Open Journal of Geology, 2013, 3, 60-70
doi:10.4236/ojg.2013.32B014 Published Online April 2013 (http://www.scirp.org/journal/ojg)
Engineerin g G e o l o g i ca l a nd Geophysical Assessment of the
2009 Jiwei Shan Rockslide, Wulong, China
Ez Eldin1*, M. A. M., Huiming Tang2,3, Yixian Xu1, Chengren Xiong3, Yunfeng Ge2
1Institute of Geophysics & Geomatics, China University of Geosciences, Wuhan, China
2Faculty of Engineering, China University of Geosciences, Wuhan, China
3Three Gorges Research Center for Geohazard, Ministry of Education, China University of Geosciences, Wuhan, China
Received 2013
ABSTRACT
This study presents the engineering geological and geophysical assessment of the June 5, 2009 Jiwei Shan rockslide,
Wulong, China. Jiwei Shan is a part of Wulong karst terrain lithologically, it’s composed of Quaternary Deposits, Jial-
ingjiang Formation, Maokou, Qixia, Liangshan and Hanjiadian Groups (chronologically from younger to older). The
surface is highly irregular (pinnached), the rocks contain two sets of fractures, networks of convoluted solution channels
and caves and there are large voids filled by soil mantle. It’s a south-north dipping limb of an anticline fold composed
of sedimentary rocks, mainly of limestone of variable composition, mudstone and shale and series of limestone depos-
ited with interbedded mudstone and shale. There are two sets of steeply dipping fractures developed in the Maokou and
upper strata of Qixia Groups; set one trending EW and set two trending nearly SN directions. The study has been con-
ducted by geological fieldwork, geophysical investigation (Vertical Electrical Sounding), petrographical and scanning
electron microscope (SEM) studies and laboratory testing on rock samples collected from Jialingjiang Formation and
Maokou and Qixia Groups. The study of the SEM photomicrographs showed that the microcrack propagations in lime-
stone indicated that the increases in crack length and micropores of limestone are indication to the weathering grade
increase from II (slightly weathered rock) to grade III and IV (moderately and highly weathered, respectively). The
Qixia Group; Middle Layer is highly weathered shale and bituminous interlayer with clear fissility, high porosity, and
gently dipping strata, it represents the sliding surface of the rockslide. It’s comparatively weak and strongly weathered
compared to the overlain EW and SN fractured stratum. Generally, the tectonic of the study area imposes controls on
the rockslide in many ways: created favourable terrain, provided sufficient rockslide prone materials such as highly
weathered limestone and shale, weak rocks, created very steep beds which reduced the stability of the highly fractured
bedrock of the slope.
Keywords: Lithology; Fractures; Weathering; Jiwei Shan Rockslide; Laboratory Tests
1. Introduction
In spite of rockslides and avalanches occurring often in
remote mountainous areas, they still draw a lot of atten-
tions of many researchers, because it is hard to predict
and frequently result in great damage. Most rockslides in
high mountainous areas often evolved into rapid moving
blocks and debris flows, traveling over long distances
and causing serious and sudden destruction of consider-
able large areas [1]. This rockslide is predisposed by tec-
tonic, geological structures, lithology, topography and
rainfall. Earthquake may also play an indirect way. The
movement of rockslide is largely controlled by the to-
pographic condition and slope geometry of the area; in
turn it influenced the mobile behaviour of the rockslide.
Massive rock slope with inclined thick bedding structure
is widely distributed in the southwestern carbonate rock
areas of China and the failure pattern is conventionally
recognized as lateral fall or topples with a short runout
distance. Due to the presence of a front a stable bedrock
towards the north of the moving block as in Jiwei Shan,
the rockmass laterally falls or topples first and subse-
quently accumulates on the lower gentler slope, secon-
dary rockslide will induced by trigger factor such as
rainfall, earthquake, …etc leading to a long distance
runout and accumulation [2] (Figure 1).
[3] simulates the movement process of Jiweishan
rockslide and [4] analyzed the geological conditions and
mining exploitation, the new failure pattern of inclined
thick bedding slope under gravity, karst and mining
process by adopting the PFC3D simulation to of Jiweishan
rockslide. The preliminary investigation carried out by [1]
revealed that, Jiwei Shan rockslide with poor geological
*Corresponding author.

Ez ELDIN ET AL. 61
conditions was mainly induced by the gravitation and the
karst effect and also affected by the previous mining ac-
tivities.
Jiwei Shan rockslide is located in Chongqing, Wulong
County; Tiekuang town; Hongbao village. It’s about 75 km
southwest of Wulong County (Figure 2). Wulong County
greatly suffered from geological disasters. Landslides,
rockfalls, ground subsidences and ground fissures take
place frequently and cause a lot of economic loss and
casualties, furthermore the sustainable development of
society and economy is restrained. In spite of these geo-
logical disasters, there are a few studies has been con-
ducted in the study area. It is situated in subtropical moist
monsoon climate of middle latitude, easily affected by
the season changing. It’s warm and wet with plentiful
rainfalls.
