DOCSLIB.ORG

International Society for Soil Mechanics and Geotechnical Engineering

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
International Society for Soil Mechanics and Geotechnical Engineering INTERNATIONAL SOCIETY FOR SOIL MECHANICS AND GEOTECHNICAL ENGINEERING This paper was downloaded from the Online Library of the International Society for Soil Mechanics and Geotechnical Engineering (ISSMGE). The library is available here: https://www.issmge.org/publications/online-library This is an open-access database that archives thousands of papers published under the Auspices of the ISSMGE and maintained by the Innovation and Development Committee of ISSMGE. Geotechnical engineering considerations for the analytical design of an adequate tunnel support system Joan Ongodia, Denis Kalumba, Civil Engineering, University of Cape Town, Graduate student & Senior Lecturer, South Africa, [email protected] Harrison Mutikanga, Brajesh Ojha Civil Engineer, Uganda Electricity Generation Company Limited, Uganda & Civil Engineer, Navayuga Engineering Company, India ABSTRACT: Tunnel excavation impacts the ground both at the surface and underneath thereby affecting the natural in-situ stability. Failure results from stress redistribution, stress relaxation and deformations around the tunnel. Ultimately, tunnel failure occurs when the loads exceed the value of the bearing resistance. Therefore, a support system comprising unique structural components is needed to resist the weight of unstable rock wedges thereby ensuring that the tunnel does not fail. Nevertheless, stability depends on an effective rock- support interaction, specifically with the rock bolt which is the main support member. In order to assess and improve stability conventional methods to design are borrowed from geology which assesses material properties by visual observation, physical identification, using rudimentary geological handy tools, charts and graphs to estimate tunnel support ranges. For stability, the specific value of the required capacity to prevent failure should be established. This paper presents the background to the engineering design of an adequate tunnel support based on the peak rock load which must be resisted to ensure the tunnel remains stable. RÉSUMÉ: L’excavation de tunnels impact le sol au niveau de la surface et en profondeur, en affectant ainsi la stabilité in situ naturelle. Des défaillances surviennent du fait de la redistribution des contraintes, le relâchement des contraintes, et des déformations autour du tunnel. En fin de compte, la défaillance du tunnel se produit lorsque les charges dépassent la valeur de résistance de soutènement. Donc, un système de support comportant des composantes structurales uniques est nécessaire pour résister au poids des rocs instables pour ainsi s’assurer contre l’écroulement du tunnel. Néanmoins, la stabilité dépend de l’interaction adéquate entre la roche et le support, particulièrement avec les boulons d’ancrage dans le roc qui est l’élément de support principal. Afin d’évaluer et d’améliorer la stabilité, les méthodes de concept conventionnelles sont empruntées à la géologie qui évalue les propriétés des matériaux par l’observation visuelle, l’identification d’aspect physique, en utilisant des outils géologiques rudimentaires, et des tableaux et graphiques pour estimer les portées souterraines. Concernant la stabilité, une valeur spécifique de la capacité requise doit être établie pour éviter la défaillance. Cet article présent la connaissance technique en concept d’ingénierie pour un support adéquat de tunnel basé sur les charges maximales des rocs instables à soutenir, et ainsi d’assurer l’intégrité du tunnel. KEYWORDS: Tunnels, Geotechnical engineering design, Rock mechanics theory, Rock load, Support 1 INTRODUCTION Presently, the accuracy of a tunnel design mainly depends on experience and geological methods used (Mohammed 2015). The methods employed by tunnel practitioners including geotechnical engineers often involve visual observation, physical identification, rudimentary hand-held tools and estimation of corresponding support parameter ranges from charts (Hoek et al. 1995). Geological materials identified are described, assessed and categorised, in order of reducing strength, as Class I, II, III, IV and V based on the Rock Mass Figure 1. Continuum scale (adapted from Kanji 2014) Rating (RMR), Q and Rock Quality Designation (RQD) (Palmström 1995, Brown et al. 1983). RMR, Q and RQD systems give an indication of the level of deformation and (1) ability of the rock to support loads. Alternatively, rock can be classified on a continuum scale as shown in Figure 1 although where σ'1 and σ'3 are major and minor effective principal the methods are generally subjective thereby giving ranges of stresses at failure, σci is the UCS for the intact rock pieces, mb is the support parameters (Kanji 2014, Ongodia 2017). the Hoek-Brown rock mass constant, s and a are rock mass Guiding standards include the tunnel lining design guide characteristic constants. (TLDG 2004), the New Australian