A construction method for treating soft foundation by multi-layer three-dimensional tracking full replacement

Abstract

The present invention discloses a construction method for treating soft foundation by multi-layer three-dimensional tracking full replacement, which relates to the technical field of water conservancy project construction and includes the following steps: decomposing the soft interlayer into a number of soft rock layers connected in sequence in the vertical direction; selecting a number of layers to be treated with treatment conditions; starting from a certain layer to be treated with conditions, decomposing it into a number of replacement adits connected in sequence; when the outermost replacement adit is excavated to a predetermined depth, backfilling the excavated part with concrete; successively excavating and backfilling the remaining replacement adits; selecting the next layer to be treated with conditions for excavation and concrete backfilling until all the layers to be treated are completely replaced with concrete; finally excavating the remaining soft rock layers and backfilling them with concrete, so as to complete the full replacement of the soft interlayer with concrete. The present invention can realize the full replacement of the soft foundation with the backfilled concrete structure, avoiding the potential safety hazards caused by the replacement of part of the soft foundation.

Description

Technical Field

[0001] The present invention relates to the technical field of hydraulic engineering construction, and particularly relates to a construction method for treating soft foundations by multi-layer three-dimensional tracking full replacement. Background Art

[0002] An arch dam is an arch-shaped water retaining structure that bulges upstream on a plane, and uses the action of the arch to transfer all or part of the water pressure to the bedrock on both sides of the river valley. Therefore, the arch dam has relatively high requirements for the shape of the river valley at the dam site and the foundation. The stability of the mountain body at the dam abutment is a necessary condition to ensure the safety of the arch dam. However, in actual projects, due to complex geological conditions, there may be faults, joint fissures, extrusion dislocation zones, rock mass weathering, unloading, soft rock masses, etc. in the rock mass at the dam abutment. To ensure the safety of the arch dam, the treatment plan for the soft foundation at the dam abutment has become a major technical problem in the design of many arch dams.

[0003] In the design plan for treating the soft foundation at the arch dam abutment, to avoid the safety risks caused by excessive excavation span and height of the soft foundation, generally, shear resistance holes, anchor holes, concrete frames, etc. are used for treatment. The essence of these treatment methods is to use the concrete structure to partially replace the soft foundation to form a force transfer body, so as to achieve the purpose of transferring the force from the upstream mountain body to the downstream mountain body. However, due to only partial replacement of the soft foundation, the stress conditions of the formed concrete structure are relatively poor, and local tensile stress often occurs during the normal operation of the arch dam, leaving hidden dangers for the safe operation of the arch dam, causing problems such as non-convergent deformation of the slope near the dam after impoundment, and even possible tensile cracks, which affect the force transfer effect, and it is difficult to ensure the safety, reliability, and durability of the project. Moreover, when using shear resistance holes, anchor holes, concrete frames, etc. for treatment, shaft or inclined shaft excavation is often required during the excavation process, and for soft surrounding rock, the construction safety risk is relatively large. Summary of the Invention

[0004] In order to solve the deficiencies of the prior art, the purpose of the present invention is to provide a construction method for treating soft foundations by multi-layer three-dimensional tracking full replacement, which can realize the full replacement of the soft foundation with a backfilled concrete structure, avoiding the safety hazards caused by partial replacement of the soft foundation; at the same time, it can also decompose the soft foundation into several replacement adits with relatively small excavation risks for treatment, reducing the safety risks of shaft or inclined shaft excavation such as shear resistance holes and frame excavation holes, and the excavation and concrete backfilling construction are also more convenient and fast.

[0005] The present invention is realized through the following technical solutions:

[0006] A construction method for treating soft foundations by multi-layer three-dimensional tracking full replacement includes the following steps:

[0007] S1: Obtain the soft interlayer to be treated, and decompose the soft interlayer into several soft rock layers that are connected in sequence in the vertical direction;

[0008] S2: Among several said soft rock strata, select several strata to be treated that have treatment conditions, and start treatment from a certain stratum to be treated that meets the conditions;

[0009] S3: Decompose a certain stratum to be treated that starts first into several replacement adits that are connected in sequence from one side to the other side of itself, and first excavate the outermost replacement adit;

[0010] S4: When the outermost replacement adit is excavated to a predetermined depth, backfill the excavated part with concrete;

[0011] S5: When the concrete reaches the support strength, excavate and backfill the remaining said replacement adits in sequence until a certain stratum to be treated that starts first is completely replaced with concrete;

[0012] S6: Repeat steps S3 - S5, select the next stratum to be treated that meets the conditions for excavation and concrete backfill until all the strata to be treated are completely replaced with concrete;

[0013] S7: Finally, excavate the remaining soft rock strata and backfill them with concrete, thus completing the full replacement of the soft interlayer with concrete.

