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The Ground Beneath Your Coastal Home

Soil Testing

A typical geotechnical engineering project begins with a review of project needs to define the required material properties. Then follows a site investigation of soil, rock, fault distribution and bedrock properties on and below an area of interest to determine their engineering properties including how they will interact with, on or in a proposed construction. Site investigations are needed to gain an understanding of the area in or on which the building a coastal home will take place. Investigations can include the assessment of the risk to humans, property and the environment from natural hazards such as earthquakes, landslides, sinkholes, soil liquefaction, debris flows , rockfalls and flooding. The Ground Beneath Your Coastal Home

Soil Test is an essential part of foundation design. Foundations are vital to the integrity of every structure being the interface with the soil or rock below. Soil has a variety of properties which can vary from place to place and from layer to layer even within the limits of the proposed structure. At times soil characteristics can change considerably within a small area. Weather, climatic changes, and site management can, in the future, affect the bearing qualities of the soil. Putting it simply, if the foundations are not designed to the carrying capacity of the soils then they will fail and so will the building.

Important design considerations are bearing capacity and settlement. Obviously the foundations must be able to support the considerable weight of the building. The soil or rock below must then bear the entire weight. Settlement may occur at different rates in different sections of the foundations. Other considerations include the ability of clay to shrink and swell with changes in moisture, eg from climatic changes, penetration of surface water or the effect of vegetation absorbing water.

A soil investigation should always be used as a guide only, to give a general indication of sub surface strata, its approximate surface movement and its capacity to bear the proposed construction for the site. The design engineer should relate this report to the specific needs of the construction proposed for this site and if further information is required, should treat a Geotechnical report as preliminary and request a more in depth investigation. These report are based on site information as at the time of investigation. If after excavation of the site footings, the soil profile is significantly different to that indicated on the bore logs, or if the building is situated in a different location to that marked on the site sketch or if any material change has occurred to the site, the report will become void.

Core Sampling Penetration

The standard penetration test (SPT) consists of using a 140-pound hammer to drive a split spoon sampler into the soil’s surface. Drop the hammer a total of 30 inches with each blow to the sampler. Repeatedly hammer the split spoon sampler–a tool with a 2-inch diameter tube attached to the bottom of an 18-inch length of pipe–6-inch depths at a time, until the total 18-inch depth is reached.

Count the total number of blows for each separate 6-inch distance covered. Discount the first 6-inch blow tally number (from 0 to 6 inches), but sum up the last two-blow tally numbers together (from 6 inches to 12 inches and 12 inches to 18 inches). This final tally of the total blows needed to propel the split spoon sampler from the soil’s depth of 6 inches to that of the 18-inch depth represents the number of blows per foot–also known as the soil penetration number. Soil penetration numbers indicate a soil’s density through resistance to penetration.

Proctor Test

Although there is only one standard penetration test for soil density, there is another testing method used to calculate soil density: the Proctor Test. Once penetration of the soil has occurred, remove a soil sample. In the proctor test, you drop a weight on the removed soil several times. Weigh the soil material and then dry it in the special soil oven for 12 hours. Now you can determine water content of the soil. Since water makes up a portion of soil, measuring it reveals if too much water is present to sustain foundations without their becoming liquefied in the event of an earthquake.

The Proctor Test aids in avoiding other potential liquefaction problems. For example, liquefaction can occur when the soil isn’t dense enough to withstand compaction efforts later, like during additional building efforts.

Field Tests

Once the standard penetration test for soil density has been done to ensure engineers can build in an area, they still need to keep checking the soil as the building process continues. Field tests can help with these types of soil density questions. Field test options include sand cones, balloon dens meter, Shelby tube and the nuclear gauge. Your use of these field testing methods ensures soil density continues to be enjoyed during the development taking place.

Site investigation is critical for coastal waterfront structures. Unsafe soil or rock conditions may lead to structural collapse, or could create a dangerous situation in a flood. The law often requires that a site be investigated for safety before permits to build will be issued, and that ongoing safety monitoring occur to detect any changes or signs of developing problems which could pose a threat to the structure.

Sandcastle Coastal Homes specializes is coastal elevated waterfront homes.