Consulting Engineers & Scientists

Geotechnical Environmental Construction Materials Pavements & Asset Management

Facilities

Geotechnical Environmental Construction Materials Pavements & Asset Management

Facilities

Geotechnical EngineeringGeotechnical Engineering Presented toPresented to

October 21, 2009

October 21, 2009

Geotechnical Engineering Approach

Four Components Field Exploration/Site Reconnaissance Laboratory Testing Report of Findings and

Recommendations Future Additional Studies/Construction

Observation

All are relative to what’s being proposed

Geotechnical Engineering Report

What we knew and what we did…– Based on our sometimes limited knowledge of the

project at the time of the study

What we encountered…– Expansive soils/bedrock, collapse-prone soils,

shallow groundwater, etc.

What it means…– Design: Foundations, Floor slabs, Retaining Walls,

Pavements– Construction: Dewatering, Earthwork, Surface

Drainage, and Maintenance

Geotechnical Engineering Report

What it means…is different for each reader– Owner– Architect– Civil Engineer– Structural Engineer– General Contractor– Earthwork Contractor– Foundation Contractor– Pavement Contractor– Landscape Contractor– Municipality– End User

Project Description andSite Conditions

The scope of the study and recommendations are based on these assumptions provided by client and project design team

Changes are often made after the Report is issued (Building Location, Number of stories, Finished floor elevation, Basement construction, Proposed Traffic, etc.)Sometimes, even site location changes!

Some owners have not seen the site– Are there stockpiles? Debris?– Drainages? Trees?– Does the site drain well?

Field Exploration – Drilling

Boring Location Map

Details the location of our borings and the location and elevation of the temporary bench mark (if applicable)

Field Exploration – Sampling

Solid or Hollow-Stem Augers

Ring Barrel Sampler or standard Split-spoon

Standard Penetration Test

Coring (very hard bedrock)

Other advanced methods such as…

Exploratory Methods

Pressuremeter Seismic Refraction Cross-hole Seismic Thermal Conductivity

Dilatometer Cone Penetrometer Borehole Shear / Vane

Shear

Ground Penetrating Radar

Subsurface Characterization

This is a description of the subsurface soil, bedrock, and groundwater conditions encountered at the time of the exploration

May also include assessment of geologic hazards

Boring Logs

1

2

3

4

5

Boring No. and Project Info

Soil Types and Descriptions

Sample Depth, Soil Classification and Field and Lab Test Data

Swell Test Result(s)

Water Level Measurements

YOUR PROJECT HERE

Your Name Here

1

23

4

5

Laboratory Testing

Common Soil Tests – In-situ Moisture Content, Dry Density– USCS and AASHTO Classification

(Grain Size, Atterberg Limits/Plasticity Index)– Expansion/Consolidation Potential

(Denver Swell Test)– R-Value/CBR (Pavements)– Sulfate Content (for Cement type)– pH & Resistivity (Corrosion)

Laboratory Testing, (cont.)

Denver Swell Testin Laboratory

Dial GaugeDial Gauge

Sample in Sample in Water PotWater Pot

Laboratory Testing, (cont.)

Swell Test Results

Percent Swell Measured After Water

is Added to Sample

Surcharge Load (500 psf)

Consolidation withIncreasing Surcharge

Load

Swell Pressure (15,000 psf)

YOUR PROJECT HERE

Engineering Recommendations

This is the part of the report that provides the design parameters and construction recommendations.

Geotechnical Considerations – Provides a brief overview of subsurface conditions that will impact the project from a geotechnical standpoint– Expansive soils– Existing fill materials– Shallow groundwater– Soft soils

Foundation Systems

Relevant geotechnical design parameters

Based on soil conditions, proposed bottom of foundation elevations, and anticipated structural loads

Foundation Systems, (cont.)

