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Pullout capacity of irregular shape anchor in sand
Measurement 46 (2013) 3876–3882
Contents lists available at ScienceDirect
Measurement journal homepage: www.elsevier.com/locate/measurement
Pullout capacity of irregular shape anchor in sand Hamed Niroumand ⇑, Khairul Anuar Kassim Department of Geotechnical Engineering, Faculty of Civil Engineering, University Technology Malaysia (UTM), 81310 Skudai, Johor, Malaysia
a r t i c l e
i n f o
Article history: Received 8 April 2013 Received in revised form 26 July 2013 Accepted 29 July 2013 Available online 8 August 2013 Keywords: Irregular shape anchor Pullout Breakout Factor Grout Excavation
a b s t r a c t This paper presents research done on a special type of irregular shape anchor and its pullout capacity. Many experiments and theoretical studies have been done on the pullout capacity of anchors. However the irregular shape anchor is an exception. A normal anchor system needs grout and excavation for installation, but installation of the irregular shape anchor involves driving the anchor into the soil and pulling it out to increase the soil compression through rotation of the anchor head. The irregular shape of the anchor presented is a new anchor system, which is a state of the art product in plate anchor design that does not need any grouting or excavation on site. According to studies, the maximum resistance of the anchor increases depending on the embedment ratio and sand compaction, which may be loose or dense sand. The experiments for this irregular shape anchor model with a length of 297 mm were conducted in a chamber box and the embedment ratio L/D used in this experiment varies between 1 and 4. The weight densities of the dry sand used for loose and dense. The results obtained show that the embedment ratio and sand weight density have significant effect on the pullout capacity of the anchor. The pullout capacity increases with increment of the embedment ratio and sand weight density. Evaluation using the dimensionless breakout factor also shows that the value increases with incrementing embedment and sand weight density. Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction An anchor is an important element widely used in the construction process to acquire stability for structures such as buried pipelines, transmission towers and earth structures. These structures are subjected to considerable vertical or horizontal pullout forces and need to be supported. Usually conventional types of anchors are used. However this type of anchor needs to be grout or excavated during installation. Thus, installation of the system tends to be time consuming due to its procedure. During the last fifty years, researches have been looking into anchor pullout capacity. However, limited work has been done on different types of anchors, resulting in very limited conclusions. The aim of this paper is to provide a better understanding
⇑ Corresponding author. E-mail address: [email protected] (H. Niroumand). 0263-2241/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.measurement.2013.07.042
of the pullout capacity of irregular shape anchors, which will provide useful information to the related field.
2. Previous experimental research works Researchers such as Mors [25], Giffels et al. [22], Balla [12], Turner [10], Ireland [11], Sutherland [28], Mariupolskii [9], Kananyan [5], Baker and Konder [8], Adams and Hayes [6], and many more, mostly dedicated their research on determining ultimate pullout capacity in sand. Subsequent variations upon these early theories have been proposed, such as Balla [12], who determined the shape of slip surfaces for horizontal shallow anchors in dense sand. He proposed a numerical method for estimating the force of anchors based on the observed shapes of the slip surfaces, as shown in Fig. 1. While Sutherland [28] in his work, concluded that the mode of failure depended on sand weight density and Kananyan [5] showed that the inclination angle of the
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Fig. 1. Failure surface assumed by Balla. [12].
