ORAL PAPER PROCEEDINGS

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1 ITA - AITES WORLD TUNNEL CONGRESS April 2018 Dubai International Convention & Exhibition Centre, UAE ORAL PAPER PROCEEDINGS

2 GBR delivery exclusively as a BIM Level 2 ½ model: Lessons learned from the new Stockholm metro design ABSTRACT Paul Evins 1 Fredrik Stenström 1 1 WSP, Stockholm, Sweden, paul.evins@wsp.com, frekdrik.stenstrom@wsp.com The decision to replace all drawings of a GBR with a BIM model influences all stages of the design process. For the GDR, it affects what data is collected and how it is collected. For the GBR, it concerns what interpretations and baselines should be shown and how they should be shown. Many of these decisions are steered by the two ends of the design process: the input data and the end users. Different end users have very different needs from the same GBR model. The challenge is finding the level of detail each group of end users requires. The input data offers its own challenges which can be overcome to some extent by software integration. This paper describes the implementation of a level 2 ½ BIM model for the new yellow line and 3 new stations for the Stockholm metro with a focus on how the GDR/GBR content was produced and used. The GDR/GBR text documents had no accompanying drawings: only the BIM model. Contractor and Owner acceptance was not an issue since the model was delivered as a complete package that requires no software installation. We delve into the pros and cons of this approach and point out pitfalls and lessons learned. Finally, we identify future advances for the Geologist producing the GBR in a BIM environment. Most of the rewards of the integrated workspace that BIM provides were realized in the Stockholm metro design. The two main advantages across all technical disciplines were coordinated visualization and clash detection. For the GDR, the arduous process of log and section compilation was removed. An unforeseen benefit of the BIM model for the GBR was its use as the primary tool for geological interpretation and planning for further investigations. The main limitations of the BIM model stem from a lack of standardized workflows: from layer delivery by technical disciplines to model review. Another weakness was the dependence on key personnel for updates. Lastly, not all geological data/ interpretations lend themselves to databases. A significant proportion of the final BIM model is devoted to the GDR/GBR. Most of the information is relevant to a Geologist. Less than half of the information was used by the Designer. The same information would be relevant to the Contractor, but may not be available due to liability. For this reason, the balance between transparency and liability should be decided early on. Little of the geological information is relevant to the Owner. The lesson learned is that the modelling process should not be started until the needs of all end users are established. Some future advances for GDR/GBR production in the BIM environment for Geologist end users include incorporating: Simplified workflows with the ultimate goal of automatic updating from the field 3d modelling and interpretation practices from the mining industry Uncertainty representation Public data sources to fill in data gaps 1

3 1. INTRODUCTION 1.1 What is BIM Level 2 ½? To fully grasp what we mean by BIM level 2.5 we first have to point out what we mean by BIM levels in general and then explain how we have implemented a balanced crossover between level 2 and 3 in the new Stockholm metro design project. There is no one absolute definition of Building Information Modelling (BIM), rather, BIM is referred to as an aggregation of technologies and processes which provides a single collaborative data repository for all project members. BIM levels incorporate many different project aspects such as: Level of collaboration, Level of sharing data between members, CAD Standards (formats/software used), Delivery, Level of information in the models (smart info), Life cycle compliance, Mindset etc. A simplified overview of the different BIM levels is shown in Figure 1. Figure 1. The levels of BIM. BIM level 0: Effectively means no collaboration at all and lack of BIM. Drafting and distribution is in 2D only and either via paper or electronic prints. BIM level 1: No real collaboration since models are not shared between technical disciplines. However the data has reached a form of structure and CAD standards are used to imply a level of conformity. Mix of 2D and 3D in digital form for drafting and distribution and usually a common data environment is used. BIM level 2: Introduces collaboration among team members and CAD standards have evolved into using common file formats (such as IFC) and electronic delivery. Files and data should easily be shared between members. 3D CAD models are used by all parties. The improved CAD standards now enables any project to combine the data in a federated BIM model (though it may not be mandatory) and thus carry out a more validated audit on the project to reduce risk of errors. 2