The regional seismic activity in Chongqing and the
surrounding counties it belongs to the medium level, and
the largest earthquake in the history is not more than the
magnitude of six [5]. The shallow epicentre of the earth-
quake lead to strongly feeling of the shake, it caused the
serious economic losses in spite that, the intensity of the
earthquake is not too high. Generally, Chongqing and the
surrounding counties are not in the level of high seismic
activity but it may affected by earthquake coming from
areas of high seismicity such as Sichuan Province.
Jiwei Shan extends along the SN direction, with east-
ern 50 - 150 m cliff. The maximum and minimum height
of Jiwei Shan at elevations of 1,442 and 1,000 m (asl),
respectively, and a height difference of 442 m. It exhibits
an undulating terrain formed by long term denudation
and plantation. At 03:00 PM, 5 June, 2009 Jiwei Shan
rockslide originated as a free fall (toppled) from the east
creek face, followed by second failure on rock mass
originated from a platform extends from south to north
and dip 30˚ towards the north. The slided material trav-
eled over the valley, it further entrained amount of debris
in its path as it was transformed into a rapidly moving
rock-debris flow over the valley, and it continued to
travel for a distance of 2.6 km. The volume of the initial
Figure 1. Showing rockfall and toppling, inclined bedding
and accumulated rockslide, modified after [2].
Figure 2. Location map showing Jiwei Shan, Wulong County,
Chongqing City.
fall has been estimated as 2.5 - 3.0 million cubic meters,
it includes mainly rocks consisted of limestone originated
from an elevation of approximately 1600 m which
“dragged along a great quantity of limestone blocks”.
The release of the rock mass was apparently facilitated
by fractures running parallel and perpendicular to the
slope face. The rockslide closed a local iron ore mine,
buried 87 miners; students and their parents and villagers,
destroyed the water pipes and stoped the electrical ser-
vice, closed the local road and caused the evacuation of
houses that were threatened by another one. The lake that
created at the posterior due to the rockslide, making it
perhaps the most catastrophic single rockslide event re-
corded in the area.
The study area has a complex geologic structure, with
variable lithologic characters, karst environment, undu-
lating mountains, and obvious elevation differences. The
geological disaster, endangering the residents, houses and
properties cost billions of yuans. This study presents the
engineering geological and geophysical assessment of
the June 5, 2009 Jiwei Shan rockslide and to find out the
factors considered to be potential triggers of the rockslide.
The study is achieved through conducting regional and
detailed geological fieldwork, tectonic study, photointer-
pretation, degree of weathering, laboratory test analysis
of rock samples collected from the rockslide repsenting
Maokuo and Qixia Groups and Jialingjiang Formation
for comparison, study of thin sections and Scanning
Electron Microcope (SEM) and application of Vertical
Electrical Sounding (VES).
2. Methods of Investigations
Prior to the visit a detailed desk study of the geology of

Ez ELDIN ET AL.
62
the study area had been undertaken, using geological
maps (scale 1:500 000) and Google earth Image. On the
visit a walkover survey was done to the rockslide area
and it’s vicinity to examine the geological exposures,
geological structures, strikes and dips, fractures and to
ascertain if there were any geological factors relevant to
the occurrence of the rockslide. During the investigation:
geological maps were studied and used during the
fieldwork, degree of weathering and bedding planes were
determined, the vertical sequences of the lithology are
investigated from the available exposures along the east-
ern face of Jiwei Shan, the sliding surface is identified
and the verification of the location of the weathered and
fresh bedrocks would be carried out. During the field-
work rock samples were collected for laboratory tests to
verify their physical properties, texture, colours, mineral
composition and cementing materials. Representative
thin sections of the rock samples have been studied
petrographically and by Scanning Electron Microscope
(SEM) in order to know their mineral composition, in-
vestigate their microstructural features and degree of
weathering of the limestone. Two profiles of Vertical
Electrical Sounding (VES) were carried out on the sur-
face of Jiwei Shan parallel and perpendicular to the rock-
slide axis in order to study the subsurface of Jiwei Shan.
3. Geology
Geology of the study area consists of rocks of the Silu-
rian, Permian and Triassic Systems. The general lithol-
ogy is arranged chronologically from younger to older as
follows: The Quaternary Deposits (Q), Jialingjiang For-
mation (Lower Triassic Formation T1j), Maokou Group
(Upper Paleozoic, Early Permian System P1m), Qixia
Group (Upper Paleozoic, Early Permian System P1q),
Liangshan Group (Lower Permian System P1l) and Han-
jiadian Group (Medium Silurian System S2h) (Figure 3).
3.1. The Quaternary Deposits (Q)
It’s composed of recent, loose and soft deposits, formed
Figure 3. Lines show the boundaries between the different
rock strata of Jiwei Shan rockslide [3]. The Lower Triassic
Formation is not shown here because it is located in the
west part of Jiwei Shan.
by the streams, winds, running water and earth filled by
man. The loose deposits are widely distributed on the
slopes bodies between erosion surfaces and the bottom of
the slopes.
3.2. Jialingjiang Formation (Lower Triassic T1j)
The Jialingjiang Formation is the main karst strata; it’s
composed of light grey, middle-thick bedded with inter-
calated thin-bedded limestone and argillaceous limestone.
