Urban Innovations in Soil Mechanics

Aisling Marie O’Carroll (MLA I AP)

Project Overview

Located in the Cordillera Central of the Colombian Andes, the Aburrá Valley is characterised by shift; shifting economies, populations, and land.  Presently, the valley basin has been entirely settled by the growing city of Medellín and its Metropolitan Area. Continued growth is now spreading up the valley’s precarious slopes. This growing peripheral population is disproportionately composed of less wealthy families, lacking the resources to provide a more secure location for settlement. These contested borderlands of the urban city are a palimpsest of cultural, economic, and social histories of the city and region. Despite the layered significance of this peripheral zone, inadequate attention is being paid to its development and appropriate use.

Over the last 40 years rapid population occurred primarily within these precarious slopes, in an uncontrolled, fragmented manner. These patterns of growth had produced a socially divided city with the highest levels of violence in the world by the mid 1980’s. Following a change in political leadership, an unprecedented project of urban transformation was implemented between 2004-2008, with the intention of reuniting the city as a whole, and addressing social, structural, and environmental aspects of the city together. Given this recent history of forward-looking governance, the city simultaneously provides a perfect case study for both site research on technical strategies for slope stabilization and the effect of top-down interventions, and a projective study on how landscape systems may be used to pre-emptively influence growth patterns in this region, through a bottom-up methodology.

Project Information

Colombia’s Aburra Valley contains 10 different municipalities, forming an urban chain through the center of the valley. The largest of these municipalities is the city of Medellin. Since 1948 these municipalities have been considered through an integrated valley master plan, enabling an understanding of the geographic region of the valley and its hinterlands.

The valley is composed of moderate to steeply sloping slopes, derived from a variety of rocks and soils.  As with any valley section, these slopes are naturally inclined to weather and wear, gradually eroding the surface and carrying sediments down to the valley floor. This process of erosion is accelerated through mass wasting of slopes, when landslides and other accelerated processes rapidly transform the structure of the slope. This natural entropic process is aggravated by anthropogenic slope modifications, thus, when one considers the patterns of growth in the valley, the incompatibilities of settlement and geophysical systems becomes evident, as well as the precarious nature of much of the valley’s housing stock [i].

Based on the findings of two recent studies by the Agustin Codazzi Geographic Institute (IGAC) in 1988 and 2000, and one completed by the Institute of Hydrology, Meteorology, and Environmental Studies in 2004, between 10-20% of Colombia is subject to high or very high levels of erosion [ii]. The Andean region, in which Medellín sits, experiences one of the highest levels of erosion in the country. This may be attributed to the low annual precipitation levels, and intense, irregular rains, which affect some of the most populated and economically active parts of the country, including Medellín, in combination with inappropriate land use practices [iii].

Much of the urban growth in the Aburra Valley is comprised of informal developments, primarily located in the unsettled steep slopes of the valley. The disorganized and unmanaged inhabitation of these slopes has led to increased risk of failure and vulnerability amongst populations. It is currently estimated that 44,600 homes in informal settlements are at risk, a number projected to increase 130% in the next 20 years. In the last 80 years, almost 800 residents in such communities have been killed by landslides [iv].

It is necessary to understand each of these dynamic systems – both the geophysical and the social – as inevitable realities in this valley. Neither process can be removed or eliminated while retaining the function and performance of the larger system – the ecological performance of the valley in the case of the geophysical systems, and the performance of the city in the case of social systems. Thus it is necessary to consider how these two might coexist.

This research approaches that question from two ways:

First, through an analysis and documentation of retroactive stabilizing techniques in precarious settlements – of particular interest are those improvements made during the city-wide transformation. This transformation process took an unprecedented lead in collaboration through an integrated top-down approach, and has proven very successful in both social and structural improvements.

Secondly, the research follows a more projective line – considering the ways in which design strategies might be implemented in order to influence future settlement patterns such that hazardous sites do not become inhabited, and alternative uses activate these slopes in ways that provide stabilization rather than accelerate the process of erosion. This second line of research was carried out through a collaborative effort between the Social Agency Lab at Harvard University, led by Professor Christian Werthmann, and the think-tank Urbam at EAFIT University in Medellin, led by Alejandro Echeverri. This collaboration was initiated over the course of my visit in Medellin through a series of meetings, workshops, and excursions.

The uncontrolled manner of growth that Medellín has experienced since the 1970’s led to a situation where many communities were not adequately serviced, and this was reflected in social and safety issues within the communities. In response to the fragmentation of the city, and growing violence within periphery communities, the city of Medellin devised a strategy of comprehensive transformation, specifically targeting those informal, periphery communities, often overlooked or denied in government strategies. Under the administration of Fajardo, an innovative and urbanistically comprehensive strategy for city improvement was devised which made it a priority to integrate geological studies and methods of controlling land use and erosion within the transformation of Medellín. Alejandro Echeverri, Director of Urban Projects, directed a team of specialists from various fields to analyse and develop social and physical improvements together. In this way, structural improvements and methods of soil control were implemented throughout the comunas of Medellín as integrated aspects of a larger transformative project.

