Question 1 of 4

Question 1 (25 marks)

Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.

(a) Site investigation process — organization and stages

A site investigation is not a single field task; it is a managed sequence that runs from the client's initial need through to construction verification, with the Engineer of Record (or Geotechnical Engineer of Record on larger projects) accountable throughout. The process below follows CFEM's staged approach and the general practice model in Clayton, Matthews & Simons.

Reading the chart left to right, top row then bottom row: the client defines the project brief and constraints (budget, schedule, land use); the desk study assembles existing geological maps, air photographs, borehole logs from adjacent sites, and regional hazard mapping; a site reconnaissance/walkover confirms access, ground exposure, and surface hazards (seeps, slope instability, fill); the Engineer of Record then sets the scope of the field program (borehole/test-pit count, depths, spacing, in-situ testing, and instrumentation) appropriate to the ground model and structure type. Field exploration (drilling, test pitting, geophysics, piezometer/inclinometer installation) is typically carried out by a specialist drilling subcontractor under the geotechnical engineer's direction; samples go to an accredited soils laboratory for index and strength/consolidation testing; the geotechnical engineer interprets the combined field and lab data into a ground model and design parameters, documented in a geotechnical data report. An independent/peer review checks the interpretation and recommendations before they are relied on for design, and the loop closes with construction-phase verification (inspection of open excavations, as-built confirmation that the encountered ground matches the design assumptions). The client and Engineer of Record sit above every stage as the decision-makers who authorize scope changes and accept residual risk; checks and balances are built in through the peer review, through the drilling/lab quality-assurance program, and through EGBC's professional practice requirements for documented judgment and sign-off at each stage.

(b) Specialist disciplines contributing to a site investigation

A geotechnical engineer coordinates, but rarely single-handedly resolves, every technical question raised during a site investigation. At least the following eight engineering-level specialists commonly contribute:

1. Engineering geologist — interprets bedrock type, structure (joints, faults, bedding), weathering profile, and geohazards (landslide, karst, seismic surface rupture) from mapping and core logging, and builds the geological model that underlies the geotechnical interpretation.
2. Hydrogeologist — characterizes groundwater levels, flow direction, and aquifer parameters; assesses dewatering requirements, contamination transport, and the effect of groundwater on slope and excavation stability.
3. Structural engineer — supplies foundation loads, tolerable settlement/differential-settlement criteria, and structural system constraints that govern the foundation type recommended from the investigation.
4. Civil/municipal engineer — defines site grading, servicing (utility trenches), and pavement/roadway subgrade requirements that the investigation must address.
5. Geophysicist — runs seismic refraction/refraction-microtremor, resistivity, or ground-penetrating radar surveys to extend point borehole data spatially (bedrock depth, buried features, water table) at lower cost than closely spaced drilling.
6. Environmental engineer — screens for contaminated soil/groundwater (former land use, fill provenance) so contamination does not surface unexpectedly during construction, and manages any Phase I/II Environmental Site Assessment.
7. Seismic/earthquake engineer — assesses liquefaction potential, site seismic classification (site period, amplification), and ground-motion parameters for structures in seismically active regions such as coastal BC.
8. Surveyor (geomatics engineer) — establishes accurate horizontal and vertical control for borehole/test-pit locations and topography, without which subsurface data cannot be tied to design drawings or to each other.

Depending on project scale, a mining engineer (open-pit/underground works), a forensic engineer (failure investigations), or a materials engineer (aggregate/borrow source evaluation) may also be engaged; the common thread is that the geotechnical engineer must know enough of each discipline's scope to ask the right question and to integrate the answer into one consistent ground model.

(c) Typical investigation budget and the cost of getting it wrong

Industry guidance and CFEM commentary place the typical site investigation cost at roughly 0.5–1.5% of total project construction cost for conventional building and infrastructure work (rising toward 2–3% for high-risk or poorly known ground such as karst, mine workings, or soft marine sediments, and falling below 0.5% only on very large, low-risk projects where economies of scale apply). This is a small fraction of total cost, but the leverage is large: an inadequate investigation routinely leads to differing-site-condition claims, redesign of foundations mid-construction, schedule delay while additional exploration is mobilized, and in the worst case, foundation distress, slope failure, or structural damage after construction. The well-known industry observation is that the cost of remediating a missed ground condition after construction starts is typically an order of magnitude (or more) greater than the cost of finding it during the investigation phase — so under-investing in exploration to save a small percentage of budget is a false economy that shifts cost (and risk) downstream, usually with added contingency, legal, and reputational cost on top.

(d) Thoroughness, budget, and risk — how they interact

Thoroughness, budget, and project risk form a closed triangle rather than three independent variables. Increasing the thoroughness of the investigation (more boreholes, deeper exploration, more laboratory testing, additional geophysics) increases the direct investigation cost, but it reduces the uncertainty in the ground model, and uncertainty is what generates risk: unexpected ground conditions, under-designed foundations, contractor claims, and construction delay. Conversely, cutting the investigation budget increases residual uncertainty and therefore transfers risk onto the construction and operation phases, where the same uncertainty is far more expensive to resolve (open excavations standing idle while additional exploration is mobilized, redesign under time pressure, contractor claims for differing site conditions). The relationship is not linear: early exploration effort resolves the largest uncertainties cheaply, and each additional borehole beyond a reasonably characterized site yields diminishing reduction in risk for the same incremental cost — the practical implication is that investigation scope should be set to the point where the marginal cost of more exploration is no longer justified by the marginal risk reduction it buys, a judgment that itself depends on project consequence-of-failure (a dam or hospital foundation justifies far more thorough exploration than a low-rise warehouse on the same ground). A well-scoped, appropriately thorough investigation is therefore risk-management expenditure, not an overhead cost to be minimized.