Ichita Shimoda

Uncovering archaeological landscapes at Angkor using lidar

Previous archaeological mapping work on the successive medieval capitals of the Khmer Empire located at Angkor, in northwest Cambodia (∼9th to 15th centuries in the Common Era, C.E.), has identified it as the largest settlement complex of the preindustrial world, and yet crucial areas have remained unmapped, in particular the ceremonial centers and their surroundings, where dense forest obscures the traces of the civilization that typically remain in evidence in surface topography. Here we describe the use of airborne laser scanning (lidar) technology to create high-precision digital elevation models of the ground surface beneath the vegetation cover. We identify an entire, previously undocumented, formally planned urban landscape into which the major temples such as Angkor Wat were integrated. Beyond these newly identified urban landscapes, the lidar data reveal anthropogenic changes to the landscape on a vast scale and lend further weight to an emerging consensus that infrastructural complexity, unsustainable modes of subsistence, and climate variation were crucial factors in the decline of the classical Khmer civilization.

The Construction Process of the Angkor Monuments Elucidated by the Magnetic Susceptibility of Sandstone

The Angkor monuments in Cambodia are mainly constructed of grey to yellowish-brown sandstones. No differences in the constituent minerals and in the chemical composition of the sandstones have been confirmed among the monuments. However, we have found their magnetic susceptibility a useful parameter by which to distinguish them. The principal monuments of Angkor Wat, Ta Prohm, Preah Khan, Banteay Kdei and Bayon, constructed from the Angkor Wat period to the Bayon period (from the beginning of the 12th century to the beginning of the 13th century AD), were investigated in detail using a portable magnetic susceptibility meter. We succeeded in dividing the periods of construction into stages. This elucidated the enlargement process of the monuments and correlated their construction stages.

AMS RADIOCARBON DATING OF WOOD SAMPLES FROM THE ANGKOR MONUMENTS, CAMBODIA

In the Angkor monuments of Cambodia, pieces of wood remain (as head frames of doorways, crossbeams, ceiling boards, etc.) in the following 8 monuments: Bakong, Lolei, Baksei Chamkrong, North Khleang, Angkor Wat, Banteay Kdei, Bayon, and Gates of Angkor Thom. Accelerator mass spectrometry (AMS) radiocarbon dating carried out on 15 wood samples collected from the above 8 monuments revealed that most of the wood samples are original, except for the head frame of a doorway in Baksei Chamkrong, the ceiling boards in the northwest tower, and a crossbeam with pivot hole in the southwest tower of the Inner Gallery of Angkor Wat. The 14C age for the head frame of a doorway in the inner wall under the central tower of North Khleang supports the hypothesis that the inner walls are additions from a later period.

Geotechnical Aspects of the N1 Tower, Prasat Sour Prat, Angkor Thom, Cambodia

This paper presents a case study of foundation of an inclined independent masonry tower in Angkor. One of the Prasat Sour Prat towers had been dismantled before reconstruction for conservation. The foundation was inclined as the same as the upper structure of the tower and spreading outwards. The inclination was considered caused by foundation failure with some differential settlements of the ground. During dismantling, the soil layers exposed on the trenched section were found rather horizontal than the inclined state that had been expected. Laterite blocks of step slope stones was found to have slid down along the soil mound of the foundation. The mechanism might have been caused by weakening of soil strength by wetting ground. Without dismantling, the real mechanism of the inclination was never known as well as the corresponding counter measures.

Dismantling and Reconstitution of Prasat Suor Prat, Angkor Thom, Cambodia

This paper presents geotechnical aspects of dismantling process of one of masonry towers named Prasat Suor Prat that had been constructed in the end of the 12 th century during the Angkor Period in Cambodia. A series of 12 towers had been constructed from south to north along the east side of Royal Plaza in Angkor Thom. One of the towers, named as N1 Tower, was found badly displaced with inclination of about 5 degrees to the north-west and horizontal spreading at the foundation level. The Tower was dismantled before restoration work by JSA (Japanese Government Team for Safeguarding Angkor) to study possible mechanism that had caused inclination of the Tower and horizontal spreading of stair stones. Dismantling upper structures as well as foundation mound were performed by archaeological trench. The trench revealed the mechanism of deformation of the structure as well as foundation. Before the dismantling, the inclination was believed to be caused by tilting of the foundation mound caused by general sliding failure of the foundation towards adjacent pond. However, it was revealed that the mound was not tilted but kept horizontal under yielded state causing only horizontal spreading. It was found that the inclination was caused by slip down of the sidestep cut stones that had covered the side slopes of the mound.

