Volcanic ash stratum diaphragm wall grooving construction method

Abstract

The invention relates to a volcanic ash stratum diaphragm wall grooving construction method, and relates to the technical field of diaphragm wall construction. The construction method comprises the steps that a construction site is selected, a groove is excavated according to the preset guide wall depth, and after the groove is excavated, concrete is poured on the top face to form a guide wall; the preparation method comprises the following steps: determining the slurry ratio through experiments, stirring 8-12 parts by weight of bentonite, 0-0.05 part by weight of carboxymethyl cellulose and 0-0.5 part by weight of sodium carbonate at a high speed for 6-8 minutes by using a slurry stirrer, and storing for more than 24 hours to fully expand the bentonite; unit groove sections are divided, slurry is injected into the guide wall, and the underground diaphragm wall is excavated in a segmented mode to form grooves; and the reinforcement cage is assembled and formed at a time, and the reinforcement cage is hoisted and put into the groove. The construction stability of volcanic ash stratum diaphragm wall grooving can be guaranteed, and potential risks and influences are reduced.

Description

Technical Field

[0001] This application relates to the technical field of diaphragm wall construction, and particularly to a construction method for excavating a diaphragm wall in a volcanic ash stratum. Background Art

[0002] Volcanic ash is usually fine particulate matter generated by volcanic eruptions. It has high porosity and instability, which may pose a threat to the stability of infrastructure. Under such geological conditions, construction workers need to face the risk of soil liquefaction, which may cause the soil to lose stability and pose a potential threat to the support structure and railway lines. Diaphragm walls are usually used to reinforce the soil and prevent landslides. However, under the complex conditions of volcanic ash strata, the construction difficulty increases significantly. Summary of the Invention

[0003] Based on this, in view of the problem of increased construction difficulty of diaphragm walls in volcanic ash strata, it is necessary to provide a construction method for excavating a diaphragm wall in a volcanic ash stratum.

[0004] To achieve the above object, the technical solution adopted in this application is as follows: An embodiment of this application provides a construction method for excavating a diaphragm wall in a volcanic ash stratum, including: Select a construction site, excavate a trench according to a preset guide wall depth. After the excavation of the trench is completed, pour concrete on the top surface to form a guide wall; Determine the mud ratio through experiments. Use 8 - 12 parts by weight of bentonite, 0 - 0.05 parts by weight of carboxymethyl cellulose, and 0 - 0.5 parts by weight of soda ash. Stir at high speed by a mud mixer for 6 - 8 minutes, and store for more than 24 hours to fully expand the bentonite; Divide the unit trench section, inject mud into the guide wall, and excavate the trench of the diaphragm wall in sections; The steel reinforcement cage is assembled into a whole at one time, and the steel reinforcement cage is hoisted and lowered into the trench.

[0005] In one of the embodiments of the first aspect, the steel reinforcement cage is successively provided with points A, B, C, D, E, and F along the longitudinal direction. Points A and F are the two end points of the steel reinforcement cage in the longitudinal direction. Points B and C are two adjacent main lifting points, and points D and E are two adjacent auxiliary lifting points. The distances between points A and B and between points F and E are both L1, and the distances between any two adjacent points among points B, C, D, and E are all L2; The bending moment of the steel reinforcement cage is satisfied as follows: +M = -M; +M=(1 / 2)qL1²; -M=(1 / 8)qL2²-(1 / 2)qL1²; It is obtained that: L2 = 2 L1; Among them, q is the uniformly distributed load and M is the bending moment.

[0006] In one embodiment of the first aspect, the side formwork of the guide wall uses composite steel formwork, and the horizontal and vertical backing ribs are both made of 80mm×80mm wooden squares, and 2 transverse supports are added every 2.0m.

[0007] In one embodiment of the first aspect, when the construction soil layer is cohesive soil, the proportion of the slurry is: 8-10 parts by weight of bentonite, 0-0.02 parts by weight of carboxymethyl cellulose, and 0-0.5 parts by weight of soda ash.

[0008] In one embodiment of the first aspect, when the construction soil layer is sandy soil, the proportion of the slurry is: 10-12 parts by weight of bentonite, 0-0.05 parts by weight of carboxymethyl cellulose, and 0-0.5 parts by weight of soda ash.

