इंटरनेटमानक Disclosure to Promote the Right To Information Whereas the Parliament of India has set out to provide a practical regime of right to information for citizens to secure access to information under the control of public authorities, in order to promote transparency and accountability in the working of every public authority, and whereas the attached publication of the Bureau of Indian Standards is of particular interest to the public, particularly disadvantaged communities and those engaged in the pursuit of education and knowledge, the attached public safety standard is made available to promote the timely dissemination of this information in an accurate manner to the public. “जान1 का अ+धकार, जी1 का अ+धकार” “प0रा1 को छोड न' 5 तरफ” “The Right to Information, The Right to Live” “Step Out From the Old to the New” Mazdoor Kisan Shakti Sangathan Jawaharlal Nehru IS 8009-1 (1976): Code of practice for calculation of settlements of foundations, Part 1: Shallow foundations subjected to symmetrical static vertical loads [CED 43: Soil and Foundation Engineering] “!ान $ एक न' भारत का +नम-ण” Satyanarayan Gangaram Pitroda “Invent a New India Using Knowledge” “!ान एक ऐसा खजाना > जो कभी च0राया नहB जा सकता ह” है” ह Bhartṛhari—Nītiśatakam “Knowledge is such a treasure which cannot be stolen” IS : 8009 (Part I ‘) - 1976 ( Reallimed2003 1993 )) ( Reaffirmed Indian Standard CODE OF PRACTICE FOR CALCULATION OF SETTLEMENTS OF FOUNDATIONS PART I SWALLOW FOUNDATIONS SYMMETRICAL STATIC SUBJECTED VERTICAL TO LOADS ( Fifth Reprint MARCH 1999 ) UDC 624’151’5’042’13 0 Copyrigh; 1976 BUREAU MANAK INDIAN OF BHAVAN. 9 BAHADUR STANDARDS SHAH ZAFAR MARG NEW DELHI 110002 Gr 9 August 1976 -/ .. G~HA Brsw~ (Alternate) ~$ea9w. ADDITIONAL DIRECTOR. Government of West . N. K. SHRI R. MALuoTnA Chandiparh Mckensies Limited. S. DIVANJI & Company. RAKsrirr(Alkmau) Commissioners for the Port of Calcutta SIiRI I. JANGLE(Altmate) The Braithwaite Burn & Jessop Construction SHRI A. G. h%w Alipm. Sum K. Block P.IS : 8009(Part I) .- _ F F .(India) Pvt Ltd. Bombay S_ S. E. s_ 0. Government of Punjab. RDSO ADDITIONAL DIRECTOR. Bombay SHRI V. RAOHAVAN (Alternate) Indian Institute ~of Technology. MATWR (Ceatintlcd41)page 2) Q Copyright 1976 BUREAU OF INDIAN STANDARDS This publication is protected under the Indian Copyright Act @IV of 1957) and reproduction in whole or in part by any means except with written permission of the publisher shall be deemed to be an infringement of copyright under the said Act. GULIUTI National Buildings Organization. C. DESHPANDE mmmion.lA~~SO (AZmfc) Public Works Department. Bombay S_ A.S’. _. KARL Pnblic Works Department.1976 Indian Standard CODE OF PRACTICE FOR CALCULATION SETTLEMENTS OF FOUNDATIONS OF PART I SHALLOW FOUNDATIONS SUBJECTED TO SYMMETRICAL STATIC VERTICAL LOADS Foundation Chaiman PROP DINNESH MOHAN Engineering Sectional Committee. GH~~I-IAL Company Limited. Calcutta S_ K. V.R~UURCH Ministry of Railways (FE). K. CI-L~TTERJEB In personal capacity (P-820. New Delhr DIRECTOR (CSMRS) DEPUTY DIKECTOR (CSMRS) (Altmutc) Rodio Foundation Engineering Ltd. HaoDE S_ S. &ACKO Srinx S. New Delhi SHRI V. N.9mill $0 . STANDARDJ S_ I$B. New Delhi DR SW K.rBlding BDC 43 Representing Research Institute (CSIR).u GUPTA calcutta SHIUH. K. BALCHANDANI (Abernatc) Indian Institute of Technology. . D. aad Haxarat SHRI A. H. Calcutta SHRIN. Bombay Sum V. c. Bengal. . GUIU (Altcmak) The Cementation Co Ltd. P. H. B. DA~NA calcutta) Simplex Concrete Piles (India) Private Limited. Bombay DR R. Centrr. MEHTA SHRI T. IS1 (Ex-@C&J Member) SHRI D. N. KAPUR (Alternate) Engineers India Limited. NAMBIAR LT-COL OMBIR SINGH MAJ LALIT CHAWLA (Alternate) SHRI B. SHRI D._ . N. PATEL SHRI D. of Settlement Guindy. Army Headquarters The Hindustan Bombay Construction Company Limited. of Madras Members SHRI S. SHRNA~TAVA DR R. P. Lucknow Ministry of Shipping and Transport. RAMAN Deputy Director (Civ Engg). Guindy. N. . Dastur and Company Pvt Ltd. B. Bombay SHRI T. S. TA~~BEKAR Indian Institute of Technology. New Delhi SHRI N. SEETHARAMAN(Alternate) Gammon India Limited. D.KAR (Alternate) Indian Geotechnical Society. ISI panel for the Preparation of Code for Calculation Shallow Foundations Convener 1)~ S. VARGHE~E DR V. M. Madras DR S. AJITHA SIMHA. NACRAJ SHRI K. S. New Delhi SHR~ V. SUBBA RAO SHRI S. REDDI (Alternate) United Technical Consultants Pvt Ltd. New Delhi PRESIDENT SECRETARY (Alternate) PROFESSOROF CIVIL ENGINEERINGCollege of Engineering. Calcutta C. N. Madras EXECUTIVEBNGINEGR(Alternate) Bombay Port Trust SHRI M. RAJU College of Engineering. M. BOOMINATHAN DR V. Government of Uttar Sam SHITLA SHARAN Pradesh. K. MUTHUKUMARAN (Alternate) Hindustan Steel Limited (Steel Authority of India). Madras Indian Institute of Technology. VENKATESAN(Alternate) Public Works Department. RAJU (Alternate) SUPERINTENDING SURVEYOR OF Central Public Works Department._ . New Delhi DR S.. Government of Tamil SUPERINTENDED ENGINEER Nadu. Roorkee DR SHAMSHER PRAKASH Public Works Department. Madras Engineer-in-Chief’s Branch. V. SAWR (AZ&mate) M.. C. SANKARAN University of Roorkee. N. SNHA SHRI R. MENON (Alternate) PROP V.I. MTJTHWKUMARAN College of Engineering. &JU New Delhi In personal capacity (F-24. Director (Civ Engg) &RI Secretq SHRI G.1976 (Continued from page 1) Members SHRI Y. New Delhi WORKS II Director General. S. SHRI A. A. Jvew Delhi) Bokaro Steel Limited. K.IS : 8009 (Part I) . RAO Central Warehousing Corporation. Guindy. Bombay In personal capacity (C-40. Calcutta Cement Service Bureau. Madras Poor P. GreenPark.I. PANTHAKY The Representing Concrete Association of India. Green Park. A. MURTHV SHRI C. New Delhi SIIRIK. SEN SHRI S. Madras 2 c - A-. K. S. New Delhi) DR V. Mining subsidence. c) Secondary compression of foundation soil.IS : 8009 (Part I) . the settlements have to be limited. 0. it will not theoretically suffer damage. the underground utility lines irrespective of the amount of settlement. to the extent possible.2.3 If a structure settles uniformly. In practice. Alternatively. 0. after the draft finalized by the Foundation Engineering Sectional Committee had been approved by the Civil Engineering Division Council. this code is prepared to provide a common basis. FOREWORD 0. Therefore. if the static load is excessive. 3 . Such non-uniform settlements induce settlement is generally non-uniform. the resulting settlement may consist of the following components : a) Elastic deformation or immediate settlement of foundation soil. subsidence due to underground erosion and other causes. But. for the estimation of the settlement of shallow foundations subjected to symmetrical static vertical loading.1 Catastrophic settlement may occur. if the estimated settlements exceed the allowable limits. Deterioration of foundation.1 This Indian Standard (Part I) was adopted by the Indian Standards Institution on 21 February 1976. and ShGnlcage of soil. the foundation dimensions or the design may have to be suitably modified. .2 Settlement causes : a) bl cl 4 may be the result of one or combinations of the following Static loading. and d) Creep of the foundation soil. of these secondary stresses.1976 hdian Standard CODE OF PRACTICE FOR CALCULATION SETTLEMENTS OF FOUNDATIONS OF PART I SHALLOW FOUNDATIONS SUBJECTED TO SYMMETRICAL STATIC VERTlCAL LOADS 0. When the load is not excessive. 0. Depending upon the permissible extent secondary stresses in the structures. may be damaged due to excessive settlement of the structure. b) Primary consolidation of foundation soil resulting from the expulsion of pore water. vibration. any method considered suitable for the type of soil met with may be adopted by the designer. 1. 