HDD RIVER CROSSING WITH SHARP BENDING RADIUS IN VERY DIFFICULT SOIL CONDITIONS

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Client: EDIL IDRAULICA Sas – Italy

Year: 2011

What I did: I made the project management and the supervision of the installation, by HDD, of three HDPE DN 560 (22 in) pressure sewer pipes under the Foglia river, Pesaro, Italy. Three directional pilot bore, with an interaxis of just 1,5 m, along a drill path with a very sharp bending radius (70 m), were successfully drilled under the river bed, facing challenging soil conditions, with big boulders and blocks of stone in a matrix of silt and clay. Although the three pilot bores were perfectly completed, on the first alignment, after completed the first final reaming at 700 mm, the first pull-back failed due to the collapse of underground unstable big blocks of rock. Despite the prohibitive soil conditions we successfully completed the pullback of the two remaining product pipes, achieving a remarkable result in a very difficult HDD work.

HDD RIVER CROSSING WITH SHARP BENDING RADIUS IN VERY DIFFICULT SOIL CONDITIONS
Plan view of the installations.
Longitudinal section of the river crossing.
The pipes to be installed - DN560 PE100 pipe. Nominal diameter of the reamed borehole: 700 mm.
A complete set of preliminary survey were done before the detailed project - in the picture a 3D geoelectrical tomography.
Rock boulders in a matrix of silt and clay, represent a challenging soil condition for HDD.
The official panel at the job-site.
Creating a laser level for depth measuring while drilling.
Continuous mud control and prime drilling fluids were crucial to face so difficult soil conditions.
The HDD rig used to complete the job (Vermeer D50 - 50.000 lbs - 23t pullback force)
Starting a pilot bore.
Starting a pilot bore.
Guiding the drilling head.
Starting the last pilot bore.
The three drill strings laying underground.
Pre-reaming stage - reamer diameter 500 mm.
Final reaming stage - reamer diameter 700 mm.
The pullback stages were carried out during the night shifts to not interfere with traffic.
First product pipe during pullback
Pullback of the second product pipe during a night shift
Pullback of the second product pipe during a night shift
The end of the second pullback.
Starting the third reaming.
The end of the third pullback.
The unexpected presence of big blocks of rocks, along the drilling path, made the work extremely difficult causing the block of the first pullback - in the picture the attempt to clear the drill path of the rocky blocks.
The unexpected presence of big blocks of rocks, along the drilling path, made the work extremely difficult causing the block of the first pullback - in the picture the attempt to clear the drill path of the rocky blocks.
Although more than 20 blocks of rock (dimension ranging in the interval 0,6 - 1,2 m) were removed, the first pipe remained definitively stuck underground.
Although more than 20 blocks of rock (dimension ranging in the interval 0,6 - 1,2 m) were removed, the pipe remained definitively stuck underground.

 

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