How deep should a bollard foundation be?

Standard non-rated bollard foundations are 24 to 36 inches deep with a 12 to 18 inch diameter. Storefront-protection installs typically use the deeper end. K-rated bollards require 36 to 60 inches deep per the manufacturer's certified ASTM F2656 configuration. Soil class and frost depth shift the spec within those ranges.

Does soil class change bollard foundation depth?

Yes. Sandy and gravelly soil supports the shallow end of the depth range. Clay soil requires the deep end because of expansive behavior and lower bearing capacity. Saturated soil drops bearing capacity by 30 to 50% and may need the deepest range plus drainage gravel at the bottom. The NRCS Web Soil Survey publishes soil-class maps for every Oregon county.

Do bollard foundations need to extend below frost depth?

Yes. Foundations placed above frost depth heave when the soil freezes and thaws. Willamette Valley frost depth is 12 to 18 inches; Cascade summits and eastern Oregon can hit 30 to 36 inches. The standard 24 to 36 inch foundation depth handles Willamette Valley conditions; deeper depths are required east of the Cascades.

What concrete strength does the foundation need?

4,000-psi concrete is the standard minimum for non-rated bollard foundations. K-rated bollards typically specify 4,000 to 5,000-psi with engineered reinforcement per the manufacturer's certified configuration. Cold-weather pours below 50 degrees F may need accelerator admixtures or insulating blankets.

Can a 6-inch concrete slab serve as a bollard foundation?

A 6-inch slab is sufficient for surface-mount bollard installations using anchor bolts, but it is not deep enough for fully embedded foundation installs. For non-rated surface-mount bollards in storefront applications, 6 inches of slab is typical. For K-rated bollards or any application requiring deeper embedment, the slab must be cut out and a deeper foundation poured.

Bollard Foundation Depth: 2026 Code-Compliant Spec Guide

Bollard foundation depth ranges from 24 inches for non-impact decorative bollards to 60 inches or deeper for ASTM F2656 K-rated installs, with soil class and impact rating driving the specific spec on every project. Cojo poured 36-inch deep footings on a 14-bollard storefront line at a Salem retail center in February 2026 because the underlying soil was glacial-till clay that needed deeper embedment than the typical sandy fill we see in Portland metro work. This guide covers the depth math by application, soil class, and impact rating.

For the broader install reference, see Bollard Installation. For K-rated specifics, see ASTM F2656 Bollards Guide. For anchor methods, see How Are Concrete Bollards Secured.

What's the Standard Bollard Foundation Depth?

The standard depth ranges by application:

Application	Foundation Depth	Foundation Width
Decorative non-impact	18 to 24 in	12 in
Standard parking-lot, non-rated	24 to 30 in	12 to 18 in
Storefront protection, non-rated	30 to 36 in	18 in
Loading dock, forklift zone	30 to 42 in	18 to 24 in
K-rated K4 / M30	36 to 48 in	24 to 36 in
K-rated K8 / M40	42 to 54 in	30 to 42 in
K-rated K12 / M50	48 to 60 in	36 to 48 in

These ranges assume standard well-drained soil. Clay, saturated, or rocky soil shifts the depth. K-rated installs follow the manufacturer's certified configuration -- the table values are typical, but specific certifications govern.

Why Does Soil Class Matter?

Foundation depth interacts with soil bearing capacity. The U.S. Department of Agriculture Natural Resources Conservation Service Web Soil Survey publishes soil-class maps for every county in Oregon, and most jurisdictions reference NRCS data during permit review.

How Do Soil Types Change the Spec?

Sandy or gravelly soil (high bearing capacity). Use the shallow end of the depth range. These soils drain well and support point loads.
Loamy or silty soil (medium bearing capacity). Use the middle of the depth range. Standard Oregon valley fill.
Clay soil (low bearing capacity, expansive). Use the deep end of the depth range. Clay also expands and contracts with moisture, which can dislodge shallow foundations.
Saturated or high-water-table soil. Use the deep end plus drainage gravel at the footing bottom. Permanently wet soil drops bearing capacity by 30 to 50%.
Rocky or compacted glacial till. Use the shallow end if excavation is feasible. The high bearing capacity makes shallower footings effective.

