Determination of Pile Bearing Capacity By In Situ Tests

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1 Determination of Pile Bearing Caacity By In Situ Tests Qani V. Kadiri Faculty of Civil Engineering and Architecture, Prishtinë, Kosova Abstract - Jablanica is located in the western art of Kosovo along the Drini river. For the uroses of oulation for this art, the government lanned construction of the bridge over the river Drini river to allow movement of the oulation of the surrounding villages across the bridge on the main road Prishtina-Peja. For the foundations of the bridge over the Drini river were alied reinforced bored concrete iles. Bridge consists of two lateral sread footings on iles. Since the terrain where the bridge is suosed consist of layer of soft clay gray colour u to 15m deth, with variable characteristics. For this urose were erformed eight concrete ile length of 15m under foundations on both sides of the river. Piles are adoting the driven ile system Ø80mm. Based on the geotechnical soil arameters obtained from laboratory and field investigations, it is determined the load bearing caacity of two concrete driven iles and also were erformed load-deformation charts for tests iles. Modulus of stiffness of clay layer is determined by field load test of ile. For this urose, are used static enetration test. In order to comare the results, on the ground near the foundations of bridges are made two field ile load test, whereby are obtained results of bearing caacity for the field load test of iles. Key words: bridge abutment, ile, static enetration, bearing caacity, skin friction, field load test. 1. INTRODUCTION For the foundations of the bridge over the Drini river were alied reinforced bored concrete iles. Bridge consists of two lateral sread footings on iles. Since the terrain where the bridge is suosed consist of layer of soft clay gray colour u to 15m deth, with variable characteristics. For this urose were erformed eight concrete ile length of 15m under foundations on both sides of the river. Piles are adoting the driven ilsistem Ø80mm. Based on the geotechnical soil arameters obtained from laboratory and field investigations, it is determined the load bearing caacity of two concrete driven iles and also were erformed load-deformation charts for tests iles. Several In-situ tests can be use to obtain direct measurements of soil roerties and geotechnical arameters. The common tests include: static enetration test, standard enetration (SPT), cone enetration test (CPT), flat dilatometer (DMT), ressuremeter (PMT), and vane shear (VST). Each test alies different loading schemes to measure the corresonding soil resonse in an attemt to evaluate material characteristics, such as strength and stiffness. Modulus of stiffness of clay layer is determined by field ile load test. For this urose, are used static enetration test. In order to comare the results, on the ground near the foundations of bridges are made two field load test of iles, whereby are obtained results of bearing caacity for the field load test of iles. 2. GEOLOGICAL DESCRIPTION OF INVESTIGATED AREA Pliocene sediments - dominate in the region of Jablanica and resented in contact with a diabase-chert formation from Radavc to Vrella. The basic This sediments are reresent by conglomerates, sands, sandy gravel sediments, sand and clay with lignite interlayer s. From drilling conducted in this locality are mostly silty clay dark gray colour with water content over 30%. Dark gray colour aears due to the resence of organic matters (fossils), some of which are redominant Viviarus and Dreissensia, under which was determined their age. Quaternary deosits reresent deosits udates on this region and have greater sread along the river terraces and are reresented by sand and gravel. 2901

2 Fig. 1 Geology ma of terrain 3. GEOTECHNICAL INVESTIGATION BY IN SITU TESTS Static enetration test In the field static enetration tests measure the resistance to enetration of the cone at its enetration in this under the influence of static force. Indentation force is alied by means of hydraulic resses, as well as the cons of cargo using more anchors. Through the hollow tube diameter 36mm freely moving steel rod diameter 15mm at the to of which there is a steel cone. The most common is 36mm diameter cone but is also used by 45mm. Figure 2 shows a cross section through the tube and cone enetrometer. Figure 2. Detail of static enetrometer Static enetration tests carried out in such a way that in the first stage using rods ressed only cone at a deth of 10cm. On this occasion, is measured the cone enetration resistance. The second hase is injected just ie to connect with cone and that when measured by lateral friction. The third hase is ressed cone and tube at the same time by a further 10 cm, so that the total sinking is about 20 cm. At this stage is measured the total enetration resistance. Figure 3 shows the hase of field tests during static enetration tests. 2902

