| Geotechnical Failures (by others) That We Can Learn From |
|
Infinity Tower, Dubai, U.A.E
A tied-back diaphragm wall was designed and constructed to support a deep excavation into sand and rock adjacent to the harbor. It required tiebacks at approximately 9 foot vertical spacing. However, a drainage structure prevented the drilling of three tiebacks near one corner. For unexplained reasons, the contractor decided not to install a corner brace. The following photos show the consequence.
Lianhuanan Road Tower, Shanghai City, China
An apartment tower was near completion, but the contractor needed to excavate for an adjacent parking garage. For unexplained reasons, the contractor did not install sheet piles. Also, he placed the excavated soils along the opposite side of the building. After a few days of rain, which probably increased the pore water pressure in the underlying clay, a shear failure developed from the stockpile to the excavation. The building was supported on a hollow core precast concrete pile which appears to be illegal in China. It had insufficient lateral resistance to prevent the collapse.Read Article Photos
Slope Failure in Nachterstedt, Germany
The town of Nachterstedt is located in northeast Germany, near the city of Magdeburg. The area was used for coal mining for 120 years. In the early 1990’s the mining was discontinued. Nachterstedt was built on a hill consisting of spoils from the mining pit.
The slope that failed in July 2009 was part of the mining spoils dump site, which was created in the 1920’s. Proper compaction of the mining spoils is questionable since there were no records maintained when the dump was created.
Lake Concordia is the excavation site of mining activities that go back as far as 120 years. When the mining was discontinued, the excavation was flooded to use as a recreational lake in 1991. The lake is still being flooded today, with its current water level being 20 meters short of the proposed final water level. Lake Concordia covers an area of 350 hectare (860 acres) and is as deep as 30 meters. The boat dock that is shown on one of the pictures was built one and a half years ago.
The land slide buried one and a half houses, a boat dock and three people under 2 million cubic meters of soil that slid approximately 100 meters into Lake Concordia. The houses that were buried under the landslide were set back 120 meters from the lake shore. Seven other houses in the neighborhood were evacuated, which means that 41 people lost their homes. When the land mass slid into the lake, a wave was created that washed a boat ashore on the other side of the lake.
A resident stated that he noticed cracks in his garage and a sink hole in his yard a few years ago but did not notify any authorities. Test borings were taken a year ago, which exposed voids in the soil.
Authorities will conduct extensive research in the following months to determine the cause for the landslide. However, it is believed that a high ground water level in the area, which is potentially rising due to the continuous flooding of the lake, is responsible for liquefying the soil. The authority that is responsible for flooding Lake Concordia stated that heavy rainfalls during the night are the reason for the slope failure. There is also a potential that the ditches, trenches and voids from the mining activities were not properly filled and compacted.
In 1951, there occurred a slope failure in the same mining area, which was believed to be caused by a rising water level that liquefied the soil.
Once the cause for the land slide is determined, the loose material will be blasted to prevent further sliding of the land mass. Photos
|
|