4 BIM Level 3: Total collaboration through a single, shared project model saved in a centralized repository (preferably cloud based). Level 3 is considered the holy grail of BIM and represents full collaboration between all disciplines. 3D-based model files complemented by a full set of connected and intelligent information such as attribute data, object information codes, survey data, time parameters (4D) and cost (5D) information. Stakeholders of all disciplines may access and modify the master file simultaneously thus eliminating errors and misunderstandings, ultimately fostering end-to-end efficiency by delayering risks of conflicting information. The collaboration model is used throughout the full life-cycle from planning stages to operational life cycle and maintenance. 1.2 BIM in the new Stockholm metro project The new Stockholm metro project uses level 2 BIM in most aspects and in some areas, such as geotechnical, level 3 BIM thus the 2.5 BIM approach. Below are some aspects of the model that could be considered level 3 BIM: All geometries are collected in one model which includes input from all disciplines. The model can be delivered and shared between all stakeholders without installation of special software. All visualization is in 3D from all disciplines that are involved in draft and design work. Open source file formats makes it possible to follow life-cycle thinking. Geotechnical investigation data is visualized in 3D and directly connected to the geotechnical database. 3D objects are created directly from the database by special scripts. Furthermore, access to geotechnical raw data can be gained by clicking on the objects. This makes the information accessible to all parties, even those without CAD knowledge. The project has not achieved a full-fledged Level 3 BIM solution where everyone seamlessly works in a single model with all data in the project but it has passed the level 2 mark and has reached a compromise while waiting for general software and file format interoperability problems in the market to be solved. 1.3 Key differences between a GBR and the Swedish IP and BP According to Essex, 2007, the purpose of a Geotechnical Baseline Report (GBR) is to set clear realistic baselines for conditions anticipated to be encountered during subsurface construction, and thereby provide all bidders with a single contractual interpretation that can be relied upon in preparing their bids. The Geotechnical Baseline Report (GBR) establishes a contractual understanding (interpretation) of the subsurface site conditions, referred to as baselines. Risks associated with conditions consistent with or less adverse than the baselines are allocated to the Contractor, and those significantly more adverse than the baselines are accepted by the Owner. (Essex, 2007). Thus, the GBR is a contract document of high importance. The GBR is a reporting tool for Geologists, a key support for Designers, background information for Contractors, and a conflict resolution base for both Owner and Contractor. A conventional GBR consists of a report with clearly identified baseline values for certain ground conditions as well as numerous 2D drawings depicting ground conditions (geology, weakness zones, etc.) along the planned construction. 3

5 In the Swedish system, two reports are produced which serve a similar purpose as a GBR: the engineering geology prognosis (IP) and rock engineering prognosis (BP). Like a GBR, a conventional IP consist of a report summarizes and interprets data from the GDR along with numerous 2D drawings depicting ground conditions (geology, weakness zones, etc.) along the planned construction. However, the IP does does not necessarily predict ground behaviour, address the impact ground conditions will have on the planned construction, or provide strict baselines which can be directly relied upon for preparing bids or allocating risk. The IP is just a description of ground conditions to support preliminary design. It may not include any mention of ground support. The IP is typically only presented in the preliminary design documents to the owner. It has a relatively low ranking in the design contract documents. During detailed design, a BP is produced as 2D drawings that specify selected ground conditions, excavation limitations, ground support and grouting for the planned construction. The BP also has a relatively low ranking in the bidding contract beneath technical specifications and the bill of quantities. The purpose and contractual status of the BIM model, be it Swedish IP or BP or a regular GBR, has a bearing on the end user needs of the BIM model and should be one of the steering principles behind construction of a BIM model. 2 STEERING PRINCIPLES The contents of any BIM model should be steered by the two ends of the design process: the input data and the end users. 2.1 Input data A BIM model can only show objects for which there is data. Therefore, what data is collected and how it is collected during the site investigation phase directly affects what the GDR portion of the BIM model will contain, and how the model will be constructed. The optimal data format for model integration is a digital database with spatial references so that the data can be visualized in 3D. However, traditional site investigation results are usually delivered in paper or.pdf format. Borehole information may be delivered as a 2D log, which while useful for a Geologist to verify measurements from different methods, cannot be easily transferred into a 3D model. Thus it is important to decide the data and data format the GDR portion of the BIM model will contain and use this to steer data collection in the field. The same philosophy applies to selecting what baselines will be shown for the GBR portion of the BIM model. Some types of data are simply not amenable to presentation at 3D objects, such as histograms of intact rock strength. In these cases, objects showing sample locations in the BIM model can be linked to relevant sections of the GBR report End user needs There are 4 main user groups for the GDR/GBR BIM model. Geologist, Designer, Contractor and Owner. Their requirements from the model differ. The Owner only needs to see the baselines that can be visualized in the model (such as the distribution of rock quality). The Contractor needs to see the baselines as well as the distribution and specifications for ground support and grouting. Other information, such as the modelled rock surface may also be useful for the Contractor. In order to make an informed design for the Contractor, a Designer essentially needs to see all 3D interpretations by the Geologist and perhaps

