Soils pt 2 Flashcards
(107 cards)
1
Q
all on sie private sewage systems consist of (3)
A
- septic tank
- distribution box
- Absorption field (trenches)
2
Q
A practical solution to on-site sewage disposal is
A
septic tank
subsurface absorption field
3
Q
The daily flow of septic tanks must be
A
less than 4546L
4
Q
what is a key component of the on-site sewage system
A
soil
5
Q
for on-site sewage systems, gravel provides
A
storage for peak flow
infiltration surface between the sewage and underlying soil
bed for pipes
protection over the pipes
6
Q
The septic tank provides
A
- primary treatment of the wastewater by separating the soils
- light solids float to surface and heavier solids settle
- clear layer of effluent between layers
7
Q
_____(no oxygen) breaks down the waste in the tank
A
anaerobic bacteria
8
Q
Liquid waste is distributed in the
A
absorption field
9
Q
The septic tank retains:
A
The septic tank:
◦ Retain fats, greases and solids
◦ Fats and greases form a sump blanket
◦ Most of this material is digested by anaerobic bacteria
◦ Tank must be pumped out regularly to remove the sludge blanket
◦ Primary treatment takes place in the tank
10
Q
A typical septic tanks removes:
A
◦ 40-50% BOD5
◦ 50-70% TSS
◦ 20-30% Nitrogen
◦ Up to 30% Phosphates
◦ Bacteria do not multiply but survive and their numbers reduced
11
Q
Distribution box
A
◦ Part of the absorption field
◦ Outlet to absorption trench
◦ Box must be level for each pipe to receive the same volume of wastewater
12
Q
The absorption field:
A
◦ Wastewater is free of fats and solids
◦ Secondary treatment of the wastewater
◦ Contains organic material and bacteria
13
Q
Building site evaluation must include:
A
Building lot size
Soil characteristics (from test pits)
Ground water table data
Percolation test data
Ground slope
Separation distances
14
Q
Components of a submission:
A
-Application signed
-Detailed diagram of lot
-Floor plan of dwelling
-Municipal approval
-Results of percolation test
-Soil strata data of site
-Depth to water table
-Design calculations
-Construction drawings
-Drawings of all construction details
-Land grades
-General description of ground conditions and Information about imported fill to be used if
necessary
15
Q
Septic tank standards:
Must be a component of all private septic systems
A
Only grey water is exempt from septic tank
Not located under a driveway or parking area
Be water tight and made out of an approved material
16
Q
depth of topsoil
A
0 - 0.3 m
17
Q
depth of sandy gravel
A
0.3 - 1.2m
18
Q
depth of sandy silt
A
1.2 -1.8 m
19
Q
ground water observed
A
1.8-2m
20
Q
minimum depth for For two compartment tanks
A
30 cm
21
Q
What is groundwater?
A
the water found underground in the cracks and spaces
in soil, sand and rock
It is stored in and moves slowly through geologic
formations of soil, sand and rocks called aquifers
22
Q
how much of the worlds freshwater is supplied by snow and ice
A
68%
23
Q
how much of the worlds freshwater is supplied by groundwater
A
30%
24
Q
how much of the worlds freshwater is supplied by lakes, ricers, etc
A
0.4%
25
How much of the worlds water supply is freshwater?
