ORIGINAL PAPER

Uplift response of symmetrical anchor plates in reinforcedcohesionless soil

Hamed Niroumand & Khairul Anuar Kassim

Received: 12 December 2012 /Accepted: 7 August 2013# Saudi Society for Geosciences 2013

Abstract The uplift response of symmetrical anchor plateswith and without geogrid reinforcement layers has been eval-uated in model tests and numerical simulations usingPLAXIS. Many parameters of the reinforcement layers wereused to reinforce the sandy soil over circular, square, andrectangular symmetrical anchor plates of various sizes. Inthe current research, different parameters, such as relativedensity of sand and embedment ratios, in conjunction withgeogrid reinforcement layer parameters including size, num-ber of layers, and the proximity of the layer to the circularanchor plate, were investigated in a scale model. The failuremechanism and the associated rupture surface were observedand evaluated. Test results showed that using geogrid rein-forcement layers significantly improves the uplift capacity ofsymmetrical anchor plates. It was found that inclusion of onegeogrid layer resting directly on top of the symmetrical anchorplate was more effective in enhancing the symmetrical anchorcapacity than the layer itself. It was also found that theinclusion of one geogrid layer on the symmetrical anchor plateimproved the uplift capacity more than the same symmetricalanchor plate embedded without a reinforcement layer. Thesingle geogrid layer was also more effective in enhancing theuplift capacity compared to the multiple geogrid layer rein-forcement approach. In general, the results show that the upliftcapacity of symmetrical anchor plates in loose and dense sandcan be significantly increased by the inclusion of geogridlayers. It was also observed that the inclusion of geogrid layersreduces the requirement for a higher L /D ratio to achieve therequired uplift capacity. The results of the laboratory and

numerical analysis are found to be in agreement in terms ofthe breakout factor and failure mechanism pattern.

Keywords Uplift response . Symmetrical anchor plate .

Circular plate . Square plate . Rectangular plate . Geogrid .

PLAXIS

Introduction

The designs of many structures need their foundation systemsto resist vertical or horizontal uplift loads. Thus, to improvethe performance of foundation systems, many guidelines forthe design and installation of anchor systems have been de-veloped. Different structures like transmission towers, tun-nels, sea walls, buried pipelines, retaining walls, etc. aresubjected to considerable uplift forces. In such structures,using tension members can prove to be an absorbing and aneconomic design solution. These tension members are anchorelements that are generally fixed to the structure and areembedded into the ground to a considerable depth so that theycan resist uplifting forces and also provide more safety to thestructure. The influence of different parameters on the upliftresponse of horizontal anchor plates in sand has been investi-gated by many researchers. Many studies (Mors 1959; Giffelset al. 1960; Balla 1961; Turner 1962; Ireland 1963; Sutherland1965; Mariupolskii 1965; Kananyan 1966; Baker and Konder1966; Adams and Hayes 1967; Andreadis et al. 1981; Dickin1988; Frydman and Shamam 1989; Ramesh Babu 1998;Krishna 2000; Fargic and Marovic 2003; Merifield and Sloan2006; Dickin and Laman 2007; Kumar and Bhoi 2008; andKouzer and Kumar 2009) have resulted in a general solutionfor an ultimate uplift capacity of anchor plates based onexperimental works in sand. In addition to this, the works ofMeyerhof and Adams (1968) until the more current works ofKuzar and Kumar (2009) investigating the behavior of sym-metrical anchor plates have also been reviewed. Further

H. Niroumand (*) :K. A. KassimDepartment of Geotechnical Engineering, Faculty of CivilEngineering, Universiti Teknologi Malaysia, Skudai, Johor Bahru,Malaysiae-mail: ham.niroumand@yahoo.com

Arab J GeosciDOI 10.1007/s12517-013-1071-6

studies (Vesic 1971; Sarac 1989; Smith 1998; Krishna 2000;Fargic and Marovic 2003; Merifield and Sloan 2006; Dickinand Laman 2007; Kumar and Bhoi 2008; and Kouzer andKumar 2009) were also supported.

