HIGHWAY EXAM

• Soil containing clay


  Troublesome, making the design and construction more difficult
• Soil with clay should not be used closer to the roadway surfaces
• Rounded particles extracted from the stream


  • Considered strong materials
• Flat and flaky particles not subjected to wear


  • Weak and variable, not suitable for various uses
• Angular or roughly cubical shape particles produced from crushing strong and tough rocks


  • Increases the resistance of soil mass to deformation when subjected to load, due to individually interlocking grains
• Rounded particles


  • Tend to roll over each other when subjected to load
• Pedology


  The science of soils
• Soils produced in like fashion from the same parent rock are assumed to possess similar engineering properties, requiring similar engineering treatment
• The number of samples to be subjected for testing could be less than what is usually required when using pedological classification
• The test results serve as a check on pedological classification, contrary to other classification methods that rely mostly on physical tests with little attention to pedological information
• If like soils occur under like conditions of materials, the slope and weathering, the soil patterns or similar landforms are also developed
• The surface drainage patterns and erosion characteristics, together with the color of the soil, reflect the kinds and nature of the soil
• Ridges with parallel axis may also reflect wind blown sand and silts
• Texture classification of soil

  • Sand
  • Silt
  • Clay
• Determining the grain size of a soil sample using the textural classification chart

  1. Spaces vertically upward starting from zero at the bottom represent clay percentage

  2. Spaces from left to right diagonally downward starting with zero at the left, represents silt

  3. Spaces from right to left diagonally downward starting with zero at the right, represents sand
• Loams


  Soil that is almost entirely a mixture of sand and silt
• Soil containing clay of less than 20%


  Classified as loam with a prefix sandy or silty added to indicate which predominates
• Soil containing 20 to 30 percent clay


  Called loam, with the term clay added to indicate the higher clay content
• All other soil


  Designated as clay with prefixes of sandy, or silty to indicate the remainder of the materials
• Unified Soil Classification System

  Introduced by the U.S. Army Corps and the Bureau of Reclamations, using letters to designate the different groups
• Symbols for coarse grain soil (more than 50% retained on No. 200 sieve)

  • GW - well graded gravel
  • SW - well graded sand
  • GC and SC - coarse materials with clay binder
  • GP and SP - poorly graded fairly clean material
  • GM and SM - coarse materials containing silts or rock flour
• Symbols for fine grain soil (more than 50% passing No. 200 sieve)

  • ML, CL and OL - fine grain soil with liquid limit less than 50, low to medium compressibility
  • MH and OH - fine grain soil with liquid limit greater than 50, high compressibility
• Quick identification of fine grain portions of the soil

  1. Mix with water to have a putty-like consistency, then form into a pat and dry completely

  2. If the pat is broken by the fingers and the dry strength is high, the plasticity of the sample is considered high

  3. If dry strength of the sample is high, it exhibits clay and colloid characteristics

  4. If the sample is a pat of fine silty sand, it will easily break in the finger

  5. Fine sand will cause the pat to feel gritty on the fingers, while silts is smooth

  6. Dilatancy or reaction to shaking - about one cubic inch of soil is mixed with water and formed into a pat of soft but not sticky consistency, then shaken and squeezed between fingers
• Soil deposit consists of solid particles and void spaces between particles, either partially or completely filled with water
• Properties of soil deposit that engineers are interested in

  • Strength
  • Compressibility
• Soil density


  Weight per unit volume
• Specific gravity of most commonly occurring rock or soil materials is between 2.30 and 3.10
• Specific gravity of soil solids lies within the range of 2.60 to 2.75
• For submerged soil, the effective soil weight becomes lighter compared to soil above water
• 62.4Pcf


  162'24lbs
• Ww : VwUw : (0.40)(62.4)

  = 24.96lbs.
• From which:


  Wt = 1d/5 +Ww = 162.24 + 24.96
• wr


  187.20lbs.
• Wt


  187.2
• vt


  1.40
• Water content: w oh = Ww x 100%


  Ws = 24.96Ibs. x 100% 162.24lbs. = 75o/o
• To relate a value given in grams per cubic centimeter (i.e. density) to pound per cubic foot (i.e. unit weight), multiply by 62.4 gn/cm3 = 62.4lbs/ft3.
• Submerged Soil


  For under water condition, the soil solid is buoyed up by pressrrs of the sugounding body of water. Therefore, the weight of srrbmerged suil, become lighter compared with the soil al-.ove water. Thus, the effective soil weight becomes the mit '*'eight when weighed rmder water. The weight of water in the voids of soil is zero when submerged, because all voids werc assumed to be filled with water, and the weight of the snlid is reduced bythe weight of water displaced.
• Therefore. the submerged weight is equal to the soil weight above the water minus the weight of water displaced.


  Wsub = Vs gs Uw - Vs gw Uw = Vs Uw (gs - gw) = Vs Uw (gs-l)
• Usub-soil


  Vs Uw (gs -1) / Vs(l+e)