Method for preventing wall-attached seepage damage of dam penetrating structure of earth dam in cold region by wedging gravel composite backfill soil

Abstract

The invention relates to a method for preventing wall-adhering seepage damage of a dam penetrating structure of a cold region earth dam by wedging gravel composite backfill soil, and belongs to the technical field of construction methods for improving safety of newly-built small reservoir earth dams or dikes in cold regions. And a backfill soil layer which is in contact with the foundation concrete cushion layer and is connected with the undisturbed soil is tamped, the laid composite backfill soil is compacted, all the layer of gravel or pebbles are tamped into the composite backfill soil, and all the steps are repeated to fill the composite backfill soil to the designed height. The method has the advantages that a certain binding force exists between the backfill soil and a building contact surface area, the compacted composite backfill soil has high strength, and gravels are laid and compacted into the compacted backfill soil, so that a good seamless binding surface between the backfill soil and the building is formed. Due to the fact that the compression modulus is improved, the anti-shearing capacity is enhanced, the backfill soil can be tightly combined with the contact face of the building through the applied pressure, wall-attached seepage water can be resisted and even eliminated, and the seepage entrainment resisting capacity is improved.

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 of newly built small reservoir earth dams or embankments in seasonally frozen soil regions and sandy backfill soil or clay with a certain degree of dispersion from being easily damaged by wall seepage in the spring. Background Art

[0002] The construction of new or risk-relief reinforcement for small and medium-sized reservoirs all involve dam-penetrating projects, such as spillways, water tunnels and spillways. In seasonally frozen soil areas, due to the short construction period, the backfill soil around the building structure is disturbed, especially the sandy backfill soil, which is easy to be rolled loose and lacks density, and may produce a certain degree of permeability. For dispersed clay, not only is the construction more difficult, but this type of soil is also very easy to disintegrate after being soaked in water, and its soil particles will be entrained by the seepage water, causing project damage. In the Northeast region, there are many projects damaged by wall seepage in spring, and the losses caused are also large.

[0003] Wall seepage damage is prone to occur in seasonal frozen soil areas under the following environmental influences: Water is stored immediately after the construction is completed. If the soil consolidation time is short, the soil that has not been completely consolidated will freeze in the winter with the dam-penetrating structure. In the spring, the air surface in contact with the dam-penetrating structure warms up quickly. A thin frost layer is formed on the contact surface between the structure wall and the fill due to the temperature changes between day and night. As the temperature rises, the thin frost layer turns into water, and under pressure, micro-seepage turns into infiltration, and then forms wall-attached seepage. Especially for sandy or dispersed soils, if the consolidation time is short, the soil that has not been completely consolidated will freeze in the winter with the dam-penetrating structure. In the spring, the air surface in contact with the dam-penetrating structure warms up quickly. A thin frost layer is formed on the contact surface between the structure wall and the fill due to the temperature changes between day and night. As the temperature rises, the thin frost layer turns into water, and under pressure, micro-seepage turns into infiltration, and then forms wall-attached seepage. Sandy or dispersed soils, due to the characteristics of the soil, will disperse when they come into contact with water, and their particles are easily entrained by the seepage water. After a certain period of time, pipe bursts may occur, such as Figure 1 As shown, this ultimately leads to project destruction.

[0004] For small reservoirs, the seepage path is short, which makes it easier to form wall seepage. The soil with insufficient consolidation is difficult to resist seepage entrainment. Over time, seepage channels may form, and finally, the project will be damaged. Figure 2 shown.

[0005] For dikes built mainly with dispersed soil, buildings passing through the dikes may also suffer from wall seepage damage in spring, such as Figure 3 shown.

[0006] It can be seen from this that it is necessary to develop a low-cost method that can both simplify the construction procedures and speed up the construction progress to effectively prevent the formation of good consolidation between the contact surface between the dam-penetrating structure and the backfill soil, and improve the backfill soil's anti-seepage, anti-entrainment or anti-scouring capabilities. This will allow general construction units to operate and improve the safety of dam-penetrating projects. Summary of the invention

[0007] The invention provides a method for wedging crushed stone composite backfill soil to prevent seepage damage to the dam-penetrating structure of earth dams in cold regions, so as to solve the existing problem of seepage damage to the dam-penetrating structure of earth dams in cold regions.

[0008] 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 composite backfill soil on the upper surface of the backfill soil layer and the upper surface of the foundation concrete cushion layer, and compacting the laid composite backfill soil; (3) Sporadically lay a layer of crushed stone or pebbles on the surface of the compacted composite backfill soil, and tamp the entire layer of crushed stone or pebbles into the composite backfill soil; (4) Compact the composite backfill soil containing gravel or pebbles at the junction with the dam-penetrating structure with a hammer, and use a fan to dry the wet layer; (5) Repeat steps (2) to (4) to fill the composite backfill soil to the designed height.