It dips 49˚ N. It’s strong and tough, it has three sets of
joints, divided the limestone into blocks nearly equal in
size. While, the silicified shale limestone is dark in col-
our, hard and tough and contains bituminous coal. It dips
34˚ N and strikes E. The fractures coinciding with the
bedding plane trend N and dip 34˚ while, the vertical
ones strike 90˚ E and dip 0˚ N.
3.3. Maokou Group (Upper Paleozoic, Early
Permian System P1m)
This Group is inhomogeneous, it forms the uppermost
layer of the Jiwei Shan (Figure 3) and it composes of:
highly weathered micrite (characterized by deep caves,
grikes, rockhead, sinkholes and erosion cracks), Highly
weathered argillaceous micritic limestone, three varieties
of fine-grained limestone (the first variety characterized
by alternating weathered lower layer has high ability to
disintegrate to soil compared to the light upper layer; it
dips 21°N and strike 290° with a thickness of 150 cm.
The second variety is dissected by vertical and horizontal
fractures which lead to form small blocks of rock mass.
The general dipping of the rock coincide with the general
orientation and the dipping of the whole rock mass. The
third variety is highly weathered and light to yellow in
colour. It represents the collapsed caves of the limestone),
Limonite limestone is very hard; pinkish; composed of
round crystals and has dark lenses of iron oxides, moder-
ately weathered and light coloured aargillaceous micrite,
and highly weathered argillaceous limestone and shale;
white; grey and pinkish coloured; soft and porous.
3.4. Qixia Group (Upper Paleozoic, Early
Permian System P1q)
Deep grey to black in colour, thick and blocky, very hard
to hard limestone layer, contains cherty nodule, knotted,
and eye-like limestone containing firestone (flint) are not
uncommon. At Jiwei Shan; Qixia Group (Figure 3) is
classified by [4] chronologically from top to bottom into
three subgroups (layers) according to their colours and
strength. The rupture surface was along this weak layer.
3.4.1. Upper Layer P31q
It represents the uppermost layer of Qixia Group; it

Ez ELDIN ET AL. 63
composes of two rock types: the dark grey, slightly
weathered and hard fine-grained silicified limestone with
a thickness of about 20 m and silicified limestone com-
posed of cryptocrystalline quartz occurs chiefly as nod-
ules in the limestone. It occurs probably as a result of
chemical changes in compressed limestone, during the
process of diagenesis. The limestone embedded in
weathered shale, its degree of weathering decreases to-
wards the center of the rock mass.
3.4.2. Mi ddl e L a yer P21q
The stratum of this layer has gentle dipped slope, it’s
densely vegetated (the eastern wall side of Jiwei Shan). It
is comparatively weak and strongly weathered compared
to the overlain beds and it consists of two rock types: a
highly weathered, thickly bedded and dark grey shale
limestone with clear fissility, overlain by highly weath-
ered shale and bituminous interlayer and crushed pinkish
limestone. The rock represents the sliding surface of the
rockslide. The shale limestone fissility can be scratched
by finger and most of the slided rocks that contained
shale are crushed and disintegrated into layers due to this
discontinuity. It’s worth to mention that, most of the
rocks of the scrap are characterized by having a layer of
shale with different thickness. This indicates that, shale
represents the weakest layer from which the rockslide
has been triggered. The shale quartz limestone is grey to
dark grey, intercalated with shale with a clear facility
which easily scratched by a hammer. The rock is highly
weathered and show clear traces of fractures and remains
of infilling light yellow clay. The wall of the fracture
shows some alteration and small water cavities (etching).
3.4.3. Lower Layer P11q
This layer is composed of limestone intercalated with
white to grey, hard and compact shale and silicified mud.
In another place, it’s alternating with shale; each layer is
about 5cm. The mudstone is resisting to weathering and
large boulders of mudstone are not uncommon. The
highly silicified and compacted limestone and mudstone
are resisting to weathering and crushing.
3.5. Liangshan Group (Lower Permian System
P1l)
It’s situated below Qixia Group; it consists of gray and
greyish-black argillaceous shales, carbonate mudstones,
bauxites and claystones with iron ores inside. The iron
manto was explored in the middle part of this layer.
3.6. Hanjiadian Group (Medium Silurian System
S2h)
It’s composed of sand and marine shale, unconformably
overlain by Liangshan Group. Studies suggested that the
source of ore forming materials was from this group. It is
rich in bauxite and hydromica.
3.7. Petrography
The polarized optical microscope was used to study the
rock samples of Jiwei Shan. This study was conducted on
all the samples. Microscopy results shed light on the
composition, texture, structure, porosity and microcracks
of the rocks (Figure 4).
4. Tectonic and Setting
Jiwei Shan is located at the northwestern flank of the
Zhaojiaba anticline, a monoclinal fold. It’s a south-north
dipping limb of an anticline fold. The karst geopatholo-
gies occur in large scale on the mountain. The limestone
beds include the exposed rocks while, marine shale cov-
ers the lower bed of the mountain. There is a clear cliff in
the eastern part of Jiwei Shan, the North Slope is gentle
dipping and the Western is slight. The way of the moun-
tain extension is corresponding to the tectonic line. The
top of the mountain is formed due to the effect of weath-
ering and erosion.
