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Muros anclados (Soil Nail Wall)

  • 1.  Muros anclados (Soil Nail Wall)

    Posted 08-13-2018 02:10 PM
    Edited by Tirza Austin 08-13-2018 02:10 PM
    Greetings to everyone.

    I have some concerns regarding the design of Soil Nail Walls. Do you have an example of calculation (design) of the wall in case of presence of phreatic level? Is it common to use threaded bars instead of cables?

    Regards,

    ------------------------------
    Andres Guzman Ing., M.ASCE
    PROFESSOR
    UNIVERSIDAD DEL NORTE
    Barranquilla
    573004284680
    ------------------------------


  • 2.  RE: Muros anclados (Soil Nail Wall)

    Posted 08-14-2018 09:57 AM
    Edited by Tirza Austin 08-14-2018 09:57 AM
    Hello there!

    Hope you are enjoying your day in Colombia, I will like to start off by mentioning I'm a student in the Cullen College of Engineering here in Houston,Texas.  I'm not a professional engineer nor masters. With that out the way I want to say great question. As I did some research on the phrases such as soil nail walls and phreatic level, I came to understand a bit better what your are asking. As I don't have an answer I have a few suggestions, in hope this can better help my understanding of civil engineering. If the cables were replaced by threaded bar, this will not change the flow of water below the phreatic surface. . . but possible can aid in saving material costs, which can be beneficial. Perhaps, using a water repellent agent that can be mixed with concrete in order to aid in moisture levels in soil. As for design, it'll be best to follow protocol/design in local cities that have been proven to endure the climate changes in your region.

    https://www.concreteconstruction.net/how-to/materials/waterproofing-admixtures-for-concrete_o
    The link above explains further the mixing on concrete in order to repel moisture.

    Forgive me for lengthy reply, as this is my first post on ASCE. Hope this helps, and good luck!



    ------------------------------
    Mike Echevarria S.M.ASCE
    B.S Civil Engineering Undergraduate
    Houston TX
    [Skyscraperboricua@...]
    [Mikeechevarria@...]
    ------------------------------



  • 3.  RE: Muros anclados (Soil Nail Wall)

    Posted 08-17-2018 09:06 AM
    Hi Mike! Thanks for your answer. Your suggestion is more than welcome! Bonding between bars and mortar and mortar and soil is a big challenge. Recently, some news has shown that phreatic waters are a big issue and our safety factors should be checked. 

    I solved the water problem increasing the pressure in the wall and modelling the wall as a slab supported in the places where nails are tensioned. Reactions are checked against the tension applied, and loads are modelled as distributed (hydrostatic pressure) according to phreatic level. According to the stresses inside the wall, some extra reinforcement should be added on the back of the wall in the nail location.

    Regards,
    AG

    ------------------------------
    Andres Guzman Ing., M.ASCE
    PROFESSOR
    UNIVERSIDAD DEL NORTE
    Barranquilla
    573004284680
    ------------------------------



  • 4.  RE: Muros anclados (Soil Nail Wall)

    Posted 08-19-2018 12:53 AM
    Edited by Tirza Austin 08-19-2018 12:52 AM
    Hello Andres,

    Thank you for replying in such a timely manner! You mentioned "bonding between bars and mortar and mortar and soil is a big challenge" this really helps me envision the complexity of the situation. As I am out of ideas I do have a few questions

    1. In the construction of the slab wall are you drilling into the earth? In my slight experience in working in earth work excavation, compaines were contracted to drill multiple 35m deep (roughly 100 feet) holes and fill them with concrete and steel bar.  If unable to tap deeply into earth perhaps extend the base of wall to distribute weight properly.

    2. How did you increase the pressure of the wall? What purpose does that serve for soil/mortar/cement? Seems like a great idea!

    Look forward from hearing from you.



    ------------------------------
    Mike Echevarria S.M.ASCE
    B.S Civil Engineering Undergraduate
    Houston TX
    [Skyscraperboricua@...]
    [Mikeechevarria@...]
    ------------------------------



  • 5.  RE: Muros anclados (Soil Nail Wall)

    Posted 08-20-2018 10:59 AM
    Edited by Tirza Austin 08-20-2018 10:58 AM
    Dear Mike, thanks for your post!

    Regarding your questions, we are drilling into the earth. The holes are 0.10 m and its length, 16 m (variable according to the vertical position). Extending the base is an excellent suggestion!

    The pressure of the wall is increased as a load (soil pressure + overload pressure + water pressure). It will help to check if the nail tension is ok.

    Phreatic level not detected during soil exploration

    Thanks again for your comments and suggestions.

    Regards,

    ------------------------------
    Andres Guzman Ing., M.ASCE
    PROFESSOR
    UNIVERSIDAD DEL NORTE
    Barranquilla
    573004284680
    ------------------------------



  • 6.  RE: Muros anclados (Soil Nail Wall)

    Posted 08-20-2018 12:23 PM
    Edited by Tirza Austin 08-20-2018 12:23 PM
    @ Andres Guzman Ing., M.ASCE Professor.
    THE COMMENT: "The pressure of the wall is increased as a load (soil pressure + overload pressure + water pressure). It will help to check if the nail tension is ok".
    These are the soil load bearing parameters, that can assist in providing adequate TENSILE CHARACTERISTICS for soil nailing Walls.
    They can be used to provide the soils properties, such as the shear strength, bearing capacity, consolidation parameters which necessary an appropriate structural design of the wall and tension cords.


