general geotechnical presentation
DESCRIPTION
Basic Geotechnical Presentation recently given at a Lunch and Learn at GallowayTRANSCRIPT
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