How to calculate the cement content in powder jetting piles

““A powder jetting pile” refers to the “dry method” in the “cement soil mixing method”. Article 11.2.1 of the \"Technical Code for Foundation Treatment of Buildings\" JGJ 79-2002: Ordinary Portland cement with a strength grade of 32.5 or higher is preferred as the curing agent. Except that for bulk reinforcement, the cement content can be 7% to 12% of the mass of the wet soil to be reinforced, it should generally be 12% to 20% in other cases. The water-cement ratio for wet cement slurry can be selected between 0.45 and 0.55. Additives can be selected based on project requirements and soil conditions, using materials with properties such as early strength, retarding action, water reduction, and cement savings; however, environmental pollution should be avoided. Section 11.3 deals with the provisions regarding “dry” construction methods: 11.3.14 Before carrying out powder spraying, it is necessary to carefully check the sealing performance and reliability of the mixing machinery, powder supply pumps, air (powder) delivery pipelines, as well as connectors and valves. The length of the air (powder) supply pipeline should not exceed 60 m. 11.3.15 For the powder spraying construction using the cementitious mixture mixing method (dry method), the machinery must be equipped with a powder metering device that has been approved by the **measurement department and is capable of instantly detecting and recording the amount of powder used, as well as an automatic recorder for the mixing depth. 11.3.16 For each full rotation of the mixing head, its lifting height shall not exceed 16 mm. 11.3.17 The diameter of the mixing head should be regularly checked, and its wear level must not exceed 10 mm. 11.3.18 When the mixing head reaches 1.5 m above the designed pile bottom, the powder spraying machine should be turned on immediately to start the powder spraying operation in advance. When the mixing head is raised to 500 mm below the ground, the powder sprayer should stop spraying powder. 11.3.19 If powder spraying is stopped due to some reason during pile driving, the mixing head should be lowered to 1 meter below the level where powder spraying has ceased; powder spraying can then be resumed to carry out mixing and lifting. 11.3.20 When powder jetting is used to form piles in soil layers with a natural moisture content of less than 30%, the surface water injection mixing method shall be employed. Therefore, what designers refer to is the \"weight ratio\"; generally, the unit weight of moist soil can be taken as 19 kN/m3. For piles that are 500 mm in diameter, the volume per meter along their length is 0.2 m3, and calculations can be carried out using this value (note that the unit here is kN, and it needs to be converted to kg, since 1 kg = 9.8 N). 19×0.2×1000 / 9.8 × 13% ≈ 50 kg; 19×0.2×1000 / 9.8 × 18% ≈ 70 kg. The quality of piles formed in sandy soil is good, so there is no need to increase the value; however, the quality of piles formed in silt or silty soil is poor, so it is appropriate to increase the value accordingly. However, attention should be paid to the specifications set by the designers regarding \"the number of sprays and stirrings\" as well as the \"lifting speed\". Also, nowadays cement of grade 42.5 is generally used. This post was last edited by tpjj on 2009-2-22 15:46]