Figure 4. Jialingjiang Formation showing: (J16) hard and
tough silicified shale limestone contains traces of coal and
(J16a) thin-section pho tomicrograph in XPL showing calcite,
silicious material with undulose extinction and micro
structure of mud. Maokou Group: (2.11) highly weathered
argillaceous limestone and shale and (2.11a) thin-section
photomicrograph in XPL showing irregular, solution seam
and microcrystalline calcite. Qixia Group: (2.7a) shale bi-
tuminous limestone with clear fissility, smooth, and slicken-
side surface resulted due to the frictional movement of the
sliding rock mass. The red arrow indicates the direction of
the rockslide and (2.7aa) thin-section photomicrograph in
XPL showing grooves, scratches and completely flattened,
forming an intensified bedding-parallel lamination.

Ez ELDIN ET AL.
64
Tectonically, it belongs to the Yangtze platform, which
is a tectonic steady region of the southern part of China.
It experienced several tectonic movements from the
Cambrian to the Cenozoic [6]. During the Cambrian and
Silurian period, a transgression-regression sediment se-
quences were detected by many researchers in this region,
which mainly composed of shallow marine carbonate
rocks. Guangxi Movement, which happened in the Late
Silurian period, leads to uplift the study area to land. The
sediment of Devonian and Carboniferous is missing and
full records of the sedimentary sequence in the Permian
and Triassic periods were detected. The area of study
went into platform mobile period in the beginning of the
Late Triassic Epoch. The sedimentary rocks (from Cam-
brian to Jurassic) were folded and fractured by Yanshan
Movement and established geologic pattern at the end of
the Jurassic period. The stratum of the nominated area is
composed of anticline (extending north- south) and syn-
cline.
The tectonic zone has offered a favourable setting for
the Jiwei Shan rockslide, and has controlled the move-
ment pattern and direction. According to the field invest-
tigations, the tectonic of the study area imposes controls
on the rockslide in many ways: created favourable terrain,
provided sufficient rockslide prone materials such as
highly weathered limestone and shale, weak rocks, cre-
ated very steep beds which reduced the stability of the
rock slope and highly fractured beds. The several sets of
fractures, the gradual weakening of the rock mass (per-
haps by chemical and mechanical weathering or dilation
from unloading by continual erosion) have lowered the
rock mass strength below the prevailing gravitational
induced stress and allowed failure to occur.
5. Fracture Orie ntation
The study area experienced several tectonic movements
from the Cambrian to the Cenozoic lead to the formation
of Jiwei Shan fractures. On Jiwei Shan, two sets of
steeply dipping fractures developed in the strata more or
less parallel and regularly spaced, sometimes their spac-
ing varies from narrow to wide [7]. One set trends EW
and dips at 71 - 80° between S10° E and S10° W. It is
smooth and flat with a high persistence of 10 - 20 m and
an interval of 1 - 3 m. The back scarp of the rockslide
traced along the strike. Set two trends SN directions
(between N15°W and N20°E) and dips at 75 - 79°, near
vertical, towards 75 - 110°. It is long and has very high
persistence and good continuity; thereby, it formed the
western boundary of the rockslide, almost parallel to the
eastern cliff. With reference to the field survey, these two
sets of fractures are almost perpendicular to each other,
which cut the strata into blocks. The strength of a discon-
tinuous rock mass is governed by the strength of the in-
tact blocks and the freedom of the blocks to rotate and
slide under different stress conditions [8]. Thereby, once
the intact blocks in the source area had well free sliding
faces and enough sliding spaces, they are easy to be trig-
gered by rainfall, medium to high intensity earthquake,
other man-made unfavorable activities like explosion or
excavation. Most of the studied fractures located towards
the north of Jiwei Shan are described as has clear visible
cavities; very few were tight or partly opened. Mostly,
they are empty, little is filled by clays and/or carbonates
and they are wet. Their surfaces are smooth, weathered,
wavy or rough.
Many vertical fractures were eroded on the surface,
under the soil and in deep beds by the rainwater, soil
solution with CO2 and the action of microorganism. Fi g-
ure 5 shows contours of dominant fractures sets obtained
on a lower hemispherical equal area projection for dif-
ferent fractures data. Because only the mean orientations
were used and also the chance of having blind zone frac-
tures are very minimal, bias correction procedures for
orientation they were not applied in this work in repre-
senting the orientation distribution of fracture sets. The
effect of orientation bias correction on the estimation of
mean orientation for the fracture sets dealt with in this
work would be negligible.
6. Hydrogeological Feature
The main supply of underground water in the study area
is the atmospheric rainfall and partial running surface
water from stagnant agricultural activities on the top of
Jiwei Shan. The occurrence of water in the bedrocks in
the study area can be classified into: fracture bearing
water, karst water and pore water. The fracture water is
mainly distributed in the fractured bedrocks of Maokou
and upper and Middle Layers of Qixia Groups.
Jiwei Shan rocks are thick; inhomogeneous, having
more lime and piping. In the Maokou calcareous rocks,
the karst water is produced from the areas of irregular
Figure 5. Contour plots of dominant fracture sets on a
lower hemispherical equal area projection for fractures of
Jiwei Shan.