Tunnelling Method (NATM), the Chinese HC standard for tunneling, the Indian tunneling standard and the adapted Czech NATM (Spackova 2012, Sousa 2 KEY CONSIDERATIONS FOR TUNNEL SUPPORT 2010, PRC 2008). Further, underground stability problems are The main geotechnical engineering considerations for analysed using mostly the non-linear Hoek-Brown failure estimation of rock loads and the corresponding tunnel supports criterion (see Eq. 1) which approximates jointed rock comprise 1) geology, 2) material properties, 3) geotechnical characteristics better than the linear Mohr-Coulomb failure parameters, and 4) the construction process (Palmström 1995). criterion because it approximates isotropic behaviour for intact Stability of the surrounding rock mass depends on geological rock (Greer 2012). conditions, residual strength, in-situ stresses, burial depth, tunnel dimensions, excavation disturbance factor and material properties which influence stress magnitudes and deformation - 1737 - Proceedings of the 19th International Conference on Soil Mechanics and Geotechnical Engineering, Seoul 2017 such as the Poisson’s ratio, Young’s modulus, shear modulus groundwater interactions (Sharp 2007). Discontinuities provide and stiffness (Greer 2012). Figure 2 illustrates the network of void spaces through which water permeates the rock mass. significant factors which control stability. Porewater pressures widen the discontinuities in the structure thereby aiding physical disintegration and eventually failure. Therefore, drainage provision is an important aspect of the support system (Bondarchuk et al. 2012). The rate of hydrogeological flows and extent of widening of the discontinuities is controlled by the minerals present both in the rock mass structure and void space infilling (Wahlstrom 1973). Clay minerals have a high affinity for water and cause swelling and squeezing of the mineral structure when wet and dry, respectively (Kanji 2014). Infillings have strong anisotropic mechanical properties thus they significantly reduce rock strength (Palmström 1995). Typical unstable wedges and potential tunnel failure Figure 2. Web of ground factors influencing stability (Jones 1989) resulting from peak rock loads in the roof, sidewalls and floor are illustrated in Figure 4. Rockbursts or popping conditions 2 .1 Geology usually occur in the roof and sidewalls resulting in collapse or The ground type and its integral structure are important to for slide, respectively, whereas unstable floor wedges usually heave stability as they directly provide anchorage for the support. Key (Viggiani 2012). Furthermore, squeezing is a severe tunnel features include the rock mass structure, type, degree of construction challenge besides mudflows and face collapses weathering, interlocking, types and orientation of discontinuity (Sousa 2010, TLDG 2004, Hoek et al. 1995). sets, persistence, roughness and width of the discontinuity Tunneling strain and squeezing behaviour can be predicted (Jones 1989). Intact rock is strong although as weathering, using charts (see Figure 5 below) in which strains above 2.7% which is a significant natural earth process, takes effect the rock indicate mandatory support (Hoek et al. 1995). An equivalent mass begins to disintegrate thereby forming discontinuities such value of the laboratory measured oedometer swell pressure is as joints and fault lines (Brown et al. 1983). Discontinuities aid applied onto the rock in the field to ensure stability the agents of weathering including erosion such that the rock (Mohammed 2015). mass eventually degenerates into soil over geological periods. The five rock classes correspond with the varying degrees of Roof wedge collapses weathering (Palmström 1995). Weak discontinuous rock is generally unstable and requires mandatory support (Bieniawski 1992). Sidewall wedge slides or displaces Geological prediction gives insight on the material condition, state, properties and responses of the ground to the construction process such that advance support is provided where necessary and the excavation sequence adjusted timely to avoid excessive Floor wedge heaves damage of the overall rock mass structure (Hoek et al. 1995). Figure 3 illustrates how probes are used to predict geology ahead of tunnel advance such that sudden failure during Figure 4. Typical unstable wedges and failure (Ongodia 2017) excavation is avoided. However, actual material characteristics and engineering parameters of the excavation should be evaluated to determine the resistance forces to be counteracted (Mohammed 2015). Figure 5. Strain and squeezing (TLDG 2004 after Hoek et al. 1995) 2.3 Geotechnical parameters Mechanical rock
Load more

Recommended publications
  • Alternative Ground Control Strategies in Underground Construction
