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 Classification

▪ All Soils classify one of four ways

1) Clay

2) Silt

3) Sand

4) Gravel

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 Stabilization

Improving unsuitable ground using soil stabilization techniques

…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.

Some FootingsShallow Spread Footings Driven or Auger Cast Pile

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

▪ Subgrade Preparation

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

▪ Subgrade use of Geotextiles

Roadways/Pavements

▪ Base Course

Roadways/Pavements▪ Design Criteria for Pavement Surfaces

– Traffic• Type

• Load

• Frequency

• Distribution

• Speed

– Facility Type to be Serviced

– Economics (life cycle cost)

Roadways/Pavements

▪ Asphalt Surface Course

Roadways/Pavements▪ Concrete Surfacing

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

Questions?Questions?

Thank YouThank You