Soils Types & Characteristic

What's The Big Deal About Dirt?

  I decided to take a pause for the cause; and talk a bit on the topic of soil. This is where it all begins, and is literally the base; foundation for the foundation; and ground for the most important of all topics. It is the lead player of the critical roll in construction. If it goes wrong here or fails, the whole system falls; literally falls; or debilitates the whole structure on which the whole framework stands. For this reason, lets take a moment to look at soil profile and characteristics, and ponder the intrinsic aspects of the subject, and search the reasons why it could be detrimental to disregard basic standard procedures and to neglect the proper steps that must be applied.

  First and foremost, the foundation of the house, and the ground on which it stands; properly understood with accurate engineering principles applied, bears it's own weight in gold. The study of soil, is worth the time to recognize certain natural characteristics, how it reacts under stress and responds to determined loads, a science all by itself. Interesting!

  Load bearing capacity of soil varies according to it's composition and water content, the higher ratio of water to soil degrades it's capacity to bear heavy loads. You would see this if you watch a work site with equipment drivers working the site. On a dry day there is no problems, but after a rain you'll observe the tracks of the heavy equipment sink into the ground and mush out from between the tire treads. The same principle applies.

  Soil is made of large or small particles derived from one or more minerals that make up solid rock and the various types are determined by the size of it's particles.

Rock Classification

Group:  Igneous (Intrusive)

Characteristics

Granite;  mostly quartz and potassium feldspar with mica, pyroxene, and amphibole

   Environment:  Deep-seated, coarse-grained pluton

Syenite;   mostly potassium feldspar with mica, pyroene, and amphibole

   Environment:  Deep-seated, medium grained pluton

Monzonite;   plagioclase and potassium feldspar with mica, pyroxene, and amphibole

   Environment:  Deep-seated, course-grained pluton

Diorite;   mostly plagioclase and quartz with abundant mica, pyroxene, and amphibole

   Environment:  Deep-seated, course-grained pluton 

Gabbro;   equal amounts of plagioclase and mica, pyroxene, and amphibole

   Enviornment: Intermediate-depth, medium- to coarse-grained pluton

Peridotite;  mostly olivine, pyroxene, and amphibole with little plagioclase

   Environment:  Very-deep-seated medium- to fine-grained pluton

Group:  Igneous (Extrusive)

Characteristics

Rhyolite;  mostly quartz and potassium feldspar with mica, pyroxene, and amphibole

   Environment:  Fine-grained fissure or volcanic eruption

Andesite;  mostly plagioclase and quartz with abundant mica, proxene, and amphibole

   Enviornment:  Fine-grained fissure or volcanic eruption

Basalt;  equal amounts of plagioclase and mica, pyroxene, and amphibole 

   Enviornment:   Fine-grained fissure or volcanic eruption

Group:  Metamorphic ( Foliated )

Classification

Gneiss;  mostly quartz and feldspar with mica, and amphibole

   Environment:  Course-grained, deep-seated

Schist;  mostly mica and platy minerals with less quartz and feldspar

   Environment:  Course-grained, deep-seated

Phyllite;  micaceous rock intermediate between schist and slate

   Enviornment:  Medium-grained, moderate depth

Slate;  feldspar, quartz, and micaceous minerals

   Enviornment:  Fine-grained, moderate-depth

Group:  Metamorphic  ( Nonfoliated )

Classification

Hornfels;  metamorphic clay materials

   Environment:  Contact with hot magma bodies

Marble;  metamorphic carbonates

   Environment:  Course-grained, deep-seated

Quartzite;  metamorphic sandstone

   Environment:  Fine-grained, deep-seated

Group:  Sedimentary  ( Clastic )

Classification

Conglomerate;  fragments of rounded gravel-sized sediments

  Environment: River and glacial deposits

Breccia;  fragments of angular gravel-size sediments

  Environment:  River and volcanic deposits

Sandstone;  coarse-grained quartz and feldspar with minor accessory minerals

  Environment:  Marine and river deposits

Siltstone;  fine-grained quartz and feldspar with minor accessory minerals

  Environment:  Marine, lake, and river deposits

Shale;  very-fine-grained sediments, mostly feldspar

  Environment:  Marine and lake deposits

Group:  Sedimentary  ( Nonclastic )

Classification

Limestone;  calcium carbonate, often with skeletal fragments

  Environment:  Marine and lake deposits

Dolomite;  calcium magnesium carbonate

  Environment:  Marine deposits and veins

Gypsum;  hydrous calcium sulfate

  Environment:  Near-shore brine pools

Chalcedony;  microscopic silica

  Environment:  Deep marine and groundwater

Soil types, as determined by particle size

• Cobbles and boulders: larger than 3 inches in diameter.
• Gravel: smaller than 3 inches and larger than number 4 seize ( approximately 1/4 inch ).
• Sand: particles smaller than number 4 seize and larger than 200 seize ( 40,000 openings per square inch ).
• Silts: particles smaller than 0.02 millimeters (mm) and larger than 0.002 mm in diameter.
• Clay: particles smaller than 0.002 mm in diameter.
  

  Having lived in New Mexico where the ground is very hard and dry, subject to flash-flooding. The soil bears looking at and to make a point, you don't have to go far in the desert to find sinkholes in the ground. These are areas in the soil where water streams flow underneath the soil and washes the  lower layers of soil away from underneath and after a short time it caves in.

  These cave-ins serve to point out the fact that a thorough surface and subsurface investigation should be performed to establish criteria for the foundation requirements of the proposed structure.