Standardisation and Archiving of Hong Kong Tunnel Logging Records

Transcription

1 Standardisation and Archiving of Hong Kong Tunnel Logging Records R.J. Sewell, D.L.K. Tang & K.J. Roberts Geotechnical Engineering Office Civil Engineering and Development Department Government of the Hong Kong Special Administrative Region 1 INTRODUCTION ABSTRACT A centralised archive of Hong Kong tunnel logging records is being established as part of the Hong Kong Geological Survey, Geotechnical Engineering Office (GEO)/Civil Engineering and Development Department (CEDD), map updating programme. The objective is to develop a GIS layer of tunnel geology as part of the dataset for the updated 1:20,000-scale digital geological maps. Since 2005, Environment, Transport and Works Bureau (ETWB) Technical Circular No. 15/2005 has required that all factual geological and hydrogeological data, such as field data from the excavation faces, obtained during construction of the tunnel works for Government projects be submitted to the Public Section of the Geotechnical Information Unit of the Civil Engineering Library in CEDD. To facilitate recording of the tunnel data, the Hong Kong Geological Survey has designed a standard template for the collection of tunnel data in the form of a rock mass mapping and classification sheet, the content of which is described. The rock mass mapping and classification sheet is modelled on internationally accepted data logging methods and practices, but modified to suit Hong Kong conditions. In addition, a computer program has also been developed to facilitate data entry, and to generate files in the appropriate database format. The rock mass mapping and classification sheet and computer program will be available on the CEDD website. It is hoped that the construction industry in Hong Kong will adopt these tools in all tunnelling projects, both public and private, and so facilitate standardisation and archiving of Hong Kong tunnel logging records. Tunnel logging records are an invaluable resource for geotechnical practitioners as they provide a factual account of visible ground conditions encountered during construction of the tunnel and associated works. As well as being an important reference for future planning of infrastructure development involving underground construction, the tunnel logging records are useful in a broad range of applications from geotechnical risk management strategy to improved geological modelling and geological map production. Many logging records from Government and private sector tunnelling projects in Hong Kong (herein the area of the Hong Kong Special Administrative Region) have in the past remained largely inaccessible in client office files (both Government and private sector). Consequently, they have run the risk of being overlooked, misplaced, disaggregated, and inadvertently discarded. To prevent the potential loss of this valuable information, and as part of its 1:20,000-scale digital geological map-updating programme, the Hong Kong Geological Survey (HKGS), GEO/CEDD, has designed a template for the collection of tunnel data in order to promote standardisation and archiving of tunnel logging records by the construction industry.

2 This paper describes the background to the design of the template (herein referred to as the rock mass mapping and classification sheet), the proposed specification for recording of the underground geological and geotechnical conditions at the excavation face, and the details of the accompanying computerised data-entry program. 2 BACKGROUND With the exception of mining and military tunnels, almost 400 km of tunnels have been constructed in Hong Kong since the late 19 th century. Of these, approximately 70% consist of water, drainage, sewage and road tunnels relating to Government projects, with the remainder made up of rail, cable tunnels and other private tunnels (HKIE, 2007). Until the early 1990 s, most tunnels were constructed by drill and blast methods. The past 15 years have seen the increased use of tunnel boring machines (TBMs) in both hard and soft rock environments. Until establishment of the HKGS in 1982 and the commencement of the 1:20,000-scale geological mapping programme, there was no established mechanism or perceived requirement in Government to systematically curate and archive tunnel logging records from Government projects. Logging records from earlier tunnel projects, such as road and water tunnels, were also either non-existent or of very poor quality. There was no standard method of tunnel logging and the HKGS was required to make special requests to obtain tunnel data that would be useful for the geological map updating programme. Extracted tunnel records generally amounted to basic summary logs of rock lithologies, and occasionally a selection of rock samples. During the late 1980s, the HKGS was fortunate to obtain information and samples from the Western Aqueduct Tunnels and the Sai O to Pak Kong water tunnel projects which were utilised for geological map updating. However, the information contained in the tunnel logs was incomplete and of variable quality. The potential for a centralised archive of logging information from Government tunnel projects was first recognised during the mid to late 1990s during the construction of deep sewer tunnels for the Harbour Area Treatment Scheme (HATS) Stage I project (formerly Strategic Sewage Disposal Scheme). Comprehensive tunnel logging records were submitted by the Drainage Services Department to the Geotechnical Information Unit of the Civil Engineering Library. However, it was soon realised that the tunnel data could not be efficiently extracted or easily adapted for use by the HKGS or geotechnical practitioners. In 2003, the HKGS embarked on a programme to update the published 1:20,000-scale geological maps and to release them in digital form. As part of this programme, a comprehensive set of geological datasets was developed and implemented on a Geographic Information System (GIS) platform. Core datasets comprising scanned records of field notes, sketches, sample descriptions, structural measurements, photographs, etc, were uploaded to the GIS, along with the first sets of tunnel data. These included tunnel logging records for HATS Stage I Tunnels, and from various water tunnels, including the Western Aqueduct Tunnels, and Sai O to Pak Kong water tunnel. 3 RECENT DEVELOPMENTS IN GEOTECHNICAL CONTROL FOR TUNNEL WORKS As a result of major ground settlement problems encountered during construction of deep sewerage tunnels for the HATS Stage 1 project during the 1990 s, the Environment, Transport and Works Bureau (ETWB) conducted a detailed review of project implementation issues (LegCo, 2004). Specific recommendations relating to geotechnical aspects of government tunnel projects arising from the review included: (1) the need for tighter controls on checking procedures, (2) improved communication between the GEO (in particular, the HKGS) and project consultants on characterization of potential problematic ground conditions, and (3) the need to pass all relevant geological information to the GEO for use in updating published geological maps and preparing new maps. In response to these recommendations, an ETWB Technical Circular on geotechnical control of tunnel works (ETWB TC(W) No. 15/2005) was issued, along with technical guidance notes on site investigation (GEO, 2005a) and geotechnical risk management for tunnel works (GEO, 2005b).