2. In such situations.1: cau toga by i . e = void ratio. should be taken into account. for a given pressure increment. = coefficient of compressibility.A coefficient utilized in the theory of consolidation. containing the physical constants of a soil affecting its rate of volume change: _k(lfe) 6 ‘yn where k = coefficient of permeability.). tne following definitions shall apply.12 subj 2.4 A settlement calculation involves many simplifying assumptions as detailed in 4. shallow foundations under symmetrical static vertical loads.9 : 2.2 This standard does not deal with catastrophic settlement as the foundations are expected to be loaded only up to the safe bearing capacity.1. therefore. are not dealt with./ 0. 2.3 soils Pi= by ( 2.4 void 2. clays and plastic silts. TERM$NOLOGY 2. it is known that in organic estimation of secondary compression.11 weig of C( 2. 4 2.8 thes the1 2. the settlement computations at best estimate the most probable magnitude of settlement.1 Coefficient of Compressibility-The secant slope. 2. Procedures for computing time rate of settlement are also given. Anaiytical methods for the estimation of settlements due to deterioration of foundations.5 1. Satisfactory theoretical methods are not available for the However. of the effective pressure-void ratio curve. the secondary compression may be important and.10 2. 0. SCOPE 1.2 Coefficient of Consolidation (c.5 In the formulation of this standard due weightage has been given to international co-ordination among the standards and practices prevailing in different countriesin addition to relating it to the practices in the field in this country.6 exp* wit) give 2. therefore.7 force S&S 2.14 2.0 For the purpose of this standard. mining and other causes are not available and.13 subjl 2.1 This standard (Part I) provides simple methods for the estimation of immediate and primary consolidation settlements of. and % yW = unit weight of water. In the present state of knowledge. 2. 7. within a soil mass to the total amount of consolidation obtainable under a given stress condition. 2. 5 .4 Compression 2.The ratio. with pressure on the log scale.5 Creep f s : a) Slow movement of soil and rock waste down slopes usually imper~ceptible except to observations of long duration. 2. 2. expressed as a percentage of the weight of the oven dry soil.8 Elastic Deformation (Immediate Settlement) . 2. 2.13 Overconsolidated Soil Deposit-A soil deposit that has been subjected to an effective pressure greater than the present effective pressure.A soil deposit that has never been subjected to an effective pressure greater than the existing effective pressure. It is numerically equal to the coefficient of compressibility divided by one plus the original void ratio.The average normal force per unit area transmitted from grain to grain of a soil mass. 2.12 Normally Consolidated Clay .The water content.7 Effective Stress (Intergranular Pressure) .It is that part of the settlement of a structure that takes place immediately on application of the load.8. expressed as a percentage of the amount of consolidation at a given time.6 Degree of Consolidation (Percent Consolidation) .11 LiqGd Li+it .The reduction in volume of a soil mass caused by the a.15 Primary Consolidation .pplication of a sustained load to the mass and due principally to a squeezing out of water from the void spaces of the mass and accompanied by a transfer of the load from the soil water to the soil solids. that is av l+e Index .9 Immediate Settlement 2.14 Pore Pressure - Stress transmitted through the pore water. - See 2. b) The time dependent deformation behaviour of soil under constant compressive stress. 2. at the boundary between liquid and plastic states of consistency of soil. 2. 2.ry bte - Pressure See 2.IS : 8009 (Part I)-1976 2. It is the stress which to a large extent controls the mechanical behaviour of a soil.The slope of the linear portion of the pressurevoid ratio curve on a semi-log plot.3 Coe%icient of Volume Compressibility-The compression of a soil layer per unit of original thickness due to a given unit increase in pressure. 2.10 Intergranular en . 17 Sensitive Clay - A clay which exhibits sensitivity. and maximum distance that water must travel in order to reach a drainage boundary.The reduction in volume of a soil mass caused by the application of a sustained load to the mass and due.y.22 Void Ratio -The ratio of the volume of void space to the volume of solid particles in a given soil mass. expressed as follows: 1-= t HE k (l+e) a.Elevation at which the pressure in the ground water is zero with respect to the atmospheric pressure. m2/kg Width of footing. 2. 2.18 Sensitivity .20 Static Cone ResistanceForce required to produce a given penetration into soil of a standard static cone. The effect of remoulding on the consistency of a cohesive soil. 2. the following symbols shall have the meaning indicated against each: av = B = c = c. 2. 2. m Constant of compressibility Compression index Static cone resistance.21 Time Factor -Dimensionless factor.Themratio of the unconfined compressive strength of an undisturbed specimen of the soil to the unconfined compressive strength of specimen of the same soil after remoulding at unaltered water content.IS : 8009 (Part I) . it will be equal to the thickness of layer in the case of one way drainage and half the thickness of layer in the case of two way drainage. = Ckd = Coefficient of compressibility.H2 t c.the soil water to the soil solids.0 For the purpose of this standard and unless otherwise defined in the text.16 Secondary Compression . 2. 3. utilized in the theory of consolidation. SYMBOLS 3.23 Water Table . containing the physical constants of a soil stratum influencing its time-rate of consolidation. The shearing resistance of soil above the base level of the foundation is neglected.19 Shallow Foundation-A foundation whose width is greater than its depth. t =He = elapsed time that the stratum has been consolidated.principally to the adjustment of the internal structure of the soil mass after most of the load has beerr transferred from. kg/cm2 6 .1976 2. 2. Modulus of elasticity. St T Total settlement Time factor t 11 Degree of consolidation WL Liquid limit . of layer._ . Maximum kg/cm2 kg/cm2 intergranular pressure. m Influence Influence k Coefficient L Length of footing. year Vertical ordinate Angular coordinate in 3D case (see Fig. Initial Ht H Thickness Z m2/year in the vertical void ratio at mid-height direction. direction.1976 cv Coefficient D Depth of footing. m d E Depth of water table below foundation.. of layer Thickness of compressible stratum measured from foundation level to a point where induced stress is small for drainage in one direction. computed for effect of depth of fiiundation. factor for immediate value for stress concentration of permeability. m ZB PO m m from one dimensional m consolidation at time t. 111’ Frolich mv Coefficient P Concentrated P t. pressure. 15) 7 _ .IS : 8009 (Part I) . -_-. haIf the thickness of compressible stratum below the-foundation for drainage in two directions. of a footing of 30 i: 30 cm. Foundation pressure._ PC Effective settlement m/year m factor of volume compressibility. kg/cm2 in 31) case (see Fig. kg Initial soed kg/cm2 kg/cm2 of soil layer. m consolidation settlement. 