1. Root pile reinforcement
1. Foundation grouting reinforcement
Applicable to the reinforcement of foundation cracks caused by uneven settlement, frost heave or other reasons. The slurry mainly uses cement slurry, and the water-cement ratio can be 0.5~0.6, or epoxy resin can be used.
(1) First, drill holes at the cracks, with no less than 2 holes on each side of the single-sided foundation;
(2) Strip foundations can be drilled along the longitudinal spacing of 1.5~2.0m, and no less than 2 rows
(3) During grouting construction, first drill holes at the original foundation cracks. The diameter of the grouting pipe can be 25mm, the inclination angle of the drill hole to the horizontal plane should not be less than 30°, the drill hole diameter should be 2-3mm larger than the diameter of the grouting pipe, and the hole spacing can be 0.5-1.0m.
(4) The grouting pressure can be 0.1-0.3MPa. If the slurry does not sink, gradually increase the pressure to 0.6 MPa. If the slurry does not sink within 10-15 minutes, stop grouting. The effective diameter of the grouting is 0.6-1.2 m. 2. Increasing the Low Foundation Area Method The increasing low foundation area method is suitable for reinforcement when the foundation bearing capacity or foundation bottom surface dimensions of an existing building do not meet regulatory requirements. Concrete or reinforced concrete sleeves can be used to increase the foundation bottom area. When the foundation is eccentrically loaded, asymmetric widening can be used; when bearing central loads, symmetrical widening can be used. To improve the reinforcement effect, measures should be taken to reduce the stress-strain hysteresis between the newly added part and the original foundation. For strip foundations, short unloading steel beams can be installed at intervals of 1.5-2m, and jacks can be used to transfer a certain proportion of the load borne by the original foundation to the newly added reinforced concrete side step beams. For independent foundations, steel pipe bracing and steel plates can be used to transfer part of the load borne by the original foundation to the newly added reinforced concrete ring beam.
3. Anchor static pressure piles
Anchor static pressure piles refer to piles that are pressed using the reaction force provided by anchor rods anchored in the original foundation. The pressed piles are generally small-section piles and are mainly used for foundation reinforcement. Its advantages are that the equipment used is simple and easy to operate, the construction does not affect the construction period, it can be operated in a small space, the load transfer process and force performance are clear, the construction is simple, and the quality is reliable. The disadvantages are that holes are left in the base and the anchor rods are complicated to embed.
The static pressure method is usually applicable to highly compressible clay layers or soft clay layers with relatively light sandiness. When the pile needs to penetrate a sandy soil interlayer with a certain thickness, its applicability must be comprehensively considered based on the pile driver’s pile pressure and final pressure, the shape, thickness, density of the soil layer, the mechanical indicators of the upper and lower soil layers, the pile type, the pile structure, the strength, the cross-sectional specifications and pile layout, the groundwater level, and the stabilization time and number of stabilization times before the final pressure.
4. Tree root pile method
The tree root pile method is applicable to reinforcement projects such as the repair and addition of existing buildings on foundation soils such as silt, silty soil, clay, silt, sand, gravel soil and artificial fill, the renovation of ancient buildings, and the crossing of subways.
(1) The diameter of the tree root pile should be 150-300mm, and the pile length should not exceed 30m. The pile layout can be straight pile type or mesh structure inclined pile type.
(2) The vertical bearing capacity of a single root pile can be determined by a single pile load test. When there is no test data, it can also be estimated according to the relevant provisions of the current national standard “Code for Design of Building Foundations” GBJ7. The determination of the vertical bearing capacity of a single root pile should also take into account the limitations of the foundation deformation conditions of the existing building and the strength requirements of the pile body material.
(3) The strength grade of the pile body concrete should be no less than C20, and the outer diameter of the steel cage should be 40-60mm smaller than the design pile diameter. The number of main bars should not be less than 3. For weak foundations, the length of the steel bar when mainly bearing vertical loads shall not be less than 1/2 of the pile length; when mainly bearing horizontal loads, the full length of the steel bar should be reinforced.
