Dynamic compaction replacement method for high-altitude depression

Abstract

The invention relates to the technical field of foundation treatment, and particularly discloses a high-altitude depression dynamic compaction replacement method which comprises the following steps: S1, geological survey and zoning: carrying out gridding survey on depression foundations with the altitude being greater than or equal to 2500m, and dividing construction sections; s2, preparing a replacement material, namely preparing a grade configuration replacement material consisting of gravel, coarse sand and an anti-freezing additive according to the soil texture of the section; s3, layered dynamic compaction replacement is conducted, specifically, replacement materials are laid in two layers, and corresponding compaction energy construction is adopted; s4, segmented jumping ramming construction is conducted, specifically, construction segments are divided along the gradient, and operation is conducted according to the interval jumping ramming sequence; s5, dynamic drainage control is conducted, drainage blind ditches are arranged, and vacuum precipitation is started according to the underground water level; and S6, quality monitoring is conducted, and the penetration resistance and the settlement difference of the displacement body are detected. The method adapts to special geological climate conditions of the high-altitude depression, the problems of freeze-thaw damage, foundation softening and the like which are difficult to deal with by a traditional foundation treatment method are solved, the bearing capacity and stability of the foundation are effectively improved, the construction efficiency is high, and environmental protection is achieved.

Description

Technical Field

[0001] This invention relates to the field of foundation treatment technology, specifically to a method for dynamic compaction and replacement in high-altitude depressions. Background Technology

[0002] High-altitude areas, due to their unique geographical environment and climate conditions, present significant challenges for the application of foundation treatment technologies. This is especially true for depressions at altitudes ≥2500m, which commonly suffer from widespread soft soil layers, shallow groundwater levels, and pronounced seasonal freeze-thaw cycles. These factors severely restrict the bearing capacity and stability of the foundation, posing a significant challenge to engineering construction. In infrastructure projects undertaken in such areas, improper foundation treatment can easily lead to uneven settlement, structural cracking, and other defects, failing to meet the foundation safety requirements of important structures such as boilers and production buildings.

[0003] Traditional foundation treatment methods, such as single-layer dynamic compaction and conventional replacement, are difficult to adapt to the complex working conditions of high-altitude depressions. Traditional replacement materials often use fixed proportions and do not dynamically adjust according to the differences in soil moisture content in different sections, making it difficult to ensure the stability of the compaction effect in the later stage. Traditional dynamic compaction is mostly a single-layer, single-impact operation, which lacks both layered and staggered compaction point layout design and segmented and orderly construction planning, and is prone to poor compaction uniformity and low work efficiency. At the same time, traditional methods rely only on simple drainage facilities, which are difficult to cope with groundwater level fluctuations in high-altitude freeze-thaw environments, which can easily lead to foundation softening. Furthermore, there are no corresponding protective measures for seasonal freeze-thaw conditions, which further exacerbates the risk to foundation stability. Summary of the Invention

[0004] The present invention aims to provide a dynamic compaction replacement method for high-altitude depressions to solve the technical problems faced in the foundation treatment of high-altitude depressions, such as freeze-thaw damage, foundation softening, and insufficient bearing capacity.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: a method for dynamic compaction replacement in high-altitude depressions, comprising the following steps: S1. Geological survey and zoning: Conduct grid-based surveys of the foundation of depressions with an elevation ≥2500m to identify the distribution of weak soil layers, groundwater level and freeze-thaw interface depth, and delineate the dynamic compaction replacement construction sections. S2. Replacement material preparation: Based on the soil moisture content of each section, prepare graded replacement materials with soil-rock ratio to ensure that the regional compaction coefficient is in the target range of 0.90-0.96 in the later stage. S3, Layered Dynamic Compaction Replacement: Replacement material is laid in two layers and point compaction is carried out using different compaction energies; S4. Segmented skip-compaction construction: Divide the construction into sections along the slope of the depression, and use a skip-compaction sequence to control the construction interval between adjacent sections. S5. Dynamic drainage control: Drainage blind ditches with a depth greater than the freeze-thaw interface are set up around the construction area. The groundwater level is monitored in real time during the dynamic compaction process, and vacuum dewatering is initiated when the critical value is reached. S6. Quality monitoring: After each layer of replacement, the penetration resistance of the replacement body is tested, and the regional compaction coefficient is measured simultaneously to control the increase in penetration resistance.

