tcxdvn 375-2006 p2 (english)

TCXDVN VIETNAMESE BUILDING STANDARDS

TCXDVN 375:2006

1st edition

DESIGN OF STRUCTURES FOR EARTHQUAKE RESISTANCE

Part 2: Foundation, retaining wall, and geotechnic issues

HÀNỘI – 2006

VIETNAM BUILDING STANDARDS TCXDVN 375 : 2006

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Design of structures for earthquake resistance

Part 2: Foundation, wall and geotechnic issues

1 General

1.1 Field of application

(1)P Part 2 of the regulation establishes requirements, criteria and prescriptsabout choosing construction location and foundation of earthquakeresistance structure. It includes regulations about choosing differentfoundation types, wall types and interactivity between structure and groundsoil under earthquake effect. Hence it complements Eurocode 7 – whichdoes not include special requirements for earthquake resistant structures.

(2)P Clauses in Part 2 apply on house buildings – Part 1 of the Regulation applybridge structure (EN 1998-2), tower, column, chimney (EN 1998-6), silo,basin, conduit (EN 1998-4)

(3)P Requirements about special design for certain structure foundation, whenneeded, can be looked up in corresponding part of this building regulation

(4) Appendix B of this regulation introduces empiric charts used to evaluatelikely liquefaction simply, Appendix E introduces simple procedure toanalyze earthquake properties of wall structure.

NOTE 1 : Appendix A provides information about relief amplificationfactor.

NOTE 2 : Appendix C provides information about pile’s static stiffness.NOTE 3 : Appendix D provides information about dynamic interactionbetween structure and ground soil.

NOTE 4 : Appendix F provides information about earthquake bearingcapacity of shallow foundation

1.2 Further reference documents for this regulation.

(1)P Part 2 of the building regulation bases from date or dateless referencematerials and clauses in other printed materials. Reference materials will bequoted at proper places in this document and other printed material listedbelow. About date materials, update changes after publishing are effectiveonly with amendment regulation. About dateless materials, latest versionsmust be used.

1.2.1 Popular reference regulations.

EN 1990 - Basics of structure design.

EN 1997-1 Geotechnic design- Part 1 : General presripts.

EN 1997-2 Geotechnic design- Part 2 : Soil investigation and test


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EN 1998-2 Design of earthquake resistant structure - Part 2 : Detailprescripts of bridge.

EN 1998-2 Design of earthquake resistant structure - Part 2 : Detailprescripts of silo structure, basin and conduit.

EN 1998-4 Design of earthquake resistant structure - Part 4 : Detailprescripts of tower, pile, chimney constructions

TCXDVN…2006Design of earthquake resistant structure - Part 1 : General , earthquakeeffect and prescripts of house structure.

1.3 Assumptions

(1)P Apply common assumptions in 1.3 in EN 1990:2002

1.4 Distinguish between principles and prescripts.

(1)P Apply prescripts in 1.4 in EN 1990:2002

1.5 Terms and definitions

1.5.1 Common terms in this whole Regulation

(1)P Use terms and definitions stated in Appendix D, Part 1 of this buildingregulation.

(2)P Use 1.5.1 of this building regulation for common terms appearingthroughout this building regulation.

1.5.2 Complemented terms used in this building regulation.

(1)P Definitions of ground soil are quoted from 1.5.2 in EN 1997-1:2004,definitions of geotechnic terms related to earthquake, e.g liquefaction, arequoted in this very building regulation.

(2) Terms used in Part 2 are defined in 1.5.2, Part 1 in this building regulation.

1.6 Symbols

(1) The following notation are employed throughout this building regulation.All symbols in Part 2 will be defined right after their first appearance forconvenience. Symbols not defined at first appearance are explained below.Symbols used only at Appendices will be defined right below them in thoseAppendices.

dE Designed action effect

pdE Horizontal strength at foundation lateral side against passive earth pressure.

ER Energy ratio in Standard Penetration Test

HF Designed horizontal inertia force originated from earthquake.

VF Designed vertical inertia force originated from earthquake.

RdF Designed shear strength between foundation’s horizontal bottom and soil.


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G Shear modulus

maxG Average shear modulus under small deformation condition.

eL Distance between anchor and wall in dynamic condition.

sL Distance between anchor and wall in static condition.

EdM Designed moment

)60(1B Standard penetration test (SPT) index normalized with respect to soil’ ownpressure and to energy ratio

EdN Designed normal force acting on horizontal foundation’s bottom.

SPTN Number of hammer blows in Standard Penetrating Test (SPT)

Pl Plasticity index of soil

dR Designed bearing capacity of ground soil.

S Coefficient of soil reaction defined inn 3.2.2.2 of this regulation.

TS Relief amplification factor

EdV Designed transversal shear force.

W Weight of sliding body.

ga Ground acceleration designed for A-type soil ( gRlg aa )

gRa Reference maximum ground acceleration for A-type ground soil.

vga Designed vertical ground acceleration.

'c Cohesive force in terms of soil’s effective stress.

uc Soil’s undrained shear strength.

d Diameter of pile.

rd Displacement of retaining wall.

g Gravitational acceleration

hk Horizontal earthquake coefficient

vk Vertical earthquake coefficient

uq Compression strength under lateral expansion condition.

r Coefficient used to calculate horizontal earthquake coefficient (Table 7.1).

sv Velocity of shear wave.

max,sv Average value of sv under small deformation condition (<10-5).


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Ratio between ground acceleration designed for A-type ground soil ga and

gravitational acceleration g.

Unit weight of soil.

d Dry unit weight of soil

l Operational importance factor.

M Differential coefficient of material parameter.

Rd Differential coefficient of model.

w Unit weight of water.

Friction angle between soil and foundation or retaining wall.

' Shear strength angle calculated with respect to effective stress.

Unit weight.

vo Soil’s own total pressure, as well as total vertical stress.

vo' Soil’s own effective pressure, as well as effective vertical stress.

vo' Soil’s undrained shear strength when subjected to cyclic load.

e' Shear stress under earthquake effect.

1.7 International system of units (SI)

(1)P Use SI units system according to ISO 1000.

(2) Besides, other units recommended in 1.7, Part 1 in this building regulationis allowed to use.

NOTE: when calculating geotechnic problem, refer to 1.6(2), EN 1997-1:2004 if need be.

2 Earthquake effect

2.1 Definition of earthquake effect

(1)P Earthquake effect must agree with definitions and concepts introduced in3.2, Part 1 of this building regulation, with regard to clauses in 4.2.2.

(2)P Combination of earthquake effect and other effects must be studiedfollowing procedure 3.2.4, Part 1 of this building regulation.

(3) Simplification in choosing earthquake effect will be introduced at theirproper place in this building regulation.

2.2 Histogram

(1)P When analysis in time domain is carried out, simulated accelerationschematic diagram as well as real schematic diagram can be utilized torecord strong displacement of ground soil. Recorded data related to


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maximum value and frequency must comply with prescripts in 3.2.3.1, Part1 of this building regulation.

(2) When investigating dynamic stability including irreversible deformation,vibrations, one must uses real acceleration schematic diagram whichachieves the earthquake data of the building location, because theypractically have low frequency and time-correlation between vertical andhorizontal displacement components. Time interval in which strongdisplacement occurs must be chosen following 3.2.3.1, Part 1 of thisbuilding regulation.

