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Full-scale testing of draped nets for rock fallprotection

Paola Bertolo, Claudio Oggeri, and Daniele Peila

Abstract: The installation of draped meshes, metallic nets installed in such a way as to lie against the rock slope surface,is one of the most common ways to protect roads and infrastructure against the detachment of small rock elements in areasprone to rock fall. Despite their frequent and worldwide application, there are no universally recognized guidelines or tech-nical standards to help engineers in their correct design, and no full-scale test results are available where the whole system,composed of several interacting structural components, is tested. In this paper, a full-scale test procedure, which is able topermit the evaluation of the global behaviour of a draped mesh, is described and the results of tests carried out on widelyused meshes are presented and discussed.

Key words: rock fall, natural risks, full-scale testing, wire mesh, cable net.

Resume : L’installation de maillage drape, des filets metalliques installes de maniere a reposer sur une surface rocheuseen pente, est une des methodes les plus courantes de proteger les routes et les infrastructures contre le detachement de pe-tites roches dans les zones propices aux eboulements. Malgre leur utilisation frequente et repandue a travers le monde, iln’y a pas de normes ni de standards techniques pour assister les ingenieurs dans le choix de la conception appropriee. Au-cun resultats d’essais a l’echelle reelle, comprenant le systeme complet compose de plusieurs elements structurants inte-gres, sont disponibles. Dans cet article, une procedure d’essais a l’echelle reelle qui permet l’evaluation du comportementglobal d’un maillage drape est decrite et les resultats des essais effectues sur des grillages typiquement utilises sont presen-tes et discutes.

Mots-cles : eboulements, risques naturels, essais a l’echelle reelle, grillage metallique, filet de cables.

[Traduit par la Redaction]

IntroductionSmall rock fragments and single rock blocks, with sizes

between 0.01 and 1.5 m3, that detach from slopes over-hanging roads and railways create one of the most frequenthazards for public transportation systems, and must be ad-dressed and controlled by the owner of the infrastructure(Peckover and Kerr 1977; Evans and Hungr 1993). Gener-ally speaking, protection interventions against rock falls canbe classified as either active or passive: the aim of an activesystem is to prevent instability from occurring, whereas pas-sive systems are designed to mitigate the effects of a pre-vious movement by intercepting and stopping falling rockblocks. Pre-stressed wire anchors, rock bolts, and groutedbars can therefore be classified as active, as they preventthe detachment of blocks from their original position. Em-bankments, ditches, net or catch-fences, and rock sheds arepassive, as they do not directly interfere in the process ofrock detachment, but control the dynamic effects of movingblocks (Peila et al. 1998, 2006). Wire mesh and cable net

slope protection systems, which are metallic cable nets orwire meshes installed directly on the slope face (Peckoverand Kerr 1977; Wyllie and Norris 1996; Ferraiolo 2005;Muhunthan et al. 2005; Bertolo et al. 2006), can be consid-ered as systems that are somewhere in between the twoabove-mentioned classes: they act mainly by covering theslope and controlling the movement of rock fragments, thuspreventing them from freely falling onto infrastructure(Ruegger et al. 2000; Flum et al. 2004; Ferraiolo and Giac-chetti 2005; Ferraiolo 2005; Bertolo et al. 2006; Peila andOggeri 2006).

Despite the worldwide application of drapery meshes, theglobal behaviour of the system has been poorly investigatedand only laboratory tests on single components of the drap-ery systems can be found in published literature, which in-clude tests on net panels under static loads or dynamicimpacts and tests on clips and cables. However, no full-scaletests have been developed that are able to verify the behav-iour of the overall system as installed on site. Furthermore,it should be observed that only a few design approaches areavailable to help a designer choose the best product and itsconfiguration for the local geomechanic conditions. Theseare usually not based on the real behaviour of the mesh and(or) net when loaded, but are based on theoretical assump-tions of the behaviour of the system (Giani 1992; Flum etal. 2004; Ferraiolo 2005; Muhunthan et al. 2005; Shu et al.2005; Valfre 2006; Sasiharan et al. 2006).