It was observed that an increase in the use of symmetricalanchor plates to resist the uplift capacity could be achieved byincreasing the size and the depth of an anchor plate, byimproving the soil in which these anchor plates are embedded,or by implementing both approaches. In some conditions,increasing the depth and the size of an anchor plate may notbe an economical solution in comparison to other alternatives.On the other hand, soil improvement can be achieved byadding a soil reinforcement layer that can resist high upliftforces. However, some studies have reported the behavior ofhorizontal anchor plates in a reinforced soil bed under upliftloads. Subbarao et al. (1988) used geotextiles as ties to studythe improvement in uplift capacity in reinforced concretemodel anchor plates embedded in sand. Studies by Selvadurai(1989, 1993) reported significant enhancement, of the order of80 to 100 %, in the uplift capacity of pipelines embedded infine and coarse-grained soil beds reinforced with geogridlayers directly above the pipeline in an inclined configuration.Krishnaswamy and Parashar (1992, 1994) studied the behav-ior of the uplift capacity of circular and rectangular anchorplates in cohesive and cohesionless soil with and withoutgeosynthetic reinforcement layers. They reported that thegeocomposite reinforcement offered higher uplift resistancein comparison to the one offered by both geogrid andgeotextile reinforcement layers. Ilamparuthi and Dickin(2001a, b) investigated how the soil reinforcement layer in-fluences the uplift capacity of model-belled piles embedded insand. They placed a cylindrical gravel-filled geogrid cell nearthe enlarged pile base and observed that the uplift capacityincreases with an increase in the diameter of the geogrid cell,sand density, pile bell diameter, and the embedment ratio. El-Sawwaf (2007) studied the influence of soil reinforcement onthe uplift capacity of symmetrical anchor plates in slopes andfound that adding one geogrid layer directly on top of thesymmetrical anchor plate is more effective in increasing theuplift capacity of the anchor plate than reinforcing the slopeitself. Recently, research was conducted (Noorzad andManavirad 2012; Javdani Naeini et al. 2012; Choobbastiet al. 2012; Fahimifar et al. 2012; Tahmasebipoor et al.2010) to derive a general solution for shallow and deepfoundations based on experimental and numerical works insoils. Thus, many research studies conducted to date aremainly focused on the uplift capacity of symmetrical anchorplates embedded in non-reinforced soil with a horizontalground surface. However, some studies have also beenconducted on symmetrical anchor plates embedded inreinforced soil. However, we believe no significant studieshave been made so far to evaluate the performance of sym-metrical circular anchor plates in geogrid reinforced layers.

Therefore, what effect the soil reinforcement layer leaves onthe stability and the rupture surface of the soil and, hence, thesymmetrical anchor plate capacity is unclear.

The current research provides information about the effectof the soil reinforcement layer on the uplift capacity of hori-zontal symmetrical anchor plates that are embedded adjacentto the soil surface. The main objectives of this research are tostudy the optimum number, size, and the best position of theincluded geogrid layer to increase the ultimate uplift capacityof symmetrical anchor plates. The research also intends tostudy the influence of embedment ratio, soil density, andbreakout factors.

Methodology

The placement of cohesionless soil is very important duringuplift tests. Similar cohesionless soil unit weights are obtainedas a basis for comparing the influence of various parameterson the uplift capacity of symmetrical anchor plates. A sandunit weight equal to 15 kN/m3 was decided for loose-packingsand, whereas it was defined as 17 kN/m3 for dense-packingsand. Loose sand conditions were obtained by using thecohesionless soil raining method. Trial tests were run to de-termine the most favorable conditions necessary before thetarget unit weight could be achieved. For cohesionless soil indense-packed sand, trial tests indicated that there was a limit-ing sand thickness before a change in sand unit weight acrossthe sand thickness becomes significant as the thickness in-creases. The standard cohesionless soil thickness was taken as50 mm because this thickness gave a consistent unit weightvalue when the cohesionless soil was rained from a certainheight measured from the top of the cohesionless soil layer.Regarding the sand-raining test, a range of falling cohesion-less soil heights were employed to verify the required heightfor the desired unit weight. The test showed that a fallingheight of 450 mm for fine sand had to be maintained every50 mm layer of geogrid to achieve a dry unit weight of 15 kN/m3. The influence of the thickness of sand on the dry unitweight was also found to be true for samples of cohesionlesssoil that had to be compacted in order to achieve the desireddry unit weight. Similar to loose sand conditions, the standardthickness of the sand sample was taken as 50 mm. Resultsshow that fine sand required a compaction time of 2 min per50 mm layer. The rationale behind this specific thickness isthat the sand soil sample gave consistent values of sand unitweight when compacted at similar duration. These compac-tion times were expected to render the sand a dry unit weightof 17 kN/m3. Uplift tests were carried out in two test boxescovering two areas. The first test box was used for failure teststhat were carried out in an area of 600×250 mm and 450 mmdeep with side glass walls to observe how sand moves in thebox and study its behavior. The second test box was used for

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uplift tests that were carried out in a box covering an area of1,000×500 mm and 1,200 mm deep. Table 1 shows the soilproperties.

Symmetrical anchor plate

Uplift tests were performed on square, circular, and rectangu-lar symmetrical anchor plates, which have been used as an-chors for structures. Model anchors with 10-mm-thick rigidplates were obtained. Experiments used 5.0, 7.5, and 10 cmdiameter circular anchor plates, 5×5, 7.5×7.5, and 10×10 cmsquare anchor plates and 20×5 and 30×7.5 cm rectangularanchor plates, totaling eight different anchor plates. Tables 2and 3 show the properties of the geosynthetic layer and thesteel anchor plates.

