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USE OF TERRESTRIAL DIGITAL PHOTOGRAMMETRY IN THE
CLASSIFICATION OF FRACTURED ROCK MASS
Saulo Nunes Sant’Anna1; Pedro Manuel
Alameda-Hernández2; Luís de Almeida Prado
Bacellar3
1Master in geotechnics, NUGEO/Escola de Minas, UFOP, Ouro
Preto/MG, Brazil.
ORCID: https://orcid.org/0000-0002-6134-2501
Email: [email protected]
2Dr, Urban Engineering Department/School of Mines/Federal
University of Ouro Preto, Ouro Preto/MG, Brazil.
ORCID: https://orcid.org/0000-0003-1830-1912
Email: [email protected]
3Ph.D, NUGEO/Escola de Minas/UFOP, Ouro Preto/MG, Brazil.
ORCID: https://orcid.org/0000-0003-1670-9471
Email: [email protected]
Abstract
The present work aims to discuss rock mass data acquisition
methods. The study area is a deactivated gravel quarry, located
in Belo Horizonte (Minas Gerais state, Brazil) where migmatized
gneisses outcrop, with frequent rockfalls. The acquisition
methods employed were the traditional slope mapping and
remote method with digital terrestrial photogrammetry. The
Slope Mass Rating (SMR) classification was applied. The results
showed differences in the structures detection ranges, where the
photogrammetry was more complete with more discontinuity
data than traditional mapping, but with the exception of oblique
structures. This deficiency is explained by the fact that the study
slope is subvertical, without hollows and protrusions, which
often allow the detection of discontinuity traces rather than
planes. However, even in these cases, photogrammetry proved to
be important as it allows the characterization of the entire slope,
which is impossible by the traditional method. Low SMR values
for planar a wedge failures coincides with the rockfall
observation, in spite of overall stability.
Keywords: Photogrammetry; Rock Mass Classification; SMR.
USO DA FOTOGRAMETRIA DIGITAL TERRESTRE NA
CLASSIFICAÇÃO DE MACIÇOS ROCHOSOS
FRATURADOS
Resumo
O presente trabalho visa discutir o uso de métodos de aquisição
de dados geotécnicos de maciços rochosos. A área de estudo é
uma pedreira de brita desativada, localizada na cidade de Belo
Horizonte (Minas Gerais, Brasil), onde afloram gnaisses
migmatizados, com constante queda de blocos. Os métodos de
aquisição empregados foram o tradicional mapeamento de talude
e o levantamento remoto por fotogrametria digital terrestre. A
classificação de maciços Slope Mass Rating (SMR) foi aplicada.
Os resultados evidenciaram diferenças nos ranges de detecção de
estruturas e a fotogrametria se mostrou mais completa, com mais
dados de descontinuidades do que o mapeamento tradicional,
com exceção das estruturas oblíquas ao talude. Esta deficiência
se explica pelo fato do talude estudado ser subvertical, sem
reentrâncias e saliências, que permitem muitas vezes a detecção
dos traços de descontinuidades e não dos planos. Contudo,
mesmo nestes casos, a fotogrametria mostrou-se importante, por
permitir a caracterização de todo talude, impossível pelo método
tradicional. A classificação SMR mostrou baixos valores,
indicando instabilidade por rupturas planares e em cunha do
maciço em alguns pontos, o que coincide com as frequentes
quedas de blocos.
Palavras-chave: Fotogrametria; Classificação de Maciços
Rochosos; SMR.
UTILIZACIÓN DE FOTOGRAMETRÍA DIGITAL
TERRESTRE EN LA CLASIFICACIÓN DE MACIZOS
ROCOSOS FRACTURADOS.
