Talking about the construction technology of wet sprayed concrete?

The following is the related content of wet shotcrete construction technology brought by Zhong Da Consulting for your reference.

Shuichongkou Tunnel is the main structure of Pingle-Zhongshan Highway, located at K 137860~K 139265. The tunnel passes through Class II ~ III surrounding rock, which is composed of slightly weathered sandstone, silty mudstone and granite, with a gravel loose structure. Wet spraying is adopted, and the waterproof reaches the second-class waterproof standard. The following is a description of wet spraying in Shuichongkou tunnel.

1 wet sprayed concrete technology test

1. 1 Select the matching tool.

① Worktable: According to the tunnel section size, make a workbench on site, with a working length of 5m (the length of a spraying operation cycle).

② Feeding platform: The height of the ejector hopper is1.5m. In order to reduce the labor intensity, a feeding platform with a height of 0.7m is set.

③ Concrete sprayer: TK-96 1 wet concrete sprayer. Its production capacity is 3 ~ 5m3/h; Horizontal conveying distance 100 meter, vertical conveying distance 30 meters.

④ Mixture mixer: forced concrete mixer, equipped with weighing equipment, scales, bench scales, etc.

⑤ Air compressor: The air supply capacity is above 0.5MPa, and the air supply volume is above 9m3/min.

⑥ Water supply equipment: ensure that the water pressure is 0. 15-0.2MPa.

All landowners slump Jane, 10* 10 compression standard mold, impermeable mold, spray plate bottom mold and other auxiliary tools.

1.2 material selection and concrete mix ratio

1.2. 1 material selection (see table 1 and table 2)

① Cement: P.O425 Yufeng brand ordinary portland cement.

② Sand: Tangyan River sand. The fineness modulus is 2.59 and the silt content is 1.8%.

③ Coarse aggregate: 5~ 15mm continuous graded granite macadam.

4 water: drinking water.

⑤ Additives. Accelerator: 8604 liquid accelerator is determined as the final field material through tests: waterproof agent: EA-C shrinkage-compensating expansive agent (internal mixing method: 14%) and TJ type high-efficiency waterproof agent (external mixing method: 3%~5%) are used in field comparative tests respectively: water reducer: TJ-G high-efficiency water reducer is selected, and the mixing amount is 0.8% ~ 60.

⑥ Drainage blind pipe. Due to the limitation of water injection thickness (the designed minimum water injection thickness is 80mm), the soft permeable spring blind pipe with an outer diameter of 30mm is selected.

1.2.2 formulation of mixture ratio

According to the technical requirements of wet spraying machine, on the basis of plain concrete mix ratio: C: S: G: W =1:2: 0.45 (cement: sand: stone: water), different admixtures: (1) EA-CJT-G are added, and the mix ratio is C: S:. The results are shown in Table 3.

It can be seen that the two mixture ratios of admixture meet C20 strength standard, so it is decided to adopt two mixture ratios as the materials for field test.

1.3 geological survey

The surrounding rocks of the tunnel are mainly Class I and III, which are located in the slightly weathered zone. Joints are developed-undeveloped, closed-slightly tensioned, local tensile, mainly torsional, smooth joint surface, a small amount of argillaceous filling, and occasionally small faults are exposed. After excavation, it is mostly wet or soaked, and obvious water outlet points are occasionally found in joint fracture zone and dike contact zone, mainly local dripping and small linear water outlet, with small water inflow. See Table 4 for the survey results of K 137900-940.

1.4 field test

1.4. 1 Determination of mix proportion of field sprayed concrete

According to the field geological investigation, 4% accelerator was added to the mixture ratio (I) and (II) respectively, and the results are shown in Table 5.

According to the test, the mixture ratio (2) is used in the seepage or dripping section. In order to ensure the quality of the rock surface with large local seepage or dripping water, the mixture ratio is changed, only fine aggregate is used instead of coarse aggregate, 6% accelerator is added, and the mixture ratio is normal before spraying 2cm thick. In the wet department or cadres. Spraying is carried out by adopting the proportion (2).