15) SId Elapsed cm2/kg load. m settlement. Eh J%! of consolidation. kg/cm2 Young’s modulus in the horizontal Young’s modulus e Void ratio e. m m Settlement corrected Sl Immediate Settlement test. m time. kg/cm2 effective pressure at mid-height R Radial ordinate Sl Settlement SC Primary St Final settlement. the properties may vary known due to sample disturbance. .1. GENERAL in / di Pr of th P’ sions of loaded area (see Table 1) A factor used in Westergaard theory Vertical stress.i IS: 8009(hrtI)-1976 oc AD = Pressure increment. the settlements at different p. 4. Then. To take into account the effect of settlement on redistribution of loads.2 The following assumptions are made in settlement analysis : a) The total stresses induced in the soil by the construction of the structure are not changed by the settlement. The methods suggested in this standard for the determination of these parameters and evaluation of the extent of overconsolidation are generally expected to yield satisfactory results. b) The efftctive stress-void ratio relationship of the soil in each layer. In this procedure. Further. settlement may cause changes in the loads acting on the foundation. C) The load transmitted by the structure to the foundation is static and vertical. the differences in settlement between different parts of the structure are worked out and also new trial values of load distribution are computed. kg/cm2 = Poisson’s ratio :: = A factor related to pore pressure parameter A and the dimen17 = a. C) State of stresses in the soil medium before the construction of the structure and the extent of overconsolidation of the foundation soil. 4. I 4.5 Unequal settlement may cause a redistribution of loads on columns. 4.1. kg/cm* CONSIDERATIONS 4-l Requirements.lrts of the structure are made compatible with the structural loads which caused them. as the settlements often 8 4 the is 1 wil ma due par 4 tha in 1 or s ThC of ! sub: . However. within each layer and average values may have to be worked out. the settlements are first computed assuming that the load distribution is independent of the settlements.4 The settlement computation is highly sensitive to the estimation of the effective stresses and pore pressures existing before loading and the stress history of the soil layer in question.1.1.3 The thickness and location of compressible layers may be estimated But often the soil properties are not accurately with reasonable accuracy.1 The following information is necessary for a satisfactory estimate of the settlement of foundations: a) Details of soil layers including the position of water table. By trial and error.: on la: PO thi 4. in clays. = 4. Therefore. b) Induced stresses on soil layers due to imposed loads can be estimated.:1 al it th Assumptions and Limitations 4.1. a trial and error procedure may be adopted. c) A deposit of several regular soil layers.6 The soil layers experience stresses due to the Imposed loads. which are affected by the superimposed loads.2. and f) An erratic soil deposit. the soil profile may be simplified into one or more layers depending upon the extent of uniformity. d) A thick clay layer resting on cohesionless layer or rock.IS: occur -over long periods. but it is customary to assume that the soil reaction is planar and compute the stresses induced in the compressible layers from simple formulae based on theory of elasticity such as Boussinesq’s and Westergaard’s equations.1 For calculation purposes. 8OfM(PartI)-1976 loads due to creep The 4. 2 is one dimensional. pared to soil and therefore. 9 r. the settlement of the rock stratum is neglected. that is. contact pressure distribution. unless the cohesive layer is thin or the cohesive soil is stiff or the cohesionless soil is very loose. c) A thin clay layer extending to ground surface and resting on cohesionless soil layer or rock. b) A thin clay layer sandwiched between cohesionless soil layers or between a cohesionless soil layer at top and rock at bottom. 4. 4. The settlement at any point is computed as the sum of the settlements of all the layers below this point.- . 1 to 6. the settlement contribution by the cohesionless soil layers will be small compared to that due to the cohesive soil layers. in structural materials the readjustment of column are often not taken note of.2. In the exceptional cases cited above. 4. whereas in _a thin clay layer shown in Fig. the average compressibility is estimated.4 The method of computation for cohesionless deposit differs from that for a cohesive deposit.1. depends upon several factors such as the rigidity of the soil. it is generally believed that the application of the methods suggested in this standard leads to errors on the safe side. 3 or a thick clay layer.2 The following are the possible types of soil formations: a) A deposit of cohesionless soil resting on rock. These soil formations are shown in Fig. Therefore. However. The use of these equations for computation of stresses in layered and non-uniform deposits is questionable. and the former may be neglected. rigidity of foundation etc. the settlement Rock is incompressible comdue to all the layers have to be estimated. The settlement of a thin clay layer shown in Fig. -__ . 4.3 Where there are both cohesionless and cohesive soil layers. For each layer.2 Soil Profile 4. the settlement depends upon lateral deformation. These different methods are stipulated in subsequent clauses. The extent of errors introduced are also not known.2.2. the different types of soil formations require different methods of settlement computation. distribution of pressure on the soil at the foundation level. 4 THICK CLAYLAYERRESTING ON COHESIONLE~~LAYEROR ROCK 0 6.1 for. ..._y*. . ‘... 5 1.: -. .IS : 8009 (Part.2. 3 THIN CLAY LAYER EXTENDINCJTOGROUPSURFACEANDRESTLNG ON COHESIONLE~~ SOIL LAYER OR ROCK 5.. 2 THIN CLAY LAYER SANDWICHED BETWEEN COHESIONLE~~ SOIL LAYERS ORBETWEENA COHE~IONLESS SOIL LAYER ATTOP AND ROCK AT BOTTOM B > H. ( 6. FIG. I) .iA&i. . &&‘$v&l: WV. :: .T :‘. . : :’ >. No limitation for Ht . I FIG.” Q ma ...n are independent layers DEPOSITOF SEVERAL REGULAR SOIL LAYERS 10 . B < Ht 5.. . .. 3. FIG. 1 DEPOSIT OF COHESIONLESS SOIL RESXING ON ROCK FIG... m.. : : ..“.’ . ::i . ‘..1976 :.. .1 FIG. : : . . . 3 . . COLLECTION of time rate of settlements. . as well as neighbouring such as rigidity of structure. A review. and e>Estimation 6. .. J _ y.$..IS : 43009 (Part I) . 6 5. ‘. 11 _- . . 2. STEPS INVOLVED 5. 1 . b) Determination of a subsoil profile. < . I I L!. .’ . ... 4 Stress analysis. of the performance of structures. -.1976 1. . I. if any.” “.. c>Other and 4 relevant of proposed structure details of the structure.1 The following independent layers ERRATIC SOIL DEPOSIT IN SETTLEMENT are the necessary COMPUTATIONS steps in settlement analysis: a) Collection of relevant information. b) Building plan givirrg the detailed layout of load bearing walls and columns and the dead and live loads to be transmitted to the foundation. c ..:.are FIG. OF RELEVANT INFORMATION 6. . in the locality and collection of data from actual settlemxt observation on structures in the locality.1 The following details pertaining to the proposed for a satisfactory estimation of settlements: are required a) Site plan showing the location structures. 4 -Estimation of settlements. .. in favourable cases. unless the proposed structure is small. In the case of cohesionless soils. consolidation test should be done on samples collected at 2 m or lesser intervals. ‘XiN-s”.: pr= the t cond the c and in tl allow artesi the c to th the e dated in th havin remoy of the t&e s proce .1 It is required that a sufficient number of borings be taken in accordance with Is : 1892-1962” to indicate the limits of various underground strata Geneand to furnish the location of water table and water bearing strata. . ANALYSIS 8.1976 6. _ _ I 1s : 8889 (Part I) . which differs only slightly from any individual borings and which is a close representation of average strata characteristics. the data should include consolidation test results on undisturbed samples [gee IS: 2720 (Part XV)-1965S].1 The total vertical pressure at any depth below ground surface is dependent only on the weight of the overlying material: The values of natural unit weight obtained for the samples at different depths.2 AS the settlement behaviour of the soil profile is affected by the drainage and possible flooding conditions adjacent to the site and presence or absence of fast growing and water seeking trees. for each one of the clay layers within the zone of stress influence at least one undisturbed sample should be tested for consolidation characteristics..2 A plot of the borings is likely to showysome irregularities in the various strata. 