[0014] In the prior art, for the replacement of some soft foundations, the formed concrete structure has relatively poor stress conditions, and local tensile stress often occurs during the normal operation of the arch dam, leaving hidden dangers for the safe operation of the arch dam, causing problems such as non - convergence of the deformation of the near - dam slope after impoundment. The present invention provides a construction method for treating soft foundations by multi - layer three - dimensional tracking full replacement, which can realize the full replacement of the soft foundation with a backfilled concrete structure, avoiding the potential safety hazards caused by the replacement of some soft foundations; at the same time, it can also decompose the soft foundation into several replacement adits with relatively low excavation risks for treatment, reducing the safety risks of the excavation of vertical shafts or inclined shafts such as shear - resistant holes and frame - excavation holes, and the construction of excavation and concrete backfill is also more convenient and fast. It is mainly applied to the treatment of soft foundations at the abutments of arch dams, but for soft foundations of gravity dams and other soft foundations that need to be treated, this design scheme can also be used for treatment.

[0015] Further optimization: The boundary of the outermost said replacement adit is the demarcation line between the soft foundation and the hard foundation.

[0016] Further optimization: Take the outermost replacement adit of each treatment layer as a detection hole for the soft foundation, so as to further confirm the boundary and shape of the soft foundation during the construction process.

[0017] Further optimization: During the process of excavating the replacement adit, it is necessary to use shotcrete and steel supports for temporary support.

[0018] For further optimization, before pouring backfill concrete in the replacement adit, several anchor bolts need to be embedded in the sidewall of the replacement adit. One end of each anchor bolt extends into the hard bedrock or the already poured concrete, and the other end is located in the replacement adit.

[0019] For further optimization, step S5 further includes the following sub-steps:

[0020] Before carrying out concrete backfill for the remaining replacement adit, the concrete that has been poured and backfilled on the periphery needs to be roughened.

[0021] For further optimization, when excavating the remaining soft rock strata, all the remaining soft foundations at the crown of the already backfilled and treated layer need to be dug out and then concrete is poured for backfill.

[0022] For further optimization, during the excavation of the replacement adit, at least one original soft rock foundation for support needs to be reserved in the middle of the excavation area, and the replacement adit is excavated around the original soft rock foundation.

[0023] For further optimization, after completing the excavation of the replacement adit around the original soft rock foundation, concrete is poured and backfilled in the circumferential area of the original soft rock foundation, and an exit passage connected to the original soft rock foundation is reserved;

[0024] After the concrete pouring and backfilling in the circumferential area of the original soft rock foundation is completed and reaches the support strength, the original soft rock foundation is excavated, and the area where the original soft rock foundation is located is poured with concrete for backfill;

[0025] After the concrete backfill of the area where the original soft rock foundation is located is completed, the exit passage is poured with concrete for backfill.

[0026] For further optimization, before excavating the layer to be treated, a construction access road connected to the entrance of the layer to be treated or a construction branch adit connected to the exit of the layer to be treated is also excavated.

[0027] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0028] The present invention provides a construction method for multi-layer three-dimensional tracking full replacement treatment of soft foundation, which can realize the full replacement of the soft foundation with a backfilled concrete structure, avoiding potential safety hazards caused by partial replacement of the soft foundation; at the same time, it can also decompose the soft foundation into several replacement adits with relatively low excavation risks for treatment, reducing the safety risks of shaft or inclined shaft excavations such as shear resistance holes and frame excavation holes, and the excavation and concrete backfill construction are also more convenient and fast. Description of the Drawings

[0029] To more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as limiting the scope. For those of ordinary skill in the art, without creative efforts, other relevant drawings can also be obtained based on these drawings. In the drawings:

[0030] Figure 1 It is a construction flow chart of a multi-layer three-dimensional tracking full replacement for treating soft foundation disclosed by the present invention;

[0031] Figure 2 It is a schematic plan view of the distribution of soft foundation at the downstream dam shoulder of a certain arch dam in Example 1 disclosed by the present invention;

