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International Journal of Civil Engineering and Technology (IJCIET) Volume 10, Issue 1, January 2019, pp.520–534, Article ID: IJCIET_10_01_049 Available online at http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=10&IType=1 ISSN Print: 0976-6308 and ISSN Online: 0976-6316 ©IAEME Publication Scopus Indexed EVALUATION AND DEVELOPMENT OF THE AVAILABLE METHODS OF PREDICTING CAPACITIES OF BORED PILES EMBEDDED IN BASRA SOIL Dr. Haider S. Al-Jubair Asst. Prof.-Member of the ISSMGE, Dept. of Civil Eng.-Univ. of Basra Mushtaq R. Daham Chief Engineer, Basra Oil Company ABSTRACT The ultimate capacities of single piles utilized in ten projects in Basra-Iraq are evaluated using: various interpretations of pile load test results; several static methods based on site investigation programs; and the finite element method via (PLAXIS-3D).For the well-behaved tests, it is realized that the load-settlement data can be best fitted by a hyperbola. Accordingly, Rollberg method well-harmonizes the test results and allows various interpretation methods to be applied on the extrapolated curves. It is found that, the static methods spread over a wide range of values. Finite element analyses exhibited good agreement to the measured values. It produces failure loads, almost, similar to that obtained from Rollberg method. The finite element analyses revealed local settlement of (0.6% - 1.8%) of the pile diameter to mobilize the ultimate skin resistance. Key words: Bored Piles, Ultimate Capacity, Static Approach, Skin Resistance, Point Bearing, Finite Element. Cite this Article: Dr. Haider S. Al-Jubair and Mushtaq R. Daham, Evaluation and Development of The Available Methods of Predicting Capacities of Bored Piles Embedded In Basra Soil, International Journal of Civil Engineering and Technology (IJCIET), 10 (1), 2019, pp. 520–534. http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=10&IType=1 1. INTRODUCTION Pile foundations are widely used in Basra citydue to the presenceof a shallowsaturated soft cohesive soil layer of variable thickness in soil profile.In order to provide the geotechnical engineers with reliable estimates to the capacity of vertical piles embedded in Basra soil, the following tasks are accomplished: http://www.iaeme.com/IJCIET/index.asp 520 [email protected] Dr. Haider S. Al-Jubair and Mushtaq R. Daham The available equations derived based on the static approach are evaluated to select and/or modify those found suitable. The methods of interpreting the pile test data are assessed in regard to the definition of capacity. The soil-pile interaction is investigated by means of a finite element model. The are a covered by the study is located within the administrative, commercial, and residential center of Basra city. Ten projects utilizing bored pile foundations serve as case studiesFigure1. The provided data sets from those projects comprise: geotechnical investigation reports and results of loading tests on both trial and working piles. Figure 1 Locations of the projects taken into consideration 2. STATIC APPROACH For a pile of (n) segments and/or penetrating a soil profile of (n) sublayers, the ultimate compressive capacity can be expressed as [2, 3]: ∑ The unit pile point resistance is usually calculated as: Where: Qu ,Qp , Qs: ultimate capacity, point bearing, and skinresistance qp: unit point bearing Ap: area of the pile point qsi: unit shaft resistance within the segment or sublayer (i) Asi: corresponding surface area http://www.iaeme.com/IJCIET/index.asp 521 [email protected] Evaluation and Development of The Available Methods of Predicting