12 ! 8. 7. To obtain initial effective pressure.. the data should include the results of standard penetration tests (see IS : 2131-19637). in which case Fork large structures. In the case of cohesive soils.\*r. DETERMINATION OF SUB-SOIL PROFILE 7. The *Code of practice for site investigation for foundations. it will be sufficient. 7.J . . However. neutral pressure values should be subtracted from the total pressure. addione bore hole at the centre may be sufficient. STRESS .1 Initial Pore Pressure and Effective Stress 8. all borings may be sufficiently alike to allow the choosing of an idealised profile.r:. 8. these informations may also be collected. rally.. should be used to compute the pressures. In general. if two exploratory holes are located diagonally on opposite corners.. Accuracy of settlement calculation improves with increasing number of consolidation tests on undisturbed samples.1.3 Adequate boring data and good judgement in the interpretation of the data are prime requisites in the calculation of settlements. In the case of thick clay layers. tvethod of standard penetration test for soils.:.+Methods of test for soils: Part XV Determination of consolidation properties. The number of samples to be tested depends on the extent of uniformity of soil deposit and the significance of the proposed structure. in the case of clay layers. 7. tional bore holes may be driven suitably. 13 r- ----. If allowed sufficient time. this case would merge with the static case. The artesian case is that in which there is upward percolation of water through the clay layer due to natural or artificial causes. 7 LEVEL OF CLAY OF CLAY STRESS PRELOADING CONDITIONS 8. 7) : types of preloading conditions that can exist are the following a) Simple static case. a condition of partial consolidation under the overburden exists._. __. the neutral pressure at any depth is equal to the unit weight of water multiplied by the depth below the free water surface.1976 possible major (see Fig.2 In simple static case and in the over-consolidated case. GROUND -me _--m-e---- WATER TABLE TOP BOTTOM EFFECTIVE FIG. This may be due to the water table having been lower in the past than at present or due to the erosion or removal of some depth of material at the top. the neutral pressure is greater than that in the previous case. In the pre-compressed or overconsoh dated case. if part of the overburden has been recently placed as for example in made up lands and delta deposits. . The identification of one of the four cases listed above for the given site conditions is essential for the satisfactory evaluation of magnitude of settlements.IS : 8889 (part I) .1. in addition to the hydrostatic pressure a seepage pressure acts upwards and reduces the effective pressure in the soil. In this case. b) Residual hydrostatic c) Artesian case. In residual hydrostatic case. case. since it includes hydrostatic excess pressure. and d) Overconsolidated case. - . the clay might have been subjected to a higher effective pressure in the past than exists at present. ~The detailed procedure and the implications are described in Appendix A. In this case. 3 marked Overconsolidated anisotropy.. 8. ESTIMATION OF TOTAL SETTLEMENTS 9. tions due to Boussinesq.1 The pressure increment is defined as the difference between the initial intergranular pressure as existed in the field prior to application The of load and the final intergranular pressure after app-lication of load.3. The residual hydrostatic excess pressure should be estimated by the methods given in Appendix A.19% 8.3. The pressure changes caused by changes in water table elevations or artesian pressures may be estimated by field observations of ground water elevations or by anticipated fluctuations in the water table or artesian pressures due to natural or man-made causes. Westergaard’s results may be used. and d) Pressure changes caused by changes in the artesian pressure below the compressible stratum.3.. 8. Boussinesq theory is applicable. deposits.1 Settlements of structures on cohesionless soils such as sand take place immediately as the foundation loading is imposed on them.3..25 The pressure increment due to imposed loads shall be determined as detailed in 8. 8. Sand deposits exhibit marked decrease in compressibility Fr6hlich’s solutions may be used for such deposits. c) Pressure changes caused by changes in the elevation of the water table above the compressible stratum.1 Estimation of Settlements AND DIFFERENTIAL of Foundation on Cohesionless Soils 9. . the Boussinesq’s solutions with may be used. 9. following may contribute to the pressure incremment: a) Pressure transmitted to the clay by other imposed loads.4 depth. For 8. Because of the difficulty of sampling these soils. by construction of buildings or b) Residual hydrostatic excess pressures. Theories Loads to Compute induced by the imposed loads are usually homogeneous and elastic half space solu- 8.- IS : 8889 (Part I) ..5 ‘For variable the for this and laminated clays can be expected to exhibit such clays. 8.3.2 Normally consolidated clays may be considered purpose and therefore.3.3.2.2 Pressure Increment 8._ -. isotropic 8.3 Selection of Stress Distribution Pressure Increment due to Imposed 8.1.1 The pressure increment determined using the isotropic.6 The details of the procedure for estimating the pressure increment due to imposed loads and the relevant charts are given in Appendix B. there are no practicable laboratory 14 . A curve showing the relationship between depth and static cone penetration resistance (. The settlement of each layer within the stressed zone due to the foundation loading. should be separately calculated using equation (1) and the results added together to give the total settlement. (1) . 8 *MetI]od . .IS :8009 (Part I) -1976 procedures for determining their compressibility cha. 8) should be prepared.t-acteristics.. on the results of static cone or dynamic penetration test or plate load tests. .2 Method Based on Skatic Cone Penetration Test — Static cone penetration tmt should be performed in accordance with IS: 4968 (Part III)1971*. CONE -LAYER Iv READING AVERAGE CONE RESISTANCE IN EACH LAYER STATIC CONE PENETRATION RESISTANCEDIAGRAM for subsurfacesounding for soik. Part III Static cone penetrationtest 15 .1. .. Consequently.. each part having approximate y same value.~eeFig. (2) CONE RESISTANCE Ckd 1 11 III 1 ACTUAL ——.. It is broken into several parts. settlement of cohesionless soil deposits may be estimated by a semiempirical method based.. J 9. The average cone resistance of each layer is taken for calculating the constant of compressibility. * . FIG. The setdement under any other pressure may be computed by assuming that the settlement is proportional to the intensity of pressure. . $Code of practice for determinstionof allowablebearing pressureon shallow foundations.2.2 to 9.2.1 For situations shown in Fig. The details are given in 9. NOTE— The standard penetrationvalue obtained in the test shall he eorreeted for overburden and for fine sand below water table as detailed in IS :6403-1971$. h 9.3 Method Based on Plate Load Test — Plate W formed at the proposed foundation level and the settlement of a 30 cm square plate under the design intensity of loading on the foundation estimated (see IS: 1888-197 1*).2 Clay Loyer Sandwichedbetween Cohsionless Soil Layers or between a CohesiotdessSoil Layer at TofJandRock at Bottom 9.2. 2 it may be assumed fiat: Sf=o and &=f&d .2. the total settlement should be computed &m Sf = Si+-sc .2. the settlement read from Fig. .1 In the case of clay layers..IS : S009 (Part I) -1976 test should be per9.1.. 