    Alternative ground control strategies in underground construction Keynote address to be presented by Evert Hoek at an International Symposium on "PRACTICES AND TRENDS FOR FINANCING AND CONTRACTING TUNNELS AND UNDERGROUND WORKS" to be held in Athens, Greece, on 22-23 March 2012 www.tunnelcontracts2012.com/ Alternative ground control strategies in underground construction Evert Hoek Evert Hoek Consulting Engineer Inc., Canada ABSTRACT Underground works vary from shallow urban tunnels to very deep tunnels and caverns in the world’s great mountain ranges. The problems encountered at and between these extremes are entirely different and require appropriate approaches to site investigation, design and construction. The establishment of reliable financial estimates, construction schedules and contract proposals can only be done once a realistic geological model has been prepared and a clear understanding of the likely behaviour of the rock mass and the groundwater conditions has been established. The conditions that control the behaviour of different kinds of excavations in a variety of geological environments are presented in the context of case histories. The aim is to provide project owners, financial managers, insurance companies and contractors with a road map that may assist them in avoiding some of the pitfalls and in considering some of the alternative strategies in the development of underground projects. 1 INTRODUCTION Tunnels have been built for hundreds of years as part of transportation systems for people, goods, water and services. Until the middle of the last century these tunnels were generally small in size and the builders sought out the most favourable geology and topography in which to build them.
    [Show full text]
  • The New Hampshire High Tunnel Story
    The New Hampshire High Tunnel Story NATURAL RESOURCES CONSERVATION SERVICE New Hampshire January 2011 BACKGROUND National High Tunnel Conservation Benefits Local Foods Initiatives 3-Year Pilot Program High tunnels can provide a number of Growing food locally, especially before significant conservation benefits such as and after the traditional growing season, NRCS offered seasonal high tunnels an increase in plant and soil quality, a helps strengthen the local economy and (officially called “seasonal high tunnel decrease in pesticide use and foliar (leaf) helps ensure the viability and profitability system for crops”) as a conservation disease, and improved energy savings. of small farms. When NH farms succeed, practice for the first time in fiscal year Many farmers who want to grow toma- valuable farmland and cultural heritage are (FY) 2010 as part of a three-year trial to toes without using pesticides often find protected. High tunnels are important tools determine their effectiveness in con- they can only do so successfully if they for enhancing the availability of local food serving water, improving soil health, are grown in a tunnel. Without rainfall, year-round. foliar disease is often reduced because the leaves stay dry. Insects that are com- “As expected, the seasonal high monly a problem in the field may not be “It is phenomenal that winter tunnel pilot has been popular in so in the tunnel because the tunnel tends farmer’s markets in NH have grown New Hampshire. In just one to disrupt their feeding patterns. Other from none four years ago to twenty year, the NRCS-NH helped fund insects that occur in a high tunnel are today.
    [Show full text]
  • Megabang for Megabucks: Driving a Harder Bargain on Megaprojects
    Megabang for megabucks Driving a harder bargain on megaprojects Marion Terrill, Owain Emslie, and Lachlan Fox May 2021 Megabang for megabucks: Driving a harder bargain on megaprojects Grattan Institute Support Grattan Institute Report No. 2021-04, May 2021 Founding members Endowment Supporters This report was written by Marion Terrill, Owain Emslie, and Lachlan The Myer Foundation Fox. Nat Manawadu provided extensive research assistance and made National Australia Bank substantial contributions. Susan McKinnon Foundation We would like to thank numerous government and industry participants Affiliate Partners and officials for their helpful comments and insights. Ecstra Foundation The opinions in this report are those of the authors and do not Origin Energy Foundation necessarily represent the views of Grattan Institute’s founding Susan McKinnon Foundation members, affiliates, individual board members, reference group members, or reviewers. The authors are responsible for any errors or Senior Affiliates omissions. Cuffe Family Foundation Grattan Institute is an independent think tank focused on Australian Maddocks public policy. Our work is independent, practical, and rigorous. We aim Medibank Private to improve policy by engaging with decision makers and the broader The Myer Foundation community. Scanlon Foundation We acknowledge and celebrate the First Nations people on whose Trawalla Foundation traditional lands we meet and work, and whose cultures are among the Wesfarmers oldest continuous cultures in human history. Westpac For further information on Grattan’s programs, or to join our mailing list, Affiliates please go to: www.grattan.edu.au. You can make a donation to support Allens future Grattan reports here: www.grattan.edu.au/donate. Ashurst This report may be cited as: Terrill, M., Emslie, O., and Fox, L.