(4) When designing a root pile, the bearing capacity of the foundation of the existing building should also be verified. When the above requirements are not met, the original foundation should be reinforced or a new pile cap should be added. 2. Foundation Reinforcement Piles 1. Replacement and Filling Method: Suitable for treating shallow, weak, and uneven foundations. Its primary functions are to increase bearing capacity, reduce settlement, accelerate drainage and consolidation of weak soil layers, prevent frost heave, and eliminate the expansion and contraction of expansive soils. 2. Dynamic Compaction Method: Suitable for treating foundations of gravel, sand, low-saturation silt and clay, collapsible loess, mixed fill, and plain fill. The dynamic compaction and replacement method is suitable for projects with lax deformation control on foundations such as highly saturated silt and soft-plastic clay. Its suitability and effectiveness must be determined through field testing before design. Dynamic compaction and replacement methods are primarily used to increase soil strength, reduce compressibility, improve resistance to vibration liquefaction, and eliminate collapsibility. For saturated clay, they should be combined with preloading and vertical drainage. 3. Sand and Gravel Pile Method: Suitable for compacting loose sand, silt, clay, plain fill, and mixed fill foundations, increasing bearing capacity and reducing compressibility. It can also be used to treat liquefiable foundations. Sand and gravel pile replacement can also be used for projects on saturated clay foundations where deformation control is lax. This allows the sand and gravel piles to form a composite foundation with soft clay, accelerating drainage and consolidation of the soft soil and improving bearing capacity. 4. Vibroflotation Method: Available with or without fillers. The filler method is commonly referred to as the vibroflotation crushed stone pile method. The vibroflotation method is suitable for treating foundations in sand, silt, silty clay, plain fill, and mixed fill. For clay soils with an undrained shear strength of at least 20 kPa and saturated loess foundations, its suitability should be determined through field testing before construction. Unfilled vibroflotation densification is suitable for treating medium- and coarse-sand foundations with a clay content of no more than 10%. Vibro-compacted stone piles are primarily used to increase foundation bearing capacity and reduce foundation settlement. They can also be used to improve the anti-sliding stability of soil slopes or enhance the shear strength of soil. 5. Cement-soil mixing method: This method is divided into deep slurry mixing (wet method) and powder spray mixing (dry method). The cement-soil mixing method is suitable for foundations of normally consolidated silt and silty soils, clay soils, silt, saturated loess, plain fill, and saturated loose sand without flowing groundwater. It is not suitable for foundations of peat soils, clay with a plasticity index greater than 25, corrosive groundwater, or soils with a high organic matter content. If this method is used, its suitability must be confirmed through testing. This method is not suitable when the natural moisture content of the foundation is less than 30% (less than 25% for loess), greater than 70%, or when the groundwater pH is less than 4. Continuously overlapped cement-mixed piles can serve as a waterstop curtain for foundation pits. However, due to their limited mixing capacity, this method is difficult to apply to clay and silt foundations with a bearing capacity greater than 140 kPa.
6. High-pressure jet grouting
This method is suitable for treating silt, silty soil, clay, silt, sand, artificial fill, and crushed stone foundations. Its suitability should be determined based on field test results when the foundation contains a large number of large-particle rocks, numerous plant roots, or a high organic matter content. It is not suitable for situations where groundwater velocity is excessive or the jet grouting fails to solidify around the grouting casing. High-pressure jet grouting piles have a greater treatment depth. In addition to foundation reinforcement, they can also serve as a waterstop curtain for deep foundation pits or dams. The maximum treatment depth currently exceeds 30 meters.
7. Preloading
This method is suitable for treating saturated clay foundations such as silt, silty soil, and backfill. According to the preloading method, it is divided into surcharge preloading method and vacuum preloading method. Surcharge preloading is divided into plastic drainage belt or sand well foundation surcharge preloading and natural foundation surcharge preloading. When the thickness of the soft soil layer is less than 4m, the natural foundation surcharge preloading method can be used for treatment. When the thickness of the soft soil layer exceeds 4m, vertical drainage preloading methods such as plastic drainage belt and sand well should be used for treatment. For vacuum preloading projects, vertical drainage shafts must be set in the foundation. The preloading method is mainly used to solve the settlement and stability problems of the foundation.
