268) ARTIGO INTERNACIONAL - DESIGN & EXECUTION OF CABLE ANCHORAD FOR REINFORCED SLOPE
PARA RETORNAR A PÁGINA PRINCIPAL CLIQUE ABAIXO
IN THE L
AST FEW DECADES, TREMENDOUS GROWTH HAS BEEN WITNESSED IN THE TECHICAL AVALANCHE PROTECTION SYSTEMS AND IT HAS EVOLVED AS AN
INDEPENDENT ENGINEERING BRANCH IN ASIAN, EUROPEAN AND AMERICAN COUNTRIES
INDEX 4
60.Interview -
A candid chat with Mr. Katikeya Kalani, President Flexituff International Limited on application of geosynthetics in river training works
63.Interview -
In Conversation with Mr. Manish Barot, Head-Technical Sales and Business Development at TechFab India
66. Case Study -
Design & Execution Of Cable Anhord For Reinforced Slope – An In-depth study on the construction of reinforced walls for prevention and mitigation of landslide using cable anchors
75.Webinar –
Excerpts from the live webinar on Avalanche Protection – The Need of The Hour
80.Interview -
Rendezvous with Dr. TN Singh, Vice Chancellor at Mahatma Gandhi Kashi Vidyapith
WWW.GEO-XCHANGE.COM | VOL..01 ISSUE .03
5
FROM THE EDITOR
The year 2020 has been full of unexpected
turn of events to say the least, being hit by a pandemic is something neither of us ever anticipated. While we are still getting accustomed to the “new normal” for me the year 2020 will be a memorable one since this was the year “GeoXchange” was born. Today, writing this note on a warm winter afternoon, I am humbled by how welcoming this industry has been of our endeavor. We at GeoXchange are grateful to each and every member of this fraternity
who has shown faith in us and given us the opportunity to tell their story. With the third issue of our magazine ready for publication, I am proud to say that we have been able to achieve, 4000 + downloads of our first two editions andatremendous response tothe series of webinars that we have been hosting. With every issue and webinar, I can see us grow from strength to strength and achieve global recognition in countries like Switzerland, USA, Italy and more.
The world is a land of diverse terrains, which also means that we are constantly dedicating resources to mitigate a multitude of plausible disasters that can greatly impact the global economy. With the onset of winters every year, my newsfeed is drowned with incidents of heavy snowfall, avalanches and stories about regions that are cut-off from civilization for almost six months because of it. As a conscious global citizen, these stories have often led to a profound awareness of this plight, with the heartbreaking understanding that perhaps not much can be done about it. When I extended my communications business and dived into the journalistic world of Geohazard mitigation earlier this year, I was surprised at how little we get to know about the efforts made by so many players in this industry to mitigate risks relate d to high altitude terrains around the world. As an ode to the voices that haven’t been heard, the third issue of GeoXchange is dedicated towards navigating the world of Avalanche Protection which is truly a need of the hour.
I sincerely hope our efforts in bringing these
GEOXCHANGE | DECEMBER 2020
NEHA BAJAJ
Editor-in-Chief coversations to the fore front will get you one step closer to knowing more about successes, projects and players of this industry. I would like to extend my thanks to everyone who helped us put this issue together, your contribution is greatly valued.
We are also gearing up for our next webinar in January. Stay tuned to know more about it along with compelling news features from the industry by subscribing to our website www.geo-xchange.com and following us on our social media handles.
As we all gear up for the coming year, here’s hoping that 2021 brings in health and happiness to everyone around us and may we get success on COVID Vaccine soon so we can be assured of safety of our loved ones. With the New Year, we at GeoXchange are also geared up and excited to further diversify our portfolio and bring to you more in-depth conversations and stories with leaders and stakeholders that go beyond the realms of natural hazard mitigation. I sincerely, hope you continue to enjoy this new chapter of our journey with us. On that note it’s time to be merry and welcome the new year! Feel free to write to me should you have any queries / recommendations.
Merry Christmas and a Happy and Prosperous New Year!
See you in February.
TEAM 6
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CASE STUDY 66
DESIGN & EXECUTION OF CABLE ANCHORD FOR REINFORCED SLOPE
Luiz Antonio Naresi Junior (Author) PROGEO, BELO HORIZONTE, BRASIL
RESUME:
This project focusses on the use ofconstruction of reinforced walls for prevention and mitigation of landslide using cable anchors in a envi- ronmently friendly way with the highest safety for the workers involved in accordaince to the guidelines of Brazil.
Cable anchors is a specialized engineering application used to an- chor reinforced concrete structures to the ground in order to contain a slope, we will describe some executive methods for the construction of a reinforced slope. It is one of the active containment solution for slope stabilization which addresses the issue of global stability, by introduc- ing a force corresponding to a stabilizing thrust that reacts against unstable masses.
