The georadar research of Sacsayhuaman archaeological complex

Sacsayhuaman

In recent years the employees of Sacsayhuaman archaeological complex witnessesed a number of destructive processes taking place at the certain sites of the complex. These consisted of the large cracks coming forth in the main walls, the shift of the stone blocks and recession of the walls (see the Drawings).

Such trend may lead to an irreversible and unrecognizable change of the complex which remains to be one of the most significant monuments of the heritage of Inca. That's why this issue raised a need to conduct a research to define the reasons of these continuous destructive processes taking place at Saksaywaman complex. Despite the state of art technologies of the modern geology and geophysics, it was difficult to find the one which allows to have a deep look into the soil and to find out the clear causes of the adverse processes influencing the constructions of the complex.

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Introduction

In the beginning of July 2012, under the guidance of the Ministry of Culture of Peru a group of geophysicists from Geo & Asociados SRL was called-off to research the current problem of Sacsayhuaman. The selection of the company was not by accident as the experts of this research company possess the technology of georadar scanning, that was developed in the Russian institute VNIISMI, and which has no analogy in the world. The georadars of “Loza” series allow exploring the geologic structure of land till the level of 200 meters below the ground surface. Such georadar researches allow the experts of VNIISMI to detect the areas of high humidity, the fissures in rock formations, crust fractures, underground objects, etc.

Research of the 4 levels of Sacsayhuaman

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Highlighted in yellow are the sections of walls where the fractures between the blocks are of significant size. Highlighted in red are the sections where the walls were destroyed.

During the research 4 cross-sections of the main levels of the complex were measured. To achieve the maximum detail of measurements the minimal step was 10 sm (the accuracy of step was metered with a measuring reel).

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The results of the measurements were sent to the Russian VNIISMI institute for further analysis and reading. Data reading was performed by Pavel Morozov, chief georadar expert of VNIISMI.
The sites under levels 3 and 4 of the wall 60-70 meters to the west of the wall slide were of most interest.

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In the demonstrated area of level 4 there was diagnosed an extensive area of fissured rocky soil. The fissured area is detected to be at the depth 10-12 meters.

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In the demonstrated zone of level 3 an extended area of fissured soil is also detected.

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An extended zone of fissured soil goes through the area of wall foundation. Such fissuring under the wall has a role of a drainage basin and a channel for the natural line gradient movement of ground waters. Uncontrollable local movement of ground waters under the wall’s foundation will lead to the washout of the easily soluble fractions of the top layer of soil and to the loss of the carrying capacity of the wall’s foundation.

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Enlarged cross-section allows to observe the areas of soil down-warping and subsidence – they are located directly under the foundation of the wall.
It is worth adding that this is not the only area of fissuring. Below are the several similar examples located at different levels.

Level 1:

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Level 2:

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Level 3:

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To prevent the further destruction of wall, it is necessary to conduct further investigation of the soil under the foundation, to detect all zones of fissuring and to track their extension. Based on the data regarding the location of the fissuring areas where the surface waters are captured and from where they flow down along the natural gradient line, it is necessary to organize the lateral drainage of the surface waters and their deflection from the wall foundation.

Analysis of the block stone surface

Extensive erosion of the surface was observed at a great number of Sacsayhuaman block stones during the georadar research by the experts of “Geo & Asociados SRL”.

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To clarify the cause of these processes the samples of materials which bear no cultural value were taken (this was approved by the staff of the archaeological unit). At the moment of preparation of this report, comprehensive analyses are still being carried out in a number of Russian laboratories – this is to get the precise information regarding the geological structure, characteristics and the chemical formula of the mentioned samples. However, the first preliminary analysis was performed yet during the georadar measurements – 2 samples were placed into an acidic medium (vinegar). After several hours the samples got dissolved almost completely with only a little amount of residue remaining.

Despite the uncertainty as to the precise chemical formula of the material, the mentioned experiment demonstrates that the stone blocks in the walls of Sacsayhuaman may gradually dissolve under the influence of acidic environment. Acidic environment in its turn is often observed in rain precipitations of many countries, which possess heavy industry where the production cycle with utilization of various acids is being violated (for example, mining industry).

To verify the mentioned hypothesis the research of the chemical content of rain precipitations is required. In case of discovery of even the slightest contents of any acids in rain precipitations, the necessary and immediate measures will need to be taken to protect the Sacsayhuaman archaeological complex. That can be done with the help of modern methods (covering the stone blocks with a protective coating, etc.).

Archaeological research of the Sacsayhuaman “Arena”

In addition, there was conducted a research of a land plot of circular shape located in the Northern part of Sacsayhuaman (hereinafter named “Arena”) since it is of high archaeological interest.

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To make the measurements easier a rectangular site within the arena was singled out. At the above drawing the 1-4 figures mark the boundaries of the measuring range. In total, 35 cross-sections were measured 50 meters each (the first cross-section was located in the direction of 1->2 and the last one was located between 3->4); the distance between the cross-sections is 1 meter. After the primary data processing it became possible to construct the 3D model of the researched area:

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The obtained data were also sent for further analysis to the VNIISMI Institute. As a result, a few interesting underground objects were detected.
Between the marks 2 and 4, almost at the very border of the measuring range, there is a flat top of a big stone. The top is located at a ground level (marked with a red arrow at the drawing below):

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Below is the radargram of this object:

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One of the VNIISMI experts deems this object to be either an underground sepulchre or a unit of a similar shape. The object is 90% hand made.

At a larger part of the measuring range (closer to mark 1) there was detected a barrow pit located at a low depth (of approximately 2 meters) with the varying length of 4 to 20 meters:

 

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At cross-section 8 at a significant depth there was discovered a big stone (marked with 1 at the drawing below) and a platform (marked with 2 at the drawing):

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Beside that, judging by the vaguely observed curves in the bottom of the left corner of the last two drawings one may assume that Arena has a bowl-shaped floor. However, the available data is not enough to make a definite statement on that, since during the measurement the regime that was applied is meant for low depths.

Conclusions

The conducted research demonstrates that there exists significant risk for the Sacsayhuaman archaeological complex. Under the walls of the main layers there were discovered the areas of fissured rocky soil which contribute to incontrollable movement of the underground waters, washout of the easily soluble fractions in the top layer of soil and lead to the loss of the carrying capacity of the walls’ foundation. Recommendations were made for elimination of the negative impact caused by defects of the rocky soil.

There was diagnosed an ability of the stone block material to dissolve when in contact with acidic environment; this creates the risk of rain precipitations containing the components of various acids influencing the blocks of stones.

At the area of “Arena” located in the Northern part of Sacsayhuaman there were discovered the underground objects  which are interesting from the archaeological point of view – a sepulcher, a barrow pit and others.

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