Title: Foundations on Collapsible Soils
1Foundations on Collapsible Soils
- Prof. Jie Han, Ph.D., PE
- The University of Kansas
2Outline of Presentation
- Introduction
- Basics and Evaluation
- Preventive Measures
3Collapsible Soils
- In arid and semiarid areas
- Strong if dry but collapse (quickly consolidate)
if wet - Sometimes called metastable soils
- Process of collapse hydroconsolidation,
- hydrocompression or hydrocollapse
- Predominantly sand and silt size particles in a
loose - honeycomb structure
- Water-softening cementing agents hold together
the - loose structure
4Driveway Drop 8 due to Collapse of Collapsible
soil
J White
5Microstructures
6Collapse of Microstructure
7Map of Collapsible Soils
KS
Dudley (1970)
8Type of Collapsible Soils
- Collapsible alluvial soils (transported by
water) and - colluvial soils (transported by gravity)
- Collapsible aeolian soils (transported by wind)
sand - dunes, (most common) loess, volcanic dust
deposits - Collapsible residual soils (formed in-place by
the - weathering of rock
9Loess in Kansas City
10Double Oedometer Tests
Insitu moisture content
?w
Strain ?
Saturated
log?
11Single Oedometer Tests
Loading (dry)
Strain ?
Wetting at constant load
?w
Loading (wet)
log?
12Example of Soil Collapse Tests
Saturated _at_ 200kPa
Dry
Wet
Crushed sand/ kaolinite 85/15
Miller et al.
13Classification of Soil Collapsibility
Potential hydrocollapse strain, ?w
Severity of Problem
0 0.01
No problem
Moderate trouble
0.01 0.05
Trouble
0.05 0.10
Severe trouble
0.10 0.20
Very severe trouble
gt 0.20
Jennings and Knight (1975)
14Hydrocollapse Strain and Normal Stress
Sudden collapse
Dry
Dry
Strain, ?
Strain, ?
Wet
Wet
log?
log?
Most collapsible soil
Loess
15Potential Hydrocollapse Strain
?w potential hydrocollapse strain
Cw hydroconsolidation coefficient
?t threshold collapse stress
?t normal stress at which hydroconsolidation
occurs
16Wetting Coefficient
Wetting Coefficient, ?
Degree of Saturation, S
17Settlement Computation
?w settlement due to hydroconsolidation
? wetting coefficient
Cw hydrocollapse coefficient
?z vertical total stress
?t threshold stress
z depth
18Preventive Measures
- Removal of the collapsible soil
- Avoidance or minimization of wetting
- Transfer of load through the collapsible soils
to the - stable soils below
- Injection of chemical stabilizers or grout
- Prewetting
- Compaction with rollers or vehiles
- Compaction with displacement piles
- Compaction by heavy tamping
- Vibroflotation
- Deep blasting combined with prewetting
- Controlled wetting
- Design structure to be tolerant of differential
settlements
19Heavy Tamping/Dynamic Compaction
20Vibroflotation
21Grouting
22Transferring Structural Loads through Collapsible
Soils
Coduto (2001)