[0009] In one embodiment of the first aspect, during the construction process of the groove hole of the diaphragm wall, slurry is replenished at any time while excavating, and the excavated slag is discharged. After the groove hole is formed by impact, the groove is cleaned and the slurry is replaced after passing the inspection. The steel reinforcement cage is hoisted within 3-4 hours after the groove cleaning and slurry replacement are qualified.

[0010] In one embodiment of the first aspect, the drilling speed of the groove hole is less than the slag discharge speed and the slurry supply speed.

[0011] In one embodiment of the first aspect, during the construction process, ensure that the slurry liquid level is more than 0.5m higher than the groundwater level and at the same time not lower than 0.3m above the top surface of the guide wall.

[0012] In one embodiment of the first aspect, when constructing the groove at the inclined rock surface part, the deviation is corrected by the method of throwing high-strength riprap into the groove hole and then re-impacting. The height of the thrown riprap is 500mm above the inclined surface; alloy steel is welded to the hammer head part and the rock surface is impacted with a low stroke.

[0013] In one embodiment of the first aspect, during the construction, the indicators of the slurry are regularly inspected, and the indicator parameters of the slurry meet: specific gravity 1.05g / cm 3 ~1.25g / cm 3 ; viscosity 20S~35S; water loss <30ml / 30min; mud cake thickness <3mm; PH value 7~11; sand content <4%.

[0014] In one embodiment of the first aspect, the adjacent unit groove sections are joint-treated with I-shaped steel plates for water stop and galvanized thin iron sheets for preventing flow-around; after the steel reinforcement cage of the previous groove section is lowered, the voids are filled with mud bags on the side of the next groove section where the I-shaped steel joint has not been excavated.

[0015] Compared with the related art, the beneficial effects of the present application are as follows: The present application provides a construction method for forming a trench of a diaphragm wall in volcanic ash strata, which can provide a slurry for protecting the wall that conforms to the geological characteristics of volcanic ash, ensure the stability of trench construction, and reduce potential risks and impacts. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0017] Figure 1 It is a schematic flow chart of the construction method for forming a trench of a diaphragm wall in volcanic ash strata in some embodiments of the present application; Figure 2 It is a schematic structural diagram of a guide wall in some embodiments of the present application; Figure 3 It is a schematic flow chart of the preparation method of the slurry in some embodiments of the present application; Figure 4 It is a schematic lifting structural diagram of a steel reinforcement cage in some embodiments of the present application; Figure 5 It is a schematic diagram of the lifting points of the steel reinforcement cage in some embodiments of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0018] In order to make the above objects, features, and advantages of the present application more obvious and understandable, the following will give a detailed description of the specific embodiments of the present application with reference to the drawings. Many specific details are set forth in the following description in order to fully understand the present application. However, the present application can be implemented in many other ways different from those described herein. Those skilled in the art can make similar improvements without departing from the connotation of the present application. Therefore, the present application is not limited by the specific embodiments disclosed below.

[0019] In the description of the present application, it should be understood that if terms such as "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. appear, the orientation or positional relationship indicated by these terms is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the present application.

[0020] In addition, if the term "and / or" appears, "and / or" is merely a correlative relationship describing the associated objects, indicating that three relationships may exist. For example, A and / or B may represent: A exists alone, A and B exist simultaneously, and B exists alone. Additionally, in this text, the character " / " generally indicates that the associated objects before and after are in an "or" relationship. If the terms "first" and "second" appear, these terms are only for descriptive purposes and should not be construed as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include at least one such feature. In the description of this application, if the term "plurality" appears, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise specifically defined.

[0021] In this application, unless otherwise clearly specified and limited, if terms such as "installed", "connected", "joined", "fixed", etc. appear, these terms should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or integrated; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium, and it may be the communication inside two elements or the interaction relationship between two elements, unless otherwise clearly limited. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0022] In this application, unless otherwise clearly specified and limited, if there are descriptions such as a first feature being "on" or "under" a second feature, etc., the meaning may be that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, the first feature being "above", "over", and "on top of" the second feature may mean that the first feature is directly above or obliquely above the second feature, or merely indicates that the first feature has a higher horizontal height than the second feature. The first feature being "under", "beneath", and "underneath" the second feature may be that the first feature is directly below or obliquely below the second feature, or merely indicates that the first feature has a lower horizontal height than the second feature.