6 some of the input data (GDR objects), such as borehole locations. The Geologist requires all GDR and GBR objects from the BIM model in order to interpret the raw data (GDR) to create the 3D interpretations used by the Designer. In summary, the Owner and Contractor use only the GBR portions of the BIM for support during construction, whereas the Designer and Geologist use the BIM model as a tool for interpretation and design. 3 BIM MODEL FROM THE NEW STOCKHOLM METRO DESIGN The new Stockholm metro extension consist of ca 4 km single- and doubletrack tunnels with 3 new stations and the expansion of an existing underground station: all excavated in hard rock. The project involves difficult ground conditions in a crowded urban underground. A master BIM model was created in Open VR for coordination between all technical disciplines (Figure 2). Later, a Navisworks BIM model was created specifically for the BP portion of the GBR. Both models contain object managers where content visibility can be controlled. The Open VR model is delivered as a self-contained.zip file with all software included (i.e. no installation or system administrator privileges are necessary). It also updates automatically with new data. The Navisworks model is also stand-alone, but requires the industry standard Navisworks Freedom freeware to run. Before and during the early stages of modelling, official requirements were established in consultation with the Owner for the contents and visualization of the GDR and GBR portions of the models. Figure 2. Isometric view of the master BIM model showing the object manager where visibility of layers within each technical discipline can be controlled. Inset - The new Stockholm subway extension in yellow. 5

7 3.1 GDR The GDR portion of the master BIM model contains the following layers (Figure 3): Borehole location Outcrops - draped over the ground surface and color-coded for: o Lithology o RMR Boreholes - hyperlinked to database logs and color-coded for: o Lithology o RMR o RQD o Hydraulic Conductivity Raw mapping data from existing underground caverns and tunnels could not be shown because their locations are classified. However, interpretations from these tunnels were shown in the GBR portion of the model as long as they did not give away the location of the underground structure. Figure 3. Some of the GDR and GBR data visualized in the master BIM model. 6

8 3.2 GBR The IP portion of the GBR was delivered in the master BIM model and contains the following layers (Figure 3): Planned tunnels and caverns Orthophoto draped on ground surface Rock surface Lithological Domains Rock Quality Domains based on histogram distributions of RMR Structural Domains based on the distribution of joint sets Weakness zones each zone color-coded by RMR and hyperlinked to an information box showing its characteristics Foliation trend lines 2D Joint sets at each mapping location hyperlinked to a database and colorcoded by significance The BP portion of the GBR was delivered as a separate Navisworks model and contains the following layers (Figure 4): Planned tunnels and caverns Rock surface Rock Quality Domains with hyperlink to distribution of RMR within each domain Ground Support Domains areas marked for standard or specific ground support with hyperlinks to 2D execution drawings Grouting Domains areas marked for standard or specific grouting with hyperlinks to 2D execution drawings Other fire, explosion, risk, inspection and maintenance specific areas Figure 4. Navisworks model showing ground support domains along parts of the tunnel and station (zoomed in to the left). The object manager Selection Tree is shown to the top right (in Swedish). 7

