PORT WORKS DESIGN MANUAL PART 3 Guide To - The University ...

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38(2) Secondary consolidationSecondary consolidation (creep) is the long-term settlement under constant effective stress.In clay, it is due to the squeezing out of the water adsorbed on the clay particles. Adsorbedwater is chemically bound to the surfaces of the clay particles, so it is not free to flow undergravity. As the adsorbed water is squeezed out, the clay particles move closer and rearrangeto a new equilibrium position, resulting in further deformation or compression.There areconflicting views as to whether secondary consolidation starts as soon as the loading isapplied or after completion of primary consolidation.(3) Creep of fillCreep is also said to occur in granular fill. Some fill exhibits time-dependent compressionwith the rate similar to that of secondary consolidation in clays. The mechanism of suchcreep behaviour of granular fill is explained by the crushing of the contact points between theparticles, which results in the reorientation of the soil particles and additional settlement.43 Assessment of Sub-soil Settlement4.3.1 Genera!This section discusses the principles of settlement analysis, based on the classical theory ofTerzaghi, which describes primary consolidation resulting from a change in loading(dissipation of pore water pressures) and secondary consolidation that takes placesubsequently with no change in pore water pressure. The classical theory assumes onedimensionalstrain and negligible lateral deformation. Since reclamation usually covers alarge horizontal area relative to the thickness of the sub-soil, these conditions are met.However, the classical theory was derived from observations of thin samples during tests inthe laboratory. In reality, it has been observed in the field that thick soil layers behavedifferently to this classical concept. There is no clear separation of the two types ofsettlement and the overall result is one of gradually reducing pore pressures and reducingrates of settlement, and excess pore water pressures may still be observed near the end ofprimary consolidation. Hence, computations based on two components of strain, one relatedto changes in effective stress and the other time dependent, not operating sequentially buttaking place simultaneously, may be a better model for more accurate prediction of settlementin thick soil layers. Estimation of pore water pressures will require advanced calculationmethods to cater for the combination of the two components of strain.
3943.2 due toThe ultimate primary consolidation settlement of a soil layer due to an applied loadingdepends on the relative magnitudes of the initial effective vertical stress acting on the soil andthe effective preconsolidation pressure, and can be estimated as follows:ForA WiCT1_/'— CT^'
Page 3 and 4: PORT WORKS DESIGN MANUALPART 3Guide
Page 5 and 6: FOREWORDThe Port Works Design Manua
Page 7 and 8: CONTENTSTITLE PAGE - !FOREWORD 3CON
Page 9: PageNo.5.3.3 Verification of Settle
Page 12 and 13: 101.2 Definition, Symbols and Refer
Page 14 and 15: 12the investigations may need to co
Page 16 and 17: 14consequences of adopting a partic
Page 18 and 19: 16(3) Installation of vertical drai
Page 20 and 21: 18The remaining layer of marine or
Page 22 and 23: 20• The rate of supply of public
Page 24 and 25: 22the shortage of public filling ca
Page 26 and 27: 24Considerations when planning the
Page 28 and 29: 262.10 Environmental ImpactsAll rec
Page 31 and 32: 293.3.1 GeneralThe reclamation sequ
Page 33 and 34: 31requires checking of the equilibr
Page 35 and 36: 33(2) Detailed Stability AnalysisTh
Page 37 and 38: 3.4 WorksIf, despite all the precau
Page 39: 374.4.1 GeneralThis chapter discuss
Page 43 and 44: 41where S pt(residml) = Residual se
Page 45 and 46: Design of surcharge preloading gene
Page 47 and 48: 45H = Fill thickness.a = Logarithmi
Page 49: 47The calculation of residual settl
Page 52 and 53: 50For monitoring of pore pressure d
Page 54 and 55: 525.3.2 of FillThis section discuss
Page 56 and 57: 54the availability of frequent moni
Page 58 and 59: 56reduce settlement problems. Howev
Page 61 and 62: 59REFERENCESAsaoka, A (1978). Obser
Page 63: 61FIGURES
Page 67 and 68: 65(1) Geotextile-\I,- i i i i i , ,
Page 69 and 70: 67Figure 5 - Method of Calculation
Page 71 and 72: 69timet + 120Piezometer installed a
Page 73 and 74: 71Slope >1Required pause in fill pl
Page 75: 73APPENDIX APREFABRICATED BAND DRAI
Page 78 and 79: 76List of ASTMD4491-92: Standard Te
Page 81: 79CONTENTSTITLE PAGE 77CONTENTS 79B
Page 84 and 85: 82t = Time from load application.c
Page 86 and 87: 84Hansbo, S. (1981).Consolidation o
Page 89 and 90: 87CONTENTSTITLE PAGE 85CONTENTS 87C
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89C OF BY ASAOKA'S METHODC.IGeneral
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91OFFigureNo.PageNo.C1 Asaoka's Gra
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94SiFinal settlementPlacement of. a
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97CONTENTSTITLE PAGE 95CONTENTS 97D
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1000.3(8.9)(3 2 )(1. 2) - 2.8836L e
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102Vertical drains dataTypeSpacingP
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104The final primary consolidation
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106The initial effective stress at
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108Table D2.6m0123M0.5711.5712.5713
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110Effective stress increment at en
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112(3) Settlement due to secondary
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114The value ofF(n) in Example D.2
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116
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118CD~5COCOCDCLCD20 -14.9Required p
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120
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122state value.Mud wave. Excessive
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124
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126dd'D ree 0e maxe minFHI pK aLeng
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128
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X1S1SD112HK 627.5 P83Port works des
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