Resumen
El presente trabajo discute el empleo de métodos de adquisición
remota de datos geotécnicos de macizos rocosos. El área de
estudio es una cantera de árido localizada en la región Este de la
ciudad de Belo Horizonte, Minas Gerais (Brasil), con
afloramiento de gneises migmatizados e desprendimientos
frecuentes. Los métodos empleados fueron la adquisición de
datos tradicional de contacto, y la remota con fotogrametría
digital terrestre y foto aérea; con el objetivo de la caracterización
de discontinuidades e identificación de estructuras lineares
ISSN: 2447-3359
REVISTA DE GEOCIÊNCIAS DO NORDESTE
Northeast Geosciences Journal
v. 7, nº 2 (2021)
https://doi.org/10.21680/2447-3359.2021v7n1ID23403
Sant’Anna, S. N.; Alameda-Hernández, P. M.; Bacellar, L. A. P., Rev. Geociênc. Nordeste, Caicó, v.7, n.2, (Jul-Dez) p.111-122, 2021 112
_________________________________________________________________________________________________
por fotointerpretación . Después de la validación, los datos
fueron introducidos en la clasificación geomecánica Slope Mass
Rating (SMR). Los resultados mostraron la mayor capacidad de
la fotogrametria para obtener datos, con la salvedad de las
estructuras oblicuas al talud. Esta deficiencia se explica por el
hecho de que el talud estudiado es subvertical y sin entrantes ni
salientes que permiten muchas veces la detección de
discontinuidades a través de los trazos. De todos modos, incluso
en estos casos la fotogrametría se mostró útil, por permitir la
caracterización de todo el talud, imposible con el método
tradicional de contacto. La clasificación SMR mostró valores
bajos a ruptura planar y en cuña, coincidiendo con los
desprendimientos puntuales observados.
Palabras-clave: Fotogrametría; Classificación de massas
rochosas; SMR.
1. INTRODUÇÃO
Correct rock slope stability analysis demands a thoughtful
discontinuity characterization, which is based on the attributes
proposed by ISRM (1978): orientation, persistence, spacing,
opening, wall roughness and weathering degree. The most
common data acquisition process is the traditional, with contact,
and considerably time-consuming. Furthermore, the contact need
leads to insecurity in some outcrops.
In the last few decades, some contactless techniques have
appeared, eliminating some operational drawbacks of the
traditional procedures. Among these new techniques, terrestrial
digital photogrammetry (TDP) (ALAMEDA-HERNÁNDEZ et
al. 2017, BUYER et al., 2016, TANNANT 2015, THOENI et al.,
2014, HANEBERG 2008, HANEBERG., 2006) is especially
interesting due to the rapidness in field and low cost, especially
when compared with RADAR (Radio Detection and Ranging) or
LiDAR (Light Detection and Ranging).
Birch (2006) defines TDP as the 3D data creation from two
or more 2D images, where the same physical point is shown in
more than one 2D image. Consequently, image quality is crucial
for good photogrammetric processing, with well-defined point
clouds. Variations in the illumination between images can be
troublesome for 3D images definition. Furthermore, in some
slopes, TDP might present limitations compared to the traditional
procedure in some outcropping geological structure detection.
This issue depends on the slope face and geological structure
relative direction.
Some authors applied TDP for rock slope classification
through Romana (1985) Slope Mass Rating (RMR)
(ALAMEDA-HERNÁNDEZ et al., 2017 and BUYER &
SCHUBERT, 2016). TDP is mainly applied to acquire
discontinuity orientations, spacings and persistences
(ALAMEDA-HERNÁNDEZ et al. 2017, TANNANT 2015,
HANEBERG 2008). The other parameters (aperture, wall
roughness, weathering and moisture) must be defined with other
procedures, generally the traditional. Those parameters complete
the Rock Mass Rating (RMR) (BIENIAWSKI, 1989).
Nowadays, TDP is mainly applied in big companies.
However, the operation security, rapidness and low cost make it
very appealing for other institution such as Brazilian local
councils. They could easily establish hazard zonification routines
regarding rock slopes. This policy could be of great help in many
settlements of the region where this study was developed.
Nevertheless, the traditional contact methods and the thoughtful
geological analysis must not be abandoned for the correct
geotechnical database maintenance.
On the other hand, abandoned querries, like the one shown in
this paper, require data validation regarding the discontinuity
origin. These quarries suffered blasting, which might cause rock
fractures that could be confused with natural discontinuities. This
identification is crucial for a correct slope stability analysis,
especially regarding deep failures.