3 PROPERTIES OF GROUND SOIL

3.1 Strength parameters

(1) In general, strength parameters under static and undrained condition can beused. With cohesive soil, appropriate strength parameter is undrained shearstrength uc , but if need be and adequate experimental evidences have beencollected, it must be adjusted for rapid rate of loading and attenuation dueto repetitive loading . With non-cohesive soil, appropriate strengthparameter is undrained shear strength under repetitive loading ucy ,

. When

calculating this value one must taken into account the accumulation of porewater pressure.

(2) It is allowable to use effective strength parameters in case pore waterpressure is generated due to cyclic loading. About rock, compressionresistance with lateral expansion uq may be used.

(3) Coefficients M for material characteristics uc , ucy , , and uq is lettered

cu , cy , qu , coefficients M for 'tan is lettered ' .

Note: Recommended values of cu , cy , qu , ' are 4.1cu , 25.1cy ,

4.1qu , 25.1' .

3.2 Stiffness parameters and resistance parameters

(1) Due to its effect on designed earthquake effect, primary stiffness parameterof ground soil under earthquake load is shear modulus G calculated asbelow:

2. svG (3.1)

Where is unit weight and sv is shear wave velocity in ground soil.

(2) Criteria to determine sv value and even its dependence on soil deformationare introduced in 4.2.2 and 4.2.3.

(3) Damping rate is viewed as an auxiliary property in case of taking intoaccount interaction between ground soil and structure, as prescribed inchapter 6.


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(4) Internal resistance due to soil’s nonlinear respond to cyclic load, andpervasive resistance due to earthquake propagation out of foundation, mustbe considered separately.

4 REQUIREMENTS IN CHOOSING BUILDING LOCATION ANDGROUND SOIL.

4.1 Choosing building location

4.4.1 General

(1)P It is necessary to evaluate building location, determine ground soil’s naturein order to ensure that the dangers of failure, slope instability, liquefactionand compactness due to earthquake are as small as possible.

(2)P Possibility of these disadvantageous phenomena must be surveyedfollowing clauses below.

4.1.2 The vicinity of active paraclase area

(1)P House of II, III, IV importance degree defined in 4.2.5, Part 1 of thisbuilding regulation is not allowed to be built in the vicinity of paraclases inwhich earthquake activity is confirmed to occur in official documentspromulgated by National Assembly authority.

(2) The event that displacements did not occur in modern stage of QuaternaryPeriod can be viewed as a sign of paraclase deactivation in most ofstructures which do not endanger public works.

(3) Special geologic surveillance must be carried out to serve town planningand important structures built near likely alive paraclases in earthquakehazard area, to determine risk of ground fracture and quake degreeafterwards.

4.1.3 Slope stability

4.1.3.1General requirements

(1)P Examination of ground stability must be carried out with structures built onor near natural slope or artificial slope, in order to ensure that safety degreeand/or working capacity are maintained under designed earthquake class.

(2)P Under effect of earthquake load, the critical state of slope is the state- whenit is exceeded - long term displacement (irreversible displacement) ofground soil state will occur with value exceeding allowable level in depthrange which can affect building structure and function.

(3) It is allowable to skip examination of I class importance buildings, ifcontrol experiment shows that ground soil at building location is stable.

4.1.3.2 Earthquake effect

(1)P Designed earthquake effect which is assumed in order to examine stabilitymust comply with definitions in 2.1


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(2)P When examining structures’ grounds stability with operational importancefactor l greater than 1 lying on or near slope, it is necessary to increasedesigned earthquake force through relief amplification factor.

NOTE : Some guidance for relief amplification factor value is given inreference appendix A

(3) Effect of designed earthquake may be simplified following rules in 4.1.3.3

4.1.3.3Analysing methods

(1)P Response of slope to designed earthquake must be calculated either byaccepted analyzing methods of structural dynamics, such as finite elementmethod, solid mass model, or quasi-static method simplified using limit ofcondition (3) and (8) of this clause.

(2)P When modeling mechanic response of ground soil, softening in responsewhen deformation increases and other consequences originated fromincreasing pore water pressure under cyclic load must be considered.

(3) Examination of stability may be carried out by simplified quasi-staticmethods at surface relief and stratum structure at which no abnormalvariation occurs.

(4) Quasi-static methods that analyze stability are similar to methodsintroduced in 11.5 of EN 1997-1:2004, excluding vertical and horizontalinertia forces of each part of soil mass and of gravitational load acting onapex.

(5)P Inertia forces due to designed FH and FV acting on soil mass, correspondingto horizontal and vertical direction, in quasi-static analysis, are calculated asbelow:

WSFH ...5.0 (4.1)

HV FF 5.0 if ratio gvg aa / is greater than 0.6 (4.2)

HV FF 33.0 if ratio gvg aa / is not greater than 0.6 (4.3)

where:

ratio between designed acceleration of A- type ground and

gravitational acceleration;

vg vertical designed acceleration of ground;.

g designed acceleration of A-type ground;

S soil action coefficient, quoted in 3.2.2.2, Part 1 of this buildingregulation;

W weight of sliding mass.

Relief amplification factor for g must be taken into account, according to

4.1.3.2(2).


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(6)P Limit state condition is used to examine sliding surface with least stability.

(7) Condition of limit service state may be examined by calculating irreversibledisplacement of sliding mass following a simplified model- including asliding solid mass which resists frictional force on slope. In this model,seismic effect must be the representative in histogram according to 2.2 andbe calculated based on designed acceleration without any dampingcoefficient.

(8)P Other simplified methods such as simplified quasi-static method introducedfrom (3) to (6)P in this clause are not allowed to used for soil that iscapable of developing pore water pressure or has significant stiffnessattenuation under cyclic load.

(9) Increase of pore water pressure must be evaluated by appropriateexperiment. In case of such experiment was not carried out, one canevaluate by experimental correlation to design preliminarily.

4.1.3.4 Examine safety degree by quasi-static method

(1)P With saturated soil in area in which 15.0. S , it is necessary to consider

possibility of strength attenuation and increase of pore water pressure dueto cyclic load as introduced in 4.1.3.3(8).

(2) With stabilized sliding surface but capable of continuing sliding due toearthquake, one must uses large deformation strength parameters. Withnon-cohesive soil, cyclic increase of pore water pressure in limit range of4.1.3.3 may be taken into account by decreasing resistance originated fromfriction with appropriate pore water pressure coefficient, commensurable tomaximum pore water pressure. Such increase may be evaluated followingguidance in 4.1.3.3(9).

(3) It is not necessary to apply attenuation of shear strength on stronglyexpanding, non-cohesive soil, e.g compact sand.

(4)P Examination of slope safety must be conducted following principlesintroduced in EN 1997-1:2004.

4.1.4 Types of soil prone to liquefaction

(1)P Attenuation of shear strength and/or stiffness due to increase of pore waterpressure in discrete, water-saturated material during ground movementcaused by earthquake, to the extent that increasing soil irreversibledeformation significantly, or making soil effective stress close to zero, fromnow on, will be classified as liquefaction.