16 * and consolidation settlements and are explained in 9.2 Estimation of Total Settlement of Foundation on Cohesive SoilS 9..2.4 Method Based on Dynamic PetutrationTest — Settlement of a fboting of pressure resting on dry cohesionless of width B under unit intensity resistance value JV.1963t). .d depends upon the pm-loading conditions.3. . (4) 9. If the water table is at a shallow depth. 9. . and s~ = settlement in metre of a fmting with a loaded 30x 30 cm under a given load p per unit area. Procedures for estimation of immediate differ for different types of soil profiles and 9. Then the total settlement of the -— proposed fotmdati& is given by: ‘ Sf = S1 . ..4. *Method of load testson soils (jist A&m). 9 shall be multiplied by the correction factor W’ read from the inset in the same figure....2.2. may be read from Fig. (5) The details of the computations of Soe.2 @ ..1.. . ~Method of standardpenetrationtestfor soils. (determined deposit with known standard penetration according to IS: 2131. + area of 9. (+%0)2 ‘- ““ (3) ““ where Sf = final settlement in metrcs for a given load of j per unit area of a footing of width B.2.2. 5 # N. z u z w d {I I @ 1 2 3 4 s . 6“ WIDTH ‘B’ OF FOOTING IN METRE WT = Water GL = Ground level.—.1O — / / N.IS : 8@9 (Part I) . .~ 0.15 1 N*2O NE25 .6 0. SETTLEMENTPER UNIT PRESSUREFROMSTANDARD PENETRATION RESISTANCE 17 WT ..5 Ii’ 7 N.1976 d/B ~y~?o v =0000: 1.9 # O*8 w o.— - 0. 9 table.0 GL B d I&% ———. FIG. and read from Fig. . the clay layer shall be divided into a number of sublayers and the settlement in each sublayer shall be computed separately. this value of volume compressibility differs ibn the field A somewhat reliable method of estimating the iield value of nw value. Then. . The compression index should be determined @m the consolidation test data (see Appendix C).3 Clay Layer Resting on CohesionlessSoil Layer or Rock 9.1 and used in equation (6) to estimate the probable settlements. Buq because of overconsolidation. In preliminary investifptio~ the compression index may also be estimated fiwxn empirical formulae. that is.3 In the case of precompressed clays. 10. . (8) 9. . But.2 If the clay is not precompressed. be possible to adopt this procedure. 1 I @ The (9j The coefficient of volume compressibility is generally obtained flom consolidation test result for the range of loading.. . .4 If the clay layer shows marked change in impressibility with depth. $Oed shall be estimated as in 9.. (10) where A== A factor reIated to the pore pressure parameter A and the ratio Ht/B. .. the clay is not extremely sensitive or highly organic. it may not be necessary to compute the settlement. ‘l%e following two empirical formulae are recommended: cc = 0“009 (~L– 10) Cc = 030 (eo–027) . [@OiY’l “ ‘-“ . .1 For caws illustrated in Fig.. .22.. settlement in this case. . in a simple static or residual hydrostatic excess or artesian case. . . 9. it may be SUf%cient to take the value of A from Table 1. the total settlement k given by the sum of the settlements of each individual sublayer. . provided.. . in such cases.. may be computed from &= Aprnv Fl . Se = Asoed . (7) . 9.. the compressibility be considerably lower than that of a normally consolidated clay. it may not the settlement.2. then...2.2.3.2.2. This value shall be used in equation (9) to obtain If the clay is heavily overconsolidated. the settlement rmy be calculated by: ‘t cc log~o f$ = &ed = ~.2. is given in Appendix C.IS :8009 (Part 1) -1976 9. (6) The initial effective vertical strms and pressure increment sbdd be obtained as detailed in 8. 1 I .2. 3 and 4.2. In the absence of data regarding the pore pressure parameter A. 7 to 1. estuarineand marineclays) 1.2 .wlidateddays 0. .4 0.8 0-6 0.2 to 0.0 Overeonsolidatedclays 0.2 PORE PRESSURE .2 0 COEFFICIENTS A CIRCLE ——-——— FIG. 10 STRIP SETTLEMENT COEFFICIENTSFOR CIRCULAR AriD STRIP FOOTINGS 19 .2 Normally eonsedidatedclays 0.OVER CONSOLIDATED 0.5 1-2 I f 0.7 Heavily ovcrem.- 1. / /0 VALUES ON CURVES ARE h B 1.0to 1.5 to 0.(Part I) -1976 IS :8009 TABLE 1 VALU= OF A TYFE OF CLAY A (1) (2) Very sensitive clays (soft alluvial.0 O*8 / O*6 tEi u) O*4 VERY SENSITIVE =.0 0. 1. d on the worst and the best conditions. . if the variation occurs over distances greater than half the width of foundation. The consolidation pressure adopted in triaxial consolidation test should be equal to the effective The values pressure a. and 1 =.t the depth from which the sample has been taken.56 0.26 1. 11 for clay layers with various ~t/~ ratio and from T~. TABLE 2 VALUES OF I FOR CLAY LAYERS OF SEMI—INFUWTE~ INFLUENCEFACTOR (Z) SHAPE ——’————— f (1) Corner (2) (3) 1. of 1 may bc determined from Fig.2.IS : 8009 (Part I) -1976 9.2 ‘The immediate settlement a flexible loadccl mea is given by: ..77 1.2.5 for clay.69 1.96 9.4 Erratic Soil Deposit 9. the settlement of each layer below the foundation should be computed and summed to obtain the total settlement. on length (L) to breadth (B) Values of E shall be determined from the stress strain curve obtained from tria. .25 2.5 p 5 !0 100 Average (4) 112 0. 20 ‘ .4.31 1.52 338 0. of (11) T\..l consolidated undrained test.20 1..83 2.3.05 1.95 136 0%8 1. The settlement contribution by cohesionless soil layers should be estimated by the methods in 9.85 0. E beneath .hcrT p = l’oisson>s ratio = 0.S=PB (1 – p’) ~ 1 the centre or corner . a That is. . [depends ratio of the footihg]. .53 210 2. similarly the settlement contribution by cohesive soil layers should be estimated by the methods in 9.64 (edge) 0.3 Several Regular Soil Layers — If the soil deposit consists of several regular soil layers. .1.xia. settlement analvsis should be bas.bIe2 for clay layers of semi-infinite extent.00 Circle Square L/B Centre Rectangle: = 1. 9.1 In variable erratic soil deposits. . . worst’ properties should be assumed under the heavily loaded regions and the ‘bet properties under the lightly loaded regions. Influence facto. the total settlement at the centre should be reduced by a rigidity factor..IS: 0 O. a heavy beam and slab raft or a massive pier. the worst properties should be assumed under the heavily loaded region and the average properties under the lightly loaded regions. a correction should be applied to the calculated S~ in the form of a depth factor to be read from Fig. 12.6 0. .2 are applicable for computing the settlement of foundations located at surface.3 VALUES OF 1.2 If the variation occurs over distances lesser than half the width of foundation.. For the computation of settlement of foundations founded at certain depth.4.t 0.5. .7 }mt=4 2 I a I I 1 1 I 4 4 o 6 8 10 FrQ.5 Correction Settlement for Depth and Rigidity of Foundation on Total 9. Corrected settlement = Sfd = S~x Depth factor 9.1 and 9.5 S009(Part I)-1976 0.. THICKNESSHt 9. for exam~le. 11 STEINBRENNER’SINFLUENCE FAGTORS FOR SETTLEMENT OF THE CORNER OF LOADED AREA L x B ON COMPRESSIBLE STRATUM OF p=O”5.1 E~ect of Depth of Foundation— The relevant equation in 9.. Total settlement of rigid foundation Rigidity factor = Total settlement at the centre of flexible foundation . . ..2 0.6 0. the settlement analysis should be based on worst and average conditions. (13) .2 Effect of the Rigidity of Foundation— In the case of rigid foundations. 08 . 9. That is. o-k 0. . (12) .5.. 21 . 0.1s : 8009 (Part I). 1976 DEPTH FACTOR & I 1 O*6 9 O*L . 12 Fox’s CORRECTION CURVES FOR SETTLEMENTS OF FLEXIBLE FoorlNGs OF L x B AT DEPTH D RECTANGULM 22 ..2 -0 FIG. years. it is sufficient to state the design criteria in terms of allowable total settlements and design accordingly.4.. 10. 