10th Asian Regional Conference of IAEG (2015)

Rock Pile, a Particular Type of Debris Accumulation in Huanren, Liaoning Province,China
Qinglu DENG(1), Faliang JIN(2) , Xueping WANG(3), Min YANG(2) and Yang LONG (1)(1) Faculty of Engineering Geology, China University of Geosciences, PR China
E-mail:dengqinglu@qq.com(2) Shenyang Railway Survey and Design Institute co., LTD, PR China, (3) Faculty of Resources, China
University of Geosciences, PR China
Abstract
In Huanren County of Liaoning Province, China, the construction ofTianshifu-Huanren railway met with the problem of rock pile, a particular type of debris
accumulation. Regarding to the rock pile, the basic engineering geological problems, suchas distribution, origin, deformation and failure model, haven't been reported before. Field
surveys and large-scale mapping were carried out in order to clarify the geological featuresand geological setting of this kind of debris slopes. This paper presents a preliminary
summarization on the characteristics of distribution, texture and slope stability of the debris
accumulation. It is believed that the debris accumulation is formed by glaciation during thelate Quaternary. Jointed quartz sandstone is breaked into rock blocks in the superficial part
under the glacial loading and ablation. Rock blocks were accumulated in site ortransported by glaciers and deposited in near slopes. The debris accumulation is preserved
due to the strong weather resistance of quartz sandstone. Though sliding failure is rarely
found, slow creep activity is observed in some area of the debris accumulation. Vegetation
or bare ground is a sign of stable or creep state of a slope.
Keywords: Huanren county of China, rock pile, engineering geological characteristics
1.

Introduction

the area of Huabozishan- Daqianshiling-Yantongshan
in Huanren county, eastern Liaoning province,
covering an area of nearly four hundred square
kilometers (figure 1). Rock piles are also scattered inother areas of eastern Liaoning province and southern
Jilin province.
The rock piles are widely spread on slopes, andcan be classified into two kinds--bare rock piles andvegetation-covered rock piles --according to whether
they are covered with vegetation.
Bare rock piles have no vegetation on theirsurfaces, and mainly exist on slopes with a slope
angle between 30°and 38°. Multiple bare rockpiles, separated or locally-connected, are often
clustered in a col (figure 2).
In the outer areas around the bare rock piles are
the vegetation-covered rock piles. Vegetated mainly
by pine, oak and small shrubs, the vegetation-coveredrock piles mainly distribute on mountain ridges andrelatively gentle slopes with slope gradient generally
within 30 °. Bare rock piles are also found in 10 to
15 ° platform in some slope toe.

In Huanren County of Liaoning Province, China,
the construction of Tianshifu-Huanren railway met
with the problem of rock piles. Rock piles are widelydistributed on the slopes, some surfaces of which arecovered with vegetation, the others are totally bare.
The thicknesses of the piles range from several
meters to dozens of meters, the maximum reaches 50
meters. The railway was formerly designed to crossthe debris slopes by tunnel, however, as the route
exploration progressed, designers became to worry
about the feasibility of the tunnel construction and thelong-term stability of the debris slope. Little has been
known about the engineering geological problems sofar, such as distribution, origin, deformation andfailure model due to limited reports. To solve theseproblems, a large-scaled (1:2000 and 1:10000)
engineering geological survey including theinterpretation of remote sensing was carried out in
Huanren County.
2.

Regional distribution of rock pile
The distribution of rock piles is concentrative in1

10th Asian Regional Conference of IAEG (2015)

Fig. 1 Geological map in Huanren area. The distribution of rock piles is consistent to the outcrop region of theDiaoyutai Formation (Pt3d). Based on Huanren geological map of scale 1:200 000; grid spacing in the map is 10km. 1- Quaternary sand-gravel soil; 2- pyroclastic and sandy conglomerate of the late Jurassic; 3- limestone andlimited shale of Ordovician; 4- limestone and shale of Cambrian; 5- Qiaotou group of the Neoproterozoic,
interbed of quartz sandstone and arenaceous; 6- Nanfen formation of the Neoproterozoic, shales withintercalations of marls; 7- Diaoyutai formation of the Neoproterozoic, quartz sandstone; 8- Liaohe group of thePaleoproterozoic, metamorphic rock such as gneiss, amphibolites, migmatite; 9- Jurassic intrusive rock ofgranite; 10- Jurassic intrusive rock of adamellite; 11- Proterozoic intrusive rock of diorite; 12- migmatite; 13attitude of bed; 14- angular unconformity; 15- fault; 16- Tianshifu-Huanren railway line in Daqianshiling, thedash line shows the tunnel.
the directions along the longitudinal slope (vertical tothe contour lines, as shown in figure 3).
A few rock piles, usually with small coveragearea, directly accumulated under cliffs, but more rockpiles are absent steep cliffs behind their slope.
The distribution of the rock piles is closely related
to the Diaoyutai Formation, Neoproterozoic (seefigure 1), in other words, the rock piles are the uniquefeatures of the Diaoyutai Formation, and they are
rarely occurred in other stratums. It is showed by therock piles distribution map of Lvjiabao (figure 3) thatrock piles are widely spread in the distribution area of
Diaoyutai Formation, and rarely occurred inmetamorphism rocks, mainly leptite, of the LiaoheGroup and in the intrusive rocks, mainly quartz
diorites, of the late Jurassic. The Diaoyutai Formationconsists of light grey quartz sandstones, the most ofwhich are thick-bedded.

Fig. 2 Bare rock piles are clustered in cols.
Bare rock piles differ from each other in shapes.
The shape can be strip, cone, saddle-shaped andskirt-shaped., etc., but they have a common
characteristic, namely their long axes are generally in210th Asian Regional Conference of IAEG (2015)3.

