EARTHQUAKE EFFECT ON SINGLE PILE BEHAVIOR WITH VARIOUS FACTOR OF SAFETY AND DEPTH TO DIAMETER RATIO IN LIQUEFIABLE SAND

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1 International Journal of Civil Engineering and Technology (IJCIET) Volume 9, Issue 4, April 218, pp , Article ID: IJCIET_9_4_14 Available online at ISSN Print: and ISSN Online: IAEME Publication Scopus Indexed EARTHQUAKE EFFECT ON SINGLE PILE BEHAVIOR WITH VARIOUS FACTOR OF SAFETY AND DEPTH TO DIAMETER RATIO IN LIQUEFIABLE SAND Raid R. Al-Omari Retired Professor, Civil Engineering Department, Al-Nahrain University, Baghdad, Iraq Abdulaziz A. Al-Kifae Professor, Civil Engineering Department, Al-Nahrain University, Baghdad, Iraq Sarmad M. Al-Tameemi Postgraduate Student, Civil Engineering Department, Al-Nahrain University, Baghdad, Iraq ABSTRACT One of the most main causes of pile foundation failure effected by earthquake stresses is liquefaction phenomenon. Shake table study was performed to examine the behavior of single pile with different factor of safety and depth to diameter ratio in liquefiable saturated loose sand induced by actual earthquake, monitoring the acceleration in soil and pile cap and the excess pore water pressure ratio, besides the pile end bearing load and pile settlement. It is concluded that, the pile factor of safety and depth to diameter ratio shows no influence on the acceleration and the liquefaction potential. Pile settlement of FS=2.5 decreased 14%, whereas it is decreased 31% for FS=3. compared to pile settlement of FS=2.. The pile settlement in cases of increasing depth to diameter ratio decreased since the penetration of the pile is deeper and extend to the layer that not liquefied. Comparable to (L/d=9.4), the final pile settlement of (L/d=6.3) is increased by 6%, whereas it is decreased 5% for (L/d=12.5). Key words: Liquefaction, Shake table, Pile factor of safety and L/d ratio. Cite this Article: Raid R. Al-Omari, Abdulaziz A. Al-Kifae and Sarmad M. Al- Tameemi, Earthquake Effect on Single Pile Behavior with Various Factor of Safety and Depth to Diameter Ratio in Liquefiable Sand, International Journal of Civil Engineering and Technology, 9(4), 218, pp INTRODUCTION One of the most causes of the dramatic damage to constructions during earthquakes is the triggering of the liquefaction in saturated sand deposit. Loose sand likely lost its contact under

2 Earthquake Effect on Single Pile Behavior with Various Factor of Safety and Depth to Diameter Ratio in Liquefiable Sand the dynamic loading of earthquake shaking, that cause increasing in the pressure of the water in the sand pore, if the soil is saturated and predominately unable to drain during earthquake. The result is a degradation in the effective confining stress of the soil with combination of loss of stiffness and strength that leads to deformations of the soil layer (Idriss and Boulanger 28) [2]. Pile foundations can be particularly vulnerable to soil liquefaction. If the soil beneath the tip of the pile becomes liquefied, then there is a reduction in the tip capacity and the pile can undergo excessive settlements. On the other hand, if the depth to which soil liquefies is rather limited, say in a relatively small magnitude earthquake, the soil surrounding the shaft may liquefy and a loss of shaft friction may be expected. This can cause an increase in the base load of the pile, which can lead to an increased settlement, (Madabhushi et al. 29) [3]. In this study, a manufactured shake table have been used to study the influence of the loose saturated sandy soil liquefaction potential on the behavior of a single pile foundation involving various pile capacity factors of safety and various pile depth to diameter ratios, focusing on the reduction in pile carrying capacity that takes place during the earthquake and the following pile settlement. 2. DESCRIPTION OF SHAKE TABLE EXPERIMENT A 1-g manufactured shake table test was carried out on single pile in liquefiable sand deposit using flexible laminar shear box Flexible Laminar Shear Box (FLSB) was used as a container to hold the tested soil and pile model. The FLSB total depth designed for containing the water saturation panel and filter layer and the tested soil specimen. The tested soil model size was mm. The manufactured shake table with FLSB are shown in Figure 1. Modified Ali Algharbi real earthquake acceleration history data was adopted. The soil employed for the model tests was quartz clean sand. The sand was air-dried, crumbled and then screened on sieve #1. Tests were performed for loose sand with relative density, (D r =33%). Table 1 summarize the properties of the employed sand. (Maymand et al. 2) [4] listed scale factors for different simulated parameter for 1-g shake table studies. The scaling factors are presented in Table 2. For current study, it was founded that λ=25 is adequate for simulating prototype parameter to model scale for all parameters considering a reasonable pile dimension in full scale. The model pile used is made from a rod of Polytetrafluoroethylene (PTFE) that is known as Teflon. The diameter of pile used was 32 mm, three different embedded lengths were investigated (2, 3, and 4) mm which its embedment (depth to diameter) ratios L/d were (6.3, 9.4 and 12.5) respectively. The pile tip was attached with an in-line type miniature load cell to measure the end bearing load, it was fixed in a hidden manner to eliminate load cell effects on soil-pile interaction near its tip. Apparently, the roughness of Teflon material is very small, thus the pile was covered with glasspaper to simulate the friction coefficients of concrete with saturated sand which is 22. The pile was combined with ( ) mm stainless steel plate pile cap. The load carrying capacity was calculated using Hansen ultimate static pile capacity equation (Hansen 197) [1]. Three different factors of safety were studied (2., 2.5, and 3.) which yielded total pile load of (.4,.32 and.27) kn respectively. Figure 2 presents the pile model editor@iaeme.com

