Study of the Pre-Hispanic Road located in the PUCP Compus, Lima, Perú by CENTRO TIERRA

Study of the Pre-Hispanic Road located in the PUCP Campus, Lima, Peru J. Vargas-Neumann, F. Jonnard, S. Gil Zacarias & J. Montoya Robles Centro Tierra, Pontificia Universidad Católica del Perú, Lima, Perú

ABSTRACT: The Pre-Hispanic Road located at the Campus of Pontificia Universidad Católica del Perú (PUCP) is one of the few remains of the Qhapaq Ñan road system that crosses the city of Lima. Its 467 meters of two parallel walls that have withstood severe earthquakes can provide valuable information on the techniques used by the Ichsma (1100–1472 A.D.) and Incas (1472–1532 A.D.) in the construction. Centro Tierra-INTE, a PUCP research team and UNESCO Chair in Earthen Architecture, is conducting a study to gain an accurate knowledge of the material and the construction technique and to propose guidelines for the conservation of this type of earthen structures so recurrent in archeological sites of the Peruvian Central Coast. The interdisciplinary study includes a bibliographic, historical, archeological compilation, soil mechanic tests, structures laboratories tests, and electronic microscopy sweep assays. Conclusions with a conservation methodology for Ichsma and Inca archaeology sites are presented. 1 INTRODUCTION The Maranga Complex is one of the most important archaeological sites in the Rimac valley. The complex covered 150 hectares (370 acres) in its heyday (Canziani, 1987). Its archaeological sites are part of what is nowadays the Parque de las Leyendas zoo (52 huacas/burial grounds), Pontificia Universidad Católica del Perú, Universidad de San Marcos, and archaeological sites including Mateo Salado and Huaca La Luz, among many others. This complex dates back to the Early Intermediate Period (Lima Culture 100–600 A.D.), and was occupied until the Late Inca Horizon (1472– 1532 AD) (Canziani, 2012). The main construction material was earth, used in applications ranging from the mortar for setting stones and small and large adobes to earthen walls and plasterwork. The site reveals the large variety and combination of building methods using earth and stone used in the Rimac valley—many of them with modifications and extensions made by various sequential cultures—and particularly the convergence of influences from the Lima, Ichsma and Inca cultures in the Maranga Complex, which flourished during the latter two cultures. A part of this complex, the Ichsma-Inca Road (see location in Figure 1), linked important sites and stretched to the Pachacamac Sanctuary in the Lurin valley. It is one of the few remains of the Qhapaq Ñan road system across the Rimac valley, and ends at an outcrop located between the Huaca Tres Palos and the Huaca La Cruz, major sites of the Maranga Complex. (L. Carrión, personal communication, March 7, 2014).

This project focuses on the walls bordering this road along a stretch of 467 meters (1532 feet) within the Pontificia Universidad Católica del Perú (PUCP) campus. Since the beginning of 2013, studies and interventions to this stretch of the road commissioned by PUCP have been underway. Masonry with new adobes has been used for consolidation and reconstruction of the original walls. As a result of this intervention, the Centro Tierra INTE, a PUCP research group specializing in earthen constructions, set out to conduct an indepth study of this type of structures, given their importance in the Rimac valley, and proceeded to request approval from the Vice President of the PUCP for this project, which began in September 2013. 2 PRECEDENTS In the archaeological sites located in the Rimac River valley, there are several precedents of wall repairs using adobe masonry to reconstruct missing portions, especially in the eroded lower wall segments, in order to regain their stability. Such repairs included emergency work, for example along the main road of the Cajamarquilla archaeological site and, later, intervention work such as in the Mateo Salado archaeological complex (Figure 2) and Huaca San Miguel in the Parque de las Leyendas, among others. On the other hand, a large variety of vertical, sloping walls, with either constant or trapezoid sections, exist in Maranga. These have been

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Figure 1. Ground plan of the Maranga Complex. Location of the Maranga Complex huacas and the PreHispanic Road in the southern section of the PUCP campus. Credit: L.Tavera. Modified by F. Jonnard.

loose soil, but with well-kneaded and soft mud, just as we make adobes. Their walls were very straight and smooth because, instead of using wooden formwork on each side, they used cloth and fiber mesh, and subsequently plastered them with the same mud. We have come to determine their shape and construction because of the large number of ancient mud walls found throughout the Lima valley that are made in this manner.” (Cobo 1964: 241). This description reveals the differences between the tapial as the term is understood today (rammedearth), and these walls mentioned above. In general, in Spanish, rammed earth fences are called tapias (a word derived from Arabic). These walls were and are made by compacting moist earth with wooden rams inside forms originally made with wooden planks, in 100 to 150 mm (4” to 6”) layers and approximately 0.60 (23”) courses, dried for a period of time before making the top courses. Therefore, any wall made in a way similar to this Mozarabic technique is called tapia, without making any construction distinctions. This study of the road’s wall materials, as well as the porosity, strength and other characteristics of its composition, propounds the need for a more accurate definition of the method used, given the great importance of this information for any recommendation on repairs or restoration of these walls. 3 OBJECTIVES AND METHODOLOGY