Capacities of Bored Piles Embedded In Basra Soil : : bearing capacity factors adjusted for depth and shape. effective overburden stress at pile point. c: soil cohesion around pile point. φ: soil angle of internal friction. The (N'c) factor can be predicted from [3]: ( ) Whereas the (N'q) factor can be obtained from Figure 2.The unit point bearingcan also be predicted based on the standard penetration blows as[3]: ( ) Reese and Wright (1977); ( ) Reese and O’Neil (1988); Figure 2 Variation of ( ) values with the angle of internal friction, (Meyerhof 1976) [9] The unit skin resistance can be predicted using the following general equation Where: α: adhesion factor. : K: : effective overburden pressure at themid-depth of penetration in soil layer. lateral earth pressure coefficient. friction angle between the soil and pile material. The values or formulas for estimating the necessary parameters, suggested by different authors are summarized in Table (1).The unit skin resistance can also be predicted based on the standard penetration blows as [3]: Meyerhof (1976); ( ) Quiros and Reese (1977); kPa ( ) http://www.iaeme.com/IJCIET/index.asp 522 [email protected] Dr. Haider S. Al-Jubair and Mushtaq R. Daham ( Reese and Wright (1993); ) 3. PILE LOAD TEST The most common test procedure in Iraq is the slow maintained load test according to The ASTM-D1143 [1].The true failure occurs when the pile plunges down into the ground without any further increase in load [9] but, many settlement based failure criteria are also in use. Other interpretation methods have been developed like [6, 8]: Davisson; Chin; Hansen (80% and 90%); Dee-Beer; Fuller and Hoy; Butler and Hoy; van der Veen; and Rollberg methods. 4. FINITE ELEMENT METHOD For the three-dimensional stress analysis, the matrix equations are [7]: [ ]⃗ ⃗ Where: [ ]=global stiffness matrix, ⃗⃗⃗ =global vector of nodal displacements ⃗ = global nodal load vector Table 1 Summary of the skin resistance parameters Cohesive Component α Source Viggiani (1993) [10] Range of application 0.70 0.35 0.55 ( O' Neil and Reese (1999) [3] ) 0.45 Salgado (2006) [10] ( )] [ Friction Component Source K and Range of application Touma and Reese (1974) [3] http://www.iaeme.com/IJCIET/index.asp 523 [email protected] Evaluation and Development of The Available Methods of Predicting Capacities of Bored Piles Embedded In Basra Soil O’Neil and Hassan (1994) [3] ( ) ( ) z: the average depth of the layer in meters. PA : atmospheric pressure (PA=100 kPa) and OCR: over consolidation ratio. A time limited license of PLAXIS-3D Foundation (2015) is used in the current study. The soil is modeled using Mohr-Coulomb criterion whereas, a linear elastic model is selected to represent pile material.In order to reduce the effect of boundaries on the results, the soil mediaare extended to minimum distances of ten times pile width from the pile edge in the lateral directions, and five times pile width below the pile tip [2].In order to model the construction process of bored piles, the excavated hole is supported byslurry with a shear strength of (10 kPa) to simulate the drilling process before pouring concrete. The excavation geometry is considered as identicalto the pile geometry. Soil properties are drawn from the geotechnical investigation reports and some parameters are specified based on correlative relations in case of lack of data [11-30]. 