The analysis for the reasons of deterioration and research works at Bayon. The understanding of the accurate present situation and technical guidance for the restoration of Bayon.

■Relation of Bayon-Angkor Thom- Angkor Monumental Area
               (Historical City Planning Survey)

To clarify the principles of citadel city formation of Angkor Thom, in the period when the Khmer Dynasty was most prosperous, we have analyzed the principles of formation of the Royal Plaza which was the important city facility of Angkor Thom, the planning procedure of Angkor Thom and the construction procedure of the Angkor region based on accurate positioning data from our survey work. By obtaining precise data by using the GPS (Global Positioning System) in order to collect an accurate data, we have been grasping the following information.

  1. Central position of the monuments
  2. Axis of the monuments
  3. Gap of the monument axis from the True North
  4. Direction between a target (mountains, river, vista, etc.)
  5. Distance (between ex. former age monument, city facilities, mountains, vista, etc.)
Together with archaeological analysis, we have been analyzing from the city planning point of view.
■Specific Investigations of the Present Situation of Bayon

1.Architectural Inventory of Bayon (Architecture /Archaeology Survey)

Not only recording the present situation of Bayon, but also seeking the original state, and construction transition. We have carefully surveyed through many traces and continuing to create the entire inventory of Bayon. Also the following works are in progress.
(1)Determining and Categorizing the Scattered Stones
vNumerous stone elements are scattered around the building. We carefully observed each characteristics and decorations, and matched with remaining elements in order to determine the original position.
(2)Excavation and the Long Trench
The excavation of the long trench that extends 80m from the inner gallery of the Bayon complex to the outer gallery and farther into the surrounding roads is the largest excavation work done in the history of Bayon studies. We were able to find interesting features like culvert-styled drainages running under the floor of the outer gallery and a horizontal tunnel under the floor of the inner gallery. In addition, the processes of construction of and modifications to the complex, the method of construction used for the inner and outer galleries and the structure and extent of the foundation trench was carefully studied.
(3)Investigation of the Drainage System
When the drainage system looses its function, it becomes one of the reasons for the tower to incline, or the movement of the gallery platform. To cope with these problems, the investigation of the present situation, and the conservation and maintenance of the drainage system is very important.

2.The Meanings of the Deity faces & the Bas-Relief (Art History Survey)
After suffering from invade of Champa or other hardships, the construction of the Bayon temple started by Jayavarman VII in the latter half of the 12th century, undoubtedly, is the state temple that gives consideration to the countrywide religious powers, and that expects to get the power of all the domestic gods and divinity. From this viewpoint, we tackled to study the character of the Bayon temple from motifs of all sculptures. In this process we have conducted (1) the investigation on the character and the production background of the deity faces decorating the towers of Bayon, (2) the investigation of various sculptures on the pediments and outer walls of Bayon, (3) the investigation on the sculptures of the Bayon period, held by the National Museum of Cambodia, Phnom Penh.
3. Monitoring the Movements of the Towers of Bayon (Building Structure Survey)
The overall trend of inclination amassed over the years could be monitored by measuring the difference between the center point of the tips of the towers and that of the base, and then calculating the incline. The inclination of 38 towers was actually measured in this way. At the middle level of the central tower, there are eight sub-towers surrounding the central one. We have installed micro crack gages between vertical opening of adjoining stones of side walls of these sub-towers. We have also continued observe the rainfall, wind velocity and direction, temperature and underground water.
4. Geological and Environmental Observations at Bayon and Angkor area
  (Geo-technology, Geology and Environmental Survey)
The material content of the sand in the Northern Library, consisting of fine sand and clay, is of good quality. However, it does not harden easily. It was necessary to re-examine the ancient construction method with a practical archaeological approach. We also carried out the first geological boring at the Angkor area in 1994. By these first experiences the base rock was found at the depth of 80-90m from the surface and basic knowledge about geological formation was obtained. After that we are using that hole for water level monitoring. Beside that, we are monitoring the environmental changes; temperature, humidity, wind speed and direction, rainfall, and so on. Serious problems are seen in the Angkor area, the water quality is getting worse and Siem Reap river doesnユt carry enough water during the dry seasons.
5. Contribution of the Magnetic Susceptibility of the Sandstone for the Analysis of Architectural Construction History of Bayon Style Monuments (Petrology Survey)
Based on the magnetic susceptibility of the sandstone blocks, the construction process and correlation of the construction period of the Bayon style monuments were elucidated. Especially, the precise measurement was carried out for the representative Bayon style monuments , Ta Prohm, Preah Kahn, Banteay Kdei and Bayon. As a result, it is revealed that the magnetic susceptibility of the sandstone blocks changes systematically with time, Based on this systematic change in the magnetic susceptibility, we succeeded in the elucidation of their construction process including other small monuments of the Bayon style.
6.Biological influence on Bayon (Conservation Science Survey)
There have been severe biodeterioration caused by trees, lichens, algae, microorganisms, termites, bats and so on at Angkor sites. It may fairly be said that Bayon is covered by lichens. And also, blackening effects and scaling-like deteriorations of stone materials can be found at Angkor sites. Many bats have been inhabiting in the Central Mass of Bayon and its surroundings, and an old termite nest was found in the foundation of the Northern Library of Bayon. We conducted experiments for lichenocides; that is, their growth inhabiting effect and removal effect against lichens and algae ware recorded for few years.
7. Bayon and the Angkor Monuments among the Local People
  (Anthropology / City Planning Survey)
Not only about the conservation and restoration of Bayon, but also important it is to the heart and spirit of the local people. We surveyed around the villages of Angkor to seek what kind of significance the monumennt has for the local Cambodians. Previously there were not so many information of the relationship between the monuments and the local people. We surveyed through interviews and investigations of there daily lifestyle. Also we have found some sets of relationship between their housing and their historical platform environment. These points are important to consider how the monument should be utilized and preserved, and how the local have their relationships with the monuments.
■Deterioration & Collapsing Mechanism of Bayon