    ------------------------------
    Olusegun Afolabi P.E., M.ASCE
    University of Lagos
    Lagos
    234803 4248600
    ------------------------------



  • 7.  RE: Muros anclados (Soil Nail Wall)

    Posted 08-21-2018 10:14 AM
    Edited by Tirza Austin 08-21-2018 10:13 AM
    Dear Olusegun,

    Thanks for your comments. Is there any distribution of responsibilities in this type of designs? In Colombia, the foundation engineer calculates the soil load bearing capacity, the length and resistance of cables. The structural designer take that capacity as a constant to design the retaining wall. Do you re-check all soil parameters and strength?

    Regards,

    ------------------------------
    Andres Guzman Ing., M.ASCE
    PROFESSOR
    UNIVERSIDAD DEL NORTE
    Barranquilla
    573004284680
    ------------------------------



  • 8.  RE: Muros anclados (Soil Nail Wall)

    Posted 08-23-2018 04:30 PM
    Edited by Tirza Austin 08-23-2018 04:30 PM
    Design information must be accurately assured during the process. Therefore, rechecking is just a necessary routine procedure for safety. 


    ------------------------------
    Olusegun Afolabi P.E., M.ASCE
    University of Lagos
    Lagos
    234803 4248600
    ------------------------------



  • 9.  RE: Muros anclados (Soil Nail Wall)

    Posted 08-22-2018 10:27 AM
    Edited by Tirza Austin 08-22-2018 10:27 AM
    Hi Andres,

    Hello everyone,

    Thanks for sharing a picture with us. Very interesting to see the actual application.

    Wow .10m deep! There is not much leg room is there? The proofing of the wall thru increasing pressure is a great idea as I mentioned before!

    How is the water pressure measured in combination with soil pressure and overload pressure?  By measuring moisture in both soil and overload?

    After viewing this picture, I've noticed excavated sections are not shelfed (stairs) like I normally will see here in Texas. We do have quite different soil, Texas clay! The walls are shelfed in order to assist as a safety measure to prevent collapse of an interior wall.
    thumbnail image


    "Shelfing technique"




    Thanks for all the information, you have been very helpful in broadening my understanding for the career of civil engineering. I would consider myself very lucky if I can take a class of yours!

    ------------------------------
    Mike Echevarria S.M.ASCE
    B.S Civil Engineering Undergraduate
    Houston TX
    [Skyscraperboricua@...]
    [Mikeechevarria@...]
    ------------------------------



  • 10.  RE: Muros anclados (Soil Nail Wall)

    Posted 09-03-2018 08:11 PM
    Edited by Tirza Austin 09-03-2018 08:10 PM
    Hi Mike, you are always welcome to attend our classes. If you come to Colombia, please let me know.
    I consider the water pressure as a hydrostatic condition (triangular distribution) with P=0 where the phreatic water appears and increasing linearly to the bottom of the wall. I should add this pressure to the uniform pressure associated with additional loads on the terrain and add it to the earth pressure (the passive condition due to nailing).
    Regarding the shelving technique, you will see it in another picture. I hope to send you this week.
    Regards,

    ------------------------------
    Andres Guzman Ing., M.ASCE
    PROFESSOR
    UNIVERSIDAD DEL NORTE
    Barranquilla
    573004284680
    ------------------------------



  • 11.  RE: Muros anclados (Soil Nail Wall)

    Posted 08-20-2018 11:01 AM
    Edited by Tirza Austin 08-20-2018 11:00 AM
    Wall bearing pressure; the wall structural capacity to effectively retain soil in the nailing process. Retaining walls are structures designed to restrain soil to a slope that it would not naturally keep to (typically a steep, near-vertical or vertical slope). They are used to bound soils between two different elevations often in areas of terrain possessing undesirable slopes or in areas where the landscape needs to be shaped severely and engineered for more specific purposes.

    ------------------------------
    Olusegun Afolabi P.E., M.ASCE
    University of Lagos
    Lagos
    234803 4248600
    ------------------------------



  • 12.  RE: Muros anclados (Soil Nail Wall)
    Best Answer

    Posted 08-15-2018 10:32 PM
    Edited by Andres Guzman 08-17-2018 07:41 AM
    First step site visual investigation with soil reinforcement company needs to be made. Preliminary layouts to be prepared with required depth and any nearby structures to be shown which may be effected. Soil investigation report to be prepared. Is the reinforcement scope temporary or permanent? Local well established soil reinforcement companies web sites to be visited and companies contacted to submit their bids, method of procedures,etc.? Note for water level presence weep holes are added at one or more levels. For normal soil rock bolts are not used. 

    ------------------------------
    Ammar Fakhoury P.E., M.ASCE
    Riyadh
    9665071 75857
    ------------------------------



  • 13.  RE: Muros anclados (Soil Nail Wall)

    Posted 08-17-2018 09:06 AM
    Edited by Tirza Austin 08-17-2018 09:05 AM

    Dear Ammar, thanks for your answer. 

    It is a temporary retaining wall. It is a wall of 200 mm of thickness. I contacted a local installer (soil reinforcement company), and they said they used cables instead of threaded bars (2 strands of 5/8" each, 300 kN, L= 16 m) and the concrete contractor is in charge of the wall construction. 

    The soil investigation report did not report the phreatic level, and this was a surprise. It was an emergency item for design....

    Thanks for your suggestion! I will consider the weep holes. Do you have ny suggestion regarding its location or distribution? The wall is 7  m in height and 40 m long.

    Regards,

    AG 



    ------------------------------
    Andres Guzman Ing., M.ASCE
    PROFESSOR
    UNIVERSIDAD DEL NORTE
    Barranquilla
    573004284680
    ------------------------------