geotechnical design of slabs on ground convention/2013... · geotechnical design of...

Geotechnical Design of Slabs‐on‐Ground

• Geotechnical Slab‐on‐Ground Subcommittee (DC‐10B)

1) New Design Standard2) New Certification Program3) Designer Guide/User Manual

New Design Standards


• Design Standard Changes‐Inclusion in 2015 IBC

• Compared to 2004 and 2007 Standard – Some changes were done to improve the intent of the written word (2004 & 2007)

– 4.1.1 Field Investigation and Laboratory Testing (2004 & 2007)

• Added a statement that field and laboratory testing should be determined by a licensed design professional based on local practice and experience.


• 1) Design Standard Changes– 4.1.2 Expansive Soils

• In sections 4.1.2.1 thru 4.1.2.4 weighted layer procedure was added to each method for determining the expansive nature of the design soil profile (2004)

– 4.3.2.2 Soil Chlorides• Sections 4.3.2.2.1 thru 4.3.2.2.3 were added to address soils chlorides (2004)

• Section 4.3.2.2.1 allows for increasing minimum concrete cover to provide corrosion protection (2004)

• Section 4.3.2.2.2 Requires encapsulated tendons (2004)• Section 4.3.2.2.3 Allows other mitigation methods approved by the Licensed Design Professional (2004)


• 1) Design Standard Changes

– 5.1.2.1.5‐Correction of γh for coarse grained soils (2004 & 2007)

– 5.1.2.2‐Method two: expansion index (EI) procedure (2004 & 2007)

– 5.1.2.3‐Method three: consolidation‐swell pressure test procedure (2004 & 2007)

– 5.1.2.4‐Method four: overburden pressure swell test procedure (2004 & 2007)


• 1) Design Standard Changes– Table 5.1‐Soil Fabric Factor Ff (2004 & 2007)

• The table was bifurcated to have a Ff of 1.0 for non‐Ch soils and three classifications for CH soils based on the condition of the soil profile

– 5.1.4‐Weighted average of Unsaturated diffusion coefficient (2004)

– 5.2.1‐Determination of Ym by computer methods (2004 & 2007)

• Ym may be determined by computer methods or when suction changes are controlled by normal environmental influences (to a depth that does not exceed 9 feet) the Stress Change Factors (SCF) tables may be used


• 1) Design Standard Changes– Table 5.2(a)‐Stress change factor (SCF) for use in determining Ym: post‐equilibrium case (2004)

– Table 5.2(b)‐Stress change factor (SCF) for use in determining Ym: post‐construction case (2004)

– Table 5.3(a)‐Stress change factor (SCF) for use in determining Ym: lawn irrigation (2004 & 2007)

– Table 5.3(b)‐Stress change factor (SCF) for use in determining Ym: flower bed case‐4 feet deep flower bed moisture (2004 & 2007)


• 1) Design Standard Changes– Table 5.3(c)‐Stress change factor (SCF) for use in determining Ym: tree drying case‐without moisture barrier (2004 & 2007)

– Table 5.3(d)‐Stress change factor (SCF) for use in determining Ym: tree drying case with 4 foot deep moisture barrier (2004 & 2007)


• 1) Design Standard Changes– 5.2.1.1‐Geographical areas with Im <‐15 or Im >+15 (2004 & 2007‐Commentary)

• Defines Post‐equilibrium condition

– 5.2.1.2‐Geographical areas with ‐15 < Im >+15 (2004 & 2007‐Commentary)

• Defines Post‐construction condition


• 1) Design Standard Changes– 5.3.1 Vertical barriers (2004 & 2007)

• Table 5.4 (a) Value of reduced em for various perimeter vertical moisture barriers for CH soils

• Table 5.4 (b) Value of reduced em for various perimeter vertical moisture barriers for non‐CH soils


• 1) Design Standard Changes– 5.3.2 Horizontal barriers (2004 & 2007)

• Table 5.4 (c) Value of reduced em for various perimeter horizontal moisture barriers for CH soils

• Table 5.4 (d) Value of reduced em for various perimeter horizontal moisture barriers for non‐CH soils

Certification Program


• 2) Certification Program– Currently committee CRT‐50 is working on a geotechnical certification program. The demand for this program has been driven by the misapplication of geotechnical design requirements by practicing engineers. Our goal is to provide better education opportunities for practicing engineers, enhancing use and application of the geotechnical aspects of Slab‐on‐Ground design.


• 2) Certification Program– Basic Types of Analysis

• Expansive Soils sites• Compressible Soils Sites• Collapsible Soil Sites• Stable Soils Sites


• 2) Certification Program– Site Design Considerations

• Climate – Post‐Construction Profiles

– Post‐Equilibrium Profiles


• 2) Certification Program– Site Parameters

• Trees and other Vegetation • Fence Lines, Trails & Roads• Slopes • Non‐uniform Conditions• Cut and Fill Sections• Drainage • Time of Construction • Landscaping • Irrigation• Dry Periods


• 2) Certification Program– Field Investigation

• Regional Practice • Considering Site Design Type (i.e., Expansive,

Compressible, Collapsible or Stable)


• 2) Certification Program– Laboratory Testing

• Soil Suction• Atterberg Limits• Particle Size Distribution• Hydrometer• Expansion Index• Swell Tests

• Swell Pressure


• 2) Certification Program– Engineering Analysis

• Selecting Soil Suction Design Envelope– Post‐Construction Envelope– Post‐Equilibrium Envelope

• Active Zone / Moisture Change Zone / Movement zone• Swelling Mode

– Center Lift‐Edge Drop– Edge Lift‐Center Drop

• Expansion Procedures‐Determining • Soil Parameters

– Soil Fabric Factor– em – ym – Bearing Capacity – Passive Resistance– Slab Subgrade Friction– Soil Weighting – Sample Calculations– Depth (9 ft, 15 ft or other and when to apply)

• Soil Movements Mitigation Techniques– Barriers – Water Injection – Moisture Conditioning

– Removal & Replacement


• 2) Certification Program– Material Considerations

• Concrete Mix• Chloride Limits• Post‐tension Materials

– Frost Heave– Non‐Uniform Soils Conditions


• 2) Certification Program– Slab on Piers– Geotechnical Report

• Report Contents– List Items

– Design Examples

Designer Guide/User Manual


• 3) Designer Guide/User Manual– Currently the Slab‐on‐Ground subcommittee members are working on developing a Designer Guide/User Manual.

– The intent of the guide/manual is to provide additional guidance and insight to the application and use of the Slab‐on‐Ground design method; improving the educational opportunities for Licensed Design Professionals and their understanding of the procedures and design methods.


• I want to Thank PTI, the dedicated members of the Slab‐on‐Ground Committee (DC‐10), the Structural (DC‐10A), Geotechnical (DC‐10B), Education & Commutation (DC‐10C) and Construction & Maintenance (DC‐10D) subcommittees.

• In addition, I would like to thank GeoTek (my employer) for their support of and commitment to Post‐tensioned Foundation Systems.

• The End

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