[0023] It should be noted that if an element is referred to as being "fixed to" or "disposed on" another element, it may be directly on the other element or there may also be an intermediate element. If an element is considered to be "connected" to another element, it may be directly connected to the other element or there may be an intermediate element at the same time. If so, the terms "vertical", "horizontal", "up", "down", "left", "right", and similar expressions used in this application are only for illustrative purposes and do not represent the only implementation.

[0024] The volcanic ash stratum is the remains of volcanic activities, providing geological history information and having an impact on resources and the environment. At some construction sites of Class VI comprehensive surrounding rock formed by volcanic ash materials, the volcanic ash materials are mainly clay minerals such as kaolinite, quartzite, and illite. The content of clay minerals in the stratum accounts for 76%, and it has engineering geological characteristics such as low natural density, ultra-high water content, super-large void ratio, high liquid-plastic limit, high compressibility, low permeability, high sensitivity, and difficulty in losing water. The comprehensive physical and mechanical indexes and drilling cores show that this semi-cemented silty clay mineral has a certain structural strength and is a structural clay with strong bonding force between soil particles. Therefore, when constructing diaphragm walls in volcanic ash strata, there are great challenges in the selection of equipment, the preparation of slurry for shaft protection, the placement of steel reinforcement cages, and the water-stop technology, etc.

[0025] Refer to Figure 1 As shown, in view of the above problems, the embodiments of the present application provide a method for constructing a diaphragm wall trench in volcanic ash strata to ensure safe and efficient construction.

[0026] The method for constructing a diaphragm wall trench in volcanic ash strata includes: S10, select the construction site, excavate the trench according to the preset depth of the guide wall. After the trench excavation is completed, pour concrete on the top surface to form the guide wall.

[0027] Specifically, when excavating the trench, use a 0.4m 3 backhoe excavator for excavation and carry out manual slope repair. When excavating to 200mm above the design elevation, use manual bottom cleaning and repair the trench wall.

[0028] Continue to refer to Figure 2 As shown, in a specific embodiment, the designed depth of the guide wall is 2200mm. After the trench excavation is completed, tie the guide wall steel bars on the trench wall. The width of the guide wall steel bars is 1.2m, and the lap joint of the longitudinal steel bars adopts a binding form with a binding length of 500mm. And place steel bar protection blocks under the longitudinal steel bars at the bottom of the trench to ensure the thickness of the protective layer. The side formwork adopts combined steel formwork, and then pour a 100mm, C15 concrete cushion on the top surface. The thickness of the top surface of the guide wall is about 200mm to prevent slurry from leaking out or rainwater from pouring back into the guide wall during construction.

[0029] Furthermore, the transverse and longitudinal back ribs of the guide wall are both selected as 80×80mm wooden squares, and 2 transverse supports are added every 2.0m to ensure the support strength of the guide wall during construction.

[0030] S20, determine the slurry ratio through experiments, stir at high speed by a slurry mixer for 6 min - 8 min, and store for more than 24 h to fully expand the bentonite.

[0031] Specifically, the slurry should be prepared with high-quality bentonite or high-quality clay. Before mixing, the slurry mix ratio should be designed based on the geological conditions of the volcanic ash formation, the trench excavation method, and the purpose, etc. The slurry is stirred at high speed by a slurry mixer for 6 min to 8 min. The newly prepared slurry should be stored for more than 24 h to fully expand the bentonite and can be used only after passing the test.

[0032] Exemplarily, the mix ratio of the slurry is shown in Table 1 below:

[0033] In a specific embodiment, when the construction soil layer is cohesive soil, the mix ratio of the slurry can be: 8 - 10 parts by weight of bentonite, 0 - 0.02 parts by weight of carboxymethyl cellulose, and 0 - 0.5 parts by weight of soda ash.

