Method for preventing wall-adhering seepage damage of dam-penetrating structure in cold region by wedging broken stone consolidated viscous backfill soil

Abstract

The invention relates to a method for preventing wall-adhering seepage damage of a dam penetrating structure in a cold region by wedging gravel consolidation viscous backfill soil, and belongs to the technical field of construction methods for improving safety of newly-built small reservoir earth dams or dikes in the cold region. The backfill soil layer which is in contact with the foundation concrete cushion layer and is connected with the undisturbed soil is tamped, the laid cohesive soil body is compacted, all the gravels or the pebbles are tamped into the cohesive soil body, and the cohesive soil body containing the gravels or the pebbles and connected with the dam penetrating structure is tamped and compacted through a hammer and filled to the designed height. The method has the advantages that pore water of the soil body is quickly discharged by a pressure compaction method of wedging the broken stones to dissipate pore water pressure in the soil body to form soil body consolidation, so that after the soil body is quickly consolidated, soil body particles resist seepage entrainment, the mechanical property index is obviously improved, and the structure is well connected with a backfill soil contact surface; and a seepage channel is effectively prevented from being formed in the contact surface of the dam penetrating structure and backfill soil, and the effect is good after multiple practical engineering applications.

Description

Technical Field

[0001] The present invention belongs to the technical field of construction methods for improving the safety of newly built small reservoir earth dams or embankments in cold regions, and is mainly used for the design and construction method technology for preventing the contact surface between the dam-penetrating structure and the viscous backfill soil of newly built small reservoir earth dams or embankments in seasonally frozen soil regions from being easily damaged by wall seepage in the spring. Background Art

[0002] The construction of new small and medium-sized reservoirs, as well as the hazard removal and reinforcement construction or embankment construction, all involve dam-penetration or embankment-penetration projects, such as spillways, water diversion tunnels, spillways and embankment-penetrating culverts.

[0003] For small reservoirs, the buildings passing through the dam are shorter, and the seepage path of the contact surface between the buildings and the backfill soil is also shorter, which makes it easier for wall seepage to form. Soil particles with insufficient consolidation are difficult to resist the entrainment of wall seepage. Over time, seepage channels may be formed, eventually leading to project damage.

[0004] At present, water conservancy projects often enter the use period immediately after the completion of construction. In seasonally frozen soil areas, newly built reservoirs are immediately filled with water, and the soil consolidation time is short, that is, it has not yet formed complete consolidation. At this time, after the soil freezes in the winter with the dam or dike structure, it warms up quickly in spring because the other side of the dam or dike structure that is not in contact with the backfill soil is directly in contact with the air or water. A thin frost layer forms on the contact surface between the structure wall and the backfill soil due to the day and night temperature changes. As the temperature rises, the thin frost layer turns into water, and this layer of water is the initiator of wall-adherent seepage. In the spring, under the action of flowing water, the reservoir water level rises, and a water film forms infiltration under the action of water pressure. After a period of time, wall-adherent seepage is formed. If the wall-adherent seepage has the effect of entraining soil particles on the suddenly soaked and melted soil, it will cause the lower part of the spillway to be hollowed out, causing damage to the project. See. Figure 1 .

[0005] During the peach blossom flood period, the water level of the reservoir rises and the water is discharged through the flood discharge tunnel. A thin frost layer will form on the backfill soil at the contact surface between the flood discharge structure wall and the backfill soil and melt quickly. The thin frost layer formed on the backfill soil contact surface will turn into a water film. Under the action of water pressure within a certain period of time, the wall seepage will form wall seepage. If the long-term wall seepage entrains the backfill soil, especially the soil particles that are suddenly soaked and melted, it may cause wall seepage damage. Figure 2 .

[0006] Many reservoir projects in the Three North Regions have failed due to wall seepage, causing great losses. In Jilin Province alone, more than a dozen small reservoirs failed due to wall seepage in the spring.

[0007] For levees, they are generally dry for a long time during the non-flood season. In the event of a sudden flood, wall seepage is likely to occur. Soil with insufficient consolidation is difficult to resist the entrainment of wall seepage. Over time, seepage channels may be formed, eventually leading to project damage.

