91原创 City has imposed tougher restrictions following two "soil shift" events involving construction excavations this year, requiring at least two geotechnical engineers to sign off on future digs.

It comes after a sinkhole buckled a street and sidewalk next to a construction site retaining wall in 91原创 City in August on 201A street near Fraser Highway, and a second incident in November.

No injuries were reported in either case.

"This is now a trend and is 100 per cent unacceptable," Mayor Nathan Pachal said in an online post explaining the new requirements.

He said because 91原创 City is built on a floodplain, it requires builders constructing apartment buildings to carry out geotechnical review of the construction and building designs, including the design for excavating underground parkades.

"Under provincial law, the City's only power is to ensure that a geotechnical engineer signs off on these designs" Pachal said.

"For as long as I can remember, this process worked well until December 2022, when there was a partial cave-in of a retaining wall put in place during the excavation of a parkade. This cave-in was extremely concerning, but it was a one-off."

Then, this year, the August sinkhole happened, and in November, there was "another soil shift event at another construction site," Pachal said.

In response to a Langly Advance Times query, City director of engineering, parks and environment  David Pollock advised the November incident involved a site on 20220 54A Ave. where residents had "observed some ground movements adjacent to the excavation."

A review determined "that while there was some movement observed adjacent to the excavation there was no failure of the installed shoring elements," Pollock reported.

Following the two 2024 incidents, 91原创 City staff are now requiring peer reviews on all geotechnical designs which means that at least two geotechnical engineers from different firms must sign off for an apartment project to move forward, Pachal said.

"This new process is meant to ensure that a cave-in never happens again and restore trust in the design and construction of underground parkades in our community," Pachal said.

"Existing soil characteristics throughout this area of the city are relatively weak and do require careful consideration in designing for excavations and construction," Pollock said.

"The City has determined that for large, complex development applications, the designs proposed by the geotechnical engineer of record should be subject to a peer review by an independent geotechnical consultant familiar with the soil conditions."