Tong Dengjin

Water, existing in different forms, is one of the important environmental factors that caused damage to outdoor cultural and historic remains such as grottoes, rock carvings, and so on. Affections of water produce or aggravate varied grotto diseases. Water permeation in grottoes occurs in arid or semi-aridity area, also in humid area. So control and treatment of water is important in the protective work of grottoes. Dazu Rock Carvings are located in the southwest area with plenty of rainfall. Permeation is a chief factor for the diseases of rock carvings. So the work of drainage and prevention of permeation in the protective work should be a long-term task.

Construction of Dazu Rock Carvings started in early Tang Dynasty, went through the late Tang Dynasty, Five Dynasties and Northern Song Dynasty, flourished in the Southern Song Dynasty. Now, there remain more than 100 spots of cliffside carvings and more than 50,000 statues. 75 spots have been protected at different levels for their cultural and historic value. Among them, the cliffside carvings at Baodingshan, Beishan, Nanshan, Shizhuanshan and Shimenshan are the spots to be protected at the national level for their cultural and historic value. Dazu Rock Carvings was inscribed on the World Heritage List in December 1999, and became the second cultural and historic remains in grotto art gaining this honor next to Mogao grottoes. It has abundant rainfall in Dazu County. So drainage and control of permeation at Dazu Rock Carvings were paid great attention to and some protective measures were adopted at the beginning of construction. This can be reflected from the structures of statue niches at all the spots of Dazu Rock Carvings. Also this is one of the reasons that the vicissitudinous Dazu Rock Carvings have been well protected as they are. After the People’s Republic of China was founded, Dazu Rock Carving art had been given a new life. Scientific methods had been adopted in the protection and administration. Protective research on grottoes has gained a certain achievement. Treatment and research on permeation has played an important part in the protection of Dazu Rock Carvings. In the long-term protective work, we have accumulated rich practical experiences and improved our theoretical level. Control and treatment of permeation for grottoes has satisfied the protective work of Dazu Rock Carvings. Due to limited space, this paper reports the following main contents in the chief clue of typical protective projects: Protection of prevention of permeation and drainage (treatment of permeation for grottoes); Environmental management of cultural relics area (treatment of water in the area); Chemical sealing of the statues, etc.

Enforcement plan of drainage tunnels at Beishan grottoes was that a trunk tunnel, measuring 45 meters long from south to north under the niche 124 to niche 169 of Beishan grottoes, was cut 5-6 meters away from the rock face, and then side tunnels from east to west were cut as exits of water under the niche 124, niche 140, niche 163 respectively, their sections were 2.5 meters high and 1.5 meters wide. The trunk and side tunnels totaled 157 meters long. The highest point of drainage ditch in the tunnel was 0.4 meters blow the ground. Additional tablets of sandstone built all the layer of mudstone on the side of the tunnel. The ceiling of the tunnel was arch. In order to fully enlarge the drainage, 170 drills, whose diameter was 0.42 meters, 3-6 meters deep, were arranged on the top of the tunnels. Lighting was installed in the tunnels so as to examine and repair.

Since the project has finished, collapse and new crevice haven’t appeared in the tunnels through the long-term observation. They are possessed of the fine characteristic of stability. Enforcement of drainage and its affiliated project of the runnels at Beishan grottoes had controlled basically the permeation of grottoes. According to observation, before the tunnel was dug in September 1989, there were 31 spots of permeation and phenomenon of water dropping and flowing in niches at Beishan grottoes. After the tunnel was completed in April to December 1994, there were only 8 spots of humidness in rain season, and no phenomenon of water dropping and flowing in niches. But there were many spots water going out in the tunnel and the flow of water was high in the tunnels. The maximum of flow got to 40 milliliter a second.

Drainage project of large tunnels at Beishan grottoes brought in effect at the beginning of 1990s was a new try on protective technique of grottoes in our country at that time. Treatment of water was very effective. It was one of the successful examples for the treatment of water of Dazu Rock Carvings and grottoes in China.

SBEN, 31m long and 7m high, is one of the representative works among the statues at Baoding grottoes. It is imposing and highly skilled. It was a masterpiece among the same kind of rock carvings. SBEN is located on the east cliffside of Dafowan. Because the spot of the statue of Nine Dragons Bathing the Prince was the only sluicing spot of surface water in the region of 0.8 square kilometers around the Sacred Pool and the important exit of groundwater, permeation at the SBEN caused by the upper layer of detained water and surface water of carved rock was very serious. Water in Sacred Pool was the main source of permeation. Due to long-term erosion of permeation, the head, breast, belly of the statue were the situation adhered by water permeating, humidness and bryophyte in rain season and by the black and gray stain of "pustule" of discoloration in arid season. These did seriously damage to the image and value of the SBEN.

Permeation of the statue had extensive source and many ways. The control of permeation was a synthetic program. Under the direction and help of the China Institute of Cultural Relics, AMD. decided to adopt the measures of treatment such as the dam preventing water, tunnel draining away water, open drain preventing water and drainage drill. In 1998, first stage of the treatment of water at the Sacred Pool was carried out .We built the dam preventing water to treat the diseases caused by the water in the Sacred Pool. According to high demand of prevention of permeation, the enforcement project of advanced technique, simple technology of construction and operation, effective prevention of permeation were adopted. So we established the dam of compound reinforced concrete.

