Is the 45-degree "affected zone" applicable to Malta??
The answer is NO.
When there is a vertical excavation, Malta’s Avoidance of Damage to Third-Party Property Regulations (SL 623.06) requires the application of the 45-Degree Affected Zone. (see figure from SL 623.06), alternatively known as the zone of influence or active failure wedge
However, this rule of thumb is largely inapplicable to the Malta’s geological context. Applying a 45-degree soil failure template to rigid rock masses is ineffective and dangerous.
Why the 45° Zone Fails in Rock
In soil, the failure zone is predictable because the material is relatively isotropic (uniform in all directions). Rock is anisotropic—it has predetermined lines of weakness. The actual "affected zone" behind a vertical rock cut can be much smaller, or catastrophically larger, than 45°.
1. The Zone Can Be Much Wider (Shallower Angles)
If the rock has continuous bedding planes, joints, or fault lines that dip toward your excavation at a shallow angle—say 30°—the failure will not happen at 45°.
The vertical cut removes the toe (the bottom support) of that 30° plane. The entire block of rock above that crack will slide into the excavation. In this case, your affected zone extends much farther back behind the excavation face than a standard 45° rule would predict.
2. Intersecting Joints Create Unpredictable Wedges
Rock rarely features just one crack. If two sets of joints intersect behind a vertical wall, they can isolate a massive, three-dimensional wedge of rock. This wedge can release suddenly, slipping out along the line of intersection. The geometry of this failure zone is entirely dependent on the compass direction and tilt of those specific cracks, completely ignoring the 45° rule.
How the Affected Zone is Actually Calculated in Rock
To safely design a vertical cut or determine how far back structures must be kept from the edge, geologists do not use a 45° rule of thumb. They use Kinematic Analysis and Rock Mass Classification Systems (like RMR or the Q-system).
If a structure or utility must be placed behind a vertical rock cut, geologists need to map the exact orientations of the rock fractures to define the true kinematic hazard zone.
Regrettably, SL 623.06 completely overlooks the essential role of professional geologists in the excavation assessment process in Malta. By failing to recognise geological expertise, public safety of Maltese residents is directly exposed to avoidable structural risks.
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Can a geologist be a Court expert?
The answer is: Yes they can.
Litigations in Court may involve issues that relate to geology, for example,
· Geological materials used in constructions,
· Rock excavation that affects third party property,
· Natural and man-made hazards,
· Unacceptable level of ground settlement
· The quality of building materials (aggregate, dimension stone)
A recent case in the Maltese Court of Appeal (11/2024 LM) presided by the Hon. Judge Lawrence Mintoff decided on the 5th February 2025 to uphold a decision of the Consumer Claims Tribunal which relied on the expert advice of a geologist.
The appellee stated ‘…the matter in question is one that falls purely within the competence of a geologist and not of an architect exercising his profession as an architect’.
The Court stated that it accepted the Tribunal’s conclusions based on the expert advice of the geologist ‘because his scientific explanation is more detailed and logical than any other explanation.’
How safe is a vertical cut in rock?
Often, the construction industry requires deep excavation for basements. But how safe is a vertical cut?
Several factors need to be considered. Firstly, the nature of the rock, its level of cementation and internal friction which depends on size, sorting, and shape of grains. More importantly, are the discontinuities in the rock. Most common discontinuities consist of joints. Joints are features produced by tension and can be horizontal or quasi vertical, depending on the nature and history of the rock. All these aspects need to be considered by the geologist.
Third party properties are directly affected by nearby vertical rock cuts. The question arises, how safe is existing third-party property affected by the excavation?
What does the Law say about this matter?
Legal framework
Subsidiary Legislation 623.06 requires a ground investigation with borehole drilling but does not give details of what should be assessed and who is the competent person to make an assessment on trial pits and rock cores.
Around the world, geologists are deemed the competent persons to make such assessments, but Maltese law is silent about this matter, creating a vulnerability which can have dangerous consequences. Moreover, the law refers to ‘expected strength of the ground materials’ and ‘the presence or otherwise of fissures’. These very vague comments in the law raise a number of questions:
1. What is the difference between the ‘expected’ and actual strength of ground materials?
2. Are fissures the only discontinuities in Maltese rock? Certainly not!
The law ignores the presence of joints (which are very common), faults and caverns.
IS IT SAFE TO BUILD ON A FAULT?
What is a fault? A fault is a discontinuity in the rock where one side has moved relative to the other.
Faults are considered by many to be dangerous, but what about Malta? Malta has many geological faults that criss-cross the islands. Most are normal fault where one block has gone down relative to the other block. However, many are inactive.
Most people, including engineers think that a discontinuity in rock is a fault. This is incorrect, since many discontinuities do not have movement associated with them. Faults are identified by special features associated with them. This is where the geologist is needed to identify whether the discontinuity in the rock is a fault or not.
Although many faults in Malta are inactive, some have been reactivated by recent tectonic movement of Africa with respect to Europe. Fault reactivation usually results in a normal fault becoming a strike-slip fault where one side slides past the other side. These faults can pose problems for buildings over them.
Legal framework
There are no laws requiring the identification of faults in Malta prior to a construction. The only reference to discontinuities in rock mentioned in the law is Legal Notice 623.06 which refers to 'fissures', which are not faults. This serious omission in Malta's laws can be fatal in case of weak material associated with faults and reactivated faults.