[0034] In another specific embodiment, when the construction soil layer is sandy soil, the mix ratio of the slurry is: 10 - 12 parts by weight of bentonite, 0 - 0.05 parts by weight of carboxymethyl cellulose, and 0 - 0.5 parts by weight of soda ash.

[0035] Refer to Figure 3 As shown, the preparation method of the slurry is as follows: After conducting raw material tests, weigh and feed the materials according to the mix ratio. Stir the bentonite (clay) with water for 5 minutes, and simultaneously stir the carboxymethyl cellulose and soda ash with water for 5 minutes, and then perform mixing and stirring for 4 minutes to obtain the slurry suitable for the volcanic ash formation. After measuring the slurry performance indicators, let it swell for 24 hours for standby to fully expand the bentonite. During the trench excavation process of the diaphragm wall, the slurry can play the roles of protecting the wall, carrying the cuttings, cooling the drill tool, and wetting the cut soil. A slurry with good performance can ensure the stability of the trench wall during trench excavation, prevent collapse, and at the same time play an extremely important role in ensuring the pouring quality of the concrete during concrete pouring.

[0036] Specifically, the index parameters of the slurry meet the following: specific gravity 1.05 g / cm3 to 1.25 g / cm3; viscosity 20 S to 35 S; water loss < 30 ml / 30 min; mud cake thickness < 3 mm; pH value 7 to 11; sand content < 4%. Through the above parameter design, the slurry fully adheres to the trench wall during the trench excavation process, ensuring the stability of the trench wall and enabling the trench excavation process of the volcanic ash formation to proceed stably.

[0037] S30. Divide the unit trench section, inject the slurry into the guide wall, and excavate the trench of the diaphragm wall in segments.

[0038] Specifically, the trenching of the diaphragm wall is the key to controlling the construction period. The main contents include the division of unit trench segments, the selection of trenching machinery, the control of trenching technology, and the measures to prevent the collapse of the trench wall, etc. First, the trench segments are divided, and the accurate positions of the segments are marked on the guide wall with red paint. At the same time, the segments are numbered according to the design. The diaphragm wall is constructed by a hydraulic trenching machine. When the trench hole reaches the final hole, hole cleaning and slurry replacement are carried out after passing the inspection.

[0039] In a specific embodiment, the trenching of the diaphragm wall can be constructed by the "grabbing and percussion method", that is, first grab the trench, and then impact to form the trench. The depth of the grab bucket trenching is determined by the soil strength. Usually, after the construction reaches the moderately weathered stratum, due to the high rock strength, the grab bucket can no longer operate, and the lower part of the rock entry is changed to be constructed by an impact drill. The impact hammer is used for skip-hole construction. First, use the cross-shaped hammer to punch to the design elevation, and then use the square hammer to repair the hole.

[0040] In another specific embodiment, the trenching of the diaphragm wall can be constructed by the "percussion and grabbing method", that is, first punch the hole, then grab the trench, and finally impact the hard rock to form the trench. First, use a pile driver to construct 3 leading holes at the left, middle, and right positions in each trench segment, and punch each hole to the design elevation. The leading holes can ensure the vertical accuracy of the trench hole and improve the excavation efficiency of the grab bucket trenching machine. When the punching is completed, the grab bucket conducts soil-grabbing operations along the leading holes. The punching provides a free face for the grab bucket to grab soil and improves the soil-grabbing ability of the grab bucket. At the same time, after the main guiding holes are formed, the soil strength is reduced under the soaking of the mud in the holes, which is beneficial to increasing the excavable depth of the grab bucket, thereby accelerating the construction progress. When encountering hard bedrock, it is still necessary to use the punching and flat chisel drilling construction.

[0041] During the trenching construction process, trenching construction may be faced at the inclined rock surface part, and there will be a large deviation in the punching verticality at the inclined rock surface part. For this reason, the method of throwing high-strength riprap into the hole and then re-impacting can be used for deviation correction, and the height of the thrown riprap is 500 mm above the inclined surface. At the same time, alloy steel is welded to the hammer head part to increase the hardness of the hammer head, and a low stroke is used to impact the rock surface.