This paper applies TDP in an old quarry with sub-vertical
slopes where low foliated highly fractured migmatitic gneisses
outcrops. TDP data validation was performed by comparing data
obtained through the traditional contact method and regional
aerial photo interpretation. The validated data were applied for
RMR and SMR classifications.
2. AREA OF STUDY
The area of study belongs to Belo Horizonte City, the capital
of the Minas Gerais Brazilian state (Figure 1). It consists of a
quarry, deactivated thirty years ago, in the Mariano de Abreu
neighbourhood. Currently, this place serves as a local welfare
facility.
The quarry area is approximately 12850 m2, with slopes
reaching 30 m high. A broad illegal settlement spreads over the
top of the quarry slope (Figure 2), some buildings are at high risk.
The slope toe is restricted due to the detected rockfall risk.
2.1. Geology
The study area is inserted in the Belo Horizonte Metamorphic
Complex, which constitutes the basement rocks of the Iron
Quadrangle (QF).
Locally, the area is characterized by migmatized gneisses,
located near a north-south thrust fault that overlaid supracrustal
rocks of the QF on an Archean basement of the Belo Horizonte
Complex (DORR, 1969).
Sant’Anna, S. N.; Alameda-Hernández, P. M.; Bacellar, L. A. P., Rev. Geociênc. Nordeste, Caicó, v.7, n.2, (Jul-Dez) p.111-122, 2021 113
_________________________________________________________________________________________________
Figure 1 - Study area localization and geological map, modified from Parizzi (2004). Universal transverse Mercator Projection; datum:
SIRGAS 2000 Zone 23S.
Figure 2 - Quarry partial view, modified from Sant’Anna (2019).
The gneisses of the Belo Horizonte Complex present a
polycyclic structural evolution, with several tectonic events of
different regimes, which can explain the great variation of
orientations of discontinuities mapped in this unit (NOCE et al,
1994).
Because they are rocks with few geotechnical problems in
relation to the supracrustals in the region, there are few works of
geotechnical classification or kinematic analysis concerning the
gneisses of the Belo Horizonte Complex. Some published works
(REIS JR., 2016; PARIZZI, 2004) classify these as RMR good
quality rock masses and identify four discontinuity set in the
surroundings of this paper area of study.
3. MATERIALS AND METHODS
3.1. Aerial photography interpretation
Aerial photography from the 50s at a scale of 1:30.000 was
analyzed. By the time, the area was sparsely inhabited yet. At this
stage of the research, the lineations identified from aerial
photogrammetry were compared with the rock mass outcropping
fractures to identify the blast-induced fractures.
3.2. Geotechnical data acquisition
For operational reasons, there were two data acquisition
stages. The first was the traditional contact method dividing the
slope into homogeneous areas around a point. The second was
the images acquisition for TDP application on each one of the
homogeneous areas. To compare, the central points of the
sampling windows of the homogeneous areas were the same for
the TDP and the traditional procedures, named in figure 3 as
"points" and "sections". There were six points in all the quarry.
The orientation data of all the accessible discontinuities were
acquired with a Brunton Clar Transit compass; an average of 50
discontinuities per point. Persistence and spacing data were
obtained with a metric tape, aperture with a millimetre ruler, and
Sant’Anna, S. N.; Alameda-Hernández, P. M.; Bacellar, L. A. P., Rev. Geociênc. Nordeste, Caicó, v.7, n.2, (Jul-Dez) p.111-122, 2021 114
_________________________________________________________________________________________________
strength with an Estwing geological hammer through the ISRM
(1978) suggested method. Weathering degree, infill presence and
wall roughness were classified according to the RMR method.
Moisture measurement was confusing because of the time
variability; some field sessions registered no water presence, and
other, continuous water leakage. This leakage was not only due
to rain but also to the human settlement at the top of the slope,
probably septic tanks according to the smell. RQD was assessed
through scanlines according to Priest and Hudson (1976)
procedure.
