Start with the question to be answered
Ask the engineer to state why investigation is needed. Examples of useful questions are whether an existing footing can support more load, whether the proposed foundation reaches suitable ground, and whether a suspected defect needs further examination. The resulting brief should identify locations, records and tests, not simply request “some holes”.
A structural inspection can lead to targeted opening-up, including exposing foundations or concealed parts of the building. The initial visual survey and the subsequent investigation are different stages, so confirm which is included in the appointment. [2]
Trial pit, borehole or another test?
Trial pits allow direct observation and sampling of shallow ground and can expose an existing footing. Boreholes can investigate deeper conditions. The specialist should select a method suited to the ground and the information required; a convenient excavator is not, by itself, a reason to choose one method. [1]
Request a written schedule of the investigation and its intended outputs. Ask whether the proposal includes only factual logs and laboratory results or also an engineering interpretation that can be used for foundation design.
What should be recorded?
For your project file, ask for a location plan, photographs with scale, the observations and test results, and an explanation of any limitations. Label information from a particular trial location accurately rather than treating it as a confirmed condition everywhere.
BGS's London and Thames Valley dataset describes regional shrink–swell susceptibility. It can inform a desk study, but it does not establish the dimensions of a hidden footing or replace physical investigation where that is needed. [3]
Excavation needs its own safety planning
HSE's underground-services guidance sets out a safe system based on planning, locating and identifying services, and safe excavation. Service drawings alone should not become permission to dig without the appropriate checks. [4]
Excavating beside a wall can affect its foundation. HSE warns about undermining adjacent structures and requires excavation hazards to be assessed and controlled. Do not enter or enlarge a trial pit on the assumption that its investigation purpose makes it safe. [5]
If investigation requires disturbing suspect building materials, assess the asbestos information before intrusive work. HSE distinguishes a refurbishment survey's intrusive purpose from an ordinary management survey. [6]
Agree reinstatement and the decision afterwards
Ask who will make the investigation area safe, reinstate disturbed finishes and secure any pit while awaiting inspection. HSE's public-protection guidance includes barriers or covers for openings and excavations and keeping unauthorised people away. [7]
Finally, ask the engineer to record how the findings change the design or what further evidence is required. A useful investigation ends with an engineering decision or a clearly defined next step, not an unexplained folder of photographs.