geotechnical engineering american bar association forum on the construction industry american bar...
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Geotechnical EngineeringGeotechnical EngineeringGeotechnical EngineeringGeotechnical Engineering
American Bar AssociationAmerican Bar Association
Forum on the Construction IndustryForum on the Construction Industry
American Bar AssociationAmerican Bar Association
Forum on the Construction IndustryForum on the Construction Industry
Presented By:Presented By:David R. Good, PEDavid R. Good, PEMueser Rutledge Mueser Rutledge
Consulting EngineersConsulting Engineers
J. Bradford McIlvainJ. Bradford McIlvainArcher & Greiner PCArcher & Greiner PC
InfrastructureCivil Works Projects for Lawyers
Soil InvestigationSoil InvestigationSoil InvestigationSoil Investigation
RockMineral based large particles
strongly bonded
SoilMineral based particles
strongly bonded
Suitability for Construction
Determine Soil Classification
▪ Sieve Analysis
– Testing Course Grain
soil
– Sediment Analysis
– Particle size distribution
small grain soil
▪ Reaction to Water
– Plasticity
• Plastic Index
– Liquid Limit
• Atterberg Limit
testing
Soil Stress
CompressibilityStrength
Function of the water in soil or capillary action of the water and the type of soil and size of soil
grains
Subsurface Exploration and Testing
Geotechnical Engineer dictates the exploration plan based on the anticipated soil conditions and the proposed construction
Sampling
Split-spoon samplingBlow count in-situ relative density
Shelby TubeMinimal disruption of sample
Boring AdvancementSolid StemHollow StemRotary DrillingCore Penetrometer Testing
Ground Improvement
Dynamic Compaction Lime Stabilization
Using Ground Improvement Techniques to build directly on improved grounds as opposed to deep foundations and or
removal and replacement techniques
…Dynamic Compaction
Weights from 6 to 30 tons dropped in free fall from heights from 30 to 75 feet
Conventional compaction from bottom up in lifts 12 inches or less
Dynamic compaction from the top down
Conventional Compaction density material from 2 to 4 feet
Dynamic compaction density material from 15 to 30 feet
…Dynamic CompactionSoil Type Use
• Highly permeable with improved drainage optimal soil.
• Low permeability soil not optimal for standard compaction.
• Intermediate soils (Silt, Clayey Silt, Sandy Silt) not as
receptive to Dynamic Compaction, several passes required.
…Dynamic CompactionDesign for soil type and ultimate use
Depth and degree of improvementType of structure to be placed on the soil
Design requirementsWeightAreaEnergy to be appliedGridPasses
Site constraintsVibrationLateral ground displacementAirborne particles
…Lime StabilizationVarious engineering properties of modified soil
Plastic IndexReduction of Liquid Limit
SwellingReduce swelling potentialDecreased affinity for water
California Bearing RatioUsual five fold increase in value
StabilityIncreased modulus and shear strength
Moisture ResistanceReduction in permeability of soil
Foundations
Spread out and transmit the structural loads into the ground at an intensity the ground can withstand without causing differential settlement
Foundations
Spreading out the concentrated load over a large area or extending the foundation deep
into the ground until it reaches a capable soil or rock layer
Foundations
The Geotechnical Engineer is to determine the depth to a suitable bearing layer for a structure’s foundation, estimating bearing capacity and the likely total differential settlement on the foundation.
Bearing Capacity
The bearing capacity of the soil or rock is the ultimate pressure that the material can support.
Estimate the likely soil bearing pressure and then apply a safety factor of 3.0 to the value to arrive at a allowable bearing pressure.
Design the size or type of foundation to maintain an allowable bearing pressure.
Determination of Soil Bearing Capacity
▪ Sand – allowable settlement criterion controls
the allowable bearing pressure
▪ Clay – related to the unconfined strength of
the clay
Settlement… …not that kindThe Engineer must select allowable bearing pressures
that allow total and differential settlement across the structure without resulting in detrimental structural damage.
Different structures for different purposes allow for different rates of settlement.
Most structures are limited to at most two inches.
Differential settlement within a structure is more critical than total settlement.
More on Settlement
▪ Settlement on Sand – Short term often described as compression or elastic.
▪ Settlement on Clay – Usually termed consolidated, and is time dependant.
Choice of Foundation
The foundation type selected for a project should be the most economical available to support project loads while meeting the settlement requirements for the structure.
Foundation types are either
shallow or deep
Shallow Foundations
▪ Isolated Column Footings
▪ Strip Footings Under Walls
▪ Combined Footings Under Multiple Columns
▪ Mat or Raft Footings
Deep Foundations
Heavy building loads or poor soils at normal excavation levels.
Pile Foundations
Driven Piles
Cast in Place Piles
Special Piles
Driven Piles
▪ Timber – Solid wood, driven into adequate soil bearing depth.
▪ Steel – Either H Beam, considered no-displacement or Closed End Pipe, considered displacement piles, compress and densifying the soil.
▪ Concrete – Pre-stressed/Pre-cast, either square, circular or octagonal, considered displacement piles.
