The basic mixture of lightweight cellular concrete (LCC) consists of cement, water, and a stable foaming agent. It is generally classified as having a density of less than 50 pounds per cubic foot (pcf), which is less than both traditional concrete and backfill materials. LCC has gained popularity in construction due to its lightweight, self-leveling, and ease of production and placement. These characteristics have made LCC a popular lightweight backfill material for mechanically stabilized earth (MSE) walls. However, there has been relatively little research on the large-scale behavior of LCC as a MSE backfill. Therefore, large-scale test results defining failure mechanisms and the strength criteria of reinforced LCC are extremely valuable. In this study, a three walled test box (10 ft wide x 12 ft long x 10 ft high) was constructed to contain the LCC. Two 5 ft tall x 10 ft wide MSE wall segments were poured and cured, before being placed as the fourth wall of the test box. The test box was built with a steel reaction frame to reduce lateral deflections during testing of the LCC that was not in the direction of the MSE wall, thus creating a two-dimensional or pseudo "plane strain" geometry. The box was filled with four lifts of Class II LCC 2.5 feet thick with ribbed-strip reinforcements at the center of each lift. After the LCC was cured, two static load tests were performed by applying surcharge to the surface of the LCC using six hydraulic jacks. The static load tests compared the LCC behavior of an MSE wall in comparison with unreinforced LCC without MSE wall panels. Multiple forms of instrumentation were used to understand the behavior of the LCC during surcharge loading. The instrumentation also helped to characterize the strength criteria for LCC based on failure in the large-scale and laboratory testing. This was done to determine the failure mechanism for the MSE wall retaining system with ribbed-strip reinforced LCC backfill. Data was gathered primarily through lateral wall pressures, lateral wall deflections, and forces induced on the ribbed-strip reinforcements. The test results show that an MSE wall with LCC backfill can withstand significant surcharge loading with limited axial and lateral deformations. However, failure occurred at surcharge pressures of about 60% of the unconfined compressive strength. The use of a retaining system significantly increased the failure loads and produced a more ductile failure mode than Class II LCC with a free-face. The active pressures observed are similar to a granular material with a friction angle (ϕ) of 34°, Ka=0.28, and a cohesion of 700 to 1600 psf for Class II LCC. Likewise, failure of the free-face occurred at a value predicted by Rankine theory with ϕ = 34° and c = 1600 psf.

Lightweight cellular concrete (LCC) is mainly a mixture of water, cement, and foam bubbles. LCC generally has a cast density between 20-60 pcf and an air content between 49-84%. LCC is often used as a fill material because it has a low unit weight which reduces settlement. LCC is increasingly being considered as a backfill behind Mechanically Stabilized Earth (MSE) walls and embankments. Although engineers are using LCC in MSE walls or free face walls (MSE wall without the concrete panels or reinforcements), there is presently a lack of information regarding the performance and behavior of LCC to guide them. This research attempts to answer questions on the design of MSE walls backfilled with LCC and free face LCC walls by providing a well-documented case history and evaluating if LCC can be modeled as a c-ϕ material. A steel frame test box (10 ft wide x 12 ft long x 10 ft high) with a MSE wall on one side was constructed for the research. The box was filled with four lifts of LCC with steel ribbed-strip reinforcements extending into the LCC behind the MSE wall panels at the center of each lift. After the LCC was cured, two static load tests were performed by applying a surcharge load to the surface of the LCC. In one test, surcharge pressure was applied adjacent to the MSE wall to produce failure of the wall system. In a second test, the surcharge pressure was placed adjacent to a free face of the LCC to produce failure. String potentiometers (string pots), load cells, pressure plates, and strain gages were used to measure the behavior of the MSE wall and free face wall during testing. These two tests provided a comparison between LCC behavior with a MSE wall relative to a LCC free face. Failure of the free face wall with unreinforced LCC backfill in this test can be predicted using Rankine’s lateral force equation using a c-ϕ model. Failure angle at the base of the free face wall was between 51-63° which corresponds with an average friction angle (ϕ) of 24° and cohesion (c) of 1575 psf with an upper bound ϕ = 34° and a c = 1285 psf. The presence of reinforcements in the LCC backfill behind the MSE wall increased the capacity of the wall to hold a surcharge load. The presence of reinforcements in the LCC behind MSE walls also led to a much more ductile surcharge pressure vs. lateral deflection curve for the MSE wall compared to the free face wall.