3 Figure 3. Phase of testing in the static enetration tests Resistance to enetration cone following exression: R is given by the P 2 R ( kn / m ) A (1) where: P imress force, A area of cross section of cone. When the cone enetrates the soil around it remains in lastic state (ruture), and resistance to enetration of the cone can be written in the following form: R V bd o (2) 2tg 2 Vbd 1.2 e tg (45 / 2) (3) Where: o is effective stress on the observed deth of the uer soil layers, - internal friction angle of soil. From these relationshis can be through resistance to enetration cone determine the angle of internal friction. However, due to the influence of ore ressure that occur during enetration through coherent materials, this method can t be determined by the angle of friction for coherent layers. Figure 4 shows the relationshi between the coefficients V bd and angle of internal friction. Figure 4. Relationshi between the coefficients V bd and angle of internal friction 4. PILE IN COHESION SOIL LAYER Common rocedure to calculate the limit load of iles consists in determining the caacity of ile base and bearing friction layer, Fig

Static methods for the calculation of limit load can be written in the following form: P P P A f A f s s s (4) where: P - ultimate bearing caacity of the base of ile, A - sectional area base of ile,

4 Static methods for the calculation of limit load can be written in the following form: P P P A f A f s s s (4) where: P - ultimate bearing caacity of the base of ile, A - sectional area base of ile, f s - unite friction layer of ile, A sk surface layer of ile. The calculation of settlement of axial loaded the individual ile that the soil below the base of ile assumed as elastic, isotroic and homogeneous material. Function of linear variable dislacement is given by exression: u A (5) After differentiation is obtained: B (6) General equation that exresses the relationshi between stress and strain is given in the following form: D (7) Where D is matrix of stiffness. Since the coefficients of influence without dimensions are calculated, settlement can be exressed by following simle exression: Fig. 5 Ultimate load-caacity of a ile where: Po - contact stresses under the base of ile, D - diameter of ile base, E - stiffness of soil, o - factor that deends on the form of the load area, 1 - factor that deends on the deth below the ground surface, I w - coefficients of influence without dimensions which deends from thickness of deformable layer under loaded area. To determine the stresses and strains under the base of the ile, the field load test of iles were carried load. The aer resents the results of field exeriments load test on iles whose bases were erformed in noncohesive soils, as well as the results of field static enetration tests, erformed in close examination of test iles. Magnitude of deformation of the soil were determined using the registered settlement of iles during load tests and the results of theoretical solutions for stresses and dislacements of circular foundations, obtained by finite element method. Also, the aer resents the results of field exeriments load test on iles, whose bases were carried out in a coherent materials. On the basis of registered resistance in the static enetration established the connection between secific skin friction and resistance to enetration of the cone. 5. LATERAL FRICTION IN CLAYS Magnitude of secific skin friction in clay materials is often determined by arameters of shear resistance. Zaavaert (1960), Eide (1961), Chandler (1968) have suggested that the lateral friction calculated by using the effective stresses which revailing in the soil: s D o o 1 E (8) I w fs K tg v (9) where: K coefficient of active earth ressure, 2904

5 φ effective internal friction of soil, - vertical effective stress. v Broms and Hellman (1968) recommended the following exression for the calculation of skin friction of iles comressed in soil: fs cu (10) where: c u undrained shear resistance of soil, α coefficient that deends on the undrained shear resistance of soil, Vijayvergiya and Ficht (1972) also include undained shear resistance of soil in exression for determining lateral skin friction: fs ( v 2 su ) (11) where λ - length of ile. Burlan (1973) has suggested following exression for calculation of lateral skin friction: fs v (12) where β= dimensionless coefficient determined from field load tests of iles. Lateral skin friction of ile at clay deosit, according to Meyerhof s (1956, 1976) results of a survey, can aroximately determine the emirical relationshi between soil resistance measured by static or dynamic enetration exeriments and analysis of ile load tests. On the basis of these studying Meyerhof recommends the following terms of the size of skin friction: where: f s N R ; fs (13) N - the number of blows for one foot enetration in the dynamic enetration, R - resistance to enetration of the cone at the static enetration. Meyerhof (1976) also indicated that the average unit frictional resistance, f sv, for high-dislacement driven iles may be obtained from average standard enetration resistance values as: fsv 2N60 (14) Where N 60 average value of standard enetration resistance. For low-dislacement driven ile Pile1 Pile 2 fsv N (15) 60 Fig. 6 Loading unloading curve for ile No.1 and