[0006] Preferably, as an improvement, the replacement material in step S2 includes crushed stone, coarse sand, and antifreeze additive, wherein the crushed stone has a particle size of 30-70mm, the coarse sand accounts for 15-25%, and the antifreeze additive is silicate cement with a dosage of 3-5%.

[0007] Preferably, as an improvement, the replacement material further includes basalt fibers with a fiber length of 12-18 mm and a dosage of 0.3-0.8 kg / m³. 3 .

[0008] Preferably, as an improvement, the specific operation of the layered dynamic compaction replacement in step S3 is as follows: the first layer of replacement involves laying a 1.0-1.5m thick replacement material layer on the surface of the weak soil layer, using 3500-4000kN... The compaction is carried out using a tamping energy of m, with a compaction point spacing of 4-4.5m; the second layer of replacement is a 0.8-1.2m thick replacement material layer laid on top of the first replacement body, using a 5500-6000kN impact energy. The m-type tamping energy can be used for point tamping, and the tamping points are staggered with the lower layer.

[0009] Preferably, as an improvement, the hammer used for dynamic compaction is a conical-bottom cast steel hammer with a cone diameter of 1.2m, a cone angle of 25°-30°, and a weight of 28-32t. The hammer bottom is provided with four vertical ventilation holes with a diameter of 50mm. Furthermore, the thickness of the single-layer replacement material is determined by the formula h=0.1σc / (γd). k) is dynamically adjusted, where h is the thickness of a single layer of replacement material (m), σc is the unconfined compressive strength of the soft soil layer (kPa), γd is the compaction density of the replacement material (kN / m³), and k is the plateau correction factor, which is 0.85-0.95.

[0010] Preferably, as an improvement, in step S4, the length of the construction section is ≤20m, the construction interval between adjacent sections is ≥48 hours, the skipping order of the interval follows the principle of "edge first, then center; low-lying areas first, then high-lying areas", and the construction time interval between adjacent compaction points is ≥2 hours.

[0011] Preferably, as an improvement, the structure of the drainage ditch in step S5 is as follows: the bottom layer is laid with geogrid with a tensile strength ≥60kN / m, the middle layer is filled with crushed stone with a thickness ≥0.6m and a particle size of 20-40mm, and the surface layer is covered with a polypropylene frost heave inhibition blanket with a weight ≥500g / m²; the critical value of the groundwater level is <1m from the ground surface.

[0012] Preferably, as an improvement, in step S6, the increase in penetration resistance of the replacement body is ≥150%, and the quality monitoring also includes settlement difference control. The settlement difference control requires that the settlement difference of each measuring point in the section be ≤5mm in 24 hours, and the next layer of construction can only be carried out after two consecutive tests meet the standard.

[0013] Advantages of this solution: 1. Strong adaptability to high-altitude environments: It specifically addresses the problems of freeze-thaw erosion and high groundwater levels in depressions at altitudes ≥2500m. The antifreeze materials and dynamic drainage system can prevent foundation cracking and softening.

[0014] 2. Excellent foundation bearing capacity: Layered dynamic compaction forms an interlocking composite foundation, customized material replacement improves the overall integrity, the penetration resistance after replacement increases by more than 160%, and the 24-hour settlement difference is ≤5mm, ensuring the stability of the building foundation.

[0015] 3. Precise and reliable construction management: segmented jump compaction reduces soil disturbance, dynamic drainage system stabilizes groundwater level, and dual-layer quality monitoring forms a closed loop to prevent later engineering defects.

[0016] 4. Balancing efficiency and environmental protection: staggered operations improve construction efficiency and shorten the construction period; environmentally friendly materials such as basalt fiber reduce ecological disturbance, and localized gradation saves transportation costs.