9 3.3 Use of the master BIM model During preliminary design, Geologists used the master BIM model to classify the rock mass along the tunnel by first extrapolating data along weakness zones to the tunnels and then extrapolating data from nearby drillholes, mapped tunnels and outcrops along foliation lines (Figure 5). Then the distribution of rock mass quality along the tunnel was used to create rock quality domains, each with their own internal distribution of rock quality. Figure 5. Methodology for extrapolating data to the planned tunnel. Left weakness zone extrapolation along the zone. Right outcrop data extrapolation along foliation. During detailed design, Designers mainly used the rock surface, weakness zones and their hyperlinked properties as well as the boundaries of and distributions within the rock quality domains. The joint sets at individual mapping locations were especially appreciated for more site-specific wedge analysis as opposed to relying on summary stereoplots of structural data over larger areas covered by the structural domains (Figure 6). 8

10 Figure 6. Wedge analysis using local, site-specific joint data from the BIM model for rock cuts at a subway entrance. 4 REWARDS Delivery of geology as 3D models has been standard practice in the mining sector, but is relatively new in the infrastructure tunneling sector where traditionally all data and interpretations have been shown as 2D drawings. A number of advantages have been realized by replacing all of the engineering geology 2D drawings with a 3D BIM model. For the Geologist, the model gives a better overview of an entire borehole and allows them to analyse the relationships between boreholes and between mapped outcrops and tunnels. Hyperlinking the raw borehole data and logs to the model still gives the Geologist the option to query the data at a more detailed level, as well as to export the data to other users. It also makes it easier to find the data. Viewing the relationship between the investigation sites (boreholes, outcrops, etc.) and the planned construction represents a major step forward in integrating the geologist s work with the engineer s design. The model becomes a communication tool that allows the geologist to be part of the design. In turn, data gaps can be identified and the model can be used as a tool to design further investigations. Since many of the objects (boreholes and their logs, weakness zones, joint sets, etc.) are generated directly from the data by scripts in the model, any changes in the mapped data are directly reflected in the model. This reduces the possibility for error during data transfer and eliminates the need to update drawings by hand. In this way, the BIM model has evolved from a visualization and data query tool to an interpretation tool. For the Designer, the model provides the full 3D context of the main geological features of interest to design, such as how weakness zones cut through the design and how rock cover varies in all directions above the design. This is especially important when weakness zones and low rock cover interact with complex station geometries that cannot be visualized in 2D drawings. Furthermore, the Designer can have the relevant parameters at hand via data hyperlinks without the need to sift through long reports. Including other technical disciplines in the master BIM 9

11 has also been useful for clash detection, for example tunnel ventilation design extending outside of the excavation contour. The BIM model has also proved invaluable for communicating design to the Owner. For the Contractor and Owner, the BIM model has thusfar been used as a communication tool during the bidding process. Construction has not begun on the project, but it is anticipated that some version of the BIM model may be of use to the Contractor. The Owner has also discovered that the BIM model can be used an effective communication tool to the public. An obvious sustainability reward was also achieved through digital delivery as opposed to the thousands of 2D paper drawings that have traditionally been delivered or printed out in similar projects. 5 LIMITATIONS Most large Swedish infrastructure projects are Design-Bid-Build. It is customary for the Designer, not the Contractor, to extract ground condition baselines from the IP. The amount of geological data was greatly reduced in the changeover from the IP model to the BP model with this in mind. In fact, the only geological data present in the BP model is the rock surface and the distribution of ground condition domains. This limitation of information was done on purpose to limit liability during bidding for construction. It is assumed that the detailed design has taken all ground conditions into account and they are not the Contractor s concern and cannot be targeted for claims. This strategy removes all of the risks associated with the uncertainties due to extrapolation of geology into the planned construction that are described below. The Owner can decide whether to provide the more detailed, IP model to the Contractor for information purposes. In the Design-Build case, the model would have been designed differently and incorporated aspects of both IP and BP models. A limitation to the master BIM model in this project was the dependence on key personnel for updates. In most organisations, only a few people have the expertise to create and administer a master BIM model. Since geological investigations started before model design, the model administrators task became more daunting due to a lack of standardized workflows for input data format, data delivery, visualization guidelines (for example what color should a granite be shown as?), reporting and model review. Delays in delivery from certain technical disciplines that plague every project became more acute in the master BIM model workspace. Not all geological data submits itself to being rammed into a database. Filtering of data into a database inevitably results in loss of details. Detailed textual descriptions, comparison tables, analyses, etc. are not amenable to 3D visualization and must remain in reports or appendices, which can be integrated into the BIM model via hyperlinks. A common expectation of BIM model delivery is that the user may find it too difficult to use. In our experience, user acceptance has not been an issue because: data integration has been handled by custom scripts the model is a self-contained file navigation is simple and intuitive instructions are thorough 10 The interpretive aspect of a GBR is more challenging when shown in 3D. In particular the extrapolation of data from the investigation site to the planned construction is