5. RESULTS AND DISCUSSION All the input data and output results are presented for the first project only. For the remaining nine projects, partial inputs / outputs are presented in the summary Tables. The first project is a sixty thousand spectator main stadium, supported on (800mm diameter) bored and cast-inplace piles to a depth of (24 m). The soil profile is shown in the measured load-settlement curve is shown in Figure 3 [11, 12]. The capacities obtained from the various interpretation methods are shown in Figures 4 through 6. The pile design load is (1400 kN), and the static load test was performed to maximum load of (2100 kN). The maximum load could not bring the test pile to plunging. All the applicable interpretation methods produced ultimate value beyond the test load. The greatest value is obtained by Chin’s method (3626.0 kN), as illustrated in Figure 4. Rollberg’s (20%D) comes after by (3597.0 kN) as in Figure 6. Rollberg’s [(10% D), (6% D) and (Elastic +D/30)] are [(3274.0 kN), (3164.0 kN), and (3015.0 kN)], respectively. vander Veen's method yields (2350.0 kN), which is the minimum value among all, http://www.iaeme.com/IJCIET/index.asp 524 [email protected] Dr. Haider S. Al-Jubair and Mushtaq R. Daham Figure 3 Soil profile and load load-settlement curve for maintained load test (project No. 1) Figure 4 Ultimate capacity by Chin’s method (Project No.1) http://www.iaeme.com/IJCIET/index.asp 525 [email protected] Evaluation and Development of The Available Methods of Predicting Capacities of Bored Piles Embedded In Basra Soil Figure 5 Ultimate pile capacity by Vander-Veen’s method (project No. 1). Figure 6 Ultimate pile capacity by Vander-Veen’s method (project No. 1). It is clear that, the Chin’s capacity is very close to the plunging load, as calculated via Rollberg extrapolated curve at a settlement of (160 mm = 20% D). The ultimate values of vander Veen’s capacity is very close to the Rollberg's value associated with a settlement of (9.4 mm = 1.2% D). The small level of test loading, the associated settlement values, and the produced trends of data rendered Davisson’s, Brinch Hansen's 80%, Brinch Hansen's 90%, De Beer’s, Fuller http://www.iaeme.com/IJCIET/index.asp 526 [email protected] Dr. Haider S. Al-Jubair and Mushtaq R. Daham & Hoy’s and Butler & Hoy’s methods as well as net-settlement criterion inapplicable for this project. The existence of numerous static methods for skin and point resistances estimation produce a big number of combinations for pile capacities. The maximum and minimum capacities are summarized in Table (2). Table (2) Ultimate extremism values by the static methods (project No. 1). Minimum values Maximum values Method Method Value (kN) Method Value (kN) Skin Resistance (Cohesive) Viggiani [10] 1029.5 O'Neil and Reese [3] 1211.3 Skin Resistance (Cohesionless) Meyerhof [3]. 263.9 Toma and Reese [3] 903.4 Point Bearing Reese & Wright [3] 1069.4 Meyerhof[9] 5150.7 Resistance Component Total Ultimate Capacity 2362.8 7265.4 The minimum ultimate static load is higher than the test load and it is almost equivalent to the value obtained by van der Veen’s method. Projecting the minimum ultimate static load on the Rollberg’s curve, gives a settlement of (9.5mm), which is equivalent to (1.25%D) whereas, the maximum value overestimates the capacities obtained by the methods of interpretation. The skin resistance component ranges from (1293.4 kN) to (2114.7 kN) while, the point bearing component ranges from (1069.4 kN) to (5150.7 kN). These two components shall be further discussed after the presentation of the finite element results. The input parameters for the finite element analysis are listed in Table 3. The finite element mesh is shown in Figure 7 whereas, the displacement contours are demonstrated in Figure 8 for a sample load. The predicted behavior is compared to the measured one in Figure 9 whereas, the computed