8. Compacted cement soil pile method
It is suitable for treating foundations such as silt, plain fill, miscellaneous fill, and clay soil above the groundwater level. This method has a short construction period, low cost, civilized construction, and easy cost control. It has been successfully applied in many projects of dangerous renovation communities in old urban areas in Beijing, Hebei and other places. 9. Cement Fly Ash Gravel (CFG) Pile Method: This method is suitable for foundations in clay, silt, sand, and self-consolidated plain fill. Its suitability for silty soils should be determined based on regional experience or field testing. A cushion layer of sufficient thickness is required between the foundation and the pile top to ensure that the pile and soil share the load, forming a composite foundation. This method is applicable to strip foundations, isolated foundations, box foundations, and raft foundations, and can be used to increase bearing capacity and reduce deformation. For liquefiable foundations, a composite foundation consisting of gravel and cement fly ash gravel piles can be used to eliminate liquefaction and increase bearing capacity. 10. Lime Pile Method: This method is suitable for foundations in saturated clay, silt, silty soils, miscellaneous fill, and plain fill. When used in soils above the groundwater level, reducing the amount of quicklime and increasing the water content of the admixture can be used to improve pile strength. This method is not suitable for sandy soils under groundwater.
11. Lime-soil compaction pile method and soil compaction pile method
It is suitable for treating foundations such as collapsible loess, plain fill, and miscellaneous fill above the groundwater level, with a treatment depth of 5 to 15 meters. When used to eliminate the collapsibility of foundation soil, the soil compaction pile method should be used; when used to increase the bearing capacity of foundation soil or enhance its water stability, the lime-soil compaction pile method should be used; when the water content of the foundation soil is greater than 24% and the saturation is greater than 65%, this method should not be used. The lime-soil compaction pile method and the soil compaction pile method have basically the same effect in eliminating soil collapsibility and reducing permeability. The bearing capacity and water stability of the foundation using the soil compaction pile method are inferior to those using the lime-soil compaction pile method. 12. Column Hammer Impact Pile Method: Applicable to foundations involving miscellaneous fill, silt, clay, plain fill, and loess. For saturated soft soil layers below the groundwater level, its applicability should be determined through field testing. The foundation treatment depth should not exceed 6m. 13. Single-Liquid Silicification and Alkali Method: Applicable to foundations involving collapsible loess with a permeability coefficient of 0.1 to 2m/d above the groundwater level. For self-weight collapsible loess sites, the applicability of the alkali method for Class II collapsible foundations should be determined through testing. 14. Comprehensive Comparison Method: When determining a foundation treatment plan, it is advisable to compare multiple methods. For composite foundations, the selection of a suitable pile construction technique and reinforcement material is based on the specific soil properties and the required bearing capacity.
Other treatment methods for foundation
Other treatment methods for foundation include: brick continuous wall foundation method, concrete continuous wall foundation method, single-layer or multi-layer strip stone continuous wall foundation method, mortar-laid rubble continuous wall (retaining wall) foundation method, etc.
3. Seedling reinforcement piles
1. Pile end post-grouting reinforcement mechanism
The pile end post-grouting technology is to use a high-pressure grouting pump to inject cement slurry or a mixture of cement and other materials through the pre-buried grouting pipe after the bored pile is formed and the pile body concrete reaches the predetermined strength. The slurry penetrates into the loose virtual tip of the pile end and combines to form high-strength concrete; as the grouting volume increases, the cement slurry continuously penetrates into the pile end bearing layer that has become soft due to mud immersion, forming a “pear-shaped body” at the pile end, increasing the bearing area of the pile end, which is equivalent to expanding the bottom of the bored pile. As the “pear-shaped body” continues to grow, its permeability is limited by the surrounding dense soil layer, causing the pressure to continue to increase. The soil layer at the pile end is squeezed, compacted, filled, and consolidated, which will effectively reinforce or compact the sediment at the bottom of the pile and the disturbed bearing layer at the pile end. This will improve the geometric and mechanical conditions of the interface between the pile and the soil, increase the bearing capacity of the soil at the pile end, and thus significantly increase the bearing capacity of the single pile.
