We come across bearing failures and settlements caused by uncontrolled fill quite often. As discussed in our blog post Different Types of Footing Problems-Part 1: Settlement, Fill materials on site that are not adequately compacted will consolidate under the load of the building and settle significantly. In this case study, we explore an actual project where the footing of the house was built over a sewer easement with uncontrolled fill.
The structure is a single-storey residential dwelling with a ‘brick veneer” construction supported on a waffle slab. The house is located in one of the western suburbs of Melbourne, and it is approximately 15 years old.
Soon after occupancy, the owner started noticing cracks predominantly at the southern side of the house. The owner informed the Builder, who inspected the house and advised the owner that the cracks were due to normal movement and initial settlement of the new house. However, these cracks have become increasingly severe over time, to the point where the owner did not feel safe using the southern part of the property.
The owner contacted MFS for a thorough forensic investigation and to identify the exact cause(s) of such severe damages to the newly built house. Our inspection of the property found significant gaps between brick walls and timber framed walls, large separations along articulation joints and total collapse of the stormwater pipes and concrete pavement at the southern side of the house.
It’s pretty clear that something went very wrong during construction of this house, given the extent of damage. We contacted Dial Before You Dig and obtained all plans for council assets in and around this property within an hour. Reviewing asset information from City West Water, we found a 3m x 5.7m easement on the southern side of the property, less than 1m from the main building– but this wasn’t reflected at all in architectural drawings of the house. Consequently, no consideration whatsoever was given by Structural Engineer to design deep footings (such as screw piles) in the vicinity of easement. Footings were built directly on uncontrolled, uncompacted fill material instead. Load from footings caused uncompacted fill materials in easement to consolidate, resulting in settling and structural failure. Immediate action was taken to design and install underpins beneath the foundation along the southern side of the house because of the damage’s severity and safety concerns. MFS Engineering designed the underpins to extend beyond the easement’s depth and angle of repose of the sewer asset.
