Lecture 6
1 / 11

LECTURE 6 - PowerPoint PPT Presentation

  • Updated On :

LECTURE 6. Soil Physical (Mechanical) Properties – Bulk density, porosity, strength, consistency. Definitions…. Atterberg limits (H. Matengu) Soil strength (L. Olver) Soil dynamics (N. Davenport) Soil micromorphology (A. Pietersen). Physical properties:

I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
Download Presentation

PowerPoint Slideshow about 'LECTURE 6' - wood

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
Lecture 6 l.jpg


Soil Physical (Mechanical) Properties –

Bulk density, porosity, strength, consistency

Definitions l.jpg

  • Atterberg limits (H. Matengu)

  • Soil strength (L. Olver)

  • Soil dynamics (N. Davenport)

  • Soil micromorphology (A. Pietersen)

Slide3 l.jpg

  • Physical properties:

    • “Characteristics of soil which can be measured by physical means and expressed in physical terms, such as colour, density, porosity, hydraulic conductivity, structure, texture and depth”

      – van der Watt & van Rooyen, Soil Science Society of South Africa

  • Mechanical properties:

    • “An expression of the materials which make up the soil…” – Pitty (1978)

  • Bulk density l.jpg
    Bulk Density…

    • Definition:

      “The mass of dry soil per unit bulk volume. Values range roughly from 1000 – 1800 kg.m-3, although higher values may be found in compacted soils.”

      – van der Watt & van Rooyen, Soil Science Society of South Africa

    • Is an expression of the proportions of solid and void in the soil matrix.

    • Strongly influenced by texture, sorting and organic matter content.

      • Why? How?

  • Why is bulk density important?

    • Influences permeability, drainage rate and penetration by roots and burrowing animals.

  • Porosity l.jpg

    • Definition:

      “The percentage volume of the soil occupied by pores and pore space.”

      • Effective pore space = part of the pore system through which fluids can move freely.

  • Strongly related to bulk density

    • Lower bulk density = higher total pore space.

  • Pore size

    • Can be divided into macropores (larger than 0.08mm), and micropores (smaller than 0.08mm).

  • Soil strength l.jpg
    Soil strength…

    • Definition:

      “A general term referring to the ability of a soil to resist deformation by applied forces, which could be any one of several types.”

    • Can be described in terms of cohesion, shear strength and adhesion.

    Slide7 l.jpg

    • Cohesion:

      • “The attraction of a substance for itself; the mutual attraction among molecules or particles comprising a substance that allows it to cling together as a continuous mass”

      • Changes as soil dries out and bulk density increases.

      • Maximum bond when soils are wet with an extremely restricted amount of water (water retreats into micropores and creates a “suction” force).

      • Commonly measured as soil’s resistance to penetration (use of a penetrometer).

      • Strongly related to soil erodibility.

      • NB in engineering.

    Slide8 l.jpg

    • Shear strength:

      “The maximum resistance to shearing stresses which a specimen or element of soil can withstand before failure occurs”

      • Depends on internal friction and cohesion

    Slide9 l.jpg

    • Adhesion:

      “Refers to a molecular attraction which holds two dissimilar substances in contact, such as water and soil particles”

      • Increases as texture becomes finer.

      • Increases with higher soil organic matter content.

      • Adhesion between soil and a foreign object can be attributed to the water film between the 2 surfaces.

      • Soil “stickiness” occurs when cohesion is less than adhesion (this is dependent on moisture content).

    Consistency l.jpg

    • The greater the amount of moisture in a soil, the more it can behave like a liquid

      • Less interaction between adjacent particles.

  • As water is added to dry soil, it passes through phases:

    • Solid

    • Semi-solid

    • Plastic

    • Liquid

  • Slide11 l.jpg

  • Shrinkage limit:

    • Limit between solid and semi-solid states.

    • Above this limit, semi-solid state is reached.

  • Plastic limit:

    • Limit between semi-solid & plastic states.

    • Soil becomes plastic and can be moulded into shapes.

    • Limit defined as the minimum moisture content at which the soil can be rolled into a thread of 3mm diameter without breaking up.

  • Liquid limit:

    • Limit between plastic and liquid states.

    • At this moisture content, the soil will flow under its own weight.

  • ad