II. Pile Type Selection and Design
With the rapid development of the national economy, my country’s high-rise building industry has also achieved great development. From the current status of existing projects, there are many problems in the construction quality. The existence of a large number of these problems will lead to damage to the building and even cause great property losses and casualties. Post-grouting technology, a crucial component of high-rise building pile foundation construction, directly impacts the overall quality of the project. To effectively improve the overall quality of high-rise building construction, several key considerations must be addressed: 1. Pile shape selection. The characteristic bearing capacity of a single pile is typically required to be no less than 4,500 kN, requiring high loads. As high-rise buildings are sensitive to settlement and deformation, the estimated compressive bearing capacity of a bored pile with a diameter of 1,000 mm and a length of 40 m (entering the bearing layer 8.8 m) is 5,498 kN. The design compared conventional bored piles, branch-plate piles, and bored piles with bottom grouting. Considering the five layers of soil, up to 26 m thick and composed of cohesive gravel, the use of bottom grouting significantly improved the bearing capacity. Therefore, the foundation design consists of 360 1000mm φ bored cast-in-place piles, each 33.5m long (the pile bottoms extend 1m into the selected five-layer bearing stratum). Grouting treatment will be applied to the pile bottoms, resulting in a characteristic compressive bearing capacity of 6000 kN for each pile. Because the five layers of crushed stone contain a significant amount of clay, the grouting holes, grouting volume, and grouting pressure require careful design and pile test testing. 2. Grouting Hole Design Based on the pile diameter and the porosity of the bearing stratum at the pile bottom, two to four grouting pipes are evenly distributed around the circumference of the cast-in-place pile reinforcement cage. Generally, larger piles with smaller porosity require more grouting pipes. Considering the 100cm diameter piles in this project and the clay content of the crushed stone at the pile bottom, two 32mm φ grouting pipes are evenly distributed around the circumference of the reinforcement cage to ensure that the grouting can envelop the pile bottom.
3. Application of post-grouting construction technology at the pile end in building pile foundation projects
With the continuous advancement of science and technology in my country, in the construction of building projects, only by selecting construction methods and technologies that are suitable for the specific requirements of the construction site can the quality of the project be better improved. This is also the focus of construction. Applying pile foundations to the construction of modern high-rise building projects can not only shorten the construction period, but also improve the quality of the construction project, providing a strong guarantee for the realization of economic and social benefits of the construction project.
1. Making grouting pipes
Under normal circumstances, the steel cage and grouting pipes must be made at the same time. Use an iron pipe with a diameter of about 25 mm to make the grouting pipe, use a threaded joint for connection, use a wire to seal both ends and make sure that its sealing meets the construction requirements. The length of the grouting pipe must be about 55 cm longer than the steel cage, the bottom of the pile must be 5 cm longer than the steel cage, and the upper part must be 50 cm higher than the concrete surface of the pile head. The grouting nozzle is set at 20 mm from the bottom of the grouting pipe. At this position, four rows of grouting holes are evenly drilled with a drill bit, with a spacing of 3 cm and a diameter of 3 mm. The grouting holes are sealed with thumbtacks. A directly identical bicycle inner tube is placed on the outside and both ends are sealed with tape. The grouting nozzle is then modified to a one-way device. The pressure in the grouting pipe causes the tire to burst during the grouting process, and at the same time, the thumbtack is ejected. The cement slurry is pressed into the gravel layer through the grouting holes and the gaps between the thumbtacks. This method can effectively prevent the grouting pipe from being blocked.
2. Distribution of Grouting Pipes
The positions of the two grouting pipes are adjusted to each other, and they are bundled on the outside of the steel cage. After the drilling construction is completed, the relevant construction operation procedures must be followed, such as cleaning the hole, lifting the drill, and lowering the steel cage. During the installation and placement of the rebar cage, the grouting pipes must be carefully maintained to prevent twisting of the rebar cage and loosening of the pipes at the threaded connections. Concrete blocks should be used to protect the nozzles to prevent friction with the hole wall, which could cause tire ruptures and blockage of the grouting holes. Strict adherence to construction requirements must be followed throughout the concrete pouring process.