Ez ELDIN ET AL. 65
limestone in which erosion has produced fissures, sink-
holes, underground streams, and caverns. The karst grows
and the output of water is very rich and the water per-
meability is really strong, water passes through fractures,
crevices, and cavities, dissolves the limestone very
slowly, enlarging the network of passageways. During
the rainy season, the water seeps from the eastern face of
Jiwei Shan where the caves and large fractures are situ-
ated. Similarly, the slope contains intensive vegetation
cover that would suggest the presence of water. Based on
this information it is inferred that the slope is mostly wet
with the water level especially Maokou and upper and
middle layer of Qixia Groups. Assuming that groundwa-
ter flow for the eastern slope is controlled by fracture
permeability, the discontinuity network derived for this
study, although simplified, suggests that flow would be
parallel to bedding in the upper parts of the slope until it
reaches the flow barrier created by the slope. Here
pore-water pressures and flow may dissipate through the
more heavily fractured rock mass.
7. Weathering
The intensive rainfall and fluctuation of temperature
during the winter and summer accelerated the process of
weathering and hence resulted in the deterioration and
weakening of limestone quality. The development of
weathering and alteration in the rocks occurs through
changes in physical properties of the rocks. The style and
rate of weathering are controlled by fractures, porosity
and permeability of the rocks, which governs the ease
with which water can enter and the weathering products
be removed. The rocks at the surface are in a continuous
state of decay while those below decompose by solution
of elements in water, which enter through discontinuities,
bedding and cross-bedding. The weathered zone may be
deep because the discontinuity continues to great depth;
this is detected in the Middle Layer of Qixia Group.
Carbonation is the chemical weathering of limestone
and dolomite rocks by rainfall. Water vapour in the air
reacts with carbon dioxide to form carbonic acid, and
then reacts with the calcium and calcium/magnesium
carbonate. The mineral changes and becomes soluble in
water. The rock dissolves in rainwater and is washed
away according to the following equations:
CaCO3 + CO2+H2O↔ Ca+2 +2HCO3 –
CaMg (CO3)2 + 2CO2+2H2O↔ Ca+2 + Mg+2 + 4HCO3 –
Carbonic and Humic acids trickle along the fractures
of limestone widening them through the weathering
processes of carbonation and solution. Rates of weather-
ing are increased by acid rain. In winter, frost shattering
further weathers the limestone.
Degrees of Weathering
The weathering of Jiwei Shan limestone has encountered
in significant problems involving the weakening of rocks
and the unstable slopes, it generally shows some anoma-
lous engineering characteristics in comparison with fresh
rock in the adjacent areas. Variation in weathering grade
(Table 1) of limestone resulted in various physical prop-
erties. Jiwei Shan limestones range in their degree of
weathering from slightly, moderately to highly weathered
corresponding to grade II, III and IV, respectively. Jial-
ingjiang Formation characterized by slightly to moder-
ately (II to III) weathered limestone, Maokou Group
range from slightly to highly (II to IV) weathered lime-
stone and Qixia Group from moderately to highly (III to
IV) weathered limestone.
8. Scanning Electron Microscope (SEM)
The microcracks, micropores and grain size of Jiwei
Shan limestone Groups were studied and the influence of
the factors mentioned above on the rock is assessed.
EDAX results evidenced the dominant Ca and Si, Mg, K,
Al, Fe, Bi and Rb are present in small quantities.
For microscopic observation, about twelve limestone
samples representing Jialingjiang Formation and Maokou
and Qixia Groups were selected from different grades of
weathering. The study of the SEM photomicrographs
showed that (Figure 6) the increase in microcrack
propagations and size of micropores in limestone indi-
cated the increases in the weathering grade from grade II
(slightly weathered rock) to grade III and IV (moderately
Table 1. Definitions of the degrees of weathering, adapted
from [9].
GradeTerm Typical Characteristics
I Unweathered
Unchanged from original state. No
evident microfracturing. Slight
discolouration on major discontinuity
surfaces
II Slightly weathered
Slight discolouration, slight weakening.
Weathering penetrates through most
discountunitues
III Moderately weathered
Considerably weakened, penetrative
discolouration. Large pieces cannot be
broken by hand
IV Highly weathered Significantly weaker than the fresh
rock. Easily brekable with hand
V Completely weathered
Original texture is present. All mi-
crofractures tend to be open. Losses
most of strength of fresh rock
VI Residual soil
Soil derived by in situ weathering but
retaining none of original texture or
fabric

Ez ELDIN ET AL.
66
and highly weathered rocks, respectively). The increase
in microcrack length was coupled with the increase in
width of the cracks as observed using SEM. Based on the
effect of weathering on pore geometry of Jiwei Shan
limestone, the porosity values increase with the degree of
weathering from grade II to grade IV. There were no
significant changes in the porosity values of the silicified
and cemented limestone. According to [10], the pore
volumes of the limestone increase proportionally with
weathering stage.
9. Laboratory Tests
9.1. Specific Gravity and Bulk and Dry Densities
The specific gravity and bulk and dry densities of the
Jialingjiang Formation and Maokou and Qixia Groups
limestone, were determined. The mean values of the spe-
cific gravity and bulk and dry densities fall within the
normal range given to the limestone (Figure 7).
