 In this video, you will see the construction process for a concrete block abutment timber deck bridge installation. All these projects are replacing failed and failing culverts, and a lot of them which were perched, which were blocking fish passage with bridges. A lot of these culverts are starting to fail, and they're starting to plug from the upstream end. And for 25 years, the streams up above haven't been used for spawning habitat. And so now we get a chance to kill two birds with one stone, so to speak, by not only removing those failing structures that are a long-term maintenance cost for us, but also opening up spawning habitat that hasn't been used for 25 years. This type of construction consists of non-reinforced concrete block abutments, steel or timber girders, and timber deck bridge. Typically this construction can be done with a medium size to large excavator. Installation involves site preparation, excavation, and placement of the abutments, girders, and rock stabilization with an excavator. The steel girder assembly can be partially prefabricated prior to delivery to the site to minimize any onsite fabrication. The installation of the timber deck consists of basic carpentry work. A concrete block abutment timber deck bridge is typically used for smaller stream crossings on private land roads or other roads that have a lower traffic volume. Abutment heights are limited to 6 feet for the concrete blocks. Span width openings are typically 20 feet or less, however, up to 40 foot spans are possible using steel girders. These bridges are usually for one lane of traffic. They can be designed for a wide variety of loading requirements depending on the anticipated traffic over the bridge. We have a lifespan for our practices in this particular practice. I think this was, it was either a aquatic organism passage or stream crossings, had the same effect. In both of those, when we have bridges or culverts, we have a 25 year lifespan. Certainly the 25 years here, if anything, all they have to do is replace the deck. The abutments and the steel girders, they should be here. There's no reason they shouldn't be here 5,100 years from now. The steps for this project and all stream smart road crossing construction projects include the following, a review of the construction plans, water control, onsite preparation prior to construction, initial excavation, setting the abutments and establishing the stream channel, installing the bridge deck, channel shaping and adjacent road backfill. Construction Drawings Review Plans Before construction starts, a design needs to be completed that shows enough detail so the bridge can be installed properly. For a bridge, the key components are the location of the bridge, the bottom elevations of the abutments and the design channel through the bridge and the bridge opening width or span. This drawing shows a cross section of the bridge as well as the elevation of both the bottom of the footings and the design channel elevation through the bridge and the bridge opening width or span. The location of the bridge, in comparison to the location of the existing culvert to be replaced, is also shown. All elevations are established from a benchmark that was set during the initial design survey. The benchmark description is provided on the construction drawings. Other sheets of the construction drawings for this site include specific details for the assembly of the bridge components and the specific requirements for water, erosion and sediment control. The construction drawings should be provided to and reviewed with the contractor prior to construction. Water Control Water control typically consists of diverting all existing stream flow around the working area of the construction site. Any groundwater encountered in the working area of the site that picks up any sediment or is dirty water is pumped from the site and run through some type of sediment basin before the water is returned to the stream. The bridge was installed in August of 2013 when flows were low. Typically, a cofferdam is constructed both upstream and downstream outside of the anticipated working area of the site. The water pooled behind the upstream cofferdam is pumped around the site back into the stream below the downstream cofferdam. Since flows for this site were so low, an upstream sump with just a minimal cofferdam was needed to pool the stream flow to be pumped around the site. A downstream sump was used to collect any groundwater encountered at the disturbed construction site. Water collected in this sump was pumped into the woods far enough from the stream that the sediments in the disturbed groundwater were filtered out before returning to the stream. For sites where the groundwater flow is higher, a temporary sediment basin may have to be constructed somewhere offsite for the disturbed groundwater to flow through before entering back into the stream below the site. Due to the low surface and groundwater flows during construction, a small pump at both the upstream and downstream sumps were adequate for all water control needed. Scheduling construction at low stream flows is ideal for minimizing the difficulty of water control. Note the fish block nets used to keep fish from entering the work area. So primarily, we're keeping the clean water clean and then any of the dirty water we try to get it clean before we go back into the stream. On-site preparation prior to construction, delivery of materials. Prior to construction, as many materials and equipment needed for the bridge construction should be brought to the site in order to minimize the time actual construction takes. This is important in order to minimize the time the road has to be closed and can be critical if there are higher stream flows and water control is more challenging. For this site, precast concrete blocks were used for the abutments with