During static jacked pile construction, the soil-squeezing effect inevitably causes pile heave. Therefore, how to solve the problem of bearing capacity reduction caused by pile heave in soft soil foundations has long been a focus of attention in the engineering field.

The soil-squeezing effect generated during static jacked pile driving causes pile heave, creating a gap between the pile tip and the bearing stratum, which leads to a reduction in pile bearing capacity.

Static jacked piles are displacement piles. During construction, under the static pressure of the static pile driver, the pile tip is pressed into the soil layer, causing shear failure of the soil mass. Under the squeezing action of the pipe pile tip, the pore water in the foundation soil layer generates an uneven hydraulic head. As the excess pore water pressure gradually increases, the initial stress state of the undisturbed soil is disturbed, thereby causing a reduction in pile bearing capacity.

Treatment Methods

(1) Grouting. Post-grouting at the pile tip (and side) of heaved piles.

(2) Supplementary piles. Add pipe piles, bored piles, or static-pressure anchor piles.

(3) Re-driving or re-pressing. Re-drive or re-press the heaved piles.

(4) Ground treatment. Generally, add flexible piles such as granular material piles.‍

Key Operation Points

The soil-squeezing effect causes problems such as pile heave, pile position deviation, pile body warping, and pile breakage, significantly reducing the single-pile bearing capacity of the pile foundation and affecting construction quality.

The main factors affecting pile heave due to soil squeezing include soil conditions, pile layout, pile diameter, pile length, construction sequence, and construction speed. Therefore, when designing and constructing static jacked piles in saturated cohesive soil layers, pile spacing should be maximized and pile diameter and length minimized as much as possible. The construction sequence should preferably proceed from the center outward to both sides or all around, from deep to shallow, from long to short, and from large to small, and skip-driving construction is best adopted. Construction speed must be strictly controlled.

Re-pressing is a scheme for treating heaved piles, featuring fast construction speed, low treatment cost, and economic reliability. The re-pressing force should preferably be controlled at twice the design single-pile bearing capacity, and the re-pressing settlement of the pile foundation should preferably be controlled to be slightly greater than the pile heave amount.

During pile driving, stress relief holes should be set according to actual engineering conditions so that excess pore water pressure and soil deformation can be fully dissipated as soon as possible.