3 Raid R. Al-Omari, Abdulaziz A. Al-Kifae and Sarmad M. Al-Tameemi Figure 1 Manufactured shake table with FLSB Table 1 Properties of used sand Soil Property Loose Sand Relative density, D r (%) 33 Dry unit weight, γ d (kn/m 3 ) Total unit weight, γ t (kn/m 3 ) Water content, W c (%) 25 Specific gravity, G s 2.65 Maximum. void ratio, e max.757 Minimum. void ratio, e min.467 Void ratio, e.661 Fine content, % 4. Effective size, D 1 (mm).162 Mean size, D 5 (mm).394 Soil classification (USCS) Poorly-graded sand, (SP) Permeability coefficient, k (cm/sec) Friction angle, φ 34 Cohesion, c (kn/m 2 ) Table 2 Shake table scaling factors simulated in a laboratory environment [4] Parameters Units Prototype Model Length L 1 1/λ Stress ML -1 T /λ Pressure ML -1 T /λ Force MLT /λ 3 Mass M 1 1/λ 3 Acceleration LT Unit Weight ML -2 T Strain editor@iaeme.com

4 Earthquake Effect on Single Pile Behavior with Various Factor of Safety and Depth to Diameter Ratio in Liquefiable Sand Figure 2 Single pile model 3. TEST PREPARATION The sand was pluviated into FLSB over the filter layer. The soil density controlled using dry sand pluviation method. Pore pressure transducers and accelerometers were embedded through the prepared sand in three depths (1, 2 and 475) mm, as in Figure 3 Figure 3 Test model layout and setup During soil profile forming, the pile was placed on the center of the BSLF surface. After the pile was placed, soil formation was resumed (that simulate board pile effect). Next to finishing soil profile formation, saturation stage was started using constant head saturation system. After sand being saturated, the system was left for 3 minutes to be stabilized before next step. Acceleration history of modified Ali Algharbi earthquake was selected. Mass was loaded above the pile cap, while the miniature load cell was measuring the static tip pile load. Then, accelerometer and gyroscope were fixed on the mass over pile cap, while three displacement transducers were linked to the center of the mass across a screw nut editor@iaeme.com