The execution of a cable anchor, as well as reinforced concrete slope, are part of the stabilizing solution of massifs and involve various en- gineering activities such as drilling in soil, alteration of rock and rock, injection of cement grout under pressure, execution of form, frame and concreting and finally the prestressing of the strands, these works are generally performed on scaffolding with manual and mechanical excavations. All services present in the execution of cable anchors in- volve serious risks to worker safety.
In most situations, site conditions involve other engineering risks such as; working at height, trench excavations and sliding slopes.
In this project, the author, who is a Civil Engineer with specialiation in Occupational Safety Engineer and Environmental Analyst, and has been working since he graduated with the art of Geotechnics, man- aged to address in detail about all the executive procedures and the corresponding approach to work with safety and prevent any damage to the environment. Protecting environment is one of the highest pri- ority for geotechnical engineers, designers, executors, occupational safety engineers and occupational safety technicians.
KEYWORDS: CALCULATION, EXECUTION, ANCHORTIRANTE, ANCHORS, SLOPE STABILIZATION, LANDSLIDE MITIGATION
WWW.GEO-XCHANGE.COM | VOL..01 ISSUE .03
67 CASE STUDY
1. PRESENTATION OF THE TIE ROD
1.1. Prestressing
If we want to take a lot of books at once, we “squeeze” them as shown in Figure 01 and thus transport them to the place we want. If we don’t press the books against each other, as shown in Figure 02, they will fall to the floor.
Figur1 1: Strong – Horizontal Force
Figure 2: Weak – Horizontal Force Source: Own Collection
This squeeze, we call “prestressing”.
It is as if we made a hole in all the books, pass- ing a threaded screw and putting a nut on each side and tightening, as shown in Figure 04.
Figure 3: The impressed fort
Figure 4: Horizontal Effort Source: Own Collection
This screw is nothing more than a type of tie rod.
2.2 Tie-in rod
The riser takes a little more work, but the idea is the same.
Do you know why our foot is forward?
CASE STUDY 68
Figure 5: Foot Support - Efforts that work. Source: Own collection.
If we cut off the tip of our foot, we will fall be- cause we lose our support.
On a mountain, the same thing happens. If we dig the foot of the mountain, it loses its support, and it slides: at the top it collapses at the bottom. If soon after we cut the mountain, we can put pressure on it (as in the books on the table), the mountain will not fall..
Figure 6: Slope collapse Fonte: Own collection
But, how to make this squeeze, if there is no one to hold on the other side?
Then someone had an idea: he drilled a hole in the ravine, tilted downwards, filled the hole with a mixture of water and cement and put an iron bar inside.
When the cement hardened, it “pulled” the iron rod out, as if it wanted to pull it out: the sticky section did not let the rod out. Then it made a floor of wood, or of steel or concrete profiles, and built a device that would not let the bar return to its original position, and released the bar. When the bar was released, it “pushed” the bank, with a force in the opposite direction to the slide, not letting the bank or mountain slip.
to the slide, not letting the bank or mountain slip. This operation of “pulling out” the bar from the ground is called “prestressing”, and when we re- quest the bar, it “presses” the ground (as in the books on the table).
This force that we apply to the bar is called “trac- tion” or “tensioning” and the bar (can be one, or several grouped together) is called tie rod.
Figure 7: Principle of the draped curtain Source: Own Collection
2. WHAT IS AN ANCHOR FOR
As we saw above, risers are therefore elements that support tensile forces and serve to balance the forces exerted by earth masses.
As we have seen, we must not delay in its execution: in general the terrains are weak (when compared to the strength of steel and concrete) and with the help of water, which is always present, they easily collapse.
Therefore, the speed and perfection in the execution of a tie, in all its phases (drilling of the land, assembly and installation inside the hole, injection of cement grout and pretension) are essential conditions, both for the work and for the safety of people who are running the same.
2.1 Type of Tie rods
Nowadays there is a huge variation of types of tie rods, we mention below the most usual ones that can be summarized in:
2.1.1 Wire tie rods
2.1.2 Wire rope tie rods
2.1.3 Rod risers
69 CASE STUDY
Figure 8: Layout of a bar tie rod Source: Own Collection
Figure 9: Tie Rod Source: Own Collection
Figure 10: Wire/Strand Holders Source: Own Collection
Figure 11: 8 Wire Rope dia 8mm Source: Own collection
Figure 12: Detail of the free section Source: Own collection
Figura 13: Middle of Anchored & Free Section Source: Own collection
CASE STUDY 70
Figure 14: Protection detail Source: Own collection
Figure 15: End of the anchored section Source: Own collection
Figure 16: Prestressed wire rope Source: Own collection
Figure 17: Bench injection tie rod Source: Own collection
3. ELEMENTS THAT MUST BE IN THE WORK
For the execution of risers, we must be in possession of the work, obligatorily of the elements that concern the execution.