[0009] The compaction degree of the backfill soil layer in step (1) is 93-97%.

[0010] The composite backfill soil in step (2) is composed of the following raw materials in parts by weight: Sandy loam or loam or dispersed soil, soil moisture content is 17-25%, 1000 parts; Grade Ⅰ or Ⅱ fly ash, 0 to 200 parts; Grade I or II slaked lime, 20 to 200 parts.

[0011] The thickness of the composite backfill soil laid in step (2) is 25-30 cm.

[0012] The width of the composite backfill soil laid in step (2) is not less than 50 cm.

[0013] In the step (2), the composite backfill soil is rolled or compacted to a density of 93% to 95%.

[0014] The particle size of the gravel or pebbles in step (3) is 2 to 5 cm.

[0015] The coverage of the scattered gravel or pebbles in step (3) is 30-80%.

[0016] In the step (4), the compaction degree at the junction with the dam-penetrating structure is greater than 97%.

[0017] The advantages of the present invention are that there is a certain bonding force between the backfill soil and the building contact surface area, and the backfill soil and the building contact surface area are basically seamlessly connected. The compacted composite backfill soil has high strength, and the gravel is laid and rammed into the compacted backfill soil, which is equivalent to applying pressure on the backfill soil and the building contact surface area, increasing the pressure of the backfill soil layer on the contact surface, and the cementitious material is directly seamlessly connected to the building, forming a good seamless bonding surface between the backfill soil and the building. Due to the increase in compression modulus, its shear resistance is enhanced, and the applied pressure enables the backfill soil to be tightly combined with the building contact surface, which can resist the wall seepage water or even eliminate the wall seepage water, that is, the ability to resist seepage entrainment is increased. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is the piping diagram formed by the seepage along the wall of the pond dam caused by the flowing water; Figure 2 This is a diagram of seepage damage along the spillway caused by sandy soil particles carried along by the flowing water; Figure 3 This is a diagram of the backfill soil loss on the contact surface of the embankment due to the rapid melting of snow and infiltration along the wall; Figure 4 This is a schematic diagram of step (1) of the present invention after the backfill soil layer is compacted; Figure 5 is a schematic diagram of the present invention after laying the composite backfill soil in step (2); Figure 6 is a schematic diagram of step (3) of the present invention in which a layer of crushed stones or pebbles is scattered on the upper surface of the compacted composite backfill soil; Figure 7 is a schematic diagram of the step (3) of the present invention after all the gravel or pebbles are rammed into the composite backfill soil; Figure 8 This is a schematic diagram of step (5) of the present invention after repeating steps (2) and (3) to fill another layer of composite backfill soil. In the figure, no crushed stone or pebble layer is tamped in. Fig. 9 This is a schematic diagram of the process of completing two layers of wedged crushed stone composite backfill soil layers after step (5) of the present invention repeats steps (2) to (4). DETAILED DESCRIPTION

[0019] Example 1 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 2 is 93%. The upper surface of the backfill soil layer 2 is flush with the upper surface of the foundation concrete cushion layer 1. Figure 4 ; (2) Lay the composite backfill soil 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. Compact the laid composite backfill soil 3 by rolling or tamping until the density is 93%. Figure 5 ; The composite backfill soil 3 is composed of the following raw materials in parts by weight: Sandy loam, soil moisture content is 17%, 1000kg; Grade I or II slaked lime, 20 kg; (3) A layer of crushed stone or pebbles 4 with a particle size of 2 to 5 cm is scattered on the surface of the compacted composite backfill soil 3. The coverage of the scattered crushed stone or pebbles 4 is 30%. Figure 6 , tamp all the gravel or pebbles 4 into the composite backfill soil 3, see Figure 7 , at this time you can see the surface is moist; (4) The composite backfill soil 3 containing gravel or pebbles 4 at the junction 6 with the dam-penetrating structure 5 is compacted by hammering, and the compaction degree at the junction with the dam-penetrating structure 5 is greater than 97%, see Figure 7 , use a fan to dry the wet layer; (5) Repeat steps (2) to (4) to fill the composite backfill soil 3 to the designed height. Figure 8 , 9 . Example 2

[0020] 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 2 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 composite backfill soil 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 composite backfill soil 3 by rolling or tamping until the density is 94%; The composite backfill soil 3 is composed of the following raw materials in parts by weight: Loam, soil moisture content is 21%, 1000kg; 100kg of grade Ⅰ or Ⅱ fly ash; Grade I or II slaked lime, 100 kg; (3) A layer of crushed stone or pebbles 4 with a particle size of 2 to 5 cm is scattered on the surface of the compacted composite backfill soil 3. The coverage of the scattered crushed stone or pebbles 4 is 55%. The layer of crushed stone or pebbles 4 is completely rammed into the composite backfill soil 3. At this time, the surface layer can be seen to be moist; (4) Compact the composite backfill soil 3 containing gravel or pebbles 4 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 5 is greater than 97%, and blow dry the wet layer with a fan; (5) Repeat steps (2) to (4) to fill the composite backfill soil 3 to the designed height. Example 3