Cast In Place Piles
Placed by drilling a hole in the ground, inserting a steel casing or cage and then filling with concrete. Advantage in low noise or vibration, but can cause subsidence
Auger Cast is by drilling but concrete is installed as the auger is withdrawn. Typically used in sandy soils.
Excavation Support
Deep excavations are used to construct underground portions of structures, often times sloped sides are utilized. If poor soil conditions are present or confined space is prohibitive steep slopes must be supported.
Site Investigation
A. Subsurface Exploration and Testinga. Borings at reasonable Spacing
b. Borings at deepest proposed structure
c. Borings at key alignments
B. Investigation and Conditions Survey of Existing Site
a. Location
b. Existing Structures
c. Existing Utilities
Excavation Support Systems
A. Wall Typesa. Soldier Pile & Lagging
b. Sheet Piling
c. CIP Diaphragm & SPTC
d. CIP Secant & Tangent Pile
B. Soil & Groundwater Conditionsa. Cohesion-less Soils
b. Cohesive Soils
C. Ground Movement & Adjacent Structures
D. Other Considerations
Design EngineeringA. Earth & Water Pressures
a. Water Pressure
b. Earth Pressure
B. General Wall & Bracing Design
C. Designing to Minimize Ground Movementa. External Groundwater lowering
b. Open Excavation for Support Wall Installation
c. Vibration During Support Wall Installation
d. Removal of Underground Elements
e. Excessive Over-Excavation below Bracing Levels
f. Poor Lagging Installation Practices
g. Bracing Design & Installation
Construction
▪ General Construction Monitoring
▪ Pre- and Post- Construction Surveys
▪ Instrumentation
Roadways/Pavements
▪ Determination of Suitable Subgrade
Analysis of Native Soils
Removal of;
Organic frost susceptible Soils
Expansive clumps of uncontrolled fill soils
Proof-Roll
Determine rutting or pumping
Accept or Reject Subgrade
Roadways/Pavements▪ Design Criteria for Pavement Surfaces
– Traffic• Type
• Load
• Frequency
• Distribution
• Speed
– Facility Type to be Serviced
– Economics (life cycle cost)
Legal Issues Presented by Legal Issues Presented by Geotechnical EngineeringGeotechnical Engineering
Limitations on LiabilityLimitations on Liability
▪ Geotechnical Engineers, like many design professionals, attempt to limit Geotechnical Engineers, like many design professionals, attempt to limit their liability to those who use their services.their liability to those who use their services.
▪ Liability limitations are usually expressed either as:Liability limitations are usually expressed either as:– The amount of fees charged for the services (or some multiple), orThe amount of fees charged for the services (or some multiple), or– A fixed dollar amount, such as $50,000A fixed dollar amount, such as $50,000– In some cases, limitation clauses are written or construed to limit In some cases, limitation clauses are written or construed to limit
liability in addition to any applicable insurance coverageliability in addition to any applicable insurance coverage▪ Limitation on liability clauses have been attacked on many grounds, Limitation on liability clauses have been attacked on many grounds,
usually anchored on claims that they are inherently unfair, that they usually anchored on claims that they are inherently unfair, that they violate public policy, or that they violate state laws that prohibit anti-violate public policy, or that they violate state laws that prohibit anti-indemnification clausesindemnification clauses
Limitations on LiabilityLimitations on Liability
▪ General rule: Most courts hold that reasonable limitation of liability General rule: Most courts hold that reasonable limitation of liability clauses are enforceableclauses are enforceable– Courts usually favor the freedom of parties to negotiate their own Courts usually favor the freedom of parties to negotiate their own
contracts and are reluctant to readjust the parties’ allocation of risks contracts and are reluctant to readjust the parties’ allocation of risks based on broad considerations of fairness or public policybased on broad considerations of fairness or public policy
– A limitation of liability clause is most susceptible to attack when the A limitation of liability clause is most susceptible to attack when the clause provides only a minimal, ineffective remedyclause provides only a minimal, ineffective remedy
– The reasonableness of a limitation of liability clause may be The reasonableness of a limitation of liability clause may be adjudicated on the basis of the circumstances of the contract adjudicated on the basis of the circumstances of the contract including the nature of the work to be performed, the cost, and the including the nature of the work to be performed, the cost, and the potential damages that a party might sufferpotential damages that a party might suffer
– When a state has passed laws related to anti-indemnification clauses, When a state has passed laws related to anti-indemnification clauses, courts may adjudicate the enforceability of the clause in light of the courts may adjudicate the enforceability of the clause in light of the statute. statute.
Limitations on LiabilityLimitations on Liability
▪ In a case with multiple parties, a limitation on liability clause In a case with multiple parties, a limitation on liability clause may not protect the designer from claims for indemnity from may not protect the designer from claims for indemnity from third parties third parties
▪ Better drafted clauses anticipate and include an express Better drafted clauses anticipate and include an express indemnification.indemnification.
▪ Other features of better drafted limitations on liability Other features of better drafted limitations on liability clauses:clauses:– Speak in terms of risk allocationSpeak in terms of risk allocation– Give upstream party (usually, project owner) a chance to get rid of Give upstream party (usually, project owner) a chance to get rid of
such a clause for a higher pricesuch a clause for a higher price– Dollar limitation no lower than feeDollar limitation no lower than fee