Experimental test

The uplift test was conducted in the geotechnical laboratory.The main objective of this experimental test was to study thestress-displacement relationship during the symmetrical an-chor plate breakout. The test set-up and the steps used in theuplift tests are described in the following sections. The testboxes were used to contain cohesionless soil as an embedmentpattern. The model symmetrical anchor plates were connectedto a pulling tendon cable for uplifting. A quasistatic rate ofpullout of approximately 1.5 mm/min was used for everyuplift test. This pullout was to ensure that the surroundingelement near the symmetrical anchor plates will have ampletime to redistribute during the uplift test. The uplift capacitywas measured by applying a load cell attached to the pullingtendon cable during the uplift test. A linear variable displace-ment transducer (LVDT) was placed at the top of the

symmetrical anchor plate holder to measure the vertical dis-placement and predict the movement of the symmetrical an-chor plate that is required to mobilize the ultimate upliftcapacity. A motor was connected to the pulling tendon cablevia the tendon steel cables. A datalogger was used to recordthe data read from the load cell and LVDT. The uplift test takesinto account only the net uplift capacity of the symmetricalanchor plates. This would mean that only the symmetricalanchor plates are involved in the analysis of their uplift ca-pacity. Tests were repeated when the desired dry unit weightwas not achieved. The reasons for rejecting a test includeddisturbance to any part of the experimental setup during theuplift tests, human error, and power shortage that resulted inthe discontinuity of the uplift test. Thus, repeating the testensured that the data obtained from the uplift test were reliablebefore it could be reviewed for analysis. The effect of theembedment ratio, the sizes of the symmetrical anchor plate,the density of sand used, the vertical spacing of the geogridlayers, the proximity of the geogrid layer to the symmetricalanchor plates, and the number of geogrid layers was alsoinvestigated as shown in Fig. 1. Table 4 shows the summaryof the uplift tests.

Failure mechanism

Failure tests were performed to study the patterns related to theextreme uplift loads and the embedment ratio for symmetricalanchor plates. The objective was to study the behavior of thefailure mechanism of loose-packed sand and dense-packedsand around symmetrical anchor plates. The dry unit weightof loose-packed and dense-packed sand used for this purposewas 15 and 17 kN/m3, respectively. Vertical intervals of50 mm were necessary so that sand could be placed on thefront face of the failure box. Loading was applied to square,circular, and rectangular anchor plates by using a loading

Table 1 Properties of the soil used in PLAXIS

Parameter value Loosepacking

Densepacking

Cohesion, c (kPa) 0.5 0.5

Residual angle of internal friction (°) 38 44

Angle of dilatancy (Ψ°=∅°−30) 8 14

Unit weight, γ (kN/m3) 15 17

Secant stiffness, E50 (kN/m2) 20,000 30,000

Initial stiffness, EOED (kN/m2) 20,000 30,000

Unloading/reloading stiffness, EUR (kN/m2) 60,000 90,000

Poisson’s ratio 0.2 0.2

Power for stiffness stress dependency, (m) 0.5 0.5

At rest earth pressure coefficient, K0 0.38 0.32

R inter 0.9 0.9

Table 2 Properties of the geosynthetic layer

Geosynthetic type Geogrid

Polymer type Polypropylene

Geogrid shape Square

Apparent opening size 21×21 mm

Tensile strength (kN/M) 60

Table 3 Properties ofthe steel anchor plates Type Steel plates

EI (kNm2/m) 163

EA (kN/m) 3.4×105

Thickness (mm) 8

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cable with a constant low rate in non-reinforced and reinforcedsand.

Breakout factor

The breakout factor was analyzed by Meyerhof (1968) as:

P ¼ f ∅;L

D

� �� LD2γ ð1Þ

The internal friction angle is a constraint for loose-packedand dense-packed sand in this test. P is considered as theultimate uplift load, D the width of the anchor plate, H theembedded depth of the anchor plate, γ the dry unit weight ofsand, ∅ the internal friction angle, and L /D the embedmentratio.

Numerical simulation

A series of two-dimensional finite element analyses wasperformed on a prototype symmetrical anchor plate-sand

system. This was done to assess the experimental model tests’results and find out the deformations’ behavior within the sandmass. The analysis was performed under the finite elementprogram, PLAXIS package (professional version 8,Bringkgreve and Vermeer 1998). PLAXIS is a geotechnicalsoftware that is used to analyze soil problems. In general, theinitial conditions include initial groundwater conditions, theinitial geometry configuration, and the initial effective stressstate. The sand layer used in this research was dry, so thegroundwater condition was not entered. The analysis wasdone by using the Hardening Soil Model.

The geometry of the prototype anchor plate-box systemwas supposed to be the same as the experimental model. Forthis prototype research, the same gradient of the model testand the same steel for the symmetrical anchor plate, as well asthe same geogrid layer and sand were used. The PLAXISsoftware enables the automatic production of 6 to 15 nodetriangular plane strain elements for square and rectangularanchor plates and axisymmetry for circular plates in the sand.The left vertical line of the geometry model was constrainedhorizontally, but the bottom horizontal boundary wasconstrained in both the horizontal and vertical directions.The sand parameters determined for the top and bottom soillayer were assumed to be similar to all sections ofunreinforced sand. For the reinforced sand, a reinforcementlayer was placed at the mentioned depth, although the suitablestrength for reduction factors between the contact surfaces andstiffness of the geosynthetics is considered. The prescribedload was loaded in increments and iterative analysis was usedto gauge the load until failure. The boundary conditionspresented ensured that the vertical boundary is free verticallyand constrained horizontally until the bottom horizontalboundary is completely fixed. The program results in six nodetriangle plane strain elements for the sand and three nodetensile elements for the symmetrical anchor plate, with thegeogrid reinforced.

