The pile and the pile-cap beam (or cap slab) at the pile top work together to transfer the loads of the superstructure to the deeper soil layers with greater bearing capacity. As an important part of the foundation, piles have always been valued by our company. Currently, for the foundation of the underground garage of our Zhengzhou Evergrande Shanshui City project, the carrier pile+cap foundation form is adopted. The carrier pile iscomposed ofa concrete pilebody and a carrier; thecarrier is composed of three parts: concrete, compacted filling material, and compacted soil; its schematic diagram is as follows

In light of the on-site construction conditions, the construction process is summarized below. Any shortcomings are open to correction.

I.Pre-construction preparation:

1.Construction personnel: each pile rig is staffed per the standard of1rig operator,1machine operator, and1material feeder, totaling3persons, which can meet on-site construction needs. In addition, there are2persons for rebar cage fabrication at the back end,2persons for dry-mix batching, and2persons for transport, totaling6persons. All the above personnel have been arranged and are in place.

2.Materials: the main incoming materials include: raw rebar, gravel, sand, and cement. All incoming materials must pass inspection by our engineer before use. The raw rebar is Anxin steel, conforming to the brand specified in the contract; the certificate heat numbers match, the rebar nameplate font is clear, the steel body markings are correct, and the rebar diameter deviation is within the allowable range. Gravel and sand may be used only after passing visual inspection and re-inspection. The cement brand is Tianrui42.5, conforming to the brand specified in the contract, and may be used only after passing re-inspection.

3.Dry-hard concrete mix proportion: according to the drawing design requirements, the mix proportion requirement isC40. After laboratory testing of raw materials, the mix proportion sheet is issued.

4.Machinery and equipment: the pile rig adopts aBosenspecial-type carrier pile rig. It has been checked and meets the construction scheme requirements. The mixer is a medium-sized free-fall mixer with a discharge capacity of350L; on site, a motorized tricycle is reserved as transport machinery, along with aBXT400-type electric welder and a500KGplatform scale. The total station,leveland steel tape have all been calibrated.

II.Acceptance of the first completed pile

After the first pile is completed, the Engineering Management Department, Chief Engineer's Office, Design Institute, and geological survey unit are organized to conduct on-site acceptance jointly. This ensures that the construction process meets the design requirements and conforms to the specification provisions. Key points and existing problems during the pile-forming process are pointed out and corrected one by one.

III.Construction process flow and control points

1) Positioning the casing: first use a compass to draw the casing positioning line with the pile point as the center; after the casing is positioned along the line, check verticality with a spirit level, then lower the casing. As shown in the figure below:

2) Determine the casing penetration depth. Using a level, calculate the casing penetration depth based on the pile top elevation, pile length, and site elevation.

TakingZH1as an example, itseffective pile lengthis9.8m, and the protected pile head is0.5m. Its design pile top elevation is-4.7; the protected pile head elevation (0.5m) is-4.2m; the measured on-site ground elevation is-3.8m; then the empty pile length=-3.8m-(-4.2m)=0.4m. The casing penetration depth is calculated as follows:

Casing penetration depth=effective pile length+protected pile head+empty pile length

            =9.8+0.5+0.4=10.7m. Mark this position on the casing.

3) Feed the compacted filling material. After the casing is driven to the predetermined position, begin feeding the compacted filling material into the casing. The filling material adopts the form of brick slag+dry mix. The brick slag fill amount is not more than1.3m³, and the dry mix fill amount is not more than0.5m³. The brick slag fill amount is based on controlling groundwater to achieve water stoppage, i.e., feed until groundwater no longer surges out. Then feeddry-hard concrete. The mixed material fill amount is controlled by the three-blow penetration.

4) Three-blow penetration. After filling is completed, check the three-blow penetration. First make a mark on the hoist rope, lift the long hammer6m, and afterthree hammer blows, measure the sinking length of the mark, i.e., the three-blow penetration length. According to the design requirements, the three-blow penetration for this project is required to be no more than20cm. If it does not meet the requirement, continue feeding filling material until it meets the design requirements. A qualified three-blow penetration indicates that the filling material is compacted densely.

5) Hoist the rebar cage into the casing. After the three-blow penetration test is qualified, the rebar cage can be hoisted in. After the rebar is lowered, re-measure the top elevation of the rebar cage; the allowable error is±5 cm; if it does not conform, adjustment must be made to ensure the accuracy of the pile top elevation.

6) After the rebar cage is in place, pile concrete pouring can begin. Lift the casing while pouring; after pouring to the elevation, withdraw the casing and vibrate promptly to ensure dense vibration before the concrete initial setting. After pouring is completed, carry out protection and marking to prevent being run over by heavy vehicles.

IV. Other matters needing attention

1) After the rebar cage is fabricated, it must be inspected in advance before lowering. Mainly check the rebar cage diameter, per pile diameter-70mmi.e., the protective layer is not less than35mm;spiral stirrupsmust be tied with a lap length not less thanLaand not less than300; the start and end ends ofrebar are coiled into a full circle. Generally, during fabrication, to facilitate lowering of the rebar cage, about200-300length is left at the bottom of the rebar cage without coiling stirrups and bent into a pointed shape to facilitate cage lowering; this length may not be counted in the effective pile length.

2) Dry-hard concrete and brick slag fill amount: before pile foundation construction, hole-forming and pile-forming tests should be carried out first to determine the fill amount, which serves as a reference for subsequent engineering pile construction.

3) Measures for sealing underground water inflow: when underground water inflow is encountered, if feeding brick slag cannot effectively stop it, cohesive soil may be mixed in, or part of the dry mix may be fed, or cement may be added directly.