Figure 2. Consolidation with new adobe masonry. Pyramid A of Mateo Salado. Photo: Mirna Soto.

graphically identified to a certain degree for classification purposes. These pre-Hispanic high solid earthen walls are commonly called tapiales (rammed-earth walls). However, definitions for these structures are still relatively unclear and ambiguous. In this paper, we conclude that they are not rammed-earth walls. As to the mechanical characteristics of the walls, they are described in generic terms (hard, weak, filled with loose soil or soil mixed with riverbed stones), but no specific studies have been conducted to arrive at conclusions as to their restoration. There are no precedents of numerical results from lab tests that may serve as comparisons in order to classify the walls or to assess their structural behavior. As to their construction, the first reference available to us was provided by Spanish Father Bernabé Cobo: “The Indians in ancient times did not make these mud walls as we do, with slightly moistened

The purpose of this research is to study the walls bordering the Pre-Hispanic Road, their geometric characteristics, the mechanics of its materials, their stability and strength characteristics, and a definition of the construction method used. Likewise, the study seeks to promote sharing and generating new knowledge about preHispanic construction methods and, as a result, propose guidelines for conservation of these types of earthen structures that are prevalent in the Peruvian central coast (Maranga, Mateo Salado, Cajamarquilla, Puruchuco, Huaycán de Pariachi and others). Given the historical, archaeological and technical components of this study, it has been conducted in two stages: The first stage was a brief bibliographic, historical and archaeological compilation to provide a reference framework. For this purpose, Inés del Águila, a researcher at the PUCP’s Riva Agüero Institute, and the archaeologist Lucénida Carrión, director of Parque de las Leyendas, were interviewed. Both researchers are considered leading experts on pre-Hispanic cultures in the Rimac valley and, particularly, on the Maranga Complex, where they have carried out heritage maintenance, restoration and conservation work for many years.

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The technical stage covers studies conducted at the PUCP Soil Mechanics and Structures labs (granulometry, Atterberg limits, volumetric contraction, compressive strength, indirect traction, consolidation and other field tests). Additionally, the assessment of degree of compaction, porosity, particle size and nature, and chemical composition was complemented by electron microscope scanning. This task was carried out in sections to allow for subsequent diagnosis based on sections and cases leading to a set of recommendations for intervention. As this is an archaeological site, studies were conducted on portions dislodged from wall surfaces buried along the sides of the road. The 19 samples studied were provided under supervision by the team of archaeologists, verifying their location and orientation with respect to the wall. 4 RESULTS The Pre-Hispanic Road was built with earth and stone, using various methods from two different cultures (Ichsma and Inca) and from different stages of these cultures. There are also vestiges of four centuries of Hispanic interventions. At a late stage of the Ichsma culture, pyramids were built using an organized filler method. Cells were formed by orthogonal walls made of riverbed stones with mud mortar, filled unsystematically with earth and stone. Perimeter walls were sloping and made of poured earth in layers from 0.15 to 0.20 meters (6” to 8”) high. Walls can be made of two or three sloping layers as necessary to make the pyramid’s platform. This structure can be seen in the Huaca Mateo Salado. Figure 3 shows the described structural elements and concepts used in the same manner as in the Road. (Vargas J. 2009). In both constructions, the top sections are completed with solely earthen walls, possibly of Inca construction, sometimes supported by riverbed stone layers, simulating Ichsma earth and stone methods. During Colonial or Republican times, stretches of walls with parallel faces may have been built using tapial methods in order to complete stretches missing as a result of earthquake damage. We must not forget that, at the least, the Pre-Hispanic Road has survived the 1687 and 1746 earthquakes, which practically leveled Lima. At a macroscopic study, the road samples collected show various compactness rates. Some are very hard and solid, while others completely disintegrate when handled. Some include a large amount of riverbed stones, while others are made of very fine soil. On limited occasions, fibers and small ceramic fragments were found. The results of the lab assays and field tests show, firstly, a lack of uniformity due to the difficulty in maintaining a source of consistent soil and consist-

Figure 3. South earthen wall of the road. The red arrow indicates the fallen riverbed stones. Photo: J.Vargas N.