Results

As shown in Fig. 2, symmetrical anchor plates experienced anincrease in the uplift capacity for every increase in the size ofthe symmetrical circular anchor plate. The increase was, how-ever, non-linear for loose-packed and dense-packed sand.Figure 2 shows symmetrical square anchor plates exhibitingnon-linear increases in the uplift capacity in the diameter orthe length of the symmetrical anchor plate when placed inloose-packed sand.

The increase in the uplift capacity with the increase in thesize of the symmetrical anchor plate, regardless of the packingconditions of the soil, is because of the increased lateralstresses acting on the symmetrical anchor plates with thedepth and increasing contact area between the symmetrical

Fig. 1 The effect of different parameters on the uplift test

Table 4 Summary of the uplift tests and simulations conducted for thevarious combinations of different parameters

Item test Conditions Cohesionlesssoil types

Anchor plate sizes 50, 75, 100, 200,300 mm

Non-reinforced

Anchor plate shapes Circular, square,rectangular

Non-reinforced

Sand unit weight Loose and dense Non-reinforced

Anchor plate’s embedded ratio 1, 2, 3, and 4 Non-reinforced

Number and vertical spacing ofgeogrid layers

B /D =1–2, x /D=0–0.5, u/D=0–1

Reinforced

Geogrid layer proximity to theanchor

B /D =1–2, x /D=0–0.5

Reinforced

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anchor plates and the embedment media. This can be under-stood from the uplift response formula derived by Balla(1961), γ AH where the size of the symmetrical anchor plateis one of the parameters used. As such, an increase in the sizeof the symmetrical anchor plate increases the uplift capacity.Figure 2 shows a geometric increase in the uplift capacity insquare anchor plates in both loose-packed and dense-packedsand. The results show the comparison of uplift capacitiesbased on different shapes of the symmetrical anchor platesand prove that symmetrical circular anchor plates have higheruplift capacities compared to symmetrical square anchorplates for both loose-packed and dense-packed sand. A sym-metrical anchor plate subjected to uplift capacity causes ex-tensive shear forces to develop adjacent to the symmetricalanchor plate. This can be understood from the formula of theuplift response where the shape of the symmetrical anchor isone of the parameters. Here, Balla (1961) used a correlationfactor for changing the uplift capacity from square to circularor strip or vice versa. The increasing difference in the upliftcapacity in the square, circular, and strip anchor plates with theincreasing size of the symmetrical anchor plate is expected,since an increase in the uplift capacity follows a geometricprogression with increasing depth. Thus, a deeply embedded

symmetrical strip anchor plate would be substantially moreresistant to uplift forces than a symmetrical square or circularanchor plate due to the geometric progression in the upliftcapacity with increasing depth of the symmetrical anchorplate. This behavior is in agreement with findings by Balla(1961), Meyrhof (1968) and Vesic (1971) and studies on theinteraction of sand with symmetrical anchor plates by relatedresearchers.

Symmetrical anchor plates in a maximum embedment ratioof L /D =4 had higher uplift capacities than symmetrical an-chor plates in the minimum embedment ratio of L /D =1. Theincreases in the breakout factor for symmetrical anchor platesembedded in loose-packed sand compared to the plates em-bedded in dense-packed sand are shown in Fig. 2. Theseincreases are, however, non-linear for loose-packed anddense-packed sand. The discussion about the uplift capacityof symmetrical anchor plates in reinforced sand involves aseparate analysis of various parameters, such as the number ofgeogrid layers, the length of the geogrid layer, the proximityof the geogrid layer to the anchor plate, and the verticalspacing between the geogrid layers. The geogrid layer is onetype of geosynthetic material used in this study. Typicalphysical and technical properties were obtained from the

Fig. 2 Variation in the breakoutfactor Nq with embedment ratioL /D for symmetrical anchorplates in both loose-packed anddense-packed sand

Fig. 3 Variation in ACR with B /D of the geogrid layer at x /D=0

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manufacturer’s data sheet as shown in Table 1. This informa-tion was needed to enable an impartial and focused review ofthe effect of each parameter on the uplift capacity of symmet-rical anchor plates during the uplift test. Another area thatmust be considered is the effect of reinforced sand on sym-metrical anchor plates.

The uplift response of the symmetrical anchor plates withand without soil reinforcement, Pu and Po , respectively, wereobtained from the displacement-uplift load curves. The upliftcapacity of the symmetrical anchor plate improvement due tosoil reinforcement is represented using a non-dimensionalfactor, called the symmetrical anchor plate capacity ratio(ACR), which assisted in comparing the test results. Thisfactor is defined as the ratio of the ultimate capacity of thesymmetrical anchor plate with the soil reinforcement layer,Pu-reinforced, to the ultimate capacity of the symmetrical anchorplate in tests without soil reinforcement layer, Po . Theseresults are discussed in the following sections. In this study,the length of the geogrid layer (B ) was not kept constant, andthe number of geogrid layers also varied in this research.