(2)P It is obligatory to forecast liquefaction when ground soil consists of loosesand on large area or thick loose sand lenses, with or without dust pclauseor clay pclause, lying beneath underground water level, and whenunderground water level is shallow. This evaluation must be carried out atvoid (ground level, underground water level) appearing throughoutstructure’s service life.


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(3)P Essential surveillance for this purpose must include at least StandardPenetration Test (SPT) on site, or Cone Penetration Test (CPT), as well asdetermination of grain size distribution curve in laboratory.

(4)P In SPT, measured SPTN value, which expresses number of beats /30cm,must be normalized with respect to the facts that apparent effective stress ofearth is 100kPa, and that the ratio between impact energy and free fallenergy is 0.6. At depths which are smaller than 3m, measured SPTN valuemust be cut down 25%.

(5) Normalization of earth pressure effect may be carried out by multiplying

measured SPTN value by the coefficient 2/1'100 vo , where vo' (kPa) is

effective stress of soil at the SPT ‘s depth and SPT ‘s time. The taken value

of normalizing coefficient 2/1'100 vo must range from 0.5 to 2.

(6) Normalization of energy requires multiplying number of beats (in clause (5)this clause) by a coefficient ER/60, where ER is 100 times equipment’scharacteristic energy ratio.

(7) For house on shallow foundation, evaluation of liquefaction may be omittedif saturated sandy soil appears only at the depth greater than 15m (measuredfrom ground surface).

(8) Liquefaction hazard may be omitted if 15.0. S and at least one of thefollowing conditions is met:

- Sand has clay content greater than 20% with plasticity index PI>10;

- Sand has dust content greater than 35% with plasticity index PI>10; andnumber of beats in SPT after being normalized with respect to earthpressure effect and energy ratio N1(60) is greater than 20.

- Pure sand, and number of beats in SPT after being normalized with respectto earth pressure and energy ratio N1(60) is greater than 30.

(9)P If liquefaction hazard can not be omitted, then it must be evaluated byreliable geotechnic methods, basing on correlation between in situobservation and repetitive shear stress which caused liquefaction in the pastearthquakes.

(10) Empiric graph of liquefaction demonstrating ground state in situ data aregiven in Appendix B. In this method, shear stress due to earthquake e maybe calculated by the following simplified formula:

voe S ..65.0 (4.4)

where:

vo soil own total pressure, other variables already appeared in expressionsfrom (4.1) to (4.3). This expression is not valid if the depth is greater than20m.


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(11)P The condition for in situ correlation method to be employed is that soil mustbe sensible to liquefaction when shear stress caused by earthquake exceedsthreshold stress an amount , these threshold stress is known to havecaused liquefaction in the past earthquakes.

NOTE : Recommended value of is 0.8, including safety coefficientwhich is 1.25.

(12)P If soil is seen to be prone to liquefaction and other following effects mayaffect foundation’s load bearing capacity or stability, then it is necessary toperform appropriate measures that ensure foundation’s stability, e.greinforcing ground and pile. (to transfer load to layer which is not prone toliquefaction).

(13) Reinforcement of ground to resist liquefaction can be: compacting soil toincrease penetration resistance out of dangerous range, or drainage methodto decrease pore water pressure due to ground quake.

NOTE: Possibility whether compacting soil is carried out or not isdetermined mainly by fine-grain content and the depth.

(14) The method that only piles foundation is used needs careful considerationbecause grave internal force may arise in pile due to lack of soil’s support inone or more liquefied layer(s), and due to inevitable inaccuracy whencalculating position or thickness of that/those layer(s).

4.1.5 Exeeding settlement of soil under cyclic load effect.

(1)P Sensitivity of soil to compactness and exceeding settlement due to cyclicstress caused by earthquake must be taken into account when soil layersdistribute on large area or there are thick saturated loose sand lenses atsmall depth.

(2) Exceeding settlement may also occur in very weak clay soil layers, becausethe shear strength decreases with cycle under long ground quake.

(3) Possibility that the compactness and settlement of the above soil types mustbe evaluated by current geotechnic methods, if necessary one may uselaboratory test with static load and cyclic load for representative samples ofstudied materials.

(4) If settlement due to compactness or cyclic strength attenuation may affectfoundation stability, then one must consider to reinforce the ground.

4.2 Surveillance and study about ground.

4.2.1 General criteria

(1)P Surveillance and study about ground, foundation materials in seismic zonemust comply with common principles as those principles for non-seismiczone, as defined in Part 3, EN 1997-1:2004.

(2) Except houses of I importance degree, in in situ surveillance it isrecommended to introduce static penetration test, pore water pressure


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measurement, because they allow us to record continuously soil mechaniccharacteristics with depth.

(3) Implement surveillance about oriented quake resistance may be required insome situation listed in $.1 and 4.2.2

4.2.2 Classification of ground soil by earthquake effect

(1)P Geotechnic or geologic figures about building area must be sufficient fordetermining average ground type and corresponding spectrum o response,as defined in 3.1 and 3.2, Part 1 of this building regulation.

(2) To hit that mark, in situ figures may be employed and combined withfigures of vicinity which has similar geologic properties.

(3) Referring to sub-area maps or seismic criteria is obligatory, with thecondition that such map or criteria must comply with (1)P in this clause andbase on in situ surveillance of ground soil

(4)P Velocity plane of shear wave in ground is considered to be the most reliableto forecast properties at each position due to earthquake effect.

(5) It is recommended to carry out in situ test to determine velocity plane ofshear wave sv in drilled hole by geophysic method for important structureslocating in seismic zone, especially in ground of D, S1, S2 type.

(6) Under all other circumstances, when natural periods of vibrations needdetermining, velocity plane of sv may be evaluated by experimentalcorrelation that includes penetration resistance of the site and othergeotechnic properties, while paying attention to that correlation’sdivergence.

(7) Soil’s internal resistance should be measured by appropriate in situ test orlaboratory test. If direct measurements are not available but the product

Sg . is smaller than 0.1g (or 0.98m/s2), one may choose resistance ratio to

be 0.03. Cohesive soil, cemented soil, and soft rock need separatelysurveillance.

4.2.3 Dependence of stiffness and damping rate on deformation degree.

(1)P Under small deformation, difference between sv obtained through in situ

test and sv obtained through deformation in earthquake simulation mustboth be notified in all calculation of soil dynamic characteristics.

(2) If building location’s ground soil belongs to type C or D, or undergroundwater level is shallow, and no component has plasticity index PI>40, onecan uses reduction factor for sv listed in Table 4.1 when lacking in specificdata. With stiffer strata and deeper underground water level, reductionfactor and variation range must be smaller.

(3) If the product Sg . is equal to or greater than 0.1g (0.98m/s2), it is

recommended to use internal resistance ratios in Table 4.1 when lacking inspecific measurements.


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Table 4.1 – Soil‘s average resistance ratio and shear wave’s average velocitysv and shear modulus G ( a standard deviation)

in the depth limit of 20m.

Groundacceleration ratio

Sg .

