By Martin van den Hemel, Richmond Review, 10 Aug. 2011
Even a moderately strong earthquake could trigger liquefaction beneath Richmond Hospital's aging north tower, and cause its foundation to sink and fail and lead to "significant building damage and possible partial structural collapse."
That's according to a structural engineering report obtained through B.C. freedom of information laws by journalist Stanley Tromp and provided to The Richmond Review.
Authored by Bush, Bohlman and Partners senior partner Clint Low, the March 3 report focused on the north tower, which was built in 1965 under the building codes of the era, "when seismic design was not a governing consideration."
Richmond Hospital is somewhat unique, the report states, in that it faces two major seismic considerations: its ability to resist lateral shaking during a quake, and the underlying soil's ability to support the foundation during a high-energy ground-shaking event.
While the current practice for large buildings involves densifying the ground to resist and prevent liquefaction, that wasn't done at the time the north tower was constructed nearly five decades ago.
Vancouver Coastal Health Authority spokesperson Anna Marie D'Angelo said long-range plans call for the north tower to be replaced, rather than upgraded.
"It will be a big project and takes time to develop," she said.
D'Angelo said the health authority does take the contents of the report seriously. She noted that the hospital's Westminster tower was built in 1997 and complies with modern earthquake standards.
Upgrading the north tower to meet current building code requirements would cost upwards of $12 million, and be a "significant and disruptive construction project," the report said.
In conclusion, Low wrote: "The soft soils underlying the hospital are prone to liquefaction under moderate and strong earthquake ground shaking. Liquefaction will lead to foundation failure and large horizontal ground displacements causing significant building damage and possible partial structure collapse. Liquefaction substantially increases the building seismic risk."
Added Low: "We rate the building as high risk."
The current building code requires a building to be able to withstand four times as much of the seismic forces as in the 1960s, and the north tower's superstructure and foundations are adequate for about 20 per cent of the 2010 code's seismic demand.
Richmond Hospital's north tower isn't the only tall Richmond building constructed during the late 1960s and early 1970s.
Simon Fraser University research professor John Clague said the phenomenon of liquefaction wasn't well known during that period. Asked earlier this year about the three tall towers across from Richmond Centre, Clague wrote that he didn't know whether their foundations were constructed taking into consideration the possibility of liquefaction.
"Ground shaking is much less of an issue than liquefaction...It is very important that the foundations of these building be seated below the liquefiable sand layer that underlies Richmond. If not, there is a problem."