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Ähnlich wie 3 Secured Drapery 2008
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3 Secured Drapery 2008
- 1. Rockfall protection systems: Secured Drapery
- 2. Why do we carry out tests on square panels 3.00 x 3.00 m? Stiffness evaluation of a superficial revetment in a full scale test - Istituto per le Tecnologie della Costruzione - CNR Actual conditions and development This is the dimension of an elementary cell, that is a part of a panel or part of a net comprising of a mesh with four anchors. In order to dimension the overall system we need to evaluate the stiffness of revetment and the load transferred to the anchors in this elementary cell.
- 3. What is “stiffness” when a force is perpendicular to the panel? Stiffness evaluation of a superficial revetment in a full scale test - Istituto per le Tecnologie della Costruzione – CNR - OM Actual conditions and development “ Stiffness ” is the force that determines a unitary deformation. In the case of a panel, “stiffness” represents the force of a rock mass able to deform the panel
- 4. HEA Panel cable Ø10, Mesh 400x400 DT Mesh Mesh 8x10/ Ø 3.00 Galfan ST Mesh Wire A.R., Ø 3.00 Stiffness evaluation of a superficial revetment in a full scale test - Istituto per le Tecnologie della Costruzione – CNR - OM Comparison between panels (completely restrained) Actual conditions and development
- 5. Test in situ Pont Bozet (AO – Italy) – mesh – test in situ Section Front
- 6. Test in situ Pont Bozet (AO – Italy) – mesh – test in situ Anchorages Push Device Hydraulic Cylinder
- 7. Test in situ Real Test Conditions: - Full Scale Sample. - Sloping Load. - Real Conditions. Pont Bozet (AO – Italia) Mesh – test in situ
- 8. Test in situ Panel HEA with knots Pont Bozet (AO) Test 21/02/2007 HEA Panel 300/10 HEA_music.wmv
- 9. Big ST with horiz cable ST no cable Big ST no cable ST with horiz cable
- 10. Test in situ DT
- 12. superficial stabilisation systems are provided with a combination of nets and anchors. Anchors are used to improve stability of the superficial part of the rock slope, by preventing the movement of the blocks on the slope. SUPERFICIAL STABILISATION superficial stabilisation
- 13. Job site Mesh is difficult to apply because the ground is very rough, with many concavities and convexities. This means that the mesh can never perfectly follow the slope profile Rock masses can always move and apply load on the mesh. Research input
- 14. Mesh is a passive element Mesh is NOT a beam. The mesh reaction to a force is a large deformation. = It is important that a mesh has high stiffness, in order to minimize rock mass movements. The mesh does not transfer forces into the stabilisation system before the rock mass moves The mesh reacts to movement of falling rock masses. Research input ?
- 15. An anchor bar is completely grouted and cannot transfer forces between the plate and foundation. A bar works only after the displacement of an unstable mass. A Nail is a passive element. Steel bar Grouting Plastic deformation of rock Plastic deformation Joint dilatancy Solid rock Research input Anchor plate mesh
- 16. stabilization with mesh and nails is a passive system Anchors play the leading role in superficial stabilisation Mesh holds the blocks detaching between anchors Research input
- 17. The maximum volume moving away depend on the residual resistance. Passive systems work in a rock mass having residual resistance. When the Safety Factor is equal to 1.0 the rock mass shows residual resistance. Job site Research input
- 19. Stiffness evaluation of a superficial revetment in a full scale test – Italian National Council for Research, Institute for Building and Material Technologies – CNR - OM
- 20. Research Outcome A mesh with high stiffness begin to work before less stiff revetment and controls better the instability
- 21. MAC.RO . 1 Stability check for superficial instabilities on rock slopes MA.CRO.1
- 22. The surface of the rock mass is a loose zone of a certain thickness . On this zone there are sets of joints dipping towards the slope which create unstable conditions. MA.CRO.1
- 24. The importance of natural joints in the rock mass A B C MA.CRO.1 D sliding asperity rupture dilatancy
- 26. Bar subjected to pure traction ( case “b” ): the joint dilatency does not affect the resistance contribution due to the bar. Bar subjected to pure shear ( case “e” ): the greater the joint dilatancy, the higher the resistance contribution of the bar. 1 3 MA.CRO.1 2
- 27. Input data for the worst joint and the anchor bar features. MA.CRO.1 Anc. Horiz. alfa Most unfavorable joint
- 28. Input data for The distance between the anchorages and The grouting
- 29. MAC.RO. 1 automatically sets the behavior of the netting It is important to describe the behaviour of the netting. MA.CRO.1
Hinweis der Redaktion
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- 2 superficial stabilisation is a complex system, in which the behavior of every single component must be considered. The resistance of the mesh subject to a load depends on the equilibrium between tensile strength and stiffness of the mesh. Often the mesh resists, but sometimes it suffers deformations that lead to the retrogression of instability or cause pockets of debris. Up to now, realistic and specific methods to design superficial stabilisation have not been developed. In order to solve the problem, Officine Maccaferri has deigned a set of tests.
