Vibrocompaction Design for Coquitlam Subsoils

Q: How much does vibrocompaction design cost in Coquitlam?

The spread depends on site size, number of treatment zones, and whether we are designing for settlement control alone or for liquefaction mitigation under the NBCC seismic hazard.

The most expensive mistake we see in Coquitlam is cutting a footing into undisturbed native till and assuming the whole site is just as solid. Thirty feet away there is a pocket of Fraser River Sand or uncompacted fill from the 1990s that nobody caught during the initial site investigation—and that is where the differential settlement starts. Vibrocompaction design fixes this before concrete goes in. We prepare site-specific treatment grids, target relative density above 70%, and specify the energy input required to reach it. For sites near the Coquitlam River or along the Lougheed Highway corridor, we often tie the design to a CPT test program: pre-treatment soundings to map the loose zones, post-treatment soundings to validate the improvement. The design package includes probe spacing, depth of treatment, backfill gradation, and vibration frequency ranges compatible with the vibroflot rigs available in the Lower Mainland.

A vibrocompaction grid designed without a pre-treatment CPT is just guesswork—and guesswork costs more than the investigation ever would.

Methodology and scope

In Coquitlam we regularly see sites where the upper 3 to 8 meters are loose to medium-dense silty sand with traces of wood debris from old land clearing. Standard compaction equipment cannot reach below about 2 meters in open granular profiles—that is where vibrocompaction becomes the rational choice. A properly designed grid achieves relative density gains of 15 to 30 percentage points in a single pass, provided the fines content stays below 12%. We define the triangular or square pattern based on the grain size curve from a grain size analysis and the target depth from the pre-treatment CPT. For mixed profiles with silt lenses we adjust the dwell time and water flushing rate to prevent bridging. The design also accounts for proximity to existing structures: within 15 meters of a foundation wall we limit vibration amplitude by reducing eccentric weight and increasing treatment time per point. On larger industrial lots in the Riverview Heights area we have used staggered-phase grids to maintain production speed while keeping peak particle velocity under the 12 mm/s threshold required by adjacent utilities. Every design is reviewed against CSA A23.3 provisions for improved ground and the relevant sections of the NBCC structural commentaries.

Local considerations

Coquitlam sits at the junction of the Coast Mountain foothills and the Fraser River floodplain—elevations range from near sea level along the river to over 1,600 meters on Eagle Mountain. The 2015 M4.8 earthquake near Pender Island reminded engineers across the Lower Mainland that loose saturated sands within 10 km of the city center are susceptible to both cyclic mobility and volumetric collapse. A vibrocompaction design that ignores the seismic demand from a crustal M6.5 event at 15 km distance is an incomplete design. We code each project for a minimum factor of safety of 1.3 against liquefaction triggering using CPT-based methods and the Boulanger-Idriss (2014) procedure. Where the groundwater table is within 2 meters of grade—common in the low-lying areas south of Brunette Avenue—we incorporate post-treatment dissipation testing to confirm that excess pore pressure ratios remain below 0.6 under the design earthquake. The NBCC spectral accelerations for Coquitlam demand this level of rigor, and we do not cut corners on it.

Technical data

Parameter	Typical value
Target relative density	70–85% (Dr) post-treatment
Maximum fines content	12–15% passing #200 sieve
Typical probe spacing	1.8–3.0 m triangular grid
Effective treatment depth	Up to 25 m with standard vibroflot
Backfill material	Clean coarse sand or 20 mm crushed gravel
Vibration frequency range	30–50 Hz (variable eccentric)
Peak particle velocity limit near structures	12 mm/s per NBCC commentary guidelines

Associated technical services

Treatment grid design and layout

Triangular or square grid spacing calculated from grain size distribution and target relative density. Includes depth intervals, dwell times, and water pressure parameters for each probe point.

Pre- and post-treatment CPT verification

Cone penetration testing before and after compaction with side-by-side comparison reports. Tip resistance and sleeve friction profiles overlaid to quantify improvement at every meter of depth.

Liquefaction mitigation design package

Seismic demand parameters for the Coquitlam area combined with treatment specifications to achieve a factor of safety greater than 1.3. Includes post-treatment pore pressure dissipation analysis.

Applicable standards

CSA A23.3 — Design of Concrete Structures (improved ground provisions), NBCC 2020 — National Building Code of Canada (seismic hazard for Coquitlam), ASTM D1586-18 — Standard Penetration Test (pre-design site characterization), Boulanger & Idriss (2014) — CPT-based liquefaction triggering procedure

Quick answers

How much does vibrocompaction design cost in Coquitlam?

What soil conditions in Coquitlam are suitable for vibrocompaction?

Clean to slightly silty sands with less than 12–15% fines passing the #200 sieve respond best. Coquitlam sites with Fraser River Sand, glaciofluvial deposits, or clean granular fill are good candidates. If the fines content is higher, we assess whether stone columns or dynamic replacement would be more effective before committing to a vibrocompaction design.

How do you verify that the compaction worked?

We specify a pre-treatment CPT baseline and a post-treatment CPT program on the same grid points. We compare tip resistance and sleeve friction at each depth increment. A relative density gain of 15 to 30 percentage points is typical. For critical structures we add crosshole shear wave velocity measurements to confirm stiffness improvement.

How close to existing buildings can vibrocompaction be used?

We design reduced-energy parameters for points within 15 meters of existing structures. By lowering the eccentric weight and extending the dwell time we keep peak particle velocity under 12 mm/s, which protects foundation walls and buried utilities. For distances under 5 meters we usually recommend switching to a low-vibration alternative such as stone columns.

What is the typical turnaround time for a vibrocompaction design?

For a standard industrial or commercial site in Coquitlam we deliver the design package within 8 to 12 business days after receiving the pre-treatment CPT data. Larger sites with multiple treatment zones or liquefaction analysis add 3 to 5 days. We can accommodate faster schedules when the drilling contractor is already mobilized.