3. Grouting Construction
The grouting operation must be completed in a single operation. The optimal method is to grout the entire pile group at once. Grouting should begin with the surrounding piles, followed by the intermediate piles. During grouting, two piles must be grouted in a cycle. Grouting should begin with pipe A of the first pile, with 65% of the total grouting volume applied. After grouting is complete, grouting should be applied to pipe A of the second pile. Then, pipe B of the first pile and pipe B of the second pile should be grouted. This construction sequence should be followed for effective grouting. It can keep the grouting time of the two pipes of the same pile for more than 30 minutes, provide sufficient space for the diffusion of cement slurry, and facilitate the post-grouting construction of the pile end.
IV. Quality control of post-grouting construction of pile end
1. When grouting at the bottom of the pile, if the pressure reaches more than 10MPa and the grouting nozzle cannot be opened, causing a grouting pipe to be blocked, the entire amount of cement slurry can be pressed into the pile end at once through another unobstructed conduit to make up the grouting quantity. For piles with completely blocked ends, supplementary grouting measures must be taken. For piles that have a large amount of grouting back at the top of the pile at the beginning of grouting, the grouting should be carefully inspected and stopped. It should be analyzed whether the grouting pipe joint is leaking or blocked, and appropriate remedial measures should be taken to ensure that it meets the design requirements.
2. During grouting, cement slurry often appears along the side of the pile or in other parts. If the cement slurry appears on other piles or the ground, it means that the pile bottom is saturated and the grouting can be stopped. If the grouting appears from the side wall of the pile, the grouting volume also meets or is close to the design requirements, and the grouting can be stopped. If the grouting appears from the side wall of the pile and the grouting volume is small, the grouting pipe can be rinsed with clean water or pressurized water, and the grouting can be restarted after the cement slurry originally injected has finally solidified and blocked the capillary pores.
3. For piles whose grouting pipes are blocked and slurry cannot be further injected, this project has formulated an emergency plan for supplementary grouting before construction. The supplementary grouting work should be carried out uniformly after the grouting work is completed. The specific method is: use a geological survey drill to drill a hole with a diameter greater than 90mm at 0.2 to 0.3m from the pile wall. The drilling depth should be 0.4-0.5m deeper than the pile end. A grouting guide tube with a grouting device should be lowered into the hole. A plastic sealing grouting pipe should also be lowered along with the grouting pipe. After the sealing grouting slurry has solidified for 3 days, the grouting should be injected using the normal post-grouting process. The specific control standards are the same as for normal post-grouting.
4. Tree Root Pile Reinforcement – Inclined Stairs
Open Genshin Impact and click on the map in the upper left corner.
Drag the map to Tianqiu Valley. You will see three teleportation points nearby that can reach the ruins cave. Select any of them to teleport there.
After teleporting there, walk to the middle platform between the three towers in Tianqiu Valley and go up the stairs.
Walk up and head to the right where the tree roots are.
At this point, you’ll see the ruins are hollow. Simply jump in and challenge the boss.
5. Tree Root Pile Construction
A. Based on pile diameter, they can be divided into the following types:
1. Small piles: Due to their small diameter, construction machinery, construction sites, and methods are relatively simple. They are often used for foundation reinforcement and composite pile foundations (such as tree root piles).
2. Medium piles: They use a variety of methods and construction techniques. They are widely used in industrial and civil construction and are currently the most commonly used type of pile.
3. Large piles: With a large diameter and an inability to expand the pile ends, they offer high single-pile bearing capacity. They have experienced rapid development over the past 20 years and are often used in heavy buildings, structures, ports, docks, highway and railway bridges, and other projects. Pile Construction Technology
B. Based on the pile construction technology, bored piles can be divided into the following categories:
1. Dry-type bored piles;
2. Mud-type bored piles;
3. Casing-type bored piles.
6. Root Pile Foundation
1. Grouting Reinforcement
Grouting reinforcement is suitable for reinforcing foundations such as sand, silt, clay, and artificial fill. It is generally used to prevent seepage and leaks, increase the strength and deformation modulus of foundation soil, and control ground settlement.
a. Drilling: An electric drill drills holes at the hole layout location to the designed elevation;
b. Pipe cleaning: Inject water to clean the hose and seamless steel pipe to check whether the grouting can be guaranteed smoothly;
c. Pipe driving: Insert the seamless steel pipe to the designed elevation in batches according to the design requirements;
d. Grouting: A mortar mixer stirs the cement slurry, which is sucked into the grouting pump and injected into the seamless steel pipe through the hose.
