Create a free account and view content that fits your specific interests in geotechnical engineering __Learn More__

This section is part of: Athanasopoulos, G. A. (2021) "Online Lecture Notes on Soil Mechanics", Geoengineer.org, DOI: https://doi.org/10.48246/GEOENG-EDU-001

Contents [show]

where,

Q : volumetric water flow rate (volume/time units)

k : coefficient of permeability (or hydraulic conductivity) (length/time units)

h_{1}: total hydraulic head in the entrance of the cylinder (length units)

h_{2}: total hydraulic head in the exit of the cylinder (length units)

L: length of the cylinder (length units)

Α: cross sectional area of the flow [(length)² units]

i = (h_{1}-h_{2}) / L : the hydraulic gradient

h_{1}-h_{2}: hydraulic head difference (length units)

The total hydraulic head has two components: a) the __elevation head__, h_{e}, is the height of a point from a random reference level and b) the__ piezometric head__, h_{p}, is the water pressure at this point divided by the unit weight of water

Flow velocity :

Infiltration rate :

i) Flow vertical to bedding planes

ii) Flow parallel to bedding planes

1) Constant Head Permeameter

2) Falling Head Permeameter

ho: initial hydraulic head

h: hydraulic head after t time

ln: natural logarithm

As the water flows through the voids, it creates forces that are applied on the soil particles in the direction of its motion.

j: seepage force per unit volume

i: hydraulic gradient of the flow

γ_{w}: unit weight of water

When the water flows through soil, __seepage forces must be taken into account__ for the calculation of the effective stresses.

When water flows upwards in soil, there is a critical hydraulic gradient value where the weight of the soil particles is counteracted by the seepage force. In that case, soil behaves like a viscous liquid and this phenomenon is called __quicksand__. The critical hydraulic gradient is given by the equation:

where,

γ_{αν}: unit weight of buoyancy

γ_{w}: unit weight of water

K_{20℃}= permeability factor at temperature of 20℃

K_{T℃} = permeability factor at temperature of T℃

n_{20℃} = water viscosity at temperature of 20℃

n_{T℃} = water viscosity at temperature of T℃

The diagrams below show the values of the fraction n_{T℃} / n_{20℃ }as a function of temperature that varies from T=12℃ to T=30℃

1) For loose, clean (without fines) sand (Hazen,1930):

k (cm/sec) = c * D^{2}_{10}

where:

c = a constant that varies from 1.0 to 1.5

D_{10}= effective grain size in mm

2) For fine to medium, clean sand (Casagrande, 1967)

k = 1.4 * e^{2} * k_{0.85}

where:

k = permeability factor for e void ratio

k_{0.85} = permeability factor for e void ratio equal to 0.85

3) The Kozeny-Carman equation for sandy soils:

Where:

c_{1} = a constant

It has been found that: C_{1} = C_{2} * D^{2.32}_{10} * Cu^{0.6}

where:

D_{10} = effective grain size

Cu = uniformity coefficient

C_{2} = a constant

4) For normally consolidated clays (1982):

where C_{3}, n = constants

Chapter 7: Earth Pressures7.2. Coulomb Theory (1776)7.1. Rankine Theory (1857)7.3. Graphical Methods7.4. Types of Retaining Structures7.5. Example ProblemsOnline Lecture Notes on Soil MechanicsChapter 2: Stresses in Soils2.1. Normal and Shear Stress2.2. Stresses as a result of the soil self-weight2.3. Stresses due to a load surcharge on the Ground Surface2.4. Example ProblemsChapter 9: Bearing Capacity of Shallow Foundations9.1. Bearing Capacity9.2. Example ProblemsChapter 3: Flow of Water through Soil3.2. Two Dimensional Flow3.3. Graphical Generation of Flow Nets

Flow Nets - Confined Flow Number of flow channels partitions nf = 4 Number of equipotentia...

What is Soil Consolidation? Soil Consolidation refers to the process in which the volume of a satu...

Problem 9.1 A square footing of width 2.25m is founded at depth of 1.5m on a sand layer which has...

Theoretical models to predict the capacity of helical piles are based on Soil Mechanics and an appr...

Introduction A standard penetration test (SPT) is one of the most popular in-situ tests carrie...

What does freezing of shafts means? Since more than hundred years ago in water bearing non-competen...

Definitions Fig.2 shows the relationship between the settlement and the applied stress on...

When flow is two-dimensional, simple application of Darcy’s law is not enough for the solution of...

Apr, 30, 2020 | Education #### Soil Compaction Test

Mar, 22, 2020 | Education #### Atterberg Limits

May, 28, 2020 | Education #### Direct Shear Test

Mar, 21, 2020 | Education #### Step-by-Step Guide for Grain Size Analysis

Oct, 21, 2019 | Education #### Unconfined Compression Test

Jul, 15, 2020 | Education #### Measurement of Specific Gravity of Soils

Apr, 21, 2020 | Education #### Cone Penetration Testing (CPT)

Jan, 01, 2021 | Education #### 7.5. Example Problems