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For the dynamic pipe installation according to the ramming technique pneumatically driven pipe ramming machines are used. These machines enable the economic installation of open steel pipes as casing or product pipes up to 4000 mm diameter over lengths up to 80 m in soils of the classes 1 – 5 (partly even class 6 – easily soluble rock) without jacking abutments.
1. Pipe installation 2. Soil removal
The pneumatically driven ramming machine has a cylindrical shape with a front, or respectively a rear cone for connecting the add-on cones, cotter segments and/or soil-removal cones/adaptors which create a tight-fitting connection between pipe and machine. When using the soil removal cones/adaptors, part of the soil core, which is carried along, can come out through two openings and exit. The application of cotter segments avoids flaring of the pipe and enables butt welding of the single pipe lengths. Bulging welding seams of spiral welded pipes have to be smoothed to level with the pipe material in the area of the segment fitting depth in order to prevent point pressure loads.
The ramming machine is driven by a conventional compressor. After being welded together, the single pipe lengths are pushed forward gradually. Due to the robust one-piece construction, TT Group’s largest ramming machine can achieve an impact energy of 40.000 Nm (at full capacity) which is transferred optimally over the complete pipe string to the pipe’s front cutting edge. The average ramming speed is 10 m/hour.
After conclusion of the ramming work, the pipe spoil is removed completely using water pressure in combination with compressed air or water pressure alone - up to ND 500 soil removal is only allowed with compressed air after having taken the appropriate safety measures. With larger pipe diameters the soil can be removed manually with the help of certain auxiliaries. (See operating instructions!)
According to the latest investigations by Prof. Dr. Stein, the wall thickness calculation following ATV-A 161 and GW 312 is basically possible; but examinations have proved that the external soil pressure, acting on dynamically driven steel pipes, due to soil weight and dynamic traffic loads, is distinctively lower than the corresponding comparative values for pipes installed with a trenchless method according to ATV-A 161. Following this, the wall thickness of the pipes could be reduced correspondingly.
The ramming machines have proved successful in practice - the Ruhrgas AG has given the rating "recommended". From a constructional point of view, the German Bahn AG prefers cased-in methods, e. g. the ramming technique, to uncased boring methods. The ramming technique is described in the German guideline ATV-A 125 and in the GW 304 Pipe Laying, as well as in other German standards.
Advantages of the technique:
- less disruption and damage of surfaces worth conserving (road surface, front gardens etc.) and minimal restoration – giving economic advantages
- low social costs because detours, half-sided barriers, traffic signal facilities etc. are avoided
- acknowlegded pipe installation technique
- short setting-up times - short installation times
- the dynamic impact when ramming can shatter obstacles and easily overcome difficult starting resistance after standstill periods. The aiming accuracy is improved because the dynamic impact shatters various soil formations within the diameter range and obstacles don’t have to be displaced or pushed aside in one piece
- no jacking abutment, no auger cutter required, which could get jammed
- the soil core remains in the pipe during ramming, i. e. no inrush of water when rivers or high water table areas are under-crossed
- minimal covering, i. e. no large-scale pits
- simple operating technique
- adaptation to all pipe diameters with special ram cones
- wide application range
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