9.2. Porosity
The mean porosity values of the Jialingjiang, Maokou
and Qixia limestones collected from Jiwei Shan recorded
Figure 6. SEM photomicrograph showing: (A) low porosity
slightly weathered limestone and (B) microcracks linking
pre-existing pores and en echelon microcracks in porous
moderately weathered limestone, (Maokou Group). (C)
Large scale surface scaling in highly porous and highly
weathered shale limestone with clear fissility and (D) large
scale surface scaling in, porous and highly weathered shale
limestone with clear fissility (Qixia Group). E. slightly
weathered limestone with a high density and (F) Unweath-
ered silicified shale limestone with a high density, (Jialing-
jiang Formation).
different values. The shale and bituminous interlayer of
Qixia Group has recorded the highest porosity while
limestone of Maokou showed relatively moderate values
(Figure 8). The higher values of porosity of Qixia Group
limestone attributed to the composition of the rock and
the low porosity of the Jialingjiang limestone can be at-
tributed to the compaction and silicification. The study of
the thin sections and SEM indicate the effect of solution
in the limestone of Maokou and Qixia Groups is
enlargement of the pores and fractures that cause more
water movement to shale and bituminous interlayer of
Qixia Group. Some types of porosity were identified in
the studied limestones and illustrated in Figure 9.
9.3. Water Absorption and Saturated Water
Absorption Capacities
The water absorption and saturated water absorption ca-
pacities of the Jialingjiang, Maokou and Qixia limestones
collected from Jiwei Shan were obtained. The intent of
this task was to quantify whether there is a correlation
between the natural porosity and the water level absorption
attained for the selected rocks. The shale and bituminous
Figure 7. Showing the average specific gravity, dry density
and bulk density of Jiwei Shan limestone.
Figure 8. Showing the average porosity of Jiwei Shan
limestones.

Ez ELDIN ET AL. 67
interlayer of Qixia Group showed the highest ability to
absorb water (3.76% - 0.04%) compared with Jialingji-
ang, Maokou limestones. Maokou limestone gave (2.51%
- 0.26%) and Jialingjiang limestone recorded (0.24% -
0.12%). There is significant correlation between the po-
rosity percentage and the water absorption in Jiwei Shan
limestone (Figure 10). The shale and bituminous inter-
layer of Qixia Group has relatively higher porosity
therefore, they have the tendency to absorb significant
amounts of water compared with Maokou limestones and
Jialingjiang.
Figure 9. SEM photomicrograph showing: (A) Fenestral
porosity formed by dissolution of the cement or matrix
sometimes caused by enlargement of microfratures. This
type of porosity was observed easily in the hand specimens.
Fracture porosity formed by fracturing, and some of them
are cemented. (B) Intraparticle porosity within individual
particles or grains is generally primary, but forms rarely by
dissolution of cement or matrix. (C) Interparticle porosity
between grains and/or particles forms via leaching or ma-
trix or cement. (D) Inter- and/or intragranular porosity
enlarged somewhat by dissolution around the original
pores.
Jialingjiang FormationMaokou GroupQixia Group
0
1
2
3
4
5
6
Porosity %, W. absorption % and Sat. w. absorption %
Limestone Formation/Group
Porosity
Waterabsorp
Saturatedwa
Figure 10. The mean porosity, water absorption capacity and
saturated water absorption capacity of Jiwei Sha n limestons .
10. Karst Processes
Jiwei Shan Karst is characterized with caves, grykes,
dissolution cracks and rockheads which display a long
history of geological evolution and an unusual range of
karst formations. Karst features mostly develop in asso-
ciation with discontinuity planes (fractures) by progress-
sive dissolution of the carbonates leaving a soft and po-
rous weathering residue and enlarged weathered fractures
[11]. Karst of Jiwei Shan has suite of fractures and voids
cut into the surface and rock mass of the limestone. Dis-
solution of rock occurs on exposed outcrops, at the top of
Jiwei Shan beneath soil, and along the fractures (Figure
11). There are many structures formed in Maokou Group
due to the process of weathering including caves located
in the eastern cliff of Jiwei Shan, Sinkholes formed by
dissolution weathering of the carbonate minerals, Grykes
are observed on the top of Jiwei Shan, their most domi-
nant system runs almost south to north; it stretches for
thirties of meters until they suddenly terminate or lost
beneath superficial deposits and Rockheads are subsoil
dissolution at the soil/rock interface creates a clean
rockhead without the gradual transition through a weath-
ering sequence in insoluble rocks, it’s extremely irregular
on Jiwei Shan karstic bedrock. The structures formed in
Jiwei Shan karst profiles tend to be more complex in
dipping limestone.
11. Geoelectrical Soundings
Two vertical electrical soundings (VES) (Jiwei Shan1
Figure 11. Rockhead, dissolution-open fissures and bedding
plane on the wall ofJiwei Shan rockslide platform.

Ez ELDIN ET AL.
68
and Jiwei Shan2) were carried out on the top of Jiwei
Shan using a Schlumberger array to investigating the
karst and displays lithological and slope deformation
features. Jiwei Shan1 is almost parallel and west of the
rockslide platform and trending S-N, the second is per-
pendicular to it. 180 m electrode spacing was selected to
reach a maximum depth of investigation of about 60 m.