[0032] Figure 3 It is a schematic elevation view of the treatment of soft foundation at the downstream dam shoulder of a certain arch dam in Example 1 disclosed by the present invention;

[0033] Figure 4 It is a three-dimensional schematic diagram of the distribution of soft rock at the downstream dam shoulder of a certain reservoir arch dam in Example 2 disclosed by the present invention;

[0034] Figure 5 It is a front view schematic diagram of the distribution of soft rock at the downstream dam shoulder of a certain reservoir arch dam in Example 2 disclosed by the present invention;

[0035] Figure 6 It is a backfill procedure diagram for the treatment of salt solution breccia in the 5th replacement adit in Example 2 disclosed by the present invention;

[0036] Figure 7 It is a backfill procedure diagram for the treatment of salt solution breccia in the 8th replacement adit in Example 2 disclosed by the present invention;

[0037] Figure 8 It is a backfill procedure diagram for the treatment of salt solution breccia in the 11th replacement adit in Example 2 disclosed by the present invention. Specific embodiments

[0038] To make the objectives, technical solutions, and advantages of the present invention clearer and more understandable, the present invention will be further described in detail below in combination with the embodiments and the drawings. The illustrative embodiments of the present invention and their descriptions are only used to explain the present invention and do not serve as a limitation to the present invention.

[0039] Example 1: As shown in Example 1 Figures 1-3 It provides a soft interlayer distributed at the downstream of a certain arch dam and its construction treatment procedures.

[0040] As shown in the attached Figure 2 figure, a soft interlayer is distributed at the downstream of a certain arch dam, and its width is B. After the force analysis and calculation of the arch dam, according to Figure 3In the vertical direction shown, the height of the interlayer that needs to be treated is H. If the weak interlayer is excavated once and then backfilled with concrete, the large height difference span during the excavation of the weak interlayer will bring huge safety hazards; and if shear holes, anchor holes, concrete frames and other methods are used for partial excavation, the stress condition of the partially replaced concrete structure is poor, which will bring safety hazards to the normal operation of the arch dam. The present invention proposes to achieve full replacement of the weak foundation by setting up a multi-layer three-dimensional tunnel to track the excavation and timely backfilling, and replace the weak rock mass with concrete that meets the stress requirements of the arch dam after excavation.

[0041] The specific construction method steps of the present invention are as follows:

[0042] 1) Decompose the weak interlayer of the arch dam shoulder that needs to be treated into several weak rock layers in the vertical direction. The height can generally be 3 to 12 meters according to the actual situation of the project to avoid the safety risk caused by excavating too high a height of the weak interlayer at one time. Figure 3 As shown, in this example, the weak interlayer within the height H range needs to be dealt with in the downstream of a certain arch dam, and it is divided into 7 layers.

[0043] 2) Each layer needs to be completely connected from top to bottom to ensure that all vertical weak interlayers can be excavated and processed. Each weak rock layer can be divided into several replacement flat tunnels with excavation sections of 3-10m×3-12m (width×height). The specific section size can be determined comprehensively based on the distribution shape of the weak interlayer to be processed, the project progress requirements, the configuration of construction machinery, etc. Figure 3 The third layer is divided into two left and right displacement tunnels, and the remaining layers can also be decomposed into two small left and right displacement tunnels. The cross-section of each displacement tunnel can be a conventional city gate tunnel type.

[0044] 3) A replacement tunnel of a certain layer can be excavated when conditions are met, and its excavation section is 3~10m×3~12m (width×height). Taking the third layer as an example, assuming that its construction traffic conditions are relatively good and the excavation conditions can be met earlier, the replacement tunnel on the left or right side can be excavated first. In this example, it is assumed that the replacement tunnel on the right side is excavated first. Due to the uncertainty of underground engineering, the replacement tunnel on the right side that is excavated first can also be used as an exploration hole for soft foundations, and its right boundary can be the boundary between soft foundations and hard foundations, so as to further clarify the actual boundary distribution of soft foundations. The temporary stability of the replacement tunnel on the right side can be solved by conventional "anchor spraying + steel support" measures according to the surrounding rock type.

[0045] 4) After the excavation of the right replacement adit on the third layer reaches the designed predetermined depth, the excavated part can be backfilled with concrete to support the upper rock mass and avoid the safety risks caused by the long-term exposure after the tunnel excavation. To ensure the stability of the backfilled concrete in the upper layer during the excavation of the lower layer, a part of the anchor bolts can be embedded in the hard bedrock before the upper layer concrete is poured, and a part of the anchor bolts are in the concrete to be poured. After pouring, the anchor bolts can play a stabilizing role in the upper layer concrete.

