Bearing Capacity Characteristics of Compacted Cement Stabilized Gravel Pile Composite Foundation

Compacted cement stabilized gravel pile can effectively control secondary disasters of subgrade, while the bearing mechanism of semi-rigid pile composite foundation is not clear. The load–settlement (Q–S) curves, pile mechanical features and pile–soil stress characteristics of the composite foundation were analyzed by field tests and numerical simulation. Moreover, the characteristic value and calculating equation of the bearing capacity were discussed. Results show that the axial force of the group pile in composite foundation increases first and then decreases with the depth, the negative friction resistance is in the upper part, the neutral point is located at one-fifth of the length below the top. The lateral friction of the lower part of the pile plays a role before the upper lateral friction, and more than 90% of the pile load is supported by lateral friction. The curve of pile–soil stress ratio is hump-shaped, the stress ratio of pile to adjacent pile center soil is 6.08–6.65, and the stress ratio of pile to diagonal pile center soil is 7.5–9.45. Q–S curve of the single pile is characterized as a sharp decline, the characteristic value of the bearing capacity can be obtained by the equation of rigid pile, and the reduction coefficient of the pile strength is 0.25. Q–S curve of the composite foundation performs a slow downward tendency, the characteristic value of the bearing capacity can be obtained by the equation of compacted cement–soil piles, it is suggested that the correction coefficient of the vertical compressive bearing capacity is 1.0, and the bearing capacity correction coefficient of soil between piles is 1.05–1.15.