Construction method of high-pressure rotary jetting pile for water-stop curtain of overflow dam in high cobble geological condition

Abstract

The present application relates to concrete construction technology field, more specifically, it relates to high pressure jet grouting pile construction method of overflow dam water stop curtain in high cobble geology. According to design drawing, the position of hole is determined in construction area;When impact hole reaches 1 / 2 of design depth, add clay to 1 / 4 of design depth, then add water;Impact drill bit impacts hole again to design depth;Fine-grained soil is stirred uniformly and backfilled to ground level to form backfill area;Triple tube method high pressure jet grouting is carried out in backfill area, when design pile top height is reached or ground appears overflow phenomenon, stop jet grouting, and clean pipeline, one high pressure jet grouting pile is completed;According to design, the rest of high pressure jet grouting piles are completed according to the above steps. The present application forms uniform and continuous curtain pile body, has integrity and high impermeability, ensures the safety and stability of the project, simplifies the construction process and improves the pile forming efficiency.

Description

Technical Field

[0001] This invention relates to the field of concrete construction technology, and more specifically, to a high-pressure jet grouting pile construction method for using high-pebble geology as a spillway dam cutoff curtain. Background Technology

[0002] High-pressure jet grouting piles are widely used in engineering fields as a water-stopping curtain for foundation pits. They are suitable for soil layers such as silt, silty soil, cohesive soil, silt, sand, and artificial fill.

[0003] High-pressure jet grouting piles are constructed by drilling to the required depth using an engineering drilling rig (or a pilot-hole jet grouting machine). A high-pressure jet grouting trolley lowers a grouting pipe equipped with a horizontal nozzle to the design elevation. High-pressure equipment then uses the nozzle to spray grout at a certain pressure. The high-pressure jet impacts and cuts the soil, causing structural damage within a certain range. The grout mixes and solidifies with the soil, forming a cylindrical pile as the grouting pipe rotates and is lifted. After solidification, it forms a cylindrical, strong, and interlocking solidified body within the soil. This process serves to stop water ingress and reinforce the soil.

[0004] The existing Chinese invention patent number CN111042167A provides a construction method for a high-pressure jet grouting pile water-stop curtain, including the following steps: S1 ground treatment; S2 measurement and setting out; S3 drilling rig positioning; S4 drilling to the designed depth; S5 high-pressure jet grouting; S6 drilling rig relocation; S7 pile formation inspection. This invention adopts a two-stage pile formation method, first spraying a clay layer, and then performing high-pressure jet grouting after the clay layer has stabilized, to prevent the concrete from directly contacting groundwater and being corroded, while also providing an anti-seepage effect.

[0005] Chinese invention patent number CN104631480A discloses a method for constructing a deep foundation pit water-stop curtain using a high-pressure jet grouting pile machine. This invention is designed for geological strata with high drilling difficulty, such as silt, cohesive soil, loess, sand, artificial fill, and gravel and mudstone layers. It involves installing grouting pipes and air injection pipes inside the drill rod of a CFG (Chemical Fluidized Ground Gas) pile machine, modifying the CFG drill bit into a down-the-hole hammer drill, and employing a construction technique of directly jet grouting to form piles after hole formation.

[0006] However, the above two methods are not suitable for hard strata such as granite, limestone, dense pebble layers, and boulder layers (particle size > 20cm). High-pressure jets cannot effectively cut through them, making pile formation difficult. Large stones may hinder the mixing of slurry and soil, potentially clogging the jetting holes or causing pile displacement, which can easily lead to discontinuous piles.

[0007] In the comprehensive water ecological management project of the Yinzhuang-Wu'an railway bridge section in Qinshui County, Jincheng City, after the completion of the overflow weir jet grouting curtain pile test pile, the pile formation was found to be unsatisfactory upon excavation inspection. Specifically, the pebbles and gravel were relatively large in diameter and contained 60%–75% stone. The pile formation effect was such that only a 20–30 cm radius around the borehole contained pure cement, and the cement slurry was barely visible outside the borehole. Visually, the cement slurry could not coat the surrounding pebbles or gravel, and it could not effectively form a continuous curtain pile body with the width required by the design.

