CASE HISTORY
The relationship between temperature and earth pressure acting on a rigidly framed earth-retaining structure (RFERS) subject to wide temperature variation was explored. A distressed RFERS open concrete garage that retains 11 m (36 ft) of soil was instrumented. After some repairs, movement of the building was monitored and recorded hourly for a period of four and a half years. The monitoring revealed complex temperature-dependent soil structure interactions. The measured displacements were used to calculate the earth pressure coefficient using closed form equations that were developed by treating the structure as an equivalent cantilever beam, and calibrating the expression using a total of 42,000 FEM models. The data indicated that the coefficient of earth pressure behind the monitored RFERS had a strong linear correlation with temperature. During the cold season the building contracted, and the retained soil followed. During the hot season, the building was unable to overcome the earth pressure, thus it expanded away from the soil, resulting in a cumulative annual displacement. The coefficient of lateral earth pressure changed by approximately 0.005/°C, varying in the range of 1.25–1.5, depending on the season. The study also reveals that thermal cycles, rather than lateral earth pressure, caused some of the structural elements to fail.
This case history demonstrates that rigidly framed earth retaining structures undergo complex temperature dependent soil–structure interaction. Displacements of a four-story rigidly-framed structure that retained 11 m (36 ft) of fill on one side only were monitored along with temperature for a period of 4.5 years. During periods of temperature decrease the structure contracted, and the soil followed it. During periods of rise in temperature, the structure underwent limited expansion movements into the soil mass at the restrained end, causing larger expansion movements, and stresses at the other end. This was not surprising since the energy needed to overcome the soil’s passive resistance was vastly larger than the energy stored in the building when it contracted under active earth pressure conditions. Expansion of the structure toward the retained soil induced an increase in earth pressure, and possibly in soil stiffness, causing it to deflect away from the soil mass to maintain the required force equilibrium, while still undergoing thermal expansion movements.
The observed building displacements were correlated to the coefficient of lateral earth pressure,K, and K was found to be linearly dependent on the building temperature; it changed by approximately 0.005/°C varying in the range of 1.25–1.5, depending on the season. A residual displacement away from the restrained soil was observed at the end of each thermal cycle. It was the thermal cycles rather than the high earth pressure that caused some of the structural elements of the building to distress and fail in order to release some the built in pressure.
Primary Reference
Iskander, M. (2013). Relationship between temperature and earth pressure for a rigidly framed earth retaining structure. Journal of Geotechnical and Geological Engineering, Vol. 31, No. 2, pp. 519-539, doi: 10.1007/s10706- 012-9606-2, Springer [link]
