SHANSEP
(Stress History and Normalized Soil Engineering
( y g g
Properties)
Present Design Practice
Present
Design
Practice
• Phi = 0 method to evaluate the stability of
saturated clayy foundation
• Phi = 0 method is considered the most critical
conditions of no drainage With drainage the conditions of no drainage. With drainage the foundation becomes stronger.
• For very stiff overconsolidated clays
Phi = 0 Method of Analysis
Phi
=
0
Method
of
Analysis
• No drainage during loading undrained
shear strengthg constants irrespectivep of the applied stress
• Limit equilibrium method of analysis phi = • Limit equilibrium method of analysis phi =
0, c = su
• su is a function of water content
Factors Affecting
Undrained Shear Strength
• Sample Disturbance reduced effective
stress 20 – 50% strengthg reduction
• Strength and Stress‐Strain Anisotropy
I h t A i t diff f il t t
– Inherent Anisotropy: differences of soil structure,
e.g., varved clays (alternate layer of silt and clay)
– Stress induced Anisotropy: rotation of principal
• Reduction of undrained shear strength • Increased shear strain at failure
Factors Affecting
Undrained Shear Strength
i ff l l d i
• Strain‐Rate Effect: one log cycle decrease in
strain rate 10 ± 5% decrease in su
– Due to plasticity and creep susceptibility
– Undrained creepp duringg shear increased porep
water pressure decreased effective stress decreased shear strength
– Slower strain rate more creep lower
strength
– UU strain rate 60%/hr 1.2 – 1.3 x strength at
Normalized Behavior
Normalized
Behavior
• Minor variation in testing procedures
NSP: Laboratory Testing Technique
NSP:
Laboratory
Testing
Technique
Undisturbed sample Undisturbed sample
OCR 1 OCR = 1
NSP: Laboratory Testing Technique
NSP:
Laboratory
Testing
Technique
l d d b d
• Consolidated by 1.5x, 2x, and 4x vm
measure su/vc constant for normalized behavior, if not constant NSP method is not applicable
• To obtain su/vc vs OCR
– Use minimumUse minimum vc as the laboratoryas the laboratory vm
– Perform tests at OCR 2 ± 0.5, 4 ± 1, 6 ± 2
SHANSEP
Method of Design
SHANSEP
– Method
of
Design
bdi id h il fil i
1. Subdivide the soil profile into component
deposits based on boring logs, FV data, visual classification, etc.
2. Obtain goodg undisturbed samplesp determine insitu stresses and
preconsolidation pressures check whether
p p
NSP concept is applicable
3 Decide the type of test and the range of 3. Decide the type of test and the range of
SHANSEP
Method of Design
SHANSEP
– Method
of
Design
4. Reconsolidate the sample to the virgin
compressionp curve reduce the stress to give the required OCR perform the shear tests obtain the required NSP from these tests obtain the required NSP from these tests
l h l h l f l (
