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GEO-E2080Foundation Engineering and Ground Improvement27th November 2019 Lightweight and recycled materials

Contents

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• Lecture objectives

• Staged construction and settlement calculations

• Use of lightweight (and alternative) materials

• Materials used in lightweight structures (lightening materials)

• Design of lightweight structures

• Recycled materials and by-products

• Additionally in lecture material: Strength increase of subsoil below existing embankments and settlement calculations

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Objectives

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After the lecture the student

• Knows the range of use and applications of lightweight and alternative materials

• Can design a lightweight structure

• Can select the most suitable lightweight material

• Knows the most commonly used recycled materials and by-products used in earthworks

Embankments: Staged construction, settlement calculations for ground improvements, strength increase of subsoil

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Staged construction• Staged construction can be a combination different ground improvement

methods or in the most simple case just an overloading of an embankment.

• Ground improvements can include: for example deep mixing (yielding columns or mass stabilization), vertical drainage, vacuum consolidation, deep compaction,…

• The idea is to overload the embankment or building base so that the settlements of final structure will be low enough or nearly non-existent.

• Usually there are several construction steps.

• Naturally the stability level has to be high enough after each construction step.

• Typically this needs monitoring too.

• If monitoring shows, sometimes lightening of embankment is needed.

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Height of embankment

Construction time Service life

Staged construction phases , check stability after each phase 1 - 5

Embank-menttime

Settlementtime

Overloading Finalization of structures

´Overloading

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Settlement calculations

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• In infra construction the most critical factor in SLS design is usually differential settlement (painumaero), not so much the total settlement.

• The rate of consolidation process (settlement) is influenced by thickness and stratification (kerrostuneisuus) of settling subsoil drainage conditions such as water permeable or impermeable

unsettling bottom layer and intermediate layers with high water permeability (e.g. sand or coarse silt)

loading history and loading steps Initial conditions compressibility and water permeability of

settling soil layers• If settlements are significant (more than 200 mm) it is necessary to

take into account the reduction of effective unit weight of soil as some layers settle below the groundwater level.

Staged construction and preloading

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• The settlement of the final structure can be significantly reduced using preloading (esikuormitus) or surcharge loading (ylipenger).

Height of the embankment

Construction time OperationPhase

Time

Height of the embankment

Construction time OperationPhase

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Water permeable intermediate layers

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• A coarse layer that works as a drainage boundary condition is a layer in which the excessive pore water pressure can dissipate and water can flow out of the clay layers

• Potential layers for boundary conditions are roughly recognized from cone penetration tests and/or based on continuous sampling.

• The relative difference in water permeability is essential, not so much the total value of permeability of the intermediate layer

Strength increase of subsoil below existing embankments

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• The subsoil under the embankment has compacted due to consolidation.

• At the same time the strength has increased.

• Strength increase does not always occur.

• The amount of strengthening can be estimated using field vane or CPTU testing through the embankment and the comparing the results with the strength of nearby soft soil.

• Based on empirical knowledge is about for NC clays:

su = 0,23 x ’p or su = 0,25 x ’p (D’Ignazio 2015)

• The strengthening can be taken into account in stability and settlement calculations.

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Calculation of the stability of an existing railway embankment

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Area 3

Area 2Area

2Area 1

Use of lightweight materials

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When lightweight materials are needed?

Discussion

Need for lightening (kevennys, keventäminen)

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• To reduce settlements and improve low stability in soft soil areas

• Earth pressure can cause harmful loads to retaining walls.

• The need for lightweight structures is increasing:

need to construct on subsoil with low bearing capacity

preparation for flood level and sea level rise also requires raising the leveling (tasauksen nostaminen) of the structure

smaller repair work costs

• Lightening is often combined with other ground improvement methods.

• Benefits are rapidity of construction, flexibility and suitability for different types of construction projects.

• Some of the lightweight materials are by-products, environmental authorization (ympäristölupa) sometimes required.

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Use of lightweight materials (kevennysmateriaalit)

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According to LiVi 2011 the use includes

• road embankments

• bridge approach embankments (tulopenkereet)

• structures with laterally varying thickness

• transition structures (siirtymärakenteet)

• noise barriers

• pipelines in both cross direction and longitudinal direction

• repair and supplementary construction

Lightening techniques can also be used in order to reduce

dynamic loads and vibrations (also in seismic zones)

horizontal earth pressure

negative skin friction (in pile structures)

Reduction of vertical loads

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NOT used in Finland

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Reduction of horizontal loads

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Lightening for road embankments

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Transition structures(siirtymä-rakenteet)

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Objective: To even out settlements

Material fromLiVI 2011

Lightening of infra structures

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Lightening of a pipeline

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Lightened noise barriers (meluesteet)

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a) Noise barrier (meluvalli)

a) Noise barrier wall (meluvalliseinä)

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Limitations of lightweight structures 1

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• The settlements might be large, if the preconsolidation pressure is exceeded.