For Salem-area projects on glacial till and clay-mixed soils, our 36 inch standard tends to be the right depth. For Portland metro on sandier soils, 24 to 30 inches usually suffices.

How Does Impact Rating Affect Foundation Depth?

The American Concrete Institute ACI 318 Building Code requires structural calculation for any anchored steel that resists impact. For bollards, that means the foundation depth must be sufficient to resist overturning under expected vehicle-impact loads.

What Lateral Load Does a Vehicle Impact Generate?

A 5,000-lb vehicle striking a bollard at 5 mph generates roughly 12,000 to 18,000 lb of peak impact force, depending on bollard stiffness. At 30 mph, the same vehicle generates 200,000 to 300,000 lb peak. Foundation depth must resist the moment created by this lateral force at the bollard's above-grade height.

The math:

Moment at base = lateral force x above-grade height
Required overturning resistance = moment x safety factor (typically 2 to 3)
Foundation depth = depth that develops sufficient lateral soil bearing to resist the moment

For non-rated bollards expecting low-speed contact, 24 to 36 inch depth handles the moment safely. For K-rated bollards expecting high-speed impact, depths beyond 48 inches are typical.

What Does ASTM F2656 Specify for K-Rated Bollards?

ASTM International publishes F2656 Standard Test Method for Crash Testing of Vehicle Security Barriers that defines K- and M-ratings for bollards. The standard does not prescribe a specific foundation depth; it tests bollard systems as configured by the manufacturer.

Each manufacturer's certified configuration includes a foundation specification that was used during the live-fire crash test. Field installation must match that specification within tolerance.

Typical K-Rated Foundation Specs

K4 / M30 P2: 36 inch deep, 24 inch square, #5 rebar mat
K8 / M40 P2: 42 inch deep, 30 inch square, #5 rebar mat with vertical ties
K12 / M50 P1: 48 to 60 inch deep, 36 to 48 inch square, #5 or #6 rebar mat top and bottom with vertical ties
Shallow-mount K4: 18 to 24 inch deep, 36 inch square, engineered cable connections to adjacent bollards

The U.S. General Services Administration Facilities Standards reference K-rated bollards for federal facility perimeter applications.

How Does Frost Depth Apply in Oregon?

Frost depth is the soil depth that freezes seasonally. Foundations placed above frost depth heave when the soil expands and contracts.

Oregon frost depths by region (approximate, per NRCS):

Willamette Valley (Portland, Salem, Eugene): 12 to 18 inches
Coast Range: 12 inches
Cascade foothills (Hillsboro, Corvallis): 18 inches
Cascade summits (Bend west, Mt. Hood): 30 to 36 inches
Eastern Oregon (Bend east, La Grande, Pendleton): 24 to 36 inches

All bollard foundations should extend below the local frost depth. The standard 24 to 36 inch depth ranges in the table above already exceed Willamette Valley frost depths. For Bend and eastern Oregon, the deeper end of the range is non-negotiable.

What About Existing Concrete Slab Underneath?

When installing bollards in a parking lot with an existing concrete slab, the slab itself can serve as part of the foundation system if it is thick enough.

6-inch slab: Surface-mount with anchor bolts is the typical method. The slab provides anchorage but not embedment.
8 to 12 inch slab over compacted base: Core-drill retrofit can work, especially for non-rated bollards.
Over-pour or thicker structural slab: May allow embedded installation by saw-cutting and excavating below the slab.

For the maintenance side after install, see our bollard curb stop painting service guide. For Salem-area projects where Cojo handles a lot of clay-soil installs, see Bollard Installation Salem.

Get a Site-Specific Foundation Spec

Bollard foundation depth is not a one-size-fits-all decision. Soil class, impact rating, frost depth, and code compliance all factor in. Cojo specs and installs bollards across Oregon with engineered foundations sized to the actual soil and threat conditions on each site. Contact Cojo for a site-specific foundation plan.