[0008] The geological conditions are almost entirely composed of pebbles and gravel, with approximately 20% of the stones being 50-60cm thick, a high proportion of about 60% being 30-40cm thick, and about 20% being less than 20cm thick. The overall stone content far exceeds 50%, increasing from west to east (right bank to left bank). The geology beneath the excavation face is still uncertain and complex. According to the "Technical Specification for High-Pressure Jet Grouting Pile Construction," high-pressure jet grouting pile construction under these geological conditions is extremely difficult and risky, and the uniformity and continuity of the pile body are difficult to guarantee.

[0009] Based on the working mechanism of high-pressure jet grouting piles, the pilot-hole construction method used in ancient riverbed construction for water conservancy projects cannot achieve the desired seepage prevention effect. During pilot-hole construction, large pebbles or boulders are encountered in the strata. The drill bit penetrates these boulders, causing them to obstruct the grout from being sprayed onto the back of the pebbles or boulders during jet grouting and lifting, thus failing to adequately mix the soil within the designed treatment area. This results in some unmixed soil layers forming seepage channels after construction, preventing the formation of a closed water-stop curtain and severely affecting the water-stopping effect. Summary of the Invention

[0010] The present invention aims to at least solve one of the technical problems existing in the prior art. To this end, the purpose of the present invention is to provide a high-pressure jet grouting pile construction method for using high pebble geology as a spillway cutoff wall, the specific steps of which are as follows:

[0011] S1. In the construction area, according to the design drawings, carry out measurement, positioning, layout and marking work to determine the location of the holes;

[0012] S2. Conduct the first impact drilling operation at the determined hole location. When the hole depth reaches 1 / 2 of the designed depth, stop the operation, add clay to the hole to 1 / 4 of the designed depth, and then add the appropriate proportion of water to the hole.

[0013] S3. The impact drill bit is used again to perform impact drilling until the designed depth is reached;

[0014] S4. Mix the fine soil evenly and fill it into the hole. Compact it every 2 meters until it is backfilled to the ground level to form a backfill area.

[0015] S5. Perform high-pressure jet grouting using the triple-pipe method in the backfill area. When the designed pile top height is reached or grout overflow occurs on the ground, the jet grouting work on the current pile should be stopped immediately. Pull out the jet grouting pipe and clean the pipeline. One high-pressure jet grouting pile is completed.

[0016] S6. Complete the remaining high-pressure jet grouting piles in sequence according to the design, following steps S2 to S5 above.

[0017] Preferably, the ratio in S2 is 2:1:0.1 for hole depth: clay depth: water depth.

[0018] Preferably, in step S4, the fine-grained soil is mixed evenly to become homogeneous soil, and test piles are made to test the amount of grout sprayed, which facilitates the determination of parameters during subsequent engineering pile construction.

[0019] Preferably, in S5, the drilling diameter of the triple-tube high-pressure jet grouting method is φ146mm, and the casing drill bit integral impact drilling process is adopted. A 100mm diameter PVC pipe or a jetting pipe is lowered into the casing. To ensure normal slurry return and slurry overflow during the jetting process, a drill bit with a diameter 20mm larger than the outer diameter of the jetting pipe is used. To ensure the verticality of the drilling, a spirit level is used to measure the horizontal direction of the machine body and the vertical direction of the vertical axis every 5 meters of drilling.

[0020] Preferably, in step S5, before grouting, the length of the jetting pipe is measured to confirm that the center line of the nozzle is consistent with the direction of the jetting pipe.

[0021] Preferably, in step S5, the grout is first prepared using ordinary Portland cement with a strength grade of P.042.5, and the water-cement ratio of the high-speed jet grout is 1:1. The mixing time of the ordinary mixer is not less than 90 seconds, and the mixing time of the high-speed mixer is not less than 30 seconds. The grout is then screened before use and is used up within 4 hours of the start of preparation.