2. Tree Root Pile Method
The tree root pile method is suitable for reinforcement projects such as the repair and addition of existing buildings, the renovation of ancient buildings, and the crossing of subways on foundation soils such as silt, silty soil, clay soil, silt, sand, crushed stone soil and artificial fill.
Drilling machines and equipment should be reasonably selected according to the foundation type, geological conditions and site conditions. Clear water wall protection can be used for soft clay, and mud wall protection must be used for silt sand.
3. Anchor static pressure pile method
The anchor static pressure pile method is suitable for foundation soils such as silt, silty soil, clay soil, silt and artificial fill.
4. Increasing the bottom area of the foundation
For foundations with similar bearing capacities after verification, the method of increasing the bottom area of the foundation can be used to increase the contact area between the foundation and the foundation, thereby reducing soil stress and achieving the purpose of strengthening the foundation.
5. High-pressure jet grouting method
The high-pressure jet grouting method is suitable for foundations such as silt, silty soil, clay soil, silt, loess, sandy soil, artificial fill and crushed stone. When the site contains a large number of large-sized boulders, a large number of plant roots or other organic matter, its applicability should be judged according to the specific conditions of the site. It should be used with caution in projects with excessive groundwater flow or water gushing.
High-pressure jet grouting is to use a drilling rig to drill a hole, insert a grouting pipe with a nozzle into the predetermined position of the soil layer, and use high-pressure equipment to turn the slurry into a high-pressure jet of more than 20Mpa, which is ejected from the nozzle to impact and destroy the soil. Some fine soil materials emerge from the water with the slurry, and the remaining soil particles are mixed with the slurry under the impact force of the jet flow, centrifugal force and gravity, and are rearranged regularly according to a certain slurry-soil ratio.
After the slurry solidifies, it forms a consolidated body in the soil, which together with the soil between the piles forms a composite foundation, thereby improving the bearing capacity of the foundation, reducing the deformation of the foundation, and achieving the purpose of foundation reinforcement.
7. Root pile reinforcement does not generate additional stress
1. Grouting reinforcement method
Grouting reinforcement method is suitable for foundation reinforcement of sand, silt, clay and artificial fill. It is generally used for anti-seepage and leakage prevention, improving the strength and deformation modulus of foundation soil, and controlling stratum settlement.
a. Drilling: An electric drill drills holes at the hole layout location to the designed elevation;
b. Pipe cleaning: Inject water to clean the hose and seamless steel pipe to check whether grouting can be guaranteed smoothly;
c. Pipe driving: Insert the seamless steel pipe to the designed elevation in batches according to design requirements;
d. Grouting: A mortar mixer stirs cement slurry, which is sucked into the grouting pump and injected into the seamless steel pipe through the hose.
2. Tree Root Pile Method
The tree root pile method is suitable for reinforcement projects such as the repair and addition of existing buildings, the renovation of ancient buildings, and the crossing of subways on foundation soils such as silt, silty soil, clay, silt, sand, crushed stone and artificial fill.
Drilling machinery and equipment should be reasonably selected according to the foundation type, geological conditions and site conditions. For soft clay, clear water retaining wall can be used, while for silt sand, mud retaining wall must be used.
3. Anchor Static Pressure Pile Method
The anchor static pressure pile method is suitable for foundation soils such as silt, silty soil, clay, silt and artificial fill.
4. Increasing the bottom area of the foundation
For foundations with similar bearing capacities after verification, the method of increasing the bottom area of the foundation can be used to increase the contact area between the foundation and the subgrade, thereby reducing soil stress and achieving the purpose of strengthening the foundation.
5. High-pressure jet grouting
High-pressure jet grouting is suitable for foundations such as silt, silty soil, clay, silt, loess, sand, artificial fill and crushed stone. When the site contains a large number of large-sized boulders, a large number of plant roots or other organic matter, its applicability should be judged according to the specific conditions of the site. It should be used with caution in projects with excessive groundwater flow or water gushing.