Reduction factor

max,s

s

maxG

G

0.10

0.20

0.30

0.03

0.06

0.10

0.90( 0.07)

0.70( 0.15)

0.60( 0.15)

0.80( 0.10)

0.50( 0.20)

0.36( 0.20)

Where:

max,s average value of s in case deformation is small (<10-5), max,s never

exceed 360m/s.

maxG average value of G in case deformation is small (<10-5).

NOTE : One may choose an appropriate value in the range of standarddeviation, according to other factors such as stiffness or soil layer. For

instance, in the first row, one can choosemax,s

s

andmaxG

Gto be larger than

0.09 and 0.08, respectively, if dealing with stiffer stratum, and vice versa.


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5 FOUNDATION SYSTEM

5.1 General requirements

(1)P Beside general requirements of EN 1997-1:2004, structure’s foundation inseismic zone must comply with the following issues.

a) Relating force generated in the upper structures must be transferred to thelower structures without causing any significant irreversible deformation asdefined in criteria in 5.3.2 .

b) Foundation’s deformation due to earthquake must meet requirements aboutstructure’s fundamental functions.

c) Foundation must be fully understood, designed and constructed followingexactly rules in 5.2 and other methods in 5.4 to reduce risk of unpredictableearthquake effects as small as possible.

(2)P It is essential to take into account the dependence of soil’s dynamicparameters on soil’s deformation and cyclic nature of earthquake load.Taking into account local reinforced soil’s or replacing soil’s parameters isalso very important, to ensure that their compactness is sufficient or theirother parameters are not too sensitive to compactness or liquefaction.

(3) With suitable reasons, or in need, substitute foundation’s materials of whichstrength factor is different from those listed in 3.1(3) may be used, providedthat they offer the same safety degree.

NOTE : for instance, strength factors applied in loading pile experiments.

5.2 Prescripts of basic designs

(1)P If the structure is not bridge or pipeline, mixed foundations such as pilesfoundation combined with shallow foundation may only be used if such mixwas proved to be appropriate. Dynamic-independent components in thestructures may also use these mixed foundations.

(2)P In choosing foundation type, one needs to consider the followings:

a) Foundation‘s stiffness must be sufficient to transfer local effect from upperstructure to lower structure uniformly.

b) When choosing foundation’s stiffness in its horizontal plane, reciprocalinfluence of horizontal relative displacement between plumb buildingelements must be notified.

c) The assumption that displacement amplitude attenuates with respect todepth is only accepted if it was proved by proper study and maximumacceleration ratio at ground surface is smaller than p times Sg . .

NOTE : Recommended value of p is 0.65

5.3 Designed effect

5.3.1 Relation inside designed structure


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(1)P Energy dissipation structure. It is obligatory to take into account the riskthat earthquake effect on energy dissipation structure’s foundation mayexceed foundation bearing capacity. Evaluation of such risk must complywith clauses in corresponding clause of this building regulation.Particularly, with house building, requirements in 4.4.2.6(2)P, Part 1 of thisbuilding regulation must be complied.

(2)P Non energy-dissipation structure. When calculating the earthquake effecton non energy-dissipation structure’s foundation, one can employ theresults that have been calculated in the condition of earthquake but neglectthe bearing capacity. Refer further to 4.4.2.6(3), Part 1 of this buildingregulation for more information.

5.3.2 Transfer of earthquake effect to ground

(1)P The following criteria about transfer of transverse force, normal force,bending moment to ground must be met in order for the foundation systemto meet 5.5(1)P. In addition, pile and column must meet criteria in 5.4.2.

(2)P Transverse force. Transverse shear force VEd is transferred by followingmechanism:

a) By designed shear strength between foundation’s horizontal bottom orfoundation’s plate and ground as described in 5.4.1.1.

b) By designed shear strength between foundation’s vertical surface andground.

c) By designed shear strength due to earth pressure at foundation’s lateralsurface, satisfying limits and prescripts as described in 5.4.1.1, 5.4.1.3,5.4.2.

(3)P The value of shear strengths combination may be at most 30 % resistancedue to be passive earth pressure when totally mobilized.

(4)P Normal force and bending moment. Normal force NEd and bending momentMEd are transferred to ground by a mechanism or a combination ofmechanisms below:

a) By vertical designed counterforce at foundation’s bottom.b) By designed bending moment generated by horizontal designed shear force

between lateral surface of deep foundation’s elements (case foundation,piles foundation, caissons…) and ground, satisfying limits and prescripts asdescribed in 5.4.1.3, 5.4.2

c) By vertical designed shear force between lateral surface of deepfoundation’s elements (case foundation, piles foundation, caissons…), orother foundation elements buried in ground, and ground.

5.4 Criteria in testing and size determination.

5.4.1 Shallow foundation or buried foundation

(1)P To test or determine size of shallow foundation or buried foundation putdirectly on ground, use the following criteria.


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5.4.1.1 Foundation (designed at ultimate state).

(1)P According to criteria about ultimate state, foundation’s sliding resistanceand load bearing capacity must be checked.

(2)P Sliding failure. In case foundation’s bottom lies above underground waterlevel, this failure is resisted by friction through horizontal pressure,according to rules in (5) of this clause.

(3) When lacking in specific studies, designed resistance due to friction offoundation lying above underground water level FRd can be calculated usingthe following formula:

MEdRd

tgNF

(5.1)

Where:

EdN designed normal force acting on horizontal foundation’s bottom.

angle of friction between structure surface and ground atfoundation’s bottom. This value may be evaluated following 6.5.3 ofEN 1997-1:2004;

M specific coefficient of material parameter, taking the value of 'tg

(refer to 3.1.(3))

(4)P If foundation lies beneath underground water level, designed shear strengthmust be evaluated based on undrained shear strength, following 6.5.3 of EN1997-1:2004.

(5) Horizontal designed shear strength Epd due to earth pressure acting onfoundation’s lateral surface may be taken into account as stated in 5.3.2,provided that appropriate measures have been applied such as compactingthe soil which fills foundation lateral, burying foundation’s wall verticallydownwards, pouring foundation’s concrete directly to clean straight soilline.

(6)P To ensure that no sliding failure occurs horizontally, the followingcondition must be satisfied:

pdRdEd EFV (5.2)

(7) If the following prescripts are satisfied simultaneously:

- The foundation lies above underground water level;

- Soil properties remain unchanged during earthquake;

- Sliding causes no bad effect on functions of any kind of life-line pipelines(water pipeline, gas pipeline, gate pipeline or communication line wire)attached to the structure;

then sliding will occur within the acceptable limit. Sliding degree must bereasonable in the structure’s overall response.


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(8)P Failure due to exceeding load bearing capacity. Load bearing capacitymust be checked with combination effect of NEd, VEd, MEd to see whether itsatisfies 5.1(1)Pa) or not.

NOTE : to examine load bearing capacity of foundation when earthquakeoccurs, expressions and criteria in Appendix A may be used. These takeinto account tilt and eccentricity caused by inertia force in structure as wellas other likely effects of inertia force on load bearing ground.

(9) It is necessary to be aware of some kind of sensible clay soil whose shearstrength may decrease, some kind of non-cohesive soil which is prone toeffect of pore water dynamic pressure which is due to cyclic load as well asdissipation of pore pressure from lower soil layers after earthquake.