1. Deterioration of Sand Stones & Bas-Relief of Bayon

The deterioration process for sand stones mainly seen in Angkor area have points in common. Physicochemical effects such as temperature change, moisture, Salt weathering, and biological effects such as plants, lichens, fungi and bacteria are so. A general method to cope with deterioration is removing organisms like algae and lichens consolidating the stone matrix, adding water proof performance, but because of the high temperature and high humidity climate of this district, we cannot always treat sufficiently with the former materials and techniques. Especially at Bayon, the deterioration of the great bas-relief at the double galleries are confronting serious situation.

2. Structural System of the Bayon Central Tower
        & Inclination Reasons of Tower Buildings
The Bayon complex is a conglomeration of 50 towers, whose outlines forms like mountains. Among various structures of the Bayon, the main tower is one of the most important and unique monument. Considering the stability from the movement monitoring of such masonry tower structure buildings like the central tower, by observing the present situation, measuring the gap opening and inclination, the following two matters, can be counted as the fundamental types of collapse. First case is that the tower leans and falls because the center of balance of the tower moves. These tendency can bee seen in the Leaning Tower of Pisa. Another case is, when the exfoliation and falling happens from the outer part because the stacked structure of stones partially weathers or displaces. These types of collapse can be predicted for the occurrence of the destruction of the entire tower structure. It is one of the important problems that a prompt measure is required
3.Present Situation of Disruption of the Bayon complex
As matters now stand, many buildings are in critical conditions of disintegrating like the central tower, the southern library heading the list. Especially the outer gallery: with the exception of part of the gopura, the whole roof has fallen down and the decorative relief of the wall is being weathered away. We carried out temporary support on some dangerous parts. As for the reorganization of the scattered collapsed elements, JSA have organized the scattered elements around the Northern Library, and beside these, others we see them piled up around various parts of the complex. Such records in some diaries, or records of where the scattered materials were moved, have not been discovered to this day. That is being one of the difficulties for the coming restoration work.
4.Monitoring of the Bayon Northern Library after the Restoration Completion
It is no exaggeration to say how long the restored building lasts afterward very much depends on the maintenance control work after the restoration work. It is obvious that one of the reasons of collapse is uneven subsidence by the movement and outflow of the sand inside the platform. In case that the restored structure comes to be in danger of collapse again, movement of pillars and walls are most likely detected first as sign. Therefore, in order to monitor subsidence we made marking to the pillars, pilasters, and for each wall. As to the movements of other parts we conduct a periodical inspection twice a year, and pay special attention to confirm if there is any cracks and damage on the restored materials, or any new deterioration happening, and carry out a suitable treatment.
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