[0042] When a hammer jamming occurs during the trenching process. During the punching operation in the trench segment with a deep rock entry, a small stroke must be achieved. When the hammer body swings, the operation should be stopped in time, and then impact again after the hammer head is stable. In addition, the round hammer head should be frequently inspected and welded to ensure the diameter size, and the verticality of the closely arranged punching should be strictly controlled. The thickness of the square hammer is 20 mm smaller than the diameter of the round hammer to ensure a certain margin when the square hammer repairs the trench. When the geological conditions are uneven and the punching is inclined due to the inclined rock surface, a punching hammer with a larger diameter can be used for construction. After the hammer head is jammed, it can be impacted by the hammer head of another drill rig, and then gradually lifted after loosening. If it still cannot be lifted out, a jack can be used to pull it out. If necessary, a diver is sent to dive to the bottom of the trench to tie the steel wire rope to the hammer body. The hammer jamming should be dealt with in time. The longer the time, the thicker the sediment, and the greater the difficulty of treatment.

[0043] It should be noted that during the trench forming process, observation should be strengthened to ensure that the trench position, depth, width, and verticality meet the design requirements. The drilling speed of the hydraulic trench forming machine should be less than the slag discharge and slurry supply speeds to avoid drill string sticking or axis deviation caused by excessive speed. Meanwhile, during the trench excavation process, the retaining slurry should be kept at a height not lower than the specified level, and the slurry should be replenished at any time. At any time, the slurry level in the trench hole should be ensured to be more than 0.5 m above the groundwater level and not less than 0.3 m below the top surface of the guide wall to prevent insufficient slurry supply and ensure the performance of the slurry in the trench and stabilize the trench wall. When forming a trench by impact, the pile position should be accurately measured and marked, and cross-shaped guide piles should be set up to detect the center position of the pile at any time to ensure the accuracy of the pile position.

[0044] After the trench section is excavated to the design elevation, move the trench forming machine and conduct trench section inspection. For example, when using ultrasonic to measure the cross-section, two points should be inspected for each trench section. When inspecting the already poured section, the verticality of the joint surface should be inspected to prevent concrete collapse caused by improper operation in the early stage, resulting in quality hazards and difficulties in lowering the steel reinforcement cage in the later stage. For the cleaning of the trench section joint, a brush wall device should be used to clean the sediment or mud skin on the joint surface. The number of times of brushing up and down should be no less than 20 times until there is no mud on the brush surface of the brush wall device to ensure the tight bonding between the new and old concrete on the joint surface. Then, conduct bottom cleaning of the trench hole. It is recommended to use a pump suction reverse circulation or air-lift special tool for bottom cleaning.

[0045] After a unit trench section is formed, use I-beam steel plate for water stop and galvanized thin iron sheet for preventing slurry bypass to treat the joint of this trench section. After the steel reinforcement cage of the previous trench section is lowered, use mud bags to fill the voids on the side of the next trench section where the I-beam joint has not been excavated.

[0046] S40, the steel reinforcement cage is assembled into a whole at one time, and the steel reinforcement cage is hoisted and lowered into the trench.

[0047] Continue to refer to Figure 4As shown, specifically, the diaphragm wall reinforcement cage is assembled into a whole at one time. The longitudinal truss bars and horizontal stiffening bars are strictly processed and manufactured according to the design. The main bars and stirrups are fixed by spot welding according to the specification requirements to improve the overall stiffness of the reinforcement cage. Positioning steel plates with a vertical spacing of 3.5 m are added on the upper and lower surfaces, and U-shaped fixing lifting rings are added at the upper end of the reinforcement cage. The position for the conduit should be reserved longitudinally in the reinforcement cage and run through up and down. The bottom end of the reinforcement cage should be treated with a reduced thickness within a range of 0.5 m. The embedded support steel plates are accurately measured on the fabricated reinforcement cage. After the reinforcement cage is fabricated, the installation elevation line is determined according to the measured elevation of the top surface of the guide wall for the groove section where this reinforcement cage is used, and is marked with red paint on the lifting rings at the top of the reinforcement cage. Positioning pads should be provided on the reinforcement cage, with a depth direction spacing of 3.5 m and 3 pads in each layer. The main bars of the reinforcement cage are connected by mechanical connections and are reinforced with a torque wrench, and the torque should meet the design and specification requirements. When the bars other than the main bars are connected by welding or binding, the number of joints and the lap length should meet the design requirements. After the reinforcement cage passes the acceptance, it is lowered into the groove as a whole at one time. The special-shaped groove section reinforcement cage at the corner is also processed and formed at one time and hoisted and lowered into the groove for positioning and installation.

