Abstract: This paper presents the results of the inclinometer monitoring and back analysis using three-dimensional finite elements in the scale pit deep excavations. Scale pit is a deep circular excavation construction with a depth of −27 m and a total diameter of 26 m. The soil layer above from the final excavation is dominated by a sandy soil layer. The retaining wall construction is a secant pile reinforced with waler beams at each excavation stage. The hardening soil model was used as soil constitutive model. The results of the back analysis show that the trend of wall deflection is close to the results of the inclinometer measurements. The maximum deflection that occurs in the wall is 5.1 mm. The effective cohesion c′ of cemented soil in the case is about 50 to 200 kPa, depend on the depth of cemented sand layer. NSPT is a number of blows for a split-barrel sampler to penetrate 30 cm into the soil during Standard Penetration Test. The soil modulus in sand soil as a result of the modeling is equivalent to 1 400 NSPT to 2 000 NSPT (unit: kPa), while for cemented sand, it is equivalent to 7 000 NSPT. This study also investigated the effect of waler beam installation and external loads on the deformations and forces that acting in the secant pile. In this case, the external load has a dominant effect in the result of wall deflections. Meanwhile, the waler beam has no significant effect for reduce the wall deflection.

Key words: deep circular excavation, inclinometer, back analysis, cemented sand, 3D finite element