[0008] If a reservoir or embankment project has not been used for a long time, such as during the repair of a slope protection project, the reservoir needs to be emptied. At this time, the backfill soil around the dam-penetrating building will shrink as the water evaporates, and tiny pores or gaps may be formed between the building and the backfill soil. In the case of a sudden inflow of water with a certain head, the infiltration under the action of water pressure will form a water film in the pores or gaps between the building and the backfill soil. As the head of water increases, the wall-sticking seepage gradually forms wall-sticking seepage under the action of water pressure, and the backfill soil particles are entrained. After a period of time, pipe bursts or soil flow may occur near the building. In severe cases, it will cause project damage, such as Figure 3 shown. Summary of the invention

[0009] The present invention provides a method for wedging crushed stones to consolidate viscous backfill soil to prevent wall seepage damage of through-dam structures in cold regions, so as to solve the problem that the contact surface between the through-dam structure and the viscous backfill soil of a newly built small reservoir earth dam or embankment in seasonally frozen soil regions is prone to wall seepage damage in spring.

[0010] The technical solution adopted by the present invention comprises the following steps: (1) Compact the backfill soil layer that is in contact with the foundation concrete cushion layer and connected to the original soil, so that the upper surface of the backfill soil layer is flush with the upper surface of the foundation concrete cushion layer; (2) Laying the clay body on the upper surface of the backfill soil layer and the upper surface of the foundation concrete cushion layer, and compacting the laid clay body; (3) Sporadically lay a layer of crushed stone or pebbles with a particle size of 2 to 5 cm on the upper surface of the compacted clay soil, and tamp the crushed stone or pebbles into the clay soil; (4) Compact the clay soil containing gravel or pebbles at the junction with the dam structure with a hammer, and use a fan to dry the wet layer; (5) Repeat steps (2) to (4) to fill the clay soil and gravel or pebbles to the designed height.

[0011] The compaction degree of the backfill soil layer in step (1) is 93-97%.

[0012] In the step (2), the weight proportion of the clay particles in the clay body is greater than 30%, and the water content is 17-25%.

[0013] The thickness of the composite backfill soil laid in step (2) is 25-30 cm.

[0014] The width of the composite backfill soil laid in step (2) is not less than 50 cm.

[0015] In the step (2), the composite backfill soil is rolled or compacted to a density of 93% to 96%.

[0016] The particle size of the gravel or pebbles in step (3) is 2 to 5 cm.

[0017] The coverage of the scattered gravel or pebbles in step (3) is 40-80%.

[0018] The compaction degree of the joint with the dam-penetrating structure in step (4) is 97-99%.

[0019] The advantages of the present invention are that the pore water of the soil is quickly discharged by the pressure compaction method of wedge-in gravel to dissipate the pore water pressure in the soil to form soil consolidation, so that after the soil is quickly consolidated, the soil particles can resist seepage entrainment and the mechanical performance index is significantly improved, so that the contact surface between the structure and the backfill soil is well connected, and the formation of a seepage channel between the contact surface of the dam-penetrating structure and the backfill soil is effectively prevented. For general low liquid limit clay and even clay with a certain degree of dispersibility, a good consolidation effect is achieved, and the anti-seepage, anti-entrainment or anti-scouring ability of the backfill soil is effectively improved. The construction procedure can be simplified and the construction progress can be accelerated. The ground material can be combined with the backfill soil to form a good connection between the dam-penetrating structure and the contact surface of the backfill soil, greatly improving the anti-seepage, anti-entrainment or anti-scouring ability of the backfill soil. No large-scale engineering equipment is required, and general construction units can operate it, which can greatly improve the safety of the dam-penetrating project. After being applied in many actual projects, the effect is good, and the engineering damage caused by wall seepage is effectively solved. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 The lower part of the spillway is hollowed out due to seepage along the wall caused by flowing water Figure 2 Peach blossom water caused wall seepage, leading to the collapse of the reservoir spillway Figure 3 Sudden water storage after slope repair caused wall seepage, resulting in soil damage to the reservoir spillway tunnel Figure 4 Construction procedures for laying crushed stone to compact and drain pore water Figure 5 The pore water of the wedged gravel is drained and blown dry to complete the compaction of a layer of backfill soil. DETAILED DESCRIPTION Example 1