After the dam built, in order to strengthen the effect, firstly, SNA--210 sand mortar preventing water of organosilicon was brushed on the head—on side of the dam, 20-30 millimeters thick. This kind of sand mortar had delicate structure, no contractility and split-up, good result of preventing water. This was the reason that high polymer organosilicon, whose principal component was methyl silicon alcohol sodium, was added to it. Its formula in proportion was that:

First stage of treatment of water for the SBEN was completed in June 1998. Through the observation of more than two years, permeation of its breast and belly got to control successfully, but two parts of its head still permeated. So the overall methods of treatment of water needed to be improved. Now the second stage of treatment design has fulfilled. Drainage tunnel, ditch and drill are integrated together. Starting with groundwater source and ways of permeation, the principle of preventing and dredging water integrated together is adopted. Drainage tunnel and drill will be designed around the ISBN to dredge water in the crevices of sandstone; Drainage ditch in the ground will draw the Forth System of water and dam the source of water in the crevices of sandstone; Also drainage ditch will be planed to draw water in Dafowan. This program will be put into effect after the approval of department concerned.

Since the work that Dazu Rock Carvings nominated for the World Culture Heritage developed, environmental management has been the key in questions. Plenty of work has been done to the environment of Baoding grottoes. As Baodingzhen is a rural town, it had no basic installment of environmental sanitation such as drainage. Domestic and industrial sewage converged into the Sacred Pool making the water in the Pool black and foul. Results of water analysis in the Pool showed that the content of chlorine ion highly amounted to 96.39 milligram a liter. It showed that water in the Pool was seriously polluted, then permeated along the rock at Dafowan and became the main factor that caused the diseases such as salt deposit and "pustule" on the surface of rock carvings. Pollution was getting increasing serious at the spots of Baoding Rock Carvings with the development of tourism. Purification of environment around the spots of Baoding grottoes became urgent. In 1996, AMD. carried out the project of tunnels draining polluted water the center of the Sacred Pool. A shaft on the northern side of the Sacred Pool was cut, 14 meters deep and 1.2 meters wide, 65 meters away from the northern side of the SBEN. Much ground water permeated into the shaft and permeation into the statue decreased. Polluted water around the Pool flowed into the shaft though pipes. Then, take the shaft as a starting point, a tunnel was cut from west to north, which has a slope of 30 degrees, and is 200 meters long, 1.5 meters wide and 1.8 meters high. For the purpose of preventing polluted water in the tunnels from permeation, the bottom and two walls, which were in 1.5 meters high range of the tunnels, were brushed by waterproof cement. A pool of disposal of sewage was built to make sewage flow into lower reaches through the disposal.

In the overall management of environment of Baoding grottoes, a project, being still worth pointing out, was that more than 330 mu of land was requisitioned; 44000 trees, grasses, arbors and bushes, 4800 square meters grassland, were planted. It could be said that this measure and the project of tunnel draining sewage mentioned above produced good results. Now, it is directly noticed that water in the pools on two sides of the SBEN is clear. And excessive nutrition in surface water caused by cultivating and applying fertilizer in the paddy field around grottoes, the high content of salt and its damage to grottoes at Dafowan were reduced. Trees and grass were rationally planted around Dafowan. On one hand, they could conserve water, reduce wind speed, purify air and slow down noise. On the other hand, transpiration of plant could also reduce frequency and scope of temperature and humidity change so that damage speed to statues lowered. These are all beneficial to the protection of grottoes.

Dazu Rock Carvings enjoy a warm and wet climate and abundant rainfall. They are located along the Chongqing-Guiyang Rain Belt that is the major region of acid rain. Weathering of Rock carvings is closely related to the environmental factor. To a great extent, it could be said that the protection of preventing statues from weathering is to prevent precipitation and acid rain. Hence, protective materials of preventing statues from weathering should have the characteristics of fine ageing-resistance, high water-resistance, and powerful pollution-resistance.

AMD. and Sichuan Provincial Institute of Cultural Relics and Archaeology have cooperated with each other for many years to develop the work of chemical protection of Dazu Rock Carvings. According to their characteristics, we are always selecting the protective material of organosilicon resin.

In March and November 1996, China Institute of Cultural relics, Sichuan Provincial Institute of Archaeology and AMD. cooperated to use the primary polymer of organosilicon resin to seal up niche 2, niche 3, niche 4,and niche 17 at Baoding grottoes with the authorization of the Sate Bureau of Cultural Relics of the People’s Republic of China. Before statues sealed, pollutant such as dust on the surface of statues must be cleared up so as to assure good results. And 0.8-model man-made compressed sprayer was used to spray. For the purpose of decrease in loss, nozzle should be kept 20 centimeters away from the surface of statues, while spraying repeatedly for several times from top to bottom. So sealing materials fully permeated weathered rock carvings. When first spraying finished, paper of intense hygroscopicity immediately was used to absorb superfluous sealing materials detained on the surface of rock carvings, especially at the sunken spots of dress and corolla of statue. To ordinary surface of rock, it was acceptable to be sprayed once again in 15 minutes. After spraying finished, workers could used a small brush to brush the position without spraying with the materials. In the whole process of protection, measures must be adopt to prevent the materials from splashing down so as not to cause pollution.

CONCLUSION

The treatment of permeation at Dazu Rock Carvings is a long—term task. Prevention of permeation, drainage, materials and technology of chemical sealing are still at the stage of further research and experiment. Meanwhile, the overall environmental management taking the treatment of water around grottoes as the dominant factor is still a very arduous task. AMD. has established two stations at two spots of rock carvings for the monitoring of environment so as to conserve environment of the grottoes. Now, we have developed the projects such as meteorological monitor and atmospheric quality monitor. For the sake of understanding and finding out situation of water quality at any time, the project of water quality monitor will be further developed from now on. So it will provide scientific data for treatment of permeation of grottoes. Treatment of natural environment just in the larger region is effective. Under the circumstance of serious pollution of environment all over our country, effect of treatment of environment in the small region is limited. All above are the problems that we have to face with and make great efforts to solve.