Does Soil Type Matter?

Understanding soil and how it plays a part in installation torque and, ultimately, equipment selection for installing Chance® Instant Foundations®.

In short, soil type and strength matter a lot! In this article about installation requirements, I talk about equipment selection and torque, but soil is another key part of the equation. Instant Foundations are designed as a pole base support for any equipment that will require wiring, such as streetlights, transformers, EV chargers, and bollards.

READ PART 1 OF THIS ARTICLE

This is the Chance Soil Classification Table. It breaks down soil types into nine classes – Class 0 through Class 8. The installation requirements for steel screw-in foundations can be based on the soil class.

CLASS

Suitable for Instant Foundation Installation?

Common Soil-Type Description

Geological Soil Description

Typical Blow Count "N" Per ASTM-D 1586

0

No – do not use

Sound hard rock, unweathered

Granite, basalt, massive limestone

N.A.

1

Yes – but will likely require pre-drilling

Very dense and/or cemented sands; coarse gravel and cobbles

Caliche, (nitrate-bearing gravel/rock)

60-100+

2

Yes – but will likely require pre-drilling

Dense fine sands; very hard silts and clays (may be preloaded)

Basal till; boulder clay; caliche; weathered laminated rock

45-60

3

Yes – but will likely require pre-drilling

Dense sands and gravel; hard silts and clays

Glacial till; weathered shales, schist, gneiss and siltstone

35-50

4

Yes – but MAY require pre-drilling

Medium dense sand and gravel; very stiff to hard silts and clays

Glacial till; hardpan; marls

24-40

5

Yes

Medium dense coarse sands and sandy gravels; stiff to very stiff silts and clays

Saprolites, residual soils

14-25

6

Yes

Loose to medium dense fine to coarse sands to stiff silts and clays

Dense hydraulic fill; compacted fill; residual soils

7-14

7

Yes

Loose fine sands; Alluvium; loess; medium - stiff and varied clays; fill

Flood plain soils; lake clays; adobe; gumbo, fill

4-8

8

No – do not use

Peat, organic silts; inundated silts, fly ash very loose sands, very soft to soft clays

Miscellaneous fill, swamp marsh

0-5

Steel screw-in foundations are not suitable for Classes 0 and 8 soils. Class 0 soils are un-weathered, solid bedrock. Class 8 soils are very soft organic soils and very loose granular soils. However, Classes 1 through 7 soils are acceptable for steel screw-in foundations. Soil classes 1-3 are dense to very dense sands and gravel, or very-stiff to hard clay soils. They will likely require pre-drilling. Classes 4, 5, 6, and 7 are suitable for installing steel screw-in foundations, although in some cases Class 4 soils may also require pre-drilling.

The installation torque required to install a screw-in foundation can be estimated based on the soil type and class. The table below estimates the installation torque for a clay or silt fine grained soil based on the Chance soil class and the foundation length. Larger drive heads and installation machines are required to install screw-in foundations into very stiff and dense soils.

Clay and Silt
Length of Instant Foundation (ft) Installation Torque (ft-lb)
Soil Class 6-7 Soil Class 5 Soil Class 4
5 6,000 10,000 14,000
7 7,000 12,000 16,000
10 9,000 13,000 17,000

Similar to the Clay and Silt Table above, the table below estimates the installation torque for a sand or gravel coarse grained soil based on the Chance soil class and the foundation length. Larger drive heads and installation machines are required to install screw-in foundations into very stiff and dense soils.

 

Sand and Gravel
Length of Instant Foundation (ft) Installation Torque (ft-lb)
Soil Class 6-7 Soil Class 5 Soil Class 4
5 4,000 6,000 9,000
7 5,000 7,000 10,000
10 7,000 10,000 15,000

 

Please note both these tables are an estimate of the required installation torque. Actual torque values will vary.

Soil class is a key factor when selecting the proper drive head and installation equipment. If you have any questions, contact our team of experts at civilconstruction@hubbell.com.

VIDEO: How to Install

 



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