Measurement 46 (2013) 3876–3882

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Measurement

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Pullout capacity of irregular shape anchor in sand

0263-2241/$ - see front matter � 2013 Elsevier Ltd. All rights reserved.http://dx.doi.org/10.1016/j.measurement.2013.07.042

⇑ Corresponding author.E-mail address: ham.niroumand@yahoo.com (H. Niroumand).

Hamed Niroumand ⇑, Khairul Anuar KassimDepartment 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 2013Received in revised form 26 July 2013Accepted 29 July 2013Available online 8 August 2013

Keywords:Irregular shape anchorPulloutBreakout FactorGroutExcavation

a b s t r a c t

This paper presents research done on a special type of irregular shape anchor and its pull-out capacity. Many experiments and theoretical studies have been done on the pulloutcapacity of anchors. However the irregular shape anchor is an exception. A normal anchorsystem needs grout and excavation for installation, but installation of the irregular shapeanchor involves driving the anchor into the soil and pulling it out to increase the soil com-pression through rotation of the anchor head. The irregular shape of the anchor presentedis a new anchor system, which is a state of the art product in plate anchor design that doesnot need any grouting or excavation on site. According to studies, the maximum resistanceof the anchor increases depending on the embedment ratio and sand compaction, whichmay be loose or dense sand. The experiments for this irregular shape anchor model witha length of 297 mm were conducted in a chamber box and the embedment ratio L/D usedin this experiment varies between 1 and 4. The weight densities of the dry sand used forloose and dense. The results obtained show that the embedment ratio and sand weightdensity have significant effect on the pullout capacity of the anchor. The pullout capacityincreases with increment of the embedment ratio and sand weight density. Evaluationusing the dimensionless breakout factor also shows that the value increases with incre-menting embedment and sand weight density.

� 2013 Elsevier Ltd. All rights reserved.

1. Introduction

An anchor is an important element widely used in theconstruction process to acquire stability for structures suchas buried pipelines, transmission towers and earth struc-tures. These structures are subjected to considerable verti-cal or horizontal pullout forces and need to be supported.Usually conventional types of anchors are used. Howeverthis type of anchor needs to be grout or excavated duringinstallation. Thus, installation of the system tends to betime consuming due to its procedure. During the last fiftyyears, researches have been looking into anchor pulloutcapacity. However, limited work has been done on differ-ent types of anchors, resulting in very limited conclusions.The aim of this paper is to provide a better understanding

of the pullout capacity of irregular shape anchors, whichwill 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], Mariupol-skii [9], Kananyan [5], Baker and Konder [8], Adams andHayes [6], and many more, mostly dedicated their researchon determining ultimate pullout capacity in sand. Subse-quent variations upon these early theories have been pro-posed, such as Balla [12], who determined the shape of slipsurfaces for horizontal shallow anchors in dense sand. Heproposed a numerical method for estimating the force ofanchors based on the observed shapes of the slip surfaces,as shown in Fig. 1.

While Sutherland [28] in his work, concluded that themode of failure depended on sand weight density andKananyan [5] showed that the inclination angle of the

Fig. 1. Failure surface assumed by Balla. [12].

Fig. 2. Failure surface assumed by Mors. [25].

H. Niroumand, K.A. Kassim / Measurement 46 (2013) 3876–3882 3877

anchors has significant effect on the ultimate pullout force.The pullout force tends to increase with an increase in theinclination angle. Extensive chamber testing programshave been studied by Murray and Geddes [7]. They per-formed pullout loading tests on horizontal strip, circular,and rectangular anchor plates in dense and medium densesand at different aspect ratios (L/B) ranging between 1 and10. The findings of their works show that the sand weightdensity, surface roughness and aspect ratio significantly af-fect the uplift capacity. It is also of interest to note that nocritical embedment depth was seen for all the tests per-formed by Murray and Geddes.

Dickin [1] performed numerous tests on 25 mm anchorplates with aspect ratios of L/B between 1 and 8 at embed-ment ratios H/B up to 8 in both loose and dense sand usingcentrifuge modeling. He concluded that the direct extrapo-lation of conventional chamber box test results to fieldscale would provide over predictions of the ultimate forcefor rectangular anchor plates in sand by more than double.