• On swamp areas lightweight structures can be used only on low-volume (vähäliikenteinen) roads.

• On flood areas the buoyant (noste) can set limitations in the selection of lightweight material.

• Composite structures, in which piling is combined with lightening of the embankment, might not be economically competitive.

• The greatest risk of differential settlements is when the lightened embankment is connected to a non-settling structure.

Limitations of lightweight structures 1

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• Reasons for failing at lightening of the embankment are underestimation of the groundwater lowering inaccurate evaluation of the consolidation state

(konsolidaatiotila) of soil design errors execution mistakes waterlogging (vettyminen) of the lightweight material

• Repairing the settlement afterwards is difficult.

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Lightweight materials

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Lightweight materials (kevennysmateriaalit)

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• Material choices depend on local conditions and availability of materials

• The most common in Finland is expanded clay (kevytsora) • Use of EPS (EPS-solumuovi) has increased, sometimes also XPS • Different materials - different ranges of use• Other lightweight materials: lightweight expanded-clay aggregate concrete

(kevytsorabetoni) foam concrete (vaahtobetoni) foam glass a recycled material (vaahtolasi) rubber tire aggregates (rengasleikkeet) With limitations; ashes, slag (kuona), Some trials with sod peat (palaturve) and wood-processing by-

products (metsäteollisuuden sivutuotteet)

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Properties of lightweight materials

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Material

Unit weight

[kN/m3]

Buoyancy

[kN/m3]

Compressive strength [kPa]

Cohesion [kPa]

Friction angle[°]

E modulus [MPa]

Thickness factor in

frost design

Expanded clay 4,0/5,0 7,0 - 0 37 50 4Expanded-clay aggregate concrete 7,0 *) 2500 - - 1500 6EPS 1,0 9,8 100 0 0 7 1Foam concrete 5,0 5,0 800 400 0 1000 4Sod peat 6,0 **) - 0 32 13Rubber tires 2,0 0 - 20 26 *)Rubber tire aggregate 6,0 0 - 10 26 6Conifer chips 7,0-9,0 3,0 - 10 26 6

*) Not relevant in the range of use of the material

**) Cannot get under water

(havupuuhake)

Conifer chips only for temporary cases or for parks!

Expanded clay (kevytsora)

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• Expanded clay = [Light Expanded Clay Aggregate (LECA)]• Ceramic, chemically neutral, uninflammable product that contains

natural minerals.• Production in kiln (uuni); the grain surface melts pyroclastic coat,

makes the surface dense and prevents the gas inside the grain from getting out

• The grains contain closed pores filled with water vapor.• Sieved into suitable grain size distribution, e.g. expanded clay for road

earthworks KS432 (grain size 4…32 mm)• One factory in Finland (Kuusankoski) • Production capacity per one kiln 400 000 m3 per year, at maximum 500

000 m3. • Enough for use in Finland, although small amounts have been imported

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Dotted line: The nominal distribution for expanded clay KS432 used in earthworks.

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Silt Sand Gravel Stones

KS432 expanded clay properties

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EPS (EPS-solumuovi)

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• EPS = Expanded PolyStyren (paisutettu polystyreenimuovi)• Granular material, contains expansive agent together with plastic.• Heating the grains turns expansive agent into gas separate

grains join together • Is sawed with (hot) wire saw to desired size slabs, blocks or pieces. • The manufacturing method creates the granular structure of EPS. • Many EPS manufacturers in Finland• The EPS used in lightweight structures is usually EPS 120 or EPS

200 (the value represents the compressive strength in short-term test with 10 % strain).

