Distribution of Stresses

When a load is placed on the ground, the stress does not stay under the load. This chapter explains how stresses are distributed through soil, starting with an overview of stresses in soils and the stresses beneath structures and embankments, and including stresses around deep underground openings.

It then turns to the strength of the soil. You will find shear strength in soils and the laboratory tests used to measure it: the drained direct shear test, the repeated direct shear test, triaxial compression tests, and the unconfined compression test. The chapter links the stresses you calculate to the strengths you measure, which is the basis of settlement and stability work.

In this chapter

• Overview of Stresses in Soilspage 265
  • Types of Soil Stresses
  • Mohr's Circle of Stress
  • Preconsolidation Stress
• Stresses beneath Structures and Embankmentspage 272
  • Effect of Foundation Stiffness
  • Limiting Contact Pressures
  • Other Factors Influencing Contact Pressure
  • Semi-Infinite, Elastic Foundations
  • Layered or Anisotropic Foundations
  • Approximate 2:1 Distribution
  • Contact Pressure and Deformation Pattern
  • Stresses Induced by Pile Loads
  • Limitations of Theoretical Solutions
• Deep Underground Openingspage 298
  • Openings in Rock
  • Loads on Underground Openings in Rock
  • Openings in Soft Ground
  • Pressure on Vertical Shafts
• Shear Strength in Soilspage 305
  • Importance of Soil Strength
  • Selection of Type of Stress Analysis
  • Comparison of Laboratory and Field Strengths
  • Selection of Design Shear Strength
• Drained (S) Direct Shear Testpage 307
  • Apparatus
  • Preparation of Specimen
  • Procedure
  • Presentation of Results
  • Simplified Procedure for Drained (S) Direct Shear Tests
  • Possible Errors
• Drained (S) Repeated Direct Shear Testpage 318
  • Apparatus
  • Specimen Preparation
  • Procedure
  • Computations
  • Presentation of Results
  • Possible Errors
• Triaxial Compression Testspage 321
  • Principles of the Triaxial Compression Test
  • Types of Tests
  • Apparatus
  • Preparation of Specimens
  • Q Test
  • Q Test with Backpressure Saturation
  • R Test
  • S Test
  • Possible Errors
• Unconfined Compression Testpage 354
  • Apparatus
  • Preparation of Specimens
  • Procedure
  • Computations
  • Presentation of Results
  • Possible Errors
  • Use of Other Types of Equipment for Undrained Shear Strength