Natchez, Mississippi

The Natchez National Cemetery (National Cemetery), the final resting place for over 7,100 U.S. veterans, stands atop an approximately 120-ft high bluff overlooking the Mississippi River in Natchez, Mississippi. Erosion, sloughing, and caving of the bluff during heavy rain events over the years resulted in regression of the top of the bluff towards the cemetery. The Department of Veterans Affairs (VA) approached the U.S. Army Corps of Engineers-Vicksburg District (MVK) to develop a concept for stabilizing the bluff. The MVK engaged Ardurra Group, Inc. (Ardurra) and Burns Cooley Dennis, Inc. (BCD) to design a solution.

BCD analyzed the soil conditions at the site and designed a slope stabilization system which made use of several innovative geotechnical technologies. The stabilization system consists of a 1,270-ft long retaining wall generally ranging in height from 35 ft to 48 ft. The wall system is comprised of over 1,000 soil nails ranging in length from 15 ft to 35 ft, and 89 prestressed anchors ranging in length from 90 ft to 210 ft, which provide resistance against both localized and global slope failures. Ardurra designed drainage systems to collect and route storm water to the bottom of the bluff.

The design and construction of the bluff stabilization system was a significant challenge due to the limited land space and access, steep slope face, and continuing regression and changing geometry of the bluff during the design and construction processes.

Roane County, Tennessee

In early 2019, following a winter of heavy precipitation, Tennessee Department of Transportation (TDOT) personnel noticed cracks were occurring in an approximately 0.4-mile-long stretch of the westbound (WB) lanes of Interstate Highway 40 (I-40) along the south slope of Rockwood Mountain in Roane County, Tennessee. TDOT contracted with a geotechnical engineering consultant to perform a detailed geotechnical exploration and monitoring program. The consultant and TDOT developed a design (contract design) which would incorporate permanent tieback anchors with reaction blocks to stabilize the landslide. The contract design called for 1,714 (3-, 7- and 9-strand) anchors with each anchor bonded into bedrock below the slide surface. In the summer of 2020, TDOT awarded the construction contract for this project to Richard Goettle, Inc. Shortly thereafter, Goettle retained Burns Cooley Dennis, Inc. (BCD) to develop a Value Engineering (VE) design for the project.

The VE design used the same concept as the contract design, but used a smaller number of anchors than was called for in the contract design. The VE design reduced the number of anchors to 605 by using larger 12-strand anchors and longer bond lengths. The reduction in the number of permanent tieback anchors by greater than 275 percent was significant, allowing a greater spacing between the anchor and reducing the potential for the very long anchors to intersect. This reduction also minimized the overall project time for drilling through the boulder-strewn colluvium and residual soils to reach below the slide plane at depths reaching 200 ft. The on-site construction of stepped reaction blocks further improved construction efficiency and reduced construction-related traffic delays on I-40.

The VE design was accepted by TDOT in June 2021. Goettle achieved substantial project completion and installation of the tieback anchors in December 2022. The VE design significantly reduced the construction time, originally projected for the contract design in May 2024. The VE design provided slightly more load capacity than the contract design.

The project received special recognition for the following reasons:

• The design incorporated relatively large 12-strand anchors, allowing for fewer anchors to be needed to achieve the desired factor of safety;
• The required length of the anchors to reach stable bedrock below the shale surface and the boulders in the colluvial soils above the slide surface presented significant challenges;
• The flexibility of the VE design and construction techniques allowed for adjustments to be made quickly without significant impacts to the project schedule or cost; and
• The VE design allowed for the project to be completed 1.5 years prior to the originally projected completion date.

The stabilization of this section of I-40 is important to provide long-term stability to this important roadway in Tennessee. Because this stretch of I-40 crosses Rockwood Mountain, it is especially important, since closure of the interstate highway would require very time-consuming detours, affecting other portions of the Tennessee transportation infrastructure.

Vicksburg, Mississippi

A strong storm on April 2, 2017 resulted in over 7 inches of rainfall over a 9-hour period in Vicksburg, Mississippi. During this intense storm event, a landslide occurred along the bluff immediately north of the Old Mississippi River Bridge and below the National Park Service’s Navy Circle Overlook. The landslide encroached on the north approach wall for the bridge and caused a regression of the bluff below the overlook.