[0046] 5) After the strength of the concrete poured in the right replacement adit on the third layer can play a supporting role, the left replacement adit on the third layer that has not been excavated can be excavated. For the soft surrounding rock of the arch crown, the measures of "anchor spraying + steel support" are adopted for support, while for the hard foundation on the left boundary and the poured concrete on the right boundary of the replacement adit, the support measures can be appropriately simplified according to the safety monitoring data.

[0047] 6) After the excavation of the left replacement adit on the third layer reaches the designed predetermined depth, the excavated part can be backfilled with concrete, and then the replacement of the soft foundation on the third layer with concrete is all completed. To ensure the quality of the combination of the backfilled concrete on the left and right sides, the old concrete that has been poured should be roughened before the new concrete is poured, and at the same time, a part of the anchor bolts are embedded in the hard bedrock and the poured concrete to strengthen the stability.

[0048] 7) Continue to process the replacement adits of other layers. Select a certain layer that meets the treatment conditions and repeat steps 3) to 6). Through the above excavation and backfilling treatment methods and steps, the entire soft foundation of the arch dam abutment that needs to be treated can be completely excavated and replaced with concrete. It should be noted that for the soft foundation that has been backfilled in the lower layer during excavation, such as when assuming to excavate the fourth layer, the third layer has completed the concrete backfilling. When excavating the fourth layer, the remaining soft foundation of the arch crown part of the third layer should be dug out together to ensure that the entire soft foundation to be treated is completely cleaned.

[0049] Through the above steps, it is possible to replace the entire soft foundation with the backfilled concrete structure, avoiding the safety hazards caused by the replacement of part of the soft foundation; at the same time, it is also possible to decompose the soft foundation into several replacement adits with relatively small excavation risks for treatment, reducing the safety risks of the excavation of vertical shafts or inclined shafts such as shear resistance holes and frame excavation holes, and the construction of excavation and concrete backfilling is also more convenient and fast.

[0050] Example 2: This Example 2 is further optimized on the basis of Example 1 to optimize the internal construction procedures of the replacement adit; as Figures 4-8 described, it is the soft interlayer distributed downstream of an arch dam of a certain reservoir and its construction treatment procedures.

[0051] A certain reservoir project is located in the upper reaches of Qianhe, a left-bank tributary, in a canyon section. The water-retaining dam is a 132-meter-high roller-compacted concrete double-curved arch dam. The elevation of the dam crest is 565.30m, and the elevation of the dam bottom is 433.30m. The lithology in the dam site area is mainly composed of unequal-thickness interbeds of limestone and salt-solution breccia of the Lower Triassic Jialingjiang Formation (T 1j ). The local span of the weak foundation is up to more than 30 meters, and the up-and-down dislocation is irregularly distributed, as shown in Attachment Figure 4 and Attachment Figure 5 . Through systematic calculation and analysis of the natural state, treatment scope, treatment plan, etc. that affect the stability and deformation of the dam, the full replacement plan proposed by the present invention is adopted for the salt-solution breccia with argillaceous cementation in the T 1j ⑤ layer within the elevation range of 433.3 - 510m on the downstream side of the left dam abutment, that is, all the weak foundation within the elevation range of 433.3 - 510m is excavated and backfilled with C20 slightly expanded concrete for compaction. According to the on-site construction traffic conditions, the weak foundation to be treated is divided into 11 replacement adits from bottom to top, as shown in Table 1 for details.

[0052] Table 1: Table of characteristics of stratified treatment of weak rocks at the downstream dam abutment of the arch dam of a certain reservoir

[0053]

[0054] In actual construction, the first adit to be excavated is the 5th replacement adit, followed by the 8th replacement adit and the 11th replacement adit. Now, taking the treatment methods of these three adits as an example to further illustrate the construction steps in the specific case of the present invention. To better reflect the situation during the construction process, the time node selected for this case is October 2020, when each replacement adit was under excavation and backfilling treatment.

