What is the primary reason Bjerrum (1974) suggested a correction factor (λ) for the undrained cohesion (cu) obtained from vane shear tests?
Explanation
Bjerrum's correction factor, λ, is an empirical adjustment applied to vane shear test results to account for the observation that the test can overestimate the operational shear strength of plastic clays, leading to potentially unsafe designs.
Other questions
What is the fundamental assertion of Mohr's theory of rupture in materials?
How does the Mohr-Coulomb failure criterion approximate the shear stress on a failure plane for most soil mechanics applications?
What is the angle (θ) of the failure plane with respect to the major principal plane, according to the Mohr-Coulomb criterion?
In a strain-controlled direct shear test on dense sand, what is the term for the shear stress reached after the initial peak failure stress, where the stress value gradually decreases and then becomes constant?
According to the drained direct shear test results shown for an overconsolidated clay in Figure 12.11, what is the cohesion intercept (c') for the residual strength plot?
What is a significant advantage of the direct shear test, despite its shortcomings?
In a consolidated-drained (CD) triaxial test, after the initial consolidation under chamber pressure σ3, how is the deviator stress (Δσd) applied?
A consolidated-drained triaxial test was conducted on a normally consolidated clay. The results are: confining pressure σ'3 = 16 lb/in.2 and deviator stress at failure (Δσd)f = 25 lb/in.2. Calculate the angle of friction, φ'.
What is Skempton’s pore pressure parameter Ā?
For a normally consolidated clay, what is the typical range for the value of Skempton's pore pressure parameter at failure, Āf?
What is the 'φ = 0 concept' in soil mechanics?
An unconfined compression test is a special type of which other test?
For a clay specimen, the unconfined compression strength (qu) is 120 kN/m2. What is its undrained cohesion (cu)?
An overconsolidated clay deposit has an average present effective overburden pressure of 160 kN/m2, an overconsolidation ratio (OCR) of 3.2, and a plasticity index (PI) of 28. Using Skempton's and Ladd's relationships, what is the estimated average undrained shear strength, cu(VST)?
What is the property of clay soils where the unconfined compression strength is greatly reduced after remolding without any change in moisture content?
A clay that turns into a viscous fluid upon remolding and is found mostly in previously glaciated areas of North America and Scandinavia is referred to as what type of clay?
What is the primary cause of strength anisotropy in cohesive soils?
According to the relationship proposed by Casagrande and Carrillo for the directional variation of undrained shear strength, which statement is true for normally consolidated clays?
In a vane shear test, if the maximum torque (T) applied is known, the undrained cohesion (cu) is calculated based on resisting moments. What does the term Me represent in the equation T = Ms + Me + Me?
Which handheld device, described as a modified form of the vane shear test apparatus, is pushed into the soil and rotated to determine the undrained shear strength (cu)?
In the shear strength equation for unsaturated cohesive soils, τf = c' + [σ - ua + χ(ua - uw)]tan φ', what does the parameter χ represent?
What is a stress path?
In a p'-q' stress path plot, what does the Kf line represent?
What is the relationship between the angle of the modified failure envelope, α, and the effective friction angle, φ', for a normally consolidated clay?
In a direct shear test on a dry sand, the normal stress is 200 kN/m2 and the shear stress at failure is 175 kN/m2. Determine the angle of friction, φ'.
What is the typical value of cohesion (c') for sand and inorganic silt according to the text?
In a consolidated-drained triaxial test on an overconsolidated clay, the failure envelope exhibits two distinct branches. What does the steeper branch (portion bc in Figure 12.23) represent?
A consolidated-undrained triaxial test was performed on a saturated sand specimen. The chamber confining pressure was 12 lb/in.2. At failure, the deviator stress was 9.1 lb/in.2 and the pore water pressure was 6.8 lb/in.2. Calculate the drained friction angle, φ'.
For a normally consolidated clayey soil, the effective stress failure envelope is given by τf = σ' tan 30°. If a drained triaxial test is conducted at a chamber-confining pressure of 10 lb/in.2, what is the deviator stress at failure, (Δσd)f?
What is the typical consistency of a clay with an unconfined compression strength (qu) of 75 kN/m2?
What is thixotropy in the context of clay soils?
In a vane shear test, three types of shear strength mobilization are assumed for the ends of the soil cylinder. Which of the following is NOT one of those assumptions?
What does the thixotropic strength ratio, as defined in the text, represent?
How does the total stress failure envelope for an unsaturated inorganic clay change as the degree of saturation increases?
In a stress path plot using Lambe's p'-q' coordinates, how is q' defined?
For a normally consolidated clay under a consolidated-drained triaxial test, what is the angle that the p'-q' stress path makes with the horizontal?
Which type of shear strength parameters should be used to determine the long-term stability of an earth embankment?
The stability of the slopes of an earth dam after rapid drawdown is a classic example that should be studied using which type of shear strength parameters?
What is the primary shortcoming of the direct shear test related to the failure plane?
Two drained triaxial tests are run on a saturated clay. For test 1, σ'3 = 70 kN/m2 and σ'1 = 200 kN/m2. For test 2, σ'3 = 160 kN/m2 and σ'1 = 383.5 kN/m2. What is the drained angle of friction, φ'1?
Using the data from the previous question (Test 1: σ'3=70, σ'1=200; Test 2: σ'3=160, σ'1=383.5; φ'1=20 degrees), calculate the cohesion intercept, c'.
What happens to the pore water pressure in dense sand and overconsolidated clay during a consolidated-undrained triaxial test as axial strain increases?
A drained direct shear test is performed on an overconsolidated clay. The normal force is 350 N, and the shear force at failure is 257.6 N. The specimen has a diameter of 50 mm. What is the shear stress at failure, τf?
What is the primary physical reason for the curvilinear nature of Mohr's failure envelope in sand, which is often approximated as linear?
What is Skempton's pore pressure parameter B?
A clay has a sensitivity ratio (St) of 12. How would this clay be classified according to Figure 12.38?
What is the defining characteristic of the total stress failure envelope obtained from unconsolidated-undrained triaxial tests on a fully saturated cohesive soil?
Which laboratory test is generally considered one of the most reliable for determining shear strength parameters due to its wide use in research and conventional testing?
In the context of the p'-q' stress path diagram, what is the equation for the modified failure envelope (Kf line) for a soil with cohesion c' and friction angle φ'?