(10) The calculation of soil’s load bearing capacity under seismic load must takeinto account strength and stiffness attenuation mechanisms even ifdeformation is small. If these phenomena are taken into account thenmaterial’s characteristic parameters may be smaller. If not, one should usevalues listed in 3.1(3).

(11) The phenomenon that pore pressure increases under cyclic load or its effecton pore water pressure (in analysis of effective stress) must be taken intoaccount by considering its effect on undrained shear strength (in analysis oftotal stress). With structure having operational importance factor I smallerthan 1.0, soil’s nonlinear response must be taken into account whendetermining irreversible deformation which occurred during earthquake.

5.4.1.2Horizontal tie-backs

(1)P Like 5.2, effects on structure caused by foundation’s relative horizontaldisplacement must be evaluated and measures must be employed to adjustdesign.

(2) With house, requirement in (1)P is considered to be satisfied if allfoundations are on the same horizontal plane, tie-back and foundation pilesare placed at foundation altitude or grillage altitude. These methods are notnecessary if: a) foundation type is A, b) foundation type is B and seismicrisk is negligible.

(3) Tie-backs on house’s ground floor can be assumed to be tie-backs if they liein the range of 1.0m from foundation bottom or grillage bottom. Afoundation plate may be employed to replace tie-backs if it is also placed inthe range of 1.0m from foundation bottom or grillage bottom.

(4) Tensile strength of these connecting elements may be estimated usingsimplified methods.

(5)P If no rules or no more accurate methods are available, then tie-backs infoundation are considered to be sufficient when all rules in (6) and (7) aremet.

(6) Tie-backs

The following methods should be applied:


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a) Tie-back must be designed to resist longitudinal force, including shear forceand tensile force:

EdSN3.0 with B type ground

EdSN4.0 with C type ground

EdSN6.0 with D type ground

where

EdN : average designed axial force in vertical elements connected under thecondition of quake resistance design.

b) Longitudinal steel must be anchored firmly onto foundation body or othertie-backs.

(7) Foundation plate

The following measures must be applied:

a) Tie-backs must be designed to resist axial force which are equal to values in(6)a) of this clause.

b) Longitudinal steel of braced area must be anchored firmly onto foundationbody or continuous plate.

5.4.1.3 Spread-footing

(1) All clauses in 5.4.1.1 may also be applied for spread-footing, but with thefollowing prescripts:

a) Capacity of total friction may be taken into account in case of a singlefoundation plate. With foundation beam’s simple mesh, an equivalentfoundation area may be considered at each intersection point.

b) Tie-backs and/or foundation plates may be viewed as connecting braces,rules about their sizes may be applied for effective width corresponding tofoundation beam width or plate width equal to one tenth its width.

(2) Spread-footing may be examined like wall in its plane range, under effectsof its inertia forces and horizontal forces caused by upper structures.

5.4.1.4 Case foundation

(1) All items of 5.4.1.3 are also used for case foundation. Besides, loadcapacity of soil at the side as regulations in 5.3.2(2) and 5.4.1.1(5) can beconsidered to all types of soil acrroding to limitations in regulation.

5.4.2 Pile and pillar

(1) Pile and pillar must be designed to resist two kinds of effect

a) Inertia forces caused by upper structures. These forces, combined withstatic load, take the designed values NEd, VEd, MEd as in 5.3.2.

b) Forces caused by earth’s deformation when seismic wave propagatesthrough.


20

(2)P Pile’s critical horizontal load bearing capacity must be examined followingrules in 7.7 of this building regulation.

(3)P Analysis of pile’s internal force, as well as displacements or rotation anglesmust base on discrete or contiguous model in order to describe exactly (orapproximately):

- Pile’s flexural rigidity;- Earth counterforce acting along pile shaft, together with consideration ofcyclic load and deformation degree in soil;

- Dynamic interaction between piles (also called dynamic effect of “pilesgroup”);- Freedom degree of/at grillage, or of/at joints between piles and structure.

NOTE : to calculate pile’s stiffness, employ expressions given in AppendixC.

(4)P One must neglect lateral resistance of soil which is prone to liquefaction orwhose strength decrease significantly.

(5) If batter piles are used then one must design them so that they can resistaxial load as well as bending safely.

NOTE : It is not recommended to use batter piles to transfer horizontal loadto earth.

(6)P Bending moment developed due to dynamic interaction are only calculatedif all following prescripts are simultaneously met:

- Ground soil’s cross-sections is of D or S1 or S2 type, and includescontiguous layer with abrupt changes;

- The building locates at area in which risk of earthquake is medium orhigh, i.e. the product ag.S exceeds 0.10g (or 0.98m/s2), and structure is of IIIor IV importance degree.

(7) Theoretically, piles must be designed in elastic limit, but in some situationplastic hinge is allowed to develop at pile top. Zone in which plastic hingeis likely to appear must be designed following 5.8.4, Part 1 of this buildingregulation.


21

6 INTERACTION BETWEEN EARTH AND STRUCTURE

(1)P Earth-structure dynamic interaction must be taken into account in:

a) Structures that P effect (second-order effect) plays important role;

b) Structures with big massive foundation or being buried such as bridge pier,off shore well foundation and silo;

c) Tall and slim structures such as tower, chimney in EN 1997-6:2004;

d) Structures above very soft soil layers, with average shear wave velocity

max,s (as defined in Table 4.1) smaller than 100m/s, e.g S1 type soil layer.

NOTE : Information about common effects and importance of dynamicinteraction between structure and earth is given in Appendix D.

(2)P Effects of earth-structure interaction of pile must be estimated following5.4.2 for all kinds of structures.


22

7 RETAINING WALL STRUCTURE

7.1 General requirements

(1)P Retaining wall structures must be designed to function during an afterearthquake without being significantly damaged.

(2) Irreversible displacement, sliding or tilt (tilt caused by earth’s irreversibledeformation), may be accepted if they meet requirements about functioningand/or aesthetics.

7.2 Choice of structures and notes about designing

(1)P Choosing structure types must base on normal functioning conditions,following general principles in chapter 9, EN 1997-1:2004.

(2)P To ensure that supplement requirements about earthquake are met, one mayneed to adjust or even choose a more appropriate structures.

(3)P Backfill materials must be graded and compacted on site so that thecontinuity with original soil is as high as possible.

(4)P Drainage system behind structure must be able to resist transient and longtime displacement while their functions are not affected.

(5)P Especially in case of aqueous non-cohesive soil, drainage system mustprove their effect at even the part below failure surface which is behind thestructure.

(6)P It is obligatory to ensure that the support earth block is supplied withenough insurance supply to prevent liquefaction under earthquake effect.

7.3 Analysis methods

7.3.1 General methods

(1)P Any methods established basing on structural dynamics’ basics, experienceand observations, is theoretically acceptable in estimating retaining wall’ssafety degree.

(2) The following issues need consideration:

a) Soil’s general nonlinear response in dynamic interaction with retaining wallstructure.

b) Inertia effect accompanying weight of soil, of structure, and of allgravitational loads may take part in interaction progress.

c) Hydrodynamic effects caused by appearance of water behind wall and/or atwall outside surface.

