Method for repairing seepage of dam body and dam foundation under high water level while drilling

Abstract

The application discloses a kind of earth-rock dam body, dam foundation is under the seepage of high water level and is drilled with the repair method of being filled simultaneously, comprising the following steps: (1) using first grouting pipe to replace drill rod, and being equipped with first drill bit to obtain the drilling and filling assembly that can be realized drilling and filling simultaneously;Using the drilling and filling assembly to carry out drilling to dam body, until drilling through cover layer, to dam foundation bedrock;(2) from first grouting pipe, lower into a second grouting pipe smaller than first grouting pipe, make second grouting pipe to first grouting pipe bottom, second grouting pipe is equipped with second drill bit, then carry out bedrock section drilling and synchronous grouting;(3) after bedrock section processing is completed, remove second grouting pipe, using first grouting pipe from bottom to top to carry out pulsating grouting to dam body.The seepage drilling and filling repair method of the application solves the problem that dam body, dam foundation drilling, grouting process is complex and repeated drilling, realizes drilling and filling simultaneously, further improves construction efficiency, construction quality and grouting effect.

Description

Technical Field

[0001] This invention belongs to the field of water conservancy and hydropower reinforcement engineering, and particularly relates to a method for repairing seepage in earth-rock dams. Background Technology

[0002] Earth-rock dams are the most widely used dam type in dam construction worldwide due to their availability of local materials, simple structure, good adaptability to deformation, and ease of construction. Currently, many earth-rock dam projects suffer from inherent deficiencies and disrepair due to age, resulting in seepage in the dam body and foundation. Some even experience seepage on the downstream slope, which can lead to seepage failure and necessitate lowering the reservoir water level or draining the dam for repairs to prevent dam collapse.

[0003] Currently, dam seepage can be treated by adding an additional seepage barrier (such as using vibratory casting, high-pressure jet grouting, or geomembrane interception methods). However, these methods have drawbacks, including shallow seepage depth, inability to penetrate the bedrock, and the need to empty the reservoir to lower the water level. Furthermore, these techniques are not suitable for dams with internal pores or seepage caused by soil conditions. Grouting is commonly used for dam seepage caused by loose fill or poor soil quality. However, without emptying the reservoir, the high head pressure difference leads to a large seepage velocity within the dam. Under dynamic water conditions, conventional grouting methods suffer from erosion, low grout retention, and poor grouting effectiveness.

[0004] Pulsed grouting is a method of seepage prevention and reinforcement of strata by repeatedly impacting loose soil with low-flowability grout under high pressure at a certain frequency, through mechanisms such as compaction, filling, and fracturing. It is commonly used for treating Quaternary overburden, karst, soft rock, and gravel strata, and is particularly suitable for loose, soft, and highly permeable strata. It is a good alternative to conventional grouting methods, but it is currently rarely used for seepage prevention and reinforcement of dams. Furthermore, the pulsed grouting seepage prevention and reinforcement technology for earth-rock dams at high water levels still has the following problems:

[0005] 1. During construction, drilling and grouting are carried out independently and separately. When drilling reaches a part of the dam with large seepage, if it is not dealt with in time, the disturbance of the drilling will not only increase the seepage of the dam, but also further aggravate the seepage damage of the dam under the high water head pressure difference, which will have an adverse effect on the stability of the dam.

[0006] 2. When using a single-drilling, segmented grouting process, if there are strata with large pores in the borehole, the grout tends to flow along the direction of the large pore channels, resulting in uneven soil compaction and inconsistent grouting effects, with some areas not properly grouted.

[0007] 3. Due to the different rock types of the dam body and dam foundation, the construction techniques are different, including drilling and grouting processes and materials. Conventionally, the upper dam body is treated first, followed by curtain grouting of the dam foundation. During dam foundation construction, drilling must be carried out from the dam top through the dam body to the bedrock contact surface. Drilling and grouting then begin below the contact surface to the designed stratum depth. The section through the dam body is only drilled without grouting, resulting in repeated drilling sections. This makes the construction process complex and time-consuming. Summary of the Invention