[0055] (1) Steps for excavating salt-solution breccia and backfilling concrete in the 5th replacement adit (EL466~473m):

[0056] Utilize the temporary construction access road built during the foundation pit excavation, enter the adit directly from the salt-solution breccia part exposed on the slope, and the cross-section of the main adit excavation is 6×7m. The excavation situation of the salt-solution breccia at EL466~473m is as shown in Attachment Figure 6As shown. Since the distribution of this layer of salt-solution breccia is relatively simple, the excavation and backfilling steps are also relatively simple. By October 2020 during excavation, there was still uncleared salt-solution breccia on the upstream side of the end inside the cave. Its property was that the upper part had low strength while the lower part had relatively high strength. The treatment method was as follows: To avoid safety risks caused by overly long excavation time, the excavated area of the 5th replacement adit was directly backfilled with slightly expansive concrete; then when excavating the salt-solution breccia replacement adit at EL473 - 480m in the upper layer, the upper half of the remaining salt-solution breccia with poor properties at EL466 - 473m was removed by local undercutting and then backfilled with concrete. The lower half of the salt-solution breccia with better strength and mixed cementation could be retained, which could meet the requirements of force transfer between the upstream and downstream of the bedrock.

[0057] (2)Steps for clearing and concrete backfilling of the salt-solution breccia replacement adit of the 8th replacement adit (EL486 - 493m):

[0058] The excavation cross-section of the main adit is 6×7m. During actual construction, it was carried out along the boundary where limestone intersects with salt-solution breccia. First, the excavation around the salt-solution breccia was completed (as shown in areas C1, C2, C3, and C4 in the attachment Figure 7 ), and the salt-solution breccia in the middle was retained as a support to ensure the stability of the cavern (as shown in areas B1 and B2 in the attachment Figure 7 ). For the remaining soft salt-solution breccia that has not been cleared (as shown in areas B1 and B2 in the attachment Figure 7 ), the method of backfilling concrete in parts to form a support and then excavating in blocks was adopted. See the attachment Figure 7 for details. To more clearly reflect the excavation procedure of the middle argillaceous salt-solution breccia, this figure selects the time period when the excavation around the perimeter was completed in October 2020 and the middle argillaceous salt-solution breccia has not been excavated yet. The steps for salt-solution breccia replacement treatment of the 8th replacement adit (EL486 - 493m) are shown in Table 2.

[0059] Table 2: Table of steps for salt-solution breccia replacement treatment of the 8th replacement adit (EL486 - 493m)

[0060]

[0061] (3)Steps for clearing and concrete backfilling of the salt-solution breccia replacement adit of the 11th replacement adit (EL506 - 513m):

[0062] The excavation cross-section of the main adit is 6×7m. Due to restrictions of the on-site terrain conditions, during actual construction, the 1# branch adit was first excavated from the 506 construction access road and entered the cave. It was carried out along the boundary where limestone intersects with salt-solution breccia. First, the excavation around the salt-solution breccia was completed (as shown in areas C1, C2, and C3 in the attachment Figure 8 ), and the salt-solution breccia in the middle was retained as a support to ensure the stability of the cavern (as shown in the attachment Figure 8in Areas B1 and B2 shown). Later, due to the need for dam foundation excavation, the 506 access road was dug through. To avoid affecting the dam construction period, a 503 construction adit was added as the construction access for later excavation and backfilling. To avoid potential safety hazards caused by too large an excavation span, for the remaining unexcavated soft salt - dissolved breccia (as shown in Areas A1, B1, and B2), the method of backfilling concrete in parts to form a support and then excavating in blocks was adopted. To more clearly reflect the excavation process of the middle argillaceous salt - dissolved breccia, this figure selects the time period when the peripheral excavation is completed and the middle argillaceous salt - dissolved breccia has not been excavated. The replacement treatment steps of the salt - dissolved breccia in the 11th replacement adit (EL506 - 513m) are shown in Table 3 in detail. Figure 8 in Areas A1, B1, and B2 shown), the method of backfilling concrete in parts to form a support and then excavating in blocks was adopted. To more clearly reflect the excavation process of the middle argillaceous salt - dissolved breccia, this figure selects the time period when the peripheral excavation is completed and the middle argillaceous salt - dissolved breccia has not been excavated. The replacement treatment steps of the salt - dissolved breccia in the 11th replacement adit (EL506 - 513m) are shown in Table 3 in detail.