ent quality along the road’s extensive length and also its probable construction in successive stretches. It is believed that the walls were built using top soil from the Rimac River deposits and river stones from its alluvial fan, which is very vast. The top layers usually have a larger content of wind-borne fine sands, while the lower layers contain clay, an essential component for good earthen construction. Plasticity limits, as determined for each sample, as well as from granulometric analysis, show that the soil is a fine particle (more than 50% of the material passes through a 200 mesh screen), slightly plastic (with a < 50 liquid limit) clayey-silt. On one hand, observation by scanning electron microscope confirms this high proportion of fine sands and silts, resulting in no tensile strength and low compression. On the other hand, most samples from the assayed sections show very little grain to grain contact, leading to the assumption that little or no compacting was carried out. Clays in the global matrix are very low and the degree of porosity reaches almost 50% in the more fragile samples. This confirms that no major compacting was used in the construction method, leading to believe that poured earth methods were used using soft and deformable molds, and the presence of imprints from 0.15 to 0.20 meters (6” to 8”) high, as observed in the Maranga Complex. Lastly, the presence of montmorillonite was determined. The percentage of montmorillonite, a highly hygroscopic clay, in relation to the total material analyzed was very low. This fact stresses the importance of geographical conditions in the wall’s conservation, since the ever-present high degree of moisture in Lima is an important factor in sustaining these structures. To test the level of material strength, compression testing was done in carved/cut probes with samples extracted from the Road. Resulting

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strengths ranged from 0.15 to 0.43 MPa (1.56 to 4.4 kgf/cm2). Current Peruvian standards specify a minimum strength of 1.2 MPa in compressed assayed cubes. (Figure 4). Assays in carved/cut probes were also done on the new adobes used in the intervention work, with results of 1.8 MPa, much higher than the original road materials. It was concluded that the original construction material has very low strength, compared to the adobe strength, which is important information for restoration or intervention efforts. It is important to note that at present there are no serious studies on the mechanical characteristics of the materials and methods used by builders in preHispanic cultures. However, current consolidation methods, such as the adobe masonry method being used in the Cajamarquilla archaeological site, are interventions made without deep understanding of the immense Peruvian heritage in earth and stone, as is the case of the Pre-Hispanic Road. The compression strength of adobe pile masonry using mud mortar, according to the Peruvian Standard NTE E.080 Adobe, is 50% of the compression strength of adobe blocks. The compression strength used in the intervention conducted in the PUCP campus is 0.9 MPa, that is, approximately 4 times more than the average strength of the Pre-Hispanic Road walls. The elasticity modulus of fragile materials, though not linear, has an initial portion that is almost linear, which is usually considered linear based on the modulus of elasticity tangential to the curve of unit efforts-deformations in compression assays. The deformability is thereby considered linear and proportional to the strength. A simple example: an original wall with a trapezoidal cross section that has lost half of its volume is replaced by an adobe masonry wall in the same shape. In an earthquake, the two half-walls, due to their differences in deformability and strength, will vibrate at different basic frequencies and will knock against each other, damaging or causing the collapse of the one with lower strength—which we know in this case to be the original heritage wall. The consolidation required in the Road must use materials and methods similar to those used originally, that is, low walls (maximum 0.20 m [8”] high) molded in layers made of poured mud. The material must be as similar as possible to the original in granulometry, deformability and strength. A method must also be developed for placing the last top layer of the new material, to be applied one month after laying and drying. We propose using a mortar of the same material, braced by thin wood slabs of sufficient size to ensure total filling of the empty space left after the drying process.

Figure 4. Compression assays on the original material of the road.

5 CONCLUSIONS Our findings have allowed us to establish a technique that would resemble the poured earth method more closely than the tapial method. However, an important component of the second part of our research is to actually experiment with such technique. This experience, based on the studied bibliography and the test results, will define a construction method with even greater certainty, since certain field criteria are difficult to be determined on the basis of the results obtained so far. It is necessary to call as much attention as possible to the problems that may arise from interventions using adobe adjacent to a much less resistant material in the walls, considering that original walls are not rammed-earth. Dissemination of this information and specific studies need to be systematized and must be supported, since the components in the earth change according to the context. This will allow for developing restoration techniques that are appropriate for each case. REFERENCES Canziani J. 1987. Análisis del complejo urbano Maranga Chayavilca. Gaceta Arqueológica Andina n.14, pp. 10–17, Lima. Canziani J. 2012. Ciudad y territorio en los Andes. Contribuciones a la historia del urbanismo Prehispánico. Fondo Editorial de la PUCP. Lima. Carrion L. 2014. Personal Communication (authors). Lima. Cobo B. 1964. Crónicas. Del Águila I. 2014. Personal Communication (authors). Lima. Vargas J. 2009. Conservación del Complejo arqueológico Mateo Salado. APT’s Annual Conference. Los Angeles.

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