Hydrogeological issues in geological hazard assessment · Hydrogeological issues in geological...

Milan, 24th October 2017

Hydrogeological issues in geological hazard assessment

Paola GattinoniResearch area: Transport Infrastructure and Geosciences

• Groundwater resources depletion

• Landslides and river dynamic

• Civil constructions (i.e. tunnels, roads)

GEOLOGICAL HAZARDS

HYDROGEOLOGICAL CONCEPTUAL MODEL

Main research topics ⇒ Engineering Geology

1. Type of aquifer ⇐ geomaterials

2. Hydraulic conductivity

3. Groundwater level

4. Hydrogeological balance

Which issues are involved in the reconstruction of the hydrogeological conceptual model ?

1. Type of aquifer




Which issues are involved in the reconstruction of the hydrogeological model ?

Alluvial (continuum)

Rocky (discontinuous or dual porosity)

Gattinoni & Scesi (2009) «Water circulation in rocks», Springer p. 165.

The development of the hydrogeological conceptual model in a rock mass requires the knowledge of the orientation and geometry of the rock joints.

Geo-structural surveys

Gattinoni & Scesi (2007): “Roughness control on hydraulic conductivity in fractures”, Hydrogeology Journal 15: 201-211.

Regime Flow equation Unitary flow rate (m2/s)

ε/Dh<0,033(surface

roughness)

Laminar

Turbolent(smooth joints)

Turbolent(rough joints)

ε/Dh>0,033(shape

roughness)

Inertial

Turbolent

Re96

=λi

ii J

geq

υ12

3

=

413160 /Re. −=λ

7/4

34/12

079.0

⋅

= iii Jegqυ

7321

.Dlog h

ε

−=λ

ii

h

i Je

D

gq 5.17.3log4

= ε

ε+=λ

51

88196.

hD.

Re

i

h

ii J

D

geq

+

=5.1

3

8.8112 ευ

9121

.Dlog h

ε

−=λ

iih

i JeD

gq 5.1

/9.1log4

=

ε

Anisotropicalluvialaquifer

Anisotropicfracturedaquifer

Isotropicalluvialaquifer

fractures

Quite unusual Typically the vertical

permeability is lower than the horizontal one (anisotropy ratio ≅ 10),

because of soil deposition cycles.

In rocky aquifers the anisotropy is

ruled by the orientation of

fractures.

1. Type of aquifer





Gattinoni & Scesi (2012) «Hydraulic Conductivity Assessment in Fractured Rock Masses: A Review of the Joints Features Influence», Horizons in Earth Science Research 6: 179-195.

k (m/s)

1. Type of aquifer





flow path, and then the recharge and discharge areas of the aquifer

Gattinoni et al. (2014): Delineation of Protection Zones for the Main Discharge Area of the Gran Sasso Aquifer (Central Italy) through an Integrated Geomorphological and Chronological Approach, J Water Res Prot 6: 1816-1832.

1. Type of aquifer





groundwater boundaries (i.e., divides, …) and interactions with surface waters


Hydrological divide

Rainfall recharge

Spring

Hydrogeological divide

Surface water suppling the

aquifer

Bedrock

Karst aquifer

Francani & Gattinoni P. (2009): “Hydrogeological aspects of Lombard Prealps karstification”, Italian Journal of Engineering Geology and Environment, 1, 117-136, 2009

1. Type of aquifer





water table changes in time

groundwater boundaries (i.e., divides, …) and interactions with surface waters


1970 1996Gattinoni et al (2003): “Pumping from quarry lakes as a measure for groundwater control in Milan: efficacy, feasability and hydrogeological constrains” – Appl Geol J 10(1): 33-46.

1. Type of aquifer





Fracture zone → connected aquifers

Shallow aquifer

Deep aquifer

i

hdhs

ht

hdSprings

Tunnel

Recharge

Deep aquiferhr qupRivers

Shallowaquifer

Gattinoni & Scesi (2006): Hydrogeological hazard assessment in medium depth tunnels, J Appl Geol 79: 69-79.

dstundownupd

dss

qqqqt

V

qit

V

−

−

+−−=∆∆

−=∆∆

1) In slope dynamic

2) In tunnel design

3) In underground infrastructures management

How can we use the hydrogeological conceptual model for geological hazard assessment?