6 Fig.6 shows the results of field exeriments driven concrete ile load test diameter Ø800mm. Results of field exeriments of static enetration, erformed close examination of test iles, are shown in Fig.7. Size of skin friction is determined based on the results of laboratory tests (12) and the results of field test of enetration (13, 14). Searation of the total caacity of ile on oint load caacity and load caacity by friction along the skin of ile was carried out according to the Van Weele rocedure. From the results, the size of the friction force calculated by equations (14) best agrees with the values of friction force obtained through the Van Weele rocedure. 6. MODULUS OF DEFORMATION OF COHESIVE SOIL Considering that to non-cohesive materials can t be obtained undisturbed samles modulus of deformation of these layers can be determined by field ile load test. For this urose, it is often used static enetration test. Most authors show linear deendence of deformation and resistance of cone enetration. So De Beer (1956) recommends the following exression: E 1.5R (16) Meyerhof and Schmertmann (1970) in a similar way determine the size of deformation: E 2.0R (17) Based on the exeriment of load tests, erformed on several iles, Van Welle (1956) came to the following deendence of deformation and resistance to enetration cone: E 60R 2 (1 ) (18) Fig. 7 Diagram of static enetration for iles No. 1 & 2 Thomas (1968), had concluded that there is a connection between the modulus of deformation and enetration resistance: E (3 12) R (19) while Trofimenkov (1974) recommends the following exression for the calculation of modulus of deformation for clayey materials, resectively: E 4.9R 123 (20) Based on the analysis of results of field load tests on iles Poulos (1979) suggests following limits for the calculation of modulus of deformation for clayey materials, resectively: E (10 40) R (21) All of the exressions assume a linear relationshi of modulus of deformation and resistance of cone enetration. The relationshi between the resistance to enetration of the cone R and comressibility index C is established by Buisman (1948) and exressed as follows: R C V c o (22) It should be noted that this articular size of coefficient Cc should be alied with caution. Based on the results of two field load test on iles, whose bases were erformed in cohesive soils, as well as on the basis of data from field tests of static enetration, is analyzed the deendencies between modulus of deformation and enetration resistance. bd c 2906

7 Results shows the magnitude of modulus of deformation E, determined by means of the above exression and using data obtained from field test load on iles are in good agreement. 7. CONCLUSION Based on obtained results we can conclude that the size of the unit skin friction can be determined using equation (12). The values of fs determined by the exression of Burland are significantly higher than those determined using data from a field load test of ile, while the values determined by the exression of Meyerhof are on the side of safety. It can also be concluded that the rocedures that are often used in ractice (equations 16, 17, 19, 20), we get too low values of modulus of deformation, and their realistic value can be determined according to the exression (21). 8. REFERENCE Bowels, J.E. (1997): Foundation Analysis and Design, The McGraw-Hill Comanies, Inc. Broms, B. And Hellman L. (1968): End bearing and skin friction resistance of iles. Journal of the Soil Mech.and Found. Div. 94, Burland, J.F. (1973) Shaft friction of iles in Clay, a simle foundamental aroach Ground Eng. 6, Das, B.M. (2010): Princiles of Geotechnical Engineering, Seventh Edition. Murthy, V.N.S. (2000): Geotechnical Engineering-Princiles and ractices of soil mechanics and foundation engineering, Meyerhof, G.G. (1956): Penetration tests and bearing caacity of cohesive soils. Ame. Soc. Civ. Eng. Proc. 82. Meyerhof, G.G. (1956): Bearing caacity and settlement of ile foundation. Journal of Geot. Eng. Div. 102, Poulos, H.G., Davis, E.H., (1980): Pile foundation analysis and design, Jon Wiley & Sons, New York Poulos, H.G., (1979): Settlement of single ile in nonhomogenious soil, Journal of Geot. Eng. Div Schmertmann, J.H. (1970): Static cone to coute static settlement over sand. Journal of Soil Mech. Found. Div. 96,

Keywords: pile, liquefaction, lateral spreading, analysis ABSTRACT

Keywords: pile, liquefaction, lateral spreading, analysis ABSTRACT Key arameters in seudo-static analysis of iles in liquefying sand Misko Cubrinovski Deartment of Civil Engineering, University of Canterbury, Christchurch 814, New Zealand Keywords: ile, liquefaction,