anchors has significant effect on the ultimate pullout force. The pullout force tends to increase with an increase in the inclination angle. Extensive chamber testing programs have been studied by Murray and Geddes [7]. They performed pullout loading tests on horizontal strip, circular, and rectangular anchor plates in dense and medium dense sand at different aspect ratios (L/B) ranging between 1 and 10. The findings of their works show that the sand weight density, surface roughness and aspect ratio significantly affect the uplift capacity. It is also of interest to note that no critical embedment depth was seen for all the tests performed by Murray and Geddes. Dickin [1] performed numerous tests on 25 mm anchor plates with aspect ratios of L/B between 1 and 8 at embedment ratios H/B up to 8 in both loose and dense sand using centrifuge modeling. He concluded that the direct extrapolation of conventional chamber box test results to field scale would provide over predictions of the ultimate force for rectangular anchor plates in sand by more than double. 3. Previous theories Many theories and numerical analyses on anchor plates obtained from the work of previous researchers such as Vesic [4], Sarac [2], Smith [3], and many more, are reported elsewhere. One of the earliest publications concerning ultimate pullout capacity of anchor plates was done by Mors [25], who proposed a failure surface in the soil at ultimate load, which may be approximated as a truncated cone having an apex angle a equal to (90°+/2) as shown in Fig. 2. The net ultimate pullout capacity was assumed to be equal to the weight of the soil mass bounded by the sides of the cone and the shearing resistance over the failure area surface was ignored. This relationship can be written as:
Pu ¼ cV
ð1Þ
where V is the volume of the soil in the truncated cone above the anchor, c is the unit weight of soil. Downs and Chieurzzi [14], based on similar theories, investigated that the apex angle is always equal to 60°, irrespective of friction angle of the soil. However, Teng [13] and Sutherland (1988) found that this assumption might lead to unsafe results in many cases with an increase in depth. Clemence and Veesaert [15] showed a formula-
Fig. 2. Failure surface assumed by Mors. [25].
tion for shallow circular anchor in sand, assuming that a linear failure made an angle of b = £/2 with the vertical axis through the shape of the anchor plate, as shown in Fig. 3. The approximate contribution of shearing resistance along the length of the failure surface was taken into consideration by selecting a suitable ground pressure coefficient value from laboratory model works. The net ultimate capacity can be given as
! 3 ; BD2 D tan 2; Pu ¼ cV þ pcK o tan ; cos þ 2 2 3 2
ð2Þ
where V is the volume of the truncated cone above the anchor, Ko is the coefficient of lateral earth pressure, with a value ranging between 0.6 and 1.5. However an average value of 1 is usually used. The finite element method (FEM) has also been used by Vermeer and Sutjiadi [17], Tagaya et al. [20], Tagaya et al. [19], Sakai and Tanaka [18]. Unfortunately, only limited evidence was obtained in these research works. Generally only a few investigations into the performance of ultimate pullout loading in numerical studies in sand were recorded. Fargic and Marovic [16] analyzed the pullout capacity of anchor plates in soil under applied vertical force. Computation of the pullout and uplift forces was performed using the FEM. A more sophisticated constitutive law is required for an exact analysis and an adequate FEM code program needs to be prepared. Thus, the methods are quite unpopular among researchers due to its com-
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Fig. 3. Failure surface assumed by Clemence and Veesaert. [15].
Fig. 5. Top view of chamber box during compacting by electrical compactor.
determine the pullout capacity of anchor plates in sand. Although it is essential to verify theoretical solutions or numerical analyses with experimental studies wherever possible, results selected from laboratory testing alone were typically specific to a designated problem. Generally, existing numerical analyses assumed a condition of plane strain for the case of a continuous strip anchor plate or axi-symmetry for the case of circular anchor plates. The researchers were unaware of any three-dimensional numerical analyses to ascertain the effect of anchor plate shape on the uplift capacity. Fig. 4. Irregular shape anchor dimensions.
plexity. Merifield and Sloan [24] used many numerical solutions for analysis of anchor plates. At present, very few rigorous numerical analyses have been performed to
4. Laboratory tests programme Laboratory tests were performed varying the embedment ratio from 1 to 4 in loose and dense sand. The local dry sand was used, which generally consists of a grain size
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Fig. 6. Rotation steps of the irregular shape anchor.
