The process of technical consolidation grouting includes grouting method, grouting section length and pressure, grouting materials, starting water-cement ratio of cement grouting and grouting conditions, grouting end standards, etc.
1. Grouting method
Commonly used grouting methods include segmented grouting, stopper grouting, staged grouting, circulating grouting and conduit or gravity grouting.
1.1 Sectional grouting method
The sectioned grouting method is to drill and grout in sections from top to bottom. Currently, the segmented grouting method is most commonly used in consolidation grouting and curtain grouting in hydropower projects. When a certain predetermined depth is reached and the grouting end condition is reached, the grouting of this section will end. Then continue drilling for the next section.
Advantages: Only the orifice pipe needs to be installed at the orifice, eliminating the need for grout stoppers, and the drilling cost is low.
Disadvantages: When there is no cover weight, attention should be paid to lifting during the grouting process. In addition, the holes must be flushed in each grouting section. If the holes are not flushed before setting, the slurry will flow back and the slurry will be wasted.
1.2 Stopper grouting method
The stopper grouting method is also called the bottom-up segmented grouting method. The grouting hole is drilled to the entire depth at one time, a water pressure test is performed, and then grouting is performed section by section upward from the bottom of the hole. Grouting stoppers or expansion plugs are used to separate the pre-selected hole sections in the grouting hole, and then grouting is carried out. When the drilling water supply does not circulate or flows due to gravity during drilling, drilling must be stopped and grouting must be carried out. When grout is expected to cross between holes, a variation of the stopper grouting method can be used, which is to utilize a multiple grout plug system. Place the grouting plug above the lowest grouting belt in all grouting holes, and then grout the holes with the maximum allowable grouting pressure to improve the grouting effect.
Advantages: Geological defects discovered during drilling can be isolated with expansion plugs and processed specifically. Only one drilling rig is required for each hole, and pressure washing and water pressure tests can be performed on small sections of the hole. There is no need to drill and clean the hole after grouting, thereby improving work efficiency.
Disadvantages: The slurry sometimes bypasses the slurry stopper along steeply inclined cracks or joints. In addition, it is difficult to seal the slurry stopper in caves or honeycomb-shaped dissolved rocks. The grouting hole diameter is limited by the grout stopper and cannot be too small. Stoppers are often lost.
1.3 Staged grouting method
Similar to the staged grouting method. First, drill holes at regular intervals to the depth of the first grouting zone, grout them with low pressure starting from the top of the rock, and then enlarge the grouting holes until the top grouting section is grouted; secondly, Drill another set of grouting holes into the second grouting section, and grout with higher pressure starting from the top of the rock. Depending on the depth of the grouting holes, a new set of grouting holes can be drilled deeper. When reaching the deepest grouting section, use the maximum pressure.
Advantages: Each deepening of the grouting section must rely on newly drilled holes to avoid slurry flushing from the hole when drilling into depth, causing slurry loss.
Disadvantages: There is a danger of lifting, and it takes more time and expense.
1.4 Circulating grouting method
The circulating grouting method requires a double-pipe grouting system. The grout inlet pipe is connected to the pump pipe and inserted into the bottom of the grouting hole. A grout return pipe is connected to the grouting orifice pipe. In this way, when the flow rate delivered by the grouting pump exceeds the flow rate of the grout injected into the rock, the grouting hole becomes an integral part of the grout circulation system. The cyclic grouting method can be used in conjunction with the above grouting methods.
Advantages: Both large and small pores can be filled.
Disadvantages: The cost is higher than the segmented grouting method and the stopper grouting method.
1.5 Gravity grouting method
Gravity grouting method is sometimes called conduit grouting method, and is often used in situations where there are large open cracks that can freely absorb grout. First, drill the hole to the full depth, insert the slurry pipe into the bottom of the hole, and pump the slurry in under pressure close to gravity. When the pressure begins to rise, slowly lift the grout pipe and continue grouting. Repeat the above steps until all holes are filled. The grout pipe is required to remain submerged in the grout throughout the grouting process.
Selection of grouting methods: Sectional grouting method and stopper grouting method are the two most commonly used methods. Both methods can usually achieve effective results. If the grouting schedule is very tight, you should consider it first The stopper grouting method is more suitable if the rock formation is horizontal, which can avoid uplifting the surface rock. If borehole water loss occurs during drilling, the segmented grouting method must be used. In order to prevent the natural mud formed by cuttings from clogging or filling the cracks in higher strata when drilling in shale or similar rock formations, the segmented grouting method can be used.
2. Grouting section length and pressure
Consolidated grouting pressure is closely related to the final grouting effect. Therefore, sufficient demonstration should be carried out when determining the grouting pressure, and on-site grouting tests should be carried out if necessary. Sure. Generally, the amount of grout suction increases as the grouting pressure increases.
The stages and pressure of consolidation grouting vary depending on geological conditions, hole depth and the presence or absence of concrete cover. Shallow holes with a depth of about 5m are generally not segmented, and the entire hole is grouted at one time. Hole depths above 8 to 10 m are generally grouted in segments. The length of the contact section is generally 1.5 to 2m, and the length of the rock section is generally 4 to 6m. In areas with good rock conditions and low permeability, the grouting section length can be appropriately increased, but generally it should not exceed 10m. In areas with broken rocks, developed cracks, and serious leakage, the section length should be shortened to 3 to 4m. When encountering large caves and fissures, special treatment should be taken.
3. Slurry water-cement ratio and grouting conditions
The selection of slurry water-cement ratio has always been a controversial issue. According to traditional theory, it is believed that for small cracks, thick slurry is difficult to pour into and can easily block the pores. . Therefore, the "Cement Grouting Construction Specifications for Hydraulic Buildings" (SL 62-94) requires that grouting should first be started at 10:1 or 8:1. However, in engineering practice, everyone feels that if slurry grouting is used, most of the water will be poured in, and the water will not be easily discharged, which will affect the grouting effect. Therefore, thicker slurry is generally used as much as possible.
In terms of grouting grout, foreign countries tend to use cement-stabilized grout. The so-called stable slurry means that the water separation rate of the slurry is not more than 5% within 2 hours. This slurry is Bingham based on its viscosity properties and cohesion.
During grouting, higher-density slurry can better drain away joint water, and joint water rarely mixes with it at the front edge of the slurry; the filling of joints is almost complete, including branch joints , because the slurry always stops spreading after reaching a maximum limited distance during the pouring process, so it will not cause excessive loss of slurry; it can accurately depict the volume of the poured slurry and the position it reaches; damage caused by excessive water discharged The risk of partially consolidated bodies is reduced.
After the slurry is solidified, the injected slurry will not emit water and form voids, so the strength of the slurry stone is slightly improved (7% higher); it has low permeability and has good bonding with the joint surface. Strength; high bonding strength; due to the uniform and dense structure of the stone, it has strong resistance to chemical dissolution and good durability.
In addition, the manufacturing process of this slurry is simple and the cost is slightly lower than that of conventional cement slurry. For example, the grouting of the Itaipu Dam in Brazil uses a cement-stabilized slurry with a bentonite content of 2%, while the 238m-high El Cajon in Honduras uses a cement-stabilized slurry with a bentonite content of 0.2%. , all achieved satisfactory results.
The preparation method of cement stable slurry is: first mix bentonite and water at a mass ratio of 1:3 to form a slurry and let it stand for 24 hours to allow for full expansion, then add cement and stir at high speed for 5 minutes. The bentonite mixed slurry is emulsified in a pump emulsifier and finally sent to an ordinary blade mixer for later use.
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