review of causes of foundation failures and their possible preventive and remedial measures by dr....

Review of Causes of Foundation Failures and Their Possible Preventive and Remedial

Measures

by

Dr. Amit SrivastavaAssociate Professor, Department of Civil & Environmental Engineering

The NorthCap University, HUDA Sector 23-A Gurgaon - 122017.

ContentsI. Introduction

II. Load transfer failures

III. Drag down and heave

IV. Collapsible soils

V. Lateral loads

VI. Construction error

VII. Unequal support

Contents

VIII.Water level fluctuation

IX. Earthquake

X. Vibration effect

XI. Foundation failure due to landslide/ slope instability

XII. Foundation failure due to uplift

XIII.Conclusion

Contents

Foundations of engineering constructions are systems that act like interface elements to transmit the loads from superstructure to, and into, the underlying soil or rock over a wider area at reduced pressure.  

Engineering structures despite being constructed with adequate strength and safety measures do fail or collapse.

“Failure is an unacceptable difference between expected and observed performance.” – Council of Forensic Engineering, ASCE

Introduction

The objective of foundation is to transfer the load of superstructure to the foundation soil on a wider area.

The uncertainties for which factor of safety is provided in geotechnical design include (a) the natural heterogeneity or inherent variability (b) measurement error, and (c) model transformation uncertainty.

Classic examples of Bearing capacity failures: Transcona Grain elevator in 1913 and Fargo Grain Elevator in 1955.

Load transfer failures

Figure 1. East side of Transcona elevator following foundation failure

Transcona elevator

• Under such circumstances, the most commonly adopted remedial measure to rectify the problem is underpinning.

• Underpinning is accomplished by extending the foundation in depth or width so that it either rests on a more supportive soil stratum or distributes its load across a greater area.

• Use of steel piers, helical anchors and micro piles are common methods in underpinning.

Preventive measures and remedies

Figure 2. Foundation Underpinning by hydraulic jacking and transfers loads to screw foundations installed into stable strata

• In plastic soils, new settlements (drag down) are often accompanied by upward movements and heave some distance away.

• In swelling and shrinking soils, hot dry wind and intense heat will often cause the soil to shrink beneath the foundation.

• Uneven saturation of the soil around foundation (located in expansive soils) can cause the soil to heave as it expands and contracts after drying.

• Similar problem of heave and contraction is observed when foundation is placed in extremely cold condition (below freezing point).

Drag down and heave

Figure 3. Pictorial representation of structural damage caused by drag down and heave

Types of settlement

Damages due to expansive soils

(i) Soil stabilization with lime, lime-fly ash, Portland cement, etc.

(ii) Control of soil moisture using plastic fabric underneath the foundation,

(iii) A thin coat of bitumen will drastically reduce the shear-force between the pile surface and the soil and reduce the negative skin friction,

(iv) Ignoring active zone of expansion and contraction by placing footing at deeper depth or providing pile/ belled piers,

(v) Heavy structure to overcome swell pressure,

(vi) Ice adhesion and resulting uplift can be avoided by using granular backfill around the foundation walls or footing pedestals

Preventive measures and remedies

• They are deposits of fine grained particles transported by wind and are characterized by constituent parts with an open packing arrangement, which forms a meta-stable state that can collapse to form a closer packed, more stable structure of significantly reduced volume.

• Collapse in such deposits can be triggered by either increasing the load on the soil or by wetting it.

• A collapse condition can lead to structure failure, landslides (depending on the topography), and tsunamis (if the soil collapses into a body of water).

COLLAPSIBLE SOILS

A ‘loess avalanche’ in Shanxi, China which killed 23 people due to structural & foundation failure of small houses on the slope & at the foot.

Other Failures

Collapsible Soil: LOESS

Figure 6. Collapse of the soil in The terraces, Glenwood, Colorado was causing settlement of the concrete retaining-wall foundations

Collapsible Soil: LOESS

• By keeping a check on the structural design, i.e., loads and foundation selection (mat foundations minimize the risk of differential settlements)

• Landscape irrigation should be restricted or eliminated, excellent drainage facilities should be underlain with an impermeable liner to prevent water from seeping into the soil

• Popular ground modification treatments for such soils include pre-wetting of the soil, dynamic compaction, Vibro-floatation, Vibro-compaction, Stone/cement columns, treating the soil with calcium chloride and/or sodium silicate solutions in order to introduce cementing that is insoluble, etc.

Preventive measures and remedies

• During an earthquake the foundation of the building moves with the ground and the superstructure and its contents shake and vibrate in an irregular manner due to the inertia of their masses (weight).

• Damage to foundations & structures may result from different seismic effects: (i) Ground failures (or instabilities due to ground failures), (ii) Vibrations transmitted from the ground to the structure, (iii) Ground cracking, (iv) Liquefaction, (v) Ground lurching, (vi) Differential settlement, (vii) Lateral spreading, and (viii) Landslides.

Failure due to Earthquake

• Lateral movement in soil is possible when there is removal of existing side support adjacent to a building. There is excessive overburden on backfill or lateral thrust on the backside of a retaining wall

• Lateral movement is also observed during earthquake when structure fails due to lateral movement of soil beneath the foundation following liquefaction

• Classic examples of such failures are: (a) major damage to thousands of buildings in Niigata, Japan during the 1964 earthquake, (b) Failure of Lower San Fernando dam which suffered an underwater slide during the San Fernando earthquake, 1971.