Fig. 7. Schematic diagram of pullout test arrangement.
varying between 0.205 and 2.36 mm. The irregular shape anchor was fabricated with blade, joints and rods and it was used as a new anchor with a customized shape, with a length of 297 mm. It was driven into sand and, upon reaching a designated embedment ratio, the rod was pulled up to rotate the anchor. The irregular shape anchor model is illustrated in Fig. 4. Two different sand beddings were used, namely loose and dense compaction. The loose and dense compaction provided an internal friction angle of 35° and 42°, respectively. While the weight densities are 14.90 kN/m3 and 16.95 kN/m3, for both loose and dense compaction with relative densities of 25% and 75%, respectively. The loose packing was obtained by raining the sand from the top of a chamber box. The chamber box is a relatively large container 1400 mm long, 700 mm wide and 1500 mm deep. A rectangular container with a hole arranged in a rectangular grid form was placed at a height of 1200 mm on top of the chamber box in order to obtain the required loose packing. The dense packing sand was compacted by using an electrical vibrator at every layer determined and covering all
Fig. 8. Variations of pullout load with embedment ratio L/D for the irregular shape anchor in loose sand conditions.
surfaces as shown in Fig. 5. The placement of the irregular shape anchor during the rotation process is shown in Fig. 6. Fig. 7 illustrates a schematic view of the pullout test performed. The pullout test has a motor displacement speed of 60 mm/min and a load cell was employed in the chamber box attachments.
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Fig. 9. Variations of pullout load with embedment ratio L/D for the irregular shape anchor in dense sand conditions.
the loose condition exhibits low displacement at low ultimate pulling load in comparison to the dense packing condition. Lower embedment ratio gives a lower ultimate pullout value at low displacement. Thus it shows that the effect of sand density does affect the ultimate pullout capacity of the irregular anchor. Generally it can be seen that, for all embedment ratios, the maximum pullout capacity shows a consistent difference of three times the value of the dense compaction compared to the loose compaction. Since the anchor used in the testing program is dedicated to a special irregular shape, as shown in Fig. 4 above, no attempt to investigate the effect of different sizes will be made. Logically, the pullout capacity will be increase with increments in its geometry properties. 5.2. Breakout factor of the irregular shape anchor in sand
Fig. 10. Variations of breakout factor with embedment ratio for dense and loose conditions.
5. Results and discussions
The following results show the variations between breakout factors and embedment ratio. The breakout factor value was obtained from the function of Pu where Pu is the ultimate capacity pullout load, weight density of loose and dense compaction, L is embedment depth, D is the irregular shape anchor model width and B is the irregular shape anchor length. It can be seen from Fig. 10 that the breakout factor increases with incrementing embedment ratio. Similar to the earlier observation, the breakout factor value is higher in dense compaction in comparison with loose compaction. Thus supporting the evidence that soil density is one of the main factors affecting the pullout capacity of the irregular shape anchor. Figs. 11 and 12 show the authors’ empirical formulas for the irregular shape anchor models in loose and dense conditions, respectively.
5.1. Pullout influence factor The results of the pullout tests of the irregular shape anchor embedded in loose and dense sand are shown in Figs 8 and 9, respectively. Observations were made of the embedment ratio influence on the pullout capacity of the irregular shape anchor. The results graphically presented in these figures illustrate the maximum model pullout load against displacement ranging between 1 and 4. It is evident that the pullout load increases significantly as the embedment ratio increases. As expected, the anchor embedded in
5.3. Comparison between results and previous theoretical analysis The relationship between the breakout factor and the embedment ratio derived from current researches and many theoretical approaches investigating anchors in loose and dense sand compaction were compared with the authors’ finding. The results of this research, involving the irregular shape anchor model, were then compared to previous theories, such as Balla [12], Meyerhof and Adams
Fig. 11. Author’s empirical formula of breakout factor with embedment ratio L/D for irregular shape anchors in loose sand conditions.
H. Niroumand, K.A. Kassim / Measurement 46 (2013) 3876–3882
Fig. 12. Author’s empirical formula of breakout factor with embedment ratio L/D for irregular shape anchor in dense sand conditions.
Fig. 13. Comparison of author’s breakout factor results of the irregular shape anchor with other researches in loose sand (RD = 25%).
Fig. 14. Comparison of author’s breakout factor results of the irregular shape anchor with other researches in dense sand (RD = 75%).
