【正文】 ?? ? If Bb≥1900mm, ??????′ = ????????′ ????? = Su=25kPa = Su=50kPa = Su≥100kPa 23:09:21 83 SIDE FRICTION ? Effective stress analysis(b method) ???? = ??????′ ? Sand ? Silts and clays ? Total stress analysis(a method) ???? = ?????? ? clays 23:09:21 84 SANDS ? For largedisplacement pile and assumes that ?? ???? =1 and ?? ??′ =: ?? = ??.????+??.???????? () ? For drilled shafts and N60≥15, ?? = ??.?????.?????? ?? (??.???? ≤ ?? ≤ ??.????) ? z in m. ? Nonlinear, layer by every 6m. ? What if N6015 ? ? Reduced by N60/15 23:09:21 85 ?? METHOD ?? = ???????? ?? = ???? ???????????? ??′ ????′ Lateral earth pressure coefficient Soilfoundation interface friction angle Static earth pressure coefficient ???? = ???????????′ ??????????????′ Soil friction angle Sand Difficult to determine. Clay Easy to determine. 23:09:21 86 SANDS ? For largedisplacement pile and assumes that ?? ???? =1 and ?? ??′ =: ?? = ??.????+??.???????? () ? For drilled shafts and N60≥15, ?? = ??.?????.?????? ?? (??.???? ≤ ?? ≤ ??.????) ? z in m. ? Nonlinear, layer by every 6m. ? What if N6015 ? ? Reduced by N60/15 23:09:21 87 SILTS AND CLAYS ? Silts ?? = ??.????~??.???? ? Clays ?? = ??.????~??.???? ? OCR ? When z, ignored the sidefriction. ? shrinkage ? Drying, lateral load, wobble 23:09:21 89 CH14 DEEP FOUNDATIONS AXIAL LOAD CAPACITY BASED ON ANALYTIC METHODS . LUO 23:09:21 90 INCREASED IN LOAD CAPACITY WITH TIME 23:09:21 91 孔隙水壓力的減少將導致承載能力的增加 ? For drilled shafts: ? ????′ for drilled shafts in sands is less than that for piles. ? The empirical formulas from O’Neill and Reese: SI: ????′ = ????.???????? ≤ ????????kPa ? preconditions: ? N60≤50 ? ?? = 5%???? ? Bb1200mm? ? ??????′ = ????????????????????′, or ? Perform a settlement analysis. 23:09:21 92 CLAYS UNDRAINED ANALYSIS ? For D/B3 and Su≤250kPa: ????′ = ????????? ? If Bb≥1900mm, ??????′ = ????????′ ????? = Su=25kPa = Su=50kPa = Su≥100kPa 23:09:21 93 SIDE FRICTION ? Effective stress analysis(b method) ???? = ??????′ ? Sand ? Silts and clays ? Total stress analysis(a method) ???? = ?????? ? clays 23:09:21 94 ?? METHOD ?? = ???????? ?? = ???? ???????????? ??′ ????′ Lateral earth pressure coefficient Soilfoundation interface friction angle Static earth pressure coefficient ???? = ???????????′ ??????????????′ Soil friction angle Sand Difficult to determine. Clay Easy to determine. 23:09:21 95 SANDS ? For largedisplacement pile 預制樁 and assumes that ?? ???? =1 and ?? ??′ =: ?? = ??.????+??.???????? () ? For drilled shafts 灌注樁 and N60≥15, ?? = ??.?????.?????? ?? (??.???? ≤ ?? ≤ ??.????) ? z in m. ? Nonlinear, layer by every 6m. ? What if N6015 ? ? Reduced by N60/15 23:09:21 96 SILTS AND CLAYS ? Silts ?? = ??.????~??.???? ? Clays ?? = ??.????~??.???? ? OCR ? When z, ignored the sidefriction. ? shrinkage ? Drying, lateral load, wobble 23:09:21 98 ?? METHOD ? Piles ?? = ?? (???? ≤ ??????????) ?? = ??.?????.?? ???? ????????? ?????????? ≤ ???? ≤ ?????????? ?? = ??.?? (???? ≥ ??????????) 23:09:21 99 ? For clay ?????????????? ?? = ???????? +?????? (?? ?? )(?????? ???????)?? ? Nu ? For unfissured clays: ? ???? = ??.??????/???? ≤ ?? ? For fissured clays: ? ???? = ??.??????/???? ≤ ?? ? Ignored the sidefriction 2Bb above the bottom UPWARD LOAD CAPACITY FOR FOUNDATION WITH ENLARGED BASE 23:09:21 100 UPWARD LOAD CAPACITY ? ?????????????? ≤ ?????????????? ?? = ???? + ?????????? ? Difference between tension and pression ? Poisson effect ? ?????????????????? = ??.?????????????????????????????? 23:09:21 101 LOADSETTLEMENT RESPONSE (????′)??????′ =???????? (????)?????? =????????≤ ?? ? d=(toe) settlement ? du=B/10 for toe bearing and 10mm for side friction. ? g=(clay)(sand) ? h= ? ???? = ?????????? ? ????=Elastic pression of deep foundation ? zc=depth to centroid of soil resistance(typically about ) 23:09:21 102 IMAGINARY FOOTING METHOD ? Applicable conditions: ? deep foundations underlain by pressible soils such that the pression of these soils is more significant than the settlements required to mobilize the side friction and toe bearing. zi=: for friction piles zi=D: for endbearing piles Linear interpolation for others ???? ?? 23:09:21 103 CH16 DEEP FOUNDATIONLATERAL LOAD CAPACITY 23:09 104 SHORT VS. LONG FOUNDATIONS ? Short foundation: ? The toe is able to rotate. ? The failure is controlled primarily by the soils ? Long foundation ? The toe is fixed ? The failure is controlled primarily by the foundation ? Flexural failure ? For timber piles D/B20 ? For steel and concrete pile ,D/B35 23:09 105 RIGID ANALYSIS ? Assume EI is infinite. ? Not accurate as the nonrigid method ? Used primarily for lightweight short lateral loaded foundation ? Streetlights ? Small highway signs 23:09 106 ? 1. A lateral load is any load that acts perpendicular to the foundation axis. Thus, shear moment are lateral loads, but axial pression or tension or torsional loads are not. ? 2. Until the middle of the twentieth century, engineers assumed that deep foundations were only able to resist axial loads, so they used batter piles to resist horizontal loads. More recently, we have reconsidered that assumption and now rely on both axial and lateral capacities. ? 3. The utilization of lateral capacities in design often produces foundations that are more economical to build, more efficient in resisting seismic loads, and possibly more reliable. ? 4. The analysis of laterallyloaded