High-pressure jet grouting is to use a drilling rig to drill a hole, insert a grouting pipe with a nozzle into the predetermined position of the soil layer, and use high-pressure equipment to turn the slurry into a high-pressure jet of more than 20Mpa, which is ejected from the nozzle to impact and destroy the soil. Part of the fine soil emerges from the water along with the slurry, and the remaining soil particles are mixed with the slurry under the impact of the jet flow, centrifugal force and gravity, and are rearranged regularly according to a certain slurry-soil ratio.
After the slurry solidifies, it forms a consolidated body in the soil, which together with the soil between the piles forms a composite foundation, thereby improving the bearing capacity of the foundation, reducing the deformation of the foundation, and achieving the purpose of foundation reinforcement.
8. What are the characteristics of tree root pile reinforcement?
(1) The spacing of the roadbed settlement observation section along the line direction is generally not more than 50m; the spacing can be relaxed to 100m for road cuttings with flat terrain and uniform foundation conditions, and embankments with a height of less than 5m; the spacing should be appropriately increased in transition sections and areas with large changes in topographic and geological conditions.
(2) A settlement observation unit (a continuous roadbed settlement observation section is a unit) has no less than 2 observation sections.
III. Principles for setting up roadbed settlement observation points
(1) Observation points at various locations are set up on the same cross section. This is beneficial for monitoring the observation points, facilitating centralized observation, unifying the observation frequency, and more importantly, facilitating the comprehensive analysis of data from various observation projects.
① In the embankment section of the main line, a complete settlement monitoring section is generally set up every 100m, and a general settlement monitoring section is set up every 50m in the middle. The monitoring sections in the transition section need to be denser. In general, in the transition section of a bridge, a complete settlement observation section is set up 5m away from the end of the platform, and a general settlement observation section is set up at 1m, 20m, 30m, etc. For transverse structures such as culverts, a complete settlement observation section is set up 5m away from the side of the culvert (preferably on the side with higher fill). In addition to being determined according to the transition section and distance, the complete settlement monitoring section should also be selected at a section with a higher roadbed or deeper reinforcement.
IV. Technical requirements for observation components and burial
The buried positions of the measuring points and observation components shall be carried out according to the design drawings, and the marking shall be accurate and the burial shall be stable. During the observation period, effective protection measures shall be taken at the observation points to prevent collisions with construction machinery and damage caused by human factors, so as to ensure that the observation work can be carried out smoothly from beginning to end and achieve satisfactory results.
(1) Displacement observation piles: The displacement observation piles shall be prefabricated with C15 reinforced concrete, with a cross section of 15cm×15cm square and a length of not less than 1.5m. A semi-circular stainless steel wear-resistant probe shall be pre-buried on the top of the pile. The buried depth of the side piles shall be not less than 1.4m below the ground surface, and the top of the piles shall not be more than 10cm above the ground. The burial method is to use a Luoyang shovel to drive into the designed depth, place the prefabricated side piles in the hole, and cast C15 concrete around the piles to ensure the stability of the side piles. The displacement observation piles shall be buried before the general roadbed is filled.
(2) Settlement observation pile: The pile body is made of Φ20mm stainless steel rod, the top is rounded and engraved with cross lines, and the bottom is welded with a hook. After the construction of the subgrade surface is completed (after the construction of the subgrade bottom layer is completed in the area with preload preloading), it is buried at the designed position of the monitoring section after measurement. The burial depth is 0.3m, and the pile is anchored with M30 cement mortar 0.15m around it, 5mm above the buried surface. The surface is treated with anti-rust treatment. After the burial is completed, the pile top elevation is measured as the initial reading according to the national second-class precision leveling measurement standard.
(3) Settlement plate: The settlement plate is buried after the foundation treatment is completed. The settlement plate consists of a base plate, a metal measuring rod (galvanized iron pipe with a wall thickness of 40mm) and a protective sleeve (hard PVC pipe with a diameter of not less than 75mm and a wall thickness of not less than 4mm). The base plate size is 50cm×50cm, and the thickness is not less than 1cm. The elevation change of the settlement plate is measured according to the national first-class precision leveling measurement standard.
①The buried position of the settlement plate should be determined according to the design measurement, and a 10cm sand pad can be placed at the buried position.
9. Tutorial on tree root pile reinforcement of roadbed slope
Normally, the backfill is to the height outside the room, that is, zero, which is also the elevation of the finished structure.