2.5
26
Advantages of groundwater(3):
◦ Superior water quality to surface water
◦ Less expensive to develop
◦ More reliable supply
27
Ground water is an Extremely important part of the ____ Cycle
Hydrologic
28
Vadose Zone
water infiltrates the ground surface and seeps
downward through a layer of soil, zone of aeration
29
Zone of Saturation
a layer of soil or rock in which all the pore spaces
or fissures are completely full of water
30
Water Table (phreatic surface)
separates these Vadose Zone and Zone of Saturation
31
no groundwater movement means the water table is
flat
32
A sloping water table indicates the ground water
is flowing
33
The water table has the same general shape as the
surface topography
34
Aquifers
A layer of soil or rock in which groundwater can move relatively freely
Confining layer is a geologic unit having little or no intrinsic permeability
35
Porosity of earth material is
the percentage of rock
or soil that is occupied by voids or pore spaces
36
Porosity equation
n = 100Vv/V
◦ n = porosity (%)
◦ Vv = volume of void space in a unit volume of material, m3
◦ V = volume of material, including both voids and solids, m3
37
Total porosity is computed from:
n = 100[1 – (ρb /ρd)]
ρb = bulk density of the aquifer material, kg/m3
ρd = particle density of the aquifer material, kg/m3
Bulk density is the mass of the sample after oven drying divided by
the original sample volume
Most soils have particle density of 2650 kg/m3
38
Porosity Ranges for Sediments
Well-sorted sand/gravel 25-50%
Sand and gravel, mixed 20-35%
Glacial till 10-20%
Silt 35-50%
Clay 33-60%
39
Properties of Aquifers(3)
Permeability refers to the characteristic of the rock that enables water
to flow though the pore spaces
Rock formations have structural features that could affect permeability
Porous rocks are not necessarily highly permeable
40
Confined aquifer
Aquifer sandwiched between two impermeable rock layers that block
the flow of water
Called artesian aquifers
If a tightly cased well is placed through the confining layer, water from
the aquifer may rise a considerable distance above the top of the
aquifer
41
Potentiometric surface
For a confined aquifer, it is the surface represented of the level to
which water will rise in a well casing tapped into the aquifer
the term potentiometric now replaces piezometric
If the potentiometric surface of an aquifer is above the land surface, a
flowing artesian well may occur
42
Unconfined aquifer
Close to the land surface
Called water-table aquifers
Continuous layers of material that will permit the movement of water
Recharged downward by seepage through the unsaturated zone
43
Recharge Area
Where precipitation infiltrates the ground to replenish the water
flowing through the aquifer
Could be remote from the point of actual water use
Important factor in land use planning and urban development
44
Groundwater Flow
Constant state of motion
Rarely level
Generally follows the shape of the ground
Groundwater flows in the downhill direction
Water table intersects the ground surface at springs, lakes, and streams
45
Types of wells
Shallow
Deep
Artesian (flowing)
46
Specific Yield
The ratio of the volume of water that drains from a saturated soil/rock
from gravity to the total volume of soil/rock
Symbol, Sy
47
Pumping wells
The water table elevation in the well before pumping is called the static
level
When well is pumped the water level will drop and stabilize to the
pumping level
Difference between the static level and pumping level is called the draw
down
The larger the draw down, the greater the well will yield
A pumping cone, or cone of depression, will form in the aquifer around a
pumping well as the water level declines
48
Seawater Intrusion
Defined as the increase in salinity of groundwater at a given location and depth
produced by acts of mankind
Intrusion in coastal aquifers (most common type but not the only type!!)
Coastal metropolitan areas dependent on groundwater
◦ States Of Florida, California, Texas, New York
49
Groundwater Banking
Called aquifer storage and recovery
Use surface water in wetter months (and years) to recharge aquifers
Direct percolation of water or injection into aquifers using wells
50
Water sources for recharge include:
◦ River water
◦ Stormwater
◦ Remote surface water
51
What is a recharge well?
Basically it is the direct opposite of a pumping well. A
recharge well pushes back surface water into the
groundwater system.
Typically lined with concrete rings having perforations.
These perforations let water seep from the sides. The rings
line the recharge well from bottom to top with a steel or
concrete ring closing it.
52
To compact
“to press closely together ”
to press the soil particles
tightly together by expelling air from the void space.
