Common Questions
Answers to the most common engineering questions we receive from clients across Sydney and NSW. Can't find what you're looking for? Get in touch with our team directly.
I live in a brick home that was built on a clayey site in the early 1980s. Recently I started to notice cracks developing in the brickwork. Is this dangerous? Will these cracks get bigger, and how do I fix the problem?
AnswerSome minor cracking in masonry walls is inevitable. Cracks up to 1mm would be expected in most houses. Large cracks up to 5mm may occur in some houses with properly designed and constructed footings. Cracks larger than 5mm are regarded as significant damage.
One of the main reasons for cracking in brickwork is water reacting with the existing clay soil. Clay has the ability to absorb moisture and swell very quickly when soaked. As the soil swells, the brickwork supported on it will camber and experience upward movement. In dry seasons, as clay loses its moisture content it shrinks back, causing cracks to open along the weakest parts of the building — mainly around windows and door openings.
It is always important to minimise changes in the clay moisture by:
Most buildings built on clayey sites prior to 1990 have footings that fall well below the recommendations in AS 2870 — largely due to deficiencies in the codes and standards of that era.
SolutionUnderpinning the foundation provides a proven solution for under-designed footings. The underpinning process involves excavating beneath the existing footing in staged sections and casting new concrete to extend the footing depth to the required level.
ANACivil can assess your existing footings, determine the required depth in accordance with current Australian Standards, and design an appropriate underpinning scheme. We manage the full engineering process from assessment through to certification.
A footing for a free-standing retaining wall 2.0m high can be as wide as 1.4m — which is impractical on many sites with limited space. What can be done to reduce the footing width?
SolutionIf the top of the retaining wall is braced or pinned against a structure, the footing width of the retaining wall can be reduced to as small as 450mm wide. Extra reinforcement must be provided in the wall to cater for the additional stresses that result from the pinned connection at the top.
ANACivil can design retaining walls of all types and sizes — including cantilever, propped, anchored and gravity walls — and provide the engineering documentation required for council approval.
What should we do if we are excavating next to an existing building, with a retaining wall to be built at a later stage? How do we protect the existing structure and the adjacent soil during the excavation period?
SolutionProvide SL82 Mesh positioned 75mm off the ground. The mesh is to be held in position using N12 galvanised hooked bars driven 0.5m into the embankment at 1.2m centres each way, then shotcrete the soil with a layer of 150mm thick concrete.
This temporary shoring solution provides immediate protection to the excavated face while the permanent retaining structure is being constructed. ANACivil can design and certify temporary shoring systems for all types of excavation and site conditions.
