How can you use geotechnical field test data to assess excavation stability?

2 Shear strength and failure criteria

Another important step in assessing excavation stability is to measure the shear strength of the soil and rock. This is the resistance of the material to sliding or slipping along a plane under applied stress. The shear strength depends on factors such as cohesion, friction, pore water pressure, and confining pressure. You can use different geotechnical field tests to estimate the shear strength of the soil and rock, such as direct shear test, triaxial test, vane shear test, and pressuremeter test. These tests will give you the values of the shear parameters, such as cohesion (c), friction angle (phi), and dilatancy angle (psi). You can then use these values to apply a failure criterion, such as Mohr-Coulomb or Hoek-Brown, to predict the conditions under which the soil or rock will fail.

3 Deformation and settlement

A third step in assessing excavation stability is to evaluate the deformation and settlement of the soil and rock due to the excavation. This is the change in shape or volume of the material caused by stress redistribution, consolidation, creep, or swelling. The deformation and settlement can affect the performance and safety of the excavation and the adjacent structures. You can use various geotechnical field tests to monitor the deformation and settlement of the soil and rock, such as inclinometer, extensometer, settlement plate, piezometer, and strain gauge. These tests will provide you with data on the displacement, strain, pore water pressure, and stress of the soil and rock.

4 Support design and analysis

A final step in assessing excavation stability is to design and analyze the support system that will prevent or limit the failure of the soil and rock around the excavation. The support system can consist of elements such as shoring, bracing, anchors, nails, piles, or shotcrete. The design and analysis of the support system should consider the geotechnical properties and conditions of the site, the geometry and depth of the excavation, the loading and environmental factors, and the safety and economic criteria. You can use various geotechnical field tests to verify the performance and effectiveness of the support system, such as load test, pull-out test, plate load test, and instrumentation. These tests will help you evaluate the capacity, stiffness, and reliability of the support system.

5 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?