[0008] The technical problem to be solved by this invention is to overcome the shortcomings and defects mentioned in the background art above, and to provide a method for repairing seepage in earth-rock dam bodies and foundations under high water levels through drilling and grouting, which features simple construction technology, high grouting quality, and minimal impact on dam stability. To solve the above technical problem, the technical solution proposed by this invention is as follows:

[0009] A method for repairing seepage in the body and foundation of an earth-rock dam under high water levels by drilling and grouting simultaneously includes the following steps:

[0010] (1) Use the first grouting pipe to replace the drill rod and equip it with the first drill bit to obtain a drilling and grouting assembly that can realize drilling and grouting at the same time; use the drilling and grouting assembly to drill holes in the dam body until the overburden layer is drilled through to 0.5-1.0m into the bedrock of the dam foundation;

[0011] (2) A second grouting pipe with a smaller diameter than the first grouting pipe is lowered into the first grouting pipe, so that the second grouting pipe reaches the bottom of the first grouting pipe. The second grouting pipe is equipped with a second drill bit, and then the bedrock section is drilled and grouted simultaneously.

[0012] (3) After the bedrock section is treated, the second grouting pipe is taken out and the first grouting pipe is used to perform pulsating grouting on the dam body from bottom to top.

[0013] In the aforementioned method of repairing leakage through drilling and grouting, preferably, when there is a stratum with high leakage in the dam body, and the drilling and grouting assembly is used to drill into the dam body to the stratum with high leakage, pulsed grouting pretreatment is performed on this stratum. The stratum with high leakage refers to a stratum where the amount of grout returned during drilling is reduced, and the reduction in grout returned is 1 / 3 or more of the original amount. Flushing fluid needs to be continuously injected into the borehole simultaneously. After the flushing fluid fills the borehole, it will return to the borehole opening. If the borehole encounters a channel with high leakage, the flushing fluid will leak into the pores, causing a reduction in the amount of grout returned to the borehole opening and a sharp drop in the liquid level. In this case, it is necessary to use the drilling and grouting assembly of the present invention to perform pulsed grouting pretreatment on this stratum.

[0014] In the above-mentioned method of repairing leakage by drilling and grouting, preferably, a high-pressure pulse grouting process is used during pretreatment, and the grout is a paste or mortar. The paste or mortar is a plastic clay-cement paste or plastic clay-cement mortar with a fluidity of 60-80mm that has resistance to dynamic water erosion. It is mainly composed of cement, crushed mud powder, water, sand and admixtures. Its initial setting time is not higher than 6 hours and its compressive strength is not higher than 5MPa.

[0015] In the above-mentioned method of repairing leakage by drilling and grouting, preferably, when drilling holes in the dam body using the drilling and grouting assembly, a stabilizing grout is simultaneously injected, which also serves as a flushing fluid and borehole wall protection; the stabilizing grout is a clay-cement grout with a fluidity of 200-240mm that has anti-filtration properties, and it is mainly composed of cement, crushed mud powder, water and additives, with an initial setting time of no more than 48 hours and a compressive strength of 0.3-0.5MPa.

[0016] In the above-mentioned method of drilling and grouting to repair leakage, preferably, the crushed mud powder is obtained by sieving local undisturbed soil through a soil crusher, with a particle size between 0.1-10mm, of which particles larger than 5mm account for no less than 20% by mass, and the mass of clay particles is no less than 25% by mass; the admixture is carboxymethyl cellulose or hydroxypropyl cellulose used to reduce filtration loss and resist water erosion.

[0017] In the above-mentioned method of repairing leakage by drilling and grouting, preferably, the first grouting pipe is a seamless steel pipe with an inner diameter of not less than 80 mm; the first drill bit is a large-diameter diamond drill bit configured according to the specifications of the first grouting pipe, and the diamond drill bit has a central hole for grouting and for the second grouting pipe and the second drill bit to pass through; the first grouting pipe and the first drill bit are connected by threads.

[0018] In the above-mentioned method of repairing leakage by drilling and grouting, preferably, the second grouting pipe is a seamless steel pipe with an inner diameter of no more than 59 mm; the second drill bit is a drill bit with an opening in the center (such as a three-flower opening drill bit) configured according to the specifications of the second grouting pipe, and the opening diameter is no less than 20 mm; the second grouting pipe and the second drill bit are connected by threads.

