Soil Mechanics Exam 1 Questions With Explanations Of Answers Graded A+.

Who is the inventor of soil mechanics? - correct answer Karl Terzaghi (cerca 1920/1930) Name 4 reasons soil is a unique engineering material - correct answer 1. Highly variable (even on a small scale) 2. Non-linear stress-strain distribution 3. Non-conservative (some soils remember their history) 4. Anisotropic (properties are different in different directions) Soil comes from weathered rock. What are the two types of weathering? - correct answer 1. Mechanical weathering: same composition as parent rock 2. Chemical weathering: reactions change mineral form of parent rock True or False: Empirical equations for hydraulic conductivity are more accurate than measured values. - correct answer False Particle Size: Important ranges - correct answer Gravel: 76.2-4.75 mm (3 in. to No. 4 sieve) Sand: 4.75-0.075 mm (No. 4 to No. 200) Silt: 0.075-0.002 mm (No. 200 to 0.002 mm) Clay: 0.002 mm (2 microns) What three things can clay refer to? - correct answer 1. Clay minerals: responsible for plasticizing of soil, interacts with water 2. Clay sized particles: 0.002 mm (2 microns) 3. Soil that is classified as a clay: a soil whose properties are greatly affected by clay minerals What are the three most common clay minerals? - correct answer 1. Kaolinite: medical uses 2. Illite 3. Montmorillonite: water forces clay to expand, expensive, huge change in volume as it absorbs/emits water A first order estimate of the hydraulic conductivity of coarse grained soils can be obtained from which grain size distribution parameter? - correct answer D(10) True or False: A pumping test can be used to estimate the hydraulic conductivity of an unconfined aquifer. - correct answer True Which of the following apply to observation or monitoring wells? (a)They are used in pumping tests. (b)They are located far enough away from test well that their water level does not decrease. (c)They are placed within the cone of depression that develops from pumping. (d)They are used to monitor changes in hydraulic conductivity from pumping. - correct answer a,c Which statements are true about field tests of hydraulic conductivity? (a)They suffer from a lack of control of boundary conditions. (b)They tend to be expensive. (c)They are only performed on aquifers. (d)They require assumptions regarding the direction of flow. - correct answer a,b,d True or False: Hydraulic conductivity and intrinsic permeability are identical terms. - correct answer False Total hydraulic head for flow of water in soils is comprised of which components? - correct answer Pressure head and elevation head What is the correct phrase to complete this sentence? The seepage or pore velocity is _______________ the discharge velocity. - correct answer greater than Compacting clay soil wet of optimum tends to produce what type of structure? - correct answer dispersed What material is the permeability test generally used for? - correct answer sands What is the hydraulic conductivity values for clean gravel, course sand, fine sand, silty sand and clay. - correct answer clean gravel: 100-1 cm/s course sand: 1-0.01 cm/s fine sand: 0.01-0.001 cm/s silty sand: 0.001-0.00001 cm/s clay: 10^(-6) cm/sec What type of weathering does clay come from? - correct answer Chemical Weathering Specific Gravity - correct answer Gs = (unit wt. of solid soils)/(unit wt. of water) *unitless *typical range between 2.6 and 2.9 True or False: It is possible to achieve a relative density of greater than 100% - correct answer True What happens to soils when dry of optimum and wetter than optimum? - correct answer Dry of optimum increases strength; wetter of optimum increases hydraulic conductivity Collapsible soil - correct answer Soil that has a certain strength/density but collapses when conditions change Metastable Soil - correct answer Sand/silt particles are held together by something soluble, so there is not particle to particle contact like other materials, which means there are lots of voids. What can trigger the collapse of a soil? - correct answer Increasing the load on the soil or wetting it. Holding bonds are destroyed and loss of volume is a consequence of collapse. Unit Weight of Water (values) - correct answer 62.4 lb/ft^3 9.81 kN/m^3 Water Content - correct answer w = Ww/Ws Degree of Saturation - correct answer S = Vw/Vv Void Ratio - correct answer e = Vv/Vs Porosity - correct answer ɸ = Vv/VT What is the sand cone method used to estimate? - correct answer Density of Compacted soils A nuclear device uses what type of radiation to estimate soil density? - correct answer Gamma With the AASHTO system, granular materials are soils which have less than what percentage of soil passing the #200 sieve? - correct answer 35 Indicate all statements that are true about the Group Index. (a)It can be zero. (b)It can be negative. (c)It can be a decimal. (d)It is always given in paratheses after the soil group designation derived from the AASHTO classification table. - correct answer a,d Relative Density Definition, Values and Meanings - correct answer Dr = (emax-e)/(emax-emin) Dr = 0 -- Loosest possible state Dr = 1 -- densest possible state *Can be expressed in terms of dry unit weight or porosity *Typical descriptions of Dr are given in Table 3.3