53
PURPOSE OF COMPACTION
Compaction of soil increases its density
and produces three important effects
1. An increase in the soil’s shear strength
2. A decrease in future settlement of the soil
3. A decrease in its permeability
54
OPTIONS FOR POOR SOIL CONDITIONS
* Alter the soil property toward optimum desired goals
-----Ways of altering soil:
- increase strength by compaction
- reduce permeability (compaction, Chemically)
- reduce compressibility (compaction)
- remove off ending soil and replace with good soil
55
Compaction is quantified in terms of a soils _______________
soil’s dry unit weight
56
ACTIONS TO ACHIEVE MAXIMUM COMPACTION
- Better compaction of a dry soil is accomplished when moisture is added
- The reason being water acts as a lubricant allowing soil to be packed more densely
-Too much water = lower density (buoyant effect)
57
ACTIONS TO ACHIEVE MAXIMUM COMPACTION
optimum moisture content
a particular moisture content at which dry unit weight is greatest and compaction best
the associated dry unit weight is know as the maximum dry unit weight
58
Compacted soil has a ________ support
improved load
59
loose soil has a ___________ support
poor load
60
Factors affecting compaction of soil (3)
1. Moisture content
2. Compaction effort
3. Type of soil
61
As the # of blows per layer increases, the maximum
dry unit weight _____ and the optimum moisture
content ________.
increases, decreases
62
Different types of rollers include
Smooth Wheel Roller
Sheepsfoot roller
Pneumatic roller
Vibratory roller
63
DYNAMIC COMPACTION
In cases where existing surface or near surface soil is
poor with regard to foundation support, a fi eld
procedure know as dynamic compaction may be
employed to improve the soils properties.
This method is carried out essentially by repeatedly
dropping a very heavy weight onto the soil from a
relatively great height.
The dropped weight may be an ordinary steel
wrecking ball, or it may be a mass especially
designed for the dynamic-compaction procedure
Typically the weight ranges from 2 to 20 tons or
higher, whereas dropping heights range from 20-100
ft.
64
**Different types of In-Place Unit Weight Test
Drive Cylinder Method – use thin wall cylinder
driven in soil to remove sample Clays, not
intended for hard soils
Volume of cylinder=volume of soil
For Low plasticity/cohesionless soils use
Rubber Balloon Method – use water
Sand Cone Method – use Ottawa sand
Both Rubber Balloon, and sand cone are
destructive testing methods
A nondestructive method would use the nuclear
moisture density apparatus.
65
A non-destructive method of In-Place Unit Weight Test
nuclear moisture density apparatus.
66
destructive method of In-Place Unit Weight Test
Rubber Balloon
Sand Cone Methods
67
SOIL STABILIZATION physical methods
physical means
field compaction,
VIBROFLOTATION,
dynamic compaction)
68
SOIL STABILIZATION is
a soil can have physical properties improved
to increase bearing capacity, increase shear strength,
decrease settlement, and reduce soil permeability
69
VIBROFLOTATION
useful for compacting thick up to 75ft (23m), in situ
layers of loose cohesionless soils. The vibrofl otation
method utilizes simultaneous vibration and
saturation.
70
Soil stabilization non-physical methods
- preloading
- special soil (mechanical stabilization),
- chemical material (chemical stabiliation), or some kind of
- fabric materials (geosynthetics) to the soil.
71
Preloading
refers to adding an artifi cial load to a
potential construction site prior to the time the
structure is built (and loaded).
The soil is improved by causing soil consolidation to
occur prior to construction and loading, thereby
decreasing subsequent settling of the structure.
adding fill or other surcharge to the natural soil in situ and allowing the
added weight to consolidate the soil naturally over a period of time
the greater the added surcharge and the
longer the time it is in place prior to construction, the
better the consolidation will be and the better the
bearing capacity of the soil will be.
72
Mechanical Stabilization
simple means of soil stabilization that is
carried out by adding soil material to the naturally
occurring soil.
The added soil material is usually mechanically mixed
with the natural soil and worked together, after which
the mixture is compacted.
Normally a blending of coarse aggregate and fi ne
grained soil is achieved in order to get a soil mixture
that possesses some internal friction and cohesion and
will thereby be workable and subsequently stable when
mixing and compaction have been completed.
73
Chemical stabilization
achieved by adding a cementing material or some kind of chemical to the soil.
The chemical material may be mechanically mixed with
the natural soil and thee resulting mixture compacted,
or the chemical material may be simply applied to the
natural soil and allowed to penetrate the soil through
the void space.
Another process is to inject the stabilizing chemical
into or through the soil under pressure; this is known
as grouting. Grouting is generally performed where it is
necessary to improve soil that cannot be disturbed.
