INFRASTRUCTURE BACKGROUND:

Allegheny County’s soil is largely made up of Pittsburgh “red beds.” This type of soil erodes easily when exposed to the weather due to its weak soil tensile strength. With frequent precipitation in the area and the increasing freeze and thaw process, landslides are increasing exponentially in Allegheny County. The soil composition of Allegheny County further exacerbates landslide events since many of its public structures are either built on, built with, or built near large bodies of soil. Cut and fill techniques to build public roads and highways utilize surrounding soil to build embankments on the side of the road or are used to support roads in areas without suitable conditions. Throughout 2018, cut and fill techniques used with red beds have caused multiple public roads to collapse in Allegheny County. The problem with unsustainable building practices is supported by the fact that over 90% of landslides in Allegheny County have manmade causes. 

PREVENTATIVE POLICIES:

Scouting out safe building sites and using geological techniques to test soil samples. This could mean drilling for soil samples or using professional equipment, such as extensometers. Extensometers measure movement of soil, stress-strain measurements, and tensile tests, which would rule out erosion-prone bodies of soil.

SHORT TERM PREVENTION:

Retaining Walls: These are structures designed to physically restrain the soil. These are normally used in areas with steep slopes or where the landscape needs to be shaped severely for construction or engineering projects. Retaining walls have been found to be a very efficient solution against landslides. There are various ways of constructing a retaining wall, the most common types being gravity walls, piling walls, cantilever walls, and anchored walls. The concern with retaining walls are costs, maintenance, affecting natural habitat for indigenous species, and scenery pollution.

Soil nails: These are amongst the cheapest measures that prevent landslides effectively. These nails can be deployed in a much shorter timeframe than comprehensives concrete retaining walls, while being more cost effective. Soil nails hold slopes together through a network of nails directing the gravity of the slope. Vegetation can be seeded over such nails and cover up the artificial component of the slope, thereby lowering visual pollution.

Drainage system: In heavy precipitation events or freeze-thaw mechanics, water could cause soil to lose friction and tensile strength. By establishing effective drainage systems to redirect the water runoff, soil cohesion could be maintained.


LONG TERM PREVENTION:

Figure 1: Concrete retaining walls in Japan

Figure 1: Concrete retaining walls in Japan

Figure 2: Soil nails used in Japan

Figure 2: Soil nails used in Japan

Vegetation: Studies have shown that tree diversity and root systems can reinforce soil cohesion and increase tensile strength naturally. The case study most natural preventative measures cite is the use of vetiver systems. Vetiver grass, which is primarily of Indian origin, are used by more than 100 countries. Vetiver can physically hold soil together through its root systems much like soil nails and retaining walls. Such a natural solution to preventative measure also keeps natural habitat disturbance for wildlife to a minimal and has almost no visual pollution. However, the concern for use of natural preventative measures in Allegheny County is the heavy contamination found within its surrounding soil. Recent efforts to introduce urban farming in Pittsburgh have been deterred by the high toxicity levels found in the soil as caused by decades of pollution from mining and steel refineries. 

Figure 3: Weyerhaeuser Corporate Headquarters merges Modernism with environmental sensitivity

Figure 3: Weyerhaeuser Corporate Headquarters merges Modernism with environmental sensitivity

Sustainable Architecture (or Green Architecture): The emerging international trend of sustainable architecture is a potential solution that combines all the benefits of long term and short term preventative measures. This trend also includes both natural and artificial solutions to preventing landslides by designing in elements from green infrastructure. In summary, sustainable architectural designs focus on minimizing human influence on the environment by choosing eco-friendly building materials and construction practices. Such practices include safeguards for air, water, and earth. Sustainable architectural designs would promote more nature-centric aestheticism while providing measures for water drainage and soil cohesion. Most importantly, these designs can incorporate all sorts of preventative measures ranging from retaining walls and vetiver vegetation, to soil nails and drainage systems, in its designs.

MITIGATION POLICIES:

GEOGRAPHIC INFORMATION SYSTEM AND SOCIODEMOGRAPHIC DATASET: 

According to the Geographic Information System analysis by Ana Caceres and Tania Lopez, there isn’t a strong evidence for low median income property owners being relegated to areas prone to landslides. There also isn’t a strong evidence that lower value properties are located near landslide prone areas. Landslide prime areas affect both neighborhoods with high and low median household income. Due to the varied income levels scatter around neighborhoods with surrounding hills, median income is not a strong indicator of susceptibility to landslide. The neighborhoods most at risk to landslides are Mount Washington and parts of Squirrel Hill, which have higher median property values, the hill district and North side, which have lower property values but are equally risk prone. However, in preventing and mitigating landslide issues, sociodemographic concerns must be addressed due to the disparity in property owner’s economic ability to redress landslide fallout. 

Figure 4: Pittsburgh Landslide Inventory and Risk Comparison by Caceres and Lopez

Figure 4: Pittsburgh Landslide Inventory and Risk Comparison by Caceres and Lopez

Figure 5: Median household income by Neighborhood in Pittsburgh and Landslide Prone Area Comparison by Caceres and Lopez with data from US Census Bureau and Western Pennsylvania Data Center

Figure 5: Median household income by Neighborhood in Pittsburgh and Landslide Prone Area Comparison by Caceres and Lopez with data from US Census Bureau and Western Pennsylvania Data Center

POLICY SOLUTIONS:

Figure 6: Plans to rebuilding Route 30 in East Pittsburgh

Figure 6: Plans to rebuilding Route 30 in East Pittsburgh

For policy solutions, we suggest that future landslide prevention and mitigation policies factor in the disparity in median income since low median income property owner’s are more exposed to financial risks of landslides. Lower income neighborhoods near surrounding hills are particularly prone to landslides and less capable of addressing potential landslide fallout, and should therefore be prioritized in both prevention and mitigation policies. These low income neighborhoods should have higher funding than high income neighborhoods in order to deploy more preventative measures such as retaining walls, soil nails, and vegetation. These areas should also have structural incentives by the local government for green infrastructure so that contractors and architects can be motivated to take part in private sector landslide prevention efforts. 

In mitigating landslide damages, we suggest that agencies such as Pennsylvania Emergency Management Office (PEMA) allot grants for property owners to apply for and use to address such damages. Factoring in sociodemographic disparities, low median income property owners should have a lower requirement in the application such as 25% of annual income, whereas high median income property owners should have higher requirements such as 40% of annual income. These funds are important because there has been a history of property owners being forced from their properties due to hillside and the lack of guarantee from the city to fix them. Low median income owners often resort to filing lawsuits against the city, which can disrupt the owners’ lives as litigation often extends over several months and these owners would not have a home in the mean time. The most recent example could be seen in the 2018 example of Randal Miller and five of his neighbors being forced out of their homes for more than 10 months due to the City of Pittsburgh condemning they properties. Special funds should also be set aside to address damages to public structures that are vital to citizens’ daily lives such as the recent landslide that disrupted Route 30 in East Pittsburgh. Route 30 is an essential highway for many daily commuters and the failure of its original retaining walls further support the importance of building practices and continuing maintenance on existing infrastructure.