Slope treatment, commonly used anti-slide pile construction technology, super comprehensive!

1 Overview

A pile is a cylindrical member that goes deep into a soil or rock layer. The anti-slide pile in the slope treatment project is to pass the slope thrust borne by the upper part of the pile to the lateral soil or rock mass at the lower part of the pile, and rely on the lateral resistance of the lower part of the pile to bear the downward thrust of the slope, so that the slope remains balanced or stable, as shown in Figure 1.

Figure 1

The anti-slide pile is similar to the general pile foundation, but mainly bears the horizontal load. Anti-slide pile is also one of the common treatment schemes in slope treatment engineering. From the early wooden pile to the modern steel pile and the reinforced concrete pile commonly used in slope engineering, the section types are circular and rectangular. The construction methods include driving, mechanical hole forming and manual hole forming. The structural types include single pile, row pile, group pile, anchor pile and prestressed anchor cable pile.
Types, characteristics and applicable conditions of anti-slide piles

(1) Type of anti-slide pile

According to the material classification of anti-slide piles, there are wooden piles, steel piles, reinforced concrete piles and composite piles.
Anti-slide piles are classified according to pile forming methods, including driven piles, static pressure piles and in-situ cast-in-situ piles. In-situ cast-in-situ piles are divided into two categories: immersed pipe cast-in-situ piles and bored cast-in-situ piles. In the commonly used bored piles, there are mechanical drilling and manual digging piles.
Anti-slide piles are classified according to structural types, including single pile, row pile, group pile and anchor pile. The common types of row pile include chair pile wall, portal rigid frame pile wall and row anti-slide pile wall (see Figure 2). The common types of anchor pile include anchor rod and anchor cable. The anchor rod has single anchor and multi-anchor. The anchor cable anti-slide pile uses single anchor, as shown in Figure 3.

 

 

Anti-slide piles are classified according to the form of pile body section, including round piles, square piles and rectangular piles, "I" shaped piles, etc.
(2) Characteristics and applicable conditions

The impact of construction vibration on slope stability shall be fully considered when the anti-slide pile is driven in. Generally, the full-buried anti-slide pile or fill slope can be used, and the underlying stratum shall be drensible. Anti-slide pile construction is commonly used in situ cast-in-place pile, mechanical drilling speed, pile diameter can be large or small, suitable for a variety of geological conditions, but the terrain is steep slope engineering, mechanical access and erection difficulties, in addition, drilling water on the stability of the slope also have an impact. The characteristics of artificial hole is convenient, simple, economic, but the speed is slow, high labor intensity, in case of bad formation (such as sand) is very difficult to deal with, in addition, the pile diameter is small manual operation difficulties, pile diameter should generally be more than 1000mm suitable for artificial hole.
Single pile is the basic type of anti-slide pile, and it is also a common structural type, which is characterized by simple, clear force and action. When the thrust of the slope is large, the single pile is not enough to bear the thrust or the single pile is not economical, the row pile can be used. The characteristics of the bent pile are large moment of inertia, strong bending resistance, small pile wall resistance, small pile body stress, and obvious advantages in weak strata. Anchors with anchor piles can be reinforced anchor rods or prestressed anchor cables. Anchors (cables) and piles work together to change the cantilever force of the pile and the mechanism of the pile completely relying on the lateral foundation reaction to resist landslide thrust, thus greatly improving the stress state of the pile body and the displacement of the pile top. It is a more reasonable and economical anti-sliding structure. However, the anchoring end of the anchor rod or cable needs to have a better formation or rock layer, and for the anchor cable, it is more necessary to have a better rock layer to provide a reliable anchoring force.
Anti-slide pile group generally refers to the combination of more than 2 rows in the horizontal and more than 2 columns in the vertical anti-slide structure, similar to the pier or platform structure, it can bear greater landslide thrust, can be used for special landslide treatment engineering or special purpose slope engineering.
2 Construction

2.1 General Procedures

The construction of anti-slide pile is mostly mechanical or artificial hole, and concrete is poured on site.
Cast-in-place pile is an underground concealed project with high quality requirements, many construction procedures, and must be completed continuously in a short period of time. Therefore, the construction should be carried out according to the procedure. Prepare technical data, prepare construction organization design and make construction preparation. The construction management system of each process shall be established according to the design requirements, relevant specifications, regulations and construction organization design. Construction, supervision, design and management of all parties of the Owner are in place, monitoring is in place, and technical services and technical tracking are in place. Ensure that the construction is carried out in an orderly, fast and high-quality manner.
The general procedure for the construction of anti-slide piles is shown in Figure 2.1.

