The proportion of bentonite slurry used in Shanghai sandy soil is 5%, that is, about 50kg bentonite with 1m3 water.
2csm construction technology 2.1 process flow CSM construction method wall (csmcuttersoilmixing) originates from the double wheel milling and mixing technology produced by baoe, Germany.
The most important stage affecting the construction safety of the foundation pit is the excavation stage.
When the surface bearing capacity is insufficient, necessary measures shall be taken to prevent mechanical instability and sufficient materials for construction shall be prepared.
The typical geological conditions of CSM construction method wall construction area are shown in Figure 1.
CSM construction method wall is the same as the underground diaphragm wall of sleeve milling process, which is divided into phase I groove section wall and phase II groove section wall.
4 road in the north, Hongqiao Road in the south, Gongcheng road in the East and Yishan Road in the West.
The test wall depth is greater than 75m.
CSM construction method wall is designed to be used for reinforcement in zone 4-16 and outside zone 4-11 of the project.
4) Excavate slurry storage tank or slurry storage ditch to solve the problem of residual slurry storage and slurry return supply during construction.
Since this is the first time to construct 75m ultra deep CSM construction method wall under complex geological conditions of soft soil, there is no precedent to follow.
1csm construction method test overview test background project Hongqiao Road plot of Shanghai Xujiahui center is located in the prosperous section of Xujiahui, adjacent to Guihua No.
The project is divided into 16 foundation pit excavation, the excavation depth is 10m ~ 33m, and the total excavation area of foundation pit is about 52000M2.
The maximum depth of the wall is 80m and the verticality is more than 1 / 500.
During the excavation process, the effective water stop measures of the foundation pit are the most important factors affecting the safety of the foundation pit.
At present, the construction methods of water stop and reinforcement of deep soil in China are mostly vertical rotation mixing, generally forming cylindrical cement soil piles, and forming cement soil pile continuum by overlapping each other.
2.2.2 lifting construction milling slurry is used for CSM wall construction.
The test control parameters are shown in Table 1.
For foundation pit construction in the urban core area, the protection of the surrounding environment must be strengthened, mainly to control the displacement propagation caused by the deformation of the retaining structure, so as to reduce the impact on the surrounding environment.
After the equipment reaches the operation position, the double wheel milling wheel shall be aligned with the center of the groove section, and the verticality of the mechanical equipment shall be adjusted to within 1 / 500.
The amount of bentonite needs to be enough to ensure the stability of soil particles after mixing with slurry.
Therefore, before the formal construction of CSM construction method wall, three in-situ wall forming tests shall be constructed first to provide technical parameters for later construction.
2) Before construction, accurately calculate and set out the coordinates of the center line of double wheel milling equal thickness cement soil mixing wall according to the design drawings and the coordinate datum points provided by the owner, recheck the coordinates, protect the pile, and notify relevant units to recheck the measurement and setting out.
3) Connect the water, electricity and gas, put the mechanical equipment in place, install the pulping, grouting and gas making equipment, and run the test run.
The premise and key to the development of deep and large underground space lies in the construction of deep and large foundation pit.
Its adaptability to the stratum is higher than other deep mixing technologies.
Double wheel milling cement soil deep mixing construction technology (CSM construction method for short) is a new underground water stop and soil retaining continuous wall construction method innovated and developed by organically combining deep mixing technology with hydraulic slot milling machine.
The process flow is shown in Figure 2.
When cutting in cohesive soil, water can be used to replace bentonite slurry during tripping, but in sandy soil, bentonite slurry shall be used.
It adapts to a wide range of strata, has a large wall depth, reduces overlapping, saves materials and construction period, and greatly reduces soil replacement, It is of great benefit to promote the breakthrough of deep reinforcement technology and efficient green environmental protection construction.
As shown in Figure 3, “P” refers to the wall of phase I slot section, and “s” refers to the wall of phase II slot section.
