HAITI’S ROCK AND SOIL ENGINEERING
Figure 7. Haitian Structural Plate Setting. Source: PBS: Scientists explain geology of Haiti Earthquake (2011)
and protection. It’s common Haitian architectural practice to construct high-walled concrete or limestone security perim- eters around important structures to mitigate high winds, flooding, hurricanes, and to deter burglary.
On the average, Port-au-Prince, Haiti’s capital and most earthquake-prone city with about a million people, receives about 50 inches of annual rainfall (
CLIMATE-DATA.org). Port- au-Prince experiences some seasonal variation in monthly rainfall. The rainy period of the year lasts for 9.9 months, from February 24 to December 20, with a sliding or day-variable 31-day rainfall of at least 0.5 inches. The most rain falls during the 31 days centered around May 22, with an average total accumulation of 2.2 inches. The rainless period of the year lasts for 2.1 months, from December 20 to February 24. The least rain falls around January 7, with an average total accumula- tion of 0.4 inches. (
WeatherSpark.com). Rainfall is generally higher and more variable in the rugged hills and moun- tains above coastal Port-au-Prince.
Physical Geographic Brief Haiti is a lush and rugged volcanic and karst carbonate island-arc with a long and varied coastline and thin alluvium. Steep slopes are prone to rapid soil and rock erosion, mass wast- ing, landslides, and debris flows. Rocks on geologic contacts are prone to slide. Carbonate rocks are prone to dissolve and form karst. Clays expand when wet and are prone to liquefaction. Haitian deforestation to replace coffee and other trees with cash vegetable crops con- tribute to hillside erosion and valley sedimentation.
Geologic Brief
To engineers, soils are loose or uncon- solidated natural rock materials while rocks are consolidated solids often sepa- rated by fractures.
According to DesRouches et al (2011),
www.aipg.org
Figure 8. Geologic map of the Island of Hispaniola. Source: Dominican Republic Geological Society (from Draper, Lewis and Gutierrez (1995)
Jul.Aug.Sep 2021 • TPG 15
The geologic evolution of Hispaniola can be traced to the Mesozoic breakup of Pangea and the creation of the Atlantic Ocean. This process resulted in the formation of the Caribbean microplate, with subduction zones forming around the margins. The geology of Hispaniola, including Haiti, consists of igneous rocks formed within a volcanic island-arc, as well as abundant marine sedimentary rocks that have accreted at the oceanic subduction margin.
Figures 7 and 8 illustrate Haiti’s general structure in the Caribbean and its surface rocks, respectively. Note the major regional Caribbean and North American plates and Enriquillo- Plantain Garden and Septentrional faults, and distribution of rock types and major geologic formations.
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