[0019] In the aforementioned method of repairing leakage by drilling and grouting simultaneously, preferably, when drilling and grouting in the bedrock section, the grouting material is pure cement grout or clay-cement grout, with section lengths of 1-2m and 5-10m respectively. The section length at the contact surface with the dam body is 1-2m, and after 2-3 sections, the section length is changed to 5-10m.

[0020] In the above-mentioned method of repairing leakage by drilling and grouting, preferably, when the first grouting pipe is used to perform pulsating grouting on the dam body from bottom to top, the grouting material is a plastic clay cement paste slurry, and the grouting section is 0.5-1m long.

[0021] In the above-mentioned method of repairing leakage by drilling and grouting, the preferred parameters for pulsed grouting are: a single pumping volume of grout greater than 15L, pumping 6-10 times per minute, and a grouting pressure of 1.5-4.0MPa.

[0022] In this invention, when using the pulse grouting method to treat earth-rock dams, the process parameters of the pulse grouting method need to be optimized. Unlike foundation treatment, when using pulse grouting technology to treat hydraulic structures, there are high requirements for the controllability of the grout, as well as the grouting pressure and volume, to avoid adverse effects on the original structure or stability of the structure. This invention can meet the process parameter requirements for treating earth-rock dams by controlling the section length, strictly controlling the grout injection volume and grouting pressure, and controlling the expansion properties of the pulse grouting material. In actual construction, horizontal and vertical displacement sensors also need to be installed to strictly monitor the deformation of the dam body.

[0023] This invention utilizes a 10mm thick seamless steel pipe as the grouting pipe. The grouting pipe has a threaded interface and can be connected to a drill bit, thus integrating the grouting pipe and drill rod. The grouting pipe can be made of 42CrMo alloy structural steel, with overall heat treatment and a tensile strength of 1080MPa. For dam body drilling and grouting, a large-diameter grouting pipe with an inner diameter of not less than 80mm is used, and the drill bit is a large-diameter diamond drill bit with an inner diameter of not less than 80mm, configured according to the grouting pipe specifications, and has a central opening. For dam foundation drilling and grouting, a small-diameter grouting pipe with an outer diameter of not more than 59mm is used, and the drill bit has a three-aperture opening, with an opening diameter of not less than 20mm. In this invention, the first and second drill bits can be existing commercially available drill bits, which are matched and connected to the grouting pipe. The method of drilling and grouting repair using the above-mentioned grouting pipe specifically includes the following steps:

[0024] (1) Use a first grouting pipe with an inner diameter of not less than 80 mm to replace the drill rod and drill the dam body from top to bottom. When encountering a large leakage stratum during drilling, pre-treat the stratum with high pressure pulse grouting. After treatment, continue drilling to 0.5-1.0 m below the bedrock contact surface.

[0025] (2) Without removing the first grouting pipe, lower the second grouting pipe with an outer diameter of no more than 59 mm into the hole to the bottom of the hole, and continue drilling and grouting the bedrock section until the designed hole depth is reached;

[0026] (3) After the bedrock section is treated, the second grouting pipe is pulled out from the hole, and the dam body is subjected to pulsating grouting treatment from bottom to top in the first grouting pipe.

[0027] More specifically, it includes the following steps:

[0028] (1) First, drill according to the designed hole position, using the first grouting pipe with an inner diameter of not less than 80 mm as the drill rod. Simultaneously inject stabilizing grout, which also serves as flushing fluid and borehole wall protection. When encountering strata with no return water and large leakage, prepare paste grout by adding crushed mud powder to change the grout consistency. Perform high-pressure pulsed grouting pretreatment on this stratum. The pretreatment range is strata where the return grout volume is small (less than 1 / 3). After treatment, continue drilling. Repeat this step when encountering strata with large leakage again, until the borehole reaches 0.5-1.0 m below the bedrock surface.

[0029] (2) Then, for the dam foundation, curtain grouting is used. The second grouting pipe is replaced, and the second grouting pipe is lowered into the hole of the first grouting pipe and then into the hole of the first grouting pipe to the bedrock contact surface. Subsequently, drilling and grouting of the bedrock section is carried out until the designed hole depth. The bedrock section can use pure cement grout or clay cement grout, with section lengths of 1-2m and 5-10m respectively. The section length at the contact surface with the dam body is 1-2m, and after 2-3 sections, the section length is changed to 5-10m.