    [Show full text]
  • MARTA Tunnel Construction in Decatur, Georgia
    . 4 I lit. 18.5 . a37 no UOT- f SC- UM TM UMTA-MA-06-002 5-77-1 7 7 -2 4 T NO MARTA TUNNEL CONSTRUCTION IN DECATUR GEORGIA— A Case Study of Impacts Peter C. Wolff and Peter H. Scholnick Abt Associates Inc. 55 Wheeler Street Cambridge MA 02138 of TR4 A( JULY 1977 FINAL REPORT DOCUMENT IS AVAILABLE TO THE U.S. PUBLIC THROUGH THE NATIONAL TECHNICAL INFORMATION SERVICE, SPRINGFIELD, VIRGINIA 22161 Prepared for U.S, DEPARTMENT OF TRANSPORTATION URBAN MASS TRANSPORTATION ADMINISTRATION Office of Technology Development and Deployment Office of Rail Technology Washi ngton DC 20591 . NOTICE This document is disseminated under the sponsorship of the Department of Transportation in the interest of information exchange. The United States Govern- ment assumes no liability for its contents or use thereof NOTICE The United States Government does not endorse pro- ducts or manufacturers. Trade or manufacturers' names appear herein solely because they are con- sidered essential to the object of this report. Technical Report Documentation Page 1 . Report No. 2. Government Accession No. 3. Recipient's Catalog No. UMTA-MA-06-0025- 77-14 4. Title and Subti tie 5. Report Date July 1977 iJfYlTfl- MARTA TUNNEL CONSTRUCTION IN DECATUR GEORGIA— A Case Study of Impacts 6. Performing Organization Code 8. Performing, Organi zation Report No. 7. Authors) DOT-TSC-UMTA-77-24 AAI 77-18 Peter Co Wolff and Peter H. Scholnick 9. Performing Organization Name and Address 10. Work Unit No. (TRAIS) Abt Associates Inc. UM704/R7706 55 Wheeler Street 11. Contract or Grant No.
    [Show full text]
  • Course Instructions
    Course Instructions NOTE: The following pages contain a preview of the final exam. This final exam is identical to the final exam that you will take online after you purchase the course. After you purchase the course online, you will be taken to a receipt page online which will have the following link: Click Here to Take Online Exam. You will then click on this link to take the final exam. 3 Easy Steps to Complete the Course: 1.) Read the Course PDF Below. 2.) Purchase the Course Online & Take the Final Exam – see note above 3.) Print Out Your Certificate Tunnel Inspection Manual Final Exam 1. This manual provides specific information for the inspection of both highway and rail transit tunnels. a. True b. False 2. As per Figure 2.8, the horseshoe tunnel shape typically exists in: a. clay b. shale c. sandstone conditions d. rock conditions 3. Regarding Ventilation Systems, tunnel ventilation systems can be categorized into ____ main types: a. one. b. five. c. three. d. four. 4. Regarding Inspection Qualifications, the inspection should be accomplished with teams consisting of a minimum of ____ individuals: a. one. b. two. c. three. d. four. 5. As per Table 3-1, the acronym PCLS stands for: a. Precast Concrete Liner Segments. b. Post-tensioned Concrete Liner Segments. c. Polymer Cast Liner Sleeve. d. Post Construction Limed Shotcrete. 6. Considering Inspection of Civil/Structural Elements, the tunnel owner should establish the frequency for up-close inspections of the tunnel structure based on the age and condition of the tunnel.