[0048] Continue to refer to Figure 5 As shown, during the hoisting process, the main hoisting point and the auxiliary hoisting point of the reinforcement cage need to be obtained first.

[0049] The reinforcement cage is successively provided with points A, B, C, D, E, and F longitudinally. Points A and F are the two end points of the reinforcement cage longitudinally. Points B and C are two adjacent main hoisting points, and points D and E are two adjacent auxiliary hoisting points. The distances between point A and point B and between point F and point E are both L1, and the distances between any two adjacent points among points B, C, D, and E are all L2; The bending moment of the reinforcement cage under stress satisfies: +M = -M; +M=(1 / 2)qL1²; -M=(1 / 8)qL2²-(1 / 2)qL1²; Combining the above formulas gives: L2 = 2 L1; where q is the uniformly distributed load and M is the bending moment.

[0050] In this way, according to the calculation of the hoisting point formula, the hoisting points of the reinforcement cage can be obtained according to the length of the reinforcement cage, and the stable hoisting of the reinforcement cage can be realized.

[0051] Lifting process of the steel reinforcement cage: Use 2 crawler cranes to lift it into the groove integrally at one time. The double-lifting multi-point lifting method is adopted for lifting the steel reinforcement cage. The reinforcement bars for strengthening the lifting points and the lifting ropes should be carefully calculated and strictly inspected and accepted. When lifting, the two cranes lift simultaneously in parallel, and then the main crane lifts while the auxiliary crane releases until the steel reinforcement cage is lifted vertically. During the lifting and movement of the steel reinforcement cage, slow and steady operation should be carried out. At the same time, a pulling rope should be tied to the lower end of the steel reinforcement cage for manual control. It is strictly prohibited to cause the vibration of the steel reinforcement cage, which may lead to the collapse of the groove wall and irreversible deformation of the steel reinforcement cage itself. After the steel reinforcement cage is aligned at the required position at the groove opening according to the design requirements, it is slowly lowered into the groove. It is strictly prohibited for the crane to release in neutral. When it cannot be lowered due to obstacles, it should be lifted again. After finding out the reasons and taking measures, it is lifted into the groove again. After the steel reinforcement cage is lowered in place, it is placed on the guide wall with a special steel shoulder pole, and the position of the steel bar coupler and the embedded parts is ensured to be accurate by controlling the elevation of the cage top.

[0052] The actual maximum lifting weight of the main crane should be the weight of a single panel of the steel reinforcement cage, and the maximum weight borne by the auxiliary crane should not be greater than 60% of the total weight of the steel reinforcement cage. Taking the heaviest single panel of the steel reinforcement cage in actual construction, about 40.4t, as an example, the maximum force on the auxiliary crane is about 40.4×60% = 24.24t.

[0053] It should be noted that the steel reinforcement cage should be inspected and qualified and approved by the supervisor before being lifted into the groove. The fabrication and placement of the steel reinforcement cage into the groove should meet the design requirements. At the same time, to ensure that the groove wall does not collapse, the steel reinforcement cage should be lifted and placed within 3h - 4h after the trench cleaning and slurry replacement are qualified. During transportation and placement into the groove, irreversible deformation should not occur. If there is deformation, it should not be forced into the groove.

[0054] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as within the scope described in this specification.

[0055] The above-described embodiments only represent several implementation manners of the present application. Their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the patent application. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present application, several modifications and improvements can still be made, and these all belong to the protection scope of the present application. Therefore, the protection scope of the patent of the present application should be subject to the appended claims.