[0030] (3) Finally, the dam body is treated by pulsating grouting from bottom to top. After the bedrock section is treated, the second grouting pipe is pulled out, connected to the first grouting pipe, and the upper dam body is grouted by high pressure from bottom to top. The grouting section is 0.5-1m long, and the grouting material is clay cement paste slurry.

[0031] When using pulsed grouting, the following parameters can be controlled: single pumping volume greater than 15L; pumping 6-10 times per minute; grouting pressure of 1.5-4.0MPa, which are determined comprehensively based on hole depth, water level difference, and hole sequence.

[0032] When grouting adjacent boreholes, the grouting interval should be at least 48 hours to ensure that the excess pore water pressure dissipates and to avoid affecting the grouting effect.

[0033] During construction, dam deformation monitoring should be strengthened, including horizontal and vertical displacement monitoring. If slight uplift occurs during grouting, measures should be taken to reduce the flow rate and pressure. After uplift, the grouting pressure should be controlled at around 0.3 MPa, and the flow rate should be controlled within 15 L / min. After continuous grouting for 10-15 minutes, normal grouting can be resumed once the uplift deformation at the orifice no longer changes.

[0034] In this invention, the grouting raw materials mainly consist of cement, crushed mud powder, admixtures, and water. The cement is ordinary Portland cement. The crushed mud powder is obtained by sieving local undisturbed soil through a soil crusher. Its particle size is between 0.1-10mm, of which particles with a diameter of 5mm or more account for no less than 20%, and the mass content of clay particles is no less than 25%. The admixtures are quick-setting agents, thickeners, and water-retaining agents that can adjust the initial and final setting times of the material and have the functions of reducing filtration loss and resisting water erosion.

[0035] Grouting materials are divided into stabilized grout and paste or mortar. Stabilized grout is a clay-cement slurry with a fluidity of 200-240 mm and a certain resistance to filtration loss. It consists of a small amount of cement, crushed mud powder, water and admixtures. It is used as a drilling flushing fluid and for self-setting and sealing of the grout. Its initial setting time is no more than 48 hours and its compressive strength is 0.3-0.5 MPa. Paste or mortar is a plastic clay-cement paste or plastic clay-cement mortar with a fluidity of 60-80 mm. It is prepared by adding crushed mud powder to stabilized grout and is used as a pulsating grouting material. When encountering formations with large leakage, a thickener is added to the paste to prepare a water-blocking paste that can resist the erosion of flowing water, or sand is added to prepare a water-blocking mortar.

[0036] Conventional pulsed grouting technology uses a paste-like grout composed of cement, clay (bentonite), admixtures, and water. This complex material composition is detrimental to on-site management. Furthermore, clay is often obtained by directly adding bentonite or by extracting slurry from a mud pit. However, because bentonite absorbs water and expands, its viscosity changes significantly over time. When preparing high-concentration paste-like grout, pipe blockage is highly likely as grouting time increases, making grout material control difficult and potentially causing structural damage after expansion. When preparing paste-like grout from a mud pit, gravity causes clay stratification, with lighter layers at the top and heavier layers at the bottom. The extracted slurry often has a low specific gravity, requiring the addition of cement powder or admixtures to prepare low-flowability paste-like grout. This results in high material costs, large cement consumption, and is neither energy-efficient nor environmentally friendly. This invention, however, uses crushed clay powder, solving the problem of excessive cement or admixture dosages in conventional paste-like grout preparation.