Jiwei Shan1 (Figure 12) produced four different resis-
tivity of layered rocks which are clearly defined by their
different resistivity layers at the various depths in in-
verted resistivity sections as follows:
A thin undulating subsurface layer with a compara-
tively low resistivity values to an approximate depth of
about 6 m. This layer of low resistivity is typical of
weathered limestone of the underlying rocks in the area.
The wavey pattern is probably due to the action of karst
process and weathering.
The area between 244 - 260 m along the x-axis in the
south of the profile shows vertical increase in resistivity
with depth from (126 - 1450 ohm.m), this area represents
the northern part of the platform in which the karst and
weathering processes are active due to the presence of
limestone discontinuities and dissolution-open fissures
from the surface to the bottom. The difference in weath-
ering degree is probably due to the inhomogeneity of the
limestone.
An intermediate resistivity layer at the intermediate
depth zone, which could represent slightly to moderately
weathered limestone material, is observed afterwards.
The depth of this layer ranges between (1297 - 1290 m)
and has a comparatively moderate to high resistivity in
the range between (642 - 3273 ohm.m).
A thick layer with a comparatively high resistivity is
also observed below the two layers of low to moderate to
high resistivity limestone resistivities. This relatively
high resistivity bedrock layer, possibly represent the
fresh limestone material with competent structural pat-
terns.
Figure 13 displays two features, one is in the east and
the second is in the west. The eastern part of the profile
includes two resistivity zones. One is given by the pres-
ence of high surface resistivity anomaly (> 1500 ohm.m)
and it points to the presence of compact limestone, it’s
located probably between two vertical discontinuities
(fractures) widen by dissolution (point 332 and 357 along
the x-axis), their depths range between 5 - 15.85 m. The
second layer is characterized by relatively low resistivity
(122 - 671 ohm.m) and depth start from 5 m and extends
to the end of the profile and it indicates the presence of
weathered limestone. The body that situated at the me-
dium depth within the second layer is characterized by
the lowest resistivity value (122 - 286 ohm.m), it’s
probably a buried cave.
The western part of the profile includes three resistiv-
ity zones. A subsurface layer with low resistivity (22-122
ohm.m) is located between 379 -395 m (along the x-axis)
and extends to a depth of 8 m. The middle layer charac-
terized by medium resistivity values (122 - 671 ohm.m)
and engulfs the upper layer. The depth of the middle
layer reaches to about 15.85 m and it’s acting as small
basin within the profile based on its lower resistivity in
relation to the background resistivity on the profile. The
first and the middle layer represent highly to moderately
weathered limestone. The third layer characterized by
higher resistivity (> 1500 ohm.m).
12. Discussion
The lithology of Jiwei Shan has great influence on the
nature, rate of weathering and rockslide process. The
petrographical study revealed that, the limestones of Ji-
wei Shan are mixtures of several lithologies and beds,
contain substantial amounts of impurities and may be-
have weakly according to their contents and have a more
complicated composition, structure and texture. There-
fore, the rate and nature of geomorphological processes,
characteristics of the exposed and subsurface materials of
the rockslide process and the catastrophic events has a
direct correlation of lithology. The limestone of Jialing
jiang Formation is generally hard and tough compared to
the other two Groups. Maokou Group characterized by
karst caves, grikes, sinkholes (solution, collapse, dropout
and buried) and erosion and dissolution cracks. The bed
Figure 12. 2D VES section along Jiwei Shan rockslide.
Figure 13. 2D VES section across Jiwei Shan rockslide.

Ez ELDIN ET AL. 69
surface is a gentle inclined slope of 30˚ which is densely
vegetated by various types of plant species. The layer is
highly fractured, comparatively weak and highly weath-
ered. This Group is inhomogeneous; it composes of
limestone characterized by different mineral contents.
The fine-grained silicified limestone of the Upper Layer
(P3 1q) of Qixia Group is played as a medium of trans-
mitting fluids coming from the overlain layers to the
Middle Layer (P2
1q), leading to increase the degree of
weathering and reducing the strength of the shale and
bituminous interlayer. The dark gray shale limestone
member of the middle layer is not affected like the below
situated shale and bituminous interlayer. The latter is
highly weathered and it represents the sliding surface of
the rockslide. The stratum of this layer has gentle dipped
slope, it’s densely vegetated. The mud intercalated lime-
stone of the Lower Layer (P1
1q) is hard, compact, inter-
calated with shale, in another place it is alternating with
shale. It worked as a sub-base below the sliding surface.
Generally, the potential failure pattern of Jiwei Shan
may be a linear shear failure of the highly weathered
shale and bituminous interlayer with clear fissility and a
single slip surface with steep gradients. Identical dips and
ground fractures at the eastern and top of Jiwei Shan are
prone to toppling collapse. Prior to the event, the lime-
stone was suffering from the intrinsic destruction of its
structure which leads to weakening the mechanical prop-
erties of rock masses, by weathering over time. Rainfall
in the study area is quite intense and contributes signifi-
cantly to the weathering of the limestones. In the Ma-
okou calcareous rocks, the karst water is produced from
the areas of irregular limestone in which erosion has
produced fissures, sinkholes, underground streams, and
caverns. The karst grows and the output of water is very
rich and the water permeability is really strong, water
passes through fractures, crevices, and cavities and dis-
solves the limestone very slowly, enlarging the network
of passageways. Therefore, the slope is mostly wet with
the water especially Maokou and upper and middle layer
of Qixia Groups. Due to this reason Maokou Group
range from slightly to highly (II to IV) weathered lime-
stone and Qixia Group from moderately to highly (III to
IV) weathered limestone. The study of the SEM photo-
micrographs showed that the increase in microcrack
propagations and size of micropores in limestone indi-
cated the increases in the weathering grade from grade II
(slightly weathered rock) to grade III and IV. The in-
crease in microcrack length was coupled with the in-
crease in width of the cracks as observed using SEM.
