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Settlement of Shallow Foundations

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Discussed Topics:
Settlement of Shallow Foundation
Immediate Settlement
Consolidation Settlement
Created By-
Md. Ragib Nur Alam
130095
Civil Engineering
Ragibnur.ce@gmail.com


Publicado en: Ingeniería
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Settlement of Shallow Foundations

  1. 1. SETTLEMENT OF SHALLOW FOUNDATION Created By- Md. Ragib Nur Alam 130095 Civil Engineering Ragibnur.ce@gmail.com
  2. 2. SHALLOW FOUNDATION  General  Immediate Settlement  Consolidation Settlement CREATED BY- RAGIB NUR ALAM CE13 EMAIL: RAGIBNUR.CE@GMAIL.COM
  3. 3. GENERAL The settlement of shallow foundation may be divided into three broad categories: 1. Immediate settlement, which is caused by the elastic deformation of dry soil and of moist and saturated soils without any change in the moisture content. Immediate settlement are generally based on equations derived from the elasticity theory 2. Primary consolidation settlement, which is the result of a volume change in saturated cohesive soils because of expulsion of the water that occupies the void spaces. 3. Secondary consolidation settlement, which is observed in saturated cohesive soils and is the result of the plastic adjustment of soil particles. CREATED BY- RAGIB NUR ALAM CE13 EMAIL: RAGIBNUR.CE@GMAIL.COM
  4. 4. IMMEDIATE SETTLEMENT CREATED BY- RAGIB NUR ALAM CE13 EMAIL: RAGIBNUR.CE@GMAIL.COM
  5. 5. IMMEDIATE SETTLEMENT General Equation (Harr, 1966)  Flexible Foundation  At the corner of foundation  At the center of foundation  Average  Rigid Foundation  2 1 . 2  s s o e E qB S   2 1 . s s o e E qB S  Es = Modulus of elasticity of soil B = Foundation width L = Foundation length   rs s o e E qB S 2 1 .                                11 11 ln. 1 1 ln 1 2 2 2 2 m m m mm mm     avs s o e E qB S 2 1 .  B L m ; ; H =  CREATED BY- RAGIB NUR ALAM CE13 EMAIL: RAGIBNUR.CE@GMAIL.COM
  6. 6. IMMEDIATE SETTLEMENT CREATED BY- RAGIB NUR ALAM CE13 EMAIL: RAGIBNUR.CE@GMAIL.COM
  7. 7. IMMEDIATE SETTLEMENT If Df = 0 and H < , the elastic settlement of foundation can be determined from the following formula:             2 2 1 22 2 2 1 2 2 2111 . 2 211 1 . FF E qB S FF E qB S ssss s o e sss s s o e       (corner of rigid foundation) (corner of flexible foundation) The variations of F1 and F2 with H/B are given in the graphs of next slide CREATED BY- RAGIB NUR ALAM CE13 EMAIL: RAGIBNUR.CE@GMAIL.COM
  8. 8. IMMEDIATE SETTLEMENT CREATED BY- RAGIB NUR ALAM CE13 EMAIL: RAGIBNUR.CE@GMAIL.COM
  9. 9. IMMEDIATE SETTLEMENT CREATED BY- RAGIB NUR ALAM CE13 EMAIL: RAGIBNUR.CE@GMAIL.COM
  10. 10. EXAMPLE Problem: A foundation is 1 m x 2 m in plan and carries a net load per unit area, qo = 150 kN/m2. Given, for the soil, Es = 10,000 kN/m2, s 0.3. Assuming the foundation to be flexible, estimate the elastic settlement at the center of the foundation for the following conditions: a. Df = 0 and H =  b. Df = 0 and H = 5 m CREATED BY- RAGIB NUR ALAM CE13 EMAIL: RAGIBNUR.CE@GMAIL.COM
  11. 11. EXAMPLE Solution: Part a. Part b.   2 s s o e 1 E q.B S   mmmSe 9.200209.0)53.1(3.01 000,10 )150)(1( 2  For L/B = 2/1 = 2    1.53, so      2 2 1 22 2111 '. FF E qB S ssss s o e   For L’/B’ = 2, and H/B’ = 10  F1  0.638 and F2  0.033, so       mmmxSe 3.160163.04)033.0()3.0(23.01)638.0(3.013.01 000,10 )150)(5.0( 222  CREATED BY- RAGIB NUR ALAM CE13 EMAIL: RAGIBNUR.CE@GMAIL.COM
  12. 12. IMMEDIATE SETTLEMENT General Equation (Bowles, 1982) 2 ' B B  2 ' L L  1 2 . 1 '.. F E BqS s s oe                       1 11 ln 11 11 ln. 1 22 22 22 222 1 NMM NMM NMM NMM MF  ' ' B L M  'B H N  Es = Modulus of elasticity of soil H = effective layer thickness, ex. 2 - 4B below foundation At the center of Foundation and F1 time by 4 BB 'At the corner of Foundation LL ' and F1 time by 1 CREATED BY- RAGIB NUR ALAM CE13 EMAIL: RAGIBNUR.CE@GMAIL.COM