[0037] Due to the different properties of the dam body and dam foundation, the drilling tools and grouting processes for the dam body and dam foundation also differ. In existing technologies for grouting seepage prevention in earth-rock dams, the dam body is generally treated first, and the dam foundation is constructed only after all the grouting holes in the dam body are completed. In this case, dam foundation construction requires drilling from the dam crest, penetrating the dam body to the bedrock contact surface, and then drilling and grouting from below the contact surface to the designed stratum depth. The portion penetrating the dam body is only drilled without grouting, resulting in repeated drilling. When encountering strata with high leakage, treating the dam body can also affect the stability of the dam body and the quality of grouting. To address these problems, the present invention provides a method for repairing seepage in earth-rock dam bodies and foundations under high water levels through drilling and grouting. This method does not lower the reservoir water level, can reach a construction depth of over 60m, has wide geological adaptability, and is convenient and efficient. The main innovations are as follows: 1. It optimizes the separate drilling and grouting procedures, achieving drilling and grouting simultaneously. 1. The process of drilling to the bottom of the hole using casing and casing, removing the drill rod, and then lowering the grouting pipe for grouting has been optimized. Instead, the drill rod is replaced with a first grouting pipe, and drilling proceeds to the predetermined stratum. Grout is then injected through the first grouting pipe and the first drill bit, avoiding the steps of removing the drill rod and casing, eliminating the need to replace pipelines, and enabling grouting while drilling. 2. During drilling, grouting is performed while drilling in strata with high leakage rates to seal seepage channels, reducing seepage stability issues caused by drilling disturbance and high seepage gradients in the dam body under high water heads, and improving grouting quality. 3. For dam body seepage, a large-diameter first grouting pipe is used, and a small-diameter second grouting pipe is lowered in the same hole for dam foundation seepage treatment, solving the problem of repeated drilling of the dam body and foundation, further improving construction efficiency, and significantly saving drilling time. 4. The use of crushed mud powder solves the problem of excessive cement or admixture additions in conventional paste grout preparation.

[0038] Compared with the prior art, the advantages of the present invention are as follows:

[0039] 1. The method for repairing seepage in earth-rock dam bodies and foundations under high water levels by drilling and grouting in this invention achieves integrated drilling and grouting, optimizes the process of drilling and grouting separately for dam bodies and foundations, and adopts a first grouting pipe and a second grouting pipe that cooperate with each other to solve the problems of complex drilling and grouting processes and repeated drilling for dam bodies and foundations, realizes drilling and grouting simultaneously, further improves construction efficiency, construction quality and grouting effect, greatly saves drilling time and has high construction efficiency.

[0040] 2. The method for repairing seepage in earth-rock dam bodies and foundations under high water levels using drilling and grouting techniques of the present invention can efficiently repair earth-rock dams without emptying the reservoir. It is convenient to construct, has minimal impact on the reinforced reservoir, and after treatment, the dam foundation permeability q ≤ 5 Lu and the dam body permeability coefficient can be less than 1 × 10⁻⁶. -5 cm / s. Attached Figure Description

[0041] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0042] Figure 1 This is a schematic diagram of the method for repairing seepage in the earth-rock dam body and foundation under high water levels using drilling and grouting techniques according to the present invention (the first drill bit below the three first grouting pipes on the right is omitted in the diagram).

[0043] Legend:

[0044] 1. First grouting pipe; 2. Second grouting pipe; 3. Dam body; 4. Large leakage stratum; 5. Dam foundation; 6. First drill bit; 7. Second drill bit. Detailed Implementation

[0045] To facilitate understanding of the present invention, the present invention will be described more fully and in detail below with reference to the accompanying drawings and preferred embodiments, but the scope of protection of the present invention is not limited to the following specific embodiments.

[0046] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0047] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0048] Example 1:

[0049] like Figure 1 As shown, a method for repairing seepage in the body and foundation of an earth-rock dam under high water levels through drilling and grouting includes the following steps:

[0050] Optimization of drill rod, drill bit, and grouting pipe structure: Seamless steel pipes with a thickness of 10mm are used as grouting pipes. The grouting pipes are connected by corrugated threads and can be connected to drill bits, thus replacing drill rods and achieving integration of grouting pipes and drill rods. The grouting pipes are made of 42CrMo alloy structural steel, with overall quenching and tempering treatment, and a tensile strength of 1080MPa. For the dam body 3 drilling and grouting, the first grouting pipe 1 with an inner diameter of not less than 80mm is used, and the first drill bit 6 is a large-diameter diamond drill bit with an inner diameter of not less than 80mm configured according to the specifications of the first grouting pipe 1, with a center opening. For the dam foundation 5 drilling and grouting, the second grouting pipe 2 with an outer diameter of not more than 59mm is used, and the second drill bit 7 is a three-flower opening type with a drill bit opening diameter of not less than 20mm.

