4.1 Results
After the grading is completed, you can view the rock mass quality classification results at any point by pushing the datum plane in the XYZ direction. The rock mass quality at a certain point can also be obtained quantitatively by extracting the isosurface map of the rock mass quality classification index RMR.
In order to verify the practicability of the quality classification method, taking the above-mentioned test area as an example. Five representative measurement points in the flat tunnel in the lower dam site area are selected to calculate the membership degree of each level, which is compared with the traditional comprehensive fuzzy judgment method to analysis. Comprehensive the rock quality index P1, RQD index P2, joint line density index P3, joint surface state index P4, groundwater condition P5 and other indexes, the rock mass quality is divided into 5 categories. Combined with on-site engineering geological survey and indoor test, the measured values of the quality indicators of each sample rock mass are shown in Table 2. The analysis results show that the method in this paper is the same as the result of the fuzzy comprehensive evaluation method ,has a high consistency with the site excavation and meets the needs of the project. The comparative analysis results are shown in Table 2.
Table 2
Comparative analysis of rock mass quality index classification results
Sample | Evaluation Index | 3D Evaluation Method | Traditional 2D method | Actual excavation results |
P1 | P2 | P3 | P4 | P5 |
1 | 47 | 30 | 0.18 | 0.49 | 15.5 | III | III | III |
2 | 51 | 46.7 | 0.44 | 0.48 | 10 | III | II | III |
3 | 30 | 38 | 0.33 | 0.33 | 16.3 | IV | III | IV |
4 | 54 | 87 | 0.28 | 0.45 | 19 | III | III | III |
5 | 52 | 71.6 | 0.51 | 0.36 | 0.05 | II | II | II |
4.2 Discussions
4.2.1 The role of 3D geological models
①Improve design quality
Under the traditional CAD model, although the division of labor is very obvious, they are all independent of each other. Because of this, the deviations in the understanding of the project between the majors are basically based on the knowledge of the major and they cannot take care of each other, it is easy to cause conflicts(CauMon Getal ,2002). After using 3D digital evaluation method technology, the BIM models established by various disciplines can be unified and integrated under the same working platform. Each discipline can work together through a unified model and a common platform then comprehensively coordinate which can effectively control the professional factors in the design(Kamat V R; 2020). It can effectively control the occurrence of errors, omissions and deficiencies in the design due to poor information transmission and untimely communication which can improve design quality and reduce changes(Wu Qiang et al, 2020).
②Effectively improve owner management methods
In the past, if the owners wanted to manage the quality, cost and schedule of the project, they had to pass professional knowledge or organization. This was because of the lack of professional knowledge(Zhang Yu et al 2002). And in 2D mode, communication is often flat, just a few drawings or a data report which is neither intuitive nor lack of timeliness. This will cause the owners and other parties in the project to have differences in their understanding of the project, resulting in more changes, lower quality and delays in the construction period(Pinto V et al 2002).After using BIM technology, the 3D visualization model established through BIM can incorporate the cost, quality, construction period and other related data information that the owner cares about into the model, such as material prices, equipment attributes, etc.which greatly improves the owner’s project management efficiency(Jia Hongbiao et al 2002). It reduces cost and waste and eliminates the gray income of other project parties. It can be said that the owner is the biggest beneficiary of BIM(Cai Hejun et al 2001).
③A weapon for project managers
The drawings formed by BIM technology are digitized and contain a wealth of data information, so that they can be integrated, analyzed and used through computers to provide reliable data support for project managers(Vistelius A B 1997). Project managers no longer need to search and recheck one by one with a dozen thick drawings in their hands as before(Hu Ruihua, Wang Qiuming 2002). Project managers only need to retrieve the information in the BIM model and database in front of the computer to accurately find the required component information,such as the layout of steel bars, the location of reserved holes, the size of components and unit prices, etc. which greatly improves work efficiency, issue instructions to the project in time and improve on-site management efficiency(De Kemp Eric A 1999). Moreover, project managers can also perform real simulation experiments on the BIM model, such as construction simulation, disaster escape demonstration, etc., so that not only can they understand the progress of the project at any time, make plans and adjust strategies at any time, but also improve the safety of the site(Mallet J L 1997). Greatly improve the quality of the project.