Large scale hydrogeological susceptibility to landslide

Tunnel inflow assessment (design phase)

Hydrogeological hazard in underground infrastructures (operational phase)

A lesson we learnedStructural and

lithological setting

Hydrogeological setting

Hydrometric level of the lake which could trigger the landslide even without rainfall.

Rainfall which could trigger the landslide even without the lake.Collapse

Gattinoni et al. (2005): “Dynamic conceptual models for risk assessment in design”, J Appl Geol 12: 35-47.

Factors controlling the slope dynamic

Predisposing factors

Morphological setting (i.e., slope angle)

Lithological (geomaterials) and structural setting (faults)

Hydrogeological setting (permeability contrasts, supply

conditions,…)

Land use (vegetation, etc.)

Triggering factors

Active tectonic (rock uplift, earthquakes,…)

Intense and/or prolonged rainfall

Groundwater and pore pressure changes

Glacial processes (i.e. snow/ice/permafrost melt)

Loading/excavation (both natural and anthropic)

After gravity, water is the main cause of landslides!

Gattinoni & Francani (2000) «Influence of the geological setting on the groundwater pore pressure in a landslide», Appl Geol J 7: 61-77.

High fracturing degree of the rock mass (or karsism)

What hydrogeological conditions favor landslides?

Gattinoni (1999) «Groundwater flow model and slope stability of a riverbank», Appl Geol J 6: 97-117.

- High permeability in the recharge zone of the aquifer

- Heterogeneities and permeability contrasts

Upward flow

Convergence of the groundwater flow towards the landslide body

Lanslide body

Low permeability layer

Sensitivity of a landslide to triggering factors (rainfall, groundwater changes, …)

1. Hydrogeological conceptual model (flow path, springs, levels, discharges)

2. Study of the hydrogeological causes that may predispose or trigger the collapse

y = -0.0267x + 1R2 = 0.8122

0

0.5

1

1.5

-15 -10 -5 0 5 10 15 20 25

Dh nel detrito [m]

Fs

Slope scale analysis

flow path

spring

∆h

∆h (m)

Gattinoni P. (2009): “Parametrical landslide modeling for the hydrogeological susceptibility assessment…”, Natural Hazard, 50: 161-178.

Groundwaterflow models

1,00E-10 1,00E-09 1,00E-08 1,00E-07 1,00E-06Recharge [m/s]

kC = 5e-6m/skC = 6e-6m/skC = 7e-6m/skC = 4e-6m/s

Stability analyses (stress-strain models)

∆h = 1÷2 m ⇒ ∆Fs/Fs ≅ 5%∆h=5÷6 m ⇒ ∆Fs/Fs≅20%

∆h (m

)

0

30

15

7,5

22,5

Large scale analysis

Results can be extended on a wide domain considering the hydrogeological processes mainly controlling the slope stability.

3D groundwater flow model at basin scale

HYDROGEOLOGICAL SUSCEPTIBILITY

DEPENDING ON THE TYPES OF MOVEMENT:

- soil slip or debris flows triggered by infiltration;

- roto-translational slides, triggered by deep groundwater concertation.

Shallowaquifer

Deep aquiferGattinoni P. (2009): “Parametrical landslide modeling for the hydrogeological susceptibility assessment…”, Natural Hazard, 50: 161-178.

The landslide, a roto-translational slide (V = 10 Mm3) evolved in flow (groundwater!), caused the evacuation of nearly 2,300 inhabitants and the destruction of one of the two main road infrastructures of the area.

The example of the large landslidein Maierato (Cz, 2010)

Before

After

Long period of slope deformation

From in situ surveys and lab tests…

…to the landslide conceptual model…

Gattinoni et al. (2011) «The February 2010 large landslide atMairato (VV, Southern Italy)», Landslides 9: 255-261.

Evaporitic limestone

Sandstone

Claystone

Drillings ⇒ geological weakness of the geomaterials

Weak rocks for lithology (very high primary porosity, behavior from plastic to quasi-liquid depending on the water content)

Weak rocks for weathering (almost no cement)



Evaporitic limestone

Sandstone

Extensional displacements, with a progressive lowering of the stratigraphic series,



Limestone

Sandstone

ClaystonePhylliticbedrock



Phylliticbedrock

Evaporiticlimestone

Sandstone

Claystone

RainfalI in the last 20 days before the collapse: 100-years return period

Max monthly rainfall of the last 60 years (ARPACAL, 2010).

