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

Bruno Giovanni; Carucci Fabrizio

Open Access

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

Bruno Giovanni

and

Carucci Fabrizio

| Mar 19, 2020

Studia Geotechnica et Mechanica

Volume 42 (2020): Issue 1 (April 2020)

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Cite

Published Online: Mar 19, 2020

Page range: 61 - 73

Received: Apr 12, 2019

Accepted: Aug 21, 2019

DOI: https://doi.org/10.2478/sgem-2019-0028

Keywords
2D local seismic response analysis, rock mass, karstic underground caves

© 2020 Bruno Giovanni et al., published by Sciendo

This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 License.

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).

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

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

Stratigraphy obtained from the core destruction borings.

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

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.

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).

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.

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)	v	K (Pa)	G (Pa)	φ (grade)	c (Pa)	σ_t (Pa)
1835	20 · 10⁶	0.25	13 · 10⁶	8 · 10⁶	25	50000	0

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

Waveform ID	Earthquake ID	Station ID	Earthquake Name	Date	Mw	Fault Mechanism	Epicentral Distance (km)	EC8 Site class
286	146	ST92	Campano Lucano	11/23/1980	6.9	normal	78	A

Geomechanical classification of the altered and the compact calcareous rock mass.

	Parameters	Values	RMR'76		GSI
Rock massAltered and karstic limestone	R₁ (compressive strength)	7	49	φ_b = 35°c_b = 0.15 MPa	49
	R₂ (RQD)	6
	R₃ (spacing of discontinuities)	15
	R₄ (joint conditions)	11
	R₅ (water conditions)	10
Rock massCompact and not altered limestone	R₁ (compressive strength)	7	62	φ_b = 40°c_b = 0.20 MPa	62
	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 Spectrum	a_g (g)	Geographic Coordinates ED50		Site class	Topographic category	Nominal Life	Functional Type	Limit State	M	R (km)

		Lat. N	Long. E
Italian Building Code 2008	0.074	17.0222	40.9185	A	T1	50 years	III	SLV	6–7	0–100

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 ID	$\frac{A_{Xmax . Top}}{A_{Xmax . Bottom}}$ {{A_{Xmax.Top} } \over {A_{Xmax.Bottom} }}		$\frac{\int_{0.2 Hz}^{2.0 Hz} Fourier Ampl . Top (f)}{\int_{0.2 Hz}^{2.0 Hz} Fourier Ampl . Bottom (f)}$ {{\int_{0.2Hz}^{2.0Hz} {Fourier\,Ampl.Top\,(f)} } \over {\int_{0.2Hz}^{2.0Hz} {Fourier\,Ampl.Bottom\,(f)} }}		$\frac{\int_{2.0 Hz}^{3.8 Hz} Fourier Ampl . Top (f)}{\int_{2.0 Hz}^{3.8 Hz} Fourier Ampl . Bottom (f)}$ {{\int_{2.0Hz}^{3.8Hz} {Fourier\,Ampl.Top\,(f)} } \over {\int_{2.0Hz}^{3.8Hz} {Fourier\,Ampl.Bottom\,(f)} }}		$\frac{\int_{3.8 Hz}^{5.6 Hz} Fourier Ampl . Top (f)}{\int_{3.8 Hz}^{5.6 Hz} Fourier Ampl . Bottom (f)}$ {{\int_{3.8Hz}^{5.6Hz} {Fourier\,Ampl.Top\,(f)} } \over {\int_{3.8Hz}^{5.6Hz} {Fourier\,Ampl.Bottom\,(f)} }}

	Without caves	With caves	Without caves	With caves	Without caves	With caves	Without caves	With caves
1	0.060	0.033	0.067	0.039	0.072	0.033	0.065	0.032
2	0.084	0.221	0.120	0.043	0.122	0.097	0.118	0.070
3	0.012	0.129	0.161	0.090	0.176	0.048	0.171	0.040
4	0.730	0.036	0.161	0.090	0.176	0.048	0.171	0.040
5	0.048	0.009	0.098	0.071	0.123	0.040	0.119	0.053
6	0.169	0.057	0.079	0.035	0.113	0.021	0.142	0.024
7	0.093	0.024	0.079	0.035	0.113	0.021	0.142	0.024
8	1.672	0.899	0.259	0.272	0.274	0.172	0.236	0.342
9	0.120	0.019	0.093	0.058	0.143	0.052	0.084	0.113

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

Article Category: Research Article

Published Online: Mar 19, 2020

Page range: 61 - 73

Received: Apr 12, 2019

Accepted: Aug 21, 2019

DOI: https://doi.org/10.2478/sgem-2019-0028

Keywords
2D local seismic response analysis, rock mass, karstic underground caves

© 2020 Bruno Giovanni et al., published by Sciendo

This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 License.

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

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

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

Geomechanical classification of the altered and the compact calcareous rock mass.

Relevant input data for the accelerograms search with the REXEL 3.5 software.

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.

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

Article Category: Research Article

Published Online: Mar 19, 2020

Page range: 61 - 73

Received: Apr 12, 2019

Accepted: Aug 21, 2019

DOI: https://doi.org/10.2478/sgem-2019-0028

Keywords2D local seismic response analysis, rock mass, karstic underground caves

© 2020 Bruno Giovanni et al., published by Sciendo

This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 License.

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

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

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

Geomechanical classification of the altered and the compact calcareous rock mass.

Relevant input data for the accelerograms search with the REXEL 3.5 software.

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.

Keywords
2D local seismic response analysis, rock mass, karstic underground caves