    [Show full text]
  • FACT SHEET: BART Silicon Valley
    Twin-Bore Single-Bore Running Tunnel Running Tunnel Utilities Utilities Up to ~60' FACT SHEET: VTA’s BART Silicon Valley Phase II Extension Project FACTTunneling MethodologySHEET: BART Silicon Valley VTA’sVTA’s BART BART Silicon Silicon Valley Phase Valley II Project Phase is a six-mile, ll Extension four-stationUp extensionProject to ~75' that will bring BART train service from Berryessa/North San José through downtown San José to the City of Santa Clara. The Phase II Project will include an approximately five-mile tunnel, two mid-tunnel ventilation facilities, a maintenance facility and storage yard, three VTA’sunderground BART Siliconstations (AlumValley Rock/28th Program Street, Overview Downtown San José, Diridon), and one ground-level station (Santa VTAClara). is extending The subway the tunnelBART regionalwill be in heavy one large rail system diameter to Milpitas,tunnel. San Jose, and Santa Clara. The 16-mile extension, called the BART Silicon Valley Program, will extend the BART system south of BART’s future Warm Springs/SouthSingle-Bore Fremont Tunnel Station in Fremont to Milpitas, San Jose, and Santa Clara. When completed, this fully grade-separatedThe tunnel will be project constructed is planned as a tosingle, include large six diameter stations andtunnel. a new The maintenance and storage facility in Santa Clara.approximately VTA’s BART 45 footSilicon tunnel Valley will Program contain istwo being independent delivered trackways,in two phases. one Thefor Berryessa Extension Project (Phaseeach direction I) is under of constructiontravel. Passenger and scheduled platforms willto open be located in 2018, within with thestations tunnel, in Milpitas and the Berryessa areaconnected of San toJose.
    [Show full text]
  • Geotechnical Performance of a Tunnel in Soft Ground
    Missouri University of Science and Technology Scholars' Mine International Conference on Case Histories in (1993) - Third International Conference on Case Geotechnical Engineering Histories in Geotechnical Engineering 03 Jun 1993, 10:30 am - 12:30 pm Geotechnical Performance of a Tunnel in Soft Ground A. B. Parreira Universidade de São Paulo, Brazil R. F. Azevedo Pontifícia Universidade Católica do Rio de Janeiro, Brazil Follow this and additional works at: https://scholarsmine.mst.edu/icchge Part of the Geotechnical Engineering Commons Recommended Citation Parreira, A. B. and Azevedo, R. F., "Geotechnical Performance of a Tunnel in Soft Ground" (1993). International Conference on Case Histories in Geotechnical Engineering. 17. https://scholarsmine.mst.edu/icchge/3icchge/3icchge-session05/17 This work is licensed under a Creative Commons Attribution-Noncommercial-No Derivative Works 4.0 License. This Article - Conference proceedings is brought to you for free and open access by Scholars' Mine. It has been accepted for inclusion in International Conference on Case Histories in Geotechnical Engineering by an authorized administrator of Scholars' Mine. This work is protected by U. S. Copyright Law. Unauthorized use including reproduction for redistribution requires the permission of the copyright holder. For more information, please contact [email protected]. !111!!111 Proceedings: Third International Conference on Case Histories in Geotechnical Engineering, St. Louis, Missouri, ~ June 1-4, 1993, Paper No. 5.55 Geotechnical Performance of a Tunnel in Soft Ground A. B. Parreira R.F.Azevedo Assistant Professor, Universidade de Sio Paulo, Brazil Associate Professor, Pontificia Universidade Cat61ica do Rio de Janeiro, Brazil SYNOPSIS The analysis of a tunnel section excavated through soft ground is presented.
