Category: Overturning factor of safety retaining wall

Overturning factor of safety retaining wall

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Join Us! By joining you are opting in to receive e-mail. Promoting, selling, recruiting, coursework and thesis posting is forbidden. Students Click Here. Related Projects. Home Forums Geotechnical Engineers Activities Earth retention engineering Forum retaining wall factor of safety analysis thread I am a homeowner in a subdivision that has gravity retaining walls that are between 3 and 5 years old. Not a geotech engineer, sorry if that is a problem.

The walls range from a foot high to about fifteen feet in height. The soil type in this area is clay. There were several collapses years ago when subdivision was still under construction but we've haven't had any problems in the past three years. We have the original design plan with wall dimensions that have the base being roughly half the wall height and an embedment ranging from six inches to 3.

We had a different engineering firm analyze the wall design and they came up with a table of "Factor of Safey" values for sliding, bearing, and overturning. The sliding values computed look horrible, with FOS values ranging from 0. The main conclusion of the analysis was that the wall design was for a different soil type friction angle deg than the clays 14 deg we have.

The analysis assumed that clay was used as backfill because a few pictures of collapses appeared to show this. At the bottom of this layer the plan shows a drainage pipe.

overturning factor of safety retaining wall

It is unknown how well this plan was followed. My basic question is regarding the analysis FOS values. Is it realistic to assume that the analysis was overconservative? Shouldn't thousands of feet of walls with a sliding FOS of 0.

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I'm a little unclear what FOS exactly means. I've heard 1. What time period does this mean?Slideshare uses cookies to improve functionality and performance, and to provide you with relevant advertising. If you continue browsing the site, you agree to the use of cookies on this website. See our User Agreement and Privacy Policy. See our Privacy Policy and User Agreement for details. Published on Mar 17, SlideShare Explore Search You.

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You can change your ad preferences anytime. Modes of failure of retaining walls. Upcoming SlideShare. Like this presentation? Why not share! Embed Size px. Start on. Show related SlideShares at end. WordPress Shortcode. Ritesh ChinchawadeGeotechnical Engineer Follow. Full Name Comment goes here. Are you sure you want to Yes No. Moonshaker Moonshaker. Show More.Retaining walls are structures designed to bound soils between two different elevations, therefore they are mainly exposed to lateral pressures from the retained soil plus any other surcharge.

Cantilever walls may be sensitive to sliding problems, particularly if founded on poor soils. This article discusses how to calculate the sliding safety factor in cantilever retaining walls. In addition to the retained backfill, retaining walls may be subject to surcharge loads at the top of retained mass, or a high water table. When the stem extends above backfill the retaining wall may be exposed to wind load.

If the retaining wall is located in a seismic zone the seismic pressures should also be considered. The image below shows schematically the pressure diagrams on a typical retaining wall. Each applied load has a particular effect on the wall. The backfill exerts a triangular lateral pressure calculated per the corresponding earth pressure theory. The surcharge produces a uniform rectangular pressure on the wall.

Factor of Safety Design of Retaining Walls

The seismic pressure is trapezoidal, with the higher pressure at the top. The action of these loads produces a bearing pressure under the footing, and a passive pressure at the front of the wall. For a more in-depth discussion of the soil lateral pressure theories and overall stability modes please see the post Cantilever Retaining Walls: Overview of the Design Process.

The horizontal pressures on the backfill side will push the wall outward, which will tend to slide on its footing. The driving force from the applied loads must be resisted by an opposite friction force at the interface of the footing base and the underlying soil, produced by the bearing pressure against the base.

In addition, the passive pressure against the front face of the wall and footing may be considered as well. When the friction plus passive forces are not high enough to counteract the pushing force, a shear key can be designed under the wall footing. This structural element will bear laterally against the soil, increasing the sliding resistance.

The position of the key along the footing is not very important, but many engineers prefer to place it just under the stem, so that the wall rebars can be extended down into the key.

Cantilever Retaining Walls: How to Calculate the Overturning Safety Factor

Per IBC This provision was removed in the IBC, without further explanation. It seems that the intent of the code is to go back to the design philosophy prior to the IBC, where this provision requiring the active pressure diagram to be extended down to the bottom of the key didn't exist. Where seismic loads are included, the minimum safety factor should be 1. Note that the load combinations are based on service loads, since the wall stability is being checked. In this example the safety factor is greater than 1.

The sliding failure mode should be checked as part of the design, considering the correct pressure diagrams at both sides of the wall.

overturning factor of safety retaining wall

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overturning factor of safety retaining wall

Click Here to join Eng-Tips and talk with other members! Already a Member? Join your peers on the Internet's largest technical engineering professional community. It's easy to join and it's free. Register now while it's still free! Already a member? Close this window and log in. Are you an Engineering professional? Join Eng-Tips Forums! Join Us! By joining you are opting in to receive e-mail. Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here. Related Projects. Hello All, I am designing the foundations for a pre-engineered metal building and would like to know what safety factor you all are comfortable to use for overturning checks.

I see that in I would think 1. Thanks for any thoughts! I think you only need to satisfy the load combinations. Using the load combinations gives you a factor of safety of 1. Exactly, some load combinations have taken to embedding the 1. My take is that the load combinations of 0. Similar for the 0. I do not consider 0.

That isn't a factor of safety of one, though? You have an inherent factor of safety in your dead load reduction. I'm not bothering to double check the way the limit states factors work in the IBC at the moment, but as an extra point of clarification I'm assuming it's a 1.

