New Zealand is experiencing a record-breaking rain season, having received approximately 539 millimeters of rain in January alone. With this volume of precipitation, slips and landslides are becoming a growing issue on the island at an accelerated rate. ENGEO’s Paul Fletcher, CMEngNZ, went live on RNZ earlier this month to discuss the geotechnical engineer’s perspective on the recent events as well as comment on the remedial processes. He offered information for those who have been affected by the recent storm events and who may be seeking help with their property damage.
Paul explained that the main factors that determine the severity of a slip come down to the steepness of slopes, the volume of water saturating the ground, and the site soil type. The Waitakere Ranges and the volcanic cones in Auckland have both experienced many slips, but the most dramatic ones occur along clifftop properties. In these regions, you will find clay soils, which are usually made up of silica, alumina, or magnesia, or all three, which when saturated with water take a long time to drain. Areas like Mission Bay have clay soil, placing the region at a higher risk of ground movement.
For homeowners who are unsure about the risk of landslides on their property, Paul explains that there are a couple of things you can do before calling Council or reaching out to geotechnical engineers. First, throw on your coat and take a walk around your property; follow where the water is flowing around the grounds and take notice if it is saturating a steep slope. In the best-case scenario, find a way to divert the water directing it away from the slope until more permanent measures can be put into place. Additionally, homeowners can inspect their property for cracks or bulging in the ground, “You’ll see cracks that form parallel to the slope and gaps opening between the curb and the asphalt. In your house you might see cracked masonry or cracks through your brickwork, sticking doors and windows, displaced retaining walls, all of those are signs that the ground is moving,” Paul states.
Depending on the severity of the slip, property owners may approach remedial repairs in a couple of different ways. For those who have worries about a potential slip, Paul suggests doing the following: contact a geotechnical professional and request them to come to the site to perform a rapid assessment. If the property already has signs of land movement, then Council will be out doing a rapid assessment, provided one has not already been performed. They will then determine if the property is safe to occupy or visit. Damage done by slips will have to be further assessed by the EQC (Earthquake Commission) which can take up to a few months to receive feedback considering the severity of the recent weather events.
Listen to the full interview now!
For more information please reach out to Paul and the team by email at firstname.lastname@example.org.