**7.3. Elimination of contaminated water outflows from the uranium deposit (Rozna, Czech Republic)**

#### **Task:**

After stopping of mining at the uranium deposit Rozna in 1996, the mine was flooded. The groundwater from the old exploited areas, rich in uranium, infiltrated into the old investigation boreholes, even though the boreholes were sealed in the past (Fig. 22). Contaminated water threatened a drinking water reservoir, and therefore it was necessary to stop the dangerous outflows from these boreholes.

#### **Solution:**

The problem was successfully eliminated by application of PU grouting using Geopur® grouting system (Fig. 23). The boreholes were sealed with grouting and the outflows of contaminated water stopped. It was proved that using PU resin of Geopur® type with foaming factor of 12 it is possible to efficiently stop seepages through porous geological environment or boreholes.

Polyurethane Grouting Technologies 329

Geopur® was used. Grouting was performed in total of 275 boreholes. The efficiency of the

grouting works was proved by monitoring of the groundwater table level.

**Figure 24.** Geological situation of sewage collector construction in Pilsen.

**Figure 25.** Drift of sewage collector in Pilsen - scheme of grouting works.

**Republic)** 

**Task:** 

**7.5. Securing of excavation of underground utility tunnel (Ostrava, Czech** 

overburden soil (gravels of the River Ostravice terrace) was minimally 2 MPa.

In the centre of Ostrava town an underground gallery was exploited (Fig. 26). According to the design of the construction, it was required that the compressive strength of the

**Figure 22.** Borehole with contaminated water seepages

**Figure 23.** Sealing of the borehole with PU grouting

### **7.4. Sealing grouting of sewage collector (Pilsen, Czech Republic)**

#### **Task:**

During exploitation of a sewage collector in Pilsen – Cernice, drainage in the surrounding area occurred due to drainage effect of the collector. Groundwater disappeared from the wells in the surrounding and drops of the surface occurred, causing even damages to some buildings. In section 4255 – 4350 m of the collector the excavation works ran in close proximity of a residential house. There was a risk of damage to the house and surface drop due to the fast drainage of the groundwater. In order to eliminate inflows into the collector, a hydrogeological survey was performed and a technology of sealing of the environment was proposed.

#### **Solution:**

During the exploitation works in the critical section (approx. 100 m), the rock mass was stabilized by PU grouting. Grouting PU materials Geopur® was used. The grouting works were performed always in advance before the exploitation to the distance of 3 m ahead of the face and were followed by exploitation of 2,5 m. Used technology enabled stopping of strong inflows of groundwater and secured higher stability of the rock mass during the exploitation works. Drainage of the surrounding area was eliminated and buildings were not threatened further by the excavation works. Total of 9516 kg of PU grouting material Geopur® was used. Grouting was performed in total of 275 boreholes. The efficiency of the grouting works was proved by monitoring of the groundwater table level.

**Figure 24.** Geological situation of sewage collector construction in Pilsen.

**Figure 25.** Drift of sewage collector in Pilsen - scheme of grouting works.
