1. IntroductionAnchors are very important elements widely used in the construction process of different struc-
tures such as buried pipelines, transmission towers and earth structures. These structures are subjected toconsiderable vertical and/or horizontal forces, which have to be supported by the anchors. Usuallyanchors need to be grouted or excavated in their application and they consist of grout, helical and platesystems. During the last fifty years, different researches have focused more on the pullout capacity of theanchors, although most researches have reported on symmetrical anchors [1-35]. The aim of this paper isto provide a better understanding of the irregularly shaped anchor and its uplift capacity, which is of highimportance for its application and can be used by design engineers. Researchers, such as Mors [23], Balla[5], Sutherland [32], Baker and Konder [4], Adams and Hayes [1], Dickin [12], Frydman and Shaham[15], Fargic and Marovic [14], Merfield and Sloan [22], Dickin and Lama [13], Kuzer and Kumar [20]were mostly concerned about the general solution of determining the ultimate uplift capacity in sand.Irregularly shaped anchors are driven tipping plate soil anchors, which are dependent on soil strength forreaction of tensile loads. After driving the irregularly shaped anchor to the required depth, the drivingtool (drive steel) is removed. The irregularly shaped anchor is then tipped and proof tested from its edge-wise-driving position to present its bearing area to the soil. Irregular shaped anchors involve inexpensiveinstallation equipment and are fast and easy to install with immediate proof test results, they also involveno grouting and no excavation is required. Irregularly shaped anchors are new and still require furtherevaluation in various soils. This current research discusses irregularly shaped anchors in sand.
Soil Mechanics and Foundation Engineering, Vol. 51, No. 1, March, 2014 (Russian Original No. 1, January-February, 2014)
An investigation into the uplift response of irregularly shaped anchors in sand is described.Factors investigated in relation to the load-displacement response are sand density andembedment ratio. The results are presented based on experimental tests in this paper. Themain aim of the study is to obtain validation between breakout factor and uplift load of anirregularly shaped anchor. The irregularly shaped anchor is a state-of-the-art in anchor sys-tems and does not need any grouting or excavation for installation in comparison to con-servative anchor systems. Laboratory model tests were conducted using an irregularlyshaped anchor system. The anchor was embedded with an embedment ration rangingbetween 1 and 7. Two types of sand packing were employed, namely loose and dense com-paction. Two dimensional tests to view the failure patterns were done that demonstrated pat-terns showing good agreement with Balla's [5] findings for anchor plates. The breakout fac-tor shows an increment with embedment ratio.
UPLIFT RESPONSE OF IRREGULAR SHAPE ANCHOR IN SAND
Hamed Niroumand, Khairul Anuar KassimUniversity Teknologi (Johor Bahru, Malaysia)
UDC 624.155.2:624.131.21
Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 1, p. 15, January-February, 2014.
2. Laboratory Tests ProgramThe irregularly shaped anchor was fabricated from steel with a width of 159 mm. It can be driv-
en vertically into sand and rotated to a full horizontal position before being pulled out. The irregularlyshaped anchor model and the installation processes are illustrated in Figure 1. The irregularly shapedanchor was pulled at a different embedment ratio varying between 1 and 7 in loose and dense sand.
The internal friction angle is 35o and 42o for loose and dense packing, respectively. Theloose packing was obtained by raining the sand from the rainier. A unit weight of 14.90 kN/m3 wasachieved for loose sand packing. A hopper with a hole arranged in a rectangular grid form wasplaced on top of the chamber box in order to obtain the required loose packing. To create thedensely packed sand, it was compacted at every 80 mm thickness for 8 minutes covering all sur-faces using an electric compactor. A unit weight of 16 kN/m3 was achieved for dense sand. Figure2 illustrates the arrangement of the uplift test. The uplift test was initialized using a motor with agear displacement speed of 60 mm/min incorporated with a load cell that was employed in test boxattachments. The irregularly shaped anchor is driven in sand to determine its tensile loads using adrive rod, with minimum disturbance to the sand. Once driven to the desired depth, an upward pullon the rod rotates the irregular shaped anchor into its position. After driving the irregular shapedanchor to the required depth based on various embedment ratios, L/D from 1 to 4, the driving toolis removed. The irregular shaped anchor is then tipped and proof tested from its edgewise-drivingposition to present its bearing area to the sand. The test box, a relatively large container that is1,400 mm long, 700 mm wide and 1,500 mm deep.
3. Test ResultsEmbedment ratio and soil density are the main variables observed in the uplift capacity of irreg-
ular shaped anchors, although failure pattern is also observed in the current research. 3.1 Embedment RatioResults of the uplift tests on the irregularly shaped anchor embedded in the loose and dense sand
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A B C
Fig. 1. Irregular shape anchor model and the installation processes.
are shown in Figures 3, a, and b respectively. The results illustrate the maximum uplift load against dis-placement for an embedment ratio between 1 and 7 for this particular model. Most of the results inloose and dense conditions show a significant peak value. At every peak value, the displacement seemsto have a similar magnitude of between 50 mm and 200 mm in loose sand.