[0021] The following steps are involved: (1) Compact the backfill soil layer 2 that is in contact with the foundation concrete cushion layer 1 and connected to the original soil. The compaction degree of the backfill soil layer is 93%, and the upper surface of the backfill soil layer 2 is flush with the upper surface of the foundation concrete cushion layer 1; (2) Lay the clay body 3 on the upper surface of the backfill soil layer 2 and the upper surface of the foundation concrete cushion layer 1 with a thickness of 25 cm and a width of 50 cm, and compact the laid clay body 3 by rolling or tamping until the density reaches 93%; The weight of the cohesive particles in the cohesive soil is 30%, and the water content is 17%; (3) A layer of crushed stones or pebbles 4 with a particle size of 2 to 5 cm is scattered on the surface of the compacted clay body 3. The coverage of the scattered crushed stones or pebbles is 40%. The layer of crushed stones or pebbles 4 is completely rammed into the clay body 3; (4) Compact the clay soil containing gravel or pebbles at the junction 6 with the dam-penetrating structure 5 with a hammer, and the compaction degree at the junction with the dam-penetrating structure is 97%, and use a fan to blow dry the wet layer; (5) Repeat steps (2) to (4) to fill the clay soil and gravel or pebbles to the designed height. Example 2

[0022] The following steps are involved: (1) Compact the backfill soil layer 2 that is in contact with the foundation concrete cushion layer 1 and connected to the original soil. The compaction degree of the backfill soil layer is 95%, and the upper surface of the backfill soil layer 2 is flush with the upper surface of the foundation concrete cushion layer 1; (2) Lay the clay body 3 on the upper surface of the backfill soil layer 2 and the upper surface of the foundation concrete cushion layer 1 with a thickness of 28 cm and a width of 70 cm, and compact the laid clay body 3 by rolling or tamping until the density reaches 95%; The weight of the cohesive particles in the cohesive soil is 40%, and the water content is 21%; (3) A layer of crushed stones or pebbles 4 with a particle size of 2 to 5 cm is scattered on the surface of the compacted clay body 3. The coverage of the scattered crushed stones or pebbles is 60%. The layer of crushed stones or pebbles 4 is completely rammed into the clay body 3; (4) Compact the clay soil containing gravel or pebbles at the junction 6 with the dam-penetrating structure 5 with a hammer, and the compaction degree at the junction with the dam-penetrating structure is 98%, and use a fan to blow dry the wet layer; (5) Repeat steps (2) to (4) to fill the clay soil and gravel or pebbles to the designed height. Example 3

[0023] The following steps are involved: (1) Compact the backfill soil layer 2 that is in contact with the foundation concrete cushion layer 1 and connected to the original soil. The compaction degree of the backfill soil layer is 97%, and the upper surface of the backfill soil layer 2 is flush with the upper surface of the foundation concrete cushion layer 1; (2) Lay the clay body 3 on the upper surface of the backfill soil layer 2 and the upper surface of the foundation concrete cushion layer 1 with a thickness of 30 cm and a width of 100 cm, and compact the laid clay body 3 by rolling or tamping until the density reaches 96%; The weight of the cohesive particles in the cohesive soil is 50%, and the water content is 25%; (3) A layer of crushed stones or pebbles 4 with a particle size of 2 to 5 cm is scattered on the surface of the compacted clay body 3. The coverage of the scattered crushed stones or pebbles is 80%. The layer of crushed stones or pebbles 4 is completely rammed into the clay body 3; (4) Compact the clay soil containing gravel or pebbles at the junction 6 with the dam-penetrating structure 5 with a hammer, and the compaction degree at the junction with the dam-penetrating structure is 99%, and use a fan to blow dry the wet layer; (5) Repeat steps (2) to (4) to fill the clay soil and gravel or pebbles to the designed height.

[0024] The present invention is further explained below through theoretical analysis.

[0025] In newly built water-retaining structural projects in seasonally frozen areas, that is, projects where the backfill soil has not yet been completely consolidated, the water level will rise rapidly due to the rapid temperature rise in spring and the rapid flow of flowing water or peach blossom water. The drainage structure will operate because the temperature of the flowing water side of its structure wall will rise while the backfill soil is still frozen. The large temperature difference will cause a thin frost layer to form on the contact surface between the backfill soil and concrete and convert it into a water film. The soil layer at the contact surface may become loose, and the pressure water molecules caused by the water head move along the water film. This is wall seepage, which is different from the bypass assumption. Wall seepage may entrain backfill soil particles. This is the cause of wall seepage damage.