12 not a mean task. The confidence in the projected ground conditions at the planned construction is limited to how well based the extrapolation is and the distance the data is projected. One advantage of the 3D model is that this distance can be communicated in a more transparent manner than in 2D drawings and in the case of this project, extrapolation information was included in the hyperlinked metatdata. At this point in time, a bill of quantities for aspects such as ground support or grouting cannot be generated directly from the BIM model. Furthermore, objects in the model are not hyperlinked to technical specifications. Both features would be beneficial to the Contractor and Owner. That said, these advantages do not exist in current non-bim GBRs. 6 LESSONS LEARNED In this project, as the BIM model evolved it became more of a tool and less of a deliverable. That is to say, although the model was a deliverable to the Owner, it was the Designers and Geologists that used it most. Geologists are eager to show the results of their investigations and there is a risk that modelling begins prematurely before the needs of the other end users have been established. In this project, geological investigations were in full swing before requirements of the BIM model were established. In the future, the contents and data delivery format to the BIM model should be decided at the earliest stage possible in a project. The level of detail and relevance to the different user groups should be clear. All of these aspects will have an impact on the level of detail and data collection methods for investigations. Even though the level of detail in this particular project exceeded the base requirements of the Owner, ultimately the time saved for the Geologist and Designer by using the model as a tool resulted in reduced cost to the Owner. The lack of preparation and attention to the BIM model at the beginning of the project had a knock-on effect throughout the modelling. One-off, ad-hoc workflows were required to import data and visualize it in the model because data had already been acquired in a non-specific format. In the future, standardized data collection and input workflows will be established before modelling begins. Integration of data into the BIM model via hyperlinks requires a strict file structure that must be maintained before and after delivery. The best solution to maintain this structure is through delivery as a self-contained package or hosting of only a single BIM model on a server. As in this project, different models may be necessary to meet the differing needs, liabilities and risks of the different users. We encourage a frank discussion between the Geologist, Designer, Owner and potential Contractors about how the model(s) will be used and what should be shown to each user. This type of transparency defines liability and limits risk for all parties. The model may approach the purpose of a true GBR which defines baselines and assigns risk. 11

13 7 FUTURE CHALLENGES As the project develops, it is the hope that the current BIM model or a new model derived from it can be expanded to meet the needs of the Contractor and Owner. This might include a construction timeline for the Contractor, for example or integration of as-built photogrammetry or laser-scanning of the completed tunnel for the Owner. In future projects there is a wish to directly couple BIM models to technical specification documents and the bill of quantities for tendering. The BIM model in this project represents an island of more detailed investigations in a sea of geological information at a more coarse resolution (typical geological survey maps). Data gaps are also present within the project area. By integrating larger scale data sources near model boundaries the Geologist could achieve a better understanding of the regional context of the area and possibly identify more relationships between weakness zones and regional trends. Extrapolation can be enhanced through variogram-based kriging and other geostatistical methods. Further research is also needed to reduce the uncertainties associated with extrapolation of weakness zones. Although the BIM modelling and philosophy for delivery of a GBR presented in this paper represents a step forward for the infrastructure tunneling sector, there is potential for more improvements. Much can be learned from the mining sector including data and workflow standards. Open standards and specifications should be established to allow as much accessibility as possible and avoid industry-focused exchange formats. The BIM model must be as accessible and user-friendly as possible. In the best case, it could be accessible through a web portal: in the worst case, through freeware. If standards and exchange formats can be successfully establish and workflows simplified, then the ultimate goal of an automatically updated BIM Level 3 model may be achieved. 12

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