This would be generally in line with the way it works in Canada. You're basically checking: 0. As mentioned above, the load combination of 0. If you're using unfactored loads, then yes, you want the factor of safety of 1.Geotechnical Info Search.

Geotechnical Forum Ask for technical help or discuss geotechnical issues with other engineers. Geotechnical Publications Free publications and resources for geotechnical engineers. Geotechnical Software Download free software and links to geotechnical software. Technical Guidance Valuable technical information for geotechnical engineers. Your questions may be answered here. Learning Center Learning and training resources for geotechnical engineers.

Career Development Tips for earning more respect and more money. Market yourself. Please look at the information and related sources for Retaining Walls in the publications or software links. Or, post a question in the Geotechnical Forum. Comprehensive step by step calculations for retaining wall analysis are provided below, or click:. Lateral earth pressures are analyzed for either "Active," "Passive" or "At-Rest" conditions. Active conditions exist when the retaining wall moves away from the soil it retains.

Passive conditions exist when the retaining wall moves toward the soil it retains. At-Rest conditions exist when the wall is not moving away or toward the soil it retains. Conditions for active, passive and at-rest pressures are usually determined by the structural engineer.

Basically, at-rest pressures exist when the top of the wall is fixed from movement.

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Some theorize that at-rest pressures develop over time, when a retaining wall is constructed for the active case. Lateral earth pressures are typically analyzed, as presented below, from one of the following methods:.

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Basically, lateral earth pressures are derived from the summation of all individual pressure stress areas behind the retaining wall. These pressure areas are triangular in shape with the base of the triangle at the base of the wall for the soil component and pore water component.

Pressure areas for surcharges are rectangular in shape, and earthquake pressures are usually analyzed with a nearly 'upside-down' triangle.

The resultant lateral earth pressure, R, is the summation of all individual lateral earth pressure components. Engineering judgment should allow for some pore water pressure behind a retaining wall due to stormwater or other water source. For a water table behind the wall, why would you analyze a partially submerged backfill? You could reasonably expect for almost every situation that a partially submerged backfill will become fully inundated during the life of the wall.Overturning and sliding checks are done to make sure the stability of retaining walls.

In addition to this, base bearing pressure is also checked to confirm whether it is within the limit. In this calculation, we are concentrating on the two stability checks of sliding and overturning.

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It should be noted that the weight of the structure has not been considered in this calculation. Even without the weight of the structure, there is a higher restoring moment.

The factor of safety against sliding is generally considered as 1. However, it could be vary depending on the design requirements. Here, the value is well above the required value. Therefore, it can conclude as an overturning check is satisfactory. Sliding can be considered in two ways. The friction force between soil and concrete or passive pressure generated by a shear key can be considered to avoid the sliding of the structure. Case No shear key, consider only friction between soil and concrete.

The weight of the structure should be considered for this calculation as it increases the reaction that leads to a higher friction force. Assume friction coefficient between soil and concrete as 0. This value may be vary depending on the ground condition. Generally, we keep the factor of safety around 1.

The actual safety factor is well above the allowable value. Therefore sliding is ok. Some of the engineers are reluctant to use the friction force along to avoid the sliding of retaining walls as the ground conditions could be varied and unpredictable.

In addition, when the height of the retaining wall is increasing, the effect of the passive pressure is considered most of the time. Even though the above calculation is satisfactory for sliding, we could proceed with this method also to get an idea about the concept.

As per the above figure, soil cover above the base is 0. It also notes that we need to check the pressure under the foundation and it should bellow the allowable bearing capacity of the soil. Skip to content Retaining Structures.Richard P. Course Outline. This course is intended for a wide range audience and in particular, the non-geotechnical engineer.

Therefore it is not an exhaustive review of the subject. The objective of the course is to discuss the three types of lateral earth pressure at rest, active and passive that apply to a wall and describe how each is calculated.

The course then uses this information and discusses the method of calculating the active earth pressure force using the Rankine and Coulomb methods described in this course. The method for calculating the factors of safety for sliding, overturning and bearing capacity are discussed.

Basic examples are provided to illustrate the concepts. This course includes a multiple-choice quiz at the end, which is designed to enhance the understanding of the course materials.

Learning Objective. When this course has been completed, the reader will be familiar with the three types of earth pressure and how each is calculated. The reader will also be familiar with how the total force resulting from lateral earth pressure is calculated and how forces are used to determine the factors of safety with respect to sliding, overturning and bearing capacity relating to retaining wall design.

These factors of safety are three of the elements required for retaining wall design. Course Introduction.

Cantilever Retaining Walls: How to Calculate the Sliding Safety Factor

Retaining walls are used for a number of practical reasons in construction. In order to design a successful retaining wall it is necessary to know how to calculate the forces that act on the wall and how to calculate factors of safety that will assure a safe design. This course intends to provide a basic understanding of the earth pressure that acts on a wall and how this pressure is resisted.

Therefore the objective of this course is to familiarize the reader with:. Course Content. You need to open or download this document to study this course.

Course Summary. Retaining wall design begins with the basics of understanding and calculating the forces that act on the wall.

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This course has provided an introduction to these forces and how they are applied to calculate appropriate factors of safety. In particular the reader should understand that:. The material presented in this course is intended only for general familiarization with the subject matter and for educational purposes. The course does not cover all aspects of the subject. Use of this material in any manner whatsoever shall only be done with competent professional assistance.

The author provides no expressed or implied warranty that this material is suitable for any specific purpose or project and shall not be liable for any damages including but not limited to direct, indirect, incidental, punitive and consequential damages alleged from the use of this material.


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