load-settlement curves for the different resistance components are shown in Figure 10. The analysis is terminated at an ultimate load of (5650.0 kN). Figure 11 illustrate the load transferred from pile to soil, whereas the variations of pile displacement with depth are illustrated in Figure 12, for various multiples of the design load. It is realized that at the design load, the point bearing has small contribution in load resistance (54.0 kN),while the skin resistance component, which is fully mobilized at a butt settlement of around (10.5mm = 1.3% D) or local displacements around (9mm = 1.1% D), and an applied load of (161% Qdesign). The point bearing component continues to increase and reaching its maximum value at a butt settlement of around (80 mm = 10.0% D), which is associated with plunging. The contributions of soil layers in skin resistance are calculated from the load differences at layer boundaries. The results are listed in Table (4).According to the transferred force within each layer and the associated pile surface area, the skin resistance parameters (α i and ) are back calculated for the static method, from the finite element results, as: i Qsi As i cui K . tan Qs4 As 4 oav 4 and the results are listed in Table (5). http://www.iaeme.com/IJCIET/index.asp 527 [email protected] Evaluation and Development of The Available Methods of Predicting Capacities of Bored Piles Embedded In Basra Soil Adhesion factors of (0.74) for medium stiff clay, (0.84) for soft clay, and (0.69) for stiff clay are higher than the values obtained by Viggiani method (0.5, 0.7 and 0.3) respectively [10]. In addition to that, the predicted -value gives a unit shear stress within the cohesionless layer that is close to the average value given by O’Neil and Hassan method [3]. The point bearing value of (3394.0 kN) is intermediate between the maximum value obtained by Meyerhof [9] and the minimum valueobtained by Reese and O’Neil [3]. The soil stress under the pile toe is (6774.0 kN/m2). Figure 7 Finite element mesh Figure 8 Displacement contours at an (project No.1).applied load of (2900.0 kN)(project No.1). Table 3 Input parameters for the finite element analysis (project No. 1) Parameter Medium Stiff Clay Soft Clay Stiff Clay Medium Dense Sand Bored Pile Diameter (800) mm (0.0-5.0) m (5.0-15) m (15-21) m (21-35.0) m (0.0-24.0) m Mohr-Coulomb Liner Elastic Symbol Unit Material F.E. Model Model -- Mohr-Coulomb Drainage Type Type -- Undrained Undrained Undrained Drained Non-porous Unit weight above phreatic level γunsat kN/m3 16.5 17.0 17.0 17.0 24.0 Unit weight under phreatic level γsat 3 18.5 19.0 20.0 20.0 24.0 2 kN/m Mohr-Coulomb Mohr-Coulomb Young's Modulus E' MN/m 27.0 8.5 65.0 56.0 28 000 Poisson's Ratio ν' -- 0.31 0.37 0.25 0.31 0.15 2 Cohesion cu kN/m 45.0 19.0 75.0 0.0 N/A Friction Angle φ' Degree 0.0 0.0 0.0 38.0 N/A Dilatancy Angle ψ' Degree 0.0 0.0 0.0 8.0 N/A Lateral Earth Pressure Coefficient k0 -- 1.0 1.0 1.0 0.384 N/A http://www.iaeme.com/IJCIET/index.asp 528 [email protected] Dr. Haider S. Al-Jubair and Mushtaq R. Daham Table 4 Contributions of soil layers in load resistance (project No. 1) Depth (m) 0 to 5 5 to 15 15 to 21 21 to 24 Load (kN) Qs1 Qs2 Qs3 Qs4 Value % Value % 1400.0 190 335 625 196 1346 96.1 54 3.9 2100.0 374 412.5 763.5 420 1970 93.8 130 6.2 2800.0 419 403 780 654 2256 80.6 544 19.4 3500.0 432 393 777 637 2256 64.0 1261 36.0 4200.0 419 403 780 654 2256 53.7 1944 46.3 4900.0 437 393 772 654 2256 46.0 2644 54.0 2256.0 39.9 3394.0 60.1 5650.0 Skin Resistance Point Bearing Table 5 Predicted skin resistance parameters (project No. 1) Load (kN) 3800 4200 4900 5650 α1 for cu1=45 kPa 0.76 0.74 0.75 0.74 α2 for cu2=19 kPa 0.82 0.84 0.84 0.84 α3 for cu3=75 kPa 0.68 0.69 0.69 0.69 for N=37 0.307 0.308 0.308 0.309 The results for all projects are summarized in Tables6& 7. Figure (9) Predicted load-settlement curve vs measured one (projectNo. 