  13. 13. IMMEDIATE SETTLEMENT  For saturated clay soil s o 21e E B.q A.AS  CREATED BY- RAGIB NUR ALAM CE13 EMAIL: RAGIBNUR.CE@GMAIL.COM
  14. 14. IMMEDIATE SETTLEMENT  For sandy soil where:  Iz = factor of strain influence  C1 = correction factor to thickness of embedment foundation = 1 – 0.5x[q/(q-q)]  C2 = correction factor due to soil creep = 1+0,2.log(t/0,1)  t = time in years  q = stress caused by external load  q =  . Df    2 0 21. z s z e z E I qqCCS CREATED BY- RAGIB NUR ALAM CE13 EMAIL: RAGIBNUR.CE@GMAIL.COM
  15. 15. Young Modulus IMMEDIATE SETTLEMENT Circle Foundation or L/B =1 z = 0  Iz = 0.1 z = z1 = 0,5 B  Iz = 0.5 z = z2 = 2B  Iz = 0.0 Foundation with L/B ≥ 10 z = 0  Iz = 0.2 z = z1 = B  Iz = 0.5 z = z2 = 4B  Iz = 0.0 CREATED BY- RAGIB NUR ALAM CE13 EMAIL: RAGIBNUR.CE@GMAIL.COM
  16. 16. EXAMPLE A shallow foundation 3 m x 3 m (as shown in the following drawing). The subgrade is sandy soil with Young modulus varies based on N-SPT value (use the following correlation: Es = 766N) Determine the settlement occur in 5 years (use strain influence method) CREATED BY- RAGIB NUR ALAM CE13 EMAIL: RAGIBNUR.CE@GMAIL.COM
  17. 17. EXAMPLE CREATED BY- RAGIB NUR ALAM CE13 EMAIL: RAGIBNUR.CE@GMAIL.COM
  18. 18. EXAMPLE Depth (m) z (m) Es (kN/m2) Iz (average) (m3/kN) 0.0 – 1.0 1.0 8000 0.233 0.291 x 10-4 1.0 – 1.5 0.5 10000 0.433 0.217 x 10-4 1.5 – 4.0 2.5 10000 0.361 0.903 x 10-4 4.0 – 6.0 2.0 16000 0.111 0.139 x 10-4  1.55 x 10-4 z E I s z    9.0 5.18.17160 5.18.17 5.015.011                x x qq q C 34.1 1.0 5 log.2.01 1.0 log.2.012              t C   mmS xxS z E I qqCCS e e B s z e 8.24 )1055.1)(5.18.17160)(34.1)(9.0( ... 4 2 0 21      CREATED BY- RAGIB NUR ALAM CE13 EMAIL: RAGIBNUR.CE@GMAIL.COM
  19. 19. CONSOLIDATION SETTLEMENT CREATED BY- RAGIB NUR ALAM CE13 EMAIL: RAGIBNUR.CE@GMAIL.COM
  20. 20. CONSOLIDATION SETTLEMENT  Normal Consolidation  Over consolidation oc   or 1 o c   o o c o c c H e C S      log.. 1 oc   or 1 o c   𝜎o +  𝜎 < 𝜎c o o c o s c H e C S      log.. 1 𝜎o < 𝜎c < 𝜎o+ 𝜎 c o c o c o c c o s c H e C H e C S          log.. 1 log.. 1 CREATED BY- RAGIB NUR ALAM CE13 EMAIL: RAGIBNUR.CE@GMAIL.COM
  21. 21. CONSOLIDATION SETTLEMENT where:  eo = initial void ratio  Cc = compression index  Cs = swelling index  pc = preconsolidation pressure  po = average effective pressure on the clay layer before the construction of the foundation =  ’.z  p = average increase of pressure on the clay layer caused by the foundation construction and other external load, which can be determine using method of 2:1, Boussinesq, Westergaard or Newmark. Alternatively, the average increase of pressure (p) may be approximated by:  bmt pppp  4 6 1 pt = the pressure increase at the top of the clay layer pm = the pressure increase at the middle of the clay layer pb = the pressure increase at the bottom of the clay layer CREATED BY- RAGIB NUR ALAM CE13 EMAIL: RAGIBNUR.CE@GMAIL.COM
  22. 22. EXAMPLE A foundation 1m x 2m in plan is shown in the following figure. Estimate the consolidation settlement of the foundation. Assume the clay is normally consolidated. CREATED BY- RAGIB NUR ALAM CE13 EMAIL: RAGIBNUR.CE@GMAIL.COM
  23. 23. EXAMPLE o o cc p pp H eo Cc S    log.. 1       2 /45.13 25.3225.31 2.1.150 .. mkNp zLzB LBq p o      mmxSc 44 5.52 45.135.52 log5.2 8.01 32.0     po = (2.5)(16.5) + (0.50)(17.5-10) +(1.25)(16-10) = 52.5 kN/m2 2:1 method CREATED BY- RAGIB NUR ALAM CE13 EMAIL: RAGIBNUR.CE@GMAIL.COM
  24. 24. ALLOWABLE SETTLEMENT CREATED BY- RAGIB NUR ALAM CE13 EMAIL: RAGIBNUR.CE@GMAIL.COM

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