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[23], Vesic [4], Rowe and Davis [27], Murray and Geddes [7] and Dickin and Laman [21], as shown in Figs. 13 and 14. Fig. 13 shows a comparison of breakout factors between this present research and other research investigating the embedment in loose compaction, while Fig. 14 shows the same comparison for dense sand compaction. According to the results, the limit equilibrium method of Meyerhof and Adams [23] appears to be the best theoretical method related to the physical results for both conditions. A higher safety factor value needs to be designed and integrated into Murray and Geddes [7] theory for deep anchor plates, while analysis of Rowe and Davis [27] theory suggests that a lower safety factor value needs to be established. Based on the comparison, the limit equilibrium method of Meyerhof and Adams [23] appears to be in agreement with the authors’ results. However, Rowe and Davis [27] results appear to be conservative, while Murray and Geddes [7] show the highest value of all the researchers. 6. Conclusion The main purpose of this research was to determine the ultimate pullout capacity and validation of the irregular shape anchor based in loose and dense sand compaction. The test performed in the chamber box shows that the limiting ultimate capacity of the irregular shape anchor model was influenced by the embedment ratio and the sand weight density. There is no overall agreement found between the authors’ results and previous theories with regard to the breakout factor and the embedment ratio. This was expected since different researchers used different assumptions in their work. Thus different conclusions are anticipated. However, close agreement of results were found in relation to the latter theories for particular embedment ratios and breakout factors. The authors’ prediction for the breakout factor for the entire embedment ratio agrees with Rowe’s and Davis’s theory in loose and dense sand. The results show close agreement between the irregular shape anchor model and anchor plates for breakout factors and the embedment ratio in loose and dense sand compactions. Determining an accurate breakout factor may lead to a complete design of the irregular shape anchor system for cohesionless soil structure, with regards to the validation of results with different theories. Although the work is not dedicated to any field subgrade, the findings are invaluable in exploring the possibilities of using breakout factors for the design of further irregular shape anchors. Acknowledgement This research was partially supported by the research Grant at UTM, Malaysia (GUP Grant).
References [1] E.A. Dickin, Uplift behaviour of horizontal anchor plates in sand, J. Geotech. Eng. 114 (11) (1988) 1300–1317. [2] D.Z. Sarac, Uplift capacity of shallow buried anchor slabs, in: Proceedings of 12th International Conference on Soil Mechanics and Foundation Engineering, vol. 12, no. 2, 1989, pp. 1213–1218. [3] C.C. Smith, Limit loads for an anchor/trapdoor embedded in an associated coulomb soil, Int. J. Numer. Anal. Methods Geomech. 22 (11) (1998) 855–865. [4] A.S. Vesic, Breakout resistance of objects embedded in ocean bottom, J. Soil Mech. Found. Div. ASCE 97 (9) (1971) 1183–1205. [5] A.S. Kananyan, Experimental investigation of the stability of bases of anchor foundations, Osnovanlya, Fundamenty i mekhanik Gruntov 4 (6) (1966) 387–392. [6] J.I. Adams, D.C. Hayes, The uplift capacity of shallow foundations, Ont. Hydro-Res. Quart. 16 (1) (1967) 1–2. [7] E.J. Murray, J.D. Geddes, Uplift of anchor plates in sand, J. Geotech. Eng. ASCE 113 (3) (1987) 202–215. [8] W.H. Baker, R.L. Konder, Pullout load capacity of a circular earth anchor buried in sand, Highway Res. Rec. 108 (1966) 1–10. [9] L.G. Mariupolskii, The bearing capacity of anchor foundations, SMFE, Osnovanlya, Fundamenty i mekhanik Gruntov 3 (1) (1965) 14–18. [10] E.Z. Turner, Uplift resistance of transmission tower footings, J. Power Div. ASCE 88 (PO2) (1962) 17–33. [11] H.O. Ireland, Uplift resistance of transmission tower foundations: discussion, J. Power Div. ASCE 89 (PO1) (1963) 115–118. [12] A. Balla, The resistance of breaking-out of mushroom foundations for pylons, in: Proceedings, 5th International Conference on Soil Mechanics and Foundation Engineering, vol. 1, Paris, 1961, pp. 569–576. [13] W.C. Teng, Foundation Design, Prentice-Hall, Englewood cliffs, New Jersey, USA, 1962. [14] D.I. Downs, R. Chieurzzi, Transmission tower foundations, J. Power Div. ASCE 88 (2) (1966) 91–114. [15] S.P. Clemence, C.J. Veesaert, Dynamic pullout resistance of anchors in sand, in: Int. Symp. on Soil Struct Interaction, Roorkee, India, 3 January 1977 through 7 January 1977, pp. 389–397. [16] L. Fargic, P. Marovic, Pullout capacity of spatial anchors, J. Eng. Comput. 