As shown in Figs. 3 and 4, tests were performed to studythe effect of reinforced sand, with various lengths of thegeogrid layer included, on the behavior of the symmetricalanchor plate located in the loose-packed and dense-packed

sand and at an embedment depth ratio between 1 and 4. In thereinforced tests, the geogrid layers were placed at equal ver-tical spacings of 0.5B , 0.75B , and 1B , with the first layerresting on the anchor plate between 0B and 0.5B. The varia-tions in the uplift capacity of the symmetrical anchor platewith u /D for a number of geogrid layers are shown in Figs. 5and 6. The figures clearly show that the behavior of the anchorplate improves with soil reinforcement. It can also be seen thatthe inclusion of the geogrid layers yields much better resultsthan from non-reinforced layers. In fact, the inclusion of onegeogrid layer resting directly on top of the anchor plate ap-proximately produces the same effect as that from the inclu-sion of multiple geogrid layers. Therefore, it was concludedthat, in terms of the uplift capacity of the symmetrical anchorplate, using one geogrid layer is better and more economicalthan reinforcing the soil itself with several layers. Hence, itwas decided to carry out the test program on the response ofanchor plates adjacent to loose-packed or dense-packed sandusing one geogrid layer placed in the symmetric state over theanchor plate.

Tables 5 and 6 show that many series of tests and simula-tions were performed on symmetrical anchor plates located inloose-packed and dense-packed sand with the inclusion of onegeogrid layer placed at various distances of 0, 0.5B , 0.75B ,

Fig. 4 Variation in ACR with B /D of the geogrid layer at x /D=0.5

Fig. 5 Variation in ACR with thenumber of geogrid layers at x/D =0 and u /D =0.5

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and 1B with B /D =1 over the symmetrical anchor plate.Tables 5 and 6 also show the variation in the uplift responsewith x /D with B /D =2 for reinforced sand. The improvementsin the uplift capacity of symmetrical anchor plates decrease asthe distance between the geogrid layer and the anchor plateincreases.Maximum gain in the uplift capacity of symmetricalanchor plates is attained when the geogrid layer is placeddirectly on top of the anchor plate.

Results of the failure mechanism

Studies on the uplift failure mechanism have shown thatsymmetrical anchor plates fail with a curved shear surface.An example of this is shown in Figs. 7 to 8. The figuresillustrate the shear failure mechanism during the uplift capac-ity for symmetrical anchor plates in non-reinforced and loose-packed and dense-packed reinforced sand. A certain degree ofcollapse was observed near the symmetrical anchor plates.With further uplift movement, the failure surface was seen tobe defined more prominently. A contributing factor towardsthe formation of the curved shaped failure would be thecollapse of soil around the symmetrical anchor plate to fill inthe void formed near the bottom of the symmetrical anchorplate. This is shown by the movement of soil particles along

the symmetrical anchor plate–soil interface that followsthe symmetrical anchor plate during the uplift forces. Thisshear zone comprising of displaced soil particles along thesymmetrical anchor plate–soil interface is, therefore, seento be influential in increasing the uplift capacity of theanchor plates. The outfitted tension trend in the reinforce-ment allows the geogrid layer to resist the horizontal shearstresses built up in the sand mass inside the loaded zoneand its movement to beside stable layers of loose-packedand dense-packed sand, leading to a broader and deeperfailure zone. Based on this result, the interaction betweensand and the geogrid layer not only results in increasingthe uplift force due to the developed longer failure surfacebut also results in extending the contact zone between thesoil and the laboratory box.

Discussion

This section provides a detailed comparison of experimentaland theoretical values for the number of programs conducted.Many researchers (Balla 1961; Meyerhof and Adams 1968;Vesic 1971; Rowe and Davis 1982; Murray and Geddes 1987;Sarac 1989; Smith 1998; Krishna 2000; Fargic and Marovic2003; Merifield and Sloan 2006; Dickin and Laman 2007;

Fig. 6 Variation in ACR with thenumber of geogrid layers at x/D =0.5 and u /D=0.5

Table 5 Variation in ACR with the proximity of the geogrid layer to the anchor plate at B /D=1

Shapes Embedment ratio Test type ACR based on geogrid layer proximity to the symmetrical anchor plate in B /D =1

L/D Plaxis/laboratory 0 0.5 0.75 1

Circular (10 cm) 4 Laboratory 1.17 1.16 1.16 1.15 1.16 1.15 1.16 1.15

Circular (10 cm) 4 Plaxis 1.17 1.15 1.16 1.15 1.16 1.14 1.16 1.15

Square (10 cm) 4 Laboratory 1.20 1.19 1.18 1.18 1.20 1.18 1.20 1.17

Square (10 cm) 4 Plaxis 1.19 1.20 1.18 1.18 1.20 1.18 1.19 1.18

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Kumar and Bhoi 2008; and Kouzer and Kumar 2009) provideevidence for the relationship between the ultimate uplift capac-ity of symmetrical anchor plates with their breakout factors.