This project was implemented as a top-down, retroactive intervention approach. The work has been incredibly successful at socially and structurally integrating the peripheral communities into the larger urban structure of the city. The project provides a case study of an unprecedented collaborative effort amongst specialists and government to devise an integrated solution for these communities. In addition to the large architectural projects and transportation improvements which have been well documented internationally, including the construction of a number of libraries and schools, as well as a cable car system, a number of smaller scale infrastructural improvements were made to both improve access in the slopes, and stabilize the slopes. The modest construction of handrails in both new and old stairs dramatically improves the accessibility and safety of mobility in the slopes. In major streets, grading, drainage, and surfacing was completed to improve the collection and movement of water, as well as facilitate transportation and commercial development. Where settlements were located in areas of particular risk, housing was removed and replaced with active public program, such as hardscape squares, often with integrated vegetation to provide a stabilizing slope cover. In these situations replacement housing was provided within the community to allow for as little disturbance as possible in the relocation process.

The transformation project provides an unprecedented example of collaborative work, and success in the reintegration of many periphery communities with the larger city. Documentation of these improvements is provided in the slides.

The second aspect of this research initiated in Medellin is the collaboration between Harvard and EAFIT on projective strategies for an integrated approach to slope stabilization and urban growth. The intention of this research is to devise a set of strategies that will allow landscape to pre-emptively influence settlement patterns, enabling the coexistence of urban, formal and informal populations, with geophysical risk. By understanding the dynamic processes of the valley as givens (both geophysical and social processes), and considering them as constraints within which we work, it becomes possible to consider how such pre-emptive strategies might be implemented to influence the structure of social systems in relation to geophysical systems.

‘By projecting precarious settlements for 2030 and 2050, [our research intiative, titled ‘Shifting Ground’], develops remedial strategies for occupied areas and anticipatory mechanisms for areas that have not been invaded yet. Our research project looks at mechanisms to establish evacuation, stabilization, and relocation procedures for existing settlements, and strategies that protect and direct new settlements away from unstable valley slopes. Overall, it seeks to generate a paradigm shift towards a more productive use of valley slopes. Shifting Ground explores the assumption that the introduction of new hill-based economies such as farming and recreation is the best protection for further settlement of the valley slopes. Shifting Ground identified the highest risk slopes as the first areas for a land use change following our conviction that the threatening force of landslides can be used as a positive power to structure a healthier valley.’ [v]

Through a series of site visits, discussions with local community members, and initial brainstorming sessions, a strategic framework was laid out for the research, which was subsequently completed over the last 8 months, establishing the foundation and argument behind the statement above – in order to reveal the potential of pre-emptive design thinking to government bodies, in order to continue this research in the future with tangible implementation strategies. Through observation on site visits we gained an understanding of the methodology of growth within these ‘informal’ settlements, which in fact are organized around their own internal system and do not grow ‘informally’ or randomly. Furthermore, the construction methods used for housing, mediating slopes, and excavation was seen, providing better understanding of potential hazardous modifications to slope, as well as the challenges in dealing with slope, and requirements for improved infrastructure.

Out of this collaborative initiative we produced a thorough study on the geological risk, as well as potential for population growth in the valley, and the sites where these pressures overlap to produce the greatest hazard. The conclusion of this phase of research was a table of strategies, intended to put forward a number of potential paths or solutions to the current issues – both in existing and future settlements. Our intention is to continue this research to produce implementable site specific strategies for a variety of sites within the periphery of Medellin.

[i] Departmento de Geología, Universidad EAFIT. El Impacto Humano. Medellín Medio-Ambiente Urbanismo Sociedad. Medellín: Fondo Editorial Universidad EAFIT. 2010. p.65.


[ii] Sanchez-Triana, Ernesto, Kulsum Ahmed, and Yewande Awe. Environmental Priorities and Poverty Reduction: A Country Environmental Analysis for Colombia. Washington, DC: The World Bank. 2007. p.398.[iii] Sanchez-Triana, Ernesto, Kulsum Ahmed, and Yewande Awe. Environmental Priorities and Poverty Reduction: A Country Environmental Analysis for Colombia. Washington, DC: The World Bank. 2007. p.397.[iv] Estrada, Claudia Helena Hoyos. Gestion del Paisaje en el Valle de Aburrá: Hacia la Conservación de laNaturaleza en la Ciudad. Medellín Medio-Ambiente Urbanismo Sociedad. Medellín: Fondo Editorial Universidad EAFIT. 2010. p.94.[v] Werthmann, Christian. Shifting Ground: Re Habitar la Ladera. Harvard University + EAFIT Universidad Medellin. 2012.


** The projective research and analysis portion of this project was completed as part of a research collaboration between the Social Agency Lab at Harvard University, and urbam, at the EAFIT Universidad, Medellin. This work was directed and advised by Christian Werthmann, Alejandro Echiverri, and Ana Elvira Velez Villa, and produced by myself, Conor O’Shea (GSD), Maya Ward Kaeret (urbam), and Santiago Orbea (urbam).