REDUCING BUG-HOLES ON TUNNEL LINING CONCRETE BY USING COVERING SHEETS
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This study focused on bug-holes on sidewalls of tunnel lining concrete. The bug-holes of lining concrete may negatively affect aesthetics and durability of NATM (New Austrian Tunneling Method) tunnels. Most bug-holes appeared on concrete surface are generated from entrapped air during consolidating concrete. In particular, the sidewall of tunnel lining is constructed with negative angles, so bug-holes are often observed on the sidewall. Seven concrete specimens were prepared to simulate conventional tunnel lining. In the experimental investigation, breathable-waterproof material sheets and permeable sheets were used. The primary experimental parameters are (a) covering-sheet materials and (b) form surfaces such as ceramic-coated steel with grooves. The study examined bug-hole distributions in the concrete specimens using the various sheets. The bug-hole distributions were quantified by using an image analysis developed in this study. The test results show that quantity of bug-holes of concrete using the sheets is lower than the quantity of concrete without sheets. It was noteworthy that the bug-holes were hardly observed in the test using the form covered with the permeable sheets.The essence of common concrete durability design is to determine the w/c ratio and the minmal,cement consumption that can meet the demand of concrete durability,This paper adopts the formula method to directly design the mixture ration of concrete by analyzing durability while considering both strength and durability.Based on the deduction of the mathematical relationships of w/c ratio,unit cement consumption and concrete strength.f cu ,the formula of w/c ratio is established that meets durability index.Then ,comparing w/c ratio that meets durability with w/c ratio that meets strength,the lower one is chosen to calculate unit cement dosage by formula(4).In this paper concrete durability is divided into frost resistance durability,carbonization durability,acid radical diffusion durability and grinding durability.
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Since the development of the new Austrian tunnelling method (NATM) in the 1960s, this technique has been applied successfully in many tunnels. However, opinions of NATM principles emerged till 2000, i.e. NATM is not a tunnelling method, but an approach covering all general principles of tunnelling. To investigate the general principles of the NATM, this study focused on tunnelling practises in the Bolu tunnel, and evaluated the conditions under which the NATM practises could be effective. The Bolu tunnel project was designed following the NATM principles. It is evident that practises adopted in this tunnel are important with respect to the NATM. In addition, it shows that the solutions to the problems encountered in this tunnel are consistent with the NATM principles. Finally, the study determines the ground types of the NATM principles and proposes associated updates.
Tunnel Construction
Railway tunnel
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Monitoring measurement was an important part of New Austrian Tunneling Method( NATM). Based on the Meihuashan tunnel construction,some items of monitoring and measurement,such as vault settlement,surrounding rock convergence,etc. were designed to explore the surrounding rock displacement. According to the measuring data regression analyses and the stability state of surrounding rock,the most reasonable time of second supporting was decided. The results showed that safe construction of Meihuashan tunnel was improved under the new second supporting time criterion.
Settlement (finance)
Tunnel Construction
Deformation monitoring
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It is important that monitor measuring is applied in tunnel in regard to NATM. The monitor measuring of NATM was studied in the Fengmeiya Tunnel in Chongzun Express. Based on the regularity and conditions of the surrounding rock deformation of monitor measuring in site, the optimum time for primary and permanent support are obtained which averting successfully accidents in construction, enhancing the construction qualities and guidance to tunnel construction in Karst areas.
Railway tunnel
Tunnel Construction
Deformation monitoring
Water tunnel
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Railway tunnel
Tunnel Construction
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Shotcrete
Railway tunnel
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Following recent problems with the New Austrian Tunnelling Method (NATM) during tunnel construction, tunnellers worldwide, and especially in the UK, have questioned its validity and proposed following the 'new' design concept of Sprayed Concrete Lining (SCL). This article explains the differences between NATM and SCL procedures and results. Two specific examples of the methods are reviewed: (1) the NATM with a central top heading and lateral second stage; and (2) the SCL with lateral galleries excavated first, then the central pillar. The NATM uses systematic rockbolting of the surrounding ground, together with a thin shotcrete shell, reinforced by one layer of wire mesh or fibre. The SCL method uses a support, composed of a 300-500mm thick shotcrete shell, reinforced by ribs, steel bars, and wire mesh layers. The surface settlement results of both methods are compared as a function of the ground conditions encountered. Two similar underground cavities at the same depth and in similar ground were excavated and supported according to the two methods. Measured settlements were compared with computed theoretical settlements. Settlements related to the SCL method seem to be larger than those of the NATM. It was found that the NATM, correctly applied, can control ground movements better, quicker, and more safely.
Shotcrete
Settlement (finance)
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Settlement (finance)
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Some problems of durability have been existing in concrete. This paper analyses factors affecting durability of concrete, summarizes the corresponding technical measures of impr oving durability of concrete, and points out the necessity and feas ibility of using High-Performance Concrete of excellent durability.
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This paper illustrates some knowledge relates to NATM construction practicing.Based on the construction of more than ten tunnels,it tells us the situation that NATM is applied during tunneling.At the same time,to give some good advice for tunneling it points out the problem happened during supporting.
Tunnel Construction
Advice (programming)
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