Engineers Corner: A Closer Look at Site Specific Shoring Plans

BY National Trench Safety

NTS stands alone as the sole trench and traffic safety equipment enterprise boasting a nationwide branch network. Our extensive, diverse inventory encompasses equipment available for both rental and sale, accompanied by traffic and trench safety engineering services. Additionally, we offer a broad OSHA-compliant training curriculum. Fundamentally, NTS is a service-oriented organization, a commitment reflected in our mission statement.


Site-specific shoring plans originated in response to OSHA Subpart P-1926.652(c) (4) Option 4, Design by an Engineer. In the standard, OSHA states:

1926.652(c)(4)(i)- Support systems, shield systems, and other protective systems not utilizing Option 1, Option 2, or Option 3, above, shall be approved by a registered professional engineer.

1926.652(c)(4)(ii)-Designs shall be in written form and shall include the following:

1926.652(c)(4)(ii)(A)-A plan indicating the sizes, types, and configurations of the materials to be used in the protective system; and

1926.652(c)(4)(ii)(B)-The identity of the registered professional engineer approving the design.

The standard, however, does not go into great detail about what the plan should look like or contain. In practice, the plan serves the needs of many different people that can become involved with an engineered shoring plan, including the contractor, his workers, OSHA, the reviewing engineer, and the lawyer, all of whom look for different things in the plan. This article looks at the site-specific engineered shoring plan, what it should contain, and the reasons why.

Site-specific plans are required when there is no tabulated data available for the shoring system that a contractor wants to use. These cases are usually where:

  • Tabulated data shoring systems, like hydraulic shores and shoring shields, for example, are being used in situations that are not described or allowed by the manufacturer’s tabulated data and or the OSHA standard. The use is not meant to circumvent the tab data, but simply to use the equipment in a way that was not envisioned by the data. For example, shoring shields with endplates are not allowed by tab data, however, it may be safe to do so as long as the loads are calculated and do not exceed the allowable strength of a shield or the plates based upon proper engineered analysis.

Another example is where single lines of hydraulic shores are sometimes used in conjunction with shields at utility crossings.

  • With tabulated data, the soils must always first be identified by the Competent Person in accordance with OSHA Appendix A. The OSHA soil types and loadings are often more conservative than an engineered soil analysis on a project-specific basis, so there is the potential to gain depth and or shore spacing using engineering calculations based on the specific site and not a generalization.
  • Shoring systems like sheet pile and wale typically are a combination of steel shapes and are not designed and marketed as shoring systems. There may be tabulated design data for the components but it still requires an engineer to apply the component data to design the system.
  • Manufactured systems like slide-rail and hydraulic brace are complicated and oftentimes are best done by an engineer. Some manufacturers do provide tabulated data for these systems that can be used in more routine applications by trained, qualified personnel experienced with the systems.

Sometimes the contractor uses engineered plans for risk management to ensure his crew is getting the correct system for the project, as well as obtaining a professional opinion to help prevent things from going wrong with the protective system. The essential difference between Option 4 and Option 1 and 2 is that an engineer is responsible for the shoring design, not the contractor. The contractor remains responsible for installing the system safely and in accordance with the plan.

Another difference between site-specific plans and tabulated data is that the plan looks at the specific location. It takes into consideration existing structures and buried facilities that affect the shoring system as well as assessing temporary surcharge loads. The site-specific plan should clearly designate the location of all buried utilities and if they are close to or interfere with the shoring system there should be notes that require the exact location prior to or during the shoring installation. Critical facilities like high-pressure gas and buried electrical lines should be clear in the plan. Problems that would delay the work in the field should be rooted out and solved at this stage of planning. This is one of the advantages of obtaining an engineered plan from an experienced engineer. The engineer will have the benefit of other similar applications and can ask additional questions related to the safety and efficiency of the system that may help the contractor select the optimal system and plan for the project.

The Competent Person and the shoring installation crew review the engineered plan for details and instructions on how to install and maintain the shoring system. Often, it may be necessary to adapt an engineered plan due to job site deviations. In this case, the Competent Person should notify the engineer when there are changes and document those changes by photograph or site inspection by the engineer and the engineer should confirm that the changes are okay or not.

Sometimes the shoring is even installed prior to getting the engineer involved. As long as no one enters or works inside the excavation during installation it is again acceptable (from employee protection from excavation hazards) as long as the engineer develops and stamps a plan, however, the contractor is taking an additional risk in doing so. There are many instances where OSHA or design side project engineers have looked at installed shoring systems and could not determine if they were installed correctly and asked that the contractor get an engineered plan before moving on. This is a simple solution to a deadlock in the field.

