One dimensional flow of water through soil

Question 1

How can water flow through earth embankments?

Answer 1

Its hard for water to flow through impervious soil, however there are weak points where water can easily flow through

Question 2

What is seepage?

Answer 2

The flow of eroded material due to the action of water.

Question 3

What happens if solids escape the soil through the flow of water?

Answer 3

The density goes down and mass slowly reduces which means less resistance and more susceptible to collapse.

Question 4

What can you use to divert water away through soil.

Answer 4

• French drains

Question 5

What is shotcrete?

Answer 5

Shotcrete is a method of applying concrete projected at high velocity primarily on to a vertical or overhead surface

Question 6

How can you increase slope stability?

Answer 6

• Use design frames
• Shotcrete
• Use built-in-drainage layers

Question 7

What can alter the degree of saturation and strength of soil?

Answer 7

Changes in environmental conditions

Question 8

How roads designed to be stable?

Answer 8

• Fill gap from natural level of soil to level of road

Question 9

What are used in conjunction with roads to transport water?

Answer 9

Outlet pipes to transport water higher elevation to a lower elevation

Question 10

What are the outlet pipes used by roads called?

Answer 10

Collector pipes

Question 11

What do you do when you have water above the base of an excavation?

Answer 11

• Install pumps in bore holes and sucks water out which will have a temporary effect
• Reduce water level

Question 12

What can boreholes also be used for?

Answer 12

Checking dryness is at right depth

Question 13

How can multiple boreholes be used?

Answer 13

Little bore holes connected to a bigger pipe

Question 14

How does water flow in terms of energy?

Answer 14

Water flows from zones of high mechanical energy to zones of low mechanical energy

Question 15

What is the hydraulic gradient?

Answer 15

∆h/l

Question 16

What are the 3 component of energy?

Answer 16

• Elevation head
• Pressure head
• Velocity head -> assumed to be negligible

Question 17

What is the difference in height of water called between two points?

Answer 17

Head loss

Question 18

What is the total head?

Answer 18

h = h_z+h_p

Question 19

What is static liquefaction?

Answer 19

Caused by a sudden loss of effective stress accompanied by vast deformations and a rapid build-up of pore water pressure that can cause soils to behave like liquids

Question 20

What is static liquefaction known as or like?

Answer 20

Quick condition - flow of water through the soil

Question 21

How do you determine the critical effective stress?

Answer 21

𝜎’_c = z𝛾’-iz𝛾_w=0
- i = h/H_2

Question 22

What is the critical hydraulic gradient?

Answer 22

i_c=𝛾’/𝛾_w

Question 23

What does upward seepage do?

Answer 23

Upward seepage reduces the vertical effective stresses in the
soil

Question 24

How can flow rate be calculated?

Answer 24

q = vA = v_sA_v

Question 25

What does seepage velocity consider?

Answer 25

The area of the voids

Question 26

What does Darcy’s Law tell us?

Answer 26

Tells us the hydraulic gradient is linearly related to velocity of the flow

Question 27

What velocities are valid in Darcy’s Law?

Answer 27

Relatively low - laminar flow

Question 28

What’s Darcy’s Law in terms of v, k and hydraulic gradient?

Answer 28

v∝ki = k∆h/l

Question 29

What does the hydraulic conductivity tell us?

Answer 29

How easy water can travel through soil

Question 30

What are the two tests for investigating permeability?

Answer 30

• Constant head test
• Falling head test

Question 31

How can you find the hydraulic conductivity in the constant head test?

Answer 31

k=QL/Aht

Question 32

How can you find the hydraulic conductivity in the falling head test?

Answer 32

k = (2.303aL/At)log_n(h_1/h_2)
- n = 10

Question 33

How does the constant head test work?

Answer 33

• Soil specimen which is submerged
• Control height of water at bottom with discharge point
• We measure amount of water discharged over time

Question 34

How does the falling head test work?

Answer 34

Water is placed into the well at a known rate and volume until the water level begins to stabilise, either at the top of the well or at a known level

Question 35

What does the diameter of the standpipe in the falling head test depend on?

Answer 35

Permeability of the soil