The Negative Environmental Impacts Associated with Reinforced Concrete Retaining Walls - Essay Example

The construction of reinforced concrete walls involves a lot of digging, drilling, blasting (in rocky areas), and other excavation work. Excavation and removal of large volumes of soil interfere with ground stability, therefore predisposing surrounding areas to landslides and earth tremors. In addition to this, large volumes of excavated soil can be washed into water bodies like rivers and streams. This causes siltation and the pollution of water bodies.

When it comes to air pollution, the manufacture of raw materials and the construction and maintenance of reinforced concrete retaining walls releases tonnes of greenhouse gases. For instance, producing one ton of cement releases one ton of CO2. It is worth noting that cement production accounts for about 8% of CO2 released globally, and a normal concrete mix requires almost 15% cement (Huntington 2007, pg. 17). A reinforced concrete retaining wall requires approximately 1320m3 of concrete so this gives us an idea of the amount of CO2 released in order to construct just one reinforced concrete retaining wall (Wynne 2001, pg. 18). Apart from CO2, there are other greenhouse gases like NOx and SOx which are also released during the construction of reinforced concrete retaining walls. Machines used in the construction of these walls also release large quantities of greenhouse gases. The table below provides a summary of the total average carbon footprint for the manufacture of raw materials, construction, and maintenance of reinforced concrete retaining walls.

Greenhouse Gas

Tonnes Released

CO2

256.429

NOx (both moving and stationary)

1.181

SOx

0.105

Question 2

            Alternatives methods of retaining systems include the following:

1. Retaining Walls built with Precast Concrete that has a revegetation Purpose

These retaining walls use hollow concrete blocks that are precast. They are leaning-type walls (U.S. Dept. of Transportation 2007, pg. 38).

                                                                                                     Crash stone (for refill)

Base Concrete

Comparison with Reinforced Concrete Retaining Wall

            This system has an environmental footprint that is much lower (up to 10 times in good designs) than the reinforced concrete retaining walls. Speed of construction and long-term durability are however at par with reinforced concrete retaining walls.

1. Segmental Retaining Walls

These retain gravity and are dependent on their mass for stability. The units are made of concrete which has both low-absorption and high compressive resistance qualities; this makes them resistant to abrasion, rot, scour, insect damage, spalling, and the impact of freeze-thaw seesaws (Reimbert 2006, pg. 27). SRW applications include, but are not limited to, backyard/front yard landscaping improvements, soil reinforcement, adding the weight and width of gravity mass, and making extensions into the backfill. In order to make SRWs environmentally friendly, cement used in concrete is now being supplemented with SCMs (supplementary cementing materials) (Reimbert 2006, pg. 45). Waste materials like blast furnace waste and fly ash are now being used in concrete mixes and have the benefit of being salvaged from being used in landfills. Another approach involves using hollow cores as alternatives to huge block precast walls. Properly designed hollow units do not compromise structural integrity and must meet strict industry uniform testing standards.

Comparison with Reinforced Concrete Retaining Wall

            Of all retaining wall systems built using concrete, this is the most environmentally friendly. The incorporation of supplementary cementing materials and waste materials in the concrete mix makes it possible to reduce greenhouse gas emissions and the release of other toxic waste materials. It is less durable compared to reinforced concrete retaining walls, but the construction process is much faster.

1. Gabion Retaining Walls

This system provides stability through its mass, and hence offers resistance to disturbing forces. It is viewed by engineers as a free draining and flexible retaining wall system. Its design procedures are based on the BS8002 design criteria (Wynne 2001, pg. 48).

Comparison with Reinforced Concrete Retaining Wall

            Of all retaining wall systems (both concrete and non-concrete), gabion retaining walls are the most environmentally friendly. As a matter of fact, they have the lowest environmental footprint (almost zero). In addition to this, their construction process is the fastest in the industry. They are however much less durable compared to reinforced concrete retaining wall systems.