First, it cannot use the type of pipes intended. “The condition of the soil on site does not correlate with the geotechnical study carried out before the construction site,” explains Mikaël Morrissette, spokesperson for the City of Trois-Rivières.
The results of the study conducted by an external firm were valid at the locations where the samples were taken, but elsewhere there were surprises.
“In the first districts, it is more difficult to know precisely the composition of the soil. The tests at the locations where the geotechnical study was carried out were consistent with the results. Except that in one place, there was sand. The other side of the street was clay, and a street further on it was sand.”
— Mikaël Morrissette, spokesperson for the City of Trois-Rivières
For this project, the City wanted to install infiltration pipes which collect water and then let it infiltrate naturally into the ground. It is this type of pipe that was put in place under rue Saint-François-Xavier.
This option therefore had to be rejected. “The heterogeneity of the soil composition means that the infiltration capacity is not the same. […] If the water does not flow at the same speed on all the pipes, it causes it to stay inside too long and is more likely to cause backups in the sumps,” explains Mr. Morrissette.
The City ultimately had no choice but to turn to conventional concrete pipes. “By the way, this modification means that we must adjust the diameter of other storm pipes in the project to ensure adequate control of the water flow.”
Contaminated soils
Another unforeseen event: contaminated soil. She encountered the same type of problem on the Boulevard du Saint-Maurice construction site last year. This is because provincial standards have been tightened in 2023. Certain soils that could be backfilled on site must now be placed on a site authorized by the Ministry of the Environment.
“Since the modification, in the middle of the construction site, additional costs may be necessary depending on the classification of the soil,” specifies Mr. Morrissette. It is difficult to accurately predict this classification before digging, especially over a large area, continues the spokesperson.
Work on Boulevard du Saint-Maurice last summer. (François Gervais/Archives Le Nouvelliste)
On Boulevard du Saint-Maurice, this change in standards for the disposal of contaminated soil resulted in additional costs of approximately $400,000. They could have been absorbed from the budget envelope of 10 million dollars.
This will not be the case for the Sainte-Cécile project, which will therefore see its budget increase from 3.8 to 4.6 million dollars.
Work in the Sainte-Cécile district began at the beginning of May and continues until September. They consist of replacing the existing underground water pipes as well as a complete reconstruction of the roadway and sidewalks of a portion of Sainte-Cécile, des Commissaires and Sainte-Angèle streets.
The pipes at this location date from the 1920s. They are therefore at the end of their life. This unitary network will make way for separate pipes, one for rainwater and the other for wastewater. This will ensure better water management in the sector.
More details on the work and the progress of the different phases are available on the City’s website.
