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) What is a site investigation?

A site investigation is the systematic, staged process of gathering, interpreting and reporting information on the ground and groundwater conditions at and around a proposed (or existing) engineering site, for the specific purpose of informing the planning, design, construction and long-term performance of the works. It combines a desk-based review of existing information with a field and laboratory program — drilling, sampling, in-situ testing, and geotechnical/geological/environmental testing — to build a defensible ground model: the stratigraphy, groundwater regime, engineering properties, and any geohazards present. The investigation is not an end in itself; its output (the geotechnical/geological report) is the technical basis on which foundation type, earthworks, excavation support, dewatering, and construction methods are selected, and against which the contractor's risk and cost are allocated. It is distinct from, and precedes, detailed design: a site investigation characterizes the ground as it actually is, rather than assuming a ground condition and designing to it.

(b) Why is a site investigation important? (at least 5 reasons)

1. Foundation and structural safety — every structure ultimately bears on or through the ground; without a verified ground model, foundation design defaults to unsubstantiated assumptions that can lead to bearing failure, excessive settlement, or slope/embankment instability.
2. Cost control — unidentified ground problems (soft/organic deposits, boulders, artesian groundwater) discovered only during construction are far more expensive to resolve than the same condition identified and designed for in advance; the investigation cost is small relative to the downstream cost of a surprise.
3. Schedule and risk allocation — a documented ground model, ideally as a Geotechnical Baseline Report, allows the ground-related risk to be explicitly priced and allocated between owner and contractor, reducing the likelihood of differing-site-condition claims and construction delay.
4. Regulatory and code compliance — building codes, provincial legislation and professional practice guidelines (e.g. EGBC's) require the engineer of record to have a documented, adequate basis for the geotechnical design, which only a proper investigation provides; a design without one is not a defensible professional record.
5. Environmental and life-safety hazard identification — the investigation is often the only opportunity to detect subsurface contamination, liquefiable soil, active faulting, or slope instability before people, structures, or the environment are exposed to that hazard.
6. Constructability — groundwater level, rock rippability, and obstruction data drive the contractor's means and methods (dewatering, shoring, excavation equipment selection), so an inadequate investigation increases construction risk even where the final design itself is adequate.

(c) Overall design process for a site investigation (steps)

The process is staged, each step narrowing uncertainty and informing the scope of the next, with a feedback loop back to the ground model if construction reveals conditions the investigation did not anticipate:

In more detail: (1) Desk study — compile geological maps, aerial photography, prior investigations, well records and utility data to build a preliminary ground model; (2) Site reconnaissance — a walkover to verify the desk study against actual surface conditions (outcrops, seepage, existing distress, access constraints); (3) Preliminary hazard identification — flag credible geohazards (soft ground, slope instability, contamination, seismic considerations) that should drive the field scope; (4) Scope and plan the field program — decide exploration method, spacing, depth, and in-situ/laboratory testing based on the ground model and project risk; (5) Field exploration — drilling, sampling and in-situ testing, executed and logged to industry-standard practice; (6) Laboratory testing — index and strength/consolidation testing of recovered samples; (7) Interpretation and ground model — integrate field and lab data into stratigraphic cross-sections, design parameters, and a defensible ground model; (8) Geotechnical report — document findings, interpretation, and design recommendations, subject to internal peer review before issue; the process closes with construction verification (as-built confirmation against the design ground model), feeding back into the ground model, and into future investigations, if actual conditions differ.

(d) Contracting between client and contractor; industry-standard contract types

Contracting for the execution of a site investigation is normally a distinct, earlier procurement from the construction contract itself: the client (owner) engages a geotechnical/geoscience consultant (or, on a design-build project, the design-builder engages one) to scope and manage the investigation, and the drilling/field contractor is separately retained (usually competitively tendered) to execute the drilling, sampling and in-situ testing under the consultant's specification and field supervision. The consultant defines the scope (borehole locations, depths, sampling frequency, testing program) in a tender package; contractors bid against a schedule of rates (cost per metre drilled, per sample, per test) rather than a lump sum, because the actual ground conditions — and therefore the effort required — are not fully known until drilling begins. The most common industry-standard arrangements are: unit-price (schedule-of-rates) contracts, the default for exploratory drilling, where the contractor is paid per unit of measured work (metres drilled by method, number of samples, number of in-situ tests) and the final total varies with actual ground conditions encountered; time-and-materials (cost-reimbursable) contracts, used where the scope is genuinely open-ended (e.g. exploratory work in poorly known ground, or emergency response) and the contractor is paid for verified labour, equipment and materials plus a fee; and lump-sum contracts, used only where the scope is precisely fixed and well-understood (e.g. a specified number of boreholes to a fixed depth in known, easily-drilled ground), since a lump sum poorly accommodates the ground-condition uncertainty inherent to exploration work. For the subsequent construction contract (once design is complete), the same range of arrangements recurs at a larger scale — unit-price, lump-sum (stipulated-sum), cost-plus, and design-build/EPC — with a Geotechnical Baseline Report increasingly used on unit-price and design-build construction contracts specifically to state the ground conditions the contractor is entitled to assume for bidding, allocating (rather than leaving ambiguous) the risk of conditions differing from that baseline.

(e) Resources acquired during the desk study; where and how to obtain them

The desk study assembles existing information before any field work is committed, so that the field program can be targeted rather than exploratory-by-guesswork. Typical resources, and their sources: