Jiang Liangwen¹, Yi Yongjin², Yang Xiang³ & Tao Weiming⁴

¹ The Second Railways Survey & Design Institute. (e-mail: teydkyjlw@263.net)

² The Second Railways Survey & Design Institute. (e-mail: teydkyjlw@263.net)

³ The Second Railways Survey & Design Institute. (e-mail: teydkyjlw@263.net)

⁴ The Second Railways Survey & Design Institute. (e-mail: teydkyjlw@263.net)

Abstract: The Yuanliangshan tunnel is a key control project, which lies between Chongqing and Huaihua. It extends 11.068 km, and the greatest depth in the tunnel is 780 m. When the tunnel cuts across the eastern limb of the Dongmaling anticline, construction encountered a sector that included a lot of well-connected karst rocks. In addition, the area is susceptible to large and intense rainfall. There were extensive and repeated inflows of water and mud-rock particularly in the section DK361+764 to DK360+873,which caused many machines and tools to be buried or damaged. So, the tunnel construction met with serious obstructions and delays and tremendously increased costs. Through initial analysis, the authors concluded that the inflowing water and mud-rock are flowing from the main piping network of an underground karst river, which is fed by rainfall. Torrential rainfall occurs frequently in anticlinal areas in the rainy season - for example, from May to September of 2003. DK 361+764, DK360+873 again experienced large, sudden and continuous inflows of water (mud, sand, gravel). Fortunately, the tunnel and lined cuttings were kept stable by draining the water-mud-gravel through sluicing drains. This indicated that it was a correct choice to adopt this scheme for renovating the east limb of the anticlinal source of the inflows. In order to guarrantee the safety of the tunnel construction and its operation, and in view of the nature of the karst and the associated water and debris inflow, the authors compared the choice of sluicing-hole drains, flat-guide drains, sealed-block and block-drains, and finally the first of these was adopted.

Key words: Karst, Level endless loop tape, water and mud-rock pouring up, Calamity, Repairing project, the TongmaLing Anticline, the YuanLiangshan Tunnel

General Outline of Geology and Geomorphology of the Tunnel

The special long tunnel of Yuanliangshan is the key control project of the planned railway, which lies between Chongqing to Huaihua railway. It extends 11.068km, the entrance of which is located on the Zhangjia dam of Xisha River’ east bank, with mileage DK351+ 465, about 549.16m high; The exit is located at the Tanchang River ’s west bank of the source of Shumawang River, with mileage DK362+533, about 503.74mhigh. It is a mongline gable slope tunnel of reservation of double line condition and flat-guide construction, with mileage of the top grade DK355+820, about 560.52 m high .The most depth in the tunnel is nearly 780 m, with corresponding mileage DK353+035 and 552.16m high. The tunnel lies in the contiguous area of fold mountain of east Sichuan , west Hubei , and Guizhou Plateau, located in the hinterland of Wuling Mountain, and cross the Maoba-Yuanliangshan area that divides the water system of Wu River from Yuan River. The tunnel is a kind of medium or low deep-cutting river valleys and terrain condition is quite difficult. Its relatively high is over 500~800 m. The geomorphological feature, with the characteristic of striped belt, is obviously controlled by tectonic situation and lithology. In addition, the geologic structure is extremely complicated that it is the joint section of arch fold bundle of beautiful hill and concave fold bundle of Guizhou river in the fold area of Sichuan, Hunan and Hubei., forming a fold carpet belt about northeast 35° in Yanshan and then suffered fold modify about northeast 18° in Xishan.. The south of the folded belt is NNE-trending ,and then gradually changes into NE~NE-trending, when oriented to north , so the general feature appears arch protruding northwest.

The main geologic structure of running tunnel includes Maoba syncline and Tongmaling anticline and its associated or secondary faults; among which DK357+665~DK362+533 is Tongmaling anticline section constituded by the sedimentary of Cambrian (∈) and Ordovician (O)carbonate rock. The lithology is mainly classified as limestone, dolomitic limestone, lime dolostone, dolostone intercalated with thihbedded marl,shale and marl limestone. The axial portion of Tongmaling anticline cuts across the Qingshan, Genshan and Yudipo. It is 60Km in length, and plain extension shapes a bit like“S”. The axial has 3 high points which can be divided into 3 sections of south, middle, and north respectively. The anticline section cut across is a portion of north section of Tongmaling anticline ,and the south is entered from Laoguashan. The high point of the tunnel is located in the slighty north of Yudipo.,appearing short axial anticline. And it is gradually plunging along the axis towards south and north directions.,and finally towards Dazhuyuan in north and then out of the zone; While inside, the length of the tunnel is 11.7Km,and axes is N20~30°E. Two wings trend to be gentler in the east (40~50°) and steeper in the west (50~80°). The axial plane is inclined to east with closely axial zone. The section between part of Laoguashan in the south of short axis anticline and Dadongshan axial zone are destoried by faults. The stratum with the longest history appearing from the core of anticline is Middle Cambrian Gaotai Formation(∈2g).The sequence of Two limbs are Middle Cambrian Gaotai Formation(∈2g), Pingjing Formation(∈2p),Upper Maotian Formation(∈3m, Genjiadian Formation(∈3 g)and stratum mainly consisting of Ordovician (O)carbonate rock(Fig.1); The anticline section develops and distributs 3 longitudinal compression faults along the stratum strike of F1, F2, F01.; Affected by multi period evolution, the core of the anticline is oritanted the compound anticline of shape M,and bedding frature and cross frature are intensely developed..The axial zone of anticline forms a mountain(extending in NNE direction) ,two wings surrounds like a valley and the kraft landform completely develop. It has the characteristics of plateau, i.e. third-order plateau with a 1100~1150m, 950~1050m and 700~800m in height. The plateau with 1100~1150m high has eluvium of dozen centimeters thick and archaic depression of imperfect modality. The two wings with 980~1050m are both be saved. The east wing is located in a line of Xujia~Yangjiagai, with the geomorphologies of miniature trough, depression, peak-cluster, or gentle slope and so on. The gentle slope zone also reserves residual clay of dozen centimeters thick. On the other hand, the west wing lies in Santan village, with the geomorphologies of gentle slop, miniature trough, depression and so on. The plateau with 700~800m high has large-scal geomorphologies of dissolution trough and peak-cluster in both the east and west wings. In the trough, the paternoster depression develops, the long axis direction of which is in accordance with that of anticline axial zone. Thus, the existence of anticline section will benefit for the mature of karst and karst water. During construction, the east wing Tongmaling anticline in Yuanliangshan tunnel on the exit section of DK361+764,DK360+873 has suffered extensive water and mud-rock pouring up time and again.

Fig. 1 Section sketch map of Tongmaling Anticline Section in Yuanliangshan Tunnel (proportion 1:10000)

Characteristics of Recharge, Runoff and Outflow of Karst Water in Tongmaling Anticline

The east and west wings of anticline are limited by non-soluble rock of Silurian System and their surrounding is cut by surface water system. The drainage base of karst water in Tongmaling is definded as the elevation of the soluble rock and non-soluble rock contiguous area which is cut across by surface water. In addition, surface watershed is almost consistent with underground watershed and the atmosphere precipitation is the only supply source for surface water and ground water.A line belt of Jianzishan (elevation-1185.5 m) ~ Yuanliangshan (1202 m) ~ LanBanDeng (1156 m) ~ DaTongshan (also named DaDongshan,1151.7 m) ~ Tea Garden (1030.4 m) nearly N-S direction, along the trend of anticline axis, is the watershed of east and west wings of anticline.The line belt of Laoshan(level-1218.3 m) ~ Jianshanzi(1185.5 m), nearly E-W direction is the watershed of the west wing of anticline. Karst water in the west wing, located in the south of the watershed, drains lognitudinally mainly along terrane to the south in the form of spring or spring groups, partly in landscape orientation. While most of watershed karst water in the west wing of anticline in the Juetai Dam~DaDongshan section, located in the north of watershed ,drains by cross frature to River Valley of Lengshui River(also named Hou River) in the form of spring or spring group, which can be used as the part of the drainage base of karst water in the section.The karst water in the section and that from the west wing of northdern DaDongshan, drain lognitudinally mainly along terrane in the north direction to cut breadthwise across Lenghe River vally anticline in the form of underground river or karst spring group. It is investigated that the lowest elevation of drainage underground river or spring group(such as Yaxueko underground river ), appearing in the west wing of this river vally ,.is about 520 m high .

It is surveyed that the elevation of the interchange between Lengshui River and ZhuPa River is about 467m high and the lowest karst spring appearing in the area of river vally which runs across the north wing of anticline is about 474 m high. So, it is considered that the karst water in the east and west wings of north anticline section, may hardly develop below 450m high. Most groundwater, located in the west wing of anticline in Juetai Dam ~ DaDongshan , drain mainly in landscape oriataton to Lenshui River (also named Hou River). The elevation of the river is 660m, which can be used as the lowest elevation for karst water development.While on the line from Baomuping to Jiazhou in the south of LanBandeng, ground water , drain mainly to XiangMa River. The elevation of the river in Jiazhou is 385m ,which can be used as the lowest elevation for karst waters development in the east wing of anticline of the section.

Above all, there is not integrated karst water system in anticline. Atmosphere precipitation is the only supply source for karst water. Besides forming surface runoff, most of atmosphere precipitation hides into underground and then forms karst groundwater runoff and finally drain to surface water system. The characteristics of recharge, runoff and outflow are: recharge dispersely by section, relatively integrated runoff along longitudinal crack-in-layer and transverse crack, and relatively integrated drain in the form of spring and ground river.according to each section and subsystem.

Hazards of Water and Mud-rock Pouring up in the West of Anticline Section of Construction Tunnel and its Analysis

Hazards of water and mud-rock pouring up during the construction

When the tunnel exit cuts across the east wing of the Dongmaling anticline to the core of karst water of vertical endless loop belt —→ season changed belt —→ horizontal endless loop belt—→sluggish stream belt in depth, the building encounter intense develop belt of the karst of east wing (i.e. pipeline network developed belt of the underground river or karst spring group), in addition too much of powerful rainfall. There were extensive water (sand,stones) pouring up time and again at the DK361+764,DK360+873,which cause lots of machines and tools buried or damaged, and the building tunneling met with obstruction seriously, We had to sustain tremendous loss in economy.

Analysis of water and mud-rock pouring up

Each spot of water pouring up at DK361+764, DK360+873, especially the spot at DK361+764, has the relatively obvious characteristics. During the construction the water pouring up appears: spraying pouring up water, turbid water, with plenty of mud and sand and also the initial water flow is extremely high, the duration time of flood peak is short, the water pouring up decreases sharply and trends to be stable and so on.

After sealed-block at DK361+764, water and mud-rock pouring up appear the characteristic of transferring.elsewhere, The Karst pipeline bedding collapsed along the right wall of the top of the cave at DK361+764, were sealed-block completely on Feb.11,2002.Then ground water was blocked up in the karst pipeline and consequently water level increases and hydraulic pressure augments. Finally, ground water, to find the way out, break the relatively failure rockmass on the left side of hance at DK361+764.(here originally a corrosion crack, Fig.3). Thus it successively caused two extensive water pouring up on Feb. 22,2002 and Mar. 3,2002 at the hance, the process of which carries lots of mud, sand and shiver stones. Afterward, the channel was seeled block by these shiver stones , mud and sand, only poured a little frature limpid water.Due to the reduction of counterpressure on the upper of the base and the weaker rockmass on the base of left wall breaked by the underground, the water pouring up bursted out around this area. Primary analysis indicated that the three sopts of karst water channel, such as the right side of the karst pipeline at DK361+764, the spot of water pouring up at the hance of the left wall and the base of left wall, should be closely connected to be the same water system. (Fig.2).

The analysis is indicated that the phenomena of water pouring up at DK361+764, from the initial intermittent, with airflow before 

Fig. 2 Karst connection in DK361+764

climax, to many spots transferring afterblocke, and finally casting plenty of rocks from water exit, shows the karst water is completely developed, many branch-shape drainage networks exist, and the turnnel exposure the main pipeling natural karst non-directly.

Each time when extensive water pouring up from each spot at DK361+764,DK360+873 etc, the water will carry lots of mud, sand an shiver stones, content 35%. The carriers come from two parts, one is the fillings and sediments from original karst cave, underground river and karst pipeline; For exemple, at DK361+764 ~ +758 section, two big corrosion fractures are bedding developed. One of them is a frature closely to exit terminal (i.e. near the top of the cave), about 0.11 m in width, filling with gray and yellow silt (mucky cohesion soil),and unmeantly carried some dolomite and limestone shiver. The other is close to entrance terminal (i.e.near the bottom of the cave), about 0.4 m in fracture width, filling with yellow silt (mucky cohesion soil), carried limestone and dolomite shiver. Because of extensive mud pouring up time after time, the fillings were washed out,  and terrane collapsed to form a kind of bedding collapsed cave with 5.4 m×3.4 m×10.0 m(height) (Fig. 3).

Fig. 3 Karst development on the right wall of Yuanliangshan tunnel

The other carrier comes from loose rockmass body of solution cavity. During the process of forming anticline of Tongmaling, through extruded ,and lately influenced by some tectonic movement. The rock body forms some horizontal veins. In addition, under the effects of efflorescence and corrosion, the rock is fragmentized, and the wall rock of solution cavity is loose, which can be carried during the process of forceful circulation and alternation of the ground water.

Each spot of water pouring up at DK361+764, DK360+873 section, if the surface without rainfall in a long time, the capacity of water pouring up will be small, stable and the water is almost limpid. When it is raining, especially after extensive rainstorm for several ten minutes~several hours, the capacity increase sharply and with lots of mud, sand or shiver stones. When last for several~ten hours or several tens hours, capacity will decrease sharply and trend to stability. For example, after one~two hours heavy rainfall on July.6,2002, an extensive water and mud-rock pouring up bursted out, instantaneous maximun is up to 27.5 m³/s, and plenty of shiver stones with mud are piled up.It is indicated that these spots are closely connected with the underground river or the krast spring group of the main pipeline networks and can directly receive the recharge from atmosphere precipitation. Due to the influence by multi-periodic structural evolvement, although the anticline is not a junction structure, the fratures in all directions develop intensively and has a good condition for recharge, runoff and outflow. There are three-class platforms which are the primary recharge souce for ground water, especially the following two pltforms, one is in the karst doline and depression belt with about 950~1050 m high, the other is in area of hudge karst trough of Paomu~Taoziping with about 700~800 m high. The atmosphere pricipitation can be rapidly absorbed and filtered and the coefficient infiltration reaches 0.6~0.8. Bedding planes fractures, corrosion fractures and accomplished karst pipeline are good tunnel for filtering.

Alternative repairing projects comparison

In order to guarrantee the safety of the tunnel building and its operation,and in view of the development of the karst and features of the poured up water and mud-rock and effect degree of the rainfall in the east wing of the anticline, We compare with the choice in the sluicing-hole drain, flat-guide drain, sealed-block and block-drain for the repairing projects about karst water (mud, sand, stones) pouring up in the east wing of the anticline ,describing as following respectively:

Sluicing-hole drain project

A sluicing-hole should be on the left 25m of the line, with 1732m in length.,profile grade 19% , and section dimension 3.5m×3.65m..And below the hole is a concrete sluicing-sink ,with 1.2m of sluicing height The end of sluicing-hole is set and controlled in accordance with corresponding plane at DK360+800. To draw the water in the sluicing-hole then drainage, lateral diversion hole(or catchment drill) is respectively set up at DK361+764,DK360+873 and other spots high in water output.

Flat-guide drain project

Flat-guide at PDK360+800~PDK362+574 section extends 1774m long, with 1.2m in construction. Below the flat-guide is a concrete sluicing-sink, with 1.2m in height. Its sluicing bottom is lower 1.99m than the groove cover of positive-hole .To draw the water in flat-guide then drainage ,a lateral diversion hole (diversion sink or catchment drill) is set up at DK361+764 and other spots high in water output .

Sealed-block project

Concrete, deliveried by high voltage pump, is used to seal-block all the karst capacities and pipelines at DK361+764, DK360+873~+950. Hydraulic pressure resistance linine is adopted to positive-hole at DK361+764 , DK360+873~+950 sections and corresponding flat-guide at PDK361+660~+820 and PDK360+820~+980 section, the intensity of flat-guide is slightly lower than positive-hole’s.

Block-drain project

Block-drain is defined as blocked karst pipeline by mud, sand and shiver stone to make clean water can pour in right quantity. In short, it means to drain water and reserve mud, sand and shiver stone.

Projects comparison

The sluicing-hole drain and flat-guide drain projects can avoid the water and mud-rock extensively pouring up in the scope of tunnel cave and their direct effects on tunnel cave and its lining cutting structure. But also the disadvangs exist. Arbitrarily draining the ground water and its belonging mud, sand and shiver stones, will influnce local entironment in the short term. It has the potential problems to make solution cavity further enlarge, and cause solution cavity and ground collapse. With respect to flat-guide project, due to the limitation of longitudinal slope, the carriers are so easy to fill up and there are lots of work lately to clean the silt.The application of flat-guide project will influnce the current construction of tunnel, discharge capacity, adverse to flat-guide as fire rescue access during the operation and reservation of double lines and still necessary to break a sluicing pipeline when building the dual lines.

The sealed-block project is adopted to make ground water find a new way out, so as to be balance again. If we can get the expected effect , there will be less trouble in the phase of railway operation. However, there are lots of unexpected factors when carrying out the project.If anticipative impact is reached, it will lessen a lot of trouble during the railroad operation. First of all, due to the influence by its high-pressure karst water, lining cutting structure is at risk; Secondly, in order to find a new exit, ground water may pouring up at the weaker position in the cave, while it is difficult to ensure the range of reinforcing lining cutting structure and Injection.

The block-drain project will neither cause lots of erosion of mud, sand and stones nor form the high hydraulic pressure, and neither threaten to tunnel lining cutting structure nor influence the entironment. It is the most reasonable in theroy. Howerer, under the current technological and equipment condition , it is difficult to realize. Sealed-block project has large in work quantities and the effect is influenced by the rock structure and technical reason.,and difficult to predict.Besides,after sealed-block, lining cutting will endure more hydrostatic pressure and both the constructed lining cutting built and flat-guide should be reinforced. In a word, the block-drain project is difficult in construction, big in engineering quantities, large in investmet, and that’s reason we adopt the drain project.

We compare time and again with the choices and finally adopt the sluicing-hole drain project. The advantages and disadvantages of each repair project see Tab.1.

Table 1. Correlation of the different regulatory programs

Conclusion

When cuts across the east wing of the Dongmaling anticline, the building encounter the sector which develop an endless loop tape, in addition to much of powerful rainfall. There were extensive water and mud-rock pouring up time and again on the DK361+764,DK360+873,which cause lots of machines and tools buried or damaged, and the building tunneling met with obstruction seriously, We had to sustain tremendous loss in economy. In order to guarrantee the safety of the tunnel building and its operation,and in view of the development of the karst and features of the poured up water and mud-rock and effect degree of the rainfall in the east wing of the anticline, We compare with the choice in the sluicing-hole drain, flat-guide drain, sealed-block and block-drain for the repairing projects about karst water (mud, sand, stones) pouring up in the east wing of the anticline, and finally we adopt the first one;from October of 2002 to April of 2003, the project of sluicing-hole drain is constructed. The rainy season from May to September in 2003, Tongmaling anticline section in Yuanliangshan tunnel encountered powerful rainfall, and many sections such as DK 361+764; DK360+873 are suffered extensive water (mud, sand, stones) pouring up suddenly and continuously. Fortunately, the tunnel and lining cuttings are safe and sound by draining the water-mud-stones through sluicing hole. That indicates it is a correct choice to adopt the sluice hole project to renovate hazards of karst water pouring up from the east wing of anticline.

References

[1]         ZHANG, Z.Y&WANG, S.T&WANG, L.S. The analyze theory of engineering geology. Geological Publishing House. Beijing 1994.

[2]         The Second Railways Survey & Design Institute. Karst engineering geology. Chinese Railway Publ. Beijing 1984.

[3]         The Karst Research group in Geological Institute of Chinese Scientific Academy. The Research of Chinese Karst. Scientific Publ. Beijing 1987.