[0022] Preferably, in the S5 method, the triple-pipe high-pressure jet grouting first delivers high-pressure water, then cement slurry and compressed air; during spraying, the predetermined spraying pressure and grout volume should be reached first, and then the grouting pipe should be gradually raised, with the overlap length of the grouting pipe being raised in sections not less than 100mm.

[0023] Preferably, in the S5 method, the triple-pipe high-pressure jet grouting continuously operates within the borehole. When the jetting pipe reaches the designed depth, cement grout and compressed air are injected. The grout is then left to stand for 1 to 3 minutes. When the injection pressure and grout quantity reach the specified levels and the grout flows out of the borehole, the jetting operation proceeds from bottom to top. When the designed height is reached, the jetting is stopped and the jetting pipe is pulled out. The lifting is stopped at the stratum boundary, and the grouting continues for 5 to 10 minutes while increasing the grout supply. When the water-cement ratio of the grout is 1:1 and 0.6:1, the corresponding grout densities are 1.5 g / cm³ and 1.6 g / cm³, respectively.

[0024] Preferably, in step S5, the triple-tube high-pressure jet grouting method performs static pressure filling and grouting in the recessed injection hole until the grout surface stabilizes.

[0025] Preferably, in S6, construction is carried out at least 48 hours apart between two adjacent high-pressure jet grouting piles.

[0026] The beneficial effects of this invention are as follows:

[0027] This invention employs an impact drilling process to break up pebbles or boulders within the rotary pile's drilling area, reducing pebble size and improving geological conditions. Breaking up large-diameter pebbles reduces the obstruction of the cement grout by the geological formation, allowing the grout to better penetrate and encapsulate the surrounding soil, thus improving the continuity and integrity of the pile. After impact drilling, homogeneous fine-grained soil is backfilled to optimize the geological structure. Simultaneously, precise proportioning of the cement grout to the fine-grained soil improves the grout's fluidity and encapsulation properties.

[0028] The backfilling with fine-grained soil makes the strata more uniform, allowing the cement grout to better penetrate and encapsulate the pebbles or gravel. While ensuring the design requirements for impermeability, the amount of cement grout used is optimized, reducing waste and lowering material costs. At the same time, the impermeability and strength of the curtain pile body are guaranteed, forming a continuous curtain pile body that meets the design requirements.

[0029] By using impact drilling for hole formation and backfilling with fine-grained soil, the geological conditions were improved, enabling the effective construction of high-pressure jet grouting piles in strata with high rock content. This expanded the applicability of high-pressure jet grouting piles, allowing them to be applied to projects with more complex geological conditions, thus improving the versatility and practicality of the technology. This invention forms a uniform and continuous curtain pile body, possessing integrity and high impermeability, ensuring the safety and stability of the project, simplifying the construction process, and improving pile formation efficiency. It also reduces rework rates, increases construction efficiency, and guarantees project quality and schedule. This invention has high practicality and promotional value, and is particularly suitable for projects with similar complex geological conditions and high rock content.

[0030] Additional aspects and advantages of the invention will become apparent from the description which follows, or may be learned by practice of the invention. Detailed Implementation

[0031] To better understand the above-mentioned objectives, features, and advantages of the present invention, the present invention will be further described in detail below with reference to specific embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be combined with each other.

[0032] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be implemented in other ways different from those described herein. Therefore, the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0033] S1. In the construction area, according to the design drawings, carry out measurement, positioning, layout and marking work to determine the location of the holes;

[0034] S2. Conduct the first impact drilling operation at the determined hole location. When the hole depth reaches 1 / 2 of the design depth, stop the operation, add clay to the hole to 1 / 4 of the design depth, and then add water to the hole in the appropriate proportion (hole depth: clay depth: water depth = 2:1:0.1).

[0035] S3. The impact drill bit performs another impact drilling operation until the designed depth is reached. The impact drill bit and drill body squeeze the water and clay in the corresponding proportion, so that the clay reaches a certain strength and adheres tightly to the hole wall, further improving the stability of the hole wall and reducing the collapse rate.

