soil mech midterm 1

soil consolidation

foundation settling over time

weathering process

the process of breaking down rocks by mechanical or chemical processes

mechanical weathering

weathering caused by expansion and contraction of rocks from the continuous gain and loss of heat without chemical composition

chemical weathering

weathering where the original rock minerals are transformed into new minerals by chemical reaction

clay minerals

a soil type formed by chemical weathering

residual soils

soil weathered/formed and stayed in close proximity or at the same place as parent rock

transported soils

soil weathered/formed and moved by glacial, alluvial, marine, aeolian, colluvial, or lacustrine soil

glacial soils

formed by transportation and deposition of glaciers

alluvial soils

transported by running water and deposited along streams

lacustrine soils

formed by deposition in quiet lakes

marine soils

formed by deposition in the seas

aeolian soils

transported and deposited by wind

colluvial soils

formed by movement of soil from its original place by gravity such as durinh landslides

metamorphism

process of changing the composition and texture of rocks without melting by heat and pressure

soil particle size classification

soils generally classified into gravel, sand, silt, clay

gravel

pieces of rocks with occassional particles of quartz feldspar and other materials. biggest out of the 4

silt

soil fractions that consists of very fine quartz grains and some flake shaped particles that are fragments of micaceous minerals. second smallest

clay

flake shaped microscopic particles of mica, clay minerals and other minerals. composed of two basic units: silica tetrahedron and alumina octahedral

plasticity

putty-like property of clays that contain a certain amount of water

kaolinite

consists of repeating layers of elemental silica and gibbsite sheets in a 1:1 lattice. bonded by hydrogen bonds

illite

consists of a gibbsite sheet sandwiched between two silica sheets. each sandwich is held by potassium bonds

montmorillonite

consists of a gibbsite sheet sandwiched between two silica sheets. each sandwich is held by van der waals bond

property of clay minerals

flat, thin plate-like shape, carry a net negative charge on their surfaces, may have a positive charge at particle ends.

diffuse double layer (DDL)

water held to the surface of the clay. gives the clay its plastic, sticky property

hydrometer

provide the particle size and quantity. measures the unit weight of a soil water suspension

consistency tests (atterberg limits)

indicate the effect water has on the clay particles (type of clay)

soil structure

geometric arrangement of soil particles with respect to one another

factors affecting soil structure

shape, size, minerology of soil particles split into two groups: cohesive soils and cohesionless soils

cohesive soils

silts and clays. if clay particles exist in water, particles may repeal or attrach each other

cohesionless soils

sand and clay. single grained or honeycombed structures where the soil particles are in stable positions with each particle in contact with the surrounding one

sieve analysis

particles larger than 0.074mm dia (sand/gravel) also known as sieve no. 200

hydrometer anaylsis

particles smaller than 0.074mm dia (silt/clay). based on principle of sedimentation of soil grains in water.

poorly graded soil

soil has small particle size bond. small frame of particle size in soil sample

well graded

particle of most sizes in good distribution. a well spread out curve.

assumptions of hydrometer anaylsis

stokes law applies, all particles are spheres, particles do not interfere with each other, no side effects from container, and specific gravity of all spheres are the same

consistency limits

add water to sand/gravel → no change

water to clay → changes physical properties and becomes sticky or plastic

plasticity in clay by absorbed water

plasticity index (PI)

PI = LL - PL

compaction

desenification of a soil by mechanical energy. essentially a proces sfor expelling air from soil, soil particles slip over each other to form densely packed system, and improves soil strength and stiffner, reduces compressibility and permeability

proctor test

provides how dry unit weight changes with moisture content under compaction.

optimal moisture content

the peak of a curve on the proctor test. max dry unit weight

zero air void curve

graph showing highest possible dry density when all air is removed from the soil

hydraulic gradient

i = -delta h / L

darcy’s law

Q / t = q = VA = kiA

Q = volume of water

t = time

q = rate of water flow

V = velocity

A = cross section area

i = gradient

dicharge velocity

v = ki