3.1. The Survey Report
It describes the type of soil or rock that we are going to drill, whether it is soft or hard,whethere there is water and if there is a ripple, etc.
This drilling report is very important which informs us, what type of equipment we are going to use, what drill or hammer we are going to use and, whether or not we have to cover the hole, the way to inject the rod, the pressures to be applied, the care to be taken so that neighboring buildings are not damaged, etc.
3.2. Tie-rod design
It shows where we should start drilling: so many meters from the top, so many meters from the ground.
Placing the tie rod in the wrong position can cause inconvenience later. For this it is very important to know where the head of the tie is in relation to the ravine.
3.3. Drawing informing the characteristic of the tie
a) If it is made of bar, wire or cordage;
b) How many bars, wires or strings;
c) How long the tie rod: free, anchored and left over (out of the ground);
d) What is the inclination to be given when drilling?
e) What type of corrosion protection:
71 CASE STUDY
f) The. painting: type of paint, how many coats;
a. sheath: individual and / or collective.
3.4. Execution bulletins
Execution reports record the history of each tie. That is why it is essential to complete and correct filling, which are: drilling, assembly, injection and pretension.
Figure18:Boultassembly,drilling&injectionbulletin Source: Own collection
Figure 19: Presetressing bulletin Source: Own Collection
4. MASSEMBLY PROCEDURE OF A TIE-ROD
First, let’s list the materials that will make up the tie: steel wires; the spacers; the hems; plastic masses; the paints; the central tube, with injection valves; the wire.
4.1. Steel wires
You have to arrive at the construction site with a certificate. The certificate shows his resistance, which we must compare with the resistance marked in the project.
4.2. Spacers
The function of the spacers is to assemble the wires or strands separately from each other, so that at the time of injection, the syrup uniformly envelops them in the anchorage area. They are placed every 0.5 meters of wire / strand or 2.5 meters in bar tie rod.
4.3. Sheaths
The sheath can be individual, collective or joint. The sheath will insulate the wires along the free stretch, from contact with the cement grout. The individual sheath is a plastic tube that we place on each rod or wire on the rod.
The collective sheath is a tube or hose that wraps all of the wires simultaneously.
The joint sheath is the use of two sheaths, individual and collective, at the same time.
The hem must also not tear. Therefore, the tie rod must be handled with care, especially when it is placed inside the hole.
4.4. Plastics
They are placed in the passage from the free zone to the anchoring zone on all ties, whether permanent or temporary. At the bottom of the tie, put the plastic putty only when the tie is final. No temporary tie rod is necessary.
4.5. The paints
Before painting, the wires or strands must be carefully cleaned on the entire surface to remove areas of oxidation, rust spots, grease and resins. Cleaning should be done by manual brushing or
CASE STUDY 72
electric circular whip brush, until total removal of the aforementioned residues. Immediately after cleaning, the wires / strands should receive the first coat of paint. This ink is composed of two components, plus the solvent. This solvent, after mixing components A and B should be added in a minimum and gradually, as necessary and sufficient, to allow applicability to the surface of the wires / strands. Do not forget to touch up the support points of the elements on the bench. After light sanding, when the paint on the first coat shows sufficient grip, that is, it does not come off the surface of the steel, it should be applied to the second coat.
Read the instructions for using the paint on the outside of the can to check the recommended curing time between coats.
Never a permanent tie must be installed without the bar, wires or strands being painted and cured.
4.6. The central tube
The central PVC tube is the “column” or “backbone” of the tie. It is around him that everything will be done. It should have the length of the rod plus one left over. In the free zone, it is smooth. In the anchoring zone, it is drilled with an electric drill, every 500 mm. There are 8
6.3 mm holes. These holes will be covered by a rubber tube 100 mm long by 2 mm thick, with side stops (collars) to prevent their displacement along the tube.
This tube is what we call a headline valve. The assembly sequence is:
1. cut the wires to the size that the project sends. Pay attention to add (increase) the length by another 1 meter or as much as the project requires;
2. sand the wires with sandpaper or with a wire brush. If it is corded, clean the cracks well;
3. paint the threads with two coats of paint, as described;
4. pass the bar, wires or strings through the spacers spaced every 50 cm or 2.5 meters on the bar. Install the injection tube (central PVC) with the bottom plug and secure the assembly with the wire. Then, install the individual sheaths on the free section of the tie, securing them firmly with the wire. If the tie is permanent, place the collective sheath.
4. MASSEMBLY PROCEDURE OF A TIE-ROD
First, let’s list the materials that will make up the tie: steel wires; the spacers; the hems; plastic masses; the paints; the central tube, with injection valves; the wire.