OSHA looks at an engineered plan from a slightly different perspective. It gives them assurance that difficult soils and difficult shoring applications are safely planned and shored. It assures that a job site hazard analysis and solution have been performed. The plan tells the OSHA inspector how to inspect and determine if it is properly constructed. In the event of an accident on the project, anywhere on the project, it gives them an opportunity to define and document additional safety violations. Option 4-Design by an engineer is OSHA’s way of promoting and allowing innovation to function within the safety standard. There is no limit to the shoring possibilities as long as it is properly engineered and installed, which encompasses the safe and effective design of the system.

The project design side engineer is looking at the plan with an eye toward fulfilling his overview and due diligence to safety of the project. It is typically a requirement that the project owner and his engineering firm establish (and consequently pay for) clear requirements for safety on the project. If there is to be excavation work on the project there is typically a contract requirement that any contractor or subcontractor meets all OSHA safety requirements. The standard of care for this can vary depending on the circumstance. From the bottom up, it may go something like this:

  • In any excavation, there should be verification that the contractor with workers in the excavation has a Competent Person and is providing worker protection from a cave-in.
  • For tabulated data applications, the submittal reviewing engineer should look at the appropriateness of the proposed equipment for the soil types and applications. Can it be installed with regard to safety and soil conditions? Is it strong enough to withstand soil and surcharge loads? Will it stabilize the trench to protect existing facilities, meet settlement and deflection requirements, and can the production work be performed (stable bottom, working room to construct)?
  • In the field, provided there is an experienced contractor and the Competent Person a complete calculation or walk-through of the data application should not be necessary. The responsibility of the contractor varies according to the application. The contractor’s means and methods should not be tampered with. Violations of the tabulated data should be noted in writing and brought up as far as it needs to go to the contractor. This is where the rubber meets the road. If you go too far you start to become partly responsible. From a legal standpoint, it is generally better to be able to raise an issue than to provide an ultimatum on how it is to be done.
  • Site-specific plans should be reviewed for elements such as clear plan and detail, notes, the inclusion of existing facilities, installation, and removal instructions if not obvious. Calculations should rely on soils report or site-specific inspections where soils are not available. Confirmation of soil assumptions conforming to dug conditions should be obtained and documented. Calculations should be clear and inclusive of tabulated information on the elements being used. The soils report and borings should be referenced. Standard engineering theories and material design codes should be apparent. Look at soil loading assumptions. Review, calculation, and confirmation of all calculations are problematic as they lead to partial ownership of the problems.
  • In cases where there are very difficult soils or water conditions, site-specific plans should always be required. If standard shoring solutions are not available they should be eliminated in the contract and acceptable solutions listed. In very complicated situations a preliminary shoring design should be developed with the project design. If standard shoring solutions are not readily available to the contractor and it is not pointed out in the specifications, there is fertile ground for the contractor to come back with impossible-to-construct claims.

The content of the site-specific shoring plan varies with the situation and there are no hard and fast rules about what should be included. In my opinion, a plan that simply shows a shoring system with soil calculations that verify that it is strong enough is not a site-specific shoring plan. Engineering is more than just drawings and calculations; it involves investigation and situational awareness. Sometimes these plans are reviewed and used extensively throughout the process and sometimes simply stuck in a file just in case it is needed. In my experience working with contractors and developing shoring plans since 1990, whenever there has been litigation whether it is by OSHA, the contractor against the project owner, or a worker harmed in the excavation process against every entity involved the site-specific plan has always been an important element in the case. As they say, “If it is worth doing it is worth doing right”. When a contractor orders a site-specific plan he should expect all of the elements discussed above to be considered in the plan and should verify that the site-specific plan does address these items. For the safety of your workers and the protection of your company, you should find a good experienced engineer that you trust and work with him/her whenever it is relevant to the shoring work you are doing. Site-specific engineering is generally not that expensive in relation to the cost of the shoring system being used. Typically one of these plans takes one to three days of an engineer’s time to develop. Deep excavations and complicated soils and circumstances would obviously increase the time spent. The fee covers time and risk to the engineer but is not looked at or billed the same as permanent project design side engineering.

At National Trench Safety we maintain a highly experienced engineering department that is committed to producing complete, thorough, site-specific engineering. Turnaround time is usually less than one week from the release of the order. We provide stamped engineered plans throughout the United States, United Kingdom, and Canada.

DISCLAIMER: the information contained in this article is provided for general and illustrative purposes only and is not to be considered Site Specific and or designated engineering for any project or work zone, nor is it to be used or considered to be tabulated data, technical data, advice and or counsel to be used on any job site. Each project is different and is the responsibility of the employer’s designated Competent Person to make decisions on what systems and methods may be used in compliance with the federal and local regulations, manufacturers tabulated data, engineered drawings, and other plans. The ideas, concepts, and or opinions expressed in this article are those of the author and not necessarily reflective of NTS’s position or view of a topic in all cases.

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