Conversely, rock fall net fences have been systematicallytested using dynamic full-scale tests, using different types oftesting devices (Smith and Duffy 1990; Gerber and Haller

Received 14 March 2008. Accepted 16 November 2008.Published on the NRC Research Press Web site at cgj.nrc.ca on4 March 2009.

P. Bertolo. Officine Maccaferri SpA, Via degli Agresti, 6,Bologna 40123, Italy.C. Oggeri and D. Peila.1 Department of Land, Environment,and Geotechnology (DITAG), Politecnico di Torino, Corso Ducadegli Abruzzi 24, Torino 10129, Italy.

1Corresponding author (e-mail: [email protected]).

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Can. Geotech. J. 46: 306–317 (2009) doi:10.1139/T08-126 Published by NRC Research Press

1997; Amman and Haller 1999; Peila et al. 1998, 2006), andit is therefore possible to compare the behaviour of the vari-ous products that have the same impact energy. Further-more, some numerical dynamic simulations based on theseresults have been developed, which allow the quality of theproducts to be improved and relevant design parameters tobe provided, such as, for example, the forces that act duringthe rock fall impact on the cable and post foundations (Caz-zani et al. 2002; Volkwein 2005; Peila et al. 2006).

Following the same approach, the importance of pursuinga suitable design for net drapery systems clearly emerges tounderstand the behaviour of the overall system consisting ofvarious combinations of nets, cables, and rock bolts. This re-sult can only be obtained using full-scale devices where thenet drapery system is installed as it would be on real projectsites and where the stressing action is as close as possible toreality.

For these reasons, a specifically designed test site that canact on a large portion of a net drapery installed as in a realsituation has been set up, and its design, its geometry, andthe results that can be obtained are discussed in detail in thefollowing sections to show the feasibility and usefulness ofthe proposed test procedure.

Wire mesh and cable nets slope protectionsystems

Among the wide range of draped wire mesh and cable

nets that are used to prevent rocks from falling from a cliffor slope, the most common ones are

� Simple wire mesh drapery systems, which are made ofmetallic wire nets fixed to the top and bottom of the cliffusing grouted steel bars and are left unanchored along theslope. The aim of this intervention is to guide loose fall-ing debris and small rock elements to the foot of theslope, thus preventing them from bouncing onto infra-structure (Fig. 1). The weight of the mesh is a relevantparameter, as the heavier the mesh, the greater the dam-pening effect the mesh has on suppressing the movementof the falling rock element (Muhunthan et al. 2005). Themesh used must also be able to resist tangential and nor-mal forces induced by the falling block that could causethe mesh to tear or be punctured.

� Fixed drapery systems made of the same type of wire netas the previous case, but confined against the slope bymetallic cables fixed to the rock using a regular patternof rock bolts, thus forcing the net to follow the slope geo-metry more closely. The aims of this intervention are:(i) to control the detachment of the rock fragments underthe net and to limit their movement inside the cable lay-out, thus preventing them from moving freely, and (ii) toimprove the stability of the slope with a regular patternof fully grouted bolts (Fig. 2).

� Cable net panels made of metallic cables connected orlinked in different ways (i.e., clips, knots, etc.) or ring

Fig. 1. Simple mesh drapery system.

Fig. 2. Fixed drapery system.

Bertolo et al. 307

Published by NRC Research Press

net panels fixed to the slope using rock bolts and thenlaced together with steel cables or other devices (Figs. 3,4). More flexible fabrics provide better conformance tothe slope geometry than stiff fabrics and reduce the dis-tance between the slope and the net, therefore reducingthe dynamic effects of falling rock elements that can da-mage the net.At present, both wire mesh and cable net slope protection

systems are commonly installed on slopes, and the basic de-sign has been modified to address a variety of slope andloading conditions so that several design variations now ex-ist. Although these basic design methods have not been sup-ported by a quantitative design methodology, these systemsusually work well. Recently, some consensus has developedamong geotechnical specialists and contractors that certainsystem elements may be over-designed. In addition, system

Fig. 4. Example of (a) normal clip and (b) knot used to fix cablesquare meshes in cable panels.

Fig. 5. Examples of test procedures for clips and knots (courtesyF. Ferraiolo, reproduced with permission). These tests are obtainedmainly by fixing one cable and pulling out the other cable whilemeasuring (a) the slipping force or (b) the breaking force.