1). http://www.iaeme.com/IJCIET/index.asp Figure (10) Predicted ultimate capacities (project No. 1). 529 [email protected] Evaluation and Development of The Available Methods of Predicting Capacities of Bored Piles Embedded In Basra Soil Figure 11 Load transfer vs depth (project No. 1) Figure 12 Pile displacement versus depth (project No. 1) Table 6 Summary of the interpretations, and static methods Project No. Pile dia. (mm) x length (m) 1 2 3 4 5 6 7* 8 9 10 800x24 600x24 800x27 1500x31 800x24.5 1000x24 800x24 1000x29 800x28 1000x30 Load Test Design/Test loads (kN) MaximumButt Settlement (mm) 1400/2100 750/1500 1400/2100 3500/5250 1250/1875 2000/4000 1250/1875 3000/4500 1600/3200 3000/4500 6.5 2.8 Davisson Chin 12.7 2.6 1500 3626 3510 Hansen 80% Vander-Veen 14.2 2350 6.25 mm net 2000 16.3 2.6 2200 2846 7937 2667 2809 6980 2149 2400 5700 2150 1920 7884 2722 23 19 16 2220 2620 2600 7452 3558 7992 2149 6800 3600 2400 3234 5000 3350 7000 4000 2870 4340 Rollberg 6%,10% 3164,3274 3279,3412 2619,2737 7787,7871 2685,2710 6551,7253 2685,2710 6232,6876 3373,3458 6744,7406 Elas+B/30, 20% 3015,3597 3135,3520 2463,2832 7645,7936 2650,2730 5779,7888 2650,2730 5560,7454 3286,3525 6056,7996 Static Min/max skin 1293,2115 792,1276 1450,2109 2925,7769 1087,2049 1436,2634 1066,1341 1598,3474 1081,2118 1942,3949 Min/max point 1069,5151 471,1705 1156,7691 3760,18237 1127,5555 1761,8004 Min/max ultimate 2363,7265 1263,2981 2606,9800 6685,26006 2214,7604 3197,10638 1609,1884 3404,14784 2237,9356 3613,12054 543,543 1806,11310 1156,7238 1761,8105 * Cohesive bearing stratum. http://www.iaeme.com/IJCIET/index.asp 530 [email protected] Dr. Haider S. Al-Jubair and Mushtaq R. Daham Table 7 Summary of the finite element method Project No. 1 2 3 4 5 6 7* 8 9 10 Pile dia. (mm) x length (m) 800x24 600x24 800x27 1500x31 800x24.5 1000x24 800x24 1000x29 800x28 1000x30 FEM Skin (kN) 2256 1210 2495 6000 1737 2234 1900 3788 1900 3400 Point (kN) 3394 1940 2945 8900 3383 5206 870 3902 2960 4740 Ultimate (kN) 5650 3150 5440 14900 5120 7440 2770 7690 4860 8140 Local sett. at ult. skin resist. (mm) 9 11 9 9 8 1.1% D 1.8% D 1.1% D 0.6% D 1% D Butt sett. at ult point resist. (mm) 80 69 91 145 93 86 105 114 104 120 10.0% D 11.5% D 11.4% D 9.7% D 11.6% D 8.6% D 13.1% D 11.4% D 13% D 12% D cu1 (kPa) / α1 45/ 0.74 50/0.73 48/0.73 50/0.74 55/0.75 45/0.79 48/0.78 50/0.76 55/0.72 45/0.75 cu2 (kPa) / α2 19/ 0.84 25/0.83 25/0.83 12/0.88 12/0.84 12/0.83 12/0.88 25/0.85 12/0.89 12/0.87 cu3(kPa) / α3 75/ 0.69 N / φo 37/38 29/36 40/39 37/38 0.309 0.354 0.396 0.312 90/0.66 65/0.71 8 9.5 9.5 10.5 11 0.8% D 1.2% D 0.95% D 1.3% D 1.1% D 75/0.68 80/0.61 39/38.7 39/38.7 0.326 0.301 Unit skin (kPa) 87 71 99 84 72 69 Unit Point (kPa) 6774 6865 5863 5039 6734 6631 1736 90/0.61 90/0.62 40/39 40/39 39/38.7 0.334 0.310 0.313 94 69 69 4880 5891 6028 * Cohesive bearing stratum. The variations of adhesion factor with undrained cohesion, and skin friction factor with the standard penetration blows, as obtained from the finite element method, are shown in Figures 14 and 15. It should be mentioned that single (average)-valued (α or ) factors are assigned for soils with similar (cu or N)-values. Figure 13 Adhesion factors for bored piles in Basrah soil http://www.iaeme.com/IJCIET/index.asp 531 [email protected] Evaluation and Development of The Available Methods of Predicting Capacities of Bored Piles Embedded In Basra