Groundwater Contamination EU Water Framework Directive (2002)

Maintain quality of drinking water

In terms of groundwater:

1. Prevent input of pollutants

2. Recharge-discharge

balance

3. Reverse current pollutant

concentration trends

4. Do all the above within 15

years

Groundwater Contamination Common contaminants:

1. Hydrocarbons (industry)

2. Pesticides

3. Human waste (sewerage)

4. Fertilisers: Nitrates

Contaminant sources:

1. Storage tanks (point source)

2. Septic systems

3. Fly-tipping of waste

4. Contaminated water courses

5. Landfills

6. Roads and railways (line

source)

7. Salt water intrusion

8. Farming (diffuse source)

9. Acid mine drainage (pyrite)

Contaminant Transport

Advection; with

groundwater

Diffusion (dilution) & dispersion

Foundations

1. Foundation types

2. Foundation design

3. Considerations

4. Examples

5. Ground improvement

Pad/strip footing Raft footing Piles

Foundation types Shallow Foundations Deep Foundations

Which foundation to use?

Geology

Geotechnical properties

Structure to be built

= suitable for task

Foundation types

Pad footing Pad & strip footings

Shallow foundations

Single pad or continuous

strip

Distribute foundation

pressure to ground over a

sufficient area

Suit the pressures that

soil/rock can withstand

Footing size dependent

on strength of foundation

materials

Pad footing for single columns

Strip footings Usually for supporting walls

Raft footing

Shallow foundations

Where ground too weak for

pads or strips

Spread the pressure over

a much wide area

Reduce the load applied to

ground

Settlement can be

managed

Prevent lateral movement

between foundations

Improve rigidity & integrity

of building superstructure

High buildings in clay NB: referred to as a slab foundation also

Raft footing Concrete & metal reinforcement

Piled Foundations Pile group

Individual Pile Types

Where bearing material

exists at depth

Driven or drilled to required

depth

a) Precast concrete

b) Steel H pile

c) Steel shell pile (hollow)

d) Continuous flight auger pile

e) In-situ cast bored pile

f) Under-reamed bored pile

(greater end bearing pressure)

Installing Piled Foundations

Driven Piles Drilled Piles

Driven in to ground by pile driver

Accommodated by lateral displacement

Diesel driver (hammer weight +

explosion)

Bachysoletanche.com

-

Hole hollowed out by auger

Filled with concrete (+/- steel rebar)

Sometimes steel cased

Continuous flight augering

Base of an offshore wind turbine

Turbine stem sits on three piles

Offshore Pile Foundations

Piled Foundations Piles support loading in two ways:

1) End bearing

Loads transmitted to layer that

pile is resting on

Terminating a pile in gravels,

dense sands or bedrock

2) Skin friction

Friction between material and

sides of pile contributes to

carrying capacity

Reality: a contribution from

both

Cohesive materials: Suction piles

Ground Settlement

Load applied during construction -> subsidence occurs; ground consolidates

As porosity decreases and grain packing increases

Foundation failures

Weight of construction

> rock strength

Compaction or

consolidation of

permeable rocks

Failure into

cavity; shear or

flexural failure

Slope profiles too

steep; increase

driving forces

Foundation Design Foundations are the part of the building structure that

transmit loads to the ground

The load that a soil/rock can support is its bearing

capacity

Soils and rocks have a range of bearing capacities due

to their shear strengths, groundwater level and

consolidation; permeabilities and grain packing

Foundation depth: confining effects, passive pressures

Clay consistency: loss of structure and consolidation

If foundation pressure for a given foundation is too

One pile to a group of piles

Foundation Design Pressures exerted by a foundation into ground

become less significant with depth; 0.2q at 3B.

Depth to which foundation bearing pressure

significant depth.

Sig

nific

ant

Depth

Foundations are designed with

high margins of safety (FoS:2-3)

Designed to ensure that:

Applied foundation pressure is less

than that which would cause soil to

shear failure

ABP: foundation type & wide range of

soil properties

3 X

Fo

un

dati

on

Wid

th

100 kPa

20 kPa

Foundation Bearing Pressures UBP ultimate bearing pressure, i.e. load at failure

Load which causes settlement greater than 10% pile

diameter

Do not want ground to fail therefore FoS applied:

SBP safe bearing pressure

UBP+ arbitrary Factor of Safety (usually 2-3)

Still potential for settlement to take place:

ABP allowable bearing pressure; SBP further

reduced to take in to account all possible failure

mechanisms.

The reduction factor applied to SBP may be

significant in soils but usually close to 1 in rocks

Allowable bearing values Category Type Value

kN/m2 Remarks

Rocks

Strong sound igneous or gneissic rocks 10,000 Assumes

foundation to

grade 1/2

rock

Strong limestone and sandstone 4,000

Schists and slates 3,000

Strong shales & mudstones 2,000

Coarse

and very

coarse

soils

Dense gravel or sand and gravel >600 Width of

foundation

>1m. Water

table below

base of

foundation

Medium dense gravel or sand and gravel

Safe Bearing Pressure

Rock Type Unweathered and

massive

Heavily fractured

or thinly bedded

Strong igneous, gneiss 10 MPa 6 MPa

Strong limestones and

sandstones

4 MPa 3 MPa

Schists and slates 3 MPa 2 MPa

Strong mudstones, weak

sandstones

2 MPa 1 Mpa

Shale, sound chalk, weak

mudstone

750 kPa 400 kPa

Can be defined in terms of rock type & weathering:

Safe Bearing Pressure Or based on rock strength and degree of fracturing:

Unconfined

Compressive

Strength

(MPa)

RQD % / Fracture spacing in millimetres

25 / 60 70 / 200 90 / 600

100 4 8 12

25 1 3 5

10 0.2 1 2

SBP for a rock of given UCS,

RQD and fracture spacing

Fewer fractures

Foundations in an area of old

mine workings To avoid subsidence:

1. Pile through to below mine workings

2. Fill mine chambers with grout

Normal footings where

subsidence at great depth

Foundations in limestone