    [Show full text]
  • Construction, Carpentry Contractors
    Carpentry Contractors 1997 Issued August 1999 EC97C-2355A 1997 Economic Census Construction Industry Series U.S. Department of Commerce Economics and Statistics Administration U.S. CENSUS BUREAU ACKNOWLEDGMENTS Many persons participated in the various The Economic Product Team, with primary activities of the 1997 Economic Census for contributions from Christina Arledge, the Construction sector. The Economic Andrew W. Hait, Barbara L. Lambert, Census Staff of the Economic Planning and and Jennifer E. Lins, was responsible for Coordination Division did the overall plan- the development of the product creation ning and review of the census operations. system to support the 1997 Economic Census product dissemination. Manufacturing and Construction Division prepared this report. Judy M. Dodds, The Geography Division staff developed Assistant Chief for Census and Related geographic coding procedures and associ- Programs, was responsible for the overall ated computer programs. planning, management, and coordination. The Economic Statistical Methods and Pro- Patricia L. Horning, Chief, Construction gramming Division, Charles P. Pautler and Minerals Branch, assisted by Susan L. Jr., Chief, developed and coordinated the Hostetter, Section Chief, performed the computer processing systems. Martin S. planning and implementation. Carla M. Harahush, Assistant Chief for Quinquen- Bailey, Michael A. Blake, Tamara A. nial Programs, was responsible for design Cole, Nina S. Heggs, Donald G. and implementation of the computer Powers, Linda M. Taylor, and Robert A. systems. Samuel Rozenel, Chief, Current Wright provided primary staff assistance. Construction Branch, Kevin J. Brian Greenberg, Assistant Chief for Montgomery and Leonard S. Research and Methodology Programs, Sammarco, Section Chiefs, supervised the assisted by Stacey Cole, Chief of Manu- preparation of the computer programs.
    [Show full text]
  • Wet Well Wonder in a Deep Sewer Tunnel
    Columbus, OH Case Story Wet Well Wonder in a Deep Sewer Tunnel This wet well is a critical piece of a system designed to intercept wet weather overflows, and it demands powerful, high-quality pumps to handle the load. Designed to reduce environmental impacts resulting from Combined Sewer Overflows (CSOs) in Columbus, Ohio, the Olentangy-Scioto- Interceptor-Sewer Augmentation Relief Sewer (OARS) is the key component in meeting this goal. This sewer tunnel will intercept wet weather overflows that currently empty into the Scioto River and instead carry the flows to the city’s Jackson Pike and Southerly wastewater treatment plants. The overall length of the OARS tunnel is just less than four and a half miles, and it includes three relief structures that divert wet weather combined sewer flow to the OARS tunnel. The OARS tunnel is sized to provide adequate conveyance capacity through 2047 for all storms contained within the typical year as defined by the city. The OARS tunnel ends at the OARS Diversion Structure just north of the Jackson Pike wastewater treatment plant, which serves as the pump station wet well. Scope Among the most interesting components of the OARS project is a 215-foot Flygt model CP3351/995 FM 800 HP 4160V, 10417 gpm deep, 60-mgd capacity pumping system and a 185-foot deep screening at192’ tdh system. The OARS pumping system consists of multiple pumps that can handle enough flow to dewater the tunnel within two days of a large flow event. The difficulty with the deep pumping system on this project is that the static head condition varies from as much as 210 feet when the tunnel is empty to as little as 15 feet when the tunnel and shafts are full.
