University of GenoaFaculty of mathematical, physical, natural sciencesDepartment of environmental studies and natural

resources

GEOTECHNICAL ANALYSIS OF MATERIAL COMING FROM LAKE BADANA WITH A VIEW TO A PROSPECTIVE

REUSE AS INERT IN CONCRETE MIXTURES

Candidate: Lorenzo Rinaldi

Supervisors: Prof. Andrea Cevasco Doc. Carlo Baracco Prof. Laura Crispini

Preamble:

The Badana dam is situated within the Bosio municipality of (AL) ; it cuts the flow of the namesake torrent –left tributary of Gorzente torrent – and was completed in 1914. It created a water reservoir of a volume of 4.69 Mm3.

Due to the events of February 2006 -conspicuous leakages between the bottom of the dam and the bedrock- it was implemented, as first safety measure, the emptying of the reservoir.

Additional research regarding the environmental risk, combined with safety regulations, has highlighted the urgency of carrying out excavations-both in the bedrock and at the bottom of the dam. In the following table we can see a first estimation of the total volume of the excavation project.

Excavation of short tunnels in the dam.5450m3

Excavation of a superficial drain system1500m3

Excavation of a new temporary road to access the site 700m3

Total7650m3

To the abovementioned volume of the excavation project, it should be added a safety margin of 20%, which will bring the final estimation to a total of9150 m3

Concerning the excavation of loose material withing the boundary of the reservoir-material that seems to present an average thickness of 1,5m- a first appraisal leads us to believe that the resulting volume may reach 19000 m3

Given the size of the excavation plan, the Italian law compels the company responsible for the project –Geotechnics Inc.- to massively reuse the material, with a view to environmental restoration.

A thorough geotechincs campaign has been planned to grant the full fucntionality of the dam after the excavation project.

Aims:

1) CLASSIFICATION OF THE BEDROCK THOUGH RMR89 INDEX

2) STABILITY ANALYSIS OF THE FLANKS OF THE MOUNTAINS GIRDING LAKE BADANA

3) ANALYSIS OF THE GEOTECHNICAL CHARACTERISTICS OF THE DAM

4) LABORATORY ANALYSES TO ENSURE THE SUITABLITY OF THE MATERIAL COMING FROM THE EXCAVATION PROJECT FOR A PROSPECTIVE REUSE AS INERT IN CONCRETE MIXTURES.

Methods:

1) GEOTECHNICAL ANALYSIS

2) DATA PROCESSING THROUGH DIPS AND ROC DATA

3) LABORATORY ANALYSES

Geological background

The area is mainly characterized by bedrocks belonging to the northern part of the geological group named Gruppo di Voltri . These bedrocks are partly overlapped by deposits of more loose material pertaining to the Bacino Terziario Piemontese.

Within lake Badana three different bedrocks can be found:

Serpentiniti milonitiche ad antigorite

Peridotiti lherzolitiche del MonteTobbio

Brecce di Costa Cravara

Figura 1 - Carta geologica dell'area circostante la diga e l'invaso di Badana

Unità Erro-Tobbio, Ultramafiti tettonitiche più o meno serpentinizzate associate a filoni

discordanti di gabbri meta gabbri ecologitici

Bacino Terziario Piemontese

Faglie

Peridotiti serpentinizzateSerpentiniti milonitiche a struttura

scistosa

Brecce di Costa Gravara, brecce grossolane a clasti

prevalentemente lherzolitici

BRECCE DI COSTA CRAVARA

SERPENTINITI MILONITICHE

PERIDOTITI LHERZOLITICHE

Geomechanical characterization of the bedrocks:

Samples have been collected and analysed in 15 different stations along the lakeshore. For each sample, the following characteristics have been analysed:

- Orientation

- Roughness (I and II order)

- Alteration

- Hydraulic conditions

- Openness

- Joint wall compressive strenght (JCS) through sclerometer.