H[m a.s.l.]

FSDrained cond.

FSUndrained cond

269.8 1.30 1.25273.7 1.25 1.20275.1 1.20 1.15283.5 1.05 1.00

Simulations were carried out by changing thegroundwater level in order to point out the criticalconditions, corresponding to an increase of thewater table of about 15 m.

From the conceptual to the 2D numerical model

Groundwater

Shear stress increment

Displacement

Similar geological and hydrogeological conditions in the whole urban area!

Is there a residual risk?

What’s the hazard in the urban area?

3D groundwater flow model

Gattinoni & Scesi (2013) «Landslide hydrogeologicalsusceptibility of Maierato…», Natural Hazards 66(2): 629-648.

180

200

220

240

260

280

300

320

180 200 220 240 260 280 300 320

Simulated

Observed

Layer 1

Layer 2

Layer 3

Layer 4

Layer 5

From model calibration…

Calibration in post-failure condition (after the landslide of February 2010).

Simulation of: - Hydrogeological

conditions, which triggered the landslide of February 2010 (pre-failure condition);

- Critical recharge in post-failure condition, which may trigger new landslides.


…to the hydrogeological susceptibility assessment

Groundwater flow rates

Water table drawdowns


Zones interested by groundwater flow

concentration

1) In slope dynamic

2) In tunnel design






Geological hazards in tunneling

Hazards for the tunnel Hazards for the environment

- Tunnel and face instability or

deformation

- Water inflow

- Gas and aggressive waters

- Water resources pollution

- Drying up or changes in spring regime

- Water table drawdown

- Surface settlements

- Landslides

Hydrogeological issues are involved in both the points of view…

Draining tunnel

Zone with springs influenced by water table drawdown

Initial water tableFinal water table

Water management and delivery system

Gattinoni et al. (2014): Engineering Geology for Underground Works, Springer, p. 305.

- High permeability geomaterials (i.e., granular soils, karst phenomena, porous or fractured rocks)

- Morphological setting (i.e. shallow tunnel, portals)

- Permeability contrast, buried river beds

- Faults or overtrhustshaving significant water supply, synclinal folds

Hydrogeological conditions which could lead to significant water inflow in tunnel:

River

SpringDetriticalcover

Fractured rock

Moraine

Tunnel

Paleochannel

Sandstones

Limestones

GranitesTunnel


Tunnel Type L.(km)

Qmax(m³/s)

Qmin(m³/s) Aquifer

Sempione (ITA - CH) Railway 19.8 1.700 0.864 Limestone

Vaglia (BO - FI) Railway 18.6 0.080 - Limestone, calcarenite, sandstone

Direttissima (BO - FI) Railway 18.5 1.200 0.060 SandstonePavoncelli bis (AV) Hydraulic 15.5 0.800 0.070 Limestone, Clay Firenzuola (BO - FI) Railway 15.1 0.277 0.070 Sandstone and marl

Frejus (T4) Highway 12.9 0.007 0.001 Several

M. Bianco (Ti) Highway 11.6 0.800 0.440 Granite Raticosa (BO - FI) Railway 10.4 0.037 - Sandstone, marl and clayGran Sasso (A24) Highway 10.2 3.000 0.600 LimestoneS. Lucia (NA - SA) Railway 10.2 1.000 0.250 Limestone

Putifigari (SS) Road 9.8 0.070 0.050 VulcanitesZuc del Bor (UD - AUT) Railway 9.3 0.700 0.650 Limestone

S. Stefano (GE - F) Railway 7.9 - alta Marly limestone, sandstoneM. Olimpino 2 (MI - CO) Railway 7.2 elevata - Limestone, sands

Serena (PR - SP) Railway 6.9 media - Calcarenites, breccia, flyschM. La Mula Hydraulic 6.3 0.200 0.800 Limestone, dolomite

Turchino (GE - AT) Railway 6.4 0.110 0.075 CalceschystsSatriano (1° salto) Hydraulic 6.4 elevata - Milonitic Granite

Gran S. Bernardo (T2) Highway 5.9 scarsa bassa Gneiss, schystS. Leopoldo (UD - AUT) Railway 5.7 3.600 alta Limestone