7.3.2 Simplified methods: quasi-static analysis

7.3.2.1Fundamental models

(1)P Fundamental models in quasi-static analysis method must include retainingwall structure and its foundation, earth block behind the structure which isassumed to be in active limit equilibrium (if the structure is flexible


23

enough), as well as any load affecting on earth block, even earth block atwall base, which is considered to be in passive equilibrium.

(2) In order for an active state of soil to happen, a sufficiently largedisplacement must occur throughout designed earthquake, this displacementmay take form in the bending of flexible structure, in sliding or rotation ofgravitational structure. With displacement which is needed to developactive limit state, referring to 9.5.3 of EN 1997-1:2004 for moreinformation.

(3) With stiff structures lying on bedrock or piles such as basement wall orgravitational wall, pressure generated will be larger than active pressure,and it is more reasonable to assume that soil is in rest state, as representedin E.9. This assumption is also applied for anchored and non-displaceableretaining wall.

7.3.3.2Earthquake effect.

(1)P In the quasi-static method, earthquake effect must be described by systemof static forces acting vertically or horizontally, which are products ofgravitational force and earthquake coefficient.

(2)P With vertical earthquake effect, upward or downward effects must beconsidered and compared to determine which of them creates the mostdisadvantageous effect.

(3) In area which earthquake happens, equivalent earthquake forces’ intensitydepends on acceptable irreversible displacement and lies within theallowable range of selected structural concepts.

(4)P When lacking detail figures, coefficients of vertical and horizontalearthquake kv , kh affecting on all mass must take the value:

r

Skh (7.1)

hv kk 5.0 if 6.0g

vg

a

a(7.2)

hv kk 33.0 in the opposite situations (7.3)

Where:

Coefficient r takes values listed in Table 7.1, depending on retaining walltype. With wall not higher than 10m the earthquake coefficient isconsidered to be invariant with respect to wall altitude.

Table 7.1 – Values of coefficient r used to calculate horizontal earthquakecoefficient.

Retaining wall type r

Gravitational wall with free wall head, capable of enduring maximumdisplacement dr = S300 (mm)

Gravitational wall with free wall head, capable of enduring maximum

2


24

displacement dr = S200 (mm)

Bending reinforced concrete wall, anchored or supported wall,reinforced concrete wall on vertical piles, displacement- restrictedbasement wall and abutment.

1.5

1

(5) If there is non-cohesive soil which is water-saturated and is easy to developpore water pressure, then:

a) Coefficient r in Table 7.1 should not take value which is greater than 1.

b) Anti-liquefaction safety coefficient should not take value which is smallerthan 2.

NOTE: Safety coefficient’s value 2 is obtained through applying 7.2(6)Pwithin the framework of simplified method in 7.3.2.

(6) With retaining wall higher than 10m and supplement information forcoefficient r, refer to E.2 for more information.

(7) Except gravitational wall, vertical effect of acceleration may be neglected inretaining walls.

7.3.2.3Designed pressure of soil and water

(1)P Total designed force acting on wall in case of earthquake must be calculatedwhile taking into account the model’s limit equilibrium condition describedin 7.3.2.1.

(2) This force can be evaluated following Appendix E.

(3) The designed force mentioned in (1)P must be considered as the resultant ofsoil static and dynamic pressures.

(4)P In case there’s no detail study about relative stiffness, displacement formand relative mass of retention wall, the application point of the force causedby soil dynamic pressure resides at the wall’s midpoint.

(5) If a wall is capable of rotating freely around its base, application point ofdynamic and static force can be considered to superpose each other.

(6)P Pressure force direction distributing on the wall together with wall normalforms an angle less than or equal to '32 in active state and equal to 0 inpassive state.

(7)P With soil lying beneath underground water level, one must distinguishbetween seepage prone status (in which water can move freely in soilskeleton) when dynamic load is present and waterproof status (in whichpractically no water drainage takes place under earthquake effect).

(8) Under most normal prescripts and with soil having seepage coefficient lessthan 5.10-4 m/s, pore water does not move freely in ground framework,earthquake effect happens practically without drainage and soil can beconsidered to be monophase environment.


25

(9)P Without hydrodynamic seepage, one must apply all the above prescriptswhile adjusting properly the volumetric soil mass and horizontal earthquakecoefficient.

(10) Adjustment in case of no hydrodynamic seepage can be conductedfollowing E.7 and E.7.

(11)P With hydrodynamic seepage, effects caused by earthquake in soil and thatin water must be viewed as independent effects.

(12) Hence, hydrostatic and hydrodynamic water pressure should be added upaccording to E.7. The application point of the former force can be assumedto lie at the distance of 80% of the saturated layer’s depth.

7.3.2.4Hydrodynamic pressure acting on outside surface of wall.

(1)P Variation (decrease or increase) of pressure with respect to currenthydrostatic pressure (caused by water oscillation on wall’s exposed surface)must be taken into account.

(2) This kind of pressure can be evaluated following E.8.

7.4 Strength and stability test.

7.4.1 Stability of ground soil.

(1)P The following test must be carried out:

- Test of overall stability.

- Test of soil local failure.

(2)P Test of overall stability must be carried out following rules in 4.1.3.4

(3)P The ultimate efficiency of ground soil must be tested both about slidingfailure and about load bearing capacity fading (see 5.4.1.1).

7.4.2 Anchor

(1)P Parts of anchors (including free cable section, anchor support, anchor head,lock constitution) must both meet: length standard and strength standard (toensure the equilibrium of soil block in case of earthquake (see 7.3.2.1)), andthe sufficient capability of bearing ground soil’s deformation caused byearthquake.

(2)P Anchor’s strength must meet standards in EN 1997-1:2004, correspondingto dynamic and long term foreseen limit.

(3)P Soil in which anchor lies must be ensured to maintain its strength to lastduring the foreseen earthquake period. Insurance supply must also beenough to prevent liquefaction.

(4)P Distance Le between the anchor and the wall must surpass Ls calculated fornon-earthquake load.

(5) Under prescripts in which soil containing anchor shoes has propertiessimilar to that of soil behind wall and some prescripts about ground surfaceelevation, distance Laa between anchor shoes in soil can be calculated viathe following formula:


26

)5.11( SLL ge (7.4)

7.4.3 Structural strength

(1)P It is necessary to prove that, under the combination effect of earthquake andother likely generated loads, equilibrium state can be achieved withoutexceeding design strength of wall and other support structural elements.

(2)P In order to achieve such goal, one needs to consider proper limit state ofstructural failure in 8.5, EN 1997-1:2004

(3)P All structure elements must be examined to ensure that they satisfy thefollowing condition:

dd ER (7.5)

Where:

Rd element’s designed strength value, which is evaluated by ways similarto that in non-earthquake situations.

Ed effects’ designed value, which are obtained from analyzing resultsrepresented in 7.3.


27

APPENDIX A (reference)

RELIEF AMPLIFICATION FACTOR

A.1 This appendix introduces some relief amplification coefficients which issimplified for earthquake effect and is used to examine earth’s slopestability. These coefficients, symbolized by ST, are initial approximatevalues and considered independently with fundamental vibration period,hence they are multiplied as an invariant ratio coefficient by coordinates ofdesigned elastic response spectrum given in Part 1 of this buildingregulation. These amplification coefficients must be priorly applied forslopes which have abnormal relief variance with respect to 2 directions,such as lengthened top and lengthened partition higher than 30m.