3 4 ROCK MASS MAPPING AND CLASSIFICATION SHEET With approximately 200 km of government-funded tunnels scheduled for construction over the next ten years, a considerable volume of factual geological and hydrogeological data is expected to be generated and transferred to the Public Section of the Geotechnical Information Unit, of the Civil Engineering Library in CEDD in accordance with ETWB TC(W) No. 15/2005. In order to promote standardization and archiving of these data, the HKGS has developed a Rock Mass Mapping and Classification Sheet (RMMCS) and associated computer program to facilitate data entry and uploading to the HKGS GIS tunnel geology dataset. These data will be referred to when preparing new or revised geological maps. The RMMCS for tunnel records (Figure 1) is based on a modified version of a similar logging sheet developed by the US Army Corps of Engineers (USACE, 2001). In addition to the recording of basic rock mass information, such as lithology, mass weathering, geological structures, overbreak, and water inflow, the sheet accommodates the Norwegian Geotechnical Institute (NGI) Q System where applicable. Figure 1: Rock Mass Mapping and Classification Sheet Generous provision is made for the recording of discontinuity data, including joints, faults, bedding, foliation, flow-banding, slickensides, etc, along with relevant details. The logging geologist is expected to follow standard guidelines for lithological description contained in Geoguide 3 (GEO, 1988), and to assign suitable formation and/or pluton names according to The Pre-Quaternary Geology of Hong Kong by Sewell et al. (2000). The RMMCS is designed to efficiently accommodate all key observations and measurements made at the tunnel face and the circumference of the adjacent tunnel side wall for each completed round of excavation. Provision is also made to annotate details of pertinent structures, such as joints, faults, and bedding planes, as well as water springs, on both a plan of the tunnel face and of the circumference of the tunnel side walls (Figure 1). It is understood that the RMMCS may not be applicable to all tunnels being constructed, particularly those using TBM methods of excavation where the ground conditions are rarely exposed in an open face suitable for