Burns Cooley Dennis was retained as geotechnical engineer by the Vicksburg Bridge Commission of Warren County to develop an approach for stabilization of the bluff and protection of the bridge abutment.

Based on BCD’s evaluation, a soil nail wall was determined to be the most appropriate and feasible solution. For over 90 percent of the wall, an environmentally sustainable soil nail wall facing consisting of a vegetated high tensile strength steel wire mesh and erosion protection matting was selected to stabilize the bluff. Directly beneath the bridge abutment, a shotcrete facing was selected to provide additional protection to the approach and the bridge end spread footing foundations.

Hayward Baker, the design-build contractor for the project, did an excellent job of installing the high-quality soil nail wall quickly and effectively despite the complexities of the project. The soil nail wall was completed within a year with minimal disturbance of the bluff.

The completed wall is unobtrusive, but essential to preserving the Old Mississippi River Bridge, Navy Circle Overlook, and the expansive views of the Mississippi River from these historic sites.

Vicksburg, Mississippi

The “Great Wall of Vicksburg” at Ameristar Casino on the Mississippi River in Vicksburg was built out of the necessity to design and construct a slope stabilization wall that would protect the southernmost portion of the Ameristar Casino site from deep-seated landslide movements, which had been occurring at the site since its construction in 1994.  Burns Cooley Dennis, Inc., as a subconsultant to Hayward Baker Inc. who was working for Pinnacle Entertainment on this project, developed an innovative design for the wall incorporating deep micropile and long pre-stressed anchors to resist those landslide forces.  Based on the load resistance provided by the wall when completed, this slope stabilization wall was one of the largest, if not THE largest, slope stabilization walls ever constructed at that time.

Vicksburg, Mississippi

Burns Cooley Dennis, Inc. (BCD) was retained by the Mississippi Department of Transportation (MDOT) to provide geotechnical engineering services related to the investigation, design, and construction of the slide stabilization system at the Signal Hill landslide on U.S. Highway 61 in Vicksburg, Mississippi. BCD recommended a ground anchor/buried anchor block stabilization system to accommodate a number of constraints at the project site. More common methods of slide stabilization were rejected because of cost and conflicts with site constraints. Use of the ground anchor/buried anchor block stabilization system allowed the design and construction to be completed in a relatively short time frame, did not require the acquisition of additional right-of-way, avoided impact of nearby high pressure gas lines, and was the most economical method to achieve the desired increase in factor of safety. The ground anchor/buried anchor block system is a unique and cost-effective method for slide stabilization. It can be used in areas where limited right-of-way and/or topography preclude the use of conventional stabilization methods and in cases where stabilization forces need to be evenly distributed over large areas. BCD’s recommended use of ground anchors/buried anchor blocks successfully stabilized the Signal Hill landslide on U.S. Highway 61 and allowed it to be restored to its original configuration with no visible evidence of the stabilization system. Hayward Baker Inc. was the contractor for this project.

Jackson, Mississippi

Burns Cooley Dennis, Inc. (BCD) was retained by the State of Mississippi Department of Agriculture and Commerce to provide geotechnical engineering services related to the investigation, design and construction of a slope stabilization system to halt a significant landslide which was threatening to damage Jefferson Street near the Farmers Market in Jackson, Mississippi.  Previous attempts to remediate this landslide had been unsuccessful. Taking into consideration numerous site constraints caused by limited right-of-way and topography, BCD recommended remediating the landslide by constructing a soil nail wall in the upper portions of the landslide and then utilizing a slope regrading stabilization system to return the lower slope to a more stable grade.

Use of the soil nail wall/slope regrading stabilization system was more cost effective than other conventional remediation methods, allowing design and construction of the wall to be completed in a relatively short time frame without requiring temporary shoring during construction. This method also avoided the closure of Jefferson Street while construction was performed and also resulted in an aesthetically pleasing wall and slope facing the Farmers Market, a popular facility which allows Mississippi farmers to sell produce directly to the public.

BCD’s work on this project was performed as part of a team consisting of Cooke, Douglass, Farr, Lemons/Ltd. Architects and Engineers; Spencer-Engineers, Inc.; Engineering Service; Birdsong Construction and Hayward Baker, Inc.

BCD received the ACEC-MS 2011 Engineering Excellence Honor Award for this project.