[0051] The dam body 3 undergoes pretreatment by drilling and grouting from top to bottom: Drilling is carried out according to the designed borehole locations, using a first grouting pipe 1 with an inner diameter of not less than 80mm as the drill rod. Stabilizing grout is injected simultaneously during drilling, serving as both flushing fluid and borehole wall protection. When encountering strata 4 with no return water and high leakage, a paste or mortar is prepared by adding crushed mud powder to change the consistency of the stabilizing grout. High-pressure pulsed grouting is then performed on this stratum for pretreatment. The pretreatment area is strata where the amount of grout returning from the borehole is reduced (less than 1 / 3). After treatment, drilling continues. This step is repeated when encountering strata 4 with high leakage again, until the borehole reaches at least 0.5m below the bedrock surface.

[0052] Curtain grouting treatment for dam foundation: Replace the second grouting pipe 2, and lower the second grouting pipe 2 into the hole of the first grouting pipe 1 until it reaches the bedrock contact surface. Then, drill and grout the bedrock section until the designed hole depth is reached. The bedrock section can use pure cement grout or clay cement grout, with section lengths of 2m and 5m respectively. The section length at the contact surface with the dam body 3 is 2m, and the section length is changed to 5m after sections 2-3.

[0053] Dam body 3 is treated by pulsating grouting from bottom to top: After the bedrock section is treated, the second grouting pipe 2 is pulled out, and the upper dam body 3 is grouted by high pressure from bottom to top using the first grouting pipe 1. The grouting section is 0.5-1m long, and the grouting material is clay-cement paste slurry.

[0054] Pulsating grouting parameters: single pumping volume greater than 15L; pumping 6-10 times per minute; grouting pressure 1.5-4.0MPa, which is determined comprehensively based on hole depth, water level difference, and hole sequence.

[0055] The aforementioned stabilized grout is a clay-cement grout with a fluidity of 200-240 mm, possessing resistance to dynamic water erosion. It is mainly composed of cement, crushed mud powder, water, and additives, and is used as a drilling flushing fluid and for self-setting and sealing of the grout. Its initial setting time is no more than 48 hours, and its compressive strength is 0.3-0.5 MPa. The paste or mortar is a plastic clay-cement paste or plastic clay-cement mortar with a fluidity of 60-80 mm, possessing resistance to dynamic water erosion. It is prepared by adding crushed mud powder to the stabilized grout. It is mainly composed of cement, crushed mud powder, water, sand, and additives. Its initial setting time is no more than 6 hours, and its compressive strength is no more than 5 MPa. The cement is ordinary Portland cement; the crushed mud powder is obtained by sieving local undisturbed soil using a soil crusher, with a particle size between 0.1-10 mm, of which particles larger than 5 mm account for no less than 20% by mass; the clay content is no less than 25% by mass.

[0056] To better understand the above solution, this embodiment provides the following specific engineering implementation case:

[0057] Chentianjiang Reservoir is a large (2) type water conservancy project mainly for irrigation, and also for power generation, flood control and aquaculture. The total reservoir capacity is 127.5 million m³. The reservoir dam is an arc-shaped rockfill core dam, and the dam body 3 adopts a clay core wall for seepage prevention. The dam was built in 1972. After more than 40 years of impoundment in 1978, leakage problems appeared. In 2018, it was determined that the permeability coefficient of the clay core wall of the dam body 3 and the permeability of the bedrock of the dam foundation 5 did not meet the specifications. It is necessary to carry out grouting and seepage prevention reinforcement treatment on the clay core wall and bedrock of the dam.

[0058] Reinforcement scheme: High-pressure pulsed grouting for seepage prevention is adopted for dam body 3, with 33,713m of grouting drilled. Static pressure grouting is adopted for dam foundation 5, with 12,330m of grouting drilled. Two rows of boreholes are installed in the middle dam section with a height ≥30m, with a row spacing of 0.7m and a borehole spacing of 1.0m, arranged in a quincunx pattern. A single row of grouting boreholes is installed in the dam section with a height <30m on both dam abutments, located in the upstream row. The first row of boreholes is located 1.2m upstream of the dam axis, and the second row is located 0.5m upstream of the dam axis. The downstream row is constructed first, followed by the upstream row.

