For the dynamic installation of steel pipes using 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.
Schematic survey of the pipe ramming method
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 strings are pushed forward gradually. Due to the robust one-piece construction, the 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.
Jobsite: Double Railway crossing near Newcastle, UK
After the ramming process is completed, the pipe spoil inside the pipe 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 rate them "recommendable". 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.
The ramming technique is suitable for installing longitudinally welded pipes • spirally welded pipes, seamless pipes, pipes with insulation protection. It enables a wide range of applications:
- Installation of steel pipes underneath buildings, roads, waterways, railway tracks, parks, etc.
- Construction of pipe roofs for tunnel structures
- Vertical applications, e.g. for foundations, sheet piling or well drilling,
- Support of HDD bores (HDD Assist).
- Renewal of pipelines (dynamic pipe bursting).
All ramming models have thoroughly been examined by the TBG (German Civil Engineering Co-operative).
Advantages of the method:
- less disruption and damage to surfaces worth conserving and minimal restoration,
- low social costs because detours, half-sided barriers etc. are avoided,
- no jacking abutments or auger cutters required which could get jammed,
- the soil core remains in the pipe during ramming, i. e. no ingress, of water when rivers or high water table areas are encountered,
- minimal depth of cover required, i.e. shallower excavations,
- adaptable for all pipe diameters with special ram cones,
- widely acknowledged and accepted simple technique,
- short set-up and installation times,
- wide application range.
Animation courtesy of Allen Watson Ltd.