23 . where U = degree of consolidation = T = t = Cv = time at which the settlement is required.1965*]. (14) F(T). This relationship is shown in Fig. .. (16) Si+ us.. (15) c~t. . . On a very important job. concrete of foundaThe coefficient of consolidation shall tion may be assumed as permeable. be evaluated from the one dimensional consolidation tests using suitable fitting methods [we IS :2720 (Part XV). depends on pressure distribution and nature of drainage. The relationship between T and U in equation (16).1 The settlement at any time. the magnitude of the differential settlement is affected greatly by the non-homogeneity of natural deposits and also the ability of the structures to bridge over soft spots in the foundation. .. ESTIIVIATION OF TIME RATE OF SETTLEMENT 10. When comidering the drainage of clay layer.. is given by: St = . the total settlement at time t..2 In the case of evaluation of time rate of settlement of structures constructed with certain construction time. But it is more difficult to estimate the ditYerential settlement than the maximum settlement. . . the procedure illustrated in Appendix D may be followed. . This is because. a detailed study should be made of the sub-soil profile and the relation between foundation movement and forces in the structure should be investigated as indicated in 4. *Methods of test for soils: Part XV Determination of consolidation properties. may be estimated by the application of the principles of Terzaghi’s one dimensional consolidation theory. Ordinarily.1 and 9...IS :8009 (Part I) -1976 9. Based on this theory. 10. m2/year. . and average coefficient of consolidation over the range of pressure involved obtained from an oedometer test. 13.6 Differential Settlement — It is usually the differential settlement rather than the total settlement that is required for designing of a foundation.. IS :8009 (Part i) -19’76 00 000 lN33N3d LuLuuLl I n ‘NOI1VCII1OSNO3 24 0 -JLO*O -1 Loo”o Soo ●O 900”0 Eoo”o 4 d200”0 100”0 1- . tters which may aid in determining which of the cases outlined in 8.1.r pressure that soil has ever undergone.nu1a.14 p (LOG SCAL .1 holds in any given case. of the e-log ji curve is produced backwards and its intersection with OD gives point E. is the ma. PC PRESSURE.E) GRAPHICALCONSTRUCTIONFOR DETERMININGFORMER MAXIMUM PRESSURE~~FoRME-I~~PCURVE 25 .2) DETERMINATION CONDITIONS A-l.tion analysis.2 Such sources of informa. FIG.litative and often sufficient for consolida.Is : 8009 (P&I)-1976 APPENDIX A (Clauses8.nd other ma.rtesian conditions a. There are several methods for quantitative estimation of the maximum intergra. point ‘0’ of ma.2 and 8. then the tangent OB and finally the bisector OD The straight line portion of the angle formed by the first and second lines. first e-log I. A-1. the water table and a. DETERMINATION PRESSURE OF MAXIMUM not the the test INTER-GRANULAR A-2. GEOLOGICAL OF PRE-LOADING PRESSURE AND IMPLICATIONS INFORMATION AND PORE PRESSURE A-l. A-2. 14). a method based on consolidation data is detailed.ximum intergranular pressure. The j value (&) corresponding to point E. In A-2.1 In this method. the horizontal line OC.tion are largely qua.2. the erosion that has occurred a. the time which has elapsed since there has been deposition of soil at site. curve (see Fig.t the site in the past ages.ximum curvature is located on the Through this point. three lines are drawn. c .1 A geological investigation of a site may yield information on the age of various strata. the pore pressures The effective stress is computed are equal to the hydrostatic pressures.2 to A-3.In principle. unless there was scope in the geologic history for the 26 soil Th Th ult inc me B-l B-l ind Bar con E-l 029 at . A-2. If there is agreement at top and at the bottom of the clay stratum (line deb). A-2. the maximum previous intergranular pressure may be determined by this method.1976 A-2. the pore pressures and consequently the effective stresses In the case of can be estimated from ground water level observation.IS : 8009 (Part I) . DETERMINATION PORE PRESSURE OF INITIAL EFFECTIVE STRESS A4 pre the the gra the Th due bY to due A-: stn A-: the SUC in AND A-3. the present effective stress will be equal to the maximum previous intergranular pressure.2 For each sample which has been tested in the laboratory.from the unit weights of the overlying material. the procedure for comparison explained above is simple. A-3. if the sample has been disturbed to an appreciable degree during or after sampling.In the residual hydrostatic case.3 Residual Hydrostatic Case . A-3. and b) There may be double drainage and an artesian condition. one of the following conditions is indicated : a) The stratum may have drainage at. If the curves coincide. the case being one involving residual hydrostatic excess. and the pore pressures and effective stresses may be estimated as given in A-3. clay layers the type of preloading conditions is identified by the geological investigations and by the estimation of the maximum previous intergranular pressure. stress may also be determined directly using the submerged unit weights below water table. In actual practice. If the samples are undisturbed.4 Limitation of the Methods .1 GeneralThe total vertical pressure at any depth shall be computed. The effective as the difference between the total and neutral pressure. These values may then be plotted-at appropriate depths on the effective pressure diagrams shown in Fig. residual hydrostatic exces: is indicated. but the past pressure curve falls to the left at the centre of the stratum. The boring data should be clearly analysed to decide which of the twos above cases holds. the pressures obtained by the method laid down in A-2. In the case of pervious layers. A-3. the top surface only.6. tend to be too low. the results obtained are satisfactory. If the past pressure curve (line gh) falls to the right of static intergranular curve then a case of precompression exists.2 Simple Static Case-In the simple static case. 7.3 The past pressure curve may then be compared with the effective pressure curve for simple static case (line db). a simple static case of a normally consolidated deposit is indicated. If there is agreement at top but the past pressure curve falls to the left at the bottom (line df). 1 The methods generally used for determination of the pressures induced by building loads are based on the mathematical model due to Boussinesq who assumed isotropy.4 Artesian Case .6 Complex Cases .There are situations where the cases can be the combinations of the four simple cases indicated in A-3. The portion of the pore pressure in excess of the hydrostatic pressure.. in the pressure increment. co-ordinate. .. APPENDIX (Clause 8. given inRl.In the precompressed case. Such complex cases require individual treatment and are not dealt with in this standard.5. (B 1) and 27 c-- . A-3. . the excess hydrostatic pressure may be assumed to vary linearly within the clay layer. B-1. A-3.1 equation for the vertical stress uz. The pressure increment in this case will be equal to the pressure increment due to building load alone unless.3. therefore. at a point Jv (see Fig. 15) due to the application of concentrated load P.5 Precompressed Case . in which case. A-3.2 With the assumptions.. homogeneity and elastic half space conditions.1976 soil layer to have undergone a greater load than the present overburden. The maximum intergranular pressure estimated in A-2 will be equal to this pressure unless there was scope for precompression in the geological history of the site.2 to A-3. the effective stress will be equal to the total pressure minus the sum of the hydrostatic and excess hydrostatic pressure. the artesian pressure is reduced either by man made or natural causes. willr ultimately be transferred to the soil grains and. B DISTRIBUTION THEORIES PRESSURE INCREMENT TO GENERAL B-1. The pore pressure will be equal to the total stress minus the effective stress. Then. co-ordinate. the change in stress due to change in artesian pressure should be added to the pressure increment due to building loads. = = 3P cos”j3 2 7rZ2 vertical angular .6) SELECTION OF STRESS COMPUTE THE B-l. the effective stress and pore pressure will be the same as in the simple static case.In the artesian case. at the surface of the soil is: c‘z = - where . the excess pore pressure should be added to the pressure increment due to the imposed loads.IS : 8009 (Part I) . 