Myoho
Geotechnical
- May 29, 2003
- 46
I am working on an combined foul and storm sewer outfall shaft that is subject to very large surge pressures (3.5Bar top to 6.5Bar at base). The shaft was constructed 40 years ago but since its construction the sewer network has greatly increased in size. In a storm event the surcharge within the outfall shaft has been calculated at 3.5 Bar pressure. A finite element analysis has been carried out which shows that under that surcharge (3.5Bar) the shaft lining goes into tension. However, the steel reinforcement is assumed to be corroded and the concrete cant take any tensile loads. To counter the 3.5Bar surcharge we want to externally prestress the shaft to 3.5 Bar (from 17mbgl to 30mbgl).
I was thinking of compaction grouting uing a Tube'a'Manchette system. A highly viscous grout with high internal friction is proposed which will be injected into the sands and gravels (compactable soil). The grout acts as a radial, hydraulic jack and physically displaces the soil particles; thus achieving controlled densification.
Just wondering if anyone has used this method before or if any one had any alternative solutions.
Shaft Dimensions:
The shaft was constructed using 240mm thick 610mm deep precast concrete segments. The outside diameter of the shaft is 6.274m and there are 11 segments and one key to each ring. The segments were bolted together using mild steel black bolts. We can assume that the black bolts have coroded over the last 40 years. The shaft was then lined with reinforced concrete and a dividing wall was constructed through the middle of the shaft to create a wet well on one side and a dry well on the other side. The lining thickness on the dry side is 203mm and 457mm on the dry side.
Geology:
Ground Level to 6mbgl - Blown sand
6mbgl to 17mbgl - Boulder Clay
17mbgl to 30mbgl - Glacial Sand and Gravels
I was thinking of compaction grouting uing a Tube'a'Manchette system. A highly viscous grout with high internal friction is proposed which will be injected into the sands and gravels (compactable soil). The grout acts as a radial, hydraulic jack and physically displaces the soil particles; thus achieving controlled densification.
Just wondering if anyone has used this method before or if any one had any alternative solutions.
Shaft Dimensions:
The shaft was constructed using 240mm thick 610mm deep precast concrete segments. The outside diameter of the shaft is 6.274m and there are 11 segments and one key to each ring. The segments were bolted together using mild steel black bolts. We can assume that the black bolts have coroded over the last 40 years. The shaft was then lined with reinforced concrete and a dividing wall was constructed through the middle of the shaft to create a wet well on one side and a dry well on the other side. The lining thickness on the dry side is 203mm and 457mm on the dry side.
Geology:
Ground Level to 6mbgl - Blown sand
6mbgl to 17mbgl - Boulder Clay
17mbgl to 30mbgl - Glacial Sand and Gravels