74
Geosynthetics
refers to the family of manufactured
materials (sheet or netlike products) made of plastics
or fiberglass.
Geosynthetics may be used to stabilize and reinforce
soil masses, such as;
- erosion control of earth slope surfaces,
- reinforcing backfi ll or retaining walls,
- reinforcing slopes or embankments,
- slope protection of open channels,
- and drainage control.
75
Geosynthetics may be used to stabilize and reinforce
soil masses, such as;
- erosion control of earth slope surfaces,
- reinforcing backfi ll or retaining walls,
- reinforcing slopes or embankments,
- slope protection of open channels,
- and drainage control.
76
better ___ is acieved by compaction
Shear strength
77
Why explore soil?
For proper analysis of soil conditions at a site it is necessary to investigate and
collect appropriate data on the soils
Soil sampling is required to obtain this data
Objective of any sampling program is to produce a sample representative of the
source soil
Soil sampling is important for groundwater monitoring
Samples of soil horizons above the water table critical to contaminant migration
78
Physical properties of soil
Grain size and distribution
Cohesiveness (if any)
Moisture content
Depth of bedrock
Depth to water table
79
Soil data required
Soil profile
o layer thickness and soil identification
Index properties
o water content, Atterberg limits (Liquid Limit, Plastic Limit) etc.
Strength & compressibility characteristics
Others (e.g., water table depth, bedrock depth)
80
Site Investigation
Look for available site data
◦ Maps
◦ Existing reports
◦ Local government requirements
Site reconnaissance
◦ Visit site
◦ Topography
◦ Site geology
◦ Talk to local people
81
METHODS OF INVESTIGATION
◦ Test pits
◦ Auger Boring
◦ Wash boring
◦ Precession boring
◦ Rotary Drilling
82
Test Pits
The depth is limited to 1-2 m
The in-situ conditions are examined visually
It is easy to obtain disturbed and undisturbed samples
Block samples
83
test pit indicate four profiles
(1) Clayey silt
(2) Sandy silt
(3) Clean sand
(4) Sandy gravel
84
Auger Boring provides the following:
◦ Representative soil and rock samples for laboratory tests (disturbed)
◦ Identify the groundwater conditions
◦ Performance of in-situ tests to assess appropriate soil characteristics (undisturbed)
85
Some of the common types of boring are
◦Auger boring (hand and mechanical)
◦Wash boring
◦Percussion boring
86
Hand Auger for
usually not practical
* For small projects in soft cohesive soils
* In hard soil and soil containing gravels, it becomes difficult
87
Auger Boring drills
a. Helical (worm types) Augers
b. Short flight Auger
c. Iwan (posthole) Auger
88
Mechanical Auger Boring
Borehole depths up to 50 m are possible with continuous-flight
augers
-Hollow stem augers are used when undisturbed samples are
required. Plug is withdrawn and sampler is lowered down and
driven in to the soil below the auger
-If bed rock is reached drilling can also take place through the
hollow stem
-As the auger acts as a casing it can be used in sand below water
table
-The soil rises to the surface along the helical blades, no
requirements to withdrawal auger
-They are not suitable for soil bore that require casing, which
demand removal of auger for driving the casing
89
problems with small-sized augers
The presence of cobbles and boulders
90
Wash boring
-Water at high pressure is pumped through hallow boring rods is
released from narrow holes in a chisel attach to the lower end of the
rods
-The soil is loosened and broken by the water jet and the up-down
moment of the chisel
-The soil particles are carried in suspension to the surface between
the rock and the borehole sites
-The rods are raised and drop for chopping action of the chisel by
means of winch
-Wash boring can be used in most type of soil but the progress is
slow in coarse gravel soils
91
issue with wash boring
The accurate identification of soil profiles is difficult due to mixing
of the material as they are carried to the surface
method is unacceptable for obtaining soil samples
92
Precession boring
Precession drilling is a manual drilling technique in which a heavy cutting or
hammering bit attached to a rope or cable is lowered in the open hole or inside a
temporary casing.
-The technique is often also referred to as 'Cable tool'.
