1 Formulation of the problem.
Usually the biggest problem encountered in water conservancy, transportation, civil engineering and municipal engineering is the treatment of silt soft foundation. Soft soil foundation has the characteristics of complex mineral composition, high natural moisture content, large natural porosity ratio, small permeability coefficient, high compressibility and low strength, therefore, the bearing capacity of the foundation is low, the uneven settlement is large, and it is easy to cause the building to slide, collapse and tilt. There are also different treatment methods for the treatment of silt soft foundation at home and abroad, mainly including excavation and replacement method, composite foundation method, drainage consolidation method, chemical reinforcement method, etc. In recent years, chemical reinforcement methods have been widely used due to their short construction period, wide range of application, simple construction, controllable consolidation shape, and good durability. The corresponding new technology of this method has developed rapidly, and the common ones are cement mixing pile construction method and high-pressure jet grouting pile construction method. The in-situ solidification technology of sludge is a new technology researched and developed on this basis, which realizes the in-situ direct construction on the surface of various silt soft foundations, solidifies the sludge in situ, and greatly reduces the amount of materials.
2. Research on in-situ solidification technology of sludge.
The in-situ solidification technology of sludge is mainly aimed at all kinds of sludge soft foundation projects, in which the consolidated material is directly stirred with the sludge on the surface of the sludge soft foundation to fully solidify the reaction and realize the in-situ solidification treatment of the sludge.
2.1 Research on cured materials.
R&D aims to improve the strength of sludge and reduce the solubility of pollutants by stimulating the activity of sludge using solidified materials. By analyzing the characteristics of tidal mud and its main chemical composition, according to the various characteristics of the chemical composition of tidal mud, the principle of gelling and curing is used, and the industrial waste slag fly ash and slag are used as the main materials, and a certain proportion of hydraulic cementitious materials, alkaline activators, expansion agents, surfactants, water reducing agents, coagulants and auxiliaries are mixed to make curing agents.
Through a large number of laboratory experimental studies, analysis and comparison, a curing agent with fast curing speed and consolidation strength can meet the design requirements of soft foundation treatment was developed. The curing agent gives full play to the activity of silicate minerals in the mineral composition of the sludge unit, and quickly produces a curing reaction, which not only makes the phase interface of each unit of the silt particles firmly combined, but also reacts with the active substances in the silt particles to form puffed cementitious substances, which can not only be chemically activated to produce bonding, but also can produce physical bonding, and at the same time, it can also seal heavy metals and organic matter to prevent the dissolution of harmful substances, so that the soil produces high strength at the same time, and also has good water stability and durability.
Taking the mud quality of a project in Ninghai as an example, the shear resistance test was carried out on the silt solidified soil with different curing agent mixing ratios and different ages, and the bearing capacity of the foundation was converted according to the plastic state. The test results are shown in Table 1. The in-situ solidification technology of silt was used for the test, and the 28-day sampling effect is shown in Figure 1. The solidified silt core sample is complete and strong, and the average strength of the core sample within the cured 8m range is 1More than 0MPa, which is higher than the strength of ordinary cement mixing pile. The curing piles are connected to form a complete curing area, and the strength of the area can be adjusted according to the replacement rate to meet the bearing capacity design requirements of different curing zones.
Table 1 Shear index of solidified soil under different curing agent mixing ratios and ages
Figure 1 28d coring of sludge solidification Figure 22. Research on construction technology.
2.2.1. Stirring uniformity study.
Combined with mechanical stirring technology and high-pressure jet spraying technology, combined with pressurized jet spraying at the same time, the full and uniform mixing of sea mud and curing agent is realized. According to the drilling speed, lifting speed and stirring rotation speed, the hydraulic diverter valve is designed to debug the technical parameters of each hydraulic motor of the silt construction machinery and equipment. It can be seen from the test that in order to achieve the full and uniform mixing of the seawater sludge and the curing agent, the number of stirring should reach more than 24 times, and the best mixing times should be determined through the field test before construction for different sludge. The drilling, lifting speed and stirring rotation speed of the equipment, and the number of lifting and lowering of the stirring rod are determined according to formula (2).
If the number of stirring times between the seafill sludge and the curing agent reaches more than 24 times as required, the corresponding relationship between the drilling and lifting speed and the stirring rotation speed is shown in equation (2).
Where: n is the number of lifting times of the stirring rod (using four stirring and two spraying, take 4);n is the rotation speed, and the rotation is min;h is the height of the blade, m;z is the number of blades, pcs;v is the lifting speed, m min.
2.2.2 Blending ratio control study.
The motor of the slurry pump is controlled by the inverter of the conveying system to realize the control of the slurry flow, and the slurry metering is monitored by installing a slurry meterAccording to the design slurry supply flow, slurry supply pressure, curing agent dosage, water-cement ratio and stirring rod lifting speed, determine the slurry supply flow rate of the mud pump according to equation (3), and debug the mud pump to set the motor power of the mud pump corresponding to the slurry supply flow.
The formula for calculating the flow rate of curing agent is shown in equation (3).
where: q is the pumping flow rate of the pump, m3 min;r is the pile radius, m;is the bulk density of the slurry, kg m3;n is the proportion of curing agent added;m is the water-cement ratio;v is the lifting speed, m min. is the number of shotcrete cycles;For the bulk density of the curing agent, kg m 3.
2.2.3. Construction process flow diagram.
The solidification construction process of the mud is shown in Figure 3.
In the construction process, the process of four stirring and two spraying is adopted, and there are two methods of four stirring and two spraying: Method 1: The first drilling, spraying and mixing construction;The first lifting, spraying and mixing construction;The second drilling, re-stirring to the design depth, no spraying;The second lifting, re-stirring to the working face, no spraying. Method 2: the first drilling, spraying and mixing construction;The first lift, no grouting;The second drilling, re-stirring to the design depth, spraying and stirring construction;The second lifting, re-stirring to the working face, no spraying. After test comparison, the first method has higher strength after solidification. According to the analysis, this is due to the fact that method 1 can ensure that there are more than 2 times of remixing for 2 shots.
Figure 3 Construction process flow diagram 3 Technical characteristics.
3.1. Good stability and low permeability.
The high-strength gelling and consolidation effect makes the solidified sludge (sludge) have good stability, small permeability coefficient and small porosity, and prevent secondary pollution caused by sludge (sludge) leaching. According to the simulation stability test analysis of a technical university, the stability of the curing product can reach 70d. After solidification, the sludge (sludge) is soaked in water under natural conditions for 5 days, as shown in Figure 4.
Figure 4 Stability Test Figure 32. Seal heavy metals, and have the functions of deodorization and sterilization.
After stable solidification treatment, there is no heavy metal dissolution in the soft base of the sludge, and the indicators meet the requirements of environmental protection.
3.3. The sludge is solidified on site, which saves costs and has high efficiency.
The solidification equipment is used to solidify the sludge in situ, without excavation and transfer, saving costs and improving efficiency.
Statement: We respect originality and also pay attention to sharing, and thank each author for their hard work and dedication. We are committed to protecting the author's copyright, only for the dissemination and sharing of new technologies and knowledge, without any other commercial profit, if there is any infringement, please contact and delete in time.