[0036] S4. Mix the fine soil excavated from the riverbed evenly to make it homogeneous soil, make test piles, test the amount of grouting, so as to facilitate the determination of parameters during the subsequent construction of engineering piles. Place a funnel at the hole opening, use an excavator to fill the hole with the evenly mixed fine soil, and compact it every 2 meters with an impact drill (the bottom is modified to be a flat plate) until the backfill reaches the ground level to form a backfill area.

[0037] S5. Perform high-pressure jet grouting using the triple-pipe method in the backfill area. When the designed pile top height is reached or grout overflow occurs on the ground, the jet grouting work on the current pile should be stopped immediately, and the jet grouting pipe should be pulled out and the pipeline cleaned. One high-pressure jet grouting pile is completed.

[0038] The borehole diameter is φ146mm, using a casing drill bit integral impact drilling process. After drilling to the pile bottom elevation, the casing and drill rod are pulled out as a whole. A 100mm diameter PVC pipe or a jetting pipe is lowered into the casing, and the pressure application is judged by the broken PVC pipe fragments. Before drilling, the hole layout is measured according to the design drawings, and the pile number, hole number, sequence number, and elevation of each hole opening are marked. The main drill rod of the drilling rig is precisely aligned with the backfill area, and a spirit level is used to measure the horizontal and vertical directions of the machine body to ensure the stability of the drilling rig. To ensure normal slurry return and slurry overflow during the jetting process, a drill bit with a diameter 20mm larger than the outer diameter of the jetting pipe is used. To ensure the verticality of the borehole, a spirit level is used to measure the horizontal and vertical directions of the machine body every 5 meters of drilling. When installing the drilling rig, it must be adjusted strictly according to the drawing requirements, with the hole position deviation less than 5cm and the hole bottom inclination rate less than 1%.

[0039] Before grouting, the length of the jetting pipe should be measured to confirm that the centerline of the nozzle is aligned with the direction of the jetting pipe, and graduations should be marked on the jetting pipe. Before high-pressure jetting pile construction, a test spray must be conducted on the ground to ensure precise adjustment of the jetting direction and swing angle. The performance of the grouting pump should be compatible with the type and concentration of the grout, and its rated working pressure should exceed the maximum grouting pressure by 1.2 times. The pressure fluctuation range should be controlled below 20% of the grouting pressure, and it must have sufficient discharge capacity and stable working performance. Ensure that the grouting pipeline can withstand 1.2 times the maximum grouting pressure. Pressure gauges should be installed at the grouting pump, grouting orifice, and grout inlet pipeline to ensure safety. Ensure that each part has sufficient pressure values, and that the pressure value at each link is greater than or equal to the design requirements to prevent accidents caused by pipeline leakage. After the ground test spray has passed the acceptance test, measures should be taken when lowering the jetting pipe to prevent the nozzle from jamming.

[0040] The grout preparation process involves ensuring that the type of grout produced is coordinated with the grout pump discharge rate, guaranteeing uniform and continuous mixing to meet the continuous grout supply requirements of the high-pressure jet grouting piles. High-pressure jet grouting uses ordinary Portland cement with a strength grade of P.042.5 and a water-cement ratio of 1:1. The mixing time with a standard mixer should be no less than 90 seconds, and with a high-speed mixer no less than 30 seconds. The grout should be sieved before use, and the entire preparation period should ideally be within 4 hours. All grout components must be thoroughly mixed, and the density, temperature, and other parameters of the grout should be determined and recorded. The storage time should not exceed 5 hours when the ambient temperature is below 10℃ and no more than 3 hours when the ambient temperature is above 10℃. If the grout storage time exceeds its effective time, it should be used at a lower strength grade or disposed of as waste grout. The temperature of the slurry should be maintained between 5℃ and 40℃; the weighing of the slurry materials can be carried out by mass or volume measurement, but the error should be controlled within the range of no more than 5%; before using the slurry, the slurry delivery pipeline and pressure gauge must be checked to ensure that the slurry can be smoothly injected into the formation; when cement slurry needs to be mixed with appropriate amounts of admixtures and additives to form a composite slurry, it must be tested and determined.