The camera positions for TDP image acquisition were close
to the slope in Section 2 and farther, around 50m, for section 1
and 3. Section 3 consists of 18 photographs that needed to be
divided into two groups due to computational equipment
limitations. Each one of the two groups gave a 3D model, or
"mosaic". Hence, the TDP data are divided into mosaic 1, the
southern part of the slope belonging to point 4, and mosaic 2, the
northern part of the slope belonging to point 5.
Figure 3 - Localization of the photogrammetrical sections and
traditionally surveyed points. Base map from Google Earth, 15
of May 2018, with geographical coordinates, modified from
Sant’Anna (2019).
The procedure followed is suggested in Alameda-Hernández
et al. (2017) and applied by Lacerda (2019). Consequently, the
distance measurements were used only for correct overlapping
but not for georeferencing. This rapid method, with no need of
control points, was proved in this paper. The materials used were
a tripod with triple bubble level, digital single-lens reflex camera
with 24mm and 50mm focal distance lenses, compass for
orienting the camera normal to the slope face and the software
Sirovision 6.2.0.13 (developed by CSIRO in Melbourne-VIC,
Australia).
In sections 1 and 3, the photographs taken had different
inclinations; consequently, some mosaics include the slope from
toe to top.
The mosaics were defined manually with the software
Sirovision merging several 3D images. A correct mosaic shows
a dense point cloud where the discontinuities shall be identified
visually. In the mosaics (Figure 4), discontinuities were
recognized through planes, when possible, and through traces
otherwise.
Figure 4 - Mosaic generated in section 2, with the planes and
traces identified; performed on software Sirovision. Modified
from Sant’Anna (2019).
After the planar structure identification, they were clustered
in sets to determine spacings and persistences further. The
images were not georeferenced, and the mosaics were eve out of
scale; thus, a reference, such as metric tape, was used for distance
values assessments. The orientations were assessed with the aid
of the compass measurements in field. The data obtained with
this procedure in the software Sirovision was exported to Dips 7
(developed by Rocscience in Toronto-ON, Canada) for kinematic
analyses for planar, wedge and toppling failures.
3.3. Rock slope RMR and SMR assessment
The data obtained were used for classifying the rock slope
homogeneous areas with RMR and SMR. RMR is very popular;
the procedures can be consulted on Bieniawski (1989) and shall
not be explained in this paper. This work only applied the basic
RMR value, the one without the relative orientations
consideration. Orientations shall be considered in the SMR, very
appropriated for sloes. The SMR is obtained by adjusting the
basic RMR with the orientation values between the slope face
and the orientation of the sets embedded in the indexes F1, F2,
F3 and F4.
The first step was to define the sets from the orientations
acquired through the traditional method and TDP.
The sets definition was performed with stereographic
projection on software DIPS 7.0 by plotting the poles; TDP data
Sant’Anna, S. N.; Alameda-Hernández, P. M.; Bacellar, L. A. P., Rev. Geociênc. Nordeste, Caicó, v.7, n.2, (Jul-Dez) p.111-122, 2021 115
_________________________________________________________________________________________________
had a previous analysis performed in Sirovision. The results were
added to the basic RMR calculi.
F1, F2 and F3 were calculated for SMR assessment for planar,
wedge and flexural toppling failure, respectively. Regular
blasting gives F4 equals zero. F1 and F2 were assessed with
equations 1 and 2 (ROMANA, 1985); F2=1 for toppling failure.
F3 was assessed with 3 (planar failure), 4 (wedge failure) and 5
(toppling failure) (TOMÁS et al, 2007):
F1= (1 - sen αj - αs)²
(1)
Where:
αj: set dip direction for planar failure and sets intersection
trend for wedge failure
αs: slope face dip direction ‘
F2 = tan2 βj
(2)
Where:
βj - main discontinuity set dip (for planar and toppling
failure)
𝐹3 = −30 +1
3arctan(𝛽𝑗 −𝛽𝑠)
(3)
Where:
ΒS - slope face angle
𝐹3 = −30 +1
3arctan(𝛽𝑖 −𝛽𝑠)
(4)
Where:
βi - main sets intersection plunge for wedge failure
𝐹3 = −13 +1
7arctan(𝛽𝑗+𝛽𝑠 − 120)
(5)
4. RESULTS AND DISCUSSION
Drainage lineations identified aerial photographs of the
quarry surroundings (Figure 5) show wide orientation variability,
with the predomination of the E-W and NNW-SSE, there is also
a NE-SW and NNE-SSW trend.