5 Raid R. Al-Omari, Abdulaziz A. Al-Kifae and Sarmad M. Al-Tameemi 4. SHAKE TABLE TEST RESULTS Various results parameters against time are presented for different pile FS and L/d. This included the resulted acceleration on the table and pile cap in addition to three depths in soil layer that are (1 mm, 2 mm, and 475 mm). The measurement of pore water pressure (PWP) and excess pore water pressure ratio (r u ) at the same mentioned depths are also displayed in the results, besides the records of pile end bearing and pile settlement Effect of Pile Capacity Factor of Safety (FS) The behavior of single pile with different factor of safety FS (2., 2.5 and 3) (ultimate design load) in liquefiable sand were studied with (L/d=9.4). The obtained results are demonstrated in Figure 4, 5 and 6. It can be seen that, the acceleration at surface and table level are equals. It is reduced at the middle soil depth and increased at pile cap (Su. et al. 213) [5]. The pile capacity factor of safety shows no influence on the acceleration as it is clarified in Figure 7. It can be founded that, the excess pore water pressure ratio (r u ) is not affected by the pile capacity factor of safety. For factor of safety (FS=2.) the recorded excess pore water pressure ratios (r u ) in the three depths were (r u1 =1.6, r u2 = and r u3 =.79) and for FS=2.5 the excess pore water pressure ratios were (r u1 =1.5, r u2 =1.1 and r u3 =.8), while (r u1 =1.3, r u2 =1.1 and r u3- =.81) were observed in case of factor of safety (FS=3.). Figure 8 shows that for all factors of safety the initial liquefaction occurs in depth of (r u1 and r u2 ). Therefore, there is no effect of factor of safety on the liquefaction potential. Pile end bearing is reduced as the pore water pressure buildups then, as the pore water pressure start to dissipate the tip load slowly raised until the dissipation ended. Comparable to pile behavior in case of factor of safety (FS=2.), the pile end bearing strength in cases of (FS=2.5 and FS=3.) shows little increase with time as the liquefaction occurs, this increment does not reach the value of the total applied load, this means that the skin friction reduced but not entirely lost. The pile settlement for these cases is not changed by the effect of liquefaction, but it is decreased since the applied load is decreased as presented in Figure 9. The settlements of the pile are (5.4d, 4.6d and 3.8d) for cases of pile factor of safety (FS=2., FS=2.5 and FS=3.) respectively. Figure 1 shows the relation of pile settlement against the factor of safety. Comparable to the factor of safety of (FS=2.), it is shown that the final pile settlement of FS=2.5 decreased 14%, whereas it is decreased 31% for FS= Effect of Pile Depth to Diameter Ratio (L/d) Investigation for the behavior of pile and liquefaction resistance were carried out with various pile effective depth to diameter ratio. Value of (L/d=6.3 and L/d=12.5) were implemented in these cases and compared to case of (L/d=9.4) of pile factor of safety (FS=2.). Figure 4, 11 and 12 present the results of these cases. Based on Figure 13 no influence of pile depth to diameter ratio (L/d) is observed on the acceleration behavior. Also, it can be concluded that the excess pore water pressure ratio (r u ) is not affected by the pile depth to diameter ratio. When (L/d=6.3), the excess pore water pressure ratios (r u ) in the three depths were (r u1 =1.6, r u2 =1.3 and r u3 =.82), while (r u1 =1.7, r u2 = and r u editor@iaeme.com

6 Acceleration (g) Settlement (mm) ACC3 ACC2 ACC1 Pile load (kn) Earthquake Effect on Single Pile Behavior with Various Factor of Safety and Depth to Diameter Ratio in Liquefiable Sand =.8) were observed in case of (L/d=12.5). Figure 14 shows that for various (L/d) values, the initial liquefaction occurs in depth of (r u1 and r u2 ) and there is no effect of the pile depth to diameter ratio (L/d) on the liquefaction potential. Pile carrying capacity shows the same behavior for any pile depth to diameter ratio; since the pile capacity depends mostly on end bearing strength. The pile settlement in these cases also not changed by the effect of liquefaction, but it is decreased since the penetration of the pile is deeper and extend to the layer that not liquefied as presented in Figure 15. The settlements of the pile are (5.7d and 2.8d) for cases of pile depth to diameter ratio (L/d=6.3 and L/d=12.5) respectively. Figure 16 shows the variation of settlement versus pile depth to diameter ratio (L/d). Comparable to the (L/d=9.4), it is shown that the final pile settlement of (L/d=6.3) is increased by 6%, whereas it is decreased 5% for (L/d=12.5), the significant decrement of pile settlement in case of (L/d=12.5) occurs because the sand at pile tip in this case is not liquefied (a) Shake acceleration vs. time (b) Pore water pressure ratio (c) Pile load (d) Pile settlement Figure 4 Test results of pile with L/d=9.4 and FS=2. Total Load End Bearing rᵤ₁ rᵤ₂ rᵤ₃ Full scale pile load (kn) Full scale settlement (mm) editor@iaeme.com

7 Settlement (mm) Acceleration (g) ACC3 ACC2 ACC1 Pile load (kn) Settlement (mm) Acceleration (g) ACC3 ACC2 ACC1 Pile load (kn) Raid R. Al-Omari, Abdulaziz A. Al-Kifae and Sarmad M. Al-Tameemi (a) Shake acceleration vs. time (b) Pore water pressure ratio (c) Pile load (d) Pile settlement Figure 5 Test results of pile with L/d=9.4 and FS=2.5 Total Load End Bearing rᵤ₁ rᵤ₂ rᵤ₃ Full scale pile load (kn) Full scale settlement (mm) (a) Shake acceleration vs. time (b) Pore water pressure ratio (c) Pile load (d) Pile settlement Figure 6 Test results of pile with L/d=9.4 and FS=3. Total Load End Bearing rᵤ₁ rᵤ₂ rᵤ₃ Full scale pile load (kn) Full scale settlement (mm) editor@iaeme.com

