FOUND. ON PROBLEM GROUND

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FOUNDATIONS IN PROBLEM GROUND CONDITIONS : 

FOUNDATIONS IN PROBLEM GROUND CONDITIONS Sohail Kibria M. Sc. Civil Engg. Chief Engineer, GT & GE Division, NESPAK

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PROPERLY DESIGNED, CONSTRUCTED & DURABLE FOUNDATIONS IN ALL GROUND CONDITIONS ENSURE SAFETY OF STRUCTURES AND THE HUMAN LIVES.

WHAT ARE PROBLEM SOILS ? : 

WHAT ARE PROBLEM SOILS ? The soils that show abnormal behavior, that is generally not recognizable by the routine soil testing, are called problem soils. These soils possess undesirable engineering properties, that may badly affect the structures, if not attended properly.

SOIL / ROCK FORMATION : 

SOIL / ROCK FORMATION SOIL DEPOSITS OR ROCK FORMATIONS ARE SELDOM UNIFORM. THERE IS LAYERING / BEDDING, THAT IS SELDOM UNIFORM. THE INCREASED HETEROGENITY ALSO CREATES PROBLEM GROUND CONDITIONS.

VARIOUS PROBLEM GROUND CONDITIONS IN PAKISTAN : 

VARIOUS PROBLEM GROUND CONDITIONS IN PAKISTAN Seismic Areas Landslide Prone Areas Swelling/Shrinking Soils Dispersive Soils Collapsible Soils Fissured Clays Sensitive (Quick) Soils Open-work Soils Liquefiable Soils Soft/Loose Ground/Fill Areas/Organic Soils Sheared Clays Slaking Rocks Cavernous Rocks Solutioning Rocks Loess and Sand Dunes Frozen Ground High Groundwater Areas Soils with Aggressive Chemicals

WHAT CAN THESE SOILS DO ? : 

WHAT CAN THESE SOILS DO ? SUDDEN / EXCESSIVE SETTLEMENTS TILTING / SINKING OF STRUCTURES CRACKS IN STRUCTURES COLLAPSE OF STRUCTURES EXCESSIVE SEEPAGE CHEMICAL ATTACK ON FOUNDATIONS

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PROBLEMATIC SOILS REQUIRE SPECIAL TESTS AND STUDIES FOR THEIR IDENTIFICATION & EVALUATION AT SITE & IN THE LAB. SUBSEQUENTLY SPECIAL MITIGATIVE MEASURES ARE REQUIRED TO BE IMPLEMENTED.

WHERE LOCATED IN PAKISTAN ? : 

WHERE LOCATED IN PAKISTAN ? We can gain from the Chinese and Russian experiences of collapsible soils, Japanese experiences of landslides and liquefiable soils, Indian experiences of swelling soils etc. Some of the areas containing problematic ground conditions in Pakistan include landsliding problems in the northern parts of Pakistran, swelling soils at D .I. Khan, Chakwal, Dera Bugti, Khairpur etc., collapsible soils at Rawat, Hub, Sahiwal etc., liquefiable soils at Chashma, Kalabagh, Kot Addu, Muzaffargarh etc., dispersive soils at Turbat etc. and soft ground conditions in the historical cities like Lahore, Peshawar, Multan, Pakpattan etc. and in the cultivated lands.

LANDSLIDE PRONE AREAS : 

LANDSLIDE PRONE AREAS CAUSES Unstable or sliding soils/rocks Water movement Earthquakes EFFECTS Sliding Total Destruction MITIGATION Stabilization of unstable slopes Taking care of drainage Construction to resist earthquakes Construction in safe areas

Soft/Loose Ground/Dumped Fill : 

Soft/Loose Ground/Dumped Fill CAUSES Wet lands Agricultural sites Old dumped fills Recent deposits EFFECTS High settlements Cracking/damage of structures MITIGATION Bypassing Replacement (if light loads and not very thick layer) Rigid Foundation system Deep foundation system Prevent water ingress

Swelling / Shrinking Soils(MONTMORILLONITE or SMECTITE, ILLITE, KAOLINITE) : 

Swelling / Shrinking Soils(MONTMORILLONITE or SMECTITE, ILLITE, KAOLINITE) CAUSES Presence of single and double layer minerals in cohesive soils attract water and swell Exposure of expansive soils supporting light structures to water EFFECT Map cracking on ground surface in dry weather Swelling with water, causing cracks in light structures Heaving of floors and pavements Conversely, shrinkage takes place in expansive soils upon reduction in moisture MITIGATION Bypassing by isolation Replacing Preventing water ingress Rigid foundation system Waffle mat Pre-wetting Lime treatment Deeper foundations