Gravere (TO - FRA) Railway 5.6 elevata 0.013 CalceschystsVado Ligure (ITA - FRA) Railway 4.9 0.200 0.050 DolomiteColle Croce (ITA - FRA) Road 4.1 scarsa bassa CalceschystsCol di Tenda (ITA - FRA) Railway 3.2 0.600 0.200 Limestone

Bypass Spriana Hydraulic 3.2 0.300 0.040 Gneiss, limestone, dolomite

Villeneuve (A5) Highway 3.2 0.200 0.001 Calceschysts

Prè Saint Didier (A5) Highway 2.8 0.100 0.080 Calceschysts, sandstoneMoro (AN - BA) Railway 1.9 0.080 - Gravels and sandsColle della Scala Railway - elevata alta Limestone

Croccetta (Paola - CS) Road 1.5 0.022 0.028 Tectonised schists

Motorway

Examples of water inflow in different types of tunnel and for different types of aquifer

The motorwaytunnel in the Gran Sasso

The Gran Sasso massifbears a wide aquifer system of about 800 km2. It’s made up mainly of limestone, in which karsismis locally well developed, and it is bounded by clastic low permeability units (mainly marls).Springs are located all along the basin boundaries. The motorway tunnel is located in the northern zone.


Ricarica:

> 1000 mm/anno

500-1000 mm/anno

250-500 mm/anno

< 250 mm/anno

Sorgenti principali

Sorgente lineare

Drenaggio tunnel autostradale

SovrascorrimentoFaglia distensiva

Direzione di flusso ipogeo principale

T2

Campo Imperatore

Gruppo 1

Gruppo 2

Gruppo 3

Gruppo 4

Gruppo 5

L'Aquila

F. Raiale

Fiumi principali

F. Aterno

F. Tirino

N

5 km

Area di cava prevista

0

1000

2000

ms.l.m.

0

1000

2000

ms.l.m.

NO SE

LEGENDA

CampoImperatore

AcquiferoAquicludeSovrascorrimentoLivello piezometrico indicativo

Direzione di flusso dell'acquiferoInfiltrazione concentrataGruppo sorgivoOpere in sotterraneo

RECHARGE MAP

The main recharge zone of the aquifer is locate in the Campo Imperatorebasin, having an elevation about 2000 m a.s.l.. Here the aquifer recharge reaches his highest value, higher than 1000 mm/y. Then, the groundwater flows towards the borders of the domain, bringing about several groups of springs.

≅ 15 m3/s≅ 2m3/s


The motorway tunnel is locate at the bottom of the aquifer and nowadays it drains about 1,5m3/s, which corresponds to less than 10% of the whole aquifer discharge.

≅ 1.5 m3/s

0

1000

2000

ms.l.m.

0

1000

2000

ms.l.m.

NO SE

LEGENDA

CampoImperatore

AcquiferoAquicludeSovrascorrimentoLivello piezometrico indicativo

Direzione di flusso dell'acquiferoInfiltrazione concentrataGruppo sorgivoOpere in sotterraneo

≅ 15 m3/s≅ 2m3/s

Southern springs

Northern springs


Hydrogeological conceptual model

Excavation and tunnel support system that minimise tunnel inflow its interferences with springs and wells

Gattinoni et al. (2014): Engineering Geology for Underground Works, Springer, p.305.

Tunnel design

Expensive geognostic surveys (geophysical surveys, drillings, in bore-hole tests)

Hydr

ogeo

logi

cal r

isk (%

)

Cost

of t

he g

eogn

ostic

surv

eys

Hydrogeological data acquisition (%)

Limit in data acquisition

Best solution

Risk

These equations have been developed for isotropic porous aquifers, but they are commonly used for discontinuous fractured aquifers, too.

Analytic equations for tunnel inflow, with the related validity range


Can analytic equation be suitable for discontinuous rock masses?

400 m

100 m

10 m

Symmetry axis

Groundwater flow modelling through a discrete approach

Coupled modelling of both hydraulic and mechanical processes in a jointed rock mass

Lithostaticload

Hydrostaticload

Water tabledrawdown

Tunnel inflows along joints

Gattinoni et al. (2009) «Tunnel inflow assessment in discontinuous rock masses:…», ITA-AITES 2009: 1-9.