    [Show full text]
  • Seismic Design of Tunnels a Simple State-Of-The-Art Design Approach
    Front,Chp1,2/Mngrph Text 1993 11/21/03 3:53 PM Page 1 1991 William Barclay Parsons Fellowship Parsons Brinckerhoff Monograph 7 Seismic Design of Tunnels A Simple State-of-the-Art Design Approach Jaw-Nan (Joe) Wang, Ph.D., P.E. Professional Associate Parsons Brinckerhoff Quade & Douglas, Inc. June 1993 Front,Chp1,2/Mngrph Text 1993 11/21/03 3:53 PM Page 2 First Printing 1993 Copyright © Jaw-Nan Wang and Parsons Brinckerhoff Inc. All rights reserved. No part of this work covered by the copyright thereon may be reproduced or used in any form or by any means — graphic, electronic, or mechanical, including photocopying, recording, taping, or information storage or retrieval systems — without permission of the publisher. Published by Parsons Brinckerhoff Inc. One Penn Plaza New York, New York Front,Chp1,2/Mngrph Text 1993 11/21/03 3:53 PM Page i CONTENTS Foreword ix 1.0 Introduction 1 1.1 Purpose 3 1.2 Scope of this Study 4 1.3 Background 4 Importance of Seismic Design 4 Seismic Design before the ‘90s 5 1.4 General Effects of Earthquakes 7 Ground Shaking 7 Ground Failure 8 1.5 Performance Record in Earthquakes 8 2.0 Seismic Design Philosophy for Tunnel Structures 13 2.1 Seismic Design vs. Conventional Design 15 2.2 Surface Structures vs. Underground Structures 15 Surface Structures 15 Underground Structures 16 Design and Analysis Approaches 16 2.3 Seismic Design Philosophies for Other Facilities 17 Bridges and Buildings 17 Nuclear Power Facilities 17 Port and Harbor Facilities 18 Oil and Gas Pipeline Systems 18 2.4 Proposed Seismic Design Philosophy
    [Show full text]
  • Planting in a High Tunnel Department of Natural Resources Conservation Service Agriculture
    United States Planting in a High Tunnel Department of Natural Resources Conservation Service Agriculture What is a Seasonal High Tunnel System? Alaska Crops A high tunnel (Seasonal Tunnel System for Crops) is a In Alaska four crops immediately come to mind as polyethylene (plastic) covered structure that allows benefitting from extended seasons, warmer growers to increase production of certain crops, grow temperatures and high market return. These are some crops that could not otherwise be grown in their tomatoes, cucumbers, corn, and peppers. They are area, and extend the length of time in the year (growing currently the most popular, as well as profitable, crops season) that the crops may be grown. for high tunnel production. Of course, this does not rule out other plants, nor does it rule out starting earlier in High tunnels often look similar to greenhouses, but are the season with cooler tolerant plants (i.e. quick maturing usually only single walled and are typically not baby greens), harvesting them and planting a second temperature controlled. The plastic covering traps crop that matures later in the season. High tunnel sunlight to raise temperatures inside the structure for the efficiency is increased by getting two or more crops a plants growing inside. The growing season can be growing season. This strategy also works if you have extended by up to four weeks by protecting crops from some plants that are incompatible because one plant potentially damaging weather conditions. Crops grown shades another. You can however, overcome shading by inside high tunnels tend to be of higher quality and spacing and/or by where you physically locate plants produce higher yields.
    [Show full text]
  • Stability Charts for a Tall Tunnel in Undrained Clay
    Int. J. of GEOMATE, April, 2016, Vol. 10, No. 2 (Sl. No. 20), pp. 1764-1769 Geotech., Const. Mat. and Env., ISSN: 2186-2982(P), 2186-2990(O), Japan STABILITY CHARTS FOR A TALL TUNNEL IN UNDRAINED CLAY Jim Shiau1, Mathew Sams1 and Jing Chen1 1School of Civil Engineering and Surveying, University of Southern Queensland, Australia ABSTRACT The stability of a plane strain tall rectangular tunnel in undrained clay is investigated in this paper using shear strength reduction technique. The finite difference program FLAC is used to determine the factor of safety for unsupported tall rectangular tunnels. Numerical results are compared with upper and lower bound limit solutions, and the comparison finds a very good agreement with solutions to be within 5% difference. Design charts for tall rectangular tunnels are then presented for a wide range of practical scenarios using dimensionless ratios ~ a similar approach to Taylor’s slope stability chart. A number of typical examples are presented to illustrate the potential usefulness for practicing engineers. Keywords: Stability Analysis, Tall Tunnel, Undrained Clay, Factor of Safety, FLAC, Strength Reduction Method INTRODUCTION C/D and the strength ratio Su/γD. This approach is very similar to the widely used Taylor’s design chart The critical geotechnical aspects for tunnel design for slope stability analysis (Taylor, 1937) [9]. discussed by Peck (1969) in [1] are: stability during construction, ground movements, and the determination of structural forces for the lining design. The focus of this paper is on the design consideration of tunnel stability that was expressed by a stability number initially defined by Broms and Bennermark (1967) [2] in equation 1: = (1) − + Fig.
    [Show full text]