A Study on the Settlement of Gravel cushion and DCM Piled Compound Foundation

Abstract

The DCM pile is applied in immersed tunnel foundation improvement first time at home in the mega project of Shenzhong Link with improved ground areas over 700000 m3. The compound foundation composed of gravel cushion and DCM piled foundation settlement law is not definite. To explore this law loading plate test in place on site is carried out and the test results show : (1)under the first order of load effect the settlement amount of the compound foundation accounts for over 60% of the total settlement, the modulus of compression of the gravel cushion is 1.5MPa being approximately 10%∼20% of normal modulus of compression; (2)under other loading effects the final deformation of compound foundation settlement curve shows stable state with the modulus of compression of the gravel cushion in range of 4.5∼12MPa which is equivalent to the normal value. The numerical analysis for purpose of the testing shows that the gravel cushion settlement accounts for larger proportion being 58.57% of the total settlement and the gravel cushion thickness, density, residual layers fallen in DCM dredging, all may be factors affecting settlement. Hence it is suggested to enhance study on the workmanship of the tunnel bed formation in order to improve the bed rigidity and anti-deformation ability.