At the same time, the rock mass characterization in the quarry
showed high dispersion on the discontinuity orientation values.
For simplicity and operativeness, sets were defined by observing
all the data obtained in the quarry. Afterwards, those sets were
compared with the structural data on each point and section
separately. Hence, the 301 orientation measurements showed
five discontinuity sets (Figure 6 and Table 1). The orientation
data obtained from TDP consisted of 370 measurements, and it
showed three discontinuity sets (Figure 7 and Table2).
Figure 5 - Drainage delineation identified on aerial photographs of the surroundings of the Mariano de Abreu Quarry. Modified from
Sant’Anna (2019).
Sant’Anna, S. N.; Alameda-Hernández, P. M.; Bacellar, L. A. P., Rev. Geociênc. Nordeste, Caicó, v.7, n.2, (Jul-Dez) p.111-122, 2021 116
_________________________________________________________________________________________________
Figure 6 - Schmidt projection of the 301 discontinuities surveyed
with the traditional contact method for clustering: J1 with higher
pole concentration than the rest of the sets. Modified from
Sant’Anna (2019).
Figure 7 - Schmidt projection of the 370 discontinuities surveyed
with TDP for clustering: F1 with higher pole concentration than
the rest of the sets. Modified from Sant’Anna (2019).
Table 1 – Slope discontinuity sets, according to the traditional
contact acquisition procedure. (SANT’ANNA, 2019).
Set Dip (o) Dip Direction (°)
J1 11 089
J2 42 100
J3 69 280
J4 78 003
J5 66 051
Locally concentrated orientation measurements showed new
discontinuity sets in specific rock mass localizations. Hence, J6
and J7 sets are more visible on points 4 and 5. TDP shows a
similar situation in Section 3 with F4 and F5 sets.
Schmidt diagrams analyses are shown in Figure 8 and Table
3 for Point 1 and Section 2; Figure 9 and Table 4 for Point 2 and
Section 1; Figure 10 and Table 5 for Point 4 and Section 3
(Mosaic 1); and Figure 11 and Table 6 for Point 5 and section 3
(Mosaic 2).
Table 2 - Slope discontinuity sets, according to the TDP
acquisition procedure (SANT’ANNA, 2019).
Set Dip (°) Dip Direction (°)
F1 80 088
F2 02 143
F3 50 120
A wide variability on the discontinuity orientations is
manifest. Being a quarry, a verification of the origin of the rock
fractures is necessary because a fracture can be natural or blast-
induced. This analysis was performed through drainage
lineations and some previous clustering performed in the same
rock massif (REIS JR, 2016; PARIZZI, 2004).
Figure 12 shows a rosette diagram with the orientation
measurements showing set J1, subhorizontal, considered a stress
relief set. This Figure shows that all the discontinuity sets found
in this paper, but J6 were already mapped or correspond to
regional delineations
Sant’Anna, S. N.; Alameda-Hernández, P. M.; Bacellar, L. A. P., Rev. Geociênc. Nordeste, Caicó, v.7, n.2, (Jul-Dez) p.111-122, 2021 117
_________________________________________________________________________________________________
Figure 8 - Discontinuity poles projection for: a) point 1 and b)
section 2. Modified from Sant’Anna (2019).
Table 3 – Discontinity sets in Point 1 and TDP Section 2.
(SANT’ANNA,2019).
Point 1 Section 2
Set Dip
(°)
Dip
Direction
(°)
Set Dip
(°)
Dip
Direction
(º)
J1 01 095 F1
72 096
J2 45 090 F2
01 243
Figure 9 - Discontinuity poles projection for: a) point 2 and b)
section 1. Modified from Sant’Anna (2019).