21 (6) (2003) 598–700. [17] P.A. Vermeer, W. Sutjiadi, The uplift resistance of shallow embedded anchors, in: Proceedings, 11th International Conference on Soil Mechanics and Foundation Engineering, San Francisco, vol. 4, 1985, pp. 1635–1638. [18] T. Sakai, T. Tanaka, Scale effect of a shallow circular anchor in dense sand, Soils Found. Jpn. 38 (2) (1998) 93–99. [19] K. Tagaya, R.F. Scott, H. Aboshi, Pullout resistance of buried anchor in sand, Soils Found. Jpn. 28 (3) (1988) 114–130. [20] K. Tagaya, A. Tanaka, H. Aboshi, Application of finite element method to pullout resistance of buried anchor, Soils Found. Jpn. 23 (3) (1983) 91–104. [21] E.A. Dickin, M. Laman, Uplift response of strip anchors in cohesionless soil, J. Adv. Eng. Software 1 (38) (2007) 618–625. [22] W.C. Giffels, R.E. Graham, J.F. Mook, Concrete cylinder anchors, Electrical World 154 (1960) 46–49. [23] G.G. Meyerhof, J.I. Adams, The ultimate uplift capacity of foundations, Can. Geotech. J. 5 (4) (1968) 225–244. [24] R.S. Merifield, S.W. Sloan, The ultimate pullout capacity of anchors in frictional soils, Can. Geotech. J. 43 (8) (2006) 852–868. [25] H. Mors, The behavior of most foundations subjected to tensile forces, Bautechnik 36 (10) (1959) 367–378. [27] R.K. Rowe, E.H. Davis, The behaviour of anchor plates in sand, Geotechnique 32 (1) (1982) 25–41. [28] H.B. Sutherland, Model studies for shaft raising through cohesionless soils, in: Proceedings, 6th International Conference on Soil Mechanics and Foundation Engineering, vol. 2, 1965, pp. 410–413.
Contents lists available at ScienceDirect
Measurement journal homepage: www.elsevier.com/locate/measurement
Pullout capacity of irregular shape anchor in sand Hamed Niroumand ⇑, Khairul Anuar Kassim Department of Geotechnical Engineering, Faculty of Civil Engineering, University Technology Malaysia (UTM), 81310 Skudai, Johor, Malaysia
a r t i c l e
i n f o
Article history: Received 8 April 2013 Received in revised form 26 July 2013 Accepted 29 July 2013 Available online 8 August 2013 Keywords: Irregular shape anchor Pullout Breakout Factor Grout Excavation
a b s t r a c t This paper presents research done on a special type of irregular shape anchor and its pullout capacity. Many experiments and theoretical studies have been done on the pullout capacity of anchors. However the irregular shape anchor is an exception. A normal anchor system needs grout and excavation for installation, but installation of the irregular shape anchor involves driving the anchor into the soil and pulling it out to increase the soil compression through rotation of the anchor head. The irregular shape of the anchor presented is a new anchor system, which is a state of the art product in plate anchor design that does not need any grouting or excavation on site. According to studies, the maximum resistance of the anchor increases depending on the embedment ratio and sand compaction, which may be loose or dense sand. The experiments for this irregular shape anchor model with a length of 297 mm were conducted in a chamber box and the embedment ratio L/D used in this experiment varies between 1 and 4. The weight densities of the dry sand used for loose and dense. The results obtained show that the embedment ratio and sand weight density have significant effect on the pullout capacity of the anchor. The pullout capacity increases with increment of the embedment ratio and sand weight density. Evaluation using the dimensionless breakout factor also shows that the value increases with incrementing embedment and sand weight density. Ó 2013 Elsevier Ltd. All rights reserved.
