Excavation in adverse geological conditions
BELES, Ethiopia – Tunnel
Introduction
This brief description is useful to highlight the different potential application of our consolidation products even in the most critical and unpredictable situations.
At chainage 6+400 m, during the excavation of the “low pressure headrace tunnel” the boring head suddenly blocked because of a massive and large collapse of the excavation front.
Among the many options available to deal with this difficulty we chose to employ polymer resins. You will find a brief description of the consolidation techniques and materials used.
Description of phenomenon and suitable solutions.
Usually, material collapse starts in the crown area then proceeds upwards and in the direction of the front advancement with such a speed that any attempt to contain it by the operators on board of the TBM is pointless. The phenomenon's effect is the sudden stop of the TBM head caused by large blocks clogging the inside of the loading blades.
Safety procedures needed to secure the excavation front and later resume excavation works consist of three different stages:
1)filling the cavity with high expansion polymer resins that support the collapsed material and prevent further material from falling;
2) consolidating the front and the crown area with low expansion ration polymer resins
3) building, if needed, an additional tunnel at the higher part of the shield to remove rocks crumbled on the excavation front and allow freeing of the boring head.
The consolidation works carried out in the Beles tunnel needed, as shown in the drawing, the use of the following materials:
- From the TBM head, using a set of properly positioned pipes, we have injected TISfoam DRY K (a high expansion ratio organo-silicate resin) in the amount needed to completely fill the cavity.
- From the TBM head, using a set of properly positioned pipes, we have injected TIS-sil STAB (a low expansion ratio organo-mineral resin) which has en exceptional mechanical resistance and adhesion.
|
 |