[0026] According to consolidation theory, the time required for the consolidation of clay soil is proportional to the square of the drainage distance, that is, the thicker the soil layer, the longer the consolidation time will last. Under the action of rapid consolidation pressure, the consolidation process of the soil layer is the process of dissipation of pore water pressure. In order to accelerate the consolidation of the soil layer, the most effective way is to shorten the drainage distance of the soil layer. In the compaction process of layered backfill, generally speaking, the pore water after strong extrusion dissipates in 6 directions. Since the layered backfill soil layer is thin and is almost simultaneously squeezed by the wedge-in gravel, the main direction of pore water precipitation after strong extrusion can only be along the upper and lower sides of the soil layer. When precipitated from the bottom, the pore water can be absorbed by the dried fill soil in the lower layer, because the compaction force on the upper side of the soil layer is the largest during the wedge-in process of the gravel, and the pore water precipitated is also the most. The precipitated pore water visible on the surface can be dried with a high-power hair dryer. This is because the pore water pressure near the drainage surface dissipates quickly, and the consolidation settlement progresses quickly, so the strain is large, while the pore water pressure near the non-drainage surface dissipates slowly and the strain is relatively small. However, since the backfill soil layer is relatively thin, the compaction pressure in the process of rapid consolidation of the backfill soil layer by wedging crushed stone decays only to a limited extent from the top of the soil layer to the bottom, and the compaction consolidation pressure is much greater than the pressure of its own weight and additional load, so that the pore water pressure dissipates quickly, and the density and anti-permeability of the backfill soil are greatly improved. Therefore, the backfill soil produced by the method of the present invention will not produce secondary consolidation deformation or the so-called creep.

[0027] The present invention adopts a method of using crushed stones as wedges to squeeze and drain water in a rolled or compacted thin clay layer, so that the pore water can be visibly discharged directly from the surface, thus achieving the purpose of minimizing the pore water drainage distance.

[0028] Theoretical and experimental results show that the method of compacting clay and then tamping in crushed stone does affect the density of backfill soil. The increase in compression modulus means that the shear resistance of the backfill soil is improved, that is, the ability of the backfill soil to resist seepage entrainment is improved. The backfill soil is quickly consolidated by compacting crushed stone, so as to prevent the wall seepage between the structure and the backfill soil from entraining soil particles.

[0029] The pore water in this method has been effectively discharged, so the pore water pressure will not increase with tamping. The appropriate amount of wedged gravel can basically reduce the porosity ratio to about 0.6. Therefore, the frost heave of the soil layer itself in winter is extremely low, and the frost heave basically has no effect on the safety of the structure.

[0030] The calculation results show that the porosity of the backfill soil compacted by crushed stone and quickly consolidated is 2% lower than that of the backfill soil compacted directly, which means that the pore water is discharged by 2% more.

[0031] The present invention is further illustrated by the results of the field construction experiment below. Generally, under the action of load pressure, the water in the pores of the original clay soil is slowly discharged, the pore water pressure gradually dissipates, the pore volume slowly decreases, the soil undergoes consolidation deformation, the effective stress gradually increases, the strength of the soil gradually increases, and the shear strength increases accordingly. With the consolidation pressure as the horizontal axis and the porosity as the vertical axis, a compression curve is drawn. As the consolidation pressure increases, the compression curve of the consolidation pressure and porosity extends downward from left to right. For disturbed soil, the curve extends downward more steeply.

[0032] In engineering, there is no time to wait for the water in the pores to be slowly drained and the pore water pressure to gradually dissipate to achieve the soil consolidation requirements. Usually, the method of adding loads such as rolling or tamping is used to accelerate consolidation. This engineering experiment uses wedge-in crushed stone to accelerate consolidation based on the layered backfill soil tamping, that is, to make the pore water drainage distance as short as possible, so that the backfill soil can be consolidated faster.

[0033] Before compaction, the soil particles are in loose contact with each other and the pores are relatively large. The compaction process applies pressure to the soil, which reduces the porosity of the foundation soil and increases its density. During the deformation of the soil, the soil particles are oriented, the large pores decrease, and they gather towards the micropores. The pore water pressure gradually dissipates, forming the compaction of the soil. The soil particles undergo irreversible changes such as changes in shape and position, and plastic hardening. When the porosity of the soil gradually decreases to the limit porosity, the tamping amount decreases and gradually approaches a certain stable value, then it can generally be considered that the foundation soil has been compacted at this time.

[0034] However, for clay, the desired compaction density may not be achieved. Generally, when the compaction density of clay reaches about 90% to 93% and the compaction amount is less than 0.3 to 0.5 cm, the effect of further rolling or compaction may not be obvious, and there may be a situation similar to that of plasticine. The main reason for this kind of problem is that the pore water cannot be discharged in time, and the pore water bears the rolling or compaction pressure.