Soil Figure 14 Skin friction factor vs. standard penetration blows for bored piles in Basrah soil Table (8) lists the ultimate bored pile capacities, as calculated based on Figures 13 and 14for ultimate skin resistance components, and Reese and O'Neil's (1988) method for point bearing component. The allowable loads adopting a safety factor of (3) and the associated butt settlement values, as obtained from the measured load-settlement relations, are also tabulated. The maximum settlement is (4.9 mm), which is equivalent to (1.7%D), and is accepted for most structures. Table 8 The predicted bored pile capacities and the associated settlement values Project No. Pile dia. (mm) Qs (kN) Qp (kN) Qu (kN) Qall (kN) Butt Settlement at Qall (mm) 1 800 2091.6 1069.4 3161.0 1053.7 1.8 2 600 1098.7 471.5 1570.2 523.4 0.6 3 800 2176.6 1156.1 3332.7 1110.9 3.0 4 1500 5794.9 3759.6 9554.5 3184.8 3.7 5 800 1694.0 1127.2 2821.2 940.4 0.7 6 1000 2381.4 1761.3 4142.7 1380.9 3.6 7 800 1727.9 542.9 2270.8 756.9 0.5 8 1000 3235.4 1806.4 5041.8 1680.6 4.9 9 800 1911.4 1156.1 3067.5 1022.5 2.0 10 1000 3454.1 1761.3 5215.4 1738.5 4.0 6. CONCLUSIONS For the studied ten projects, the following conclusions can be drawn: Pile load tests in Basrah are usually used as proof tests, even for the trial piles. Piles are rarely tested to failure. For a well-conducted test (with no problems), the load-settlement data can be fitted with a considerable degree of accuracy by a hyperbola. According to that, Rollberg method simulates the test results in a good manner and permits the application of many interpretation criteria on the extrapolated curves. http://www.iaeme.com/IJCIET/index.asp 532 [email protected] Dr. Haider S. Al-Jubair and Mushtaq R. Daham Davisson’s, BrinchHansen 90%, De-Beer’s, Fuller-Hoy’s, and Butler-Hoy’smethods could not be applied for small settlement load test data ranges. The same is applicable for the (0.25 in) net-settlement criterion. The ultimate pile capacities obtained from the load tests using Chin’s method are almost equal to their counterparts obtained from Rollberg method at failure (plunging). Brinch Hansen's(80%) and van der Veen's methods give lower values. The ultimate pile capacities obtained using the various static methods of predicting skin resistance and point bearing components, spread over a wide range. The finite element analyses via PLAXIS show good agreement to the measured data. They produce failure loads, almost, similar to that obtained from Rollberg interpretation method. The finite element analyses revealed local settlement of (0.6%D – 1.8%D) to mobilize the ultimate skin resistance. The computed unit skin friction ranges between (69 kPa) and (99 kPa). The butt settlement values necessary to produce the ultimate frictional point resistance are (8.6%D – 13.1%D).The computed ultimate bearing stress range is (4880 kPa – 6865 kPa). Figures (14 and 15) can be utilized to calculate the ultimate skin resistance and Reese and O'Neil's (1988) method can be used to calculate the point bearing component. A safety factor of (3) is recommended to predict the allowable pile capacity. All the predicted allowable loads are less than the proposed design loads. REFERENCES [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] ASTM D1143/ D1143M,(2013), “Standard Test Methods for Deep Foundations Under Static Axial Compressive Load”, 11 pp. Fleming, K. and Weltman, A. 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Al Fao Company for Geotechnical and Soil Investigation (Mar, 2017), “Pile Static Load Test, Al-HaramaimBuilding”, (No. 45). http://www.iaeme.com/IJCIET/index.asp 534 [email protected]