TECHNICAL | CONCRETE


PROJECT EXAMPLE: M4-M5 LINK TUNNELS, SYDNEY


The M4-M5 Link Tunnels in Sydney, Australia, are approximately 7.5km-long and accommodate up to four lanes of traffic in each direction with spans up to 23m in the main lines and 34m in transition caverns. The project connects the new M4 Tunnels with the M8 Tunnels to form the 33km-long WestConnex Motorway, mostly underground. Like many road tunnels in Sydney, these tunnels are designed as drained structures and adopt PSCL for a 100-year design life. In wet sections of the tunnel, a sprayed waterproofing membrane


was adopted where the primary lining is still designed to resist all ground loads and the applicable residual water pressure in the long- term. The secondary lining design is designed without relying on long- term shear transfer by the membrane to resist operational loads and, as a redundancy, also the residual ground water loads. Sprayed concrete strength. ● Primary & secondary lining: 40MPa, flexural tensile strength, fR1k= 3.5MPa, and fR4k = 3.0MPa


● Lining thickness: primary lining is 110mm with 35kg/m3 fibres; secondary lining is 125mm with 35kg/m3 1kg/m³ of polypropylene (PP) fibres for fire resistance


of steel of steel fibres and


The use of high-performance end-hooked steel fibres Dramix 4D 65/35BG was effective in achieving the desired high-level performance ground support characteristic design fr4 = 3.0MPa. Production testing confirmed performance with only minor and, as


expected, outliers. The high-performance fibre combined with the consideration of compressive membrane action (CMA) allowed for the design of very thin FRPSCL (t = 90mm) with an assumed unbonded condition with high capacity demonstrated by both numerical


modelling and large-scale field tests. The consideration of CMA effects were confirmed by load-bearing capacities that were some 3-6 times greater than those estimated by conventional design methods based on pure flexural/bending resistance. The outcomes were very positive:


● Reductions in the amount of sprayed concrete used on the project by 27,000m3


(15% in thickness) and reinforced steel fibres by 830 tonnes (10%)


● Reduction of more than 33,000 tonnes of embodied carbon (CO2 from sprayed concrete


● Cost savings to the project by minimising materials e)


● The removal of 9,000 heavy vehicle movements of Sydney’s local and main roads


Above: M4-M5 Link Tunnels in Sydney, Australia


The carbon emission during construction by


conventional methods as drill & blast is more than by using tunnel boring machines (TBMs). Results showed that, in the case of such conventional


tunneling, materials are responsible for approximately 60% to 80% of the total impacts depending on the impact indicator.3 Changing temporary the shotcrete lining and


permanent cast-in-place (CIP) liner to PSCL and improving the mix design could lead to CO2


savings of


up to 75%. Excessive structural design using cast-in-place


concrete or other lining structures, where used in the current practice, have a significant impact on excavated volumes, construction time, construction cost, and CO2 emissions. Many groups are currently conducting research that


already shows positive conclusion, such as SUPERCON, in Norway. The final results from the SUPERCON project are yet to come, and hopefully the findings from the project could contribute to more effective tunneling with less carbon emissions.4 Main impact of this research:


12 | July 2023


In-situ cast concrete lining: ● 8cm + 8cm sprayed concrete ● 40cm in-situ cast ● Results in 130kg CO2


e/m2 higher)


PSCL ● 8cm + 4cm + 6cm sprayed concrete ● Results in 52kg CO2


e/m2 tunnel


START FROM RELEVANT MATERIAL PROPERTIES A permanent sprayed concrete type of tunnel lining should be considered in the same way as any other permanent concrete structure. For structural use, mechanical performance of spray


fibre reinforced concrete (SFRC) lining must be verified in accordance with a performance-based approach. Model Code 2010 allows a comprehensive design approach for FRC. This approach can be extended to sprayed FRC if a correct characterisation of the mechanical properties of the material is made, and with particular regard to the residual tensile strength. Particularly when working with SFRC, it is important


tunnel (probably much


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