Balme de Rencurel dam – Determination of the dynamic mechanical properties l France

Identification of possible voids in the structure

Borehole geophysics was a means of imaging and quantifying grouting works efficiency.

The century-old gravity dam of “Balme de Rencurel” is 22 m high and located on the Bourne river.

During the process of a refurbishment program, grouting works were carried out inside the core of the dam to strengthen its resistance and enhance its impermeability.

The aim of the geophysical survey was to assess the efficiency of the grouting works.

The improvement of the dynamic mechanical properties of the cyclopean concrete forming the dam was assessed using Cross Hole seismic tests and seismic tomography (3D imaging).

The survey was divided into four distinct stages:

– Initial state prior to grouting works (Stage 1)

– After dam waterproofing works (Stage 2)

– After strengthening grouting works (Stage 3)

– 2 month inspection after completion of stage 3 (Stage 4)

Seismic imaging allowed us to locate areas presenting lower seismic velocities even after grouting works (Stage 4), and to compare these values to the ones obtained within an untreated section.

Final synthesis highlighted the most decompressed areas, where the probability of finding voids (even after grouting works) was the highest.

A comparison with coring results confirmed the correlation between low velocity materials and poor concrete quality.

Borehole geophysics was a means of imaging and quantifying the efficiency of grouting works.