1. Introduction An anchor is an important element widely used in the construction process to acquire stability for structures such as buried pipelines, transmission towers and earth structures. These structures are subjected to considerable vertical or horizontal pullout forces and need to be supported. Usually conventional types of anchors are used. However this type of anchor needs to be grout or excavated during installation. Thus, installation of the system tends to be time consuming due to its procedure. During the last fifty years, researches have been looking into anchor pullout capacity. However, limited work has been done on different types of anchors, resulting in very limited conclusions. The aim of this paper is to provide a better understanding
⇑ Corresponding author. E-mail address: [email protected] (H. Niroumand). 0263-2241/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.measurement.2013.07.042
of the pullout capacity of irregular shape anchors, which will provide useful information to the related field.
2. Previous experimental research works Researchers such as Mors [25], Giffels et al. [22], Balla [12], Turner [10], Ireland [11], Sutherland [28], Mariupolskii [9], Kananyan [5], Baker and Konder [8], Adams and Hayes [6], and many more, mostly dedicated their research on determining ultimate pullout capacity in sand. Subsequent variations upon these early theories have been proposed, such as Balla [12], who determined the shape of slip surfaces for horizontal shallow anchors in dense sand. He proposed a numerical method for estimating the force of anchors based on the observed shapes of the slip surfaces, as shown in Fig. 1. While Sutherland [28] in his work, concluded that the mode of failure depended on sand weight density and Kananyan [5] showed that the inclination angle of the
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Fig. 1. Failure surface assumed by Balla. [12].
anchors has significant effect on the ultimate pullout force. The pullout force tends to increase with an increase in the inclination angle. Extensive chamber testing programs have been studied by Murray and Geddes [7]. They performed pullout loading tests on horizontal strip, circular, and rectangular anchor plates in dense and medium dense sand at different aspect ratios (L/B) ranging between 1 and 10. The findings of their works show that the sand weight density, surface roughness and aspect ratio significantly affect the uplift capacity. It is also of interest to note that no critical embedment depth was seen for all the tests performed by Murray and Geddes. Dickin [1] performed numerous tests on 25 mm anchor plates with aspect ratios of L/B between 1 and 8 at embedment ratios H/B up to 8 in both loose and dense sand using centrifuge modeling. He concluded that the direct extrapolation of conventional chamber box test results to field scale would provide over predictions of the ultimate force for rectangular anchor plates in sand by more than double. 3. Previous theories Many theories and numerical analyses on anchor plates obtained from the work of previous researchers such as Vesic [4], Sarac [2], Smith [3], and many more, are reported elsewhere. One of the earliest publications concerning ultimate pullout capacity of anchor plates was done by Mors [25], who proposed a failure surface in the soil at ultimate load, which may be approximated as a truncated cone having an apex angle a equal to (90°+/2) as shown in Fig. 2. The net ultimate pullout capacity was assumed to be equal to the weight of the soil mass bounded by the sides of the cone and the shearing resistance over the failure area surface was ignored. This relationship can be written as:
Pu ¼ cV
ð1Þ
where V is the volume of the soil in the truncated cone above the anchor, c is the unit weight of soil. Downs and Chieurzzi [14], based on similar theories, investigated that the apex angle is always equal to 60°, irrespective of friction angle of the soil. However, Teng [13] and Sutherland (1988) found that this assumption might lead to unsafe results in many cases with an increase in depth. Clemence and Veesaert [15] showed a formula-
Fig. 2. Failure surface assumed by Mors. [25].