[0059] Construction challenges: Due to the high water head, which can reach up to 60m, the loose soil structure of the dam body's three core walls, and the uneven permeability of the dam foundation, there are problems such as large grout absorption, easy grout leakage, and difficulty in control during grouting.

[0060] The method of drilling and grouting to repair seepage in the earth-rock dam body and dam foundation under high water level, as described in this embodiment, is used for the reinforcement and repair of the above-mentioned Chentianjiang Reservoir dam, including the following steps:

[0061] (1) A seamless steel pipe with a thickness of 10 mm and an inner diameter of 80 mm is used as the first grouting pipe 1, and a first drill bit 6 (large diameter diamond drill bit) with an inner diameter of 80 mm of the same size is connected by thread to form the drilling and grouting assembly of the dam body 3; a seamless steel pipe with an outer diameter of 59 mm is used as the second grouting pipe 2, and a second drill bit 7 (three-flower open drill bit) with an outer diameter of 59 mm of the same size is connected by thread to form the drilling and grouting assembly of the dam foundation 5.

[0062] (2) Drill holes downwards from the top of the dam, and simultaneously use a small-volume grouting pump to inject a stable grout (clay-cement grout) with a flowability of 200-240 mm into the hole until drilling to 1.0 m below the bedrock contact surface. When encountering a large leakage stratum 4 with a significant reduction in grout return and a reduction of more than 1 / 3 during drilling, increase the amount of broken mud powder to adjust the grout flowability to 60-80 mm to make clay-cement paste grout, and perform high-pressure pulse grouting on this stratum. When the grouting reaches the end standard in Table 1, change the grout consistency to 200-240 mm and continue drilling downwards. Repeat this step when encountering a large leakage stratum 4 with a reduced grout return.

[0063] (3) The drilling and grouting assembly of the dam foundation 5 is re-inserted into the borehole of the dam body 3 until the bottom of the hole, and the dam foundation 5 is drilled and grouted in sections from top to bottom. The grouting material is pure cement grout with a concentration that changes from thin to thick in stages. The grouting section length is 2m / section below the bedrock contact surface. After 2 sections, the section length is changed to 5m / section.

[0064] (4) After the drilling and grouting of dam foundation 5 is completed, the drilling and grouting components of dam foundation 5 are removed, and the grouting material is changed. Clay cement paste with a fluidity of 60-80mm is injected into the borehole of dam body 3. The drilling and grouting components are extracted from bottom to top and high-pressure pulse grouting is carried out. The grouting section is 0.5m long.

[0065] Table 1: Parameters of High-Pressure Pulsating Grouting

[0066]

[0067] Note: Pumping frequency is 6-8 times / min, and the pumping volume is 20L each time; grouting can be stopped when one of the following conditions is met: (1) The injection volume reaches the maximum value V max And the grouting pressure reaches the minimum value P min (2) The grouting pressure reaches its maximum value P. max And the injection amount reaches the minimum value V min hour.

[0068] The treatment effect of the dam body 3 of Chentianjiang Reservoir after the above grouting treatment is shown in Table 2 below:

[0069] Table 2: Permeability coefficients of pilot holes and inspection holes

[0070]

[0071] Before grouting, the average permeability coefficient of pilot hole J3 was 5.48 × 10⁻⁶. -4 cm / s, after grouting, the average permeability coefficient of inspection hole SJ3 was 8.22×10 cm / s. -6 The permeability was measured in cm / s. There were 13 test sections, all of which passed, resulting in a 100% pass rate. In pilot hole J51, the average permeability coefficient before construction was 6.69 × 10⁻⁶ cm / s. -4 cm / s, and after construction, the average permeability coefficient of each section of borehole SJ4 was 6.51×10 cm / s. -6 cm / s, 13 test sections, 13 qualified sections, pass rate 100%.

[0072] After the dam body 3 was constructed, the water injection test results of the inspection holes were all less than 1.0 × 10⁻⁶. -5 cm / s, meeting the design requirements.

