Soils Investigation

1. Soils Investigation

2. Why Test the Soil? • Buildings are supported by soil • Engineering properties of soil are highly variable • Engineers need reliable soil information for structural and site design

3. The knowledge gained from soil investigation allows the engineer to make estimates for: • Bearing Capacity of the soil • Settlement of the Foundation (amount and rate) • Earth Pressure – both lateral and vertical • Drainagecharacteristics • Wastewater Disposallimitations

4. What Is Soil?

5. Minerals SAND GRAVEL Clay Silt

6. Soil Information • Preliminary Information: USDA Web Soil Survey http://websoilsurvey.nrcs.usda.gov/ • Soil Testing/Analysis • Previous soils investigations on or near the site • Site inspection and simple soil testing • Soil borings taken at proposed foundation locations • Local Building Department or Other Codes and Regulations

7. USDA Web Soil Survey http://websoilsurvey.nrcs.usda.gov/

8. Soil Boring Log

9. Soil Testing Unified Soils Classification System • (USCS) is a method for identifying and grouping soils • First developed by Casagrande for military construction of airfields

10. Unified Soil Classification System • Coarse-Grained • Fine-Grained • Highly Organic Only particles sizes smaller than 3 inches are considered in the USC System.

11. Soil Color • Can vary with moisture content • May indicate the presence of certain chemicals or impurities • Dark brown /black may indicate organic material • Gray, olive green indicates inorganic soils • Red or yellow may indicate iron oxides • Gray-blue or gray-yellow indicates poor drainage • White to pink may indicate silica, calcium carbonate, or aluminum compounds

12. Coarse vs. Fine-Grained Soils • Coarse-GrainedSoils described by grain size • Fine-Grained Soils described on the basis of their plasticity

13. Gravels range from 3 inches down to the size of peas Sieve Analysis Silt and clay can pass through the #200 sieve

14. Sieves #4 sieve (¼ in. squares, similar to hardware cloth) #40 sieve (similar to window screen)

15. Gravel Sand Boulder CobblesSilt & Coarse Fine Coarse Medium Fine >12” 12” 3” ¾” #4 #10 #40 #200 <#200 Clay Baseball sized Grain Size (Gradation) Pea sized Rock salt sized Sugar sized NOTE: Particles finer than fine sand (#200 sieve) can not be seen by the naked eye at a distance of 8 inches.

16. Gravel and Sand Graded Soils Coarse-Grained Soils can be defined by how the particle sizes are distributed within the soil sample. • Well-Graded Soils providea good representation of all particle sizes from the largest to smallest.

17. Gravel and Sand Graded Soils Coarse-Grained Soils can be defined by how the particle sizes are distributed within the soil sample. • Poorly-Graded Soils • Uniformly Graded –Soil particles are nearly the same size. • Gap Graded–Contains both large and small particles, but the graduation continuity is broken by the absence of some particle sizes

18. Gravel and Sand Clean and Dirty • Clean soil contains little or no fines (<5%). • Dirty soil contains an appreciable amount of fines (>12%). • Silty • Clayey

19. Clay and Silt Plasticity Fine-grained soils are classified bythe plasticity of the soil. Plasticity refers to the consistency of fine-grained soils as the water content varies.

20. Soils Groups These letters are used in combination to indicate soil classifications.

21. Sieve Analysis Results USCS Classification for Coarse-Grained Soils • Coarse-grained soil (granular soil) has more than half of the soil grains visible to the naked eye • If the percentage of GRAVEL and SAND is greater than 50% of sample, then the soil is a course-grained or granular soil. SAND if more than half of the coarse grains are smaller than #4 sieve GRAVEL if more than half of the coarse grains are larger than #4 sieve

22. Sieve Analysis Results USCS Classification for Fine-Grained Soils Fine-grained soils (cohesive soils) contain greater than 50% SILT and CLAY particles. • In addition to the sieve analysis, the following tests will be performed to determine the plasticity characteristics of the fine-grained soils(in lieu of LL and PL). Dry Strength–crushing characteristics Dilatancy–reaction to shaking Toughness–consistency near plastic limit

23. Soils Test Results for Fine-Grained Soils

24. Clay and Silt Plasticity In lieu of dry strength, dilatancy, and toughness,ATTERBERG LIMITS can be used to classify fine-grained soils. • Plastic Limit (PL) –lowest moisture content at which soils can be rolled into 1/8 in. dia. thread without breaking • Liquid Limit (LL) –minimum moisture content at which soil will flow when a small shear or cutting force is applied • Plastic Index (PI) – difference between the LL and PL PI = LL - PL

25. USCS Soil Classification Chart

26. Plasticity Chart

27. Soil Classifications for Foundations • Sand and gravel – Best • Medium to hard clays – Good • Soft clay and silt – Poor • Organic silts and clays – Undesirable • Peat – No Good/Avoid

28. Estimated Soil Bearing Capacities

29. Resources Sowers, G.F. (1979). Introductory soil mechanics and foundations: geotechnical engineering. New York, NY: Macmillan Publishing. Lindeburg, M. R. (1994). Civil engineering reference manual (9th ed.). Belmont, CA: Professional Publications, Inc. Guthrie, P. (2003). Architects portable handbook: First step rules of thumb for building design. NY: McGraw-Hill. Unified soil classification. Retrieved August 5, 2004,from http://www.hydro.unr.edu/homepages/benson/ classes/hydro/uscs.html

30. Resources U.S. Army Corps of Engineers. (1953). The unified soil classification system.U.S. Army Technical Memorandum, No.3-357. US Army unified soil classification system. Retrieved August 5, 2004, from http://www.adtdl.army.mil/cgi- bin/atdl.dll/fm/5- 472/apb.pdf

31. Image Sources Fox, A. (photographer). University of South Carolina U.S. Army Corp of Engineers. Technical Manual FM5-410 Soils Engineering