Thrust blocks design for water pipelines

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Thrust blocks design for water pipelines

 

Author: Ng, Vitus
Title: Thrust blocks design for water pipelines
Degree: M.Sc.
Year: 1993
Subject: Water-pipes -- China -- Hong Kong -- Design and construction
Water-pipes -- China -- Hong Kong -- Design and construction -- Computer programs
Hong Kong Polytechnic -- Dissertations
Department: Dept. of Civil and Structural Engineering
Pages: 1 v. (various pagings) : ill. ; 31 cm
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b1132500
URI: http://theses.lib.polyu.edu.hk/handle/200/1432
Abstract: 1 Aims and Objectives The aims and objectives of this dissertation are:- (a) to carry out a critical review of Water Supplies Department's current design practices of thrust blocks for water pipelines ; (b) to recommend improvements and alternative methods for the design of thrust blocks; and (c) to prepare a computer program in the form of knowledge-based expert system for the design of thrust blocks. 2 Literature Survey and Appraisal of Current Design Practices Appraisal of the current design practices for thrust blocks (Chapters 3 & 5) based on the literature survey (Chapter 4) identified the following areas which require improvement:- (a) soil parameters for estimation of passive earth pressure, which affects the stability analysis of thrust block under pipeline testing condition, are conservative (5.6, 5.7); (b) necessity of provision of thrust blocks on steel pipelines (5.11); (c) guidelines for the estimation of safe anchorage length in steel pipelines (5.12); and (d) the assumption on the percentage of total thrust to be taken by thrust block in steel pipelines (5.13, 5.14). 3 Alternative Designs for Thrust Blocks The feasibility of alternative thrust restraining methods, including use of self-anchoring joints in ductile iron pipelines (6.2), use of ductile iron pipes with rigid joints (6.3), reinforced concrete sheathing (6.4), thick wall pipes (6.5) and alternative materials for thrust block (6.6), indicates that there is no better alternative than using conventional mass concrete thrust block. 4 Recommended Design Practices for Thrust Blocks The main recommendations for improving the design of mass concrete thrust blocks are as follows:- (a) A consistent set of soil parameters is adopted for estimation of passive earth pressure and base friction of block (7.4, 7.6 & 7.9); (b) The necessity of the provision of thrust blocks at steel pipelines depends on the availability of anchoring force due to pipe friction (7.11); (c) Guidelines for estimation of the anchoring force on steel pipelines due to pipe friction with provision to allow for possibility of pipeline being exposed by other utilities (7.12, 7.13 & 7.15 - 7.20); and (d) The percentage of total thrust to be taken by thrust block is related to the buried length of pipeline (7.15 - 7.20). 5 Merits of Recommended Design Practices The main advantages of the recommended practices are:- (a) Better reflection of the true forces at pipe fittings on ductile iron and steel pipelines (9.2.2) which may mean reduction of the size of thrust blocks; (b) Thrust block for steel pipelines are only required to be designed for working pressure under most circumstances (9.3.1 - 9.3.6); and (c) Thrust blocks are not required on steel pipelines when sufficient anchoring force due to pipe friction is available (9.3). 6 Development of Expert System for Thrust Block Design An expert system is developed based on the recommended practices (Chapter 8) which takes into account the effects of groundwater on the thrust block (7.14). 7 Updating of Current Design Practices for Thrust Blocks After the successful verification of the recommended practices and the expert system by a trial on site (Chapter 10), the current design practices for thrust blocks in Water Supplies Department are updated based on the recommended practices (Chapter 11).

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