Flashcards
soils 2014 exam
Cards in this deck (28)
- 1Explain the spt blow count normalisationSpt need to be corrected to a common engergy (60-70%) ratio so results using different equipment can be compared
SPT may be normilised to value at 100kpa for particular types of emperical correlation - 2give adv nd limit of cone pentration testingadv
-cheap
-continuous log ( good at identifying soils layers)
- semi analytical relationships between angle and soil type
limits
no borehole (visual inspection
- not good for gravels or hard clay - 3for displacement piles in sand why is there a limiting shear stressTs,lim : ensures that the unit shaft resistance doesnt increase proportionally with depth due to friction fatigue.
- 4a maximum bearing capacityNq is found using peak angle...
which decreases with stress level - 5explain embedded retaining wallsembedded retaining walls
- rely on passive resistance not weight
- can be cantelivered or propped
-fail geotechnically by overturning, sliding bearing capacity
- structurally by bending or shearing - 6explain swedish slip circle meth for slope stabilitycan be used for more complex slopes
- dirent soil layers
surface loads
tension cracks - 7sketch load settlement curves for the shafte and end bearing of a typical bored pile vs friction pile explain shapesimage on phone
Qt reuires some displacement to mobilise bse resistance. Qb is large proportion for bored piles capacity - 8state two factors that influence the spacing and depth of site investigation boreholes and tril pitsconstruction planned
variabilty of the soil impacts on spacing - 9when and why do u use fadums chart over newmarks chartnewmarks chart can do foundations made up of any shape
fadums chart can superimposed results can b done for multiple soil layers - 10for group capacity of piles what are the alphap factors for soil- soil and pile - soilsoil-soil = 1
pile soil = 0.5 - 11give adv and dis for precast piles over bored and cast in clay soilsadv
- workmanship of precast is easier to monitor
-stiffer initial response
dis
-noise
overhead room requirements
-max capacity limitations - 12explain what type of soil the shear vane is most suited to, what parameters can be determined and how the test is conductedshear vane is best suited to soft clays but is suitable for silts and medium stiff clays. not suitable for sands and gravels..
- measures cu in the field
- conducted by inserting the shear vane into the bottom of the borehole abouse 150mm deeper to avoid distrubance and rotated at a constant speed. therefore resistance is a function of cu - 13what 2 insitu tests can be used to find cu `shearvane
pressuremeter test
-conducted by self boring or menard
-spt if ocr is known - 14after design calculations ( bishop method) a engineer finds a low FoS for the slope ? how ?ordinary meth used give 5-20% lower fos
A more critical slip surface is found - 15what do u use to determone the stability of a slope in the short term long termshort - swedish slip
long- bishops meth - 16why/ when do we use deep foundationif soil surface is soft ( to reach a more appropiate soil type)
- if there are high horizontal lods or uplift
- if scour can occur ie as deep foundations are less affected by scour - 17displacement vs non displacement pilesdisplacement
pushes soil radially / vertically
-installed by jacking and driving
-leads to high horizontal stress in soil
non displace pile
-hole is bored and then filled
- less stiff soil as it is not pre loaded - 18give examples of remedial options for a failure prone slopedrainage ( shallow or deep)
- soil anchors
-soil nails
retaining walls
- piles
-geogrids
-recompaction - 19explain tension cracks on retaining wallsopen dry tension cracks reduces lateral stress on the active side of the wall ( good for stability)
flooded tension crack increases lateral stress on the active side ( bad for stability) - 20what are the design gravity walls formulaoverturnng
f = stabilising / overturning
ie weight moment/ Pa* distance
sliding
f = w * tan (angle) + Pp
/ Pa - 21why is it common to reduce or ignore the soils passive resistance in design calc for a gravity retaining wallThe soil neeeds to develop considerable strain to develop full passive resistance and this is unacceptable in terms of serviceability
- 22explain how standard penetration testing is carried out and what measures can be taken for quality data- carried out in bore holes,
apparatus is driven 150mm into sol by a falling weight. Sampler driven an addition 'N' times untill 300mm disp
ensure
- apparatus is vertical
well trained personal
measure energy ration
well maintained equipment - 23categorise the following piles 1-driven pile 2-concrete intruded pile 3 - bored and cast in place pile 4 - driven and cast in place piles 5 - jacked or pressed pilenon displacement = 2,3
displacement = 1,4,5 - 24explain friction fatigue of displacement piles in sandlower shear stresses at the top of the pile than towards the tip. cyclic shearing during pile driving reduces the interface shear zone, causing a loss in horizontal stress and therefore shear stress
- 25explain gravity retaining walls and embedded retaining walls - what are the key considerations to choose between themgravity: typically constructed of rock, unreinforced concrete or masonry, rely on self weight to protect against sliding and overturning
Embedded typially steel sheet piles, reinforced concrete piles or panels driven into the ground
- relies on the passive pressure at the front of the wall and sometimes props
Key considerations
size, water , tightness, cost , disturbance of soil - 26assumptions for rankines theory (retaining walls)- soil is homogeneous and isotropic
-critical shear surfce is a plane
- ground surface is horizontal
-the wall is infinitely long
- the wall moves slightly activating the active and passive pressures
- thrust is parallel to the ground surface
- interface between soil and wall is frictionless - 27why do tension cracks not appear on the passive side of retaining wallas stress horizontal is greater than stress vertical
- 28discuss how various properties of a granular soil such as silt, sand or gravel could be estimated by in situ testing include 3 examples of particular tests that are in geotechnical use and the results that may be optained from themin situ testing can be used to estimate various design properties of granular soils such as, angle crit , angle max, void ratio / density, stiffness.
spt ( resistance, N blow count, correlated to relative density, angle , if particle size is known)
-cpt ( qc , qs, Rf, used to determine soil type
self boring pressuremeter
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- Flashcards on soils 2014 exam , created by adam_longley on 27/10/2014.
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