16) of the loaded area.Is : iNJfB(PartI)-1976 B-13 With the assumptions given in B-1. de computation of vertical normal stress ul due to a uniformly distributed load p on a circular area with radius R at a depth e below the centre (see Fig. = * k- 1 ~+(R/z)~ a FIG. due to a uniformly distributed load Q on any area of known geometry.N FIG. may be obtained fro&: 312 1 . I5 STRESSES AT POINT. The procedure is to draw the given loaded area on the chart with the point below which the stress is required coinciding with the centre 0 of the chart. . 28 . Newmark). . = p x IB x number of influence areas *z where P = intensity of given loading. In the chart. The number of influence areas enclosed in the chart by the given loaded area are counted and the stress ue is then estimated as: . This chart may be used to estimate the vertical normal stress at a depth z below a point JV.. 16 VERTICALSTRESSU~BELOWTHE CENTRE OF CIRCULARFOOTING This equation has been represented in a chart form by Newmark and is shown in Fig. 17. 0. (B 3) .. one influence area-is defined as the area included between two consecutive radial lines and circular area..1. (B 2) . . and za = influence value marked at the bottom of the chart (Boussinesq. The scale should be chosen so that the depth z at which the stress is required is equal to unit distance AB marked in the chart. 1976 \ Influence value = O-005 FIG. . 17 INFLUENCE CHART FOR VERTICAL PRESSURE(Boussnmq CASE) 29 I .I .IS : SO09 (Part I I I). IS : 8009 (Part I) .001 FIG.N at depth z below the corner of a rectangular baded area with a uniformly distributed load. SCALE DISTANCE TX A-8 INFLUENCE VALUE .1 Alternatively. NORMALLY CONSOLIDATED CLAYS B-2. 19 INFLUENCECHARTFORUNIFORMVERTICALNORMALSTRESS ( WESTERGAARD SCALE) 30 .. and B = width of the loaded area. . IB L = length of the loaded area.1 From the point of view of compressibility.0. therefore. the vertical normal stress up at a point . the Boussinesq solution given in El is applicable. 18. (B 4) us= $x&I where = a function of L/z and B/r. may also be estimated using the chart shown in Fig.3.. . From the chart uz is estimated from the expression: . . normally consolidated clays may be considered as effectively isotropic and. E-2. .1976 B-1.. F 4 .26 o-24 FIG. 18 AREA COVERED UNIFORM NORMAL mlN CHART FOR RECTANGULAR AREA _UNIFORMLY LOADED (~~OUSSINESQ CASE) 31 1 .1976 0.I8 : 8009 (Part I) . . Till such time a clear picture of a satisfactory generalised stress-strain relationship in soils 32 . it is difficult to make defmite statements regarding the accuracies obtainable when formulae based on the theory of elasticity The solutions from are used for stress determinations in soil masses.2 The influence chart. due to a uniformly distributed load on a given area.= and vertical directions. PRECOMPRESSED CLAYS B-3.1 Many overconsolidated and laminated clays can be expected to exhibit marked anisotropy. The procedure for using the chart is the same as illustrated for Fig. 19. B-5. When the above solutions are used for estimating stresses in soils. to calculate the normal stresses a. homogeneous.. B-3.1 In the present state of knowledge. experimental evidence indicates that -$ is considerably less than 1.‘_ . are the Young’s moduli in the horizontal E. VALUABLE DEPOSITS B-5. with a depth L below the ground surface using Westergaard’s solution is shown in Fig.1976 B-3. elastic theory which have been mentioned earlier are rigorously correct only for ma.terials in which stresses and strains are proportional. LIMITATIONS B-6. 17. DEPOSITS case of sands.- -_ IS : 8009 (Part I) . particularly if the laminations are varved. B-6. 20 may be used. Hence. whVich Published is perfectly elastic and isotropic in every horizontal direction. B-4. and this condition satisfies the assumption of Westergaard that Eh infinity. at a point. where Eh. is calculated using a procedure similar to that illustrated for Fig. the inaccuracies that occur because the soils are not elastic.1 ?)Z= SAND In the J- 1--2/L and ~1 is the Poisson’s 2--2/A ratio for the soil. sands present the case of a model.1 In many instances.and E. are of unknown magnitude and are not well understood. 17. The unit distance AB marked in the chart corresponds to a depth vet.2 For estimating the normal stress CT._. Moreover each of the above solutions is valid only for the specific conditions upon which it is based. The vertical stresses a. the chart shown in Fig. variable deposits are to be treated as a simple. isotropic and elastic case for purposes of computation of vertical stresses. where B-4. . B-4. experimental evidence suggests that the distribution of uZ in sand can be reasonably computed from the semi-empirical equation of Friihlich with a concentration factor or index m’ = 4.at a depth t below the surface of the soil with decreasing compressibility with depth. -1976 is evolved. . 20 INFLUENCE CHART FORVERTICAL STRESS (FR~HLICH CONCENTRATION FACTOR m'=4) 33 .IS : 8009 (Part I)-. the following broad guidelines may be followed in estimating the induced stresses in soil masses due to applied surface loads-: a) Normally and lightly overconsolidated clays : l&/E. approximately one Influence value = Boussinesq solution 0005 FIG. 21 (b). a line is drawn from 6 parallel to cd. 34 o-4 .. 21(c).~$.4 eo. The laboratory curve is represented by KU in Fig. The vertical line The field e-log p curve should pass through this point.2~ and 9. curve. it may be taken that the line aef represents the field compression curve.. Accordingly. it is assumed that the field curve between B. in order to obtain a labotatory rebound curve. 21(c).1.2.1976 b) Heavily overconsolidated clays 1. as shown in (a) in Fig. PROCEDURE FOR OVERCONSOLIDATED CASE C-2. 21.” IS : 8009 (Part I) .1 In the normally consoiidated case.2.1 The construction requires unloading the sample in increments after the maximum pressure has been reached. If the clay is of ordinary sensitivity...2. and$e is a recompression tory there is little difference in slope_ between rebound and recompression curves. its intersection with the vertical at Bc is denoted by a’. the projection of the bottom portion of the laboratory compression curve will meet the e.1 The procedure for obtaining the field compression curve from the C-2.5 c Eh/E.4e0 line as shown in Fig. .) or very close to it.< 3 c) Sands Eh/Ev<l d) Variable Westergaard Frijhlich with m’=4 Boussinesq . laboratory oedometer curve is as follows. if the soil is extra sensitive. Between b and a’ a smooth curve is sketched in as indicated in Fig. Therefore. FO) and f is the point where the laboratory compression curve meets the e=0. where f is the intersection of the downward extension of the steep straight portion of KU and the horizontal line e=0.3) PROCEDURE FOR OBTAINING THE FIELD COMPRESSION CURVE C-l. C-2. of the clay a.. PROCEDURE FOR NORMALLY CONSOLIDATED CASE C-l. solution deposits APPENDIX C (Clauses 9. and effective overburden pressure &. Point b represents the void ratio e. and PC is parallel to the laboratory rebound curve. Since in the laboracurve between &. . pc corresponds to the maximum consolidation pressure as determined by The portion of the field e-log p the graphical construction given in A-2..s it existed in the ground before sampling. the field curve is given by af where (I is the point (eo. line at the point a (eO.2. The field curve for pressures above & is approximated by the straight line a’f. PO FIG.1976 a PRESSURE 2lA (LOG Normally SCALE) consolidated APPROX PRESSURE- case 2lB sic PRESSURE 2lC 21 SCAL sensitivity O-L e. (LOG Clay of ordinary Overconsolidated (LO6 SCALE ) case CONSTRUCTION FOR APPROXIMATINGFIELD RELATION BETWEEN e AND p GRAPHICAL 35 .IS : 8009 (Part I) . 