making tunnelling safe

by:Gewinn     2019-08-28
Under the leadership of the busy Bukit Bintang, the construction of the Basheng Valley MRT has reached a crucial stage.
Only a year from the tunnel-
The boring work of Basheng Valley MRT Sungai BulohKajang line (SBK Line)concludes.
By the end of this year, there were only two tunnels
Boring machine (TBMs)
Mining will still be carried out and the last unit will be retrieved from the ground on May 2015.
At present, five TBMs are working to form 9. 5km-
Long tunnel.
Supervised by Sdn Bhd, a project owner Volkswagen express transport company, which is a contractor for the underground section of MMC Gamuda KVMRT (T)Sdn Bhd (MGKT)
, Is currently working around the clock to ensure TBMs are running at optimal efficiency.
\"When the Shield encounters relatively uniform ground conditions, it is easier to tunneling.
These machines are geological conditions.
Specifically, this means that they are always tailored to suit the unique ground conditions of each project.
But things get a bit interesting when these ground conditions change, \"said Dr. Ooi Lean Hock, head of geographic technology at MGKT.
Ground conditions for this particular project are particularly challenging, as the SBK line tunnel has to go through two major soil formations: the deposited rock and sand formations of Mount Kenny and the limestone formations of Kuala Lumpur.
The former is a typical and more predictable geological structure, widely found near Kuala Lumpur and in the Basheng Valley, but the limestone formations in Kuala Lumpur are highly weathered karst.
This extreme karst is very beautiful-think about the limestone hills of Ipoh, where there are corners, gaps and passages everywhere, and some people connect with others through a maze, these mazes do not even dare to explore the experienced caves.
However, from a 3D perspective, the karstic formation looks like a piece of Swiss cheese, and the gaps are often filled with groundwater;
This, together with the surrounding ground, forms a balanced system.
\"As a tunnel passes through these gaps, the big challenge comes-the balance is quickly disturbed.
\"The groundwater and mud required for the machine to maintain the working pressure will dissipate rapidly through the Channel Network,\" said Ubull Din Om, general manager of MGKT underground engineering . \".
\"That is why it is so hard to build a large tunnel through the karst;
During the construction of Highway 9, we learned a lot of painful lessons. 7km-
Long Rain management and road Tunnel (SMART),” he adds.
From 2003 to 2007, two TBMs took four years to complete a tunnel for SMART, which was officially opened in 2010.
In that project, which was almost entirely built through karst, there were many examples of ground sinking, including some sinkholes-but thankfully, smart tunnels traveled under relatively sparsely populated areas of the valley.
\"Although it is already very challenging to mine through karst, this becomes more difficult when tunnel excavation has to pass through karst layered with other soil profiles. Tunnel-
When dealing with even ground conditions, boring machines are the most effective, whether it\'s all the rocks, all the soft soil or all the sand.
But when ground conditions are mixed, people and machines are pushed to the limit, \"said Ubull.
This month, a pair of TBMs will enter an area of undulating karst layered with the material of the Kenney mountain layer-an interface that appears in a rather unpredictable pattern that tunnel workers hate.
The difficult area is within the vicinity of Fahrenheit88 and Menara Keck Seng, a shopping mall in Jalan Bukit Bintang.
In this position, the tunnel stacks one on the top of the other, and the top of the upper tunnel is only 16 metres from the ground.
\"We have to be very vigilant when the TBMs tunnel goes through this area.
Our operators must choose the most appropriate \"driving mode\" and be extra vigilant, to minimize the possibility of any interference to the surrounding surface while guiding the machine through this challenging rock extension
\"The soil mixture,\" said Ubull.
To minimize the risk of each element of the MRT Project (whether involving a tunnel or not), the first is to conduct a comprehensive ground survey by collecting samples from drilling holes and other geophysical technologies.
\"Traditional research may not always provide sufficient information to assess factors such as variability within a rock block, the exact location of the fault zone, or the supportup times (
Measurement of the time the tunnel wall maintains its shape after excavation)
Softer ground
All of these factors are important when drilling the large diameter tunnel required for the Malaysian MRT system-the outer diameter of the typical tunnel is 6.