[0063] Table 3: Replacement Treatment Steps of Salt - Dissolved Breccia in the 11th Replacement Adit (EL506 - 513m)

[0064]

[0065] The treatment of the other layers is basically similar to the above - mentioned three layers, and will not be elaborated in this article. As of the end of 2023, the excavation and backfilling treatment of the salt - dissolved breccia on the downstream side of the left dam shoulder of this reservoir has been completed. No production safety accidents occurred during the process, and the effect of the backfilled concrete is also good. No cracks or other situations were found, indicating the safety and reliability of the present invention.

[0066] The specific embodiments described above further elaborate on the purpose, technical solutions, and beneficial effects of the present invention. It should be understood that the above - mentioned are only specific embodiments of the present invention and are not used to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A construction method for treating soft foundation by multi-layer three-dimensional tracking full replacement, characterized in that, It includes the following steps: S1: Obtain the weak interlayer to be processed, and decompose the weak interlayer into a number of sequentially connected weak rock layers in the vertical direction; S2: Among the number of weak rock layers, select a number of layers to be processed that meet the treatment conditions, and start the treatment from a layer to be processed that meets the conditions; S3: Decompose a layer to be processed that starts first into a number of sequentially connected replacement adits from one side to the other side of itself, and first excavate the outermost replacement adit; S4: When the outermost replacement adit is excavated to a predetermined depth, backfill the excavated part with concrete; S5: When the concrete reaches the support strength, sequentially excavate and backfill the remaining replacement adits until all the concrete replacements of a layer to be processed that starts first are completed; S6: Repeat steps S3 - S5, select the next layer to be processed that meets the conditions for excavation and concrete backfilling until all the layers to be processed are completely replaced with concrete; S7: Finally, excavate the remaining weak rock layers and backfill them with concrete, thereby completing the full concrete replacement of the weak interlayer.

2. The construction method of a multi-layer three-dimensional tracking full replacement for treating soft foundation according to claim 1, characterized in that, The boundary of the outermost replacement adit is the demarcation line between the soft foundation and the hard foundation.

3. The construction method for treating soft foundation by multi-layer three-dimensional tracking full replacement according to claim 1, characterized in that, Take the outermost replacement adit of each treatment layer as a detection adit for the soft foundation to further confirm the boundary and shape of the soft foundation during the construction process.

4. The construction method for treating soft ground by multi-layer three-dimensional tracking full replacement according to claim 1, characterized in that, During the excavation of the replacement adit, temporary support shall be carried out by shotcreting and steel support.

5. The construction method of a multi-layer three-dimensional tracking full replacement for treating soft foundation according to claim 1, characterized in that, Before pouring backfill concrete in the replacement adit, a number of anchor bolts shall be embedded in the side wall of the replacement adit. One end of the anchor bolt extends into the hard bedrock or the already poured concrete, and the other end is located in the replacement adit.

6. The construction method for treating soft foundation by multi-layer three-dimensional tracking full replacement according to claim 1, characterized in that, The said step S5 further includes the following sub - steps: Before backfilling the remaining replacement adits with concrete, it is necessary to roughen the concrete that has been poured and backfilled on the periphery.

7. A construction method for treating soft foundation by multi-layer three-dimensional tracking full replacement according to claim 1, characterized in that, When excavating the remaining weak rock layers, it is necessary to dig out all the remaining soft foundation at the crown of the already backfilled and treated layers and carry out concrete pouring and backfilling.

8. A construction method for treating soft foundation by multi-layer three-dimensional tracking full replacement according to any one of claims 1 to 6, characterized in that, During the excavation of the replacement adit, at least one original soft rock foundation for support shall be reserved in the middle of the excavation area, and the replacement adit shall be excavated around the original soft rock foundation.

9. A construction method for multi - layer three - dimensional tracking full replacement treatment of soft foundation according to claim 8, characterized in that: After completing the excavation of the replacement adit around the original soft rock foundation, pour and backfill the circumferential area of the original soft rock foundation, and reserve an exit passage connected to the original soft rock foundation; After the concrete pouring and backfilling of the circumferential area of the original soft rock foundation are completed and reach the support strength, excavate the original soft rock foundation and pour and backfill the area where the original soft rock foundation is located; After the concrete backfilling of the area where the original soft rock foundation is located is completed, pour and backfill the exit passage with concrete.

10. A construction method for treating soft foundation by multi-layer three-dimensional tracking full replacement according to claim 1, characterized in that Before excavating the layer to be processed, a construction access road connected to the entrance of the layer to be processed or a construction branch tunnel connected to the exit of the layer to be processed is also excavated.

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