Post date: Jan 14, 2018 12:41:24 AM
Tunnel is not indicative of infrastructure technologies available in a state or a country. Why would you need a tunnel when there are other options available? I myself would not want a tunnel construction and a tunnel in my road design. Let us look at this issue from traffic management, engineering design, safety and cost.
1. Traffic management
The reason for this tunnel is due to 4 dimensional constraints where you are looking at 3D space constraints as well as time constraint. The traffic flow status at this area is rated as F by level of service which need to debottlenecking and at the same time should not be redundant based on KK outer ring road (KKORR) project which is part of Pan Borneo project. Second, the traffic design is to cater the upgrading of the Sepangar port where RM2.4 billion under 11th Malaysia Plan for Sabah Development Corridor (SDC) projects which include the expansion of Sepangar Bay Container Port from 500 thousand twenty foot equivalent units (TEUs) to 1.25 million, with projection increase of 5% to 6% per annum. This is the main reason why the tunnel is built so that it will not affect traffic (limiting congestion within the port area) within the vicinity (arterial and collector roads' capacity to be maintained) while upgrading of the highway linking KK to Tuaran via HR203/HR204.
2. Engineering
Based on engineering philosophy, where things are simple, we don't complicate it. Engineering does not see grandeur as an achievement but rather sees practicality as a pragmatic solution. In this case, tunnel is the last resort since it would have the same traveling distance with the existing road to the designed destination. Why tunneling?
There are a few requirements which make it substantial to select this expensive engineering apart from distance.
a) the road gradient is essential when it comes to the majority of the traffic users of this road. Most trucks would prefer to have gradient of under 10% for optimal performance. Similar to roads designed for fire engine access, the gradient have to be under 10%. When you bore holes from point A to point B, you can have a straight line with slight difference on the vertical height at inlet and outlet points. Second, imagine this, how do you mobilize the tunnel boring machine (TBM) to a location when the existing road have critical crest and sags? Think about the practicality of the first order of the construction method/stage.
b) road geometry is another key feature for the design where it ease the mobility when transporting large or bulk item such as refinery columns. If an access road is built with various superelevations, crest and sags; it is harder for transportation of such items using articulate extension(s) to the prime mover.
c) Rock engineering is vital in this application. Most of the areas around KK are undulating, the unsuitability of constructing a tunnel is due to weathering of some rock formation. In a journal by Tating et al. (2013) entitled “Weathering affects on discontinuity properties in sandstone in a tropical environment: case study at Kota Kinabalu, Sabah Malaysia”, it is appropriate to make some assumptions in regard to weathering effect on discontinuity properties in sandstone at the project site when deciding n engineering construction on rock masses which affects the mechanically and integrally. It is reckoned that provision should be made for tensional discontinuities, shear discontinuities, periodic sedimentation, metamorphism or chemical decomposition. These should be interpreted in the light of local soil types and import soil type(s). This substantially increase the likelihood of variation, construction time and risk. If you understand the slope guideline requirements by JKR, permanent anchors for the tunnel requires the high safety factors for tensile resistance and considering the creep and corrosion. Now, certain anchors require periodical destressing process in order to perform accordingly. This substantially increase the construction cost and maintenance cost in the long run.
In some places in Peninsular Malaysia, tunnel is considered accordingly based on the 4 dimensions i mentioned earlier and another addition which make tunnel a choice is due to the karstic condition of possible alignment/corridor which does not provide sufficient bearing for standard axle and is in danger of possible sinkhole.
These are the main elements which i consider worth for a brief discussion rather than in-depth engineering discussion.
3. Safety
Tunnel is not the best facility for motorway in comparison to open field road. The road shoulder is limited and in case of accidents, it is hard to extract users from within the tunnel. Second, ventilation is another issue.
But from another perspective, why this tunnel is a good addition for Sepanggar port? In any case of possible industrial disaster, the tunnel will be a great shelter from blast since its orientation is 90 degree from most hazards there.
4. Cost
It is not cheap to build a tunnel and certainly it would take a lot of time to construct. Tunnel takes time to bore and therefore parallel with the increment of labor cost due to time. Apart from that, from engineering aspect, there are so many variables which need to be taken in consideration and risk aversion which leads to substantial variation order. In this case, the cost shot up from RM66 million to RM82 million for a 600m long twin tunnel.
5. Technologies in Sabah
While Peninsular have their expensive tunnel, in Sabah, we have our expensive secant wall. It is also a complex construction which need a lot of geotechnical calculations and state of the art construction methods. There a lot of other geotechnical advances in Sabah than parts of Peninsular Malaysia if you choose to learn about it.
6. At the end of the day, a tunnel is just an engineering solution depending on justified needs when it comes to constraints. Remember, function over form or form follows function philosophy. Why do we need to cite Hong Kong in this case? Geologically, Hong Kong have similar rock geology like us (that is why we adopt GEOSPEC 5 code) but they have constrained space, that is the reason why tunnel is built. Do they have the luxury for open-field highway like us? No!