Some researchers (Balla 1961; Meyerhof and Adams 1968;Vesic 1971; Rowe and Davis 1982; and Murray and Geddes1987) dedicated their works to proposing different theories tounderstand the uplift capacity of horizontal anchor plates. Thissection provides information about how this study comparesto the existing theories. Figures 9, 10, 11, 12, 13, and 14 showa comparison between the theoretical values and the experi-mental values as forwarded by various researchers (Balla1961; Meyerhof and Adams 1968; Vesic 1971; Rowe andDavis 1982; Murray and Geddes 1987). These researchersproposed various theoretical values based on the curved fail-ure model through experimental and analytical evaluations innon-reinforced sand.

Figures 9, 10, and 11 show the comparison betweenthe theoretical values for the breakout factor with thecurrent results based on numerical and experimental anal-ysis. The overall trend indicates that, for the number oftests and models conducted, experimental and numericalvalues are in close agreement and similar to values ofBalla (1961) for circular anchor plates, Vesic (1971) forsquare anchor plates, and Meyerhof and Adams (1968) forstrip anchor plates.

Comparisons of the experiment’s theoretical and numericalpredictions for symmetrical anchor plates in dense-packedsand are shown in Figs. 12, 13, and 14. The values of thebreakout factor from the experimental laboratory testing are inclose agreement and similar to values obtained by Balla(1961) for circular and square anchor plates, and Meyerhofand Adams (1968) for strip anchor plates. For symmetrical

Table 6 Variation in ACR with the proximity of the geogrid layer to the anchor plate at B /D=2

Shapes Embedment ratio Test type ACR based on geogrid layer proximity to the symmetrical anchor plate in B /D =2

L/D Plaxis/laboratory 0 0.5 0.75 1

Circular (10 cm) 4 Laboratory 1.15 1.15 1.16 1.19 1.18 1.16 1.19 1.17

Circular (10 cm) 4 Plaxis 1.15 1.15 1.17 1.19 1.18 1.16 1.19 1.19

Square (10 cm) 4 Laboratory 1.20 1.20 1.18 1.18 1.19 1.18 1.23 1.21

Square (10 cm) 4 Plaxis 1.20 1.20 1.18 1.18 1.19 1.18 1.23 1.21

Fig. 7 State of sand after commencement of uplift forces in non-reinforced dense-packed sand

Fig. 8 State of sand after the commencement of uplift forces inreinforced dense-packed sand

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anchor plates shown in Figs. 12, 13, and 14, numerical resultsusing PLAXIS values are seen to be much lower than thetested values of the breakout factors using laboratory tests,which is in agreement with values obtained by Balla(1961) for circular and square anchor plates and Meyerhofand Adams (1968) for strip anchor plates. Figures 12, 13and 14 also show that the breakout factor increases sig-nificantly with anchor embedment depth for geogrid andnon-reinforced layers. In addition to this, the inclusion ofone geogrid layer placed over the symmetrical anchorplate also produces a greater breakout factor than that ofthe same symmetrical anchor plate embedded without thereinforced layer.

Empirical relationship for reinforced sand

Based on the results, the variations of non-dimensional upliftresponses with embedment ratio are plotted. The tests arebased on loose and dense conditions to derive the behaviorof symmetrical anchor plates (such as square, circular, and

rectangular plates) in reinforced sand. Tests in loose sandconditions consist of three parts. The first part employedsquare plates with side lengths of 50, 75, and 100 mm witha various number of reinforced layers and various x /D , B ,and u /D . While the second part employed circular plateswith various diameters of 50, 75, and 100 mm with avarious number of reinforced layers and various x /D , B ,and u /D . The third part employed rectangular plates withlengths of 200 and 300 mm with a various number ofreinforced layers and various x /D , B , and u /D . Similartests were made for symmetrical anchor plates in denseconditions.

The empirical relationship for symmetrical square andcircular anchor plates of length and diameter, respectively,of 50, 75, and 100 mm and rectangular plates of 200 and300 mm in loose sand conditions using reinforced layerswere developed by combining both non-dimensional upliftresponses to obtain average values. These methods werealso adopted for dense conditions. The relationship betweenvarious parameters was plotted for symmetrical anchorplates. The empirical relationship was developed from test

Fig. 9 Comparison of thebreakout factor between theexperimental results and thetheoretical and numericalpredictions for circular anchorplates in loose-packed sand

Fig. 10 Comparison of thebreakout factor between theexperimental results and thetheoretical and numericalpredictions for square anchorplates in loose-packed sand

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results. A linear regression was employed to obtain a linearrelationship of all data included. In square plates, this enablesthe following empirical relationship to be derived:

Nq ¼ 1:17þ 2:88 L=Dð Þ−0:12 Nð Þ ð2Þ

For dense sand conditions, similar methods to those usedwith loose sandwere adopted. Thus, the empirical relationshipfor square anchor plates in dense sand conditions can beexpressed as:

Nq ¼ 2:23þ 4:24 L=Dð Þ−0:14 Nð Þ ð3Þ

Where L /D and number of reinforced layers (N ) give alinear equation by means of linear regression with a coeffi-cient of regression. As the confidence level has been set at95 % in the analysis, the p value of significant variablesshould be less than 0.05. According to the analysis,“embedment ratio” and “ratio of geogrid width to platewidth” have significant impact on the overall servicequality. The impact of “embedment ratio” is positive and

the impact of “ratio of geogrid width to plate width” isnegative. In circular plates, this enables the following empir-ical relationship to be derived as:

Nq ¼ 1:36þ 2:79 L=Dð Þ−0:12 Nð Þ þ 0:06 B=Dð Þ ð4Þ

For the dense sand conditions, similar methods used withloose sand were adopted. Thus, empirical relationships forsquare anchor plates in dense sand conditions give:

Nq ¼ 2:23þ 4:24 L=Dð Þ−0:14 Nð Þ ð5Þ

The embedment ratio, L /D , and number of reinforcedlayers (N ) give a linear equation by means of a linear regres-sion with a coefficient of regression. As the confidence levelhas been set at 95 % in the analysis, the p value of significantvariables should be less than 0.05. The “embedment ratio” and“ratio of geogrid width to plate width” have significant impacton the overall service quality. The impact of “embedmentratio” is positive and the impact of “ratio of geogrid width toplate width” is negative. Equations 2, 3, 4, and 5 are valid for

Fig. 11 Comparison of thebreakout factor between theexperimental results and thetheoretical and numericalpredictions for rectangular anchorplates in loose-packed sand

Fig. 12 Comparison of thebreakout factor between theexperimental results and thetheoretical and the numericalpredictions for circular anchorplates in dense-packed sand

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symmetrical anchor plates in loose and dense sand conditionswith a restriction of L /D ≤4.

Conclusion

From the detailed analysis given above, the findings of theparametric study can be summarized. Based on the experi-mental and the numerical studies carried out on different sizesof square, circular, and rectangular symmetrical anchor platesembedded adjacent to an experimental box at two sand den-sities with and without the geogrid reinforcement layer, thefollowing conclusions can be made:

& Including the geogrid reinforcement layer in the laborato-ry test chamber significantly increases the symmetricalanchor plate's ultimate pullout capacity embedded in sand.

& In cases where the design requirements call for high upliftresistance, the soil reinforcement layer can be consideredas an economical solution and can be used to obtain thedesired uplift capacity of the symmetrical anchor plate

instead of increasing the embedment depth or the size ofthe anchor plate.

& In terms of the uplift capacity of the anchor plate, placingone geogrid layer over the anchor plate is seen to be morecost-effective than using multiple sand reinforcementgeogrid layers. The most favorable location for includingthis geogrid layer is directly on top of the symmetricalanchor plate.

& In terms of the uplift capacity of the symmetrical anchorplate, including multiple geogrid layers over the symmet-rical anchor plate is not more cost-effective than using asingle geogrid layer. In terms of the reinforced conditionon the symmetrical anchor plate using multiple geogridlayers, the optimal space between the multiple geogridlayers should be 0.5B.

& An increase in the soil density and the embedment depthleads to an increase in the uplift capacity.

& Including a geogrid reinforcement layer in the laboratorychamber significantly increases the uplift force because ofthe developed longer failure surface, but it also resultsin extending the contact zone between the soil and thelaboratory box.

Fig. 13 Comparison of thebreakout factor between theexperimental results and thetheoretical and the numericalpredictions for square anchorplates in dense-packed sand

Fig. 14 Comparison of thebreakout factor between theexperimental results and thetheoretical and the numericalpredictions for rectangular anchorplates in dense-packed sand

Arab J Geosci

Acknowledgments This research was partially supported by theresearch Grant at UTM, Malaysia (GUP Grant), and the project name is“uplift response of symmetrical anchor plates in grid fixed reinforced incohesionless soil”.

References

Adams JI, Hayes DC (1967) The uplift capacity of shallow foundations.Ontario Hydro-Research Quarterly. 1–13

Andreadis A, Harvey R, Burley E (1981) Embedded anchor response touplift loading. J Geotech Eng 107(1):59–78

Baker WH, Konder RL (1966) Pullout load capacity of a circular earthanchor buried in sand. Highw Res Rec 108:1–10

Balla A. (1961) The resistance of breaking-out of mushroom foundationsfor pylons. Proceedings 5th International Conference on SoilMechanics and Foundation Engineering. 1: 569–576

Bringkgreve R, Vermeer P (1998) PLAXIS-finite element code for soiland rock analysis, version 7. Plaxis BV, The Netherlands.