Figura 2 - Ubicazione delle stazioni di rilevamento geomeccanico

1

2

3

8

9

10

4

11

15

7

14

6

13

5

12

Baracco C., Minetti L. (2000)

The information gathered from the analysis enabled us to classify the bedrock through the RMR89 index

The emptying of the reservoir allowed us to thoroughly verify the stability of the lakeshore by taking samples in areas that normally would be underneath the water surface.

CLASSIFICAZIONE DELL'AMMASSO ROCCIOSO-SISTEMA RMR89

Località: Diga di Badana ed invaso

Litologia : peridotiti serpentinizzate/sepentiniti milonitiche

N. PARAMETRO VALORI PUNTI FONTE

compressione 25-50MPa 4 mis.sclerom.(1)

1 monoassiale

roccia integra 50-100MPa 7 prove comp.monoas.(2)

25-50% 8 osservazione

2 <25% 3 carote

3 spaziatura dei rilievi su affioramento

giunti osservazione carote

4 condizioni dei vedere

giunti tabella 3bis

condizioni asciutti 15 osservazione

5 idrauliche dei umidi 10 dei giunti in sito

giunti

B orientazione dei

giunti

TOTALE PUNTI 62

RMR 38

CLASSE

AMMASSO

NOTE (1) valori di resistenza della roccia adiacente le discontinuità, rappresen

tano la resistenza della roccia in condizioni di esposizione superficiale

(2) valori di determinati in laboratorio su provini di roccia integra,

possono essere riferiti alla resistenza della roccia in profondità.

I valori ed i relativi punteggi in italico sono riferiti alle condizioni peggiori

rilevate alla scale di affioramento od osservati sulle carote.

I due valori di Indice RMR calcolati indicano il campo di variabilità della

qualità della roccia in ammasso, in genere i valori prossimi al limite

superiore possono essere riferiti alla roccia profonda mentre i valori

prossimi al limite inferiore possono essere associati alle condizioni

dell'ammasso roccioso esposto in affioramento.

n.c

II - (III) buona / (discreta)

IV - (III) scadente / (discreta)

RQD

200-600mm

60-200mm

10

8

22/13

N. PARAMETRO VALORI PUNTI FONTE

1-3m (bassa) 4 rilievi su

3-10m (media) 2 affioramento

<0,1mm (chiusi) 5 rilievi su affioramento e

0,1-1mm (legg.aperti) 4 osservazione carote

rilievi su affioramento e

osservazione carote

assente 6 rilievi su affioramento e

sabbioso <5mm 4 osservazione carote

legg. / mod. alterati 4 rilievi su affioramento e

alterati 2 osservazione carote

TOTALE 22/13

NOTE I valori totali indicati rappresentano in campo di variabilità delle condizioni dei

giunti

CLASSIFICAZIONE DEI GIUNTI - SISTEMA RMR89

E4 riempimento

E5 alterazione

E3 scabrezzaleggermente scabri

lisci

3

1

E1 persistenza

E2 apertura

DISCONTINUITY ORIENTATION

Stability analysis:

The data gathered from the structural analysis have been processed using DIPS (Hoek and Diederichs, 1989), to construct the following diagrams:

DENSITY OF THE POLES

PREFERENTIAL PATTERNS OF DISCONTINUITY

Although there is a significant dispersion of the discontinuities, four preferential patterns have emerged:

F1 dip immersion between 180° and 260°, inclination between 30° and 50°.

F2 dip immersion between 320° and 6°, inclination between 65° and 80°.

F3 dip immersion between 340° and 10°, inclination between 5° and 15°.

F4 dip immersion between 140° and 170°, inclination between 50° and almost vertical.

The presence of random plans of discontinuity could be justified by the limited number of measures it has been possible to take.

Knowing the JRC and the JCS, the shear strength of rock discontinuities can be calculated by using the Barton-Bandis failure criterion.

