Many years after construction, the old dam in Holmfirth, United Kingdom, must be renewed. The old structure was getting weak, and new regulations requested a redesign and the reinforcement of the dam. Approximately 23 new layers, 30 cm thick, of new material, had to be placed and compacted, homogeneous in shortest possible time to max. density. The mix of gravel and loam was placed with a track type dumper and spread with an excavator. To ensure that water does not penetrate the construction, a trench, made of gravel, ensures the proper accumulation of the surface water into a newly designed drainage system.

For the main compaction a BW 213 DH was used.

 
Technical Data:

Operating Weight:  12 700 kg
Axle load Drum:  7400 kg
Static Linear Load: 34,7 kg/cm
Drum With:  2130 mm
Frequency:  30 / 36 Hz
Amplitude:  2 / 1 mm
Centrifugal Force: 300 / 225 kN

Compaction execution

To achieve the max. compaction and efficiency, the high amplitude with high compaction force were in use. The layers must be compacted with at least two passes in the specified adjustments for the roller. The full width of the dam is compacted in two tracks. The compaction finished at 1m from the dam shoulder to avoid dangerous situations with the roller. Barriers, positioned in the forefront of compaction prevent the operator being close to the soft shoulder.
 

After compaction is finished, control measurements with a nuclear gauge were taken. One control point on each track, positions are carried out by random sampling.
 
 
Imagine, two samples on an area of about 250m²?

To improve the informational value of the measurements with the gauge, the contractor decided using area coverage measurements with MCA 3000. During the compaction process, all movements of the roller and the compaction values have been shown on display and stored on the unit with a  time stamp and position for further evaluations. 
 
The values on the left side from the operator’s screen, where the relative values are displayed, the operator sees that the target value (13) is achieved (green) and mostly over the target (red). On the right side of the screen, the compaction progress is shown. Here the operator can see that the compaction progress has stopped (green and magenta). In this case, no further compaction with the current roller is possible.
For further analysis with Compaction Project Manager, the data have been transferred on to a PC

The screenshot below from the PC-analysis shows a very homogeneous compaction result.

 
O  Checkpoints defined using the mapped results in the post-processing software on the PC.

The cross-check between the IC values collected with MCA3000 and the results measured with the nuclear gauge allow the setup of the target IC-values for this site. Following this procedure, a significant increase in data reliability is secured. The same amount of manual checks provides a much higher validity of the measurements now.

Findings:

Higher data density for compaction values, measurements were taken where it is most significant, higher security in achieving the required density and reduction of compaction efforts by stopping compaction when target values are reached. Time for compaction reduced, increased productivity and reduced time for completion.