Choobbasti AJ, Saadati M, Tavakoli HR (2012) Seismic response of pilefoundations in liquefiable soil: parametric study. Arab J Geosci5(6):1307–1315

Dickin EA (1988) Uplift behaviour of horizontal anchor plates in sand. JGeotech Eng 114(11):1300–1317

Dickin EA, Laman M (2007) Uplift response of strip anchors in cohe-sionless soil. Adv Eng Softw 1(38):618–625

El Sawwaf MA (2007) Uplift behavior of horizontal anchor plates buriedin geosynthetic reinforced slopes. Geotech Test J 30(5):418–426

Fahimifar A, Abdolmaleki A, Soltani P (2012) Stabilization of rockslopes using geogrid boxes. Arab J GeoSCI. 1–13

Fargic L, Marovic P (2003) Pullout capacity of spatial anchors. J EngComput 21(6):598–700

Frydman S, Shamam I (1989) Pullout capacity of slab anchors in sand.Can Geotech J 26:385–400

Giffels WC, Graham RE, Mook JF (1960) Concrete cylinder anchors.Electr World 154:46–49

Ilamparuthi K, Dickin EA (2001a) Predictions of the uplift responseof model belled piles in geogrid-cell-reinforced sand. GeotextsGeomembr 19:89–109

Ilamparuthi K, Dickin EA (2001b) The influence of soil reinforcement onthe uplift behaviour of belled piles embedded in sand bed. GeotextsGeomembr 19:1–22

Ireland HO (1963) Uplift resistance of transmission tower foundations:discussion. J Power Div ASCE 89(PO1):115–118

Javdani Naeini A, Choobbasti AJ, SaadatiM (2012) Seismic behaviour ofpile in three-layered soil (case study: Babol City Center Project).Arab J GeoSCI. 1–11

Kananyan AS (1966) Experimental investigation of the stability of basesof anchor foundations. Osnovanlya, Fundamenty i mekhanikGruntov 4(6):387–392

Kouzer KM, Kumar J (2009) Vertical uplift capacity of two interferinghorizontal anchors in sand using an upper bound limit analysis. JComputer Geotechnic 1(36):1084–1089

Krishna YSR (2000) Numerical analysis of large size horizontal stripanchors. Ph.D. Thesis, Indian Institute of Science

Krishnaswamy NR, Parashar SP (1992) Effect of submergence onthe uplift resistance of footings with geosynthetic inclusion.Proceedings of Indian Geotechnical Conference, Surat, India,pp. 333–336

Krishnaswamy NR, Parashar SP (1994) Uplift behaviour of plate anchorswith geosynthetics. Geotexts Geomembr 13:67–89

Kumar J, Bhoi MK (2008) Interference of multiple strip footings onsand using small scale model tests. Geotech Geol Eng 26(4):469–477

Mariupolskii LG (1965) The bearing capacity of anchor foundations.SMFE Osnovanlya, Fundamenty i mekhanik Gruntov 3(1):14–18

Merifield R, Sloan SW (2006) The ultimate pullout capacity of anchors infrictional soils. Can Geotech J 43(8):852–868

Meyerhof GG, Adams JI (1968) The ultimate uplift capacity of founda-tions. Can Geotech J 5(4):225–244

Mors H (1959) The behaviour of most foundations subjected to tensileforces. Bautechnik 36(10):367–378

Murray EJ, Geddes JD (1987) Uplift of anchor plates in sand. J GeotechEng ASCE 113(3):202–215

Noorzad R, Manavirad E (2012) Bearing capacity of two close stripfootings on soft clay reinforced with geotextile. Arab J GeoSCI.1–17

Ramesh Babu R (1998) Uplift capacity and behaviour of shallow hori-zontal anchors in soil. Ph.D. Thesis. Dept. of Civil Eng. IndianInstitute of Science. Bangalore

Rowe RK, Davis EH (1982) The behaviour of anchor plates in sand.Geotechnique 32(1):25–41

Sarac DZ (1989) Uplift capacity of shallow buried anchor slabs. Proceed-ings, 12th International Conference on Soil Mechanics and Founda-tion Engineering. 12(2):1213–1218

Selvadurai APS (1989) The enhancement of the uplift capacity ofburied pipelines by the use of geogrids. Geotech Test J ASTM 12:211–216

Selvadurai APS (1993) Uplift behaviour of strata grid anchored pipelinesembedded in granular soils. Geotech Eng 24:39–55

Smith CC (1998) Limit loads for an anchor/trapdoor embedded in anassociated coulomb soil. Int J Numer Anal Methods Geomech22(11):855–865

Subbarao C, Mukhopadhyay S, Sinha J (1988) Geotextile ties to improveuplift resistance of anchors. In: Mandal JN (ed) Proceedings of theFirst Indian Geotextiles Conference, Oxford & IBH, Bombay, India,December 1988, pp. F.3–F.8

Sutherland H. B. (1965) Model studies for shaft raising through cohe-sionless soils. Proceedings 6th International Conference on SoilMechanics and Foundation Engineering. 2: 410–413

Tahmasebipoor A, Noorzad R, Shooshpasha E, Barari A (2010) Aparametric study of stability of geotextile-reinforced soil above anunderground cavity. Arab J GeoSCI. 1–8

Turner EZ (1962) Uplift resistance of transmission tower footings.J Power Div ASCE 88(PO2):17–33

Vesic AS (1971) Breakout resistance of objects embedded in oceanbottom. J Soil Mech Found Div ASCE 97(9):1183–1205

Arab J Geosci