The peak value for uplift load in dense sand is twice as high in comparison with the loose con-dition. In addition, the displacement in the dense condition to reach the maximum uplift load is aboutthree times greater than in the loose condition. The peak value for uplift load in the dense conditiondoes not respond to a similar magnitude of displacement as in the loose condition. Thus, it can be con-cluded that displacement is dependent on the embedment depth, whereby the deeper the embedmentdepth, the higher the displacement to reach maximum uplift capacity. However, the current researchinvolves a special type of anchor that requires rotation in the sand that can thus change the variables.During most tests in dense sand, the uplift load slowly increases with anchor displacement throughoutthe various stages, and the rate of increase eventually reduces as the maximum (peak) resistance isapproached.
3.2 Sand DensityThe sand density shows significant effect on the load performance of the uplift response for the
irregularly shaped anchor. As is reasonably anticipated, maximum resistances at a particular embedmentdepth increase with sand packing and embedment ratio. The peak resistance is well defined, especiallyfor those with L/B = 7 in dense sand. However, for irregular shaped anchors in loose sand, and for deep-er anchors in both kinds of sand packing, a characteristically ductile response is observed.
3.3 Breakout FactorThe breakout factors are obtained from the function Pu /γ LBD, where Pu is the ultimate uplift
load, γ is the unit weight of loose/dense sand, L is the embedment depth, D is the irregular shapedanchor model width and B is the length of the irregularly shaped anchor. It is clearly evident that thebreakout factor increases with increment of the embedment depth and soil density. Figure 4, a and bshow breakout factor and embedment ratio relationship of irregularly shaped anchors in loose and densesand, respectively. As can be anticipated, maximum breakout factors at a particular embedment depthincrease with sand packing and embedment ratio.
3.4. Failure MechanismThe failure mechanism tests were performed to give insight on the failure pattern occurring at
extreme uplift loads and embedment ratio. At the initial stage of the pulling, sand close to the proximi-
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Fig. 3. Variations of uplift load with embedment ratio (L/D) for irregular shaped anchor in a) loose sand; and b) dense sand.
a b
ty of the anchor compressed in an inverted cone shape. The deformation layer progresses upwards as thepulling continues, thus forming a clearer inverted truncated cone shape above the anchor. The failurezone progressively moves and the surrounding sand replaces the void formed at the departure of theanchor. As the anchor moves out, a crater forms at the surface showing that soil replacement is occur-ring in the void left behind by the anchor. Upon final departure of the anchor, an inverted truncatedcone forms as a failure pattern.
The failure pattern shape formed in loose sand is smaller than the failure pattern in dense sand.It was shown that the length of the rupture plane in loose sand is shorter than in dense sand. Rational-ly, the ultimate capacity of the embedment model in loose sand was lower than the ultimate capacity ofthe embedment model in dense sand. The deformation lines model in dense sand is clearly visualized incomparison to those of the loose sand model. The results show similarity of failure patterns for bothconditions with Balla's finding [5].
4. DiscussionRelationships between breakout factors and embedment ratios derived from a number of theoret-
ical approaches are shown in Figure 5, a, and b for loose and dense sand, respectively, which alsoinclude results from the author's analysis for comparison purposes. The relationship between the break-out factors and the embedment ratios derived from the author's findings based on Fig. 4 and previous
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a b
Fig. 4. Relationship between breakout factor with embedment ratio L/D in a) loose sand; and b) dense sand; ) model; ___) linear.
L/DL/D
a b
Fig. 5. Comparison of author's results of irregular shape anchor model with previous theoretical findings in a) loose sand; and b) dense sand; 1) author’s empirical formula; 2) Balla; 3) Meyerhoff and Adams; 4) Vesic; 5) Rowe and Davis; 6) Dickin and Laman.
L/DL/D
1
1
2 2
33
4 4
5 5
6 6
Bre
akou
t fa
ctor
Bre
akou
t fa
ctor
Bre
akou
t fa
ctor
Bre
akou
t fa
ctor
researchers approaches towards loose and dense sand are shown in Figure 5, a. The author's results wascompared to previous findings such as Balla [5], Meyerhof and Adams [21], Vesic [34-35], Rowe andDavis [27], Murray and Geddes [24] and Dickin and Laman [13] of irregularly shaped anchor models.Previous researchers used regular anchor plates such as rectangular plates in their tests, although thegeometry of those plates were similar to the irregularly shaped anchor in this current research.
According to the results, Balla [5], Meyerhof and Adams [21], Vesic [34-35], Rowe and Davis[27], Murray and Geddes [24] and Dickin and Laman [13] show a close agreement with the author'sfindings. A higher value of safety factor needs to be used by Meyerhof and Adam [21] for deep anchorplates, while others provide a lower safety value factor to be used in the design base on the dimension-less breakout factor values. Similar to breakout factor values in dense sand, findings by otherresearchers in comparison with the author's findings show a good agreement, except for those of Mey-erhof and Adam [21]. Dickin and Laman's [13] values show that the state-of-the-art centrifugal model-ing techniques show a promising way to predict uplift capacity of the anchor via stress manipulation.
5. Conclusion The author's prediction for the breakout factor for the entire embedment ratio agrees with those
values from Balla [5], Vesic [34-35], Rowe and Davis [27] and Dickin and Laman [13] for both looseand dense conditions. It also shows a close agreement between the irregular shaped anchor and anchorplates in regard to breakout factors and embedment ratios for both loose and dense sand. The develop-ment of breakout factors could lead to a prototype design of irregularly shaped anchor systems for soilstructures with respect to validating results derived from various theories. Although the work done is notdedicated to any particular sub grade condition, it was thought to be invaluable in initializing the designconcept for an irregular shaped anchor in future.
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