[0073] After treatment, the permeability of dam foundation 5 is q≦5Lu, meeting the design requirements. The overall seepage prevention and reinforcement effect is good.

Claims

1. A method for repairing seepage in the body and foundation of an earth-rock dam under high water levels through drilling and grouting, characterized in that... Includes the following steps: (1) A drilling and grouting assembly is obtained by replacing the drill rod with the first grouting pipe and equipping it with the first drill bit; the drilling and grouting assembly is used to drill holes in the dam body until the overburden layer is drilled through to the bedrock of the dam foundation; stabilizing grout is injected at the same time when drilling holes in the dam body using the drilling and grouting assembly. (2) A second grouting pipe with a smaller diameter than the first grouting pipe is lowered into the first grouting pipe, so that the second grouting pipe reaches the bottom of the first grouting pipe. The second grouting pipe is equipped with a second drill bit. Then, drilling and grouting are carried out in the bedrock section. When drilling and grouting are carried out in the bedrock section, the grouting material is pure cement grout or clay cement grout. (3) After the bedrock section is treated, the second grouting pipe is taken out and the dam body is grouted from bottom to top using the first grouting pipe. When the dam body is grouted from bottom to top using the first grouting pipe, the grouting material is plastic clay cement paste slurry. There are strata with large leakage in the dam body. When drilling the dam body to the strata with large leakage using drilling and grouting components, the strata are pretreated by pulsed grouting. The strata with large leakage refers to the strata where the amount of grout returned during drilling is reduced, and the amount of grout returned is reduced by 1 / 3 or more of the original amount. The first grouting pipe is a seamless steel pipe with an inner diameter of not less than 80 mm; the first drill bit is a diamond drill bit configured according to the specifications of the first grouting pipe, and the diamond drill bit has a central hole; the first grouting pipe and the first drill bit are connected by threads. The second grouting pipe is a seamless steel pipe with an inner diameter of no more than 59 mm; the second drill bit is a drill bit with an opening in the center configured according to the specifications of the second grouting pipe, and the opening diameter is no less than 20 mm; the second grouting pipe and the second drill bit are connected by threads.

2. The leak repair method while drilling while pumping according to claim 1, characterized in that, The pretreatment process uses a high-pressure pulsed grouting process. The grout is a paste or mortar. The paste or mortar is a plastic clay-cement paste or plastic clay-cement mortar with a fluidity of 60-80mm that has resistance to water erosion. It is mainly composed of cement, crushed mud powder, water, sand and admixtures. Its initial setting time is not higher than 6 hours and its compressive strength is not higher than 5MPa.

3. The leak repair while drilling and while pumping method of claim 1, wherein, The stabilized slurry is a clay-cement slurry with a fluidity of 200-240 mm that has anti-filtration properties. It is mainly composed of cement, crushed mud powder, water and admixtures. Its initial setting time is no more than 48 hours and its compressive strength is 0.3-0.5 MPa.

4. A leak repair method while drilling while pumping according to claim 2 or 3, characterized in that, The crushed mud powder is obtained by sieving local undisturbed soil through a soil crusher. Its particle size is between 0.1-10mm, of which particles larger than 5mm account for no less than 20% by mass, and the mass of clay particles is no less than 25% by mass. The additive is carboxymethyl cellulose or hydroxypropyl cellulose used to reduce filtration loss and resist water erosion.

5. The leak repair method while drilling while pumping according to any one of claims 1 to 3, characterized in that, When drilling and grouting the bedrock section, the section lengths are 1-2m and 5-10m respectively. The section length at the contact surface with the dam body is 1-2m, and after 2-3 sections, the section length is changed to 5-10m.

6. The leak repair method while drilling while pumping according to any one of claims 1 to 3, characterized in that, When using the first grouting pipe to perform pulsating grouting on the dam body from bottom to top, the grouting section length is 0.5-1m.

7. The leak repair method while drilling while pumping according to claim 6, characterized in that, The parameters of the pulsating grouting are as follows: single pumping slurry volume is greater than 15 L, pumping 6-10 times per minute, and grouting pressure is 1.5-4.0 MPa.

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