1.4.2 influence of rock surface cleanliness

We divide the rock surface to be measured into two parts: A (cleaning) and B (maintaining the original excavation surface). We will remove the basin at the bottom and fasten it on the rock surface. By default, steel bars will be pulled in the middle, and concrete will be sprayed until the basin is full. After 28 days, it will be pulled to failure with an anchor puller. The uplift force of rock surface A is obviously greater than that of rock surface B, and the resilience of rock surface A is also less than that of rock surface B. The test results are between 0.2 MPa and 0.9 MPa, and the failure form of rock surface A is analyzed. ① There are many shiny granite timely particles on the bonding surface, which shows that the timely particles in granite are one of the factors that affect the bonding strength between granite and shotcrete. (2) There are some granite schists on the failure surface, which shows that the failure of the specimen first occurs on the micro-joint surface inside granite, which proves that before shotcreting, the sprayed rock surface must be kept free of loose rock, clean, oil pollution and impurities. In the area where the joints of surrounding rock are well developed, it is necessary to use steel mesh and anchor rod to strengthen the overall support function of shotcrete layer and surrounding rock.

1.4.3 Impact of groundwater

We divide the rock surface to be measured at the vault of K 1379 10~920 into two parts: A (installing drainage system) and B (unstable). After spraying, by observing the surface of sprayed concrete, there are two main types of water leakage on the surface of sprayed concrete: one is wet stain, and there is no obvious water mark on the surface of sprayed concrete, which mainly appears in the arch after spraying, showing a large sheet shape; The other is that obvious water drops are dripping on the surface. The results after 28 days are shown in Table 6.

It can be seen that blind pipes can be set for drainage, re-injection or direct plugging for the rock surface with large water dripping or seepage. From the field test, it is difficult to achieve the effect of seepage prevention and plugging by one injection, mainly because the groundwater distribution of the first injection is not concentrated, and it is difficult to find the water outlet point with a large inflow. Therefore, in the case of more groundwater and higher waterproof requirements, layered water injection method is adopted.

1.4.4 influence of raw materials

The same materials provided above are divided into A (washed aggregate) and B (original) for trial mixing, and sprayed on the same rock surface with the same water-cement ratio. Compared with B, A has the advantages of high concrete strength, high cohesive force and small rebound, which proves that the cleanliness of aggregate is very important for shotcrete.

The influence of water cement ratio 1.4.5;

For wet sprayed concrete, if the water-cement ratio is too large, the rapid setting effect will become worse, the rebound will increase and the concrete strength will be low; The water-cement ratio is small, the construction jet is difficult, the cement hydration is insufficient, the strength is low and the rebound is increased. The test spray is carried out with C/W = 0.4 ~ 5.0, and the effect is better when C/W = 0.45.

1.4.6 Influence of construction temperature

The setting time of cement increases with the increase of temperature. When the temperature reaches 30℃, it is unfavorable to the final setting time and later strength of concrete mixed with accelerator. The temperature of sprayed concrete should be 15~25℃.

1.4.7 Influence of coating thickness

If the primary spray layer is too thick, the spray layer will crack under the action of self-weight, resulting in a large area collapse; If it is too thin, most of the coarse aggregate will rebound. Only mortar remains in the spraying layer, which will affect the spraying effect and quality. Through field test, the thickness of sprayed layer on arch is 6 cm, and that on side wall is 8 cm.

1.4.8 Influence of wind pressure and water pressure

If the wind pressure is too high, the jet velocity is too high and the rebound increases; If the wind pressure is too small, the spraying force will be weakened, the compactness of concrete will be poor, and the strength will be affected; Too low water pressure will also affect the construction quality. The wind pressure is 200 n/cm2 and the water pressure is 2 10 n/cm.

2 Determination of wet shotcrete technology

2. 1 Selection and control of raw materials

Using the above raw materials, coarse aggregate should be sieved for 0.5mm before mixing, and then washed with water; In order to reduce shrinkage cracks, fine aggregate should be medium-coarse sand with fineness modulus greater than 2.5, and should be sieved by 0.5mm before mixing.

2.2 Determination and selection of mixing ratio

For the seepage or dripping section (such as K 1379 10-920), Tl-type mixing is adopted, and its ratio is c: s: g: w: TJ =1:2: 0.45: 0.04. Mixing accelerator 4‰ For the rock surface with large local water seepage or dripping, change the mixture ratio, only use fine aggregate instead of coarse aggregate, add 6% accelerator, spray 2cm thick first and then spray according to the normal mixture ratio. When the wall is dry or wet (such as K 137920-930), the mixing ratio is c: s: g: w: ea-c: lt-g =1:2: 2: 0.45: 0.12: 0.8%.

2.3 Control of injection machinery

TK-96 1 wet spraying machine is equipped with 5m long workbench, 0.7m high feeding platform, forced concrete mixer and air compressor. During work, it is required to have good sealing performance, no water leakage and no air leakage.

