St. Cloud Hospital
St. Cloud Hospital in St. Cloud, MN, is the site of a $225-million expansion project to add a new hospital wing as well as a larger warehouse, distribution center, and loading dock. Five hundred new parking spaces are also being added.
The majority of the wall was built using Redi-Rock 28-inch blocks and is reinforced with geogrid in every course. About 200 square feet of the wall was constructed using Redi-Rock 41-inch gravity blocks to minimize excavation at the hospital’s property line, due to the presence of underground utilities close to the building. The gravity blocks allowed the wall in this section to be built without geogrid, which kept the wall construction from disturbing the neighboring property and saved the neighbor’s mature trees. Normally, the Redi-Rock walls have a 4-degree angle of batter to them, but special blocks were made that stack completely vertically, producing a zero-batter wall.
Hardrives Inc. supplied the blocks for the project. The company’s Dominic Lundebrek described the site: “There’s a big hillside that goes down to the river, and a loading dock and a truck entrance to the hospital are at the bottom of the hillside. Right now they’re accessing it from the south end on a little, narrow trail. But the hospital expansion will block that access road. So they needed to build a new road from the north end to access the bottom of the hill, and that’s the main thing these retaining walls did— allow the construction of roadways going down the bottom of the hill. The retaining wall stands about 33 feet high at the tallest point, on the riverbank.”
At some points, the wall is less than 100 yards from the riverfront. Lundebrek adds, “It was a pretty steep hill there to start with, at the river bluffs. It was too steep to punch a road down, so the retaining wall kept the soil back and allowed us to carve a trail down to the bottom.”
Located so close to the Mississippi, the project had environmental issues as well. “It was a pretty tight spot,” he explains, “and they were concerned about any runoff or concrete. We had to be real careful about everything, making sure everything was contained and nothing could get into the river.”
For backfill, mostly onsite material was used, but some difficulties were encountered. “There was some heavy, dark, silty clay soil when they got down to the bottom, only a few feet from the top of the river level,” says Lundebrek. “They had to excavate that and put some good stuff back in. The backfill for the wall was what they had excavated for the roadways, but most of it they had to screen because there was larger rock in there; they had to get all the large rocks out so they didn’t cut through the geogrid. They had to screen everything. I believe 2 or 3 inches was the largest rock they would allow because of the geogrid.”
The drainage system used 4-inch drain tile with access points punched through the base of the wall approximately every 50 feet where a drain was put in.
The total size of the retaining wall was approximately 25,000 square feet. An unusual feature is the uncommon bond pattern used. While most retaining walls have a one-half bond pattern, meaning that each course of block is offset by half the length of the block below, the St. Cloud Hospital walls have a one-third bond pattern, so that each course of block is offset by one-third. This required installation crews to custom-cut a portion of the blocks in each course to create a unique look for the hospital’s walls.
Margaretville Bridge
The East Branch of the Delaware River, together with a number of tributaries, runs through the village of Margaretville in upstate New York. One of those tributaries is Bull Run Creek, and flooding from major storms had caused severe damage to its six-lane Walnut Street bridge.
“We were replacing flood-damaged stone walls that were on either side of the stream,” explains Andy Bell, president of A.S. Bell Engineering. “Bull Run Creek runs down through the village, and it crosses under three or four structures before it gets to the Delaware River. We had replaced one structure the previous year where they had a three-sided box culvert, and then we just continued the project on either side with a Stone Strong retaining wall.”
He adds, “While it’s not a long bridge, it’s geometrically challenging along its entire length as it winds and curves on a downhill slope over the creek with two skewed angles. So we needed to construct bridge walls that curve concentrically around the creek’s bend—and we needed to do it quickly before the next snowfall. Steel beams and a concrete poured deck would simply take too long.”
The Stone Strong Systems cavity-fill retaining wall blocks, provided by LHV Precast, served two purposes. They lined the creek bed and provided bridge deck support at the abutments. “We actually capped the walls with concrete and made a bridge seat out of them, and put precast slabs on them for a bridge,” says Bell.
Because the channel winds through the neighborhoods and was getting close to the existing houses, there was no room for the use of geogrid. Furthermore, as Bell explains, “There was no need to use a geogrid. The Stone Strong walls are such that for that height wall you don’t need geogrid—they’re self-standing. For the most part, the blocks are filled with stone. Under the bridge seat, we filled them with concrete.”
A separate drainage system was unnecessary because the stone-filled hollow cores of the retaining wall blocks act as the unit’s drainage system. The concrete-filled portions supporting the bridge deck were narrow enough not to cause drainage concerns.
Asked to identify the biggest challenge of this project, Bell says, “Mostly geometry! The two walls on either side of the creek were on concentric circles, and the street itself was on almost a 45-degree skew with the stream at that point. It didn’t make a nice 90-degree angle under the bridge; it was actually on an arc. There are three panels of the precast bridge slabs that we put down at one dimension of skew, and downstream three are on a different skew angle, so it was definitely a challenge.”
Another issue was the tight working space, with houses nearby. “We closed the road off,” says Bell. “It’s a relatively narrow street. Getting the crane in there to set the pieces and wires was a little tough. The beauty of these blocks is you can set them with a large excavator, so it wasn’t until we got to the bridge slabs that we needed the crane. You can just offload the blocks right from the truck and set them right down with a large excavator right into the stream and backfill them. We actually put a temporary dam upstream and downstream of the site and pumped the water around the site. We didn’t actually work in the stream.”