The texture characteristics of the slope debris
accumulation around the entrance of theDaqianshiling tunnel

decay and few minerals. The humus soil is only tensof centimeters in thickness, many rock blocks are still
exposed to the slope surface, from whichaccumulation structure can be clearly observed. Theparts below the humus soil layer are rock blockaccumulation with a structure similar to that of thebare rock piles.
The yellow colluvial deposits, consisting of rockblocks and rubble with silty clay filling in interspaces,
is located on the slopes outside the tunnel entrance.
Most sizes of the blocks, which compose of over 50
percent of the layer, are between 0.2 m and 0.5 m.
The rubbles usually range in size from 0.02 m to 0.15
m. Both of the rubbles and rock blocks are
sub-angular and made up of quartz sandstones (figure6). The soil consists mainly of yellow clay and silty
soil and has a content of 10 percent or so. It shows alush vegetation in the colluvial deposit area.
The vegetation-covered rock piles lie over thecolluvial deposits. A construction road has been madeon the slope lying in the front edge of rock piles, from
where the contact relationship of two kinds of debrisaccumulations can be observed (Figure 7). On thewhole, the gray overlying layer stretches out likefingers where were once a relatively low-lying area.
All of the above indicate that the rock piles form after
colluvial deposits.

A engineering geological mapping at a scale of
1 : 2000 has been conducted in the slope areas aroundthe entrance of Daqianshiling tunnel. The results areshown in figure 4. Three kinds of accumulations canbe discriminated on the slope, namely bare rockpiles，vegetation-covered rock piles and colluvial
deposits.
Large areas of bare rock piles occur in the north(rock pile A and C), the south (rock pile B) and theupper part (rock pile D) of the slope of the tunnel
entrance. The coverage area of rock pile B, the largest
one among them, is about 400m×400m. The barerock piles are simply made up of accumulated rockblocks. The blocks, which are hard and angular,consist of quartz sandstones and pebbled quartz
sandstones. The general diameters of the blocks are
between 0.5 m and 1.5 m while the maximum canreach 2 m to 3 m and the minimum only dozens ofcentimeters. The rock piles are of aerial structure,
without fine grain filling, and nonsorted (figure 5).
Rock piles existing in areas covered with a lot ofvegetation outside the bare rock piles are calledvegetation-covered rock piles. On the surface of thiskind of rock piles lies a thin layer of humus soil
which consists of dead plants that have begun to0200

400 mFig. 3 Distribution of rock piles in Lvjiabao. 1- alluvial deposit of Quaternary; 2- bare rock pile; 3vegetation-covered rock pile; 4- Diaoyutai formation of the Neoproterozoic; 5- Liaohe group of the Proterozoic;
6- intrusive rock of the Late Jurassic; 7- railway in construction, the dash line is tunnel

310th Asian Regional Conference of IAEG (2015)

04080 mFig. 4 Engineering geological map of Daqianshiling tunnel entrance slope. 1- alluvial; 2- colluvial; 3- bare rockpile; 4- vegetation-covered rock pile; 5- number of bare rock piles; 6- Daqianshiling tunnel

Fig. 5 Open structure of rock pileFig. 7 Rock piles lying over colluvial deposit.
4.

Results and discussion

The rock piles in the area of Huanren county areprobably not the product of rock avalanche.
Coarse grained debris accumulation on hill side areusually categorized into a kind of debris originatedfrom rock avalanche. Some researchers hold this viewthat the rock piles in Huanren county belong to talus(Qu and Liu 2011, Li 2013). However, somephenomena don't support the view. Firstly, most of
the slopes covered by rock piles have no steep cliff at
slope head. And then, the texture and block size ofthe rock piles changes very little from the top to thefoot of the slopes. This phenomenon is not inaccordance with the avalanche deposits which aresupposed to differ greatly among different parts, suchas the average size of rock blocks is much larger in

Fig. 6 Yellow colluvial deposit consisting of rockblocks and rubble with silty clay filling in interspaces

410th Asian Regional Conference of IAEG (2015)

the front than in the back of the slope. Moreover, rockpiles are also found on the platform, or river terrace,in slope foot. With a low gradient surface, the rockpiles on the platform differ to a talus.
The debris accumulations in Huanren county areprobably the product of glaciation during the late
Quaternary. Under the loading by thick glaciation andfollowed unloading by glacial ablation, it is speculated
that jointed quartz sandstone is breaked into rockblocks in the superficial part. Rock blocks accumulated
in site or transported by glaciers and deposited in thenear slopes. On the view of glaciation, some featuresof rock piles can be well explained, such as even sizes,
poorly graded, and appearance in gentle slopes.
Nevertheless, more concrete evidence of glaciation as
well as the formation and accumulation mechanism
remains to be further researched.
Bare rock piles and vegetation-covered rock piles
probably represent two kinds of states of the debris
slopes—stable and active. The appearance of the barerock piles, with a long axis direction vertical to thecontour lines, indicates a sign of activity undergravity. There is a relatively steep slope at bare rockpiles, on which slope the rock blocks are prone tomove downward. Tilted and saber-like trees in thetransition zone between bare and vegetation coverdebris accumulations also indicate the creep activityof the bare slope. It is the continuous deformation andlack of fine-grained filling that make the vegetationdifficult to maintain in bare rock block accumulation.
Acknowledgements
The work was funded by the National Basic
Research Program of China (973 Program)(No.2011CB710601).

References
Li, Y.J. (2013): Study on alignment and survey
methods in talus area. Journal of railway
engineering society, Issue 10, pp.1-4.
Qu, J.H. and Liu, J.W. (2011): Research on
distribution features and conformation of BenxiDiaoyutai landscape. Journal of Liaoning Normal
University (Natural Science Edition), Vol.34, No.3,
pp.383-387.

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