- Laboratory tests, or big or small, do not allow "model" the actual conditions of bond which are presented in the book, with mesh affixed to the anchors (strong link) and in the adjacent meshes (weak link) . For this cause have been prepared in Pont Boset a testing ground scale, with anchors in real grid 3 x 3 m Le prove di laboratorio a grande e piccola dimensione non rendono consentono di modellare la vera condizione di vincolo che si realizza in opera, con le rete fissata da ancoraggi (vincoli forte) e da rete sui lati (vincolo debole). Per questo motivo è stato realizzato in Italia a Pont Boset una campo prove in grandezza vera, per una maglia di ancoraggi 3 x 3 m.
- The thrust of the hydraulic cylinder is 20 tonnes. It is installed in a shelter dug into the rock wall, which can rotate and placed in the direction of least resistance of the mesh. The shield thrust is the same used in laboratory tests on samples of great dimension (scale). He also directed the shield can freely according to the mesh of least resistance. This field test has allowed compare the behavior of the mesh in the conditions "ideal" laboratory with the actual conditions of application and the real links . La spinta del martinetto è 20 t. Il martinetto è installato in una nicchia nella roccia dove può ruotare e disporsi secondo la direzione di minore resistenza della rete. Lo scudo di spinta è il medesimo utilizzato per le prove di laboratorio su campioni di grande dimensione. Anche lo scudo è libero di disporsi secondo la minore resistenza della rete. Questo campo prove ha quindi consentito di confrontare il comportamento della rete a provata nelle condizioni ideali di laboratorio e nelle condizioni di applicazione con vincoli veri.
- El campo de pruebas de Pont Bozet ha permitido, en síntesis, verificar, en condiciones de carga y vínculos realistas, la real deformación de la malla en obra y la resistencia de la malla en realción con los anclajes Pont Bozet's testing ground has allowed, in synthesis, to check, in conditions of load and realistic links, the real deformation of the mesh in work and the resistance of the mesh in relation with the anchorages Il campo prove di Pont Boset ha consentito in sintesi di verificare in condizioni di carico e vincolo realistiche la reale deformazione della rete in posata in opera opera e la resistenza della rete in corrispondenza degli ancoraggi.
- El panel se deforma pero no cede de forma brusca ni presenta roturas. Velocidad de video acelerada. Toma lateral. The panel is deformed but is not deformed sharply, does not even present breaks. Speed of video accelerated. Lateral capture. el pannello si deforma, ma non dà cedimenti improvvisi o rotture. Filmato accelerato
- En igualdad de condiciones de instalación todas las mallas han dado deformaciones dramáticas. La malla o red que ha desarrollado más rápidamente oposición al movimiento del cilindro ha sido el panel HEA, seguido del SteelGrid BO150 y la malla Triple Torsión. La malla de simple torsión no ha opuesto prácticamente ninguna resistencia a causa de su elevadísima deformación. En otras palabras: la eficacia de una malla, es decir, la rapidez con la que se opone a los desprendimientos, no depende de la resistencia del alambre si no del modo en que ha sido “tejida” o fabricada. In the same conditions of installation all the meshes have given dramatic deformations. The mesh or net that has developed more rapidly opposition to the movement of the cylinder has been the panel HEA, followed of the SteelGrid BO150 and the Triple mesh Twist. The mesh of simple twist has not objected practically any resistance because the highest deformation that present. In other words: the efficiency of a mesh, that is to say, the rapidity with the one that is opposed to the detachments, does not depend on the resistance of the wire if not of the way of which it has been "woven" or made. A parità di condizioni di installazione tutte le reti hanno dato deformazioni drammatiche. La rete che ha sviluppato contrasto più rapidamente è la HEA panel, seguita dalla rete Steelgrid e dalla doppia torsione. Le reti a semplice torsione non hanno sviluppato praticamente alcuna resistenza a causa dell’elevatissima deformazione. Tradotto in altri termini significa che l’efficacia di una rete, cioè la sua rapidità nel contrastare il movimento di frana, non dipende dalla resistenza del filo, ma dal modo con cui è tessuta.