[0035] For soil that meets the design requirements, the layered filling method can be used to backfill soil close to the vertical wall of the dam structure, with a filling thickness of no more than 30 cm and a filling width of no less than 50 cm. After the rolling is completed, a layer of crushed stone or pebbles with an average thickness of about 2 to 5 cm is spread on top, and the tamping is forcibly driven into the compacted soil layer to forcefully compact the soil. Figure 4 .

[0036] This method of wedging gravel and compacting has a short pore water drainage path, which allows the pore water to be quickly discharged. At this time, water can be seen being squeezed out on the surface, and the discharged water can be quickly blown dry by a fan, and the pore water pressure is quickly dissipated. Especially for soil that is not turned over and dried enough, the squeezed water is more obvious. It can effectively reduce the porosity of the soil, and use compaction and drainage to achieve the purpose of rapid consolidation to improve the anti-seepage, anti-entrainment or anti-scouring capabilities of the backfill soil. Use a fan to blow dry the discharged pore water, and the compaction and drainage process of this layer of backfill soil is completed, and the next layer of backfill soil can be constructed, such as Figure 5 .

[0037] The most critical part is the interface between the backfill soil and the building, which can be compacted by hammering. The compacted backfill soil at the interface with the building will not only squeeze out the pore water, but also make the clay particles in the soil directly stick to the building contact surface, thus improving the connection effect between the backfill soil and the contact surface.

[0038] Field test results show that the dry density of backfill soil can reach 1.71g / m 3 .

Claims

1. A method for wedging crushed stones to consolidate viscous backfill soil to prevent wall seepage damage of dam-through structures in cold regions, characterized in that: The following steps are involved: (1) Compact the backfill soil layer 2 that is in contact with the foundation concrete cushion layer 1 and connected to the original soil, so that the upper surface of the backfill soil layer 2 is flush with the upper surface of the foundation concrete cushion layer 1; (2) Laying the clay body 3 on the upper surface of the backfill soil layer 2 and the upper surface of the foundation concrete cushion layer 1, and compacting the laid clay body 3; (3) A layer of crushed stones or pebbles 4 with a particle size of 2 to 5 cm is scattered on the upper surface of the compacted clay body 3, and the layer of crushed stones or pebbles 4 is completely rammed into the clay body 3; (4) Compact the clay soil containing gravel or pebbles at the junction with the dam-penetrating structure 5 with a hammer, and dry the wet layer with a fan; (5) Repeat steps (2) to (4) to fill the clay soil and gravel or pebbles to the designed height.

2. The method of wedging crushed stone to consolidate viscous backfill soil to prevent wall seepage damage of dam-through structures in cold regions according to claim 1 is characterized in that: The compaction degree of the backfill soil layer in step (1) is 93-97%.

3. The method of wedging crushed stone to consolidate viscous backfill soil to prevent wall seepage damage of dam-through structures in cold regions according to claim 1, characterized in that: In the step (2), the weight proportion of the clay particles in the clay body is greater than 30%, and the water content is 17-25%.

4. The method of wedging crushed stone to consolidate viscous backfill soil to prevent wall seepage damage of dam-through structures in cold regions according to claim 3, characterized in that: The thickness of the composite backfill soil laid in step (2) is 25-30 cm.

5. The method of wedging crushed stone to consolidate viscous backfill soil to prevent wall seepage damage of dam-through structures in cold regions according to claim 3, characterized in that: The width of the composite backfill soil laid in step (2) is not less than 50 cm.

6. The method of wedging crushed stone to consolidate viscous backfill soil to prevent wall seepage damage of dam-through structures in cold regions according to claim 3, characterized in that: In the step (2), the composite backfill soil is rolled or compacted to a density of 93% to 96%.

7. The method of wedging crushed stone to consolidate viscous backfill soil to prevent wall seepage damage of dam-through structures in cold regions according to claim 1, characterized in that: The particle size of the gravel or pebbles in step (3) is 2 to 5 cm.

8. The method of wedging crushed stones to consolidate viscous backfill soil to prevent seepage damage to the dam structure in cold regions according to claim 1, characterized in that: The coverage of the scattered gravel or pebbles in step (3) is 40-80%.

9. The method of wedging crushed stones to consolidate viscous backfill soil to prevent wall seepage damage of dam-through structures in cold regions according to claim 1, characterized in that: The compaction degree of the joint with the dam-penetrating structure in step (4) is 97-99%.

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