[0041] The triple-pipe high-pressure jet grouting method first delivers high-pressure water, then cement slurry and compressed air; during spraying, the predetermined spraying pressure and grout volume should be reached first, and then the grouting pipe should be gradually raised. The overlap length of the grouting pipe in the segmented lifting should not be less than 100mm.

[0042] The triple-pipe high-pressure jet grouting method involves checking that the grouting pipe has descended to the designed height. After the nozzle reaches the designed height, it is inserted to a predetermined depth. After acceptance by the supervisor, high-pressure jet grouting begins. Utilizing jet grouting technology, the jetting pipe rotates and rises, forming columnar piles in the stratum. Air and grout must be continuously supplied. The high-pressure jet grout works continuously within the borehole. When the jetting pipe reaches the designed depth, cement grout and compressed air are injected (usually introduced after 30 seconds). The mixture is then left to stand for 1 to 3 minutes. When the injection pressure and grout volume reach the specified levels and grout flows out of the borehole, the jetting operation is carried out from bottom to top at a preset lifting, rotating, or swaying speed. When the designed height is reached, jetting is stopped and the jetting pipe is withdrawn. The lifting speed depends on the stratum and grout return conditions. Lifting is stopped at the stratum boundary, and static jetting is performed for 5-10 minutes while increasing the grout supply. During the jetting process, the supervisor's instructions must be followed, and the density of the cement grout must be tested periodically. When the water-cement ratio of the slurry is 1:1 and 0.6:1, the corresponding slurry densities are 1.5 g / cm³ and 1.6 g / cm³, respectively. During the spraying process, it is necessary to constantly monitor and check the pressure of the mud / water pump, the slurry flow rate, the air pressure and air volume of the air compressor, the drilling rig speed, the lifting speed, and the slurry consumption to ensure that these factors meet the requirements. At the same time, during the construction process, the operation process curve should be recorded and plotted in a timely manner.

[0043] During high-pressure jet grouting, if a sudden drop or rise in pressure occurs, or if the grout concentration or volume at the orifice becomes abnormal, construction should be stopped immediately to identify the cause and take appropriate action. When connecting, disconnecting, or replacing the jetting pipe, it should be done quickly to avoid orifice collapse or pipe blockage. After connecting or disconnecting the pipe, the lower pipe position should be 0.5m lower than the original stopping height before a second jetting overlap, ensuring vertical continuity. If high-pressure jetting is interrupted for any reason, it should be stopped immediately, and the depth of the interruption recorded for prompt resumption. In case of mechanical failure, downtime should be minimized. If insufficient grout jetting affects the designed diameter of the grouting layer, re-jetting should be performed. When dealing with large-area grout leakage or overflow, the condition of the soil layer, the overall effect of jet grouting, and the rationality of the jet grouting process parameters can be understood by observing the grouting status.

[0044] Backfilling is performed after the spraying work is completed. The grout will solidify and release water, causing depressions on the surface of the solidified body. Static pressure grouting is required to fill the depressions in the spray holes until the grout surface is stable. When spraying in clay or silt layers, the grout that has overflowed must not be backfilled. During the backfilling process, the time, number of times, grout volume, amount of cement used, and quality of backfilling must be recorded.

[0045] S6. Complete the remaining high-pressure jet grouting piles according to the above steps in sequence according to the design, with at least 48 hours between construction of two adjacent high-pressure jet grouting piles.

[0046] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the invention by those skilled in the art. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the invention should be included within the scope of protection of the invention.