8 Settlement (mm) Acceleration (g) ACC3 ACC2 ACC1 Pile load (kn) Depth (mm) Earthquake Effect on Single Pile Behavior with Various Factor of Safety and Depth to Diameter Ratio in Liquefiable Sand Pile cap Table Acceleration, (g) FS=2. FS=2.5 FS=3. Figure 7 Variation of acceleration vs. (FS) Pile settlement (mm) Pile final settlement (mm) d 2 FS=2. 4 FS=2.5 1d 6 FS= d 3d 4d 5d 6d Pile settlement per pile diameter, (S/d) Figure 8 Variation of (r u ) vs. (FS) Figure 9 Variation of settlement for different (FS) Figure 1 Variation of final settlement vs. (FS) FS=2. FS=2.5 FS=3. Pile capacity factor of safety, FS FS=2. FS=2.5 FS=3. Pile capacity factor of safety, FS Depth rᵤ₁@1 mm rᵤ₂@2 mm rᵤ₃@475 mm 6d 5d 4d 3d 2d 1d d Pile final settlement per pile diameter, (S/d) (a) Shake acceleration vs. time. (b) Pore water pressure ratio (c) Pile load (d) Pile settlement Figure 11 Test results of pile with L/d=6.3 and FS= Total Load End Bearing rᵤ₁ rᵤ₂ rᵤ₃ Full scale pile load (kn) Full scale settlement (mm) editor@iaeme.com

9 Pile settlement (mm) Pile final settlement (mm) Depth (mm) Settlement (mm) Acceleration (g) ACC3 ACC2 ACC1 Pile load (kn) Raid R. Al-Omari, Abdulaziz A. Al-Kifae and Sarmad M. Al-Tameemi (a) Shake acceleration vs. time. (b) Pore water pressure ratio (c) Pile load (d) Pile settlement Figure 12 Test results of pile with L/d=12.5 and FS= Total Load End Bearing rᵤ₁ rᵤ₂ rᵤ₃ Full scale pile load (kn) Full scale settlement (mm) Pile cap L/d=6.3 L/d=9.4 L/d= Depth rᵤ₁@1 mm rᵤ₂@2 mm rᵤ₃@475 mm Table Acceleration, (g) Figure 13 Variation of acceleration vs. (L/d) d L/d=6.3 L/d=9.4 L/d=12.5 Figure 15 Variation of settlement for different (L/d) 1d 2d 3d 4d 5d 6d Pile settlement per pile diameter, (S/d) L/d=6.3 L/d=9.4 L/d=12.5 Pile length to diameter ratio, L/d Figure 14 Variation of (r u ) vs. (L/d) L/d=6.3 L/d=9.4 L/d=12.5 Pile length to diameter ratio, L/d Figure 16 Variation of pile settlement vs. (L/d) 6d 5d 4d 3d 2d 1d d Pile final settlement per pile diameter, (S/d) 5. CONCLUSIONS 1-g shake table tests were carried out to examine the behavior of single pile of different factor of safety and depth to diameter ratio in liquefiable saturated loose sand in flexible laminar editor@iaeme.com

10 Earthquake Effect on Single Pile Behavior with Various Factor of Safety and Depth to Diameter Ratio in Liquefiable Sand shear box induced by modified Ali Algharbi earthquake. It concluded that, the acceleration at surface and table level are equals, it is reduced at the middle soil depth and increased at pile cap. The pile capacity factor of safety and depth to diameter ratio shows no influence on the acceleration and the liquefaction potential. The final pile settlement of FS=2.5 decreased 14%, whereas it is decreased 31% for FS=3. compared to pile settlement of FS=2.. The pile settlement in cases of increasing depth to diameter ratio decreased since the penetration of the pile is deeper and extend to the layer that is not liquefied. Comparable to (L/d=9.4), the final pile settlement of (L/d=6.3) is increased by 6%, whereas it is decreased 5% for (L/d=12.5). The significant decrement of pile settlement in case of (L/d=12.5) occurs because the sand at pile tip in this case is not liquefied. REFERENCES [1] Hansen, J. B. A Revised and Extended Formula for Bearing Capacity. Bulletin of the Danish Geotechnical Institute, 28, 197, pp [2] Idriss, I. M. and Boulanger, R. W. Soil Liquefaction During Earthquakes. 2nd Edition, Earthquake Engineering Research Institute, 28. [3] Madabhushi, G., Knappett, J. and Haigh, S. Design of Pile Foundations in Liquefiable Soils. 1st. Edition, Imperial College Press, 29. [4] Maymand, P., Reimer, M., and Seed, R. Large scale shaking table tests of seismic soil-pile interaction in soft clay. Proc. 12th World Conf. Earthquake Eng. New Zealand, 5, 2, pp.915. [5] Su, D., Ming, H. Y. and Li, X. S. Effect of shaking strength on the seismic response of liquefiable level ground. Engineering Geology, 166, 213, pp editor@iaeme.com