Based on the effect of weathering on pore geometry of
Jiwei Shan limestone, the porosity values increase with
the degree of weathering from grade II to grade IV.
Tectonics of the study area exerted a fundamental con-
trol on the lithology and movement of groundwater, by
creating a favorable environment for triggering the rock-
slide. Bedding attitude and dipping situation of the beds
played a great role in the occurrence of Jiwei rockslide.
The two fractures sets tend to weaken the rock mass,
accelerating the process of weathering, decrease the
strength of the rocks and created good channels for ver-
tical and horizontal water movement within the lithology
of the slope. The monocline fold of Jiwei Shan increased
the dipping of the beds and created tension fractures on
the top of the southern part of Jiwei Shan. The continu-
ous fault that located along the south side of Jiwei Shan
it’s probably has the responsibility of creating the intense
fracturing and by a way or another it has influence on
weakening the rock mass. The fracture sets of Jiwei Shan
cut across the limestone of Maokou and the middle layer
(P2
1q) of Qixia beds but, do not cross through the weaker
shale and bituminous limestone interlayer.
The physical tests performed on representative sam-
ples from the lithology indicate that, the relatively high
porosity and elevated water absorption of shale and bi-
tuminous interlayer of Qixia Group is due to their com-
position and moderately to highly degree of weathering
but, the medium porosity and water absorption were ob-
served in Maokuo is attributed to the nature and cement-
ing diagenesis of limestone. The presence of micrcracks
and fissility planes in shale and bituminous interlayer of
Qixia Group increases the porosity. Higher porosity in-
creases the surface area and raises water intake capacity,
thus accelerating both physical and chemical disintegra-
tion. Water replaces the soluble minerals, thereby en-
hancing the porous structure. Moreover, shear stress is
reduced in shale and bituminous interlayer due to water
absorption. The discontinuities of shale and bituminous
interlayer constitute a weak plane with little shear
strength that is further reduced due to the effect of water
infiltration. The overlain limestone beds with their pre-
sent karstic condition easily slide along the bedding and
fissility planes of the shale and bituminous interlayer
slope with the assisting of the tectonics of Jiwei Shan.
The VES of Jiwei Shan1 revealed the presence of
limestone discontinuities and dissolution-open fissures
from the surface to the bottom in the northern part of the
platform and relatively, the low resistivity indicates the
activity of the weathering process. Also, Jiwei Shan2
revealed fractures widen by dissolution, buried cave and
small basin below the subsurface within the profile.
The layer above and below the slip surface is charac-
terized by impermeable and low porosity silicified lime-
stone and hard and compact mud intercalated limestone,
respectively. Rainfall water infiltrates through fractures
of the overlying strata saturate the shale and bituminous
interlayer and do not reach the impermeable and the low
porosity lower layer. The development of the rockslide is
promoted by the steep dipping beds in the direction of

Ez ELDIN ET AL.
70
the slope and by presences of two sets fractures crossing
each other in almost 90°. Thus the highly fissile and
weathered shale and bituminous interlayer limestone
interface tends to become a weak plane of extreme insta-
bility.
13. Conclusions
The study concluded that, geology and tectonic settings
have offered a favourable setting for the Jiwei Shan
rockslide, and have controlled the movement pattern and
direction and provided sufficient rockslide prone materi-
als. The several sets of fractures and the gradual weak-
ening of the rock mass perhaps by weathering have low-
ered the rock mass strength and allowed failure to occur.
Dissolution of rock occurs on exposed outcrops, at the
top of Jiwei Shan beneath the soil, and along the frac-
tures. There are many structures formed in Maokou
Group due to the process of weathering including caves,
grykes, dissolution cracks and rockheads which display a
long history of geological evolution and an unusual range
of karst formations. These structures weakened the rock
mass of Jiwei Shan.
The highly weathered shale and bituminous interlayer
limestone of the Middle Layer, Qixia Group, represents
the sliding surface of the rockslide. The shale limestone
characterized by clear fissility. It’s worth to mention that,
most of the rocks of the scrap characterized by having
shale layer of varied thickness. This indicates that, shale
represents the weakest layer from which the rock slide
has been triggered.
The terrain and it is vicinity is still unstable, and con-
tinual rainfall on the weak and highly weathered lime-
stone will cause another slope under the conditions
which led to past instability.
14. Acknowledgements
The work was funded by the National Basic Research
Program of China (973 Program; No. 2011CB710600),
the Special Fund for Basic Research on Control of Dis-
aster Landslide Induced by Great Engineering Projects
(No. 2011CB710604, 2011CB710605 and 2011CB
710606). We gratefully acknowledge Limin Wang and
Huang Rong for their assistance during the geophysical
field works.
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