- As we see in the force diagram, there is no action if the netting lies in a perfect plane between anchorages. In fact the netting starts its action only when the blocks come away from the rock mass. Netting can not develop active force of stabilization as nails.
- Anchoring placed through a joint can be subject to a wide range of stresses. These can range from pure pull out stress - case b in picture 1 – to pure shear stress – case e. In case E the joint dilatency interacts with the anchorage bar which will be stretched when the sliding movement starts. In this way the dilatancy increases the stabilizing contribution of the anchorage. In case B the dilatency doesn’t interact with the bar capacity. Than, as indicated in picture 2, the stabilizing contribution of the bar depends on delta - the angle delta between the axis bar and the normal line to the sliding surface, and the dilatancy of the joint. The diagram 3 shows the relationship between the angle delta in the X axis, and the stabilizing contribution of the bar with various dilatancy level for the case of a bar with yield 430 Newtons per square millimeter. When delta = 0, that is pure shear stress, the resistance contribution of the bar is low whit evident difference depending on the dilancy of the joint.
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- 17 The second observations is that the unstable portion at the moment lies on the rock slope. Therefore, in the worst situation, the resisting force is the same as the driving force, otherwise it were less it would mean that the fall has already taken place. When the rock mass lies in limit equilibrium, we know the resisting force even if we don’t know the friction angle and the cohesion. This observation simplifies the geomechanical problem where there are a lot of unknown quantities. It is possible to implement a simple geomechanical model in order to calculate the drapery with netting and nails. if he resistance force is solely due to the friction angle it is impossible for the slope angle to be greater than the friction angle.
- 2 superficial stabilisation is a complex system, in which the behavior of every single component must be considered. The resistance of the mesh subject to a load depends on the equilibrium between tensile strength and stiffness of the mesh. Often the mesh resists, but sometimes it suffers deformations that lead to the retrogression of instability or cause pockets of debris. Up to now, realistic and specific methods to design superficial stabilisation have not been developed. In order to solve the problem, Officine Maccaferri has deigned a set of tests.
- Then it becomes very important that the netting has low deformability because it prevents many blocks of rock from coming away and helps the work of the anchorage. If the deformability of the netting is high, the blocks come away from the surface. The low deformability is the most important property of the netting for superficial stabilisation.
- 15 To improve the calculation, Maccaferri has produced a new software called macro 1, that takes in account the experience from many job sites. The software is based on some observations, in order to obtain a simple and realistic geomechanical model.
- 15 The first observation is that generally it is possible to identify the thickness of the superficial portion of the rock mass. This portion is identified by joint and weakened rock, or boulders fit against each to others. Then, acting with a general outline, we can identify the average beta inclination of the slope and the loose zone which is parallel to the slope. The unstable part can be identified by blocks and bridges of weakened rock (as in H and E); by concentrations of small blocks (case A); and by concentrations of rough blocks (case B)
- 16 Working in a simplified way the following can be recognised: The average beta slope inclination The thickness S of the loose portion parallel to the slope A set of joints dipping in an unfavourable way with alpha inclination Agendo in modo schematico, si riconoscono allora: Il pendio di inclinazione media beta Una zona rilassata di spessore S parallela al pendio Un set di giunti immergenti in modo sfavorevole con inclinazione alfa
- 28 Netting can only have a limited effect in controlling the movement between the joints because it is too flexible. But it does prevent many blocks of rock from coming away from the rock mass and in this way it helps the work of the anchorage. The work to be done by anchorage is related to the roughness of the joint. The roughness is due to the asperity of the joint surface. It resists the movement caused by the driving force. The driving force overcomes the roughness resistance in proportion to how far the joint opens. This is called the dilatancy of the joint. The resistance of the joint at this stage is called the “peak resistance”. When the maximum opening of the joint is reached, the rupture of the asperity starts and the sliding movement gets faster. The resistance of the joint at this stage is called the “residual resistance”. In the photo A and B there is the development of a sliding surface of a large sliding rock mass. In photo C e D there are details of the joint surface. The movement is indicated by the two red arrows. We can see both the rupture of the asperity with the green arrow and the dilatancy of the joint with the orange arrows.
