Infrastructure
Civil Works Projects for Lawyers
American Bar Association
Forum on the Construction Industry
Geotechnical Engineering
Presented By:
John Doe
Your Engineering Group,
Inc,
Prepared By:
Vincent Martinez
VITAL Consulting Group
Soil Investigation
Suitability for Construction
Rock
Mineral based large
particles strongly bonded
Soil
Mineral based particles
strongly bonded
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
Compressibility
Strength
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 sampling
Blow count in-situ relative density
Shelby Tube
Minimal disruption of sample
Boring Advancement
Solid Stem
Hollow Stem
Rotary Drilling
Core Penetrometer Testing
Ground Improvement
Using Ground Improvement Techniques to build directly on
improved grounds as opposed to deep foundations and or
removal and replacement techniques
Dynamic Compaction
Lime Stabilization
…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 Compaction
Soil 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 Compaction
Design for soil type and ultimate use
 Depth and degree of improvement
 Type of structure to be placed on the soil
 Design requirements
 Weight
 Area
 Energy to be applied
 Grid
 Passes
 Site constraints
 Vibration
 Lateral ground displacement
 Airborne particles
Lime Stabilization
Improving unsuitable ground using soil
stabilization techniques
…Lime Stabilization
Various engineering properties of modified soil
 Plastic Index
 Reduction of Liquid Limit
 Swelling
 Reduce swelling potential
 Decreased affinity for water
 California Bearing Ratio
 Usual five fold increase in value
 Stability
 Increased modulus and shear strength
 Moisture Resistance
 Reduction 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 Footings
Shallow 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 kind
The 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 Testing
a. 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 Types
a.
b.
c.
d.
Soldier Pile & Lagging
Sheet Piling
CIP Diaphragm & SPTC
CIP Secant & Tangent Pile
B. Soil & Groundwater Conditions
a. Cohesion-less Soils
b. Cohesive Soils
C. Ground Movement & Adjacent Structures
D. Other Considerations
Design Engineering
A. Earth & Water Pressures
a. Water Pressure
b. Earth Pressure
B. General Wall & Bracing Design
C. Designing to Minimize Ground Movement
a.
b.
c.
d.
e.
f.
g.
External Groundwater lowering
Open Excavation for Support Wall Installation
Vibration During Support Wall Installation
Removal of Underground Elements
Excessive Over-Excavation below Bracing Levels
Poor Lagging Installation Practices
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
Questions?
Thank You