3. Previous theories

Many theories and numerical analyses on anchor platesobtained from the work of previous researchers such as Ve-sic [4], Sarac [2], Smith [3], and many more, are reportedelsewhere. One of the earliest publications concerning ulti-mate pullout capacity of anchor plates was done by Mors[25], who proposed a failure surface in the soil at ultimateload, which may be approximated as a truncated cone hav-ing an apex angle a equal to (90�+/2) as shown in Fig. 2.The net ultimate pullout capacity was assumed to be equalto the weight of the soil mass bounded by the sides of thecone and the shearing resistance over the failure area sur-face was ignored. This relationship can be written as:

Pu ¼ cV ð1Þ

where V is the volume of the soil in the truncated coneabove 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 assumptionmight lead to unsafe results in many cases with an increasein depth. Clemence and Veesaert [15] showed a formula-

tion for shallow circular anchor in sand, assuming that alinear failure made an angle of b = £/2 with the verticalaxis through the shape of the anchor plate, as shown inFig. 3. The approximate contribution of shearing resistancealong the length of the failure surface was taken into con-sideration by selecting a suitable ground pressure coeffi-cient value from laboratory model works. The netultimate capacity can be given as

Pu ¼ cV þ pcKo tan ; cos2 ;2

� �BD2

2þ

D3 tan ;23

!ð2Þ

where V is the volume of the truncated cone above the an-chor, Ko is the coefficient of lateral earth pressure, with avalue ranging between 0.6 and 1.5. However an averagevalue of 1 is usually used.

The finite element method (FEM) has also been used byVermeer and Sutjiadi [17], Tagaya et al. [20], Tagaya et al.[19], Sakai and Tanaka [18]. Unfortunately, only limitedevidence was obtained in these research works. Generallyonly a few investigations into the performance of ultimatepullout loading in numerical studies in sand were re-corded. Fargic and Marovic [16] analyzed the pulloutcapacity of anchor plates in soil under applied verticalforce. Computation of the pullout and uplift forces wasperformed using the FEM. A more sophisticated constitu-tive law is required for an exact analysis and an adequateFEM code program needs to be prepared. Thus, the meth-ods are quite unpopular among researchers due to its com-

Fig. 3. Failure surface assumed by Clemence and Veesaert. [15].

Fig. 4. Irregular shape anchor dimensions.

Fig. 5. Top view of chamber box during compacting by electricalcompactor.

3878 H. Niroumand, K.A. Kassim / Measurement 46 (2013) 3876–3882

plexity. Merifield and Sloan [24] used many numericalsolutions for analysis of anchor plates. At present, veryfew rigorous numerical analyses have been performed to

determine the pullout capacity of anchor plates in sand.Although it is essential to verify theoretical solutions ornumerical analyses with experimental studies whereverpossible, results selected from laboratory testing alonewere typically specific to a designated problem. Generally,existing numerical analyses assumed a condition of planestrain for the case of a continuous strip anchor plate oraxi-symmetry for the case of circular anchor plates. Theresearchers were unaware of any three-dimensionalnumerical analyses to ascertain the effect of anchor plateshape on the uplift capacity.

4. Laboratory tests programme

Laboratory tests were performed varying the embed-ment ratio from 1 to 4 in loose and dense sand. The localdry sand was used, which generally consists of a grain size

Fig. 6. Rotation steps of the irregular shape anchor.

Fig. 7. Schematic diagram of pullout test arrangement.

Fig. 8. Variations of pullout load with embedment ratio L/D for theirregular shape anchor in loose sand conditions.

H. Niroumand, K.A. Kassim / Measurement 46 (2013) 3876–3882 3879

varying between 0.205 and 2.36 mm. The irregular shapeanchor was fabricated with blade, joints and rods and itwas used as a new anchor with a customized shape, witha length of 297 mm. It was driven into sand and, uponreaching a designated embedment ratio, the rod waspulled up to rotate the anchor. The irregular shape anchormodel is illustrated in Fig. 4.

Two different sand beddings were used, namely looseand dense compaction. The loose and dense compactionprovided an internal friction angle of 35� and 42�, respec-tively. While the weight densities are 14.90 kN/m3 and16.95 kN/m3, for both loose and dense compaction withrelative densities of 25% and 75%, respectively. The loosepacking was obtained by raining the sand from the top ofa chamber box. The chamber box is a relatively large con-tainer 1400 mm long, 700 mm wide and 1500 mm deep. Arectangular container with a hole arranged in a rectangulargrid form was placed at a height of 1200 mm on top of thechamber box in order to obtain the required loose packing.The dense packing sand was compacted by using an elec-trical vibrator at every layer determined and covering all

surfaces as shown in Fig. 5. The placement of the irregularshape anchor during the rotation process is shown in Fig. 6.

Fig. 7 illustrates a schematic view of the pullout testperformed. The pullout test has a motor displacementspeed of 60 mm/min and a load cell was employed in thechamber box attachments.

Fig. 9. Variations of pullout load with embedment ratio L/D for theirregular shape anchor in dense sand conditions.

Fig. 10. Variations of breakout factor with embedment ratio for denseand loose conditions.

