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The National Academies

NCHRP 22-51 [Pending]

Impact of Soil Stiffness on the Performance of Crash Testing and Roadside Safety

  Project Data
Funds: $250,000
Contract Time: 24 months
Staff Responsibility: Christopher McKenney

BACKGROUND

AASHTO’s Manual for Assessing Safety Hardware (MASH, 2016) contains the testing procedures used to evaluate various roadside safety features. MASH testing guidelines were intended to provide consistent and reproducible tests. One significant change in MASH is the use of standardized soil stiffness to provide consistency in the performance of safety barriers embedded in soil.  The development of stiffness criteria was based on testing in various U.S. test facilities utilizing soil criteria described in NCHRP Report 350: Recommended Procedures for the Safety Performance Evaluation of Highway Features, which did not specify soil types or the optimal hardware installations. The MASH specification for soil stiffness defines a minimum stiffness for the response of a standard W6x16 steel post surrogate to dynamic loads for a specified soil type and correlates this response to a static load test to be performed as part of each soil-based crash test.

Since the implementation of MASH testing, concerns with this new soil stiffness criterion have been noted. The first of these is the lack of a maximum stiffness limit. Highly stiff soils can negatively impact system performance, and there is concern that lack of an upper stiffness limit does not provide consistent testing between laboratories and various installations. Other potential issues relate to optimization of the current testing for identifying salient properties of a variety of soils utilized by various crash testing facilities.

Over the past few years, many crash tests have been performed on a variety of systems under MASH criteria. The opportunity to evaluate the efficacy of and potentially improve the new stiffness-based soil criteria is timely and critical to the continued improvement of roadside safety. Since MASH is the standard for evaluation of roadside safety devices, the research could affect state departments of transportation (DOTs) and other transportation agencies. Research is needed to review the current MASH soil specifications and evaluation procedures to ensure consistency in crash testing and develop proposed language for consideration by AASHTO to incorporate the research results in the next update of MASH.

OBJECTIVE

The objective of this research is to evaluate the impact of soil stiffness on the performance of crash testing and roadside safety.

RESEARCH PLAN

The research plan should (1) include a kick-off teleconference with the research team and NCHRP convened within 1 month of the contract’s execution; (2) address how the proposer intends to satisfy the project objective; (3) be divided logically into detailed tasks necessary to fulfill the research objective and include appropriate milestones and interim deliverables; and (4) incorporate opportunities for the project panel to review, comment on, and approve milestone deliverables.

Accomplishment of the project objective will require at least the following tasks.

TASKS

PHASE I — Planning

Task 1.  Conduct review of literature and MASH testing data. The MASH testing data shall come from a cross-section of crash testing facilities. Review dynamic bogie and static instrumented post-test results performed during crash testing for each facility and correlate this to barrier performance.

Task 2. Review the test installation procedures and inspect the soil conditions at crash test facilities. Soil conditions shall include, but not be limited to, native and fill material soil type, width and depth of fill material, gradation, compaction, soil density, moisture content, and moduli.

Task 3. Identify sections of MASH that will be impacted by the results of the research findings. Develop proposed draft language for consideration by AASHTO to incorporate the research findings in the next update of MASH (herein called AASHTO Deliverable). The goal of the modifications is to more accurately reflect barrier performance during crash testing, with consideration given to soil conditions.

Task 4. Develop a plan to test the proposed AASHTO Deliverable. Submit, for NCHRP approval, a test plan for validation of potential modifications to MASH soil specifications and testing criteria.

Task 5. Prepare Interim Report No. 1 that documents the work completed in Tasks 1 through 4, and provides an updated and refined work plan for the remainder of the research no later than 6 months after the contract award date.  The updated plan must describe the process and rationale for the work proposed for Phase II.

 

PHASE II — Testing and Final Deliverables

Task 6. Execute Task 4 according to the approved Interim Report No. 1.  Based on the test results and data analysis, modify the proposed AASHTO Deliverable as needed.

Task 7. Submit final report and project deliverables. Project deliverables shall include: (1) a conduct of research report documenting the entire research effort; (2) the AASHTO Deliverable with draft language for the implementation of the findings for consideration by AASHTO in a future update of MASH; and (3) implementation plan.

 

STATUS: Proposals have been received in response to the RFP.  The project panel will meet to select a contractor to perform the work.

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