Simulations for different joint set:• dip and dip direction;• spacing (1 – 12 m);• surface aperture (1.29e-6 – 2.04e-6 m);• connectivity (50 – 100%);

• tunnel depth (15 – 260 m);• water table (15 – 135 m).

Over 1000 simulatons

E/45°- O/45°

E/30°- O/30°- O/10° E/0°- O/45°

E/60°- O/60°

E/0°- O/90°

E/30°- O/30°

E/30°- O/30°-E/30°-E/60°-O/30°- O/60°


Joints spacing and aperture

0,00E+00

5,00E-06

1,00E-05

1,50E-05

2,00E-05

2,50E-05

3,00E-05

3,50E-05

1,20E-04 1,50E-04 1,80E-04 2,10E-04

Q si

mul

ata

(m³/s

/m)

Apertura (m)

S = 12 m

S = 10 m

S = 8 m

S = 7 m

S = 6 m

S = 4 m

Tunnel inflow linearly increases with joints frequency.

Tunnel inflow increases with

joint aperture with a power law.

0,00E+00

1,00E-05

2,00E-05

3,00E-05

4,00E-05

5,00E-05

6,00E-05

7,00E-05

0,000 0,100 0,200 0,300 0,400

Q si

mul

ata

(m³/s

/m)

Frequenza (1/m)

2.04e-4 m1.92e-4 m1.78e-4 m1.62e-4 m1.29e-4 m

E/30°- O/30°

E/30°- O/30°

Qsim

ulat

ed

Frequency

Qsim

ulat

ed

ApertureGattinoni et al. (2009) «Tunnel inflow assessment in discontinuous rock masses:…», ITA-AITES 2009: 1-9.

Tunnel depth

0

30

60

90

120

150

1,2E-04 1,3E-04 1,4E-04 1,5E-04 1,6E-04

Prof

ondi

tà(m

)

Aperuta idraulica (m)

E/20°-O/20°

E/60°-O/60°

E/0°-E/45°

E/70°-O/70°

0,00E+00

5,00E-07

1,00E-06

1,50E-06

2,00E-06

2,50E-06

3,00E-06

3,50E-06

4,00E-06

4,50E-06

0 50 100 150 200 250 300

Q si

mul

ata

(m³/s

/m)

Profondità (m)

E/0° - O/45°

E/20° - O/20°

E/60° - O/60°

E/70° - O/70°

Joints aperture exponentially decreases with tunnel depth.

Tunnel inflow exponentially

decreases with tunnel depth. Q

simul

ated

Depth

Dept

h

Aperture


0,00E+00

1,00E-06

2,00E-06

3,00E-06

4,00E-06

5,00E-06

6,00E-06

7,00E-06

8,00E-06

9,00E-06

0 20 40 60 80 100

Q si

mul

ata

(m³/s

/m)

Inclinazione (°)

Joints dip

0,00E+00

1,00E-05

2,00E-05

3,00E-05

4,00E-05

5,00E-05

6,00E-05

0,0E+00 1,0E-06 2,0E-06 3,0E-06 4,0E-06Q

sim

ulat

a (m

³/s/m

)

Keq (m/s)

E/90° - E/0°

E/30° - O/30°

E/80° - O/80°Qsim

ulat

ed

Qsim

ulat

ed

For the same value of equivalent permeability, tunnel inflow depends on joint dip.

Joints dip

550 joints intersections

213 joints intersections

Orientation of the permeability tensor

Joints connectivity


Comparison between analytic formula and numerical results for different joint networks

The comparison points out that the analytic formulas overestimate the tunnel inflows and that the overestimation is bigger for geostructural setting having discontinuities with higher dips.

Gattinoni & Scesi (2010) «An empirical equation for tunnel inflow assessment: application to sedimentaryrock masses», Hydrogeol J 18: 1797-1810.