Drilled Piers (Caissons) or Helical Piles• Heavy Loads• Expansive Clays / Claystone Bedrock• Resist axial loads, lateral loads, and uplift

by socketing into bedrock• Socket must be below anticipated wetting

Spread Footings/Slabs/Mats• Light Loads• Non- to Low Expansive Materials• Alternative with Overexcavation of

expansive soils, usually requires additional evaluation

Lateral Earth Pressures

This section provides recommendations for the design and construction of CIP retaining or basement walls

Information used to resist soil pressure/movement

For MSE walls there are special considerations

Lateral Earth Pressures

Special Wall Projects– Not a standard

recommendation, but design plans and/or design parameters can be provided for specialty retaining walls

– May require additional exploration

– MSE walls are cheap and flexible, but movement may be unacceptable

– Imported, granular backfill almost always is recommended

Floor Slabs-On-Grade

This section provides recommendations for design and construction of floor slabs-on-grade including subgrade preparation to mitigate unsatisfactory conditions (fill, swelling soils, etc.)

Generally cannot eliminate movement Owner, Design Team

may want alternatives

Risk vs. Cost

Pavements

Pavement sections are based on: Traffic and Soils

Traffic is rarely known Assumptions should be

confirmed

AASHTO CDOT NAPA ACI FAA

Pavements, (cont.)

Swell Mitigation - Every Agency is different Overexcavation and moisture-conditioning Removal and replacement May include Chemical treatment – Lime, fly ash,

cement

Surface drainage main key in long term pavement subgrade performance– Base course can provide a pathway for water and

formation of a bathtub if roadway grades are not right

– Backfill curb and maintain good drainage(silt fence can be a problem!)

– May need to install edge drains behind curb

Earthwork- Overview

This section provides recommendations for stripping, subgrade preparation, dewatering, fill materials, moisture/compaction specifications, maximum slopes, shrink/swell estimates, etc.

Earthwork Recommendations

Observation and testing of Engineered Fill and Structural Fill are key to long-term performance– Breakdown/processing of materials is key to

achieve proper compaction and swell mitigation– Water almost always required to achieve

compaction and swell mitigation. Higher moisture contents required in expansive clays to reduce swell/settlement potential, but may lead to pumping

– Higher compactive effort may be needed to limit settlement of deep fill zones

Earthwork Recommendations

Provide Recommendations for maximum permanent slopes– Generally 3:1 (H:V) is recommended for clays

and loose sands– Retaining walls (often tiered walls) are used to

steepen slopes; however, without thinking about slope stability analyses, this can be dangerous

– Tiered walls tend to be designed to make an overall slope of 1:1

– This is generally unsafe, especially with landscaping

Additional Recommendations

Seismic Site Classification (ReMI)

Exterior Flatwork - subgrade preparation, swell mitigation

Underground Utility Design/Construction – groundwater, flexibility, corrosion, etc.

Cement Type

Additional Recommendations

Entire report depends on Surface Drainage…

– Slope grades away from buildings and onto pavements (no ponding behind curbs)

– May require swales, chases, area drains– Landscaping recommendations for areas

near buildings/infrastructure– Recommendations for discharge of

downspouts away from the building– Available for Geotechnical review…

Observation of finished product

Appendices

Boring Location MapLogs of BoringsLaboratory Test Results and

SummaryReport Terminology and General

Notes– USCS– Definitions

Other: Traffic/Pavement Calculations

Construction Observation and Materials Testing

Important for proper documentation that recommendations have been followed per geotechnical report, project plans, and specs

Provides a high level of quality assurance for owners/buyers

Does not replace contractor’s quality control

Construction Observation and Materials Testing

Proofroll observation Fill compaction testing Bearing strata evaluation Utility Trench Backfill Subgrade testing ICC Reinforcing and Structural Steel

Inspections Masonry observations and testing Mix Design Review Concrete, asphalt, and other materials

testing

Services Offered, but not limited to…

Foundation QC Testing

Osterberg Cell/Load Testing Pile Dynamic Analyses Cross-hole Sonic Logging Pulse-echo Integrity Tests Small-strain Dynamic Load Tests Geotechnical Instrumentation

» Slope Inclinometer» Settlement Devices» Pore Pressure Devices

Geotechnical Field Methods

Polymer Slurry-Drilled Shafts Cast-in-place Displacement Piles Secant/Tangent Walls Ground Improvement Soil Nailing Soil Rock Anchors Mini-piles Light-Weight Fill

Questions and Discussion

Reliable ■ Responsive ■ Convenient ■ Innovative