A.2 With angle of slope smaller than 15o, relief effects may be neglected,whereas if local relief changes too abnormally, specific study is required.With higher angles, apply the followings:

a) Independent partitions and slopes: use Sr>1.2 for positions near the top.

b) Tops whose width is much smaller than foot’s width. It is recommended touse ST 1.4 near slope’s top whose average slope angle is greater than 30o

and to use ST 1.2 for smaller slope angle.

c) Existence of non-cohesive soil layers on the surface. If there are non-cohesive soil layers on the surface, minimum value ST given in a) and b)should be increased at least 20%.

d) Amplification coefficient’s variance with respect to space. Value of ST maybe assumed to decrease in linear manner from partition or top, and takevalue 1 at slope foot.

A3 In general, in the range of slope top, earthquake amplification attenuatesrapidly with respect to depth. Therefore, relief’s effects taken into accountwith analysis of stability are maximums and are almost only on the surfacealong top’s edge, and are much more smaller on deep sliding surface wherefailure surface come across top foot.


28

APPENDIX B (compulsory)

EXPERIMENTAL GRAPHS USED TO ANALYZING SIMPLIFIEDLIQUEFACTION

B.1 General.

Experimental graphs are utilized to analyze simplified liquefaction to studycorrelation between in situ test and repetitive shear stresses which is knownto be the liquefaction cause during past earthquakes. On horizontal axis is akind of soil property measured on site, such as normalized penetrationresistance or shear wave velocity vs, on the vertical axis is repetitive shearstress due to earthquake, usually normalized with effective soil’s ownpressure 0'v . Limit curve of repetitive resistance is displayed in all graphs,divides the graphs into zones including non-liquefaction zone (on the right)and likely liquefaction zone (on the left and the top of the curve).Sometimes more than one curve are represented, for example curvescorresponding to fine-grained soil or soil with different earthquakeintensities.

Except static penetration resistance, it is not recommended to useexperimental liquefaction standards when liquefaction occurs in soil layersor soil beds thinner than tens of cm.

When gravel content is rather high but observational data is not sufficient toestablish a reliable liquefaction graph, possibility of liquefaction can not beexcluded.

B.2 Graphs basing on SPT index.

The graph in Figure B.1 is one of the many graphs that are being mostwidely used for pure sand and silt sand. SPT index is normalized with soilself pressure and with energy ratio N1(60) following the way described in4.1.4.

Liquefaction seems to occur at values higher than certain threshold of e ,because soil‘s response is elastic and there’s no accumulation of pore waterpressure. Therefore, limit curve may not be extrapolated toward origin ofcoordinates. If one wish to apply this criterion for earthquake with intensitydifferent from Ms = 7.5, where Ms is surface wave intensity, thencoordinates of the curve in Figure B.1 should be multiplied by coefficientCM given in Table B.1

Table B.1 – Values of coefficients CM

MS CM

5.5

6.0

6.5

2.86

2.20

1.69


29

7.0

8.0

1.30

0.67

B.3 Graphs basing on static penetration resistance CPT. Basing on manystudies about correlation between static penetration resistance and soil’sresistance against liquefaction, graphs having the form similar to that inFigure B.1 have been established. Such direct correlations should be usedprior to indirect correlations using relation between SPT index and staticpenetration resistance CPT.

B.4 Graphs basing on shear wave velocity vs. This characteristic is consideredto be a promising standard to estimate liquefaction possibility in soil typewhich is hard to sample (for example silt sand or sand) or hard to penetrate(for example gravel). Recently there have been significant advance inmeasuring vs on site. However, correlation between vs and soil’sliquefaction resistance is still being studied and should not be used withoutconsultancy from specialists.

NOTE :

0've - repetitive stress ratio curve 1 : 35% fine grains

A - pure sand curve 2 : 15% fine grains

B – silt sand curve 3 : <3% fine grains

FIGURE B.1 - Relation between stress ratios causing liquefaction andN1(60) for pure sand and silt sand with earthquake Ms = 7.5.


30

APPENDIX C (compulsory)

PILE HEAD’S STATIC STIFFNESS

C.1 Pile’s stiffness is defined as force (moment) put on pile’s head to create unitdisplacement (rotation) along the same direction (displacement/rotationangle along other directions equals to zero), and is symbolized as KHH

(horizontal stiffness), KMM (bending stiffness) and KHM = KMH (bending-horizontal displacement stiffness).

Symbols used in Table C.1 :

E earth elastic modulus, equals to 3G;

Ep pile material’s elastic modulus;Es earth’s elastic modulus at the depth which equals to pile diameter;d pile diameter;

z depth of pile sinking.

Table C.1 – Expressions of static stiffness of soft pile sunk into 3 types of soil

Type of soil

s

HH

dE

K

s

MM

Ed

K3

s

HM

Ed

K2

dzEE s /. 35.0

60.0

s

p

E

E80.0

14.0

s

p

E

E60.0

17.0

s

p

E

E

dzEE s /. 28.0

79.0

s

p

E

E77.0

15.0

s

p

E

E53.0

24.0

s

p

E

E

sEE 21.0

08.1

s

p

E

E75.0

16.0

s

p

E

E50.0

22.0

s

p

E

E


31

APPENDIX D (reference)

STRUCTURE-SOIL INTERACTION (SSI): GENERAL

EFFECTS AND IMPORTANCE

D.1 Due to structure-soil interaction, earthquake reaction of structure on softpillow, such as structure on deformable ground, will differ fr….om reactionof the same structure but on hard ground (clamped at its foot) subjected toan equivalent free field excitation, because of the following reasons:

a) Displacement of foundation system on soft pillow differs from that of freefield and may include a very important vibrating component of structureclamped at its foot.

b) Fundamental vibration period of the structure on soft pillow is longer thanthat of structure clamped at its foot.

c) Natural vibration periods, vibration modes and partial pattern coefficients ofstructure on soft pillow differ from those of structure clamped at its foot.

d) Total damping rate of structure on soft pillow includes both internal andexternal damping rates occurring at the contact surface between soil andfoundation, in addition to damping rate of upper structure.

D.2 With most of public buildings, interactions between soil and structure areadvantageous because they decrease bending moments and shear forces indifferent elements in the upper structure. With structures listed in chapter 6,on the contrary, the interaction effects between soil and structure may bedisadvantageous.


32

APPENDIX E (compulsory)

SIMPLIFIED ANALYZING METHOD FOR RETAINING WALLSTRUCTURE

E.1 Theoretically, coefficient r is defined as ratio between acceleration valuecausing irreversible displacement corresponding to existing connection andacceleration value corresponding to equilibrium limit state (displacementstarts to occur). Hence with wall allowing greater displacement coefficient rtakes greater value.

E.2 With retaining wall structure higher than 10m, one may consider theproblem is in one dimension with free field wave propagating vertically,and value may take the mean value of horizontal maximum accelerationalong the structure’s height for more accuracy to use in expression (7.1).