Claims

1. A high-pressure jet grouting pile construction method for overflow dam cutoff curtain in high pebble geology, characterized by: The specific steps of the construction method are as follows: S1. In the construction area, according to the design drawings, carry out measurement, positioning, layout and marking work to determine the location of the holes; S2. Conduct the first impact drilling operation at the determined hole location. When the hole depth reaches 1 / 2 of the designed depth, stop the operation, add clay to the hole to 1 / 4 of the designed depth, and then add the appropriate proportion of water to the hole. S3. The impact drill bit is used again to perform impact drilling until the designed depth is reached; S4. Mix the fine soil evenly and fill it into the hole. Compact it every 2 meters until it is backfilled to the ground level to form a backfill area. S5. Perform high-pressure jet grouting using the triple-pipe method in the backfill area. When the designed pile top height is reached or grout overflow occurs on the ground, the jet grouting work on the current pile should be stopped immediately. Pull out the jet grouting pipe and clean the pipeline. One high-pressure jet grouting pile is completed. S6. Complete the remaining high-pressure jet grouting piles according to the design, following steps S2 to S5 above. The ratio in S2 is 2:1:0.1 for hole depth: clay depth: water depth. The fine-grained soil in S4 is mixed evenly to become homogeneous soil, and test piles are made to test the amount of grout sprayed, which facilitates the determination of parameters during subsequent engineering pile construction.

2. The high-pressure jet grouting pile construction method for overflow dam cutoff curtain in high pebble geology as described in claim 1, characterized in that: The drilling diameter of the triple-tube high-pressure jet grouting method in S5 is φ146mm. It adopts the integral impact drilling process of casing drill bit. A 100mm diameter PVC pipe or jetting pipe is lowered into the casing. To ensure normal slurry return and slurry overflow during the jetting process, a drill bit with a diameter 20mm larger than the outer diameter of the jetting pipe is used. To ensure the verticality of the drilling, a spirit level is required to measure the horizontal direction of the machine body and the vertical direction of the vertical axis every 5 meters of drilling.

3. The high-pressure jet grouting pile construction method for overflow dam cutoff curtain in high pebble geology as described in claim 1, characterized in that: Before grouting, the length of the jetting pipe in the triple-pipe high-pressure jetting method described in S5 is measured to confirm that the center line of the nozzle is consistent with the direction of the jetting pipe.

4. The high-pressure jet grouting pile construction method for overflow dam cutoff curtain in high pebble geology as described in claim 3, characterized in that: In the S5 grouting process, the grout is first prepared using ordinary Portland cement with a strength grade of P.042.5 and a water-cement ratio of 1:1 for high-speed jet grout. The mixing time is no less than 90 seconds for ordinary mixers and no less than 30 seconds for high-speed mixers. The grout is then sieved before use and must be used up within 4 hours of preparation.

5. The high-pressure jet grouting pile construction method for overflow dam cutoff curtain in high pebble geology as described in claim 1, characterized in that: In the S5 method, the triple-pipe high-pressure jet grouting first delivers high-pressure water, then cement slurry and compressed air; during spraying, the predetermined spraying pressure and grout volume should be reached first, and then the grouting pipe should be gradually raised. The overlap length of the grouting pipe in the segmented lifting should not be less than 100mm.

6. The high-pressure jet grouting pile construction method for overflow dam cutoff curtain in high pebble geology as described in claim 5, characterized in that: In the S5 triple-tube high-pressure jet grouting method, the high-pressure jet grout works continuously inside the borehole. When the jetting pipe reaches the designed depth, cement grout and compressed air are injected. Then, the grout is left to stand for 1 to 3 minutes. When the injection pressure and the amount of grout injected reach the specified values ​​and the grout flows out of the borehole, the jetting operation is carried out from bottom to top. When the designed height is reached, the jetting is stopped and the jetting pipe is pulled out. The lifting is stopped at the stratum boundary. The grouting is left to stand for 5 to 10 minutes and the grout supply is increased. When the water-cement ratio of the grout is 1:1 and 0.6:1, the corresponding grout densities are 1.5 g / cm³ and 1.6 g / cm³, respectively.

7. The high-pressure jet grouting pile construction method for overflow dam cutoff curtain in high pebble geology as described in claim 1, characterized in that: In the S5 method, the triple-tube high-pressure jet grouting is used to perform static pressure filling and grouting in the recessed injection hole until the grout surface is stable.

8. The high-pressure jet grouting pile construction method for overflow dam cutoff curtain in high pebble geology as described in claim 1, characterized in that: In S6, construction shall be carried out at least 48 hours apart between two adjacent high-pressure jet grouting piles.