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If we look at landslides from the earth’s perspective we can define them as a condition towards stress relaxation and minimization of potential energy. The earth is trying to come to equilibrium. Landslides are formed either from natural conditions such as erosion of slope toe, geological uplifting etc or are manmade when extensive excavation or loading is taking place in the foot or the top of a slope respectively. These are the main reasons why landslides form but the triggering mechanisms for a landslide to occur may be different.
In my opinion the most important triggering factor for a landslide to occur is the modification of groundwater or pore pressure conditions. This issue becomes more important if we consider the climate change which is producing different rainfall conditions with abrupt changes on ground water conditions.
Due to weather pattern changes, ancient, dormant or newly formed landslides will start to occur all and all more frequently. This will affect the economies and life worldwide and is something that needs to be addressed not only from geotechnical engineers and geologists but also by government officials, politicians and decision makers in general.
Landslides will become a hot topic in the near future, here are some very interesting blogs dealing with this issue:
People interested in geotechnical engineering are watching closely the colliery landslide at Hatfield Stainforth, in Northern England that is still in progress. Since February 13nth reports and photos on the landslide’s progress are coming in.
Thanks to Prof. Dave Petley’s (Durham University UK) landslide blog, the info and the photographs are really spectacular. According to his first estimation the size and the geometry of the toe bulge suggest a bearing capacity failure. The very wet weather of last few months, triggered the landslide with a rotational geometry.
Due to the size of landslide mass, stabilization will be highly difficult. The railway line is expected to be closed for some time.
In these cases where the amount of soil mass is prohibiting, it might be better to wait for the landslide system to find progressively its own balance, before intervening with further stabilization measures.
Have we lost our ability to think? Have we learned that we only need to ask questions and not try to solve the problem ourselves?
In linkedin groups for geotechnical engineers and other forums I have seen (and many times replied) to questions for geotechnical problems without even the necessary information. This is poor engineering which we should try to avoid. Many times practicing engineers or students pose questions without even try to find the answer for themselves.
I think it would be much better and more efficient if the Questioner would provide also his proposal. For example, instead of posting a question like “what type of shear strength parameters can I use to evaluate a soil sliding mass?” it would be much better to post: “I am evaluating a soil sliding mass which has moved xxx(mm) and I think I should use residual friction angle for the sliding surface, what is the group’s opinion?” This type of question includes thinking of the problem and a possible solution which the group can evaluate and reply if it thinks is appropriate or there are other solutions.
We should try hard to promote geotechnical engineering and increase our intelligence and experience of the subject and not try to find the easy way for someone else to solve our problem.
An expressway tunnel in central Japan whose ceiling collapsed in December, killing nine, became fully operational Friday after a 68-day hiatus, its operator Central Nippon Expressway Co. said.
The nearly 5-kilometer-long Sasago Tunnel in Yamanashi Prefecture became fully usable again ahead of the previously targeted reopening date later this month as restoration work was hastened ahead of the upcoming long weekend when traffic is expected to increase.
The Ministry of Land, Infrastructure, Transport and Tourism gave its go-ahead on the grounds that all safety issues have been cleared.
Some bereaved relatives of the victims are taking issue, however, with the road operator’s policy to prioritize the tunnel reopening before the cause of the fatal accident has been fully clarified.
The tunnel restarted partial operation on Dec. 29 after tunnel collapse with half of the lanes reopened to traffic.
Tunnel collapse can happen for a number of reasons such as: inadequate ground investigation, shallow ground conditions, inadequate support measures, cost optimization, inexperienced contractors, inadequate supervision, delays of excavation and support erection.
A moderate 5.7 magnitude earthquake in Chile, happened on Sunday 10 February 2013, according to USGS. There are no immediate reports of casualties or damage.
The epicenter of the Chile earthquake was approximately 24 kilometers northwest of Cartagena kai 4o kilometers south of Valparaiso.
In February 2010, a massive 8.8 magnitude earthquake hit Chile at central Maule region, generating tsunami waves, killing 500 people.
Chile is a country with a huge seismic history, considering that lies above the converge of the Nazca Plate and the South American plate. For this reason Chile has been the site of many historical earthquakes, including the largest earthquake ever recorded.
In recent history numerous headlines present tunnel collapses in major cities. One can ask why so many failures? I would like to provide some insight regarding this issue.
The following reasons can produce a single cause or combined effect that can result in ground tunnel collapse during tunnel construction in urban areas:
- Inadequate ground investigation due to condense building construction.
- Continuous differentiation of shallow ground conditions due to manmade structures, faulty utilities seeping fresh water, sewage or storm water etc. Especially in shallow ground the mechanical properties of the soil may have been modified from one building block to another.
- Inadequate support method of excavation. Especially in difficult and complex ground condition with mixed face conditions (strong rock and soft soil are encountered on the tunnel face).
- Cost optimization of excavation and support. This can lead to reduced support measures or higher advance rates of excavation to meet deadlines and follow inappropriate scheduling.
- Cost optimization with selection of inappropriate tunnel boring machine (TBM) that can accommodate most of the encountered conditions but not all.
- Inexperienced contractors and design engineers with local conditions, especially for international projects.
- Inadequate supervision of construction works.
- Delays of excavation and support erection due to unforeseen conditions such as archeological discoveries, union strikes etc.
These are the most usual conditions (many other may exist) that can produce tunnel collapses. Unfortunately most of them are related to cost reduction or cost optimization. This is especially true in low bit contracts for investigation, design or construction.
Usually after a tunnel collapse has been formed and its causes are evaluated, it is found that
it could have easily been avoided. The most interesting outcome is that the cost of repairs usually is far more that the cost required for a better initial investigation, or design or construction!
On Monday afternoon (28/1/2013), three buildings collapsed after subsidence in Guangzhou. The incident happened near a metro tunnel construction site.
It is reported that metro workers spotted land subsidence near the project site and immediately the area was evacuated, hence no casualties have been reported. The subsidence area was about 10m deep and extended about 100m2.
It is also reported that the area is temporary stabilized by backfilling concrete into thesubsidence. The site is monitored for risk assessment.
Tunnel construction with a fast pace and lowered standards could lead to disaster. Land subsidence can be caused by a variety of factors. Tunneling in urban areas always includes careful consideration and monitoring of land movement.