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Difficult Soils

This document discusses three types of problematic soils for construction: expansive soils, collapsible soils, and soft/compressible soils. Expansive soils swell when wet and shrink when dry, which can damage structures. Collapsible soils have a loose structure when dry but settle significantly when wetted. Soft soils are prone to large settlements. The document recommends techniques like chemical stabilization, moisture control, surcharging, deep foundations, and soil improvement or replacement to address these problematic soil types.

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Muhammad Asharib Shahid
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340 views14 pages

Difficult Soils

This document discusses three types of problematic soils for construction: expansive soils, collapsible soils, and soft/compressible soils. Expansive soils swell when wet and shrink when dry, which can damage structures. Collapsible soils have a loose structure when dry but settle significantly when wetted. Soft soils are prone to large settlements. The document recommends techniques like chemical stabilization, moisture control, surcharging, deep foundations, and soil improvement or replacement to address these problematic soil types.

Uploaded by

Muhammad Asharib Shahid
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as PDF, TXT or read online on Scribd
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Foundations on Problematic or Difficult Soils

•EXPANSIVE OR SWELLING SOILS


•COLLAPSIBLE SOILS
•SOFT OR COMPRESSIBLE GROUND
EXPANSIVE SOILS

Such soil undergoes large volume changes


when their environment is changed; swell when
moisture increases and shrinks when moisture
is decreased
Such soil are characterized by presence of clay
mineral like Illite & Montmorillonite.
Generally classified as CH, MH, or OH by
Unified Classification System.
Expansive Soils are known to cause severe
damage to civil engineering structures resting
on it.
(International Building Code 2006: Section 1802.3.2)

Expansion Potential Very Low Low Medium or High Very High


Moderate or Critical
Liquid Limit (LL) 0-20 20-35 35-50 50-70 70-90
Plasticity Index (PI) 0 – 10 10 – 15 15 – 25 25 – 35 >35
Expansion Index 0 - 20 21 - 50 51 - 90 91 - 130 >130
(EI)
% Swell at ơv= 6.9 - 0-2 2-6 6 - 10 >10
kPa

•PI = Plasticity Index = LL-PL

•EI= 1000(hp-ho)/ho = 10 (% primary swell)

•ơv= Surcharge Pressure


3
DAMAGE CAUSED BY SWELLING OF SOIL

Cracks (repaired) in residential buildings


(Shah Abdul Latif University, Khairpur)
DAMAGE CAUSED BY SWELLING OF SOIL

Failure of Walls
(Shah Abdul Latif University, Khairpur)
DAMAGE CAUSED BY SWELLING OF SOIL

Lifting of floor slab due to Swelling of underneath soil


DAMAGE CAUSED BY SWELLING OF SOIL

Crack in Wall Cracks in Exterior Wall


DAMAGE CAUSED BY SWELLING OF SOIL

Cracks in Pavement Uneven Roads


Shrinkage cracks at DG Khan Site Shrinkage cracks at DG Khan Site

Gomal University, Dera Ismail Khan Gujranwala (Nandipur) Site


o Chemical Stabilization
o Moisture control
o Through control of placement
condition
o Pre-wetting
o Soil Replacement
o Blending with non swelling soils
 Surcharge Loading
 Constructing on slab-on-grade beam
which may be supported by piles
 Improve drainage around building
 Avoid watering (irrigation) around building
 Avoid constructing slab-on-grade floors
 Prewetting before construction
 Make foundations rigid
 Bypass such soil through Piles
Structure of Collapsible Soil Stress ~ Strain Behavior

Failure Mechanism: When such soils are relatively dry, pose high strength
but upon wetting/saturation, their structure is collapsed and the results is
large settlement of the foundation
Preventive Measure: Pre-wetting, Deep foundation, Water control etc.
 Pre collapse before the construction by in-
situ compaction, i.e., Dynamic compaction
 Prewetting
 Excavate and re-compact to break the
structure
 Grouting
 Improve drainage to avoid wetting
 Include soft clays, highly organic soils, etc
 Prone to large settlement
 Try to avoid placing foundations and bypass
by deep foundation
 Soil replacement within influence zone
 Provide rigid foundation to cater differential
settlement
 Pre-consolidation by fill loading, Sand drains
 Improvement techniques
 Delay construction when consolidation is
underway

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