Based on the comparison between the numerical results and the tunnel inflows calculated with the Goodman equation, the following empirical relation was pointed out:

bGaQQ =

Q (m3/s) = tunnel inflow in discontinuous rock mass, QG (m3/s) = tunnel inflow by Goodman’s equation,

a and b are empirical dimensionless coefficients depending on:dip of discontinuities, hydraulic conductivity anisotropy ratio, orientation of hydraulic conductivity tensor.

b = ln3.463 F 0.0342

a = 3.448F 0.8834 for F < 13.2411F 0.6805 for F ≥ 1

ϕα 5.0

max

min1cos

=∑=

KK

nF

n

ii

Where:n is the number of discontinuity sets,αi is the dip of ith discontinuity set,Kmin and Kmax are the minimum and maximum components of the hydraulic conductivity tensor,

ϕ= -1 if θmin > 45°

1 if θmin ≤ 45°

θmin is the angle between Kmin direction and the horizontal plane

Gattinoni & Scesi (2010) «An empirical equation for tunnel inflow assessment: application to sedimentaryrock masses», Hydrogeol J 18: 1797-1810.

5.5 km

300 m

Example: The “Monte Giglio” Tunnel

Flysch

FlyschConglomerate

Marls

Sandstone

The medium-depth tunnel interests sedimentary rocks of the Lombardy Series.It is located below the water table for a length of 5.5 km, with no waterproofing.

Gattinoni et al. (2010) «Empirical equation for tunnel inflowassessment: application to a case history», ICHE 2010: 1-10.

13 2458 7 6

Flysch

FlyschConglomerate

Marls

Sandstone

The tunnel was divided into hydrogeological homogeneous stretches. For each one, the

hydraulic conductivity tensor and the corresponding equivalent hydraulic

conductivity were calculated based on the structural surveys and on depth pumping

tests, that allowed to consider the decreasing of permeability with depth.


13 2458 7 6

12345678

In some cases, the hydraulic conductivity ellipses (in the vertical plane orthogonal to the tunnel) show a great anisotropy, with the main hydraulic conductivity parallel to the vertical direction, such as for stretches 2, 4 and 6. As a consequence, for these cases the Goodman equation gives the highest overestimation, whereas the empirical relation allows an estimation of the tunnel inflow that better reproduces the observed values.

0

0,005

0,01

0,015

0,02

0,025

0,03

0,035

12345678

Tunn

el in

flow

[m3 /

s]

Q Goodman Q formula Q observed


1) In slope dynamic

2) In tunnel design






Water table rise in Milan and itsinterferences with underground infrastrictures

The rise of the groundwater table has been about 8-10 m in the northern area, 4-5 m in the central zone of Milan and 2 m in the southern one.This rising trend interferes with the structures and infrastructures, bringing about both management troubles for the railway urban system and safety issues for the structures.

Loweringtrend

Risingtrend

Rise from 2000 to 2014

Examples of interference between groundwater and underground structures and infrastructures

The metro line green, which was designed to function in dry conditions, now lies below the water table, involving important waterproofing works.

If the groundwater trend will go on with the same rate, in the next ten years static problems will be triggered, even in presence of waterproofing lining.

The model domain covers an area with high density of hydrogeological data.

Subsurface geological data (CARG)

Source

DepthBottom surface

Aquifer A

Uppersurface

Aquifer B

Bottom surface

Aquifer BTotal

CARG 1020 731 361 2112

Quite good accuracy in the reconstruction of the aquifer geometry:

Shallow aquifer

Semi-confined aquifer

Aquitard

Gattinoni et al. (2016) «Geological map of Italy– Milan 118», Italian Geological Service.

LAYER 2

Horizontaldiscretization

Verticaldiscretization

Grid composedby cells (2,5 m x 2,5 m)

8 layers to representAquifer A* (Layer 1-6),

aquitard (Layer7) and Aquifer

B* (Layer 8)

GRID DEFINITION

* ENI-Regione Lombardia aquifer definition

N

S

Garibaldi Station

Aquifer group B

Aquifer group A

Aquitard

Vertical discretisation: 3 main layers

In order to simulate the metro tunnels (shown in black), the shallow layer was further divided in 6 sub-layers.

Gattinoni et al. (2014) «A 3D model of the aquiferof Milan (Northern Italy)», SGEM, 2: 3-10.

