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2D numerical analysis of the seismic response of a karst rock mass: importance of underground caves and geostructural details Cover

2D numerical analysis of the seismic response of a karst rock mass: importance of underground caves and geostructural details

Studia Geotechnica et Mechanica
Volume 42 (2020): Issue 1 (April 2020)
By: Bruno Giovanni and  Carucci Fabrizio  
Open Access
|Mar 2020

Figures & Tables

Figure 1

Amplification factor (a) and spectral ratio (b) values above an underground cave inside a homogeneous and isotropic subsoil crossed by Vs waves, based on the parametric variation of the cave diameter (from [7] modified).
Amplification factor (a) and spectral ratio (b) values above an underground cave inside a homogeneous and isotropic subsoil crossed by Vs waves, based on the parametric variation of the cave diameter (from [7] modified).

Figure 2

Geological map of the territory in which the study area is located (from [16] modified).
Geological map of the territory in which the study area is located (from [16] modified).

Figure 3

Electric tomography n.1: resistivity values and projection of cores drilling S1 and S2 (from Technical Department of the municipality of Turi (BA) – modified).
Electric tomography n.1: resistivity values and projection of cores drilling S1 and S2 (from Technical Department of the municipality of Turi (BA) – modified).

Figure 4

Location of geological surveys and section of the geological and geomechanical model.
Location of geological surveys and section of the geological and geomechanical model.

Figure 5

Stratigraphy obtained from the core destruction borings.
Stratigraphy obtained from the core destruction borings.

Figure 6

Stratigraphies obtained from rotation drills with continuous coring, RQD trend along verticals and depth of the rock samples for geotechnical laboratory tests.
Stratigraphies obtained from rotation drills with continuous coring, RQD trend along verticals and depth of the rock samples for geotechnical laboratory tests.

Figure 7

Geomechanical model section used for the LSR evaluation; the upper karst cave has a height of L= 4.00 m and a width of D= 3.00 m.
Geomechanical model section used for the LSR evaluation; the upper karst cave has a height of L= 4.00 m and a width of D= 3.00 m.

Figure 8

Acceleration–period spectrums of the combinations no 8 and accelerogram/velocity time–history of the two earthquakes chosen (red circled) for the LSR analysis: X-component (a) and Z-component (b).
Acceleration–period spectrums of the combinations no 8 and accelerogram/velocity time–history of the two earthquakes chosen (red circled) for the LSR analysis: X-component (a) and Z-component (b).

Figure 9

Trend of displacements in the Y-direction (left) and plastic zones (right) in the geomechanical model with two overlapping underground caves: in static (above) and dynamic (below) conditions.
Trend of displacements in the Y-direction (left) and plastic zones (right) in the geomechanical model with two overlapping underground caves: in static (above) and dynamic (below) conditions.

Figure 10

LSR amplification/deamplification, as X-accelerations FA, in each of the control points at the ground level of case study model.
LSR amplification/deamplification, as X-accelerations FA, in each of the control points at the ground level of case study model.

Mechanical parameters of rocks and discontinuities (based on laboratory tests) of the geomechanical model_

VEGETAL SOIL AND “RED SOILS”
r (Kg/m3)E (Pa)vK (Pa)G (Pa)φ (grade)c (Pa)σt (Pa)
183520 · 1060.2513 · 1068 · 10625500000

Main data of the seismic events extracted from the database for the X-acceleration (above) and the Z-acceleration (below)_

Waveform IDEarthquake IDStation IDEarthquake NameDateMwFault MechanismEpicentral Distance (km)EC8 Site class
286146ST92Campano Lucano11/23/19806.9normal78A

Geomechanical classification of the altered and the compact calcareous rock mass_

ParametersValuesRMR'76GSI
Rock massAltered and karstic limestoneR1 (compressive strength)749φb = 35°cb = 0.15 MPa49
R2 (RQD)6
R3 (spacing of discontinuities)15
R4 (joint conditions)11
R5 (water conditions)10
Rock massCompact and not altered limestoneR1 (compressive strength)762φb = 40°cb = 0.20 MPa62
R2 (RQD)13
R3 (spacing of discontinuities)15
R4 (joint conditions)17
R5 (water conditions)10

Relevant input data for the accelerograms search with the REXEL 3_5 software_

Target Spectrumag (g)Geographic Coordinates ED50Site classTopographic categoryNominal LifeFunctional TypeLimit StateMR (km)
Lat. NLong. E
Italian Building Code 20080.07417.022240.9185AT150 yearsIIISLV6–70–100

FA, calculated in the absence and presence of karst caves, as ratio of the maximum X-acceleration and ratio of the Fourier’s amplitudes spectrum in three ranges of frequency_

Output Point IDAXmax.TopAXmax.Bottom{{A_{Xmax.Top} } \over {A_{Xmax.Bottom} }}∫0.2Hz2.0HzFourier Ampl.Top (f)∫0.2Hz2.0HzFourier Ampl.Bottom (f){{\int_{0.2Hz}^{2.0Hz} {Fourier\,Ampl.Top\,(f)} } \over {\int_{0.2Hz}^{2.0Hz} {Fourier\,Ampl.Bottom\,(f)} }}∫2.0Hz3.8HzFourier Ampl.Top (f)∫2.0Hz3.8HzFourier Ampl.Bottom (f){{\int_{2.0Hz}^{3.8Hz} {Fourier\,Ampl.Top\,(f)} } \over {\int_{2.0Hz}^{3.8Hz} {Fourier\,Ampl.Bottom\,(f)} }}∫3.8Hz5.6HzFourier Ampl.Top (f)∫3.8Hz5.6HzFourier Ampl.Bottom (f){{\int_{3.8Hz}^{5.6Hz} {Fourier\,Ampl.Top\,(f)} } \over {\int_{3.8Hz}^{5.6Hz} {Fourier\,Ampl.Bottom\,(f)} }}
Without cavesWith cavesWithout cavesWith cavesWithout cavesWith cavesWithout cavesWith caves
10.0600.0330.0670.0390.0720.0330.0650.032
20.0840.2210.1200.0430.1220.0970.1180.070
30.0120.1290.1610.0900.1760.0480.1710.040
40.7300.0360.1610.0900.1760.0480.1710.040
50.0480.0090.0980.0710.1230.0400.1190.053
60.1690.0570.0790.0350.1130.0210.1420.024
70.0930.0240.0790.0350.1130.0210.1420.024
81.6720.8990.2590.2720.2740.1720.2360.342
90.1200.0190.0930.0580.1430.0520.0840.113
DOI: https://doi.org/10.2478/sgem-2019-0028 | Journal eISSN: 2083-831X | Journal ISSN: 0137-6365
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Language: English
Page range: 61 - 73
Submitted on: Apr 12, 2019
Accepted on: Aug 21, 2019
Published on: Mar 19, 2020
Published by: Wroclaw University of Science and Technology
In partnership with: Paradigm Publishing Services
Publication frequency: 4 issues per year
Keywords:
2D local seismic response analysis,
rock mass,
karstic underground caves
Related subjects:
Geosciences,
Geosciences, other,
Materials sciences,
Composites,
Porous materials,
Physics,
Mechanics and fluid dynamics

© 2020 Bruno Giovanni, Carucci Fabrizio, published by Wroclaw University of Science and Technology
This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 License.

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