Fig. 6. Examples of of test results on clips and knots obtained withthe laboratory device shown in Fig. 5b (courtesy Officine Macca-ferri S.p.A., reproduced with permission). HEA, steel cable net.

Fig. 7. View of the tests carried out at Istituto per la Tecnologiadella Costruzione – Consiglio Nazionale delle Ricerche (Italian Na-tional Research Council) using (a) a cone-shaped and (b) a round-shaped punching element (Bonati and Galimberti 2004, reproducedwith permission).

Fig. 3. Cable net panels.

308 Can. Geotech. J. Vol. 46, 2009


failures under a variety of loading conditions have occurredover the last decades, indicating that certain design elementsmay in fact be under-designed for the desired application.

Although incomplete geotechnical site characterizationand inappropriate applications have been responsible forsome system failures, the lack of understanding with regardsto load transfer from the mesh or net to the rock bolts andconfining cables, as well as system load capacity, remains afundamental design obstacle (Muhunthan et al. 2005).

To correctly choose and design these interventions, thegeological and geomechanical characterization of the rockslope, which is necessary to define the loads induced by thefalling rock element, must be coupled with the behaviour ofthe loaded net system. This must take into consideration that

the performance of the system is influenced by external fac-tors, such as anchorage type and pattern, slope geometry,and installation procedures on the slope, and internal factors,such as the fabric weight, stiffness and flexibility of the net,puncture strength, and corrosion resistance.

Laboratory tests on the meshes and on thenet components

A variety of mesh types that can be used in drapery sys-tems exist, but they are all mainly characterized by the fol-lowing parameters:

� mass per unit area� punching resistance

Table 1. Summary of the large-scale laboratory tests developed by Bonati and Galimberti (2004) with the device of Fig. 7b with differentconstraints of the mesh panel on the rigid frame. The results of these tests (Bonati and Galimberti 2004; Ferraiolo 2005) are used forcomparison with the results of the full-scale site tests.

Test No. Type of mesh Test geometry and constraints used1 HEA panel (3 m � 3 m size), 10 mm diameter

cable elementary mesh (300 mm � 300 mm)

2 HEA panel (3 m � 3 m size), 10 mm diametercable elementary mesh (300 mm � 300 mm)

3 Double-twisted wire mesh (3 m � 3 m size)

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� tensile strength of the individual mesh wires or cablesand of net and panel samples

� tensile strength of the junction of the cables (for cablepanels)

� mesh flexibility, which depends on the fabric geometryand assembly.

Several different types of test have been performed by thevarious manufacturers of these products to test these proper-ties.

The characterization of clips or steel wire knots (Fig. 4)can be performed by stressing the elements inside a cali-brated test traction rig. These tests should allow the slipping

force of the cable through the clip or the knot and the break-ing force of the junction system (Figs. 5, 6) to be measured;however, these tests are greatly influenced by the adoptedboundary conditions. The results of some tests carried outusing the laboratory device of Fig. 5b are reported in Fig. 6.

Punch tests on large-sized samples of the nets have theaim of modelling the action of a punching block thatstresses the net and consist of a punching element that isforced against a portion of net that is anchored to a metallicframe.

Tests on square mesh samples using a cylinder-shapedpunching element with 100, 150, 200, and 600 mm diametermetal with the plate face acting on the net were reported byAgostini et al. (1988), Ballester et al. (1996), Majoral et al.(2008), and Fresno (2008).

More recently, Bonati and Galimberti (2004) developed alarge-scale test procedure, which used both a cone thatmeasured 780 mm in height and 680 mm in diameter at thebase (Fig. 7a) and a 1500 mm diameter, 200 mm high, con-crete round-shaped element (Fig. 7b) as punching elements.In these tests, the net panel was fixed onto a rigid horizontalsquare frame (3 m � 3 m), and then the cone or the roundedpunching element were pulled normally into the net in thecentre of the panel. Some of the results of this research(summarized in Table 1) are compared with the results ofthe present study to show the influence of the boundary con-dition of the obtained results.

