FE-Geotech

Slope failure along planar surface

Assumption: The slope will fail along planar surface passing through the toe of the slope. FS = Tff/Tmob

Po

Effective in-situ stress

Sigma prime O

Effective overburden pressure

Normally consolidated

Effective overburden pressure equals Preconsolidation stress

Deep foundations

Extend deep into the soil to transfer the structural load to deep competent soils superior to shallow foundations b/c of load capacity most expensive and requires more time. Dt is much larger than the foundation width B (Dt/B)>10

Methods to stabilize slopes

Grading Drainage Geogrid/Geotextile layers and geofibers Piles/piers/anchors/nails Lightweight fills Ground improvement techniques Blending with chemical/additives that improve shear strength properties of the soil

Cr

Recompression index Slope of virgin compression curve: = Delta e/log (p2/p1)

Secondary consolidation

Reduction in volume of soil mass due to adjustment of INTERNAL STRUCTURE OF SOIL mass after most of the load has been transferred. Soil particles readjust, reorient, and crush.

Time rate of consolidation

Time required to achieve some degree of consolidation

Mobilized shear force along slip surface

Tmob Tmob=Wm sin alpha s

Differential settlement

Unequal settlement of the various parts of a building, which may cause excessive stresses in the structural frame or tilting of the building.

Geogrids

Used for soil reinforcement to add tensile capacity to soils. Stabilization and Reinforcement Earth walls-mechanically stabilized Reinforced slopes Reinforced aggregate layers under foundations

Consolidation test

a laboratory test in which a soil mass is laterally confined within a ring and is compressed with a known force between two porous plates Recompression-flatter slope Preconsolidation-steeper slope

Geosynthetics

geotextiles, geogrids, geomembranes, geofibers, and geocomposites

How will the size of mineral crystals in an igneous rock change if the magma is cooled at a slower rate

it will increase

Examples of sedimentary rocks

sandstone limestone conglomerate

Examples of metamorphic rocks

slate phyllite schist gneiss quartzite marble

Settlement of fine grained soils

1) Intermediate/elastic 2) Primary consolidation 3) Secondary compression (creep)

Over consolidated (OC)

1) Settlement occurs as recompression 2)Settlement of the first part is recompression and the second is primary compression.

Consolidation

A time-dependent process of increasing the density of a saturated low permeability soil under pressure by expelling water from soil voids

What are exapmles of igneous rocks

Basalt andesit rhyolite granite and diorite

Shallow footings

Bear at shallow depths within a few feet of the ground surface. Rely on shallow soil to provide enough bearing capacity and limit total/differential settlements. Foundation depth (Dt) is less than its width (B)

Common chemical additives

Cement Fly ash Lime and cement kiln dust Grout Hydrated lime Alum Gypsum Agricultural lime Magnesium chloride

Delta sub p

Change in stress due to the application of load. Calculated at the center of the consolidating layer.

Geomembranes

Continuous polymeric sheets that are impermeable. Used for liners and covers in water, liquid, and leachable containments Low permeability HDPE-high density polyethylene PVC-Polyvinyl chloride Reinforced polypropylene

Influence

I - depends on the shape of the loaded area and the location of the point where the stress is calculated.

e sub 0

Initial void ratio (before consolidation)

Geotextiles

Manufactured, permeable textiles currently used in reinforcing or stabilizing civil engineering projects Woven-weaving individual monofilament, multifilament, and/or silt-film yarns into sheets (high tensile strength)---Used where reinforcement/stabilization of a road subgrade is needed. Nonwoven-continuous filament/short staple fibers joined together by chemical/thermal bonding/needle punching (methods) that result in random fiber orientation. (high porosity and permeability, lower strength and higher elongation)---Used to filter/separate

Uniform settlement

No negative effect on most structural components. Access to structure can present difficulties-> utilities can be damaged

Based on preconsolidation stress and effective overburden pressure clays are classified in two categories

Normally consolidated (NC) Overconsolidated (OC)

slope stability

Potential of soil covered slopes to withstand and undergo movement, ie. groundwater, and extreme loading conditions Factor of safety=(Available shear strength)/(mobilized shear stress) along any potential failure surface Stronger the soil->larger the shear strength->higher the factor of safety for slope stability

Sigma ' sub c

Preconsolidation stress Max stress to which the soil was consolidated

High permeability soils

Sands and gravel-Coarse grained soils Faster rate of settlement

Primary consolidation

Settlement is the result of water expulsion from soil pores

Intermediate or elastic settlement

Settlement occurs rapidly

Low permeability soils

Silts and clays Fine grained soils Takes time for primary consolidation settlement to occur

Average degree of consolidation

St = settlement time Sp/Sult = total predicted settlement

Compression Index (Cc)

Starts at the reconsolidation pressure and becomes steeper! Empirical relationship =0.009 (LL-10)

Shearing resistance along the slip surface calculated from Mohr Coulomb theory

Tff Tff=cLs +Wm cos alpha tan phi

Geocomposites

consist of a combination of geosynthetic components; are usually sheet or edge drains consisting of a prefabricated core to which a geotextile filter is bonded.