Earthquake & Liquefaction

Figure 7. (a) Building Failure during 1964 Niigata, Japan Earthquake, (b) Failure of lower San Fernando dam in 1971 (c) Retaining wall failure (d) Failure of Showa bridge during 1964 Niigata earthquake in Japan

Earthquake & Liquefaction

Figure 13. Typical example of overturning of a building due to liquefaction of the foundation soil during the Kocaeli earthquake, Turkey, August 17, 1999, Magnitude 7.4

Liquefaction mitigation measures

(i) Soil Improvement Options

(a) Densification, Deep Dynamic Compaction

(b) Hardening Technique, Grouting,

(ii) Structural Option, Piles or Caissons extending below the liquefiable soil

(iii) Quality Assurance , in taking mitigation measures

(i) Proper planning of Subsurface Investigation,

(ii) Analysis and Design and

(iii) Construction Control and Supervision.

(iv) For small scale damages underpinning of structures is suggested.

Additional measures and remedies

• There are two common sources of construction errors, i.e.,

(I) Temporary protection measures (Error relating to temporary shoring, bracings and temporary coffer dams),

(II) Foundation work itself.

Construction error

Foundation not aligned properly

Punching failure of foundation

Lack of proper investigation

Few cases indicating major Construction failure

Figure 9. (a) apartment building was constructed, (b) it was decided for an underground garage to be dug out. The excavated soil was piled up on the other side of the building (c) Final failure of building

•This paper presents a classic case of poor construction practice due to which foundation failure of a building in Shanghai, China took place

Construction error

• There is no remedy for such massive failures but definitely preventive measures in terms of “supported excavation system” for “deep excavation problems” can be adopted to avoid such failures.

• Soil nailing is the latest and most widely used technique for supporting the vertical excavation near an existing building.

• A classic application of soil nailing technique is reported in which soil nail support of excavation system for the embassy of the Peoples republic of China in the United States was carried out.

Preventive measures and remedies

Figure 10. (a) Design details of soil nail wall section (view from E) (b) work executed for supporting vertical excavation using soil nailing technique

Soil Nailing Technique

• Footing resting on different type of soil, different bearing capacity and unequal load distribution will result in the unequal settlement or what we call as differential settlement.

• The Tower of Pisa in Italy is a classic case study.

Unequal support

Figure 11. Different strategies applied to prevent the tower from collapse

• Rise in GWT reduces the bearing capacity of the soil and on the other hand rapid fall in the GWT causes ground subsidence or formation of sinkholes due to increased overburden effective stress value.

• Formation of sinkhole is another major cause of foundation failure due to increased water usage, altered drainage pathways, overloaded ground surface, and redistributed soil.

• According to the Federal Emergency Management Agency, the insurance claims for damages as a result of sinkholes has increased 120% from 1987 to 1991, costing nearly $100 million.

Water level fluctuation

Figure 12: Formation of sinkhole due to ground water table fluctuation

• Construction activities such as blasting, pile driving, dynamic compaction of loose soil, and operation of heavy construction equipment induce ground and structure vibrations.

• Ground vibrations from construction sources may affect adjacent and remote structures in three major ways, i.e.,

(I) structure vibration with/without the effect of resonance structure responses,

(II) dynamic settlement due to soil densification and liquefaction,

(III) pile driving and accumulated effects of repeated dynamic loads.

Vibration effect

• Monitoring and control of ground and structure vibrations provide the rationale to select measures for prevention or mitigation of vibration problems, and settlement/damage hazards. Active or passive isolation systems are adopted in this regard.

Preventive and remedial measures

• Foundation failure due to rapid movement of landmass over a slope results when a natural or man-made slope on which structure exists becomes unstable.

• The major causes of slope instability/ landslide can be identified as (i) Steep slope, (ii) Groundwater Table Changes / heavy rainfall, (iii) Earthquakes and other vibrations, and, (iv) removal of the toe of a slope or loading the head of a slope

Foundation failure: slope instability

Figure 14. Foundation failure of existing facility due to landslide/ slope instability

• Modifying the geometry of the slope,

• Controlling the groundwater,

• Constructing tie backs,

• Spreading rock nets,

• Providing proper drainage system,

• Provision of retaining walls, etc.

• Soil nailing Technique

Preventive and remedial measures

• One of the major causes of foundation failure due to uplift is presence of expansive soil beneath the foundation.

• Swelling clays derived from residual soils can exert uplift pressures, which can do considerable damage to lightly-loaded or wood-frame structures.

• In case of pile foundations that are used to resist the uplift forces due to wind loads, such as, in transmission line towers, high rise buildings, chimney, etc., the available uplift resistance of the soil becomes the one of the most decisive factor in defining the stability of foundation.

Foundation failure due to uplift

• The paper reviewed and discussed the various causes of foundation failure as well as their possible preventive or remedial measures through case studies.

• The work will be useful for practicing engineers in identifying the potential foundation problem in advance and taking necessary and appropriate action for mitigation purpose.

Conclusion

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