This type of test allows the behaviour of different netpanels to be compared with several different boundary con-ditions (as the net can be connected to the metallic frame indifferent ways), providing the load–displacement curves ofthe net panel, one of the most relevant parameters that needsto be taken into account in the design. It should be pointedout that the obtained results are greatly influenced by thechosen constraint conditions. Therefore, even though thetests provide valuable results for the characterization of thenet, they are not directly applicable to the design, as it is

Fig. 8. Front view of the full-scale test field and schematic draw-ing. The rock mass irregular geometry was imposed to reduce thesize of the right upper corner of the lateral net. It has been verifiedthat this change in geometry did not significantly altered theboundary conditions of the tested net panel. BEL, bottom extremeleft; BER, bottom extreme left; BL, bottom left; BR, bottom right;LEL, lower extreme left; LER, lower extreme right; LL, lower left;LR, lower right; TEL, top extreme left; TER, top extreme right;TL, top left; TR, top right; UEL, upper extreme left; UER, upperextreme lright; UL, upper left; UR, upper right.

Fig. 9. Sketch of the field test: vertical section.



not possible to define beforehand the boundary conditionthat can be obtained on the rock slopes in reality.

Tests where a net panel is anchored to a rigid frame thatis able to apply a traction force to one side were carried outto evaluate the deformability versus the tensile strength of aportion of a mesh or net panel (Agostini et al. 1988; Muhun-than et al. 2005).

All the tests previously described should be considered asmaterial index tests of the various elements, but their resultsare only partially representative of the real behaviour of thedrapery system installed on site. To obtain a more realisticforce–displacement relationship of a drapery system, it is

necessary to perform full-scale experiments where the sys-tem is installed as in reality.

Full-scale test device

The full-scale test device was set up on a real verticalrock slope located at the town of Pont Boset in Aosta Valley(northern Italy) where an almost 6 m � 6 m wire mesh orcable net was installed using a square anchorage patternwith a 3 m interaxis (which is the most common). Thetested portion of the net (3 m � 3 m) was therefore con-nected with the rock mass exactly as in reality, and the lat-

Fig. 10. Installed transducers and their positions at the test site.

Table 2. Full-scale tests.

Test No. Type of mesh Type of drapery system installed1 HEA panel (3 m � 3 m panel), 10 mm diameter cable;

mesh size 400 mm � 400 mm, without edge cableCable net panels; anchorage bolt inserted in the edge mesh of the

net panel2 HEA panel (3 m � 3 m panel), 10 mm diameter cable;

mesh size 400 mm � 400 mm, without edge cableCable net panels; the panel is the one already deformed after test

1; anchorage bolt inserted in the edge mesh of the net panel3 HEA panel (3 m � 3 m panel), 10 mm diameter cable;








net panel7 Double-twisted wire mesh Fixed drapery system with crossed reinforcing cables connected

to the anchors (pattern 3 m � 3 m) with a square 150 mm �150 mm plate

8 Double-twisted wire mesh Fixed drapery system with sub-horizontal reinforcing cables con-nected to the anchors (pattern 3 m � 3 m) with a square150 mm � 150 mm plate

9 Double-twisted wire mesh Simple mesh drapery system

Bertolo et al. 311


eral portions of the net acted as the boundary conditions ofthe tested sample (Fig. 8).

A 2.3 m long hydraulic jack, which can apply a maximumforce of 200 kN, was installed in a hole drilled inside therock mass and was used to load the drapery system througha rounded 1.5 m diameter, spherical-cap-shaped load distrib-utor. The jack force was applied to the net with an inclina-tion of 458, which was considered to be a reference valuefor standard testing because it is the average value amongthe dip of downslope sliding joints. The jack was fixed tothe rock slope at the head of the hole through a collar and acylindrical coupling pin, in such a way that the breech couldmove a few degrees for force-balancing purposes, therebyavoiding piston-rod bending (Fig. 9). It was connectedthrough a ball joint to a spherical-cap steel load distributor:this shape was chosen to transfer an evenly distributed ho-mogeneous load and to avoid overstressed areas and sharppoints, which could hook and damage the tested product,thus making the obtained results difficult to be interpretedand compared.

The test was carried out according to the following proce-dure:

� the drapery system was installed on the vertical slopethrough the installed bolts as it is usually done in practice

� the jack was activated and the rod came out and pushedthe spherical cap against the mesh product

� the test was stopped when the meshes or the cables of the

Fig. 11. Schematic drawing of the HEA panel and photo of theconnection condition at the test site.