Technical properties of EPS

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EPS structures

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Road embankment from EPS Abutment backfill for a bridge (Sillan taustapenkereen täyttö)

EPS embankment – Design

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• Old standards: 150-200 mm thick reinforced concrete slab on top of EPS-embankment Objectives:

to protect the lightweight material from oil to increase the bearing capacity of the structure

• New studies: The reinforced concrete slab is not always necessary in lower class roads

However the pavement structure (päällysrakenne) must be braced (jäykistää)

• Protection with a plastic membrane (EPS is pyrophoric material)• EPS used without a slab compressive strength should be at least

120…150 kPa• EPS below the slab compressive strength at least 100…120 kPa. • International research: Use of EPS below the groundwater level and in

seismic zones

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Reclaimed/recycled car tires

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• The unit weight of tire products is 4-6 kN/m3, unit weight of wet tires is a bit higher than the unit weight of water, do not float or absorb water

• Elastic thick pavement structure required• The environmental competence has to be ensured • The most important properties of a tire lightweight structures are

can be used in flood areas high compressibility when constructing requires thick pavement structure layers (low module) high water permeability demands authorization from an environmental authority not eligible on ground water areas must be protected for fire safety reasons low expenses no need for buoyancy design

Properties of tire lightweight materials

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Compacted 5,9-8,2 kN/m3

Hydraulic permeabilityLike for gravel or higher

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Tire lightweight structures 1

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Test structure made of tire bales (rengaspaali)

Spreading of tire aggregate (rengasrouhe)

Tire lightweight structures and materials 2

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Tire aggregates RL1 – RL3 Tire granulate

Tire powder is also available for special cases, like flexible pavements.

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Tire lightweight structures 3

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Other lightweight materials

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Other materials• lightweight expanded-clay aggregate concrete (kevytsorabetoni)• foam concrete (vaahtobetoni)• foam glass (vaahtolasi) made from recycled glass• rubber tire aggregates (rengaskeventeet) With limitations ashes slag (kuona) sod peat (palaturve) wood-processing by-products (sivutuotteet)

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Design of lightweight structures

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Design of lightening (kevennys)

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• Based on stability and settlement calculations• Behavior of lightweight material as a part of stability

calculations • Lightweight structure design often begins with settlement

calculations.• The objective in lightweight structure design is usually so

called total lightening (kokonaiskevennys) in which the new structure doesn’t cause extra load to the subsoil or the final load is smaller than the original load.

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Partial lightening (osittainen kevennys)

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• Partial lightening can be justified if: the settlements have mostly

happened …or will happen relatively fast high groundwater level if it might not be possible to

reach the depth of excavation needed for total lightening

• Selection between total and partial lightening depends also on construction costs

Design of total lightening

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. (1)

. ′ (2)

qrak = load of the course layers above groundwater layer (grak · hrak)qkev = load of the lightweight material above groundwater layer (gkev · hkev)+ (gkev · htä)q’kev = load of the lightweight material below groundwater layer (g’kev · h’kev)qw = load caused by the dropped (lowered) ground water level dueconstruction (g’kev )· h’DW

qkaiv.maa = load of the excavated ground on lightweight structure (gmaa · hkev)+ (g’maa · h’kev)h’DW = drop of groundwater level (estimated)

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Principle

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In this method it is assumed that the lightweight structure lowers the groundwater level and so drains the ground. This doesn’t usually happen.

Lightened embankment

Initial conditions

Original Ground surface

Another method (same principle, different markings)

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Total compensation (100%) is determined so that the verticalnet load pnetto is zero on the original ground level:

pnetto = pkuorma - pkevennys = 0

pkuorma = Vertical stress caused by the load above the originalground surface, kPa

pkevennys = Lightening effect caused by the expanded clay soilreplacement below the original ground surface, kPa

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Calculation example lightweight (expanded clay) material 1Input data :

• Unit weight of embankment 20 kN/m3

• Unit weight of expanded clay 5 kN/m3

• Unit weight of dry crust 18 kN/m3 and below GW 8 kN/m3

• Effective unit weight of clay under ground water 6 kN/m3

• Thickness of embankment 1 m

• Thickness of pavement layers above expanded clay 0,8 m

• Ground water level -1 m

pkuorma = weight of the embankment above the expanded clay + weight of the expanded clay wedge above the ground surface = 0.8m · 20kN/m3 + 0.2m · 5kN/m3 = 17.0 kPa

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Calculation example lightweight (expanded clay) material 2pkevennys =

0.36m x (20kN/m3 - 5kN/m3) = 5.4 kPa (settling part of embankment)

0.64m x (18kN/m3 - 5kN/m3) = 8.32 kPa (dry crust part)

0.36m x (8kN/m3 - 0kN/m3) = 2.88 kPa (settling part below GW)

sum. 16.6kPa < 17.0kPa => extra lightening from soft clay is needed 0.4 kPa

0.07m x 6kN/m3 ~ 0.4kPa => total thickness of an expanded clay layer = 0.2 + 0.36 + 1.0 + 0.07 = 1.63 m.

Leena’s comment: a bit funny example, there is settlements, even though there is no extra loading to the soil.