Table 4 - Discontinity sets in Point 2 and TDP Section 1. (SANT’ANNA, 2019).
Point 2 Section 1
Set Dip
(°)
Dip
Direction
(°)
Set Dip (°)
Dip
Direction
(°)
J2 33 103 F1 72
096
J3 50 265
J5 55 051
Sant’Anna, S. N.; Alameda-Hernández, P. M.; Bacellar, L. A. P., Rev. Geociênc. Nordeste, Caicó, v.7, n.2, (Jul-Dez) p.111-122, 2021 118
_________________________________________________________________________________________________
Figure 10 - Discontinuity poles projection for: a) point 4 and b)
section 3 (mosaic 1). Modified from Sant’Anna (2019).
Table 5 - Discontinity sets in Point 4 and TDP Section 3 – Mosaic 1. (SANT’ANNA, 2019).
Point 4 Section 3 – Mosaic 1
Set Dip
(°)
Dip
Direction
(°)
Set Dip
(°)
Dip
Direction
(°)
J1 06 086 F1 80 095
J2 42 101 F2 03 165
J4 82 357 F4 48 282
J6 36 213
Figure 11 - Discontinuity poles projection for: a) point 5 and b)
section 3 (mosaic 2). Modified from Sant’Anna (2019).
Table 6 - Discontinity sets in Point 5 and TDP Section 3 –
Mosaic 2 (SANT’ANNA, 2019).
Point 5 Section 3 – Mosaic 2
Set Dip (°)
Dip
Direction
(°)
Set Dip (°)
Dip
Direction
(°)
J3 69 281 F1 80 095
J7 67 099 F5 67 260
F4 32 103
.
Sant’Anna, S. N.; Alameda-Hernández, P. M.; Bacellar, L. A. P., Rev. Geociênc. Nordeste, Caicó, v.7, n.2, (Jul-Dez) p.111-122, 2021 119
_________________________________________________________________________________________________
Figure 12 - Comparison between sets and drainage delineations directions. J: discontinuity sets surveyed manually in this work; D:
Drainage delineations defined in this work RE: discontinuity sets from Reis Jr (2016); PZ: discontinuity sets from Parizzi (2004).
Modified from Sant’Anna (2019).
Regarding the six sets identified in the aerial photographs, it
can be observed a main N-S trend, almost the same direction of
most of the quarry slope face. Not many outcropping oblique
discontinuities in the slope face were detected with TDP. The
intact rock strength, high fracture degree of the rock mass and the
quarry operation gave almost vertical slopes with small and
geometrically well-defined irregularities. This geometrical
peculiarity and the relative orientation between the slope face and
these delineations made it difficult to identify these structures
with TDP; trace recognition was needed. This might be seen as a
TDP limitation.
Figure 13 shows the correlation between the sets identified
with the TDP data and with the traditional contact method. Those
sets show parallelism with the slope face.
Regarding discontinuity conditions, traditional sampling
showed some common characteristics for all the quarry. For
instance, all the discontinuities close to the slope toe were
unweathered, rough and planar, and closed or with unfrequent
apertures, always below 5 mm. RQD range goes from 60 to 85 in
all the quarry.
Water presence on the rock mass is very variable; some days,
the discontinuities were dry, but there was a continuous leakage
in other moments, even on the dry period. The origin of this water
is probably in the houses at the top of the slope, as shown in Fig.
2. Consequently, the RMR hydrogeologic parameter was set to
7.
Regarding discontinuity geometry, subhorizontal
discontinuity sets, J1 and F2, showed high persistence. The other
discontinuities showed low trace length, mainly below one meter.
Most spacing values were centimetric, but some values were
above one meter (Figure 14).
