Question 1 of 5

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.

Planning and designing a site investigation for a high-rise building within a Canadian city means running the staged process below — from the client's initial brief through to construction-phase verification — so that the report scope, resourcing, and budget are all set deliberately rather than improvised once drilling has already started.

(a) Major topics / report headings

The major topics that a site investigation for an in-city high-rise must cover, and which become the major headings of the final investigation report, are: Introduction (project description, building footprint/height and estimated loads, purpose and scope of the investigation, terms of reference); Site Description (location, topography, current land use and history from the desk study — particularly important in a built-up city block where prior demolished structures, old foundations, or buried utilities may be encountered); Investigation Procedure (field methods, borehole/test-pit locations and depths tied to a site plan, sampling and in-situ testing methods used, laboratory testing program); Subsurface Conditions (stratigraphy, soil/rock unit descriptions, groundwater observations, presented with borehole logs and a site plan); Discussion/Interpretation (engineering assessment of the ground conditions relative to the proposed tower, including any identified hazards such as fill, contamination, or liquefiable sand); Design Recommendations (foundation type — shallow raft vs. deep piles/caissons for a high-rise — allowable bearing or pile capacity, settlement estimates, lateral earth pressures for a multi-level below-grade parkade, seismic site class, groundwater/dewatering and excavation/shoring guidance); Construction Considerations (excavatability, temporary shoring adjacent to existing structures/property lines — a particular concern within city limits — vibration/noise constraints, and quality-assurance/inspection recommendations during construction); and Limitations (the standard closing statement on the report's applicability and the point-sample nature of the data). Appendices carry the borehole/test-pit logs, laboratory results, and site plan.

(b) Resources required

Conducting the investigation draws on three distinct categories of resource. Human/professional resources: a geotechnical Engineer of Record to direct and interpret the program, plus specialist input as needed — an engineering geologist for bedrock/geohazard mapping, a hydrogeologist for groundwater, a geophysicist for indirect subsurface profiling, and (given the urban setting) a surveyor for horizontal/vertical control tied to the legal survey fabric. Physical/field resources: a qualified drilling subcontractor with a rig suited to the anticipated ground and to access constraints on a constrained city lot (auger, mud-rotary, sonic, or CPT rig), sampling and in-situ testing equipment, and an accredited geotechnical laboratory for index and strength/consolidation testing. Information resources: the desk-study material itself — published geological and terrain maps, historical air photographs, the municipality's own utility as-built and prior-permit/geotechnical-report archives, a provincial water-well database, and the applicable codes (NBCC, CFEM, municipal building bylaw). Within city limits specifically, utility-locate (one-call) services and adjacent-property access agreements are an additional resource that must be arranged before any field mobilization, and a vibration/settlement monitoring resource (Q2) should be budgeted alongside the exploration program itself given the proximity of neighbouring structures.

(c) Investigation budget as a percentage of project cost

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 work, rising toward 2–3% for high-risk or poorly known urban ground (a high-rise on a former industrial lot, deep excavations near adjacent structures, or suspected old fill/foundations) 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, foundation redesign mid-construction, schedule delay while additional exploration is mobilized, and in the worst case foundation distress or damage to adjacent structures during a deep excavation — a particular exposure for a high-rise tower in a dense city setting. 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.