Soils & Geological Report

What is a soils report

Soils reports, also called “Geotechnical Soils Reports” are prepared by a licensed geotechnical engineer or by a registered civil engineer experienced in soils engineering. Geotechnical soils report explains how the engineer determined the load bearing capacity of soil and rock of your property, and the plasticity of the soils or clays. The intent of the report is to analyze the subsurface conditions and provide geotechnical conclusions and recommendations for the foundation repair or construction method. Sometimes a geotechnical soils report is necessary before a foundation construction or repair can be performed or even quoted. These reports can only be prepared by a licensed geotechnical engineer and the cost can range from hundreds to thousand of dollars. We can help you select an experienced geotechnical engineer for your project.

Generally a soils report will contain some or all of the following information:

  • Review of the geologic history and history of prior excavation and fills
  • Field reconnaissance of the site and its vicinity
  • Scope of work done, investigative methods, sampling methods, logs of borings or test pits, elevations of borings or test pits for reference of materials and samples to finished grade or footing elevations, and the identification of the elevations
  • Location of all samples taken, surface and subsurface
  • Groundwater conditions and potential future natural and artificial seepage effects
  • (USCM) Unified Soil Classifications of Materials
  • Material competency and strength of the existing soils
  • Pertinent engineering geologic attributes (clayey, weak, loose, alignments, fissility, planar boundaries, pervious or water-bearing parts, susceptibility to mass wasting, erosion, piping or compressibility)
  • Bearing capacity and/or shear strength of sample areas
  • Consolidation or settlement potential
  • Expansion potential

Whether a soils report is required depends on the types of the soils present on the building site. The soils report gives an understanding of the earth conditions affecting a building. Soils report is usually required in areas with expansive or low strength soils, for buildings whose foundation will be supported by a landfill, for projects on steep slopes or where an extensive grading will be done, and in locations with high ground water or within FEMA floodplains.

The National Cooperative Soil Survey identifies and maps over 20,000 different kinds of soils in the United States. Most soils are given a name, which generally comes from the locale where the soil was first mapped. Named soils are referred to as soil series. Soil survey reports include the soil survey maps and the names and descriptions of the soils in a report area. Here is a link to the United States Department of Argriculture web site on soils for further research. More information can also be found at SoilReport.net.

Soils reports are always obtained before any construction begins. The engineer who designs the foundation uses the soils report in determining what kind of foundation design to select so potential problems such as differential settling over time will be avoided.

Soils report methods

There are various methods used to test the soils in preparing a report, including drilling core samples, driving steel rods into the soil to determine density and the presence of rock, creating test pits and using a seismograph.

Too many houses are constructed with foundations that are inadequate for the soil conditions that exist on the site. Because of the lack of suitable land, homes are often built on marginal land that has insufficient bearing capacity to support the substantial weight of the structures, which over time results in dangerous structural failures. Additionally, there are many areas of the country where the near surface soils consist predominately of expansive clays that shrink and swell extensively as their moisture content fluctuates.

If the bearing soils consist of expansive clays, foundation movement can occur if wetting and drying of the clays does not occur uniformly across the entire slab. Any of the following can cause moisture in the soil to fluctuate: vegetation (roots), wet and dry rain cycles, evaporation, poor or no drainage and plumbing leaks.

Slab-on-grade foundations depend upon the uppermost soil layers to provide sufficient bearing capacity to support the structure and keep the foundation stable. If the bearing soil was insufficiently compacted prior to construction, the foundation is subject to settlement as the supporting soil consolidates over time. Repairing a home whose foundation failed is a challenging and expensive project. Compacting and preparing soil before any foundation is built is worth every penny. Below are some home failures caused by failed soils:

We can help you identify the source of your foundation failure and propose the solution to your structural problems.

 

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