Tuesday, October 30, 2012
Loots Groundwater International did groundwater modelling for dewatering installation for the Barangaroo project in Sydney, Australia. Requested by Pumpability PTY was to research if the dewatering installation design was sufficient. Different well placements are compared with 3D modelling in a wide range of permeability values. Results are based on transient calculations with MicroFEM software.
The results were presented in a dewatering report to present to the supervisors of the project. The size of the construction are was approximately 250 x 150m and total lowering of groundwater was about 10m.
The modelling was challenging because vacuum wellpoints were used at the pile walls, the practical drawdown limit was modelled. Another challenge was the steep (sandstone) bottom and leaks through fractures simulation.
|Example drawdown after 60 days dewatering with a|
Monday, October 29, 2012
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|Figure 1 - lowering groundwaterlevel (effect three different methods)|
In figure 1 an example project can be found, this project was in the Netherlands. The client requested to calculate possibilities. Bottlenecks:
- The current groundwater level was found, also the lowest and highest groundwater level in the last decade was determined based on archive research and calculation
- Inside the -0.8m contourline ground settlements were expected
- Other buildings around project area are might be permanent damaged by ground settlements
- Difficulties discharged groundwater, no nearby capacity. Limiting discharge recommended
Three different building methods were modelled:
- FIGURE 1 LEFT - Long steel sheets around excavation to close aquifer and for stability
- FIGURE 1 MIDDLE - Short steel sheets plus mixed in place barrier + dewatering installation, with simulated seepage at corners
- FIGURE 1 RIGHT - No measures only dewatering installation for stability of slopes, concluded not recommended because to much groundwater lowering when dewatering period is 4 weeks. Also prognosis discharge was above capacity
Recommendations were made for the client his project preparation. Also a dewatering supervision was offered, Loots Groundwater International check if measures are good enough to tackle the bottlenecks. After start dewatering we offer troubleshooting, new measures, due new insights (for example calculate extra pumpcapacity because the soil seems to be higher permeablity as assumed when looking to discharge and groundwater lowering)
Friday, October 26, 2012
Dewatering is often a small part of the total amount of costs for building excavation or for underground pipelines/infrastucture. Environment can be effected by dewatering for example:
- nature/agriculture that is harmed by groundwater lowering
- buildings/infrastructure damaged by ground settlements (unavoidable consequence of the effective stress increases that result from groundwater lowering)
- (groundwater) contamination displacement (for example contamination can move to drinkwater area)
- archeology or wooden piles/underground objects are damaged by lowering groundwater level
By investigation and 3D modelling measures can be calculated based on the data. A good prognosis of the effects is the result of calculation The exact effects are often never calculated, in each report concludes with expected ground behaviour by dewatering.