All those parameter values acquired in field were applied for
the basic RMR assessment, for points and sections. Results
confirm a good quality rock mass (Table 7). Those data were used for SMR assessment, with the
geometric characteristics regarding sets and slope face. The slope
face angle at points 1, 2, 4 and 5 ranged from 80 to 90 degrees,
East dip direction. At points 3 and 6, the slope face was not so
vertical, and the dip direction is West and South. On the latter,
no TDP application was possible due to the dense vegetation and
other obstacles.
Sant’Anna, S. N.; Alameda-Hernández, P. M.; Bacellar, L. A. P., Rev. Geociênc. Nordeste, Caicó, v.7, n.2, (Jul-Dez) p.111-122, 2021 120
_________________________________________________________________________________________________
Figure 13 - Pole projection comparison between sets defined with
TDP data (F) and with the traditional contact survey (J). Modified
from Sant’Anna (2019).
Table 7 – Basic RMR values on mapped points and TDP sections.
(SANT’ANNA,2019).
Position RMR
(BÁSIC)
Local RMR
(BÁSIC)
Point 1 75 Section 1 75
Point 2 72 Section 2 73
Point 4 68 Section 3 – Mosaic 1 78
Point 5 76 Section 3 – Mosaic 2 71
The kinematic analysis performed on Dips showed
compatibility with some kinds of failure, especially wedge and
planar. In some cases, SMR took very low values (Table 8),
mainly due to the F3 value, which regards the relationship
between slope angle and set dip, or intersection plunge. The
parallelism between sets and slope face also gives low SMR
values.
Hence, SMR values, even below 20, suggest failures;
however, the only observed failures are the frequent rockfalls,
with the evidence of the blocks at the toe and the scars on the
slope face. The scar shapes show planar-like and wedge-like
failures; in this paper, low SMR values indicate rockfall.
Figure 14 - Sub-horizontal discontinuities persistence overview
in set 1 (several meters); and spacing overview on set J5 (several
centimeters). Modified from Sant’Anna (2019).
Table 8 – SMR values for the failure types with kinematic
compatibility. (P: planar; W: Wedge; T: Toppling).
(SANT’ANNA,2019).
Position RMR SMR Type Position RMR SMR Type
Point 1 75 24 P Section
1
72 36 P
75 68 W 72 12 W
Point 2 73 35 P Section
2
77 72 P
73 48 W 77 70 T
Point 4
68 46 P Section
3
Mosaic 1
72 65 P
68 39 W 72 55 T
Point 5 76 35 P Section
3
Mosaic 2
75 61 P
75 58 W
5. CONCLUSIONS
The studied rock mass complexity, with an enormous
structure variability regarding orientation and persistence meant
serious difficulty on the discontinuity clustering task. The reason
for this variability is the tectonic environment, with polycyclic
structural evolution and the proximity of a thrust fault, and the old
blasting in the quarry.
The comparison between the discontinuity sets found with
TDP, with the traditional contact method, with the aerial
photography interpretation, and those from previous publications,
show that those sets have a tectonic origin.
TDP showed difficulties in identifying the discontinuities
outcropping oblique to the slope face. Furthermore,
discontinuities outcropping with a small plane were difficult to
identify with TDP; this is frequent in this rock mass, with strong
intact rock but highly fractured. For other lithologies, with
foliation or bedding planes, this issue would be the opposite, and
TDP would be especially appropriate.
Regarding the rock mass classification, SMR value pointed to
high failure probability, and it is valid in this situation for
rockfalls.
6. REFERENCES
ALAMEDA-HENÁNDEZ. P.; HAMDOUNI. R. E.;
IRIGARAY, C. CHACON, J.(2017). Weak foliated rock
slope stability analysis with ultra-close-range terrestrial
Sant’Anna, S. N.; Alameda-Hernández, P. M.; Bacellar, L. A. P., Rev. Geociênc. Nordeste, Caicó, v.7, n.2, (Jul-Dez) p.111-122, 2021 121
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Received in: 23/11/2020
Accepted for publication in: 04/07/2021
Sant’Anna, S. N.; Alameda-Hernández, P. M.; Bacellar, L. A. P., Rev. Geociênc. Nordeste, Caicó, v.7, n.2, (Jul-Dez) p.111-122, 2021 122
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