E.3 Total designed force acting on retaining wall at its back, Ed , is given by thefollowing formula:

wdwsvd EEKHkE 2)1(*2

1 (E.1)

Where:

H wall’s height;Ews static water force;

Ewd dynamic water force;

* soil’s unit weight (will be defined from E.5 toE.7);

K earth pressure coefficient (static and dynamic);

kv vertical earthquake coefficient (refer to expressions (7.2) and (7.3).

E.4 Earth pressure coefficient may be calculated following Mononobe andOkabe formulas:

With active states:

If d'

2

2

)sin()sin(

)'sin()'sin(1)'sin(.sin.cos

)'(sin

d

ddddd

dK (E.2)


33

If d'

)sin(.sin.cos

)(sin 2

dd

K

(E.3)

With passive states (without regard to friction between earth and wall):

2

2

)sin()sin(

)'sin('sin1)'sin(.sin.cos

)'(sin

dddd

dK (E.4)

The following symbols are used in the expressions above:

d' soil’s designed shear strength angle value, which means

'

1 ''

tg

tgd ;

, tilt angle of wall back and fill soil surface with respect to horizontaldirection as shown in Figure E.1;

d designed friction angle between soil and wall, which means:

'

1

tg

tgd

angle which is defined from E.5 to E.7 below.

The expression for passive state should be used priorly for vertical wallsurface o90 .

E.5 Underground water level beneath retaining wall. Earth pressure coefficient.

Here the following parameters are employed:

* volume weight of soil (E.5)

v

h

k

ktg

1 (E.6)

Ewd = 0(E.7)

where:


34

kh horizontal earthquake coefficient (refer to expression (7.1)

On the other hand, one may use tables and graphs applied in static condition(only gravitational loads exist), with the following supplements:

v

hA k

ktg

1 (E.8)

and

v

hB k

ktg

1 (E.9)

The whole system of wall-soil rotates by the corresponding angle A or B .The gravitational acceleration is replaced by the following value:

A

vA

kgg

cos

)1( (E.10)

or

B

hB

kgg

cos

)1( (E11)

E.6 Impermeable soil bearing dynamic load lying beneath underground waterlevel – Earth pressure coefficient.


w * (E.12)

v

h

w k

ktg

1

(E.13)

Ewd = 0 (E.14)

Where:

saturated unit weight of soil;

w unit weight of water.


35

E.7 Permeable soil bearing dynamic load lying (high permeability) beneathunderground water level – Earth pressure coefficient.


w * (E.15)

v

h

w

d

k

ktg

1

(E.16)

Ewd = 2)'(12

7Hk wh (E.17)

Where:

d dry unit weight of soil;

H’ height of underground water level, measured from wall base.

E.6 Hydrodynamic pressure on outside surface of wall.

This pressure q(z) may be calculated following the steps below:

zhkzq wh .8

7)( (E.18)

Where:

hk horizontal earthquake coefficient, r = 1 (refer to expression (7.1));

h free water level height;

z vertical coordinate with the coordinate origin placed at water surface.

E.9 Force which is caused by earth pressure acts on stiff structure

For stiff, clamped structure, active state can not develop in the soil, andwith vertical wall and horizontal fill soil, dynamic force due to earthpressure increment may take:


36

2... HSPd (E.19)

Where:

H wall’s height;Application of force may be assumed to be midpoint of wall’s height.


37

Active

Passive

Figure E.1 – Convention for angles in formula used to

calculate earth pressure coefficient.


38

APPENDIX F (reference)

EARTHQUAKE LOAD BEARING CAPACITY OF SHALLOWFOUNDATION

F.1 General expression. Endurance against failure of a shallow band-shapedfoundation’s load bearing capacity placed on a homogeneous surface maybe examined by the following expression relating earth strength, designedeffects (NEd, VEd, MEd) at altitude of foundation placing, to inertia forces inearth:

01

1

1

1

1

'

'

'

dkkc

cc

hkkc

cc

NFmN

MFf

NFmN

VFe

T

MM

T

TT (F.1)

Where:

maxN

NN EdRd ;

maxN

VV EdRd ;

max.NB

MM EdRd

(F.2)

Nmax foundation’s maximum force bearing capacity under effect ofcentrally applied load, which is defined in F.2 and F.3;

B foundation’s with;

F soil’s dimensionless inertia force, defined in F.2 and F.3;

Rd model‘s coefficient (these coefficient are given in F.6)

a, b, c, d, e, f, m, k, k’, cT, cM, cM’, , are parameters’ values whichdepend on soil type, and are defined in F.4.

F.2 Pure cohesive soil. With Pure cohesive soil or water- saturated non-cohesive soi, maximum force bearing capacity under vertical load effectcentrally applied Nmax is determined by the following formula:

Bc

NM

2max (F.3)

Where:

c Soil’s undrained shear strength cu for cohesive soil, or soil’sundrained shear strength for non-cohesive soil subjected to cyclic load ',ucy .


39

M specific coefficient of material property.

Dimensionless inertia force of soil is determined by the formula:

c

BSaF g .... (F.4)

Where:

volume weight of soil;

ga designed acceleration of A type ground ( ga = gRa1 );

gRa maximum reference acceleration of A type ground.

1 operational importance factor.

S soil coefficient defined in 3.2.2.2, Part 1 of this building regulation.

The following restraints is applied in the expression of total force bearingcapacity:

1,10 VN

F.3 Pure non-cohesive soil. With dry soil and saturated non-cohesive soil butnot generating significant pore water pressure, maximum load bearingcapacity of foundation under vertical centrally applied load Nmax iscalculated by the formula below:

NBg

agN v 2

max 12

1

(F.6)

Where:

g gravitational acceleration;

av vertical acceleration of ground, may take the expression 0.5ag.S ;

N load bearing capacity coefficient, which is a function of designed

shear strength angle d' ( d' consists of specific coefficient of material

property M of 3.1(3), refer to E.4)

Dimensionless inertia force in earth is calculated by the formula:


40

d

g

g

aF

'tan. (F.7)

The following restraint is applied in the general expression:

')1(0 kFmN (F.8)

F.4 Parameter’s values. Table F.1 contains parameter’s values in the generalexpression representing soil’s load bearing capacity of various types in F.2and F.3

Table F.1 – Parameter’s value used in expression (F.1)Pure cohesive soil Pure non-cohesive

soil

a 0.70 0.92

b 1.29 1.25

c 2.14 0.92

d 1.81 1.25

e 0.21 0.41

f 0.44 0.32

m 0.21 0.96

k 1.22 1.00

k’ 1.00 0.39

ct 2.00 1.44

cM 2.00 1.01

c’M 1.00 1.01

2.57 2.90

1.85 2.80

F.5 In most of normal prescripts it is allowable to take F as 0 with cohesivesoil. With non-cohesive soil it is allowed to neglect F if ag.S<0.1g (whichmeans ag.S<0.98m/s2).

F.6 Model coefficient Rd takes the values listed in Table F.2


41

Table F.2 – Values of model coefficient Rd

From fairlycompact to

very compactsand

Dry, non-cohesive sand

Saturated,non-cohesive

sand

Unsusceptibleclay

Susceptibleclay

1.00 1.15 1.50 1.00 1.15

tcxdvn 375-2006 p2 (english)

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