The strength of rock discontinuities has been calculated for the following conditions, which are the most common and representative within the water reservoir:

Condition 1: JRC= 4 JCS=20MPa

Condition 2: JRC= 6 JCS=20MPa

Condition 3: JRC= 8 JCS=20MPa

Condition 4: JRC= 4 JCS=10MPa

Condition 5: JRC= 6 JCS=10MPa

Condition 6: JRC= 8 JCS=10MPa

For each of these conditions we have determined the friction angle by using ROCDATA.The data obtained indicate an oscillation in the values of friction angles from a minimum 27° to a maximum of 32°.

Breaking limits for condition 6 (JRC=8 , JCS=10 MPa)

Station 1

DIPS has been used to evaluate the stability of the lakeshore. In particular, it has been analysed which discontinuity plans, combined with a certain friciton angle, can generate unstable conditions and landslides.

Having taken samples all along the lakeshore enables us to construct an overarching table regarding the risk of landslides within the reservoir.

1 ALTO J2 MODERATO J1-J3 ALTO

2 NON SUSSISTE LIEVE J1 NON SUSSISTE

3 MODERATO J(random) NON SUSSISTE NON SUSSISTE

4 NON SUSSISTE MODERATO J2 ALTO

5 NON SUSSISTE NON SUSSISTE LIEVE

6 NON SUSSISTE ALTO J4 ALTO

7 NON SUSSISTE MODERATO J(random) NON SUSSISTE

8 NON SUSSISTE NON SUSSISTE NON SUSSISTE

9 NON SUSSISTE ALTO J2 ALTO

10 NON SUSSISTE NON SUSSISTE NON SUSSISTE

11 NON SUSSISTE NON SUSSISTE MODERATO

12 NON SUSSISTE NON SUSSISTE NON SUSSISTE

13 NON SUSSISTE LIEVE J2 MODERATO

14 NON SUSSISTE NON SUSSISTE NON SUSSISTE

15 NON SUSSISTE NON SUSSISTE NON SUSSISTEpochi dati per valutazioni

attendibili

QUADRO RIASSUNTIVO DEL LIVELLO DI RISCHIO DI INSTABILITA'

MODO DI ROTTURA

OSSERVAZIONI

J1XJ2, J2XJ3

J(random)

J1XJ2, J2XJ3

pochi dati per valutazioni

attendibilila scistosità non genera

blocchi di dim. sign.

J1XJ3

J(random)

J2XJ3

J2XJ3, J2XJ4, J3XJ4

SCIVOLAMENTO DI

PIANI

SCIVOLAMENTO DI

CUNEIRIBALTAMENTO

STAZIONESET SET SET

With a view to a future reuse as inert in concrete mixtures, the material coming from the excavation at the bottom of the dam has undergone several laboratory analyses

Laboratory analyses:

All the analyses have been carried out by the laboratory C.S.G. Palladio of Vicenza.Eight samples have been examined to evaluate the possible presence of Asbetos and. Furthermore, to verify the concentration of harmful minerals in the body of the dam, further chemical analyses have been carried out on 3 samples.

Sample Sand Thickness of the loose material at the bottom of the dam

Parameter Unit of measure

Value

Crisotilo % p/p <0.1

Crocidolite % p/p <0.1

Amosite % p/p <0.1

Tremolite % p/p <0.1

Antofillite % p/p <0.1

Actinolite % p/p <0.1

Conclusions:

The bedrock surrounding the Badana reservoir presents a RMR89 index between 38 and 62. Therefore, the quality of the rock varies from below-average (Class IV) to good quality (Class II).

From the investigation, carried out using DIPS, it can be asserted that the global risk of instability of the lakeshore is generally modest.

Possible landslides can only concern the left flank (stazions 1-9), while the right flank does not present conspicuous risk.

The left flank also presents (stations 4;9) critical conditons for the detachment of rock wedges.

None of the 8 samples have shown a sufficiently high concentration of asbestos to create health concerns.

Moreover, the concentration of potentially harmful substances such as Nickel, Cadmium, Arsenic in the body of the dam is well within the limits imposed by the lItalian legislation (as established by the D.Lgs 16 Jan. 2008 n° 4).

Therefore, the material coming from the excavation project presents all the required characteristics to be wholly reused-after the necessary process of chipping- as inert in concrete mixtures.