1 The instantaneous curve at time t/2 shows the settlement KF. 03 equals CE.1976 APPENDIX D (Clause 10. It may be assumed that the excavation and the replacing of an equivalent load have no effect on settlement. but often they are not considered to be of sufficient importance. The diagonal OF intersects time t and point H. and it will be assumed that no appreciable compression of the underlying strata will occur until this point is reached. offset to the right by one half of the loading period. Actually some rebound and some recompression aiways occur during this period. from point C on the instantaneous curve. the loading diagram may be approximated by a straight line as shown ‘by the dotted line in Fig.1 In the construction of a typical structure. do va in ch. on the basis of instantaneous loading. At time t the load acting is t/t1 times the total load. APPROmTE MEJX-IOD DUE TO TERZAGHI D-2. and the settlement KF should be multiplied by this ratio. OF SETTLEMENT DUB r0 TYPE ‘OF LOADING CONSTRUCTION GENERAL D-l. D-2. D-2. and they can be studied in detail.2 At any smaller time t the settlement determination is as follows. 22. Thus H is a point on the settlement curve. on the instantaneous loading curve. D-2. 22). the elapsed time from 36 thl it D” D.3 Beyond point E the curve is assumed to be the instantaneous curve CD.2.2) TIME RATE D-l. In the loading interval. zero time being measured from point A. ch. and as many points as desired may be obtained by similar procedure. D-2. Thus. The time from this point until the building is completed will be designated as the loading period. point E is obtained on the corrected curve. Thus.Is : 8009 (Part I) . is equal to that at time l/2 t. such as the upper curve of Fig. the application of load requires considerable time. The net load does not become positive until the building weight exceeds the weight of excavated material. the settlement at time t.1 The time settlement curve for the given case. According to the assumption made in this method. for example. This may be done graphically as indicated in the figure. after construction is completed. giving a settlement at H which equals (t/Q x KF. 22. cot CO1 . and the loading progress may be shown graphically by a diagram. is obtained by the consolidation theory and shown (line OCD of Fig. The time at which this occurs is represented by point A of the figure. ht of :d by &able iched. D-3.4. 23A and hence the former may be used if the consolidation is less than 50 percent so that the accuracy of the final result . 23A and 23B are used for this purpose. to be 1 L----CONSTRUCTION $Al.IN I Yload hown t load r. In this method. The value of each small square in Fig. does not involve an approximation of the loading diagram with linear variation as in the previous method.N4A nstan(line ‘ading t line tp tion llows. :ment ucally point point :ained PERIOD ASSUMED EFFECltVE LOADING PERIOD FIG. GRAPHIGAL SOLUTION D-3. curve :> DJ from ---d N EO U S 1 l/2 t1 zstan- t KF. mated td the tually eriod.1 An alternative graphical solution for construction type of loading. 22 TERZAGHI’S APPRCXIMATE METHOD the start of loading until any given settlement is reached is greater than it would be under instantaneous loading by one half of the loading period. 23B is only half of the corresponding value of Fig. the charts shown in Fig. The small squares in the chart represent a given fraction of consolidation as noted in the particular chart. It is to be noted that the mirror reflection is to be obtained by warping the time factor axis of the time load curve to suit the corresponding scale in the reflected part of the chart.. The horizontal axis represents the time factor. corresponding to time t. is determined as follows.1976 can be increased. the consolidation at time 1. The number of squares under this curve multiplied by the value of each square is equal to the consolidation at time t. 38 . Then. as shown in Fig.. 24. The vertical axis is the load axis. 24.- Y _. D-3.2 The load time factor curve is drawn on the chart as a mirror reflection starting from the time factor l-.___IS : 8009 (Part I) . Let the time load curve be as shown in Fig. The time axis is first replaced by the time factor axis. TIME 238 FIG. 23 Chart with FACTOR value 67891 T of each small square .IS : 8009 (Part I) .19’76 0 1 lo” 2 4 68 5 2 1 rl.6 la8 2*i .=@025% CHART FOR FINDING CONSOLIDATION DUE To CoNsTRucTIoN TYPE LOADING 39 1*2 I*4 1. 0 TIME 0 2. 24 CURVE OF 40 O-25 O-3 1-o .0 TIME IN YEARS LOAD f IME 0.2 FAC TOR USE C:o%oLATIoN CHART 0.0 0 1-O l*O 2*0 3.0 2*5 3=0 TIME FACTOR 400 5*0 6.1 FIG. Fig.1.Substitute )-1971* ‘. Alterations (Page ‘ IS 7. foot-note . 7. 12. legend) ( Page 32. Substitute Substitute ‘ “52 Substitute last line ) - Substitute ‘ C’ for c c ‘. ‘for _$z ’ ’ r~’ for ‘ qz ‘.2.1. clause 9. clause : 1892-1962* ‘. ( Page 12.AMENDMENT NO.0. ^ the existmg foot-note: ‘ *Code of practice 15 ( Par>IT?Fl97f* (Page the existing lint with clause ‘for ‘ *Method for subsurface (jirsf revision ) . investigations ‘ IS : 4668 ( Part III with along ‘ * ’ mark j - for sub-surface 15.1. 6. clause B-3. and for soils (jirst reoision).1.3 formed Method Based at the proposed on Plate Load Test - foundation level Plate load test should be perand the settlemrnt of a square c . equation 2 ) ( Page 22.1. - r C ’ for c c ‘.0. . Delete for the existing clause: ( 9. clause 5 ) - line ( Page 15.2 clause 9. ’ ‘ IS : 4968 for : Part III Static cones penetration test the following the for following Substitute Substitute ’ JGr the following for foundation c * ’ mark ) - sounding with its explanation. foot-note foot-note: ( Page 16. symbol S1 ) - ( Page 12.3 ) - ~‘IS: Substitute 1892-1979* lines 2 3 ) .2. c&se 3.’ 2) - Substitute 9. 1 MAY 1981 TO IS : 8009 ( Part I J-1976 CODE OF PRACTICE FOR CALCULATION OF SETTLEMENTS OF FOUNDATIONS PART I SHALLOW FOUNDATIONS SYMMETRICAL STATIC SUBJECTED VERTICAL TO LOADS Corrigeatda (Page 3. and SC = Soecl -To be exact. clause 3. cm ’ a given load intensity per unit .plate under the design (see IS: 1888-1971” ). the efft-ct of water tablr on the bearing capacity of the foundations may be different from that for the load test. Therefore.2. ’ ( Page 16.1.4. = Size of test plate.2.4.’ Addendum ( Pqe 7.2 to 9. The designer to add the settlement due to the sand layers or not. ( Page the existing last sentence ) - 16.If the water tnbIe is at shallow depths or if it is expected that the water tab!? for the foundations will be different from what is obtained at the time of the field !oad test. sentence: Substitute the following for ‘ If the water table is at a shallow depth. 2 it may be assumed that: Sr = 0. The details are given in 9. the settlement read from Fig. clause 9. cm of test plate under B1. clause 9. tion is given by: intensity of loading on the foundation estimated Then the total settlement of the proposed founda- & = s B(B C ____!L. 9 shall be divided.. 9 may be suitably adopted for the load test and the foundations ‘. NOTE The details of the computations of Soee depends upon the preIoading conditions._- ’ +3Oj B.2.1 shown Substitute the following for the existing clause: For situations in Fig.0 ) -Add the following symbols at appropriate places: ’ S.2.(B+30) 2 1 NOTE .1 )‘- ‘ 9. the settlement of the sand layers may also have to he has to use his discretion whether added to the computed value of Sf .2. then. the water table correction given in Rg.2.2.2. by the correction factor w’ read from the inset in the same figure. = Settlement area. clause B-1.3.AMENDMENT NO. 2 JULY 1990 TO XS 8009 ( Part 1 ) : 1976 CODE OF PRACTICE CALCULATION OF SETTLEMENTS OF FOUNDATIONS PART 1 SHALLOW FOUNDATIONS SUBJECTED SYMMETRICAL STATIC VERTICAL LOADS [ Pa.ce2X. expression ( R 2 ) 1- tta. India .the existing matter: Substitute FOR TO the following ! / I (BDC4:.) Printed at Simco Printin Press. Delhi.