4 logging. Nevertheless, it is possible that geological logs of the tunnel face could be obtained at intervals whilst a TBM is stopped for routine maintenance. The RMMCS is sufficiently versatile to allow adaptation for logging of tunnels of all shapes and sizes, as well as adits and shafts, following the same procedures as those described above. Using the RMMCS, the tunnel geologist should feel confident that all relevant logging details can be recorded adequately at the excavation face. It is hoped that practitioners will provide feedback to the GEO to further improve its design. The RMMCS, in Excel file format, is freely available for download from the CEDD website: Submission of factual geological and hydrogeological data to the Geotechnical Information Unit, of the Civil Engineering Library in CEDD is not a requirement for privately funded tunnel projects. Nevertheless, it is suggested that the RMMCS is adopted as the de facto Hong Kong standard for recording of tunnel data. Moreover, it is hoped that all logging data from future tunnel projects, both Government and private sector, will be lodged with the GEO/CEDD to ensure the efficient, effective and reliable archiving by the HKGS under its GIS tunnel geology dataset, so as to make this valuable resource available to all geotechnical practitioners. 5 ROCK MASS MAPPING COMPUTER PROGRAM In order to facilitate digitisation and transfer of tunnel logging geological data to the GIS layer of tunnel geology in the appropriate format, the HKGS has developed a computerised data entry form based on the RMMCS. The computer program is written in Visual Basic 6.0 on a Windows platform and requires the commonly available MS-Access 2000 software for operation. The program allows for adding new records, and editing or deleting existing records. Each record accommodates the details of one completed RMMCS, except for annotations of the excavation face and tunnel side walls. Data entry is menu-driven and divided into five main sheets comprising General Information, Geotechnical Content, Geological Structure, Joint data, and NGI Q values. Data fields on each sheet must be completed satisfactorily before the program allows for progression to the next sheet. The opening page comprises a summary of general information, including chainage, lithology, material weathering, mass weathering grade, and water inflow, along with six buttons that reveal detailed information on geological contacts, faults, bedding/foliation, dykes/sills/veins, joint data, and NGI Q values (Figure 2). The left hand column permits selection of specific tunnel sections for rapid selection and review. A useful feature of the program is that it allows inputting of lithological changes within selected tunnel chainages. By specifying the grid coordinates for CH+0, the chainage and tunnel depth records for each record can be automatically converted into Hong Kong 1980 Grid coordinates suitable for later 3D-modelling and generation of shape files on a GIS platform. An export function allows the generation of output files either in a printed report format, or in an Excel file format. 6 CONCLUSIONS Standardization of data collection and recording is essential to successful communication and data-sharing. The development of a centralised, computerised repository of detailed tunnel logging information for Hong Kong tunnels will have far-reaching benefits to local geological practitioners and the broader geotechnical community as a whole. ACKNOWLEDGEMENTS This paper is published with the permission of the Head of Geotechnical Engineering Office and the Director of Civil Engineering and Development, Government of the Hong Kong Special Administrative Region. The assistance of Messrs M. F. Ho and Y. K. Lai of the Planning Division, GEO/CEDD, in developing the computer program that accompanies the Rock Mass Mapping and Classification Sheet is gratefully acknowledged.

5 Figure 2: Screen Image of the Opening Page of the Digital Tunnel Data Entry Form Based on Information Recorded in the Rock Mass Mapping and Classification Sheet. REFERENCES ETWB Geotechnical Control for Tunnel Works. Environment, Transport and Works Bureau Technical Circular (Works) No. 15/2005, Hong Kong SAR Government, 12 p. GEO Geoguide 3: Guide to Rock and Soil Descriptions. Geotechnical Engineering Office, Civil Engineering Department, The Government of the Hong Kong Special Administrative Region, 189 p.

6 GEO 2005a. Site Investigation for Tunnel Works. Technical Guidance Note No. 24 (TGN24). Geotechnical engineering Office, HKSAR Government, 8 p. GEO 2005b. Geotechnical Risk Management for Tunnel Works. Technical Guidance Note No. 25 (TGN25). Geotechnical Engineering Office, HKSAR Government, 10 p. Hong Kong Institution of Engineers (HKIE) Tunnels and caverns in Hong Kong. Invited Paper. Commemorative Volume of the 40th Anniversary of the Southeast Asian Geotechnical Society, Malaysia, 8-11 May LegCo Review of project implementation issues of Harbour Area Treatment Scheme (HATS) Stage 1. Paper for discussion by Legistlative Council Panel on Planning Lands and Works on 29 June 2004, CB(1)2221/03-04(03), Legislative Council, HKSAR, 20 p. Sewell, R.J., Campbell, S.D.G., Fletcher, C.J.N., Lai, K.W. & Kirk, P.A The Pre-Quaternary Geology of Hong Kong. Geotechnical Engineering Office, the Government of the Hong Kong Special Administrative Region. 181 p. USACE Engineer Manual Geotechnical Investigations. US Army Corps of Engineers.