 

Selection of 2.2 pile setting process

The pile-setting process is also called the hole-forming method or the hole-forming process. There are many types of cast-in-place pile construction, and the main type of non-compaction pile is commonly used in anti-slide pile construction. Correct and appropriate selection of pile technology, in order to ensure the construction quality and construction period. The applicable scope and characteristics of various pile-setting processes are shown in the table below.

 

2.3 construction technology

1, according to the design drawing to release the pile position, clear out the platform position, excavation surface inside high outside low, for drainage.

2. Manual pile excavation and wall protection construction

① Measurement and positioning: Measure and place the axis according to the site coordinates provided by the design, determine the 4 side piles of the pile body according to the axis, and then do a good job of protecting the side piles. The allowable deviation of the pile position is 10mm. The excavation can only be carried out after the supervisor's review and acceptance and relevant procedures have been completed.
② Locking operation: first set up the formwork according to the size of the orifice to ensure that the thickness of the lock concrete is not less than 40cm, and the lock concrete is 45cm higher than the original ground.
③ Pile excavation: use short-handled shovel and hoe to excavate the clay layer; use pneumatic pick to construct when entering the sandstone layer; if it is difficult to construct with rock pneumatic pick, use drilling and blasting.
④ Transportation: A vertical transportation support is erected on the pile hole, and the hoisting machine is used as the lifting soil transportation equipment. The lifted muck is transported to the designated spoil yard in time to avoid environmental pollution.
⑤ Wall protection construction: the wall protection concrete adopts the method of mechanical mixing, manual pouring and vibrating rod tamping. Slump control in 8~10cm. The principle of one section of excavation and one section of support shall be adopted, and the depth of excavation shall not exceed 2m. Each section shall be taken as a construction cycle for downward construction. Wall C20 reinforced concrete, 20cm thick. Insert vertical reinforcement (25cm into the lower section) between sections to improve the integrity of the retaining wall. The formwork shall be connected and fixed with clamps and fasteners to ensure rigidity. The formwork removal can only be carried out after 8 hours of concrete pouring for the protective wall.
⑥ 36V safe voltage is used for lighting in the pile, and special waterproof bulb is used for lighting bulb in the hole to ensure safety.
⑦ Safety measures: the ladder pendant is embedded at the lock opening, and it is convenient to hang the ladder with feet and hands when waiting for a certain depth. When the construction personnel go up and down, they must go up and down with feet and hands. A rain-proof protection shed is set up on the pile opening, and a protection fence should be set up around the pile opening. Under the hole must ensure ventilation, and at any time to detect whether there is harmful gas, once found harmful gas, the construction personnel must immediately evacuate, take ventilation to dilute the concentration of harmful gas, in the determination of absolute safety, can continue construction.
⑧ Inspection: after pile forming, the size of pile body, elevation of hole bottom, center line of pile position and verticality of shaft wall shall be comprehensively measured, and construction records shall be made. After the supervision and relevant quality inspection personnel jointly check and identify the holes one by one and meet the design requirements, the concealed works shall be checked and accepted, and then the reinforcement cage shall be made and hung, and the concrete shall be poured.
Pile retaining wall must meet the following requirements:
a. The thickness of the protective wall, the provision of the lap bar, and the concrete must meet the design requirements.
B. after the hole pile is opened, the pile wall concrete shall be poured as soon as possible, and the pouring shall be completed at one time on the same day.
c. Concrete for retaining wall shall not be poured when the formwork is flooded by water.
D. found that the protective wall has honeycomb, leakage phenomenon, should be timely to block or diversion.
4) Blasting in hole of anti-slide pile
① Initiate with electric detonator.
② It is necessary to shoot holes, and it is strictly prohibited to expose the charge. For soft rock, the depth of the shot hole shall not exceed 0.8 meters, and for hard rock, the depth of the shot hole shall not exceed 0.5 meters. The number, position and oblique insertion direction of the blast holes shall be determined according to the direction of the rock formation section. A group in the middle shall be centrally cut out, and the sides shall be obliquely inserted around.
③ Strictly control the dosage, mainly loosening. Generally, the middle hole is filled with 1/2 section of nitramine explosive and the side hole is filled with 1/3~1/4 section.
④ Emulsion explosives should be used for holes with water holes, and misfires should be avoided as far as possible. If there are misfires, they should be handled according to safety regulations.
⑤ The support near the blast hole shall be reinforced to avoid hole collapse caused by the explosion of the support.
⑥ Smoke shall be discharged quickly after blasting in the hole. Measures such as putting an electric blower into the bottom of the hole to blow air can be adopted.
⑦ Blast hole layout of anti-slide pile