[0017] 5. High technical scalability: It forms a complete foundation treatment technology system, providing a replicable paradigm for similar high-altitude depression infrastructure projects, and promoting high-quality development of high-altitude infrastructure. Attached Figure Description

[0018] Figure 1 This is a flowchart of the overall process of dynamic compaction replacement of the present invention; Figure 2 This is a flowchart of the layered dynamic compaction replacement process of the present invention; Figure 3 This is a schematic diagram of the cross-sectional structure of the drainage blind ditch of the present invention. Detailed Implementation

[0019] The basic implementation examples are as follows: Figure 1-3 As shown: In a high-altitude depression infrastructure project at an elevation of 2800m, the high-altitude depression dynamic compaction replacement method of this invention was used for foundation treatment. The specific implementation process is as follows: 1. Geological survey and zoning A 10m×10m grid was used to arrange survey points. Drilling and static cone penetration tests revealed that the surface layer (0-3m) consisted of silty clay with a water content of 45%, the groundwater level was 0.8m below the surface, and the freeze-thaw interface was 1.2m deep. Based on this, the construction area was divided into three sections: A (low-lying waterlogged area), B (transition zone), and C (relatively dry area).

[0020] 2. Preparation of displacement material Different replacement materials were prepared according to the soil conditions of each section: Section A consisted of 70% crushed stone (50-80mm), 20% coarse sand, 5% silicate cement, and 0.8kg / m³ basalt fiber; Section B consisted of 75% crushed stone (40-60mm), 20% coarse sand, 4% silicate cement, and 0.6kg / m³ basalt fiber; Section C consisted of 80% crushed stone (30-50mm), 17% coarse sand, 3% silicate cement, and 0.3kg / m³ basalt fiber. All fibers were evenly mixed at the mixing plant.

[0021] 3. Layered dynamic compaction replacement A cast steel hammer with a cone base diameter of 1.2m, a cone angle of 28°, a weight of 15t, and four 50mm vent holes was used for construction. The first layer of replacement material in section A was laid 1.5m thick, using a 4000kN... A replacement pier with a diameter of 2.0m and a depth of 2.5m is formed by 10-15 impacts at a spacing of 4.5m using a compaction energy of m. After the first layer passes inspection, a second layer of replacement material with a thickness of 1.0m is laid, using a 6000kN compaction energy of m. The compaction energy is m, and the compaction points are offset from the lower layer by 1.75m. At the same time, combined with the parameters of section A (σc=35kPa, γd=20kN / m³, k=0.9), the calculated h=0.19m is used, but it is actually adjusted to 1.5m in actual construction to ensure the replacement effect.

[0022] 4. Segmented jump compaction construction Each section is divided into construction segments of 15-20m in length. Construction is carried out in the order of "edge first, center second, low-lying areas first, high-lying areas second". The edge segment A1 of section A is worked first, followed by segment A3 after an interval of 48 hours, and then segment A2 in the middle after an interval of 48 hours. The construction interval between adjacent compaction points is ≥2 hours.

[0023] 5. Dynamic drainage control A 2.0m deep drainage ditch is constructed, with a bottom layer of 65kN / m geogrid, a middle layer of 0.8m thick 35mm granulated gravel, and a top layer of 550g / m² polypropylene frost heave inhibitory blanket. Water levels are controlled by an automatic water level monitoring system. Automatic vacuum dewatering is achieved through the coordinated operation of water level sensors, a data transmission module, a central controller, and a vacuum dewatering unit. Water level sensors are buried at key locations in the construction area to collect groundwater level data in real time, which is then fed back to the central controller via the data transmission module. When the groundwater level is 0.9m below the surface, the central controller automatically issues a start command. After the vacuum pump of the vacuum dewatering unit starts, it forms a negative pressure drainage channel through the main water collection pipe and branch filter pipes. A sealing membrane ensures the airtightness of the construction area to improve dewatering efficiency. During the drainage process, the water level sensor continuously monitors the water level. When the water level drops to a safe threshold of ≥1.2m below the surface, the central controller commands the vacuum pump to stop, achieving automated closed-loop control of the groundwater level.

[0024] 6. Quality Control After each layer of replacement, testing points were set at the center and edge of the pier. The penetration resistance of the replacement body in section A was found to be more than 160% higher than that of the original foundation. At the same time, settlement observation points were set up at 5m×5m and continuously observed for 48 hours. The 24-hour settlement difference of each section's measuring points was ≤5mm. After two consecutive tests that met the standards, the next layer of construction was carried out. Finally, the foundation treatment effect met the engineering design requirements.