-Usually a tripod is used to support the tools.
-By moving the rope or cable up and down, the cutting or hammering bit loosens
the soil or consolidated rock in the borehole, which is then extracted later by
using a bailer.
-Just as with hand auger, a temporary casing of steel or plastic may be used to
prevent the hole from collapsing.
-When the permanent well screen and casing are installed, this temporary casing
has to be removed.
93
Precession boring
Advantages
Percussion can remove boulders
and break harder formations,
effectively and quickly through
most types of earth
* Percussion drilling can in principle
deal with most ground conditions
* Can drill hundreds of feet (one
well hand-drilled in China in 1923
was over 4000 feet deep)
* Can drill further into the water
table than dug wells, even drilling
past one water table to reach
another
94
Precession boring Disadvantages
* The equipment can be very heavy
and relatively expensive
* Especially in harder rock the
method is slow (weeks, rather
than days)
* When temporary casing has to be
used, the time taken driving and
removing it can significantly
increase drilling time
* Equipment costs are high and the
method is slow (resulting in high
cost per drilled meter).
95
ROTARY DRILLING
-Primarily intended for investigation in rock, but also used in soils
-The drilling tool (cutting bit or a coring bit) is attached to the lower
end of hollow drilling rods
-The coring bit is fixed to the lower end of a core
-Water or drilling fluid is pumped down the hollow rods and passes
under pressure through narrow holes in the bit or barrel
-The drilling fluid cools and lubricates the drilling tool and carries the
loose debris to the surface between the rods and the side of the hole
-There are two forms of rotary drilling, open hole drilling and core
drilling
-Open hole drilling is generally used in soils and weak rock for
advancing the hole
-Drilling rods can then be removed to allow tube samples to be
taken or in-situ tests to be carried out
96
Rotary Drilling
Advantages
In soils the drilling progress is much faster than with other
investigation methods
Disturbance of the soil below the borehole is slight
97
Rotary Drilling Limitations
The method is not suitable if the soil contains a high percentage
of gravel/cobbles, as they tend to rotate beneath the bit and will
not brake up
The natural water content of the material is liable to be increased
due to contact with the drilling fluid
98
Geophysical Techniques
Indirect Methods
Seismic
*Electrical Resistivity
*Electromagnetic (EM)
*Ground Penetrating Radar (GPR)
99
Geophysical Techniques
Indirect Methods
Advantages
*Non-Destructive
*Cost Effective
*Provides Preliminary or
Supplemental
Information
100
Soil Sampling Disturbed
◦ In situ structure not retained
◦ Suitable for water content, classification, compaction
101
Soil Sampling Undisturbed
◦ Less disturbed
◦ Suitable for shear strength, consolidation, permeability
102
Soil Sampling
The following are used to collect soil samples:
Test pits (disturbed and undisturbed)
Split Spoon/SPT sampler (disturbed)
Tubular soil samplers (undisturbed)
Thin-wall tube/Shelby tube (undisturbed)
103
Number of samples Depends upon:
◦ Time constraints
◦ Topography
◦ Cost factors
◦ Reasons for sampling
104
How many samples do we take?
Recommend at least 20 single samples per 10,000m2
105
To what depth do we sample?
usual sampling depth is up to 20 cm in arable land or
10cm in pasture
Undisturbed soil samples are obtained
with a cutting cylinder with minimum capacity of 100cm3
106
Standard Penetration Test (SPT)
As the sampler is driven into the soil the number of blows are
countered
Simple test to perform; particularly useful in noncohesive soils
SPT uses a split spoon sampler
Split spoon sampler is attached to a drilling rod and driven into the soil
using a drop hammer
A 623 N hammer falling 762 mm is used to drive the sampler 457 mm
into the soil
107
Errors in SPT testing
Factors that lead to errors in SPT, blow count;
-Careless work on behalf of boring crew
-Hydrostatic pressure not kept in boring hole, therefore soil
becomes quick
-Interference with the guides used for dropping the drive weight
-The strings for the drill rod, too tight or too loose
-Not removing all the soil from the bottom of the hole