67 m, much higher than doubledecker bus! Shared Dr. Ooi.
MGKT began in 2006 and conducted preliminary geological research by conducting preliminary soil sampling along the underground route of the tunnel;
Stretching under Jalan Bukit Bintang has proved particularly difficult to sample (
There is no form of traffic diversion)
Because it\'s almost all built above.
Besides that, there\'s a near-
The authorities concerned do not have a good record of underground utilities, and since contractors conducting excavation are often surprised to find that even after using state to complete a ground scan, no cables and water pipes are foundof-the-
Art equipment for detecting buried objects.
The tunnel is about 30 metres underground on average, and the deepest part is at the Pasar Rakyat MRT station, 45 metres deep.
According to Ubull, it is not easy to conduct a preliminary soil survey at the initial stage.
\"But we appreciate the understanding that there are companies and companies that will allow us access when testing has to be done at a specific location.
\"There are similar restrictions on building protection work, but we are happy that most owners agree with our requirements, which helps us to get the work we need done,\" said Ubull . \".
Dr. Ooi said that the preliminary field survey study included 69 drilling holes, geophysical surveys of sections near the tunnel and stations located in karst.
\"Additional ground surveys were conducted during the detailed design and early construction phases, with more than 400 drilling and geophysical measurements covering more than 9 km drilling holes.
\"We have to collect samples of disturbed and undisturbed soil for visual inspection and laboratory testing,\" Dr. Ooi explained . \".
To investigate the soil conditions of the station site located within limestone, the drilling is drilled to a depth of 10 m below the final excavation level, or through a 10 m continuous cavity
Enter the limestone in a deeper place.
Up to 1 drill can be drilled in key drilling holes.
6 times the depth of excavation, in the case of the Cochrane MRT station site, the depth of excavation is 20 metres lower than the final excavation depth of 32 metres.
\"On limestone-based rock, our geological technology team collected core samples to assess rock quality by observing weathering conditions and fracture states, the quality of which is determined by the penetration rate of rock water and the hydraulic power generated by cracks
\"However, the information obtained from drilling must be handled with care, as it is not possible for us to drill as many holes as possible throughout the tunnel route.
\"In order to fill the information gap that extends between drilling holes, we have to conduct geophysical surveys to provide bridging information,\" Dr. Ooi said . \".
These geophysical measurements include gravity, seismic refraction, multi-channel analysis of surface waves, resistivity, and intermittent layer scanning of seismic Wells.
\"All these measures will reduce-although never completely eliminated-the risk of encountering unforeseen ground conditions,\" Dr. Ooi warned . \" He added that there is no room for complacency and everyone must maintain a healthy respect for the ground at all times.
On the bright side, MGKT has not encountered any major geological problems since the start of station excavation and tunnel work in 2012, strongly suggesting that the initial geological survey and calculation are correct.
Advanced Foundation treatment MGKT must also consider unstable ground conditions on the tbms path.
\"As part of best practices for detecting major or major anomalies on the ground, ground handling will be carried out to stabilize the ground so that the TBM can pass through the area as smoothly as possible.
\"This engineering involves grouting, including injecting grouting control into existing cracks and caves in the rock formation to prevent water from infiltrating,\" Dr. Ooi said . \".
During the tunnel construction,
The time monitoring of the tunnel Palm surface pressure is carried out in the inside of the TBM control room and in the monitoring center above.
The building \"located within the\" scope of impact \"of tunnel construction will be fitted with settlement marks and other automated instruments to help the surveyor determine how much settlement or movement has occurred (if any ).
With this information, the settlement level can be determined (if any)
During and after the tunnel works through the area.
This paves the way for the next remedial action, if needed, \"Dr. Ooi shared.
State is used though-of-the-
The art equipment, construction technology and integrated management of Bukit Bintang is still a very difficult task.
Of course, the sign of \"success\" will be in the next two months, when two TBMs tunnels pass through Fahrenheit88, nothing is noticed.
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