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The Norwegian Geotechnical Institute was concerned about development in the area where the rapid clay landslide occurred. After extensive completion work, the developer received the green light.
After the violent and rapid clay landslide in Gjerdrum, there have been many questions about why housing construction was allowed in a high-risk area. New documents show that the Norwegian Geotechnical Institute gave the green light to the development and that the developer met the requirements.
After the rapid clay landslide, a desperate developer stated:
– I can not understand it. We’ve used racing experts all the time, Odd Sæther told Romerikes Blad.
Read more: Eirik Grønolen (31) died in the Gjerdrum landslide
Already on the same day as the rapid clay landslide, police confirmed that an investigation would be launched.
– The aim is to clarify why such an accident could happen, stated police lawyer Bjørn Arne Tronier.
The online newspaper previously mentioned that as early as 2005 a high risk of rapid clay mudslides was warned, several years before development fully began.
Recently, the Norwegian Geotechnical Institute (NGI) published all the geotechnical survey reports and professional advice in consultation with the developer, the municipality and NVE. In the press release, NGI goes a long way toward complying.
– NGI provides advice, but the responsibility for carrying out security measures does not lie with us. From what we can see from the review, this work has been done in accordance with the current requirements of the Planning and Construction Act and other guidelines. A more comprehensive review of the case could provide answers to this, says NGI CEO Lars Andresen.
After the landslide, seven people were found dead and three missing.
The online newspaper has thoroughly reviewed all the reports.
Read more: The police: – You can live several days if you have air
Great job for safety
In the first document, a clay rapid landslide risk assessment with an action plan from NGI dated 07.24.2003, the institute writes that the zoning plan with development will contribute to greater stability in the area and less risk of landslides. of Earth.
“The favorable impact of the zoning plan on the stable conditions depends first and foremost on the filling in Fjelstadbekkdalen for the establishment of the road system for this part of the area. Other land planning required to implement the zoning plan is assumed to be relatively moderate and therefore will not be critical to safety against major landslides. “
The report notes that Ask vestre’s risk level is “medium” and must be reduced to “low” before it can be built in accordance with the Urban Planning and Planning Act. The law states that in the case of new buildings, the frequency of repetition of landslides must be less than once every 1000 years.
Also read: Royal couple shocked by landslide disaster: – It’s absolutely horrible
NGI highlights two areas that need to be further improved before the zoning plan is implemented and development begins.
Following a meeting between the developer and NGI in September of the same year, a new report will be published in November. It concludes that extensive development work needs to be done by the developer, and that NGI will then verify the work before development can take place with the home.
A new report will be published next year in September 2004, once the stabilizer fill has been largely completed. The memorandum applies to the Ash center area (B9). Technicians write:
“The analyzes show that the safety against landslides is satisfactory. Therefore, it is not necessary to extend the stabilizer filler further downwards relative to what is stated in our technical note of 19.11.2003 “.
Read more: Rescued Norwegians call NVE
The memorandum notes that erosion protection will be needed to prevent stability from deteriorating over time.
The following year, the developer will commission a new memorandum, in January 2005. The total development will include approximately 150 new homes in the area.
In the original 2003 note, NGI recommended a fill at the bottom of the valley in the area of about 5 meters and increasing to 7 meters in the middle and lower parts. This will provide “satisfactory security”.
In the developer’s plan, a fill height of approximately 3 meters is proposed, increasing to 5 meters. To obtain a better evaluation basis, NGI performed further stability analyzes. They conclude that the plan is not satisfactory and propose to raise the land one more meter in relation to the developer’s plan.
Read more: These ten have been lost since the landslide: – We hope and pray for a miracle or two to happen
In the next two NGI notes, it is written in detail how protection against backfill and creek erosion should be performed. Extensive measurements are required. At Fjelstadbekken, the watercourse of just over 500 meters will rise in height. It should be filled with well-graded shot blasting stone, large stones should be inserted, and natural gravel should be used.
In the clay underground, a layer of sand 20 cm thick will be placed for every 1.4 meters of clay. The clay layer should be crushed so that there is as little air content as possible. Heavy wheel loaders and fully loaded trucks should be driven to compact the ground tight enough. Filling can only be done in the period from May to September.
Read more: New photos from the landslide site show the extent of the rapid clay landslide in Gjerdrum
Landslides during work
Next, NGI will carry out an inspection of the area in May 2006. The following year, NGI will carry out a new inspection after a landslide.
‘The reasons for the landslide are a combination of the large precipitation before the landslide and that the meteorite masses have been of somewhat variable quality. The upper masses are arranged as winter work with risk of snow and remixes. Likewise, the sanitary landfill is available without systematic compaction and without any type of drainage. “
In this way, large parts of the masses are removed, drained to remove the water content, and reused. The planning work is thus completed and you get an approved NGI seal.
“The planning work done for Nystulia has resulted in a significant improvement in the overall stability for the entire area between the Ask center and Finstadbekken, including Ingelstun and other old buildings. The area now has satisfactory security, “it says in the latest NGI report.
“Before these planning works, the stability conditions here were not satisfactory in terms of calculation and the conditions deteriorated over time due to the continuous erosion of the stream. The area is now secured against further erosion and stability is improved by extensive filling of the creek gullies. ‘
– Basically fast clays are stable masses, where in Norway we build houses to live. It is too early to say what is causing the landslide that has affected Gjerdrum. The police have opened an investigation and a thorough review of the incident and the course of events will be carried out. This will be an extensive and thorough job. Hopefully here we get answers about causality and what we can all learn from it. Out of respect for the subsequent work, therefore, we do not wish to comment further on the course of events and evaluations that have taken place previously, says NGI manager Lars Andresen.
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