Fig. 12. Photo and schematic drawing of the double-twisted wiremesh. The wire has a diameter of 3 mm and the D value of theelementary mesh is 80 mm.

Fig. 13. Picture of the HEA tested panel as installed at the test site.LL, lower left; LR, lower right; UL, upper left; UR, upper right.

Fig. 14. Double-twisted wire mesh drapery system installed at thetest site with crossed reinforcing cables (test No. 7). LL, lower left;LR, lower right; UL, upper left; UR, upper right.

Fig. 15. Double-twisted wire mesh drapery system installed at thetest site with subhorizontal reinforcing cables (test No. 8). LL,lower left; LR, lower right; UL, upper left; UR, upper right.



tested product failed, when the jack exerted its maximumpressure or when the jack reached its maximum rodstroke.The system shown in Fig. 10 allows the real behaviour of

the drapery system to be understood and also allows theevaluation of the load–displacement curve of the installeddrapery system and other performance indicators of the sys-tem behaviour, such as the force induced on the bolts andthe most appropriate cables to be used for the system, thuspermitting the design optimization.

Testing

Tests were carried out on different types of drapery systemsmade of steel cable net panels (HEA panels) and double-twisted wire meshes, which are also installed as fixed draperysystems (Table 2). The HEA panels (Fig. 11) used are manu-factured from a 10 mm diameter cable with a metallic core, anallowable tensile strength of 63 kN (the cable is a 6 � 19 WSwith reference to European codes EN 12385 and EN 10264-2),and different elementary mesh sizes: 300 mm � 300 mm and400 mm � 400 mm. The net panel is formed by winding thesingle steel cable back and forth along a predetermined pathto create the grid. This cable is secured at each intersectionwith a knot obtained by looping a pair of 3 mm steel wireswith a strength of about 400 N/mm2. The two bindings tightlyenvelop the cables as they cross each other. The cables thatform the mesh are closed by an aluminium-swaged connectionwith a resistance of no less than 90% of the cable breakingload. The panel cable is usually connected to a perimeter ca-ble, which closes the panel edges, has a 16 mm diameter, andfacilitates the in situ assembly of the system. The perimeter ca-ble was not installed in the tests so that the deformability, thestrength of the mesh, and the maximum force transmitted tothe anchorages, could be tested directly without any interfer-ence from the perimeter cable (Fig. 11). The panels are thenlinked together by a 10 mm diameter cable with a metalliccore that sews the meshes of the two adjacent panels. Thedouble-twisted wire mesh is made of steel woven wire (3 mmdiameter), with a tensile strength ranging between 350 and550 N/mm2, manufactured to form a hexagonal-shaped mesh(Fig. 12). The steel wire is heavily galvanized with a galfan al-loy (zinc, aluminium, and misch metal alloy). Two adjacentmesh panels are then linked together with metallic clips.

The HEA panels to be tested were fixed to the slope andthe bolt tip was inserted into the corner mesh (Fig. 11) as is

usually done in practice. These points were then fixed withsquare steel plates (150 mm � 150 mm) and tightened witha nut (Figs. 11, 13). Similar cable panels were placed aroundthe tested panels to have the same boundary conditions: thelateral panels were laced together and to the central panelwith 10 mm diameter cables. The fixed drapery system witha double-twisted mesh was installed as usually done in prac-tice and was reinforced by installing 10 mm diameter cablesto a load of 3 kN directly connected to the bolt pattern. Twodifferent layouts of the reinforcing cables were chosen: thefirst one to form a cross over the tested mesh portion (testNo. 7, Fig. 14) and the second one with subhorizontal cables(test No. 8, Fig. 15). The simple mesh drapery system (testNo. 9) was only connected with boundary cables located atthe top and bottom of the slope; therefore, these cables wereat a distance of 6 m.

The following parameters were monitored during thetests: the total forces acting on the upper left (UL) and the

Fig. 16. Example of the HEA panel behaviour during test No. 3 after (a) 30 s, (b) 60 s, (c) 120 s, and (d) 180 s from the beginning of thetest.