Claims

1. A construction method for forming a trench of a diaphragm wall in a volcanic ash stratum, characterized in that, Including: Select a construction site and excavate a trench according to the preset depth of the guide wall. After the excavation of the trench is completed, pour concrete on the top surface to form the guide wall; Determine the mud ratio through experiments, using 8-12 parts by weight of bentonite, 0-0.05 parts by weight of carboxymethyl cellulose, and 0-0.5 parts by weight of soda ash. Stir at high speed for 6-8 minutes by a mud mixer and store for more than 24 hours to fully expand the bentonite; Divide the unit trench section, inject mud into the guide wall, and excavate the trench of the diaphragm wall in sections; The steel reinforcement cage is assembled into a whole at one time, and the steel reinforcement cage is hoisted and lowered into the trench.

2. The construction method of the trench forming of the diaphragm wall in the volcanic ash stratum according to claim 1, characterized in that, The steel reinforcement cage is successively provided with points A, B, C, D, E, and F along the longitudinal direction. Points A and F are the two end points of the steel reinforcement cage in the longitudinal direction. Points B and C are two adjacent main lifting points, and points D and E are two adjacent auxiliary lifting points. The distances between point A and point B and between point F and point E are both L1, and the distances between any two adjacent points among points B, C, D, and E are all L2; The bending moment of the steel reinforcement cage satisfies: +M=-M; +M=(1 / 2)qL1²; -M=(1 / 8)qL2²-(1 / 2)qL1²; Obtained: L2 = 2 L1; Wherein, q is the uniformly distributed load and M is the bending moment.

3. The construction method of the trench for the diaphragm wall in the volcanic ash stratum according to claim 1, characterized in that, The side formwork of the guide wall uses combined steel formwork, and the transverse and longitudinal backing strips are both 80mm×80mm wooden squares, and 2 transverse supports are added every 2.0m.

4. The construction method of forming a trench for a diaphragm wall in a volcanic ash stratum according to claim 1, characterized in that, When the construction soil layer is cohesive soil, the ratio of the mud is: 8-10 parts by weight of bentonite, 0-0.02 parts by weight of carboxymethyl cellulose, and 0-0.5 parts by weight of soda ash; Or, when the construction soil layer is sandy soil, the ratio of the mud is: 10-12 parts by weight of bentonite, 0-0.05 parts by weight of carboxymethyl cellulose, and 0-0.5 parts by weight of soda ash.

5. The construction method of the trench forming of the diaphragm wall in the volcanic ash stratum according to claim 1, characterized in that, During the construction process of the trench of the diaphragm wall, supplement mud at any time while excavating, and discharge the excavated slag. After the trench is formed by impact, after passing the inspection, carry out trench cleaning and slurry replacement. The steel reinforcement cage is hoisted and completed within 3-4 hours after the trench cleaning and slurry replacement are qualified.

6. The construction method of the diaphragm wall trench excavation in the volcanic ash stratum according to claim 5, characterized in that, The drilling speed of the trench is less than the slag discharge speed and the mud supply speed.

7. The construction method of diaphragm wall trench excavation in volcanic ash stratum according to claim 5, characterized in that, During the construction process, ensure that the mud level is more than 0.5m higher than the groundwater level and not less than 0.3m above the top surface of the guide wall.

8. The construction method of the trench excavation for the diaphragm wall in the volcanic ash stratum according to claim 5, characterized in that, When constructing the trench at the inclined rock surface part, correct the deviation by the method of throwing high-strength riprap into the trench and then re-impacting. The height of the thrown riprap is 500mm above the inclined surface; weld alloy steel on the hammer head part and use a low stroke to impact the rock surface.

9. The construction method of the diaphragm wall trench in the volcanic ash stratum according to claim 1, characterized in that, During the construction, regularly check the indicators of the slurry. The indicator parameters of the slurry should meet the following requirements: specific gravity 1.05 g / cm 3 ~1.25 g / cm 3 ; viscosity 20 S~35 S; water loss < 30 ml / 30 min; mud cake thickness < 3 mm; pH value 7~11; sand content < 4%.

10. The construction method of the trench forming of the diaphragm wall in the volcanic ash stratum according to claim 1, characterized in that, Adjacent unit trench sections are treated with I-beam steel plates for water stop and galvanized thin iron sheets for preventing flow-around; after the steel reinforcement cage of the previous trench section is lowered, fill the gap with mud bags on the side of the next trench section where the I-beam joint has not been excavated.

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