Measured Performance of Braced Excavation

by T. William Lambe, (F.ASCE), Edmund K. Turner Prof. of Civ. Engrg.; Soil Mech. Div., Dept. of Civ. Engrg., MIT, Cambridge, MA,
L. Anthony Wolfskill, (M.ASCE), Res. Assoc. in Civ. Engrg.; Soil Mech. Div., Dept. of Civ. Engrg., MIT, Cambridge, MA,
Ing H. Wong, (A.M.ASCE), Res. Asst. in Civ. Engrg.; Soil Mech. Div., Dept. of Civ. Engrg., MIT, Cambridge, MA,


Serial Information: Journal of the Soil Mechanics and Foundations Division, 1970, Vol. 96, Issue 3, Pg. 817-836


Document Type: Journal Paper

Abstract: This paper documents the measured performance of a test section of braced excavation for a subway. The excavation was 37 ft wide and 58 ft deep, and five levels of struts were installed. The subsoil consists of fill, silt, till and rock. The water table was from 6 ft to 8 ft below ground surface. The instruments installed were slope indicators, piezometers, and strain gages. The typical horizontal inward movement of the sheeting was 5 in., and the maximum movement on one sheeting was 9 in. A maximum surface settlement of 7 in. occurred outside the excavation. Large drops in pore pressure occurred in the soil over a distance (greater than 70 ft) far back from the excavation. The strut loads measured showed a wide variation but the average maximum values, except in the top strut, were less than half the design loads. The maximum strut loads occurred at an intermediate state of excavation. Details of construction procedure greatly influenced the behavior of the braced excavation.

Subject Headings: Excavation | Struts | Bracing | Maximum loads | Load factors | Quality control | Soil pressure | Subways

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