Collector "Centrum" in Ostrava

At the beginning of this year, in the same way as 8 years ago in Prague, a construction of a service collector "Centrum" in Ostrava was started as a part of enlarging the sewerage system of the Ostrava city. The collector in Ostrava, similarly to the one in Prague, is being sunk by the "New Austrian method", i.e. by a horizontal articulation of a stope into two cuts with temporary lining and subsequent final lining. In contrast to the Prague collector, the one in Ostrava is being sunk largely under the ground water level, which means certain increased risks in terms of the driving works. The Zakládání staveb, Co., is carrying out works at this construction for a major contractor - the Subterra, Co.; these works include securing a collector driven in the described way with a sanitation "envelope" by an upward jetgrouting carried out by individual sections. This method of securing the driving was utilised for a stope of a part of connecting and branch chambers and in the place of the underpass of the collector line under the Nádražní Street where a tramline is operated, which represents a higher risk in the course of the underground work construction.

For the part of the collector line secured in this way the driving was divided into individual sections of a driving length of up to 9,0 m. A calotte of such section takes a shape of a part of truncated cone and it enables grouting over the stope calotte as a subsequent driving step while retaining a minimal cross section of the collector. Such each section of the collector driving is closed with a stable face made of reinforced sprayed concrete.

A sanitation envelope made by jetgrouting is formed by mutually interlapping individual columns with a minimal guaranteed diameter of 600 mm. According to the type of securing as well as the requirements of the supplier of driving works, the envelopes were formed by up to 21 pieces of individual columns. The sanitation envelope made of jetgrouting was compact in all secured sections of driving and it attained the required compactness according to the project requirements; grouting of the soil was homogenous and its geometry met the prescribed criteria of tolerance.

Drilling and grouting works were carried out with the drilling set Casagrande M5 SD that is especially adjusted for upward drilling in the underground. In the course of securing the driving of the K7 chamber, which is anaclastic, a specially assembled drilling set MSV 741 with a fitted lateral lafette was used for grouting of the face no.3 (breaking face normal to the existing direction of driving).

In connection with the collector driving the Zakládání staveb, Co., secured at this construction the building of the Museum of Ostrava that is located in close proximity of the collector line. The securing is carried out by shielding the structure from the area of subsidence by a jetgrouting screen.

Grouting works carried out so far by the Zakládání staveb, Co., at this construction - especially sanitation grouting of the calotte stope and sides of the collector gallery - enabled the major contractor to realise subsequent safe and, first of all, fast driving, thus accelerating the construction of the whole underground work.

Text: Ing. Martin Čejka, Pavel Pavlů

Picture #1Picture #2Picture #3
Photo 1 |
Ground plan of the sanitation grouting of chambers.
Photo 2 |
View of the compact sanitation grouting of side of the collector gallery.
Photo 3 |
View of the drilling set Casagrande M5 SD when driving from the S14 shaft into the collector gallery.