1) Boundary and internal conditions

Wells

No flow elements

Q well: ≈ 11 m3/s

SPECIFIED HEAD SPECIFIED FLOW FLOW DEPENDENT HEAD

Constant head -piezometric

survey in March 2014

River (Lambro, Seveso, Olona)

No flow elementrepresenting the tunnels,

metro stations and foundations

2) Input equivalent hydraulic conductivity interpolation

45 cm/y

5 cm/y

80 cm/y

shallow aquifer

semi-confined aquifer

aquitard

Gattinoni et al. (2016) «Influence of underground structures and infrastructures on the groundwater level in the urban area of Milan, Italy», Int J Sust Develop and Planning 12: 176-184.

Average hydraulic gradient ≈ 1% Local hydraulic gradient ≈ 20% Hydraulic gradient for suffusion ≈ 40%

STEADY STATE CALIBRATION (March 2014)

Absolute residual mean: 14 cmScaled absolute residual mean: 0.2%

1) Local water table drawdown due to the impermeableinfrastructures

2) Velocity vectors and velocity values in a cross-section nearby the Garibaldi station

Increasing

Decreasing

Gattinoni et al. (2016) «Influence of underground structures and infrastructures on the groundwater level in the urban area of Milan, Italy», Int J Sust Develop and Planning 12: 176-184.

Probability distributions of: (a) the recharge multiplying factor(b) the withdrawal decreasing

Stochastic modelling of groundwater flow for hazard assessment along the underground infrastructures in Milan (northern Italy)

Gattinoni et al. (2018) «Stochastic modelling of groundwater flow for hazard assessment along the underground infrastructures in Milan (northern Italy)», TUST (in press).

Average groundwater rise simulated with the stochastic approach

Metro station Scenario∆H50% ∆H75% ∆H95%

Garibaldi1 3.12 3.38 4.13Repubbl.2 2.93 3.14 3.34P.Venezia1 2.71 2.89 3.09Domodos.2 3.08 3.28 3.53Centrale1 2.99 3.2 3.42

Lotto1 3.20 3.41 3.69Cadorna1 2.81 3.01 3.19Duomo3 2.60 2.79 2.95Loreto2 2.76 2.95 3.18Piola2 2.56 2.95 2.97Zara2 3.03 2.74 3.49

Lambrate2 2.51 3.25 2.92

Water table changes (in m) in some metro stations: ∆H50%, ∆H75% and ∆H95%are respectively the 50%, 75% and 95% percentiles of the simulated values.


Probability occurrences of water table in some metro stations, compared to their bottom and top altitudes.


Flooding hazard map of the metro tunnels

Probability that the water table exceeds the

bottom altitude, for each metro line.


MITIGATION SOLUTIONS

RECHARGE MODIFICATION:- Decreasing of infiltration rate

in the domain (parasite water reduction, bettermanagement of irrigationchannels, etc.)

- Restoration of the originalhydraulic connection of the surface network

PUMPING MODIFICATION:- Increasing pumping rate in

aquifer A (10%-30%)

DRAINAGE TUNNEL:- floodway-diverter of the

Seveso River

Gattinoni & Scesi (2017) «The groundwater rise in the urban area of Milan and its interactiosn with underground structures and infrastructures», TUST 62: 103-114.

MITIGATION SOLUTIONS

Scenario Hypotesis ∆h (m)

Area of interest

I1 Recharge reduction 25%in the whole domain

-0.7 Highest values equal to -1m in the western zoneof Milan

I2 Draining tunnel (totaldischarge ≈ 2 m3/s)

-2.5 Highest values equal to -5 m nearby the tunnel

I3_10 Pumping rate increase of10% in aquifer A

-0.3 Located in the centralarea of Milan

I3_30 Pumping rate increase of30% in aquifer A

-1.0 Located in the centralarea of Milan

I1+I2 Superimposition ofscenarios I1 and I2

-3.0 Similar to scenario I2 butwith a larger extensionof the drawdown

I1+I3_30 Superimposition ofscenarios I1 and I3_30

-1.5 Generalized over thewhole domain, with maxvalues in the central area

Non-structural measures can easily manage the short term hazard, whereas in the long term an integration between structural and non-structural measures will be necessary.


A drainage system located at the bottom of the metro tunnels would havekept the water table below the infrastructures, avoiding this kind of hazard.

Prevention would have been the best solution!


Hydrogeological model is a key factor in geological hazard assessment and prevention!

Learn from yesterday, Live for today,Hope for tomorrow.The important thing is not to stop questioning

Albert Einstein

Maierato landslide

Thank you for your attention!Sempione tunnel

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