3880 H. Niroumand, K.A. Kassim / Measurement 46 (2013) 3876–3882

5. Results and discussions

5.1. Pullout influence factor

The results of the pullout tests of the irregular shape an-chor embedded in loose and dense sand are shown in Figs8 and 9, respectively. Observations were made of theembedment ratio influence on the pullout capacity of theirregular shape anchor. The results graphically presentedin these figures illustrate the maximum model pullout loadagainst displacement ranging between 1 and 4. It is evidentthat the pullout load increases significantly as the embed-ment ratio increases. As expected, the anchor embedded in

Fig. 11. Author’s empirical formula of breakout factor with embedmen

the loose condition exhibits low displacement at low ulti-mate pulling load in comparison to the dense packing con-dition. Lower embedment ratio gives a lower ultimatepullout value at low displacement. Thus it shows that theeffect of sand density does affect the ultimate pulloutcapacity of the irregular anchor. Generally it can be seenthat, for all embedment ratios, the maximum pulloutcapacity shows a consistent difference of three times thevalue of the dense compaction compared to the loose com-paction. Since the anchor used in the testing program isdedicated to a special irregular shape, as shown in Fig. 4above, no attempt to investigate the effect of different sizeswill be made. Logically, the pullout capacity will be in-crease with increments in its geometry properties.

5.2. Breakout factor of the irregular shape anchor in sand

The following results show the variations betweenbreakout factors and embedment ratio. The breakout factorvalue was obtained from the function of Pu where Pu is theultimate capacity pullout load, weight density of loose anddense compaction, L is embedment depth, D is the irregularshape anchor model width and B is the irregular shape an-chor length. It can be seen from Fig. 10 that the breakoutfactor increases with incrementing embedment ratio. Sim-ilar to the earlier observation, the breakout factor value ishigher in dense compaction in comparison with loose com-paction. Thus supporting the evidence that soil density isone of the main factors affecting the pullout capacity ofthe irregular shape anchor.

Figs. 11 and 12 show the authors’ empirical formulas forthe irregular shape anchor models in loose and dense con-ditions, respectively.

5.3. Comparison between results and previous theoreticalanalysis

The relationship between the breakout factor and theembedment ratio derived from current researches andmany theoretical approaches investigating anchors inloose and dense sand compaction were compared withthe authors’ finding. The results of this research, involvingthe irregular shape anchor model, were then compared toprevious theories, such as Balla [12], Meyerhof and Adams

t ratio L/D for irregular shape anchors in loose sand conditions.

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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3882 H. Niroumand, K.A. Kassim / Measurement 46 (2013) 3876–3882

[23], Vesic [4], Rowe and Davis [27], Murray and Geddes[7] and Dickin and Laman [21], as shown in Figs. 13 and14. Fig. 13 shows a comparison of breakout factors be-tween this present research and other research investigat-ing the embedment in loose compaction, while Fig. 14shows the same comparison for dense sand compaction.

According to the results, the limit equilibrium methodof Meyerhof and Adams [23] appears to be the best theo-retical method related to the physical results for both con-ditions. A higher safety factor value needs to be designedand integrated into Murray and Geddes [7] theory for deepanchor plates, while analysis of Rowe and Davis [27] the-ory suggests that a lower safety factor value needs to beestablished. Based on the comparison, the limit equilib-rium method of Meyerhof and Adams [23] appears to bein agreement with the authors’ results. However, Roweand Davis [27] results appear to be conservative, whileMurray and Geddes [7] show the highest value of all theresearchers.

6. Conclusion

The main purpose of this research was to determine theultimate pullout capacity and validation of the irregularshape anchor based in loose and dense sand compaction.The test performed in the chamber box shows that the lim-iting ultimate capacity of the irregular shape anchor modelwas influenced by the embedment ratio and the sandweight density. There is no overall agreement found be-tween the authors’ results and previous theories with re-gard to the breakout factor and the embedment ratio.This was expected since different researchers used differ-ent assumptions in their work. Thus different conclusionsare anticipated. However, close agreement of results werefound in relation to the latter theories for particularembedment ratios and breakout factors. The authors’ pre-diction for the breakout factor for the entire embedmentratio agrees with Rowe’s and Davis’s theory in loose anddense sand. The results show close agreement betweenthe irregular shape anchor model and anchor plates forbreakout factors and the embedment ratio in loose anddense sand compactions. Determining an accurate break-out factor may lead to a complete design of the irregularshape anchor system for cohesionless soil structure, withregards 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 possibilitiesof using breakout factors for the design of further irregularshape anchors.

Acknowledgement

This research was partially supported by the researchGrant at UTM, Malaysia (GUP Grant).

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