2.4 Control of mixing process

Strictly control the water cement ratio, and the measurement of admixture and water must be accurate. The feeding sequence and mixing time are: coarse and fine aggregate-cement-admixture (mixing for 90S)- water (mixing 12Os)- discharging.

2.5 rock surface treatment and water seepage treatment

Rock surface treatment. Carefully check the size of the excavation surface, remove loose dangerous stones, and carry out local treatment in advance if there is too much under-excavation; Clean the spraying surface with high-pressure wind or water, and clean the dust and sundries on the excavation surface; Inspection mark for thickness of buried spray layer. Leakage treatment. Do a good job in drainage: install soft spring blind pipes and lay two kinds of blind pipes. One is to set a circumferential blind pipe every 5 meters, and set drainage holes at the ends of blind pipes on both sides of the side wall. The other is to set a local blind pipe at the centralized water outlet or the surface water spraying point, which is connected with the adjacent circumferential blind pipe.

2.6 Injection steps

(1) Before spraying, adjust the water cement ratio according to the wetting degree of the rock surface. (2) The injection shall be carried out in sections, blocks and blocks, and the injection shall be carried out from bottom to top according to the wall first and then the arch. The nozzle should make a uniform clockwise spiral rotation on the sprayed rock surface, move horizontally for half a circle, and the spiral diameter is about 20~30cm, or adopt S-shaped reciprocating motion. (3) When spraying, the segment length shall not exceed 6cm, and the segment shall be down first and then up, and the segment size shall be 2m*2m. ④ The distance between the nozzle and the rock surface is lm, and the nozzle is perpendicular to the sprayed surface and slightly inclined to the just sprayed part (the inclination angle is about 80). It is advisable to spray more at the depression of rock surface, and spray less at the protrusion.

2.7 Control of wind pressure and water pressure

Because the length of the conveying pipe is 40m, the regulated wind pressure is 200 N/cm2, the water pressure is 2 10N/cm2, and the water pressure in the water supply system should not be greater than 40N/cm2. In order to ensure the stability of the water supply pressure, a pressure water tank is adopted.

2.8 Determination of Injection Thickness

One-time molding thickness: vault 6cm, side wall 8cm: used for water seepage or dripping area. Spray a layer of fine aggregate concrete with a thickness of 2cm first, and then spray concrete to the design thickness.

2.9 Interval time control of stratified injection.

When 15℃~25℃, 8604 liquid accelerator should be used and sprayed again after 30min.

2. 10 curing

After the final setting of sprayed concrete 1h, spray water on the sprayed surface for curing for not less than 7d.

To sum up, the technological process of shotcrete is as follows: anchor and shotcrete platform in place → spray surface pretreatment and thickness control → wet spraying machine start preparation → batching and mixing → slump determination → mixture transportation → side wall concrete shotcrete → shutdown operation → maintenance.

3 Quality inspection after injection

First, follow-up inspection after wet spraying was completed, and no surface cracks were found. However, there are many pits on the spray surface. Because the working wind pressure of wet spraying is too high, the speed of material beam is high and the effective thickness of concrete with many pits is insufficient, a layer of 1~3cm cement mortar is sprayed on the concrete surface.

Secondly, the concrete surface is wet and there is no obvious water mark. Through drilling investigation, it is found that the waterproof effect is better when the spraying thickness reaches 6~8cm at a time. If the spray thickness is too small, it will form flooding, which has a wide range and can be treated with shotcrete.

Thirdly, the outlet of the blind pipe section is completely drained, and the leakage of concrete surface near both sides of the blind pipe is obviously less than that in the middle, which shows that the material selection and installation method of the blind pipe is correct.

Fourthly, when the sprayed concrete specimen is cut and inspected, its surface pores are mostly oval, closed and disconnected, which will not form seepage channels and reduce impermeability. 28d specimen strength meets the requirements.

Fifthly, the coating thickness is basically ensured by burying the detection nails.

4 conclusion

First, from the waterproof point of view, the spraying thickness is 12~ 15cm, and the spraying effect will be better if it is layered, with a layer of 6~8cm.

Second, hanging mesh and shotcrete must be used to implement integral support in the area where the joints of surrounding rock are well developed.

Thirdly, the accuracy of concrete proportion measurement is the key to the quality of wet spraying, and quality inspection and supervision should be strengthened in site construction to ensure the waterproof effect and quality durability of shotcrete structure.

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