4.2.2 The advantages of 3D digital evaluation method
(1)The establishment of the model provides a new technical approach for the cognition and expression of engineering geological rock masses and provides comprehensive information for the analysis and judgment of the geologists(Kulatilake W 1990). The 3D model not only can enable geologists to escape the limitations of traditional 2D speculation but also make the geological speculation based on 3D models is more reasonable. It also makes the subsequent increase of exploration points more scientific(Zheng Wentang et al, 2020).
(2)Different from the traditional 2D engineering geological condition analysis, based on the 3D geological model, the values of related parameters on all exploration points can be imported through the database in the GeoBIM software and assigned to the 3D geological model of the dam site area(Zhang Chong et al 2006). The geological parameters of the rock mass around a point can be automatically obtained through interpolation. Through the 3D geological model, you can intuitively view the rock quality index RQD value, saturated uniaxial compressive strength value, water permeability Lu value and other geological parameters at any point(Jiao Yuyong et al 2000). GeoBIM software automatically generates the equivalent surface of a certain index, for example, the equivalent surface of the rock quality index RQD = 80% and the area of the rock quality index RQD > 80% in the rock formation is judged by the equivalent surface which is for the engineering geological classification of the dam foundation rock mass(Itasca Consulting Group Inc 2003). It is of great significance to judge the rock quality at the location of the dam foundation.
(3)The modeling results provide an accurate geological visualization model, paving the way for the application and promotion of 3D design in the future,providing model data for the design, construction, exploration layout and numerical simulation analysis of the project and providing visual reference for the analysis of designers and design(Liao Qiulin et al 2005). The 3D model serves the actual production application, changes the traditional working mode and thinking and improves the production efficiency and accuracy(Wang Weihua; Li Xibing 2005).
(4)By exporting the modeling data, 3D collaborative design with hydraulic engineering, construction and other professions can be realized. In theory, it is possible to import finite difference, finite element and other numerical simulation software to analyze the stability of foundation pit excavation and realize the true value of modeling(Zhu Fusheng et al, 1997).
4.2.3 The disadvantages of 3D digital evaluation method
Through the cooperation and efforts of various professional and technical personnel, the application potential of 3D digital evaluation method in geological engineering has been initially explored which has laid a good foundation for further improvement of engineering construction and management(Zhong Denghua et al 2005). However, judging from the current development of BIM, there are still some shortcomings in the application technology of 3D geological analysis:
(1)BIM applications are all partial applications and the application points are relatively single. There is a lack of correlation between various applications, and there is no overall effect(Pan Wei et al 2004). The results are still "information islands", and they have not reached the full coverage of process and professionalism(Wang Chunxiang et al 2003). BIM has short information boards. It is difficult to play the overall role of BIM.
(2)The application lacks a master plan. From the experience of foreign BIM promotion and application, the driving force of BIM comes from the government and the owners, but the domestic engineering industry owners start BIM work late and the top-level design is not perfect, resulting in the lack of a unified action program when carrying out BIM work(Zeng Qianbang et al 2005), and the lack of a unified technical structure which resulting in poor scalability and promotion of research results, hindering the promotion of BIM applications(Yan Huiwu et al 2004).
(3)Lack of a unified engineering BIM standard, there are big differences between different links of different software, data interoperability is poor, data is difficult to integrate into effective information(Pu Hao et al 2005). It is difficult to achieve effective transmission and storage of data information. For example, in actual projects, the BIM model prepared by the design institute cannot be delivered to the construction company for construction, and the construction company re-models it according to its own standards, and the data fails to flow and waste is serious(Wu Jiangbin; Zhu Hehua 2005).
(4)The current benefits of BIM are not obvious and there are no relevant documents in the engineering industry that put forward rigid requirements for the use of BIM technology which has led to the lack of enthusiasm for some companies to promote BIM(Zeng Qianbang; He Xiaoping 2006).