete liners the sections in the library range from standard rebar and I-beams to wire meshes widely available in Europe and North America. Phase2 7.0 also allows users to create customized libraries with additional reinforcement types. Support capacity envelopes for reinforced liners Phase2 plots two types of strength envelope, a moment-thrust envelope and a shear forcethrust envelope, for defined reinforcement and concrete Reinforcement database Support capacity envelopes for liner on circular tunnel 6

7 sections. Each strength envelope plot is based on the properties of the support components and a userspecified factor of safety. Also shown on each plot are points that indicate the actual moments, thrust and shear forces calculated at various locations along the reinforced liners of interest. Points falling outside an envelope indicate failure or unsatisfactory performance. Explicit modelling of jointbolt interactions in the real world, whenever a bolt crosses a joint and the joint slips or opens, forces develop in the bolt to resist the movements. In the new version of Phase2, this important behaviour is explicitly captured and leads to more realistic results. Computational Speedup Incorporation of Fast Intel Solver Routines Phase2 7.0 enables users to make the most of their time by speeding up calculations by as much 1-1/2 times (compared to previous program versions). As well, the new program can compute models with much larger degrees of freedom and numbers of elements. In one test case, Phase2 performed a shear strength reduction (SSR) stability analysis (consisting of 11 separate model runs) of a jointed rock slope with 69,000 six-noded elements and 310,000 degrees of freedom in 8-1/2 hours! Of also great importance is the fact that version 7 is less affected by the presence of elements with poor aspect ratios. These enhancements were accomplished through incorporation of Intel s library of matrix solver routines. Enhanced Model-Development Capabilities Quite often, geotechnical engineers, especially at feasibility stages, do not have adequate information on the properties of rock masses and soils. As a result, reasonable first estimates of input properties are of great benefit. Phase2 7.0 can directly access RocLab and RocData (Rocscience programs for determining or estimating the parameters of linear and non-linear strength envelopes for rock and soil). It can then import strength and deformation data from these programs directly into a finite element model. This feature enables engineers to make better use of the database of intact rock properties from over 700 credible, published test records included in RocData. Calculation times have decreased by up to 1-1/2 times, with the ability to handle much larger files. 7

8 Easily import material properties from RocData to Phase 2 Alternatively, you can use the GSI parameter calculator dialog built into Phase2, to assist with determination of parameters for the Generalized Hoek-Brown criterion. GSI parameter calculator for Generalized Hoek-Brown criterion 8

9 To reduce the amount of user effort spent on creating Slide (Rocscience s conventional limit equilibrium slope stability program) equivalents of Phase2 SSR slope models, version 7 has a one-click option for generating Slide files. The version also includes enhancements such as the ability to: Specify an SSR search area of arbitrary polygonal shape Shrink or expand an external boundary Change the overall slope angle Insert stages into an existing model or delete stages from it Define staged pore pressure grids Save results for stages which have been completely analyzed, if a user chooses to abort a computation Indicate the directions of slip of opposing joint surfaces Display a property table for all soil and rock materials to enhance screen captures and reports Concluding Remarks In this article, we have seen how user input played a defining role in determining new features for Phase We have briefly covered a few of the major features in this version. Using their own practical problems as test cases, 70 beta testers have thoroughly evaluated the program and verified its enhanced capabilities. They experienced how Phase2 can help expand the frontiers of geotechnical design and analysis. Now that the final version has been released, would you consider downloading your trial version today and exploring things for yourself? 9