 

5). Fabrication of reinforcement cage

① The rebar materials used must have the warranty and test report.
② When processing steel bars, the overlapping positions of main reinforcement shall be staggered, within 35d and not less than 500mm, and the number of joints within the scope shall not exceed 50% of the total stressed steel bar area. The welding of main reinforcement must ensure that the lap length is not less than the specification value. No joint shall be set for longitudinal main reinforcement within 2m below the pile top. The horizontal reinforcing bars must be spot-welded with the longitudinal bars to form a firm reinforcing cage, so as to ensure that the reinforcing cage is not deformed or twisted.
③ 22# iron wire shall be used for binding between stirrup and main reinforcement. The binding shall be firm and spot-welded properly.
6). Acoustic tube installation
① After the binding of the reinforcement cage, the sound tube shall be installed. The sound tube shall be a metal tube with an inner diameter of not less than 40 mm and a thickness of not less than 3mm. The sound tube shall be bound at the four corners of the inner side of the reinforcement cage, and the binding shall be firm.
② The bottom of the acoustic tube is welded and closed with thin steel plate. When the same acoustic tube is connected, it is welded with steel casing. The upper end is closed with wooden plug. There is no foreign matter in the tube, and the connection is smooth and no water leakage. The pipe orifice shall be more than 100 mm higher than the pile top, and the height of the acoustic pipe orifice shall be consistent.7). Pile core concrete pouring

① The supervision unit is requested to check the pile reinforcement in the hole, and the pile core concrete can be poured only after the acceptance is qualified.
② Before pouring, carefully check that the machines and tools are in good working condition, the materials used meet the requirements, and the mixture ratio of the mixing team is clear.
③ Assign special personnel to stand by and make records of concrete pouring of pile core.
4 in the mixing of concrete, in strict accordance with the proportion of concrete ingredients, concrete mixing time of not less than 90 seconds, slump control in the range of 8~10CM.
⑤ Dry pouring method is adopted for pouring: in the process of concrete pouring, string tube is adopted to ensure that the end of string tube is not more than 2M away from the concrete pouring surface, so as to prevent coarse aggregate and cement mortar from being discrete and segregated. The pile core concrete shall be vibrated once every 0.3 meters with an inserted vibrator to ensure the compactness of the pile core concrete. Each pile core must be continuously irrigated, and no facility joints shall be left. After pouring the pile core concrete, water shall be sprinkled for curing after 8 hours, and the curing period shall not be less than 7 days. When pouring the pile core concrete, prepare the concrete test block, carefully maintain it, and send it for inspection after reaching the age.
2.4 construction quality control

(1) General requirements

Anti-slide pile is a project with high quality requirements, and the construction quality of slide pile is directly related to the success or failure of the project. Therefore, the control of construction quality is particularly important. Construction must adhere to the principle of quality first, the implementation of total quality management.
Anti-slide piles are mostly cast-in-place piles, and several key processes such as hole formation (including drilling and hole cleaning), lower reinforcement cage and concrete pouring should be specially carried out. When each process is completed, quality inspection shall be carried out in time. If the previous process is not clear, the next process cannot be carried out to avoid hidden dangers.
During construction, each construction site shall be equipped with a full-time quality inspector to conduct a comprehensive inspection and supervision of the construction quality, and the quality responsibility shall be implemented to the person and to each pile. The quality control of cast-in-place piles mainly refers to the quality standards and control methods of drilling, hole cleaning, steel cage production, placement, concrete preparation, pouring and other technological processes. The design documents and national or industrial standards shall prevail, and specific standards and requirements that are practical and easy to operate shall be formulated.