Fig. 17. Load–displacement curve measured during tests (Table 2):1–2 on HEA panels with mesh 400 mm � 400 mm (dashed–dottedlines); 3–6 on HEA panels with mesh 300 mm � 300 mm (solidlines), and results of the laboratory test Nos. 1 and 2 (dashed lines)(Table 1).

Bertolo et al. 313


lower left (LL) anchors; the displacement, normal to theslope, of the central point between the upper left (UL) andthe upper right (UR) anchors of the central square of thesetup system; the jack rod displacement; and the load ap-plied by the jack. All the tests were stopped when the jackreached the maximum force of 200 kN or the maximum al-lowed displacement (measured orthogonally to the originalplane of the panel at the centre of the load distributor) ofabout 1500 mm (Fig. 16). Owing to the results of all thetested systems, it was possible to obtain the force–displacement curve that describes their behaviour under realboundary conditions. From the tests on the HEA panels, itcan be seen that after the first stage where the panel deformsunder very low loads while the cables of the mesh are ten-sioned, the curve starts to rise in a steeper and in an almostlinear way; that is, the panel is able to react against the fall-ing rock mass by stopping its movement (Fig. 17). Thesecurves show that, at real job sites, it is very difficult to ten-sion mesh panels and cables to apply a pre-load to the faceto confine the rock blocks; therefore, these systems gener-ally act as passive systems (from a structural point of view)by supporting the load transmitted by the already fallingblock. If the results obtained with the panels with a300 mm � 300 mm mesh and with a 400 mm � 400 mmmesh are compared, it is clear that the second type of meshis more deformable than the first one. After all the tests on

HEA panels, no deformations were observed in the centralpoint between the UL and the UR anchors. This resultmeans that the zone stressed by the falling block is mainlythe portion of the mesh confined by the four surrounding an-chorages. The forces measured on the confining anchoragesin the tests are summarized in Table 3, which shows that theapplied force is regularly distributed over the anchor pointsaround the panel stressed by the load distributor. During allthe tests, it was seen that the mesh squares near the anchorsand in the region between the loading frame and the anchorswere very deformed, resulting in a romboedrical shape(Figs. 18, 19). The meshes were stretched in the directionof the centre of the load distributor, forcing the knot to slip(but neither the panel cables nor the knots broke at anypoint). The importance of the real flexible boundary condi-tions is demonstrated by the observation that the lateral pan-els followed the central panel movement during the test, butno relevant local deformations on the cable or on the knotswere observed. If the full-scale obtained curves and the lab-oratory curves obtained by Bonati and Galimberti (2004) arecompared, it is clear that the real boundary condition givesmore deformable curves than the laboratory tests for both acomplete connection of the meshes with the frame and for aconnection of only eight points at the panel edges.

The tests on the double-twisted wire mesh installed as afixed drapery system (test Nos. 7 and 8) or as a simple

Table 3. Forces applied on anchorages. LL, lower left; UL, upper left.

Anchorage UL Anchorage LL Confining cables

TestNo.

Max. appliedforce (kN) Max. axial force (kN)

Max. tangentialforce (kN)

Max. axialforce (kN)

Max. tangentialforce (kN) Force (kN)

1 143 Dynamometer broken (dueto large displacement)

25 60 10 —

2 180 Dynamometers not installed 65–70 5–7 —3 180 Dynamometer broken (due

to large displacement)37 70 10 —

4 185 70 30 Dynamometersnot installed

Dynamometersnot installed

—

5 200 Dynamometers not installed Dynamometersnot installed



—

6 196 Dynamometers not installed Dynamometersnot installed



—

7 15 2–3 2–2.5 6–7 0 20 (pretension 3 kN)8 38 5 12 7 0 40 (pretension 3 kN),

lower cable9 14 5.5 0 1 0 0

Fig. 18. Test effects on the HEA panel after test No. 3: (a) lateral view of the mesh panel after the jack has been retracted; (b) frontal viewof the mesh panel after the jack has been retracted; (c) knots that have slipped.