4.1. Steel wires
You have to arrive at the construction site with a certificate. The certificate shows his resistance, which we must compare with the resistance marked in the project.
4.2. Spacers
The function of the spacers is to assemble the wires or strands separately from each other, so that at the time of injection, the syrup uniformly envelops them in the anchorage area. They are placed every 0.5 meters of wire / strand or 2.5 meters in bar tie rod.
4.3. Sheaths
The sheath can be individual, collective or joint. The sheath will insulate the wires along the free stretch, from contact with the cement grout. The individual sheath is a plastic tube that we place on each rod or wire on the rod.
The collective sheath is a tube or hose that wraps all of the wires simultaneously.
The joint sheath is the use of two sheaths, individual and collective, at the same time.
The hem must also not tear. Therefore, the tie rod must be handled with care, especially when it is placed inside the hole.
4.4. Plastics
They are placed in the passage from the free zone to the anchoring zone on all ties, whether permanent or temporary. At the bottom of the tie, put the plastic putty only when the tie is final. No temporary tie rod is necessary.
4.5. The paints
Before painting, the wires or strands must be carefully cleaned on the entire surface to remove areas of oxidation, rust spots, grease and resins. Cleaning should be done by manual brushing or
73 CASE STUDY
5. ANCHOR INJECTION PROCEDURE
The rod injection serves to transfer the load by adhering the bars / wires / strands to the ground, in addition to creating an additional protective layer to the paint so that they do not oxidize over time in direct contact with the water in the subsoil. This work step is carried out in two phases.
6. PROCEDURE FOR TENSION AND PRETENSION
After 7 (seven) full days of the curing of the injected cement (CP-II-E-32) or 3 (three) full days when using the initial high strength cement (CP- V-ARI), the tie rod may be intended .
Every tie must be tested with a load greater than the one it will actually work on.
7. CALCULATION OF SLOPE STABILITY:
For the calculation and dimensioning of the containment system, we will take into account the section of the thrown curtain that has a height of
5.00 m and comprises 20.00 m in length.
Calculation of active active thrusts: Soil 1: y (kN/m³) = 1,8
C (kPA) = 2,0 0 (º) = 26
Active buoyancy coefficient:
• Ka = 0,390
• √Ka = 0,625
sha = Z.Ka – 2.C.√Ka + q.Ka
Elevation pressure EL. 99,30 (Top containment) sh = – (2 x 2,0 x 0,625) + (8,0 x 0,390)
sh = 0,624 tf / m²
Elevation Pressures EL. 94,30 (Toe containment) sh = (1,8 x 5,0 x 0,390) – (2 x 2,0 x 0,625) +
(8,0 x 0,390)
sh = 4,138 tf / m²
Diagram of the acting pressures:
Figure 44: Actuating pressure diagram Source: Own Collection
Containment pushes:
E1 = 0,624 x 5,00 = 3,120 tf / ml E2 = 3,514 x 5,00 = 8,785 tf / ml
2,0
Total active Thrust:
3,120 + 8,785 = 11,905 tf / ml
Curtain length: 20,00 m Buoyancy Total:
11,905 tf/m x 20,00 m = 238,10 tf
For the uses of SAS Prestressing – CT= 35 tf, 238,10 tf : 35 tf/anchor = 6,80 anchors Adopted 16 anchors - FS= 2,35 - ok!
8. CONCLUSION:
We conclude that the solution presented has a safety factor above that recommended in Global Stability and Containment. In Global Stability, the containment system has a safety factor of 1.656, after the insertion of elements resistant to active efforts, such as rods and piles. The soil parameters adopted were described above.
CASE STUDY 74
In the Stability of Containment, the risers are dimensioned with a safety factor of 2.35, also above the recommended which is 2.0. The section analyzed was the 20.00 m contention, which is 5.00 m high with 16 of the SAS Proten- sa Ø 32 mm in diameter CT = 35 tf in the lengths indicated in the project.
ACKNOWLEDGEMENT
To all who directly or indirectly participated in the execution of this work, especially SAS and Progeo Engenharia Ltda for their contribution.
REFERENCES
NARESI JR, Luiz Antônio. Curtains with risers. 2014. Available at: www.naresi.com. Accessed on: 07/04/2015.
NARESI JR, Luiz Antônio. TRINDADE, Sérgio. Hillside Containment. Foundations and Geotechnical Works Magazine. In focus. Rudder Publisher. Edition 55. Year 6. p. 66-77, May.
2015.
NARESI JR, Luiz Antônio. Work safety in Containment Works with the Use of Tie Rods, (2008) Master’s Dissertation, Post-Graduate Program in Occupational Safety Engineering, Department of Civil Engineering, Federal University of Juiz de Fora, 150 P.