tion for shallow circular anchor in sand, assuming that a linear failure made an angle of b = £/2 with the vertical axis through the shape of the anchor plate, as shown in Fig. 3. The approximate contribution of shearing resistance along the length of the failure surface was taken into consideration by selecting a suitable ground pressure coefficient value from laboratory model works. The net ultimate capacity can be given as
! 3 ; BD2 D tan 2; Pu ¼ cV þ pcK o tan ; cos þ 2 2 3 2
ð2Þ
where V is the volume of the truncated cone above the anchor, Ko is the coefficient of lateral earth pressure, with a value ranging between 0.6 and 1.5. However an average value of 1 is usually used. The finite element method (FEM) has also been used by Vermeer and Sutjiadi [17], Tagaya et al. [20], Tagaya et al. [19], Sakai and Tanaka [18]. Unfortunately, only limited evidence was obtained in these research works. Generally only a few investigations into the performance of ultimate pullout loading in numerical studies in sand were recorded. Fargic and Marovic [16] analyzed the pullout capacity of anchor plates in soil under applied vertical force. Computation of the pullout and uplift forces was performed using the FEM. A more sophisticated constitutive law is required for an exact analysis and an adequate FEM code program needs to be prepared. Thus, the methods are quite unpopular among researchers due to its com-
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Fig. 3. Failure surface assumed by Clemence and Veesaert. [15].
Fig. 5. Top view of chamber box during compacting by electrical compactor.
determine the pullout capacity of anchor plates in sand. Although it is essential to verify theoretical solutions or numerical analyses with experimental studies wherever possible, results selected from laboratory testing alone were typically specific to a designated problem. Generally, existing numerical analyses assumed a condition of plane strain for the case of a continuous strip anchor plate or axi-symmetry for the case of circular anchor plates. The researchers were unaware of any three-dimensional numerical analyses to ascertain the effect of anchor plate shape on the uplift capacity. Fig. 4. Irregular shape anchor dimensions.
plexity. Merifield and Sloan [24] used many numerical solutions for analysis of anchor plates. At present, very few rigorous numerical analyses have been performed to
4. Laboratory tests programme Laboratory tests were performed varying the embedment ratio from 1 to 4 in loose and dense sand. The local dry sand was used, which generally consists of a grain size
H. Niroumand, K.A. Kassim / Measurement 46 (2013) 3876–3882
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Fig. 6. Rotation steps of the irregular shape anchor.
Fig. 7. Schematic diagram of pullout test arrangement.
varying between 0.205 and 2.36 mm. The irregular shape anchor was fabricated with blade, joints and rods and it was used as a new anchor with a customized shape, with a length of 297 mm. It was driven into sand and, upon reaching a designated embedment ratio, the rod was pulled up to rotate the anchor. The irregular shape anchor model is illustrated in Fig. 4. Two different sand beddings were used, namely loose and dense compaction. The loose and dense compaction provided an internal friction angle of 35° and 42°, respectively. While the weight densities are 14.90 kN/m3 and 16.95 kN/m3, for both loose and dense compaction with relative densities of 25% and 75%, respectively. The loose packing was obtained by raining the sand from the top of a chamber box. The chamber box is a relatively large container 1400 mm long, 700 mm wide and 1500 mm deep. A rectangular container with a hole arranged in a rectangular grid form was placed at a height of 1200 mm on top of the chamber box in order to obtain the required loose packing. The dense packing sand was compacted by using an electrical vibrator at every layer determined and covering all
Fig. 8. Variations of pullout load with embedment ratio L/D for the irregular shape anchor in loose sand conditions.
surfaces as shown in Fig. 5. The placement of the irregular shape anchor during the rotation process is shown in Fig. 6. Fig. 7 illustrates a schematic view of the pullout test performed. The pullout test has a motor displacement speed of 60 mm/min and a load cell was employed in the chamber box attachments.
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Fig. 9. Variations of pullout load with embedment ratio L/D for the irregular shape anchor in dense sand conditions.
the loose condition exhibits low displacement at low ultimate pulling load in comparison to the dense packing condition. Lower embedment ratio gives a lower ultimate pullout value at low displacement. Thus it shows that the effect of sand density does affect the ultimate pullout capacity of the irregular anchor. Generally it can be seen that, for all embedment ratios, the maximum pullout capacity shows a consistent difference of three times the value of the dense compaction compared to the loose compaction. Since the anchor used in the testing program is dedicated to a special irregular shape, as shown in Fig. 4 above, no attempt to investigate the effect of different sizes will be made. Logically, the pullout capacity will be increase with increments in its geometry properties. 5.2. Breakout factor of the irregular shape anchor in sand
Fig. 10. Variations of breakout factor with embedment ratio for dense and loose conditions.