Measurement of the Joint Displacement Along Masonry Wall Using Digital Photogrammetry for the Structural Stability of the Borobudur Temple, Indonesia

For the preservation and restoration of masonry structures, it is significantly important to evaluate their stability properly and measurement of cracks/joints along masonry walls will be useful to investigate the deformation of masonry structures. In this study, the newly developed crack/joint deformation measurement system using digital photogrammetry was applied to investigate the structural stability of the Borobudur Temple, Indonesia. In the newly developed crack/joint measurement system, a pair of reflective targets is employed at the measurement points around the cracks/joints as gauges and the digital camera image of the targets is obtained by taking photos using digital camera. Employing image processing and photogrammetry, the two dimensional displacement in local coordinates of the cracks/joints can be calculated from digital images of targets. For the site investigation and measurements in the Borobudur Temple, five different joints along the masonry wall (with high possibility for displacement) were selected and monitored. After 8 months of the monitoring, the normal displacement of about 0.6 mm was observed at two of five selected joints and groundwater will play important roles for joint displacement.

Identifying damaged areas inside a masonry monument using a combined interpretation of resistivity and ground-penetrating radar data

The Bayon Complex in the Angkor heritage site, Cambodia, has been damaged by weathering. To plan its long-term preservation, it is essential to investigate its internal structure and the degree of damage within the masonry monument. This study shows results of ground-penetrating radar (GPR) and electrical exploration surveys, and an interpreted section of the internal structure and moisture distribution in the masonry monument. The GPR can detect boundaries between stone blocks and between stone blocks and compacted soil. Electrical resistivity can indicate moisture distribution with high reliability in combination with GPR sections. The top surface zone of the terrace structure of this monument is composed of three layers of stone blocks, and the zone below a depth of 55–60 cm is composed of compacted soil. Rainwater penetrates into the terrace through gaps between the stone blocks and drains from vertical walls through cavities in the top part of the compacted soil. Damaged areas are limited to a part of the terrace, and a large area has remained in good condition. This study shows that a combination of electrical resistivity and GPR data is useful for investigating the internal structures and classifying the degree of damage to old stone structures. This study shows results of ground-penetrating radar and electrical exploration surveys, and an interpreted section of the internal structure and moisture distribution in the Bayon Complex in the Angkor heritage site, Cambodia. Rainwater penetrates into the monument through gaps between stone blocks and drains from vertical walls through cavities in the top part.

A PROPOSED RATIONAL BEHIND THE ANCIENT KHMER'S DIMENSIONAL PLANNING AT THE BENG MEALEA

Based on the results of previous studies on planning methods and procedures of various Khmer monuments, we attempted to analyze the case of Beng Mealea. The construction measure is considered to be 411mm, however, dimensional inconsistencies are revealed in details of some parts. The objective of this paper is to examine the planning methods and process of Beng Mealea temple by a restorative approach. Judging from the result of analysis, the planning of Beng Mealea was started with double-enclosure temple layout, and subsequently developped, probably on the way of construction, to triple-enclosure. In consequence, we can see several traces of modification in its dimesional disposition. The method and technique of this temple planning is uncharted in a sense, different from that of any other Khmer monuments we studied before.

Classifying destruction areas in a stone structure from joint interpretation of resistivity and ground-penetrating radar data

The Bayon Complex in the Angkor Heritage Site, Cambodia has been destructed by weathering effect. Investigating the structure and the progressive degree of destruction inside the masonry monument is needed to preserve it for a long time. This study shows the survey results of electric exploration and groundpenetrating radar (GPR) and the interpreted sections of internal structure and moisture distribution. GPR can detect boundaries between stone blocks and a boundary between a stone block and a compacted soil layer. Electric resistivity can estimate moisture distribution using composed structures estimated from the GPR. The top subsurface area of the terrace structure of the monument is composed of three layers of stone blocks and the area below the depth of 55 cm or 60 cm is composed of compacted soil. Rainwater invades into the terrace through between stone blocks and drains from a vertical wall through cavities in the top zone of the compacted soil. Destruction areas are limited in a part of the terrace and wide areas keep good conditions. This study shows that the joint interpretation of resistivity and GPR data is useful to investigate internal structures and to classify destruction degrees of old stone structures.