hybrid drain geosynthetics for fine-grain soil improvements

Download Hybrid Drain  Geosynthetics  for fine-grain soil improvements

Post on 24-Feb-2016




0 download

Embed Size (px)


Consolidation pressure ( p=20,50,100,200,400 kPa ). H . Drain face. PWP-3 PWP-2 PWP-1. u. 150mm diameter. Kanto loam slurry. Drain layer. Hybrid Drain Geosynthetics for fine-grain soil improvements. Chandan Ghosh Prof. & Head [ Geohazards ] National Inst. of Disaster Management - PowerPoint PPT Presentation



Hybrid Drain Geosynthetics for fine-grain soil improvementsChandan GhoshProf. & Head [Geohazards]National Inst. of Disaster ManagementMinistry of Home Affairs, Govt. of India



PWP-1H Consolidation pressure (p=20,50,100,200,400 kPa)Drain faceu150mm diameter

Kanto loam slurryDrain layer1Large strain slurry consolidationDo slurry behave similar to normal soil?Do PWP in slurry different from normal Terzaghi soil?Can internal PWP be measured?Do k, Cv, Cc, mv are constant with consolidation pressure?Permeability direct and from Consolidation theory differ much?3

Typical application/troubles!!

Important!!!Drain flow capacity

Problem domain Local/problematic soilsLoad typesDrain/reinforcementTime dep. Sett.?Cloggingflow capacity changes under confinementGeosynthetics as drainDrain clogging and efficiency in flow under pressureIn-plane and x-plane flow be measured?Index properties of geosyntheticsInternational codal practiceEvaluation of clogging from slurry stageDrain efficiency hybrid drain system6AIM of present researchTo recommend suitable drain system for field applicationTo assess nature of clogging and flow capacity of drains confined in fine-grained soil7Research needs Flow capacity of synthetic drains placed in-situAssessment of clogging and its preventionRecommending design flow capacity of drains based on available hydraulic index test dataUse of synthetic materials for improving fine-grained soils8Geosynthetics used

Geocomposite-AGC-ANonwoven ANW-ANonwoven BNW-BNonwoven CNW-C

Nonwoven coverWoven fabric

9Grain size distribution

In-plane flowX-plane flow10Clogging mechanism

Geosynthetic clogged by Kanto loamConsolidation of soil ideal vs naturalCan we measure excess PWP directly?Can excess PWP exceeds applied load increment?What if load increment ratio varies from 0.5 to 3?What if applied pressure is increased in steps or in one go - say from p=0 to 400kPa?How Excess PWP varies with H or with r?How different is k if measured in a large specimen?11AIMwhat happens inside slurry when loaded upto 400kPa How different are all parameters?Drained water and settlement how are they related?To check soil bevaviour and looking into gap theory and practice12Leh cloud burst - 2010Slurry formationMud slidesPrevention of mud slides

Measuring in-plane flow and drain efficiency using a large dia consolidation apparatusMeasuring internal PWP during testValidation of consolidation theory



Cloud burst at Leh, 4-5 Aug 2010Boundary Wall of DIHAR Broken by slurry 1516Apparatus developed

Basis of developingexperimental methods

1617Test procedure

PWP-3PWP-2PWP-1Data loggerAirpressure regulatorSilty claysampleSetting PWP tipsCompacting sand baseGeocomposite as boundary drain filterSilty clay slurryBlinding of Geocomposite filterParticle blinding (a)(c)(b)(d)(f)(g)(e)Silty clay220 mm150mm1718Flow tests in drains placed within Kanto loam and silty clay during consolidation Soil slurryDrain (120x50mm)Consolidation pressureDrain pipe

Kanto loam slurryDrain layer1819

Various in-plane flow tests carried at in-situTest situation double layer drain system Double layer drain and in-situ state

Geocomposite-AGC-ANonwoven ANW-ANonwoven BNW-BNonwoven CNW-C

2.7mm thick4mm thick5.5mm thick6.2mm thick20Various drains tested in-situ during consolidation of slurry

Toyoura sand21Status of drains after test

22Permeability factor in-situ

Permeability factor = k-no clog drain/k- soilPermeability factor >105, which is satisfactoryWith increasing pressure this factor increases, which is also a good indication23Flow tests in drains placed within Kanto loam and silty clay during consolidation Soil slurryDrain (120x50mm)Consolidation pressureDrain pipe

Kanto loam slurryDrain layer24Average in-plane flow capacity

Flow in HYBRID drain is the highestWithout sand mat flow is the low, NWC drain is the lowestConfining pressure causes 70 to 80% reduction in GC drainClogging of drainsHow to evaluate clogging?How to remove clogging of drains? ultrasonic removalHybrid drains combination of geotextile and sand mat2526Clogging of geocomposite

Inner woven part

Kanto loam

Silty clayNonwoven cover26Large dia 1D consolidationCan PWP be measured directly?Slurry and normal soil states at 50 kPaVariation of internal excess PWP with height ?Do excess PWP attains 100% immediately after applied pressure?Direct and indirect permeability are they same?k, p, mv, Cc, Cv are these constant with p?Can we measure Drained water during consolidation?

27Consolidation from slurry stageKanto loam slurry (is there a relation between LL and slurry water content?)Why p=50 kPa?- transition from slurry to Terzaghi soil

Kanto loam slurryDrain layer28At p=400kPa (dia =150mm, H=57mm)29Kanto loam local soil and silty clay - commercialMaterialKanto loam (local soil)Silty clay (commercial)Plasticity LL %108.137.7 PL %82.316.4 PI25.821.3Natural water content (%)1013Particle density, s (Mg/m3)2.6872.612d max (kN/m3)7.6611.96Optimum w%8217Initial void ratio of slurry 6.70-8.002.30-3.30Grain size Clay, Silt, Sand10%, 27%, 63%43%, 55%, 2%Triaxial (UU), uu, cuu40, 19.6 kN/m2- - - (CU), cu, ccu250, 5.9 kN/m2- - -3031Excess pore water pressure ratio (u/del p)Vertical strain of slurry sample32t50 at p=400kPa33Is there a unique transitional stage at p=50kPa?343536373839mv, Cv, k are not constant404142With more p, u/p reduces43Excess PWP (p=20 to 400kPa)44PWP-3PWP-2PWP-1H50 Consolidation pressure (p=50 kPa)Drain faceu150mm diameter45PWP inside specimen46PWP-3PWP-2PWP-1H50 Consolidation pressure (p=50 kPa)Drain faceu150mm diameter47Excess PWP is more than net increase in p484950Permeability - direct5152e p curve535455New developmentsNew multi-purpose test apparatus developedFlow capacity at in-situ state & increasing confinementExcess pore water measurement inside specimenDirect measure of k, vertical strain, drained water55ConclusionsTransition between slurry and normal Terzaghi soil state occurred at consolidation pressure of 50 kPa. Water content at this transition state found fairly close to the respective liquid limits of the Kanto loam and silty clay.Peak excess PWP represents the state at which soil undergoes maximum rate of compression. e-log p curves for slurry state and normal soil state are different and it has two separate Cc values.

56Thank you57


View more >