[0025] The above descriptions are merely embodiments of the present invention, and common knowledge such as specific technical solutions and / or characteristics are not described in detail here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the technical solutions of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. A method for dynamic compaction and replacement in high-altitude depressions, characterized in that, Includes the following steps: S1. Geological survey and zoning: Conduct grid-based surveys of the foundation of depressions with an elevation ≥2500m to identify the distribution of weak soil layers, groundwater level and freeze-thaw interface depth, and delineate the dynamic compaction replacement construction sections. S2. Replacement material preparation: Based on the soil moisture content of each section, prepare graded replacement materials with soil-rock ratio to ensure that the regional compaction coefficient is in the target range of 0.90-0.96 in the later stage. S3, Layered Dynamic Compaction Replacement: Replacement material is laid in two layers and point compaction is carried out using different compaction energies; S4. Segmented skip-compaction construction: Divide the construction into sections along the slope of the depression, and use a skip-compaction sequence to control the construction interval between adjacent sections. S5. Dynamic drainage control: Drainage blind ditches with a depth greater than the freeze-thaw interface are set up around the construction area. The groundwater level is monitored in real time during the dynamic compaction process, and vacuum dewatering is initiated when the critical value is reached. S6. Quality monitoring: After each layer of replacement, the penetration resistance of the replacement body is tested, and the regional compaction coefficient is measured simultaneously to control the increase in penetration resistance.

2. The method for dynamic compaction and replacement in high-altitude depressions according to claim 1, characterized in that: The replacement material in step S2 includes crushed stone, coarse sand, and antifreeze additive, wherein the crushed stone has a particle size of 30-70mm, the coarse sand accounts for 15-25%, and the antifreeze additive is silicate cement with a dosage of 3-5%.

3. The method for dynamic compaction and replacement in high-altitude depressions according to claim 1, characterized in that: The replacement material also contains basalt fibers with a fiber length of 12-18 mm and a dosage of 0.3-0.8 kg / m³. 3 .

4. The method for dynamic compaction and replacement in high-altitude depressions according to claim 1, characterized in that: The specific operation of the layered dynamic compaction replacement in step S3 is as follows: The first layer of replacement involves laying a 1.0-1.5m thick replacement material layer on the surface of the weak soil layer, using 3500-4000kN... The compaction is carried out using a tamping energy of m, with a compaction point spacing of 4-4.5m; the second layer of replacement is a 0.8-1.2m thick replacement material layer laid on top of the first replacement body, using a 5500-6000kN impact energy. The m-type tamping energy can be used for point tamping, and the tamping points are staggered with the lower layer.

5. The method for dynamic compaction and replacement in high-altitude depressions according to claim 1, characterized in that: The hammer used for dynamic compaction is a conical-bottom cast steel hammer with a cone diameter of 1.2m, a cone angle of 25°-30°, and a weight of 28-32t. The hammer bottom has four vertical ventilation holes with a diameter of 50mm. The thickness of the single-layer replacement material is determined by the formula h=0.1σc / (γd). k) is dynamically adjusted, where h is the thickness of a single layer of replacement material (m), σc is the unconfined compressive strength of the soft soil layer (kPa), γd is the compaction density of the replacement material (kN / m³), and k is the plateau correction factor, which is 0.85-0.

95.

6. The method for dynamic compaction and replacement in high-altitude depressions according to claim 1, characterized in that: In step S4, the length of the construction section is ≤20m, the construction interval between adjacent sections is ≥48 hours, the skipping order of the interval follows the principle of "edge first, then center; low-lying areas first, then high-lying areas", and the construction time interval between adjacent compaction points is ≥2 hours.

7. The method for dynamic compaction and replacement in high-altitude depressions according to claim 1, characterized in that: In step S5, the drainage ditch is constructed with a bottom layer of geogrid with a tensile strength ≥60kN / m, a middle layer of crushed stone with a thickness ≥0.6m and a particle size of 20-40mm, and a surface layer of polypropylene frost heave inhibition blanket with a weight ≥500g / m². The critical value of the groundwater level is <1m from the ground surface.

8. The method for dynamic compaction and replacement in high-altitude depressions according to claim 1, characterized in that: In step S6, the increase in penetration resistance of the replacement body is ≥150%, and the quality monitoring also includes settlement difference control. The settlement difference control requires that the settlement difference of each measuring point in the section be ≤5mm in 24 hours, and the next layer of construction can only be carried out after two consecutive tests meet the standard.

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