Some additives can also be added appropriately according to needs, such as fly ash, retarder, etc.
Some water stops are required to reach a depth of 80m or deeper, some need to pass through the sand layer into the rock stratum, and others need to complete soil retaining and water stop in a limited space, It is urgent to study and develop new construction technology for water stop and reinforcement of deep soil.
The “hard milling method” is also adopted for the wall construction in this test.
This construction method is also commonly referred to as “hard milling method”.
The amount of bentonite depends on the composition of powder and clay in the formation and the quality of bentonite itself.
2.3 key construction technologies 2.3.1 construction preparation 1) remove obstacles, level and compact the construction site, and the working surface is greater than 11m.
2.2 preparation and preparation of milling slurry 2.2.1 drilling down construction milling slurry usually uses bentonite slurry or water during drilling down, which depends on local geological conditions.
The first phase groove section wall shall be constructed first, and the second phase groove section wall sleeve milling construction shall be carried out between the two first phase groove section walls after the construction has reached a certain hardness.
The main purposes of this test are: 1) to test the wall forming construction capacity of mechanical equipment; 2) Study the control standards of key parameters such as construction process and verticality; 3) Study the impact of wall construction process on the environment; 4) The wall quality after mixing was studied.
Stability means that the stones and sand particles on the upper part of the mixing head will not precipitate a lot and hinder the lifting of the mixing head.
The test results show that the CSM construction method has little impact on the surrounding environment, good uniformity of the wall, and greatly improves the impermeability of each soil layer.
There are 3 trial walls.
The commonly used slurry composition includes cement, bentonite and water.
The joints are overlapped by sleeve milling for 30cm and arranged 2m outside the edge line of underground continuous wall.
During the down milling construction, water or bentonite slurry is injected to liquefy the soil, and the flow is about 0.6m/m33 ~ 1m / M33.
For cohesive soil, water is usually used; For low cohesive soil or non cohesive soil, bentonite slurry shall be used.
It is recommended to use cement content (25%) and water cement ratio of 1.2 ~ 1.5 in the stratum to be treated.
Two theodolites are used to correct X and Y directions, and the allowable plane deviation is ± 20mm..
The construction of deep and large foundation pit will have to face a series of technical problems, such as geological conditions, complex distribution of water and soil pressure, strong hydrodynamic pressure in deep sand layer, great construction difficulty and great risk.
Ordinary portland cement is generally used.
Through milling and mixing the underground in-situ soil and cement slurry, it forms a continuous wall with equal thickness that can be used in water stop, soil retaining, reinforcement and other fields.
There are 49 CSM construction method walls in total, with wall thickness of 1.0m, wall width of 2.8m and wall depth of 75m.
2.2.3 mix proportion design and slurry of liquefied soil mass according to the construction experience under similar geological conditions, the 28d strength of the designed CSM wall is at least 1.2MPa.
Germany baoe mc64 double wheel milling deep mixer 2.3.2 the relocation and positioning shall be safe and stable.
However, the geological conditions in most areas are complex.
Application case of SMC construction method experimental study on construction of ultra deep water soil mixing wall based on double wheel milling Xun weizhuo Abstract: in view of the unprecedented problem of the double wheel milling water soil mixing wall construction method (CSM method) under the deep and complex geological conditions of soft soil, the CSM method test was first carried out.
Additives mainly include liquefying agent, stabilizer and retarder, which are used to improve the performance of mud.
The successful implementation of CSM wall forming test not only provides technical support for subsequent engineering application, but also provides reference experience for similar projects in the future.
Key words: double wheel milling; Deep mixing; CSM construction method; Experimental research introduction With the rapid development of urban construction, the demand for underground space is increasing, and the development of underground space to ultra deep and ultra large has become the mainstream trend.
The planned wall depth is 80m, the wall thickness is 1m, the wall width is 2800mm for each CSM method, and the lap width is 300mm.
