BACKGROUND
    In 1986, Eggers and Hirsch conducted a series of static tests on wood and steel guardrail posts embedded in two different types of soils with embedment depths of 18 inches, 24 inches, 30 inches, and 38 inches.(1) The objective of these tests was to determine the effects of post type, embedment depth, and soil conditions on load-deformation characteristics of a guardrail post. A mathematical model developed to predict guardrail post load capacity was also verified using these test results.
    In 1987, Hirsch and Beggs conducted a research on the use of W-beam guardrails on low-fill bridge length culverts, where the soil-fill depth of the culverts was not enough to achieve full embedment depth of the guardrail posts.(2) Two crash tests were conducted with seven consecutive wooden posts in the impact region installed at 18 inches and 27 inches of embedment depths, respectively. Both tests were unsuccessful. It was noticed that the posts rotated and pulled out of the soil simultaneously. It was concluded that sufficient embedment depth was needed to increase friction force that prevents the posts from pulling out readily. It was also noticed that adequate embedment depth was needed to develop required bending strength or lateral load capacity.
    In 2003, Herr et al. developed a W-beam guardrail system for installation in rock-soil foundation.(3) This was a W152x13.4 steel post systems that was supported on 27 posts. In a crash test, the W152x13.4 steel posts were installed in concrete (to simulate rock) by drilling three overlapping 203-mm diameter holes that were 165 m apart at their centers and were 610 mm deep. The holes were backfilled with compacted ASTM C33 coarse aggregate. The system was successfully tested for NCHRP Report 305 at Test Level 3. The researchers conducted some further bogie testing of guardrail posts and gave recommendations for installation of guardrail posts in situations where rock is encountered at various depths below the ground.
    In 2004, Bligh et al. conducted a study to evaluate crashworthiness of strong post W-beam guardrail with pavement mow-strips being used arounds its posts.(4) Mow-strip dimensions, materials, and depths were varied in 17 dynamic bogie impact tests with wood and steel posts. These tests were numerically simulated and full-scale finite element models were developed using these sub-component models. Predictive simulations were performed to evaluate various mow-strip configurations and a concrete mow strip with grout-filled leave-outs was selected for full-scale crash testing. crash tests were successfully performed with wood and stell posts installed in 18 inch x 18 inch grout-filled leave-outs. It was recommneded that a "leave-out" area in the most strip should be built around each post and that the leave-out area should allow at least 180 mm of post deflection at ground level. The top 4.5 inches of the leave-out area re backfilled with low-strength grout mix with a 120 psi compressive strength or less.

OBJECTIVE
    The objective of this research is to develop cost-effective guidelines for placement of W-beam guardrail posts in rock by optimizing current placement guidelines and by investigating sensitivity of W-geam guardrail performance to post embedment depth.

BENEFITS
    This research would identify cost-effective solutions for placement of guardrail posts in rock and result in significant savings in guardrail installation in areas where rock is encountered by minimizing the number and depth of cored holes.

WORK PLAN
    This research will be completed in two phases. In the first phase, TTI will develop guidelines for installation of W-beam guardrail posts in situations where rock is encountered. These guidelines will be developed based on pendulum testing, previously available full-scale crash test data, and simulation analyses. The participating states will review the guidelines at the end of the first phase. If the states find the guidelines suitable, a second phase will be funded through the pooled-fund for verifying the guidelines through full-scale crash testing.

Final Report - May 2009

 
QUARTERLY PROGRESS REPORTS:

September 2008 Progress Report
June 2008 Progress Report
March 2008 Progress Report
December 2007 Progress Report
September 2007 Progress Report
June 2007 Progress Report
March 2007 Progress Report

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(1.) Eggers, D.W. and Hirsch, T.J. (1986). "The Effects of Embedment Depth, Soil Properties, and Post Type on the Performance of Highway Guardrail Post." Research Report 405-1, Texas Transportation Institute, Texas.
(2.) Hirsch, T.J. and Beggs, D. (1987). "Use of Guardrails on Low Fill Bridge Length Culverts." Research Report 405-2F, Texas Transportation Institute, Texas.
(3.) Herr, J.E., Rohde, J.R., Sicking, D.L., Reid, J.D., Faller, R.K., Coon, B.A., and Polivka, K.A. (2003). "Development of Standards for Placement of Steel Guardrail Posts in Rock." Research Report TRP-03-119-03, Midwest Roadside Safety Facility, Nebraska.
(4.) Bligh, R.P., Seckinger, N.R., Abu-Odeh, A., Roschke, P.N., Menges, W.L., and Haug, R.R. (2004). "Dynamic Response of Guardrail Systesm Encased in Pavement Mow Strips." Research Report 0-4162-2, Texas Transportation Institute, Texas.