II. How to choose the material for foundation backfill?
Clay can be used as the soil material, but when using it, you must pay attention to its water content to ensure that it meets the regulations. If the water content exceeds the range, it cannot be used, otherwise it will affect the quality of the fill. In addition, silt or expansive soil cannot be used as soil material.
III. What are the precautions for backfill construction?
1. Before backfilling, you must check whether there are any holes or debris such as tree roots above the base soil. If there are any, they must be cleaned up, otherwise it will affect the construction effect.
2. When backfilling, the quality of the soil to be used must be inspected, and its type, moisture content, particle diameter, etc. must be checked to ensure compliance with relevant regulations. In particular, the moisture content cannot be too high, otherwise measures must be taken, such as drying, loosening, etc.
3. During construction, if it is larger than the base surface, just press the edges tightly to ensure its quality. After backfilling, if there are no requirements, the slopes need to be tidied and the width of the slopes maintained at 0.5 meters. In addition, when backfilling, if some places are not compacted in place, they need to be filled by manual bulldozing.
4. After the backfill is completed, the outer layer needs to be leveled with a line. The places that exceed the standard height must be leveled immediately, and the places below the standard must be repaired. 10. Root Pile Reinforcement Methods for Brick-Concrete Structures: 1. Common Foundation Reinforcement Methods: Increasing the Foundation Base Area, Reinforced Grouting, Static Anchor Piles, and Root Pile Methods. Increasing the Foundation Base Area is applicable when the bearing capacity or base area of an existing building’s foundation does not meet design requirements. A concrete or reinforced concrete jacket can be used to increase the base area. Reinforced Grouting is applicable to cracks and damage caused by uneven settlement, frost heave, or other factors. Static Anchor Piles are applicable to strengthening and rectifying foundations in silt, silty soils, clay, silt, and artificial fill. Root piles, also known as grouting piles, are applicable to strengthening foundations in silt, silty soils, clay, silt, sand, crushed stone, and artificial fill. 2. Common Wall Reinforcement Methods: Mortar Surface Layer, Steel Mesh Mortar Surface Layer, and Reinforced Concrete Slab Wall. The mortar surface layer method is suitable for static and seismic reinforcement with a minor increase in bearing capacity; the steel mesh mortar surface layer method is suitable for static and seismic reinforcement with a significant increase in bearing capacity; the reinforced concrete slab wall method, forming a masonry-concrete composite wall, is suitable for static and seismic reinforcement with a significant increase in bearing capacity. The latter two reinforcement methods can also significantly improve the wall’s deformation resistance. 3. Common Brick Column Reinforcement Methods: Concrete Jacket Reinforcement and External Steel Encasing. Concrete jacket reinforcement can be used when the cross-section’s flexural and shear bearing capacity is insufficient. External steel encasing reinforcement can be used when the cross-section’s flexural bearing capacity is severely insufficient and increasing the cross-section size is not permitted. 4. Commonly Used Reinforcement Methods for Concrete Beams: Bonding steel to reinforce the normal sections of concrete beams, reinforcing the normal sections with reinforcement, and reinforcing the normal sections of simply supported beams with carbon fiber sheets. These three methods are suitable for increasing the bearing capacity of normal sections. Prestressed screws are used to reinforce the inclined sections of beams: this method is suitable for increasing the bearing capacity of inclined sections. Encasing steel to reinforce simply supported beams and prestressed tension rods are suitable for increasing the bearing capacity of both normal and inclined sections. 5. Commonly Used Reinforcement Methods for Concrete Floor (Roof) Slabs: Bonding steel to reinforce the tensile areas of the slabs and applying carbon fiber sheets are suitable for increasing the bending capacity of the normal sections. Beams should be installed near openings with concentrated loads or when the opening width or diameter is greater than 1000mm. Floor (roof) slab crack repair: Cracks can be either stabilized or unstable. Different reinforcement methods should be used based on the crack’s cause, crack width, crack depth, stability, whether the steel bars are corroded, and the purpose of the repair. Crack reinforcement methods include surface treatment, grouting, filling, and applying a penetrating waterproofing agent. The purpose of crack repair is to enhance waterproofing, load-bearing capacity, and durability.