- 29 Laboratory tests show that normal stress causes the joint to close during movement and resists dilatancy. The upper diagram shows the displacement of the joint under shear stress in the X axis, and the opening of the joint caused by movement in the y axis. With sigma = 0, the joint shows a large dilatancy, while with sigma = D , where D is the highest normal stress level, the dilatancy becomes very low. Then, if we had displacement of the joint without dilatancy, we would have to increase the normal stress. This is represented by the horizontal broken line in the upper diagram. We can control the dilatancy simply by using an anchorage across the joint. The lower diagram shows the shear stress in the Y axis and the displacement in the X axis. When dilatancy is possible, that is when the stress is low as in the red line of the upper diagram, there is a large difference between the peak and residual resistance to shear stress, as in the case of the green line. On the other hand, when dilatancy isn’t possible, there is a small difference between peak and residual resistance. The superficial part of the rock mass is loose in comparison with the internal one and the pressure on the joint is very low. Small movements (less than 2 cm) are normally sufficient to reach a state of “residual resistance”. Then the joints are in the same state as shown on the red line. From the diagrams it can easily be seen why anchoring is effective in underground and rock slope consolidation.
- 30 Anchoring placed through a joint can be subject to a wide range of stresses. These can range from pure pull out stress - case b in picture 1 – to pure shear stress – case e. In case E the joint dilatency interacts with the anchorage bar which will be stretched when the sliding movement starts. In this way the dilatency increases the stabilizing contribution of the anchorage. In case B the dilatency doesn’t interact with the bar capacity. Than, as indicated in picture 2, the stabilizing contribution of the bar depends on delta - the angle delta between the axis bar and the normal line to the sliding surface, and the dilatency of the joint. Diagram 3 shows the relationship between the angle delta in the X axis, and the stabilizing contribution of the bar with various dilatency levels for the case of a bar with a yield of 430 Newtons per square millimeter. When delta = 0, that is pure shear stress, the resistance contribution of the bar is low with an obvious difference depending on the dilancy of the joint.
- 30 Anchoring placed through a joint can be subject to a wide range of stresses. These can range from pure pull out stress - case b in picture 1 – to pure shear stress – case e. In case E the joint dilatency interacts with the anchorage bar which will be stretched when the sliding movement starts. In this way the dilatency increases the stabilizing contribution of the anchorage. In case B the dilatency doesn’t interact with the bar capacity. Than, as indicated in picture 2, the stabilizing contribution of the bar depends on delta - the angle delta between the axis bar and the normal line to the sliding surface, and the dilatency of the joint. The diagram 3 shows the relationship between the angle delta in the X axis, and the stabilizing contribution of the bar with various dilatency level for the case of a bar with yield 430 Newtons per square millimeter. When delta = 0, that is pure shear stress, the resistance contribution of the bar is low whit evident difference depending on the dilatency of the joint.
- 30 Anchoring placed through a joint can be subject to a wide range of stresses. These can range from pure pull out stress - case b in picture 1 – to pure shear stress – case e. In case E the joint dilatency interacts with the anchorage bar which will be stretched when the sliding movement starts. In this way the dilatancy increases the stabilizing contribution of the anchorage. In case B the dilatency doesn’t interact with the bar capacity. Than, as indicated in picture 2, the stabilizing contribution of the bar depends on delta - the angle delta between the axis bar and the normal line to the sliding surface, and the dilatancy of the joint. The diagram 3 shows the relationship between the angle delta in the X axis, and the stabilizing contribution of the bar with various dilatancy level for the case of a bar with yield 430 Newtons per square millimeter. When delta = 0, that is pure shear stress, the resistance contribution of the bar is low whit evident difference depending on the dilancy of the joint.
- superficial stabilisation is a complex system, in which the behavior of every single component must be considered. The resistance of the mesh subject to a load depends on the equilibrium between tensile strength and stiffness of the mesh. Often the mesh resists, but sometimes it suffers deformations that lead to the retrogression of instability or cause pockets of debris. Up to now, realistic and specific methods to design superficial stabilisation have not been developed. In order to solve the problem, Officine Maccaferri has deigned a set of tests.