5. Results and discussions
The following results show the variations between breakout factors and embedment ratio. The breakout factor value was obtained from the function of Pu where Pu is the ultimate capacity pullout load, weight density of loose and dense compaction, L is embedment depth, D is the irregular shape anchor model width and B is the irregular shape anchor length. It can be seen from Fig. 10 that the breakout factor increases with incrementing embedment ratio. Similar to the earlier observation, the breakout factor value is higher in dense compaction in comparison with loose compaction. Thus supporting the evidence that soil density is one of the main factors affecting the pullout capacity of the irregular shape anchor. Figs. 11 and 12 show the authors’ empirical formulas for the irregular shape anchor models in loose and dense conditions, respectively.
5.1. Pullout influence factor The results of the pullout tests of the irregular shape anchor embedded in loose and dense sand are shown in Figs 8 and 9, respectively. Observations were made of the embedment ratio influence on the pullout capacity of the irregular shape anchor. The results graphically presented in these figures illustrate the maximum model pullout load against displacement ranging between 1 and 4. It is evident that the pullout load increases significantly as the embedment ratio increases. As expected, the anchor embedded in
5.3. Comparison between results and previous theoretical analysis The relationship between the breakout factor and the embedment ratio derived from current researches and many theoretical approaches investigating anchors in loose and dense sand compaction were compared with the authors’ finding. The results of this research, involving the irregular shape anchor model, were then compared to previous theories, such as Balla [12], Meyerhof and Adams
Fig. 11. Author’s empirical formula of breakout factor with embedment ratio L/D for irregular shape anchors in loose sand conditions.
H. Niroumand, K.A. Kassim / Measurement 46 (2013) 3876–3882
Fig. 12. Author’s empirical formula of breakout factor with embedment ratio L/D for irregular shape anchor in dense sand conditions.
Fig. 13. Comparison of author’s breakout factor results of the irregular shape anchor with other researches in loose sand (RD = 25%).
Fig. 14. Comparison of author’s breakout factor results of the irregular shape anchor with other researches in dense sand (RD = 75%).
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[23], Vesic [4], Rowe and Davis [27], Murray and Geddes [7] and Dickin and Laman [21], as shown in Figs. 13 and 14. Fig. 13 shows a comparison of breakout factors between this present research and other research investigating the embedment in loose compaction, while Fig. 14 shows the same comparison for dense sand compaction. According to the results, the limit equilibrium method of Meyerhof and Adams [23] appears to be the best theoretical method related to the physical results for both conditions. A higher safety factor value needs to be designed and integrated into Murray and Geddes [7] theory for deep anchor plates, while analysis of Rowe and Davis [27] theory suggests that a lower safety factor value needs to be established. Based on the comparison, the limit equilibrium method of Meyerhof and Adams [23] appears to be in agreement with the authors’ results. However, Rowe and Davis [27] results appear to be conservative, while Murray and Geddes [7] show the highest value of all the researchers. 6. Conclusion The main purpose of this research was to determine the ultimate pullout capacity and validation of the irregular shape anchor based in loose and dense sand compaction. The test performed in the chamber box shows that the limiting ultimate capacity of the irregular shape anchor model was influenced by the embedment ratio and the sand weight density. There is no overall agreement found between the authors’ results and previous theories with regard to the breakout factor and the embedment ratio. This was expected since different researchers used different assumptions in their work. Thus different conclusions are anticipated. However, close agreement of results were found in relation to the latter theories for particular embedment ratios and breakout factors. The authors’ prediction for the breakout factor for the entire embedment ratio agrees with Rowe’s and Davis’s theory in loose and dense sand. The results show close agreement between the irregular shape anchor model and anchor plates for breakout factors and the embedment ratio in loose and dense sand compactions. Determining an accurate breakout factor may lead to a complete design of the irregular shape anchor system for cohesionless soil structure, with regards to the validation of results with different theories. Although the work is not dedicated to any field subgrade, the findings are invaluable in exploring the possibilities of using breakout factors for the design of further irregular shape anchors. Acknowledgement This research was partially supported by the research Grant at UTM, Malaysia (GUP Grant).
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