Brimmell Engineering: Geotechnical Considerations - 17A Jedburgh Rd

Re: 7 Lot Subdivision accessed from Bishan Place, View Royal Geotechnical Considerations

This letter discusses rock removal at the northwest corner of the development, where the proposed strata road enters from Bishan Place. Photos are attached.

Although the property has a Jedburgh Rd. address, the strata road will come in on the north side via Bishan Place. The first part of this alignment is challenging due to outcropping bedrock. This feature rises 3+/- m above pavement level and has an east-west length between 18 m and 8 m on the north and south sides of the alignment respectively. The rock is hard, Wark gneiss typical of the Victoria area. There are existing homes nearby to the northwest and southwest.

The proposed rock removal is doable with appropriate care. Selecting the right blasting contractor helps avoid problems. Western Grater and HHS are the recommended choices. Pre-blast surveys will be needed on potentially affected properties, particularly the two close ones. Blasting tends to be problematic. Potential difficulties include vibration-related damage such as cracking, vibration-related settlement, damage to windows due to percussion, danger from flying rocks, advection of carbon dioxide or other noxious gases. Advection is locally very rare although not unknown.

Of these potential problems all but advection can be mitigated through combination of:

• limiting blast energy
• securely covering blasts with mats
• directing blast energy (and any potential flying debris) away from structures which in this case would be to the north or east
• providing seismographs at both the nearby houses and modifying procedures in the event of unacceptable readings

It is the responsibility of the blasting company to do the pre-blast surveying, come up with a procedure appropriate for conditions, and provide adequate insurance coverage.

I trust that this information meets your present requirements. Please do not hesitate to contact the writer if there are questions.

Yours truly,

Richard Brimmell, P.Eng. for Brimmell Engineering Ltd.

cc: Westbrook Consulting Town of View Royal Engineering Dept.