 

 

Problems needing attention in 2.5 construction

Pre-reinforcement pile safety requirements and prevention and control measures:

(1) The on-site technical director shall conduct comprehensive, specific and targeted safety technical disclosure to the construction team before construction, including workplace and safety protection measures, safety operation procedures and safety precautions, and carry out regular safety self-inspection. Manual lifting equipment is strictly prohibited.
(2) The construction site shall be hung with safety signs, especially the main construction parts, operation points and dangerous areas, and the main access ports shall be hung with relevant safety signs. Construction machinery and equipment shall be provided with safety operation procedures.
(3) Before starting tunneling, make construction preparations to prevent rockfall and collapse, and first remove gravel and sundries within 2m around the wellhead; In the ground excavation with relatively broken soil, the wellhead must be supported, the lock port should be 0.45m higher than the ground surface, and safety helmet must be worn when entering the pile foundation pit.
(4) Measures for the collapse of the protective wall: after digging the 1-meter pile hole in each section, the protective wall construction shall be carried out immediately, the protective wall concrete shall be poured, and the protective wall formwork shall be removed after 8 hours. The upper and lower protective walls shall be reinforced with a lap length of not less than 10cm. To avoid the phenomenon of dripping sand and silt on the protective wall, which will cause the protective wall to sink and crack due to its own weight, anchor rods can be appropriately added to the protective wall in the broken section to prevent the protective wall from slipping.
(5) All equipment, facilities, safety devices, tools and labor protection articles on the construction site shall be inspected frequently to ensure intact and safe use. The quality of the earth-moving basket and whether the hanging rope are firmly fastened shall be checked frequently to prevent the underground construction personnel from being injured by falling soil and stones. Regularly inspect the quality of hoisting frame winch, pulleys and lifting ropes to prevent possible accidents such as breakage and falling off.
(6) If blasting operation is required for pile hole excavation, the blasting flying stone control shall cover the gun cover at the lock position.
(7) When the depth of the pile hole exceeds 8m, the ground is equipped with an air supply device to the hole, and the air volume is not less than 25L/S. When chiseling stones at the bottom of the hole, the air supply must be increased.
(8) The pile hole shall be provided with C20 reinforced concrete retaining wall, and special personnel shall be assigned to regularly check the construction quality and deformation of the concrete retaining wall of the pile hole.
(9) The wellhead retainer shall be 0.3m higher than the ground to prevent sundries from the wellhead from falling into the pile hole and injuring personnel. The ladder must be placed in the pile hole, and it must be extended to the working face with the increase of the digging depth for safe use. The construction personnel must use the ladder up and down, and it is forbidden to use the electric hoist to lead people. No drunken operation, no smoking and open fire operation in the hole.
(10) For pile openings that have been filled with concrete or are being dug, manhole covers and fences must be provided.
(11) After pumping water in the hole, the special power supply for pumping water must be cut off before the operators can operate in the pile hole. It is strictly prohibited to operate with power supply. The digging personnel must use the safety ladder when going up and down the hole; The tools needed in the well must be delivered with special ropes. The ropes shall be checked at any time and replaced immediately if there is any broken wire. Throwing in any well is prohibited. The continuous operation of downhole operation personnel should be 2h, and the longest shall not exceed 3h. The downhole operation personnel shall be changed frequently and the downhole operation shall be rotated. Reliable communication, such as walkie-talkie, shall be provided at the upper and lower well holes. Operators in the hole shall pay close attention to the situation in the hole and shall not leave the post without permission.
(12) The installation and removal of all power and electrical lines in the construction site must be under the special management of certified electricians, and electrical appliances must be strictly grounded, connected to zero and use leakage protectors. Each pile hole must be separated from the electricity supply, and it is strictly forbidden to use one gate with multiple holes and one gate for multiple purposes. "Three-phase and five-wire" must be adopted, and the overhead height of wires on the construction site shall not be less than 3m from the ground, with good insulation.
(13) After the pile hole is accepted, the pile body reinforcement cage shall be hoisted in place immediately. When the reinforcement cage is hoisted into the hole, collision damage to the hole wall shall be prevented.
(14) Bamboo veneer or wood board shall be used to cover the wellhead after hole forming and before concrete pouring, and safety warning measures shall be provided.