SWELLING CLAY MINERALS : 

SWELLING CLAY MINERALS

IDENTIFICATION OF SWELLING SOILS : 

IDENTIFICATION OF SWELLING SOILS

INDICATION OF DEGREE OF SWELLING : 

INDICATION OF DEGREE OF SWELLING

SWELL MITIGATION AT GOMAL UNIVERSITY, D.I. KHAN : 

SWELL MITIGATION AT GOMAL UNIVERSITY, D.I. KHAN

DISPERSIVE SOILS : 

DISPERSIVE SOILS CAUSES Presence of high Na ions in the soil, in comparison to total quantity of Na, K, Ca & Mg ions EFFECTS Dispersion of soil grains even in still water Quick erosion of soils Loss of soil cover Reduction of uplift resistance in tie-down anchors MITIGATION Provision of protective layer Provision of filters Addition of lime

DISPERSIVE SOILS : 

DISPERSIVE SOILS Zone-B Zone B C

COLLAPSIBLE SOILS : 

COLLAPSIBLE SOILS CAUSES In arid/ semi-arid areas, temporary bonds develop between soil grains. These bonds dissolve upon wetting and under pressure EFFECTS Sudden subsidence of soils upon wetting Damage to the structures on such soils MITIGATION Prewetting Compaction Replacement Rigid Foundation Bypassing such soils Preventing water ingress

COLLAPSIBLE SOIL GRAINS : 

COLLAPSIBLE SOIL GRAINS

USBR COLLAPSE CRITERIA : 

USBR COLLAPSE CRITERIA

COLLAPSE STUDY IN LAB. : 

COLLAPSE STUDY IN LAB.

COLLAPSIBLE SOILS : 

COLLAPSIBLE SOILS

RIGID FOUNDATIONS TO RESIST COLLAPSE OF SOILS : 

RIGID FOUNDATIONS TO RESIST COLLAPSE OF SOILS

LIQUEFIABLE SOILS : 

LIQUEFIABLE SOILS CAUSES Fine to medium sands, under high groundwater table, develop very high pore water pressure under seismic / pulsating loads. EFFECTS The shear strength of soils becomes very low, as the pore pressure rises. Structures may tilt, sink or get cracked. Loss of life may also occur. MITIGATION Ground improvement by various means Deep foundations Construction on raised ground

GRAIN SIZE OF LIQUEFIABLE SOILS : 

GRAIN SIZE OF LIQUEFIABLE SOILS

EVALUATION OF LIQUEFACTION POTENTIAL : 

EVALUATION OF LIQUEFACTION POTENTIAL

DYNAMIC COMPACTION : 

DYNAMIC COMPACTION

VIBROCOMPACTION : 

VIBROCOMPACTION

GROUTING AND GRAVEL DRAINS : 

GROUTING AND GRAVEL DRAINS

SHEARED CLAYS : 

SHEARED CLAYS CAUSES The presence of fissures causes low shear strength to mobilize at failure The main reason is overconsolidation and the stress relief, causing direct tension cracking EFFECTS Low shearing strength called residual strength is available for design Shearing may trigger sliding at low loads MITIGATION The presence of sheared clays can be taken care of in design, once it is indicated in the lab. test results

SOILS WITH AGGRESSIVE CHEMICALS : 

SOILS WITH AGGRESSIVE CHEMICALS CAUSES Unleached soils in arid areas Rise of groundwater table, rich in salts EFFECTS Sulphate attack on bricks / concrete Chloride attack on steel MITIGATION Use of appropriate cement Water proofing of substructures Use of rich / impervious concrete mixes Coating of steel

CONCLUSIONS AND RECOMMENDATIONS : 

CONCLUSIONS AND RECOMMENDATIONS The following broad conclusions are drawn and recommendations are made for the design of safe foundations on problematic sites: Adequate amount of field and laboratory studies must be carried out to investigate the possibility of the presence of a problematic soil. In case, the presence of a problematic soil is confirmed, supplementary testing for quantification of the relevant parameters must be carried out. The most cost-effective remedial measures must be subsequently evolved, in keeping with the indigenous technology. The engineering institutions must consider launching a comprehensive research program, for a detailed study of problem soils and preparation of national guidelines, for the design of safe foundations in such conditions.

THANK YOU : 

THANK YOU

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