One,Project Overview： 

Engineering Reputation states: Taizhou Port Logistics Park Phase I Compaction Project

General Contractor: Nantong Wujian Yuejin Construction & Installation Engineering Co., Ltd.

Direct Subcontractor: Shandong Hengding Foundation Engineering Co., Ltd.

The total area of this project is approximately 18,000 square meters. The original terrain was residential buildings, which have now been leveled and filled with 40cm of mountain pebble, with good surface geology. The well-point layout for the trial compaction area as of April 20, 2018, was completed. Compaction tests were conducted on April 23rd. This section elaborates on the trial compaction process, argues the issues discovered during the process, and provides construction recommendations.

Two,Original Geotechnical Data:

Layer: Fill soil: Gray, loosely structured, primarily composed of silt and silty clay; locally mixed with bricks and stones on the surface, uneven soil texture. Thickness is generally 0.8-1.4 meters. Poor engineering properties, not suitable for direct use.

② Layer: Silt loam interbedded with thin layers of silt; gray, moist, plastic, lustrous, containing some organic matter and a few decayed plants, low in dryness, locally interbedded with thin layers of silt, moderately dense. Layer thickness: 4.6 to 9.0 meters, high compressibility, poor engineering properties.

③ Layer: Silty clay, silt clay with thin sand layers: Silty clay, gray-brown, soft plastic, wet, containing iron-manganese concretions, slightly lustrous, moderate dryness, moderate toughness; silt clay, fluid plastic, glossy, containing organic matter and a small amount of decayed plants, low dryness, interlayered with sand, slightly dense. This layer is 4.3 to 6.0 meters thick and has poor engineering properties.

④ Layer: Silt interbedded with silty loam: gray, moderately dense, saturated, mineral composition primarily quartz, poor particle grading, rounded particle shape, contains a small amount of feldspar and mica flakes. Silty loam, moderately dense. Layer thickness: 1.7～3.3m, medium compressibility, medium foundation soil, general engineering properties.

The overall soil quality is average, with poor engineering characteristics, and lacks sand layers, resulting in poor permeability.

Section 3:Trial Compaction Parameters and Process:

Precipitation points are 4m x 4m apart, with well points spaced 4m and 6m apart.

The Fuzhuang heavy industry QUY50B has a first-hand crawler compactor, weighing 15 tons, with a lifting height of 12 meters and a compaction impact energy of 1800KN.m.

Initial groundwater level was shallow and stable at 0.81m. The groundwater lowering work began on April 21st. Continuous precipitation in the trial compaction area was observed, with the water flow slightly larger at first, which gradually decreased after a day, and the groundwater level stabilized around 1.5m-1.6m. As of April 23, 2018, the majority of the water extracted from the trial compaction area was air, with minimal water output, and the groundwater level remained controlled at 1.5m-1.6m. According to the geological survey report and field tests, the foundation soil is mostly silt-loam clay, with poor permeability and fewer sand layers. During the well-drilling process, the materials returned to the surface are mainly clay and silt-loam soil.

On April 23rd, a compaction test was conducted, with a total of 6 rows and 8 columns, amounting to 48 points. On average, each point was compacted 3 times, with an average settlement of 60 cm. The compaction results were favorable, with no heaving or uncontrollable settlement observed in the vicinity. During the compaction process, due to the hammering, overflow was noticed at three points adjacent to the wells, which gradually dissipated post-compaction and was absorbed by the wells. The standing water left in the compaction pit was pumped out using a pump.

Due to overflow at certain well points after three hammering strikes, based on our company's many years of joint dewatering and compaction construction experience, we propose suggestions in our construction plan to withstand "springy soil" during the stopping compaction process.

FourCompaction construction handling recommendation:

Due to the different properties of clayey silt loam compared to sandy soil, sandy soil has better permeability, allowing groundwater levels to easily drop below 2.5 meters. However, clayey silt loam naturally exhibits poor permeability, acting like a "sponge." During construction, the occurrence of "springy soil" must be strictly avoided.

So, our recommendation is to adopt a well-proven solution in the compaction process of precipitation compaction projects: "start light, then heavy, fewer blows, more passes." Gradually compact the foundation, expelling excess moisture from the soil mass, and gradually strengthen the foundation from the top down to the bottom, ultimately enhancing the bearing capacity of the foundation.

V. Specific Construction Plan:

① The precipitation engineering continues, and the compactor performs several blows, with each compaction point receiving two blows, inserted in the middle of the well points, gradually lowering the water level during the compaction process.

② To facilitate the dissipation of pore water around the well point, after one round of compaction, allow it to dissipate for a day. Then, use an excavator to level the compaction pit, and backfill the pile with soil to make it even with the pit.

③ Perform a second round of tamping, with each tamping point receiving 2-3 strikes, and the spacing between tamping points being 4m x 4m.

④ Remove one row of well points and perform full compaction construction. The full compaction capacity is 1000KN.m, with each point being struck once, and the hammer impressions overlap.

⑤ Subsequently, mechanical vibration compaction is performed, with orthogonal compaction being flattened twice.

Six, Conclusion

With our company's many years of joint dewatering and compaction construction experience, the dewatering compaction for silt loam is a mature solution with excellent construction outcomes. After compaction, the bearing capacity of the foundation is ≥120KPa, and all auxiliary design requirements meet the design standards.