mesh drapery system (test No. 9) show that this mesh ismuch more deformable than the cable panels. It was there-fore impossible to reach the maximum jack force with thetest device, because the mesh exhibited a large plastic defor-mation at a low applied force (Fig. 20), reaching the maxi-mum allowable displacement. After test Nos. 7, 8, and 9,practically no elastic recovery was observed and the meshmaintained its deformed shape even when the load distribu-tor was retracted (Figs. 21, 22). Few breaks of the wire were

observed and in particular, local ruptures near the anchorsand local deformations of the elementary meshes were re-corded. When crossed cables were used, the load distributorwas deflected by the cables after only 200 mm of displace-ment and the test was stopped to prevent the damage of thejack (Fig. 23). This result shows that when using this geom-etry, it is important to take into account, at the design stage,that the block could slip below the cables. Large deforma-tions at a very low load were also observed when testingthe simple drapery system (test No. 9, Fig. 24), which is ingood agreement with previous test results (Muhunthan et al.2005; Sasiharan et al. 2006).

Fig. 20. Load–displacement curve measured during test Nos. 7, 8,and 9 on double-twisted wire mesh (Table 2) compared with theresults of laboratory test No. 3 (Table 1).

Fig. 21. Geometry of the panel at the end of test No. 8 (Table 2).Notice the large deformation allowed by double-twisted wire mesh.

Fig. 19. Position of the slipped knot after test Nos. (a) 1, (b) 3, and(c) 4.

Bertolo et al. 315


Conclusions

For the correct design procedure of a drapery system, it isimportant to understand the real behaviour of the overall sys-tem — the assembly of the wire mesh or the cable panel, thecables and bolts, and the forces applied to the rock bolts —taking into account the way that they are usually installed bythe workers (usually climbers suspended by ropes). It is alsoclear that these relevant data cannot be obtained from testsof individual system components because the boundary con-

ditions of the system greatly influence test results. It is nec-essary to develop full-scale test procedures to take intoaccount real boundary conditions. The proposed test proce-dure supplies the full-scale behaviour of the tested productand allows experimental load–displacement curves to be de-termined in a simple and accurate way.

This is exactly what engineers need to design drapery sys-tems, as the knowledge of how much a mesh deforms undera defined load is a key value for the evaluation of the be-haviour at a serviceability limit state of a system. Further-more, the field test allows different products to be tested inthe same configuration or the same product to be installed indifferent configurations (e.g., with different boundary condi-tions), thus reproducing what happens on site and allowingfor easy comparison of the results. Finally, the procedurealso gives useful information on the plastic deformation ofthe product, the anchor load, and the load on the reinforcingelements, such as the cables, thus permitting their correctdesign (anchor length and diameter). The tests that havebeen carried out show that the situation obtained in the realinstallations can be different to that observed in laboratorytests and that usually larger deformations occur before thesystem starts to react against the moving block. This is dueto installation problems that are unavoidable in practice.Therefore, for the correct design of a drapery system, it isnecessary to take into account the real displacement–loadcurve of the whole system and to consider that, usually be-fore reacting, the mesh can reach large displacements, thusallowing the detachment of the block from the slope andtherefore, changing the load application direction and value.On the other hand, laboratory tests are easier to perform,control, and monitor; and their results therefore permit agreater reproducibility. The proposed full-scale device per-mits the results to be compared and permits finding of thecorrection factors that can be used to take into account thereal site conditions.

AcknowledgmentsThis study was financially supported by Officine Macca-

ferri S.p.A. within a research project coordinated by Prof.D. Peila and, partly, by Italian Ministry of Research andUniversity (PRIN 2007). The Officine Maccaferri S.p.A.and Geosistemi S.n.c. technicians are gratefully acknowl-edged for their help during the tests. Special thanks are dueto Dr. Giorgio Giacchetti and Eng. Bruno Rossi who gener-ously shared their ideas and suggestions. The authors havecontributed to the same extent to the development of this pa-per. The test site is managed jointly by DITAG – Politec-nico di Torino (Torino, Italy) and Officine MaccaferriS.p.A. (Bologna, Italy).

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Fig. 22. Detail of the deformed mesh around LL anchorage aftertest No. 8.

Fig. 23. Condition of the test site when test No. 7 was stopped toavoid deflection of the jack.

Fig. 24. Permanent plastic deformation of the mesh after test No. 9.



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