steel girders and timber components for the bridge deck. The steel girders were preassembled in two sections in order to minimize on-site fabrication time. Required earth fill or gravel fill needed for the backfill of the abutments and road construction associated with the bridge should be stockpiled on site as much as possible. There are typically on-site storage limitations. However, stockpiling at least some of the earth fill or gravel fill can save time during the installation, especially if the fill source is a long distance from the site. Construction start, initial excavation. If carefully done, a large portion of the excavation can be done before the water control is initiated as long as sediments can be kept out of the stream. Here's the pipe prior to the start of excavation. A portion of the road fill over the existing pipe was removed prior to dewatering being initiated. Dewatering was not needed up to this point as all excavation was kept away from the stream. Here the dewatering has been initiated since the excavation is getting closer to the stream. All flow through the pipe has been stopped and is now being pumped around the work area. The pipe is left in place to allow for a working area for the excavator to install the far side abutments. This is important as there is only one excavator on site, so all work has to be done from one side. On larger sites, an excavator may be needed on both sides since all of the work area cannot be accessed from one side. Setting the abutments and establishing the stream channel. The excavation for the abutments is dug down to the bottom of the bedding required for the concrete block abutments. Typically six inches of coarse gravel or crushed stone is placed under the abutments for the bedding material. So the excavation has to be dug at least six inches below the design elevations of the base of the abutment. Here they are excavating for placing the bedding material and then placement of the bedding material up to the elevation of the base of the abutment. The bedding material should be placed approximately one foot wider than the abutment concrete blocks for adequate support. Prior to the final excavation and placement of the bedding material, the final alignment of the abutment is set for the proper place of the bedding material and concrete blocks. Now both abutments are in place along with the rock, rip, wrap, reinforcement. The channel elevation and shape has also been established. The center of the channel through the bridge is one foot higher than the base of the abutments. Placing the base of the abutment one foot lower than the design channel bottom and placing the rock, rip, wrap, reinforcement at the base of the abutments will prevent the undermining of the bridge abutments. We get the footers, what we anticipate down to at or lower than what we would anticipate in a channel scour, so we just want to keep the footer stable. In between there, the channel underneath the bridge, if that will form a low flow channel, we've even seen gravel bars form underneath the bridge, as long as we keep those footers stable, however, whatever dynamics happen in the channel, that's fine because channels do that anyhow. Installing the bridge deck. A steel girder system was used for the bridge deck. For smaller bridges with lighter load requirements, wooden girders are sometimes used. For this site, the steel girder assembly was preassembled in two sections prior to delivery to the site. The preassembly helped save time for the girder placement and provided it for better precision in girder assembly. Here they have installed the two sections of the steel girders. Now the entire steel girder is in place. Next is placement of the transverse timbers. The upper portion of the bridge deck consists of 8 inch by 8 inch cross or transverse timbers with 3 inch thick running planks nailed to the transverse timbers. These are typically spaced 1 inch apart and are held together with 3 inch thick travel surface or running planks that are nailed to the transverse timbers. The entire wooden deck is then fastened to the steel girders with a steel plate, bolt, and channel iron assembly. Here is the completed bridge deck. And then the road backfill is even to the top of the travel surface and running planks. Completed bridge channel shaping and adjacent road backfill. Here is the completed bridge and adjacent road backfill. The backfill behind the concrete block abutments is placed in 6 to 12 inch lifts that are mechanically compacted with a hand compactor. The backfill for the road beyond the abutment backfill is typically just compacted with larger equipment such as an excavator or bulldozer. Even though the road fill beyond the abutment backfill is not mechanically hand compacted, it still should be placed in lifts no greater than 12 inches with adequate compaction between lift placements. This will help to minimize settling in the road surface especially closer to the bridge. Note the channel shape as it is slightly concave in the center section of the channel to ensure an initial low flow channel under the bridge. The amount of rip-rap reinforcement against the abutments should be limited to only the amount needed to minimize encroaching on the stream channel bottom. If the opening for the bridge is properly sized, sediments will be deposited upstream, downstream and under the bridge to form a continuous natural low flow channel. With a properly sized opening, the natural channel continues uninterrupted under the bridge and can adjust according to storm intensities and sediment transport loads. Support for the production of this video comes from Poland Spring, the Sewol Foundation and the USDA Natural Resources Conservation Service. StreamSmart is a collaboration of the following partners. Thank you to the following organizations and individuals who helped make this video possible.