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Img10032
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Item Code: 1849
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Following compaction, a number of test pits were dug where aggregates up to 3/4-in.-size had been placed under the membrane liner. Examination of these areas showed the liner had bulged around the aggregates, but in no case had the aggregates punctured the liner.
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Img10004
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Item Code: 1821
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Various methods of embankment protection had been used in this area including rock riprap, wire-cage (rail-bank) rock, shown here, and soil-cement. Following the flood, a survey of embankment protection methods found soil-cement the only method to have performed well.
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Img10005
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Item Code: 1822
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Performance of the more than 30 soil-cement projects in the area was considered outstanding. As a result, Pima County, in which Tucson is located, allows only soil-cement bank protection or requires a 500-ft. setback from major waterways.
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Img10024
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Item Code: 1841
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A much less elaborate conveyor belt system is shown here placing soil-cement slope protection for one of three sewage lagoons at Sterling, Colorado.
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Img10025
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Item Code: 1842
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In planning a slope protection project, consideration should be given to whether a definite stairstep feature similar to this seven-year-old marina in Texas is desired.
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Img10027
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Item Code: 1844
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Compacting the edges simultaneously with compaction of the horizontal layer. To minimize breakage along the edge, it is recommended the edge be compacted at an angle no less than 45 degrees to the horizontal.
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Img10028
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Item Code: 1845
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In addition to edge compaction, another method achieving strong durable edges is to trim off the loose outside material using a type of “cookie cutter” shown here.
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Img10003
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Item Code: 1820
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In October 1983, severe flooding, which exceeded the one in 100 year event, occurred in portions of the Tucson area. The normally dry major waterways were forced to carry peak flows ranging from 25,000 to 45,000 cu. ft. per second, with velocities up to 20-ft. per second. There was extensive riverbank erosion and property damage. Of the 42 bridge crossings in the Tucson area, 35 were closed by the flooding -- 15 of them for more than one day.
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Img10006
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Item Code: 1823
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Again in 1993, both Tucson (shown here) and Phoenix were subjected to prolonged flood waters. Following this second major test of soil-cement bank protection, the Pima County Flood Control District concluded in its report of the January 1993 floods that (1) “remarkably, a little damage to soil-cement bank stabilization occurred”, and (2) monies expended since 1983 to provide a higher level of protection to vulnerable areas contributed to a considerably lower amount of damage in 1993 when compared to the 1983 flood.
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Img10008
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Item Code: 1825
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On this project Texas, central-plant-mixed soil-cement was hauled and dumped into a storage bin at the bottom of the slope. (Black bow in background.) A front-end loader then fed a spreader as it traveled down the 3H:1V slope. Much less effort was required to place the soil-cement from top to bottom than if the soil-cement had to be pushed up the slope. Compaction in this case was accomplished by multiple passes of a D-6 dozer equipped with cut grousers or street pads.
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Img10012
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Item Code: 1829
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While most drop structures are built straight across the waterway, seven drop structures at a Denver suburb provided an attractive curved structure resembling natural sandstone layers. In addition to its durability, another advantage of soil-cement is that it blends into its natural surroundings.
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Img10014
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Item Code: 1831
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Soil-cement was used successfully to line this 1.5-acre ash slurry pond serving the San Juan Power Plant near Fruitland, New Mexico. A major advantage of soil-cement compared to other types of liners, such as clay or synthetic membrane liners, is soil-cement hardens with age into a strong durable material similar to concrete. It provides an excellent paved surface to support operating and maintenance equipment that, in this case, is used to periodically remove ash, which settles to the bottom of the pond.
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Img10022
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Item Code: 1839
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A typical soil-cement placement operation for stairstep slope protection consists of a dump truck, which feeds a spreader, followed by some type of compaction equipment. For most granular soils, a rubber tired or vibratory steel-wheel roller is used.
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Img10013
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Item Code: 1830
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Soil-cement can also serve as an excellent low permeable liner. During the 1950’s, soil-cement was being used to line a number of small 4-to-6-acre water storage reservoirs like this one in southern California.
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Img10015
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Item Code: 1832
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Wastewater treatment ponds such as this one in Taft Heights, California, have been lined with soil-cement.
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Img10010
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Item Code: 1827
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The compaction of the soil-cement is then accomplished by a self-propelled vibratory roller working up and down the slope.
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Img10023
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Item Code: 1840
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Soil-cement can also be placed by conveyor belt. This photo was taken in 1978 during construction of the largest soil-cement project to date. One-point-two-million cubic yards of slope protection for the cooling water reservoir at the South Texas Nuclear Power Plant near Bay City, Texas. This self-propelled conveyor belt allows the width of the soil-cement to be reduced from 8.0-ft. to 6.9-ft.
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Img10026
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Item Code: 1843
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A feathering of the edges, like this eight-year-old dam facing just outside Indianapolis, Indiana, is acceptable. Even after eight years, compaction markings are still visible. However, because the edges are feathered, there is a lack of thickness and, consequently, slight breakage of these edges can be expected to occur. For soil-cement to perform properly, it needs to be well-compacted and this becomes a particular problem when considering the edges. Contractors have devised many ways to treat the edges.
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Img10029
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Item Code: 1846
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Some cracking in soil-cement is to be expected. Most cracking is caused by either foundation displacement or shrinkage. Cracks caused by foundation displacements can be minimized by proper preparation of the foundation. Shrinkage cracks can be minimized by proper curing. In some cases, filling the reservoir with water immediately after final compaction can greatly reduce the likelihood of shrinkage cracking. Field studies conducted on soil-cement projects indicated the majority of cracks were less than one-thirty-second of an inch wide. In addition, actual inspections of drained reservoirs show the cracks will seal themselves with silt, clay, and other sediments.
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Img10033
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Item Code: 1850
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Inspection of the test section one year after construction indicated the soil-cement to be in excellent condition. The exact design of the composite liner system would vary depending upon application and other requirements, including leachate collection and recovery systems. When the top layer of soil-cement would be exposed to heavy operating equipment, a thicker soil-cement layer over the geomembrane should be considered.
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