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Discussion

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• Total compensation (täysi kompensaatio) is not always needed for the whole lightened area or it is impossible to reach with reasonable excavating depths

• In this case the partial compensation can be targeted which means 50 % compensation (pkevennys = 0.5 x pkuorma => total thickness of an expanded clay wedging = 0.80 m).

• At the borders of bridges or raft pilings (paalulaatta) usually3…5 m long transition slab (siirtymälaatta)

Length of transition structures (siirtymärakenne)

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Determination based on maximum changes in longitudinal gradient (pituuskaltevuuden muutos):

ss S

LL

S

Ss secondary settlement (can also be primary settlement or thecombination of primary and secondary settlements),

δ is maximum change in longitudinal gradient

In the design of transition structures one can (in some cases) take into account the maintenance cycles of the pavement structure (repaving, uudelleenpäällystys)

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Other evaluations related to the design

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• Buoyancy design (nostemitoitus) if the lightweight structure is below the groundwater level (flood areas, water areas nearby)

• Freezing and slipperiness risks. At least 700 mm thick pavement structure (päällysrakenne) layer for road structures and for streets 400…450 mm

• Design of pavement structure: Low module of lightweight materials and the weaker compaction of the layers above

• EPS + reinforced concrete slab for higher class roads• EPS + braced pavement structure (reinforcements, stabilization

etc.) for lower class roads

Road embankments – Expanded clay and EPS

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↑ Expanded clay structure

↓ EPS structure

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Recycled lightweight materials in the noise barrier alongside Ring 1

Recycled EPS

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Recycled EPS

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Kehä I

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The settlements of the tire embankment were so big thatthe highest part was madeof EPS blocks as well.

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Recycled materials and by-products

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Where alternative materials can be used in road and street structures?

Subgrade or embankment filling

Filter layer

Subbase layer

Pavement, wearing courseBase

Slope filling

In all these layers alternative materials can be used! ’Besides these there are many more application areas.

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What properties are needed in each layers?

UUMA2 tuotteistamisohje

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Recycled materials and by-products

• Multiple recycled materials (uusiomateriaalit) function aslightweight fills.

• What are by-products and recycled materials in earthworks? slags (kuona) from metallurgic industry mineral demolition products (mineraaliset purkituotteet) and

waste from construction industry ashes and desulphurization end products (rikinpoiston

lopputuotteet) from energy production process waste from forest and paper industry reclaimed/recycled (käytöstä poistetut) car tires And many others

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Slags from metallurgic industry

• Some of the slags belong to waste legislation (jätelainsäädäntö),some are products.

• Slags used in infra construction: Blast furnace sand (masuunihiekka, MaHk) OKTO-insulation (OKTO-eriste) Air-cooled blast furnace slag (Ilmajäähdytetty masuunikuona)

and blast furnace crusher run (masuunikuonamurske) OKTO and steel slag crusher run (OKTO- ja

teräskuonamurskeet)• Slags cane be used e.g. in road construction and earthworks • Blast furnace sand (product, not waste) can also be used in deep

stabilization and as a concrete ingredient

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Mineral demolition products and waste from construction industry

• Crushed concrete (Betonimurske) road and street construction field and courtyard

construction earthworks for housing construction

low quality materials can be used in fills and noise barriers

• Reclaimed asphalt (asfalttirouhe) Raw material for asphalt

concrete

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Ashes from energy production Energy sources

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ImportCoalOthersWooden fuelWater and windPeatNuclear powerGasOil

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Ashes from energy production

• Fly ash (lentotuhka) of coal (80-100 % of production) and bottom ash (pohjatuhka)

• Fly ash is fine grained (resembles silt), hardening material

• Bottom ash grain size distribution resembles coarse sand, little strength increase

• Ashes can be used in road and street construction fills and embankments soil binders in deep stabilization earthworks for housing construction surface structures of landfills

• Heavy metals might limit use

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Noise barrier for Highway 4

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Highway 4

Crushed rock

Ground surface

Surface layer clay

Crushed concrete

Stabilized clay, ash Mass exchange

GEO-EV Kiertotalousinfrarakentamisessa kurssi

• On mahdollista, että myös lukuvuonna 2020-2021 (ehkä kevät2021) järjestetään Kiertotalous infrarakentamisessa kurssiyhdessä TY:n kanssa.

• Kurssilla käydään läpi tarkemmin uusiomateriaalit ja niidenkäyttökohteet.

• Laajuus 5 op. kieli Suomi.

• Tarkempia tietoja loppu myöhemmin.

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