[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 2 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 composite backfill soil 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 composite backfill soil 3 by rolling or tamping until the density reaches 95%; The composite backfill soil 3 is composed of the following raw materials in parts by weight: Dispersed soil, soil moisture content is 25%, 1000kg; Grade Ⅰ or Ⅱ fly ash, 200kg; Grade I or II slaked lime, 200 kg; (3) A layer of crushed stone or pebbles 4 with a particle size of 2 to 5 cm is scattered on the surface of the compacted composite backfill soil 3. The coverage of the scattered crushed stone or pebbles 4 is 80%. The layer of crushed stone or pebbles 4 is completely rammed into the composite backfill soil 3. At this time, the surface layer can be seen to be moist; (4) Compact the composite backfill soil 3 containing gravel or pebbles 4 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 5 is greater than 97%, and blow dry the wet layer with a fan; (5) Repeat steps (2) to (4) to fill the composite backfill soil 3 to the designed height.

[0022] During construction, it should be noted that the composite backfill soil after mixing should be able to be held in a ball by hand, indicating that the cohesion meets the standard, and it should break into pieces when squeezed, indicating that the water content is appropriate.

[0023] If the reservoir storage time and construction time are less than 20 days, the cementitious material should be appropriately increased. Under normal circumstances, the strength of the composite backfill soil that meets the rolling standards can reach more than 500Pa at the time, and can reach more than 800KPa in 20 days. Moreover, the composite backfill soil has a very good bond with the contact surface of the building.

[0024] The following experimental example illustrates the basis of the composite backfill soil test method. When building a dam with loam, sandy loam or even dispersed soil, due to the nature of the soil, the ability to resist seepage water entrainment at the contact point with the vertical wall of the building is poor. For small projects, the seepage path is short, and it is easy to produce wall seepage with soil particles entrained, causing soil flow damage. The soil must be modified before it can be used for backfill around the dam building.

[0025] Loam, sandy loam or even dispersed soil has one thing in common, which is the looseness of its poor water erosion resistance. When encountering flowing water, fine particles are easily eroded and carried by the water flow, especially for soil with a certain degree of dispersion. After encountering water, the sticky structure of its clay particles disintegrates by itself and disperses into clay particles of the original grade. The ability to resist water penetration damage is very low, so it is easy to cause the soil to produce serious soil flow and lead to penetration damage under the action of flowing water. Backfill soil used for dam-through buildings is very likely to produce soil flow and even pipe burst damage under the action of penetration pressure.

[0026] The key to solving this problem is to improve the cohesion of the backfill soil, that is, to add cementitious materials to the backfill soil to form composite soil to improve the cohesion of the backfill soil, so that the soil structure at the contact surface with the building does not form seepage or remains intact after seepage water. To this end, the present invention has conducted experiments for making composite backfill soil.

[0027] The backfill soil at a certain location has strong dispersion, with a dispersion of up to 95%. Direct application may have potential safety impacts on the project. The laboratory evaluation standard for dispersion is shown in Table 1 Table 1 Pinhole test evaluation soil dispersion standard

[0028] In order to ensure the safety of the project, highly dispersible soil was selected and cementitious materials were added to conduct experiments on producing composite backfill soil with the minimum dosage.

[0029] Test Materials: ① Take high dispersibility soil on site, the water content is 17.4% 1000g according to the design requirements ② 40g of grade I or II fly ash ③ 20g of grade I or II slaked lime The three materials were mixed evenly and then compacted to a compaction degree of 93%. Then, a penetration ring knife was used to take samples. The materials were sealed in a plastic bag and left to stand for 12 hours before being tested. The results are shown in Table 2.

[0030] Table 2 Pinhole test results of modified dispersed soil Sample No. Test water head (mm) Duration (min) Final flow rate (mL / s) Water color at the end of the test Final hole diameter (mm) Result determination N1 1020 5 2.60 Clear 1 Non-dispersible soil N2 1020 5 2.23 Clear 1 Non-dispersible soil According to the results of this pinhole test, even highly dispersed soil can meet the requirements of non-dispersed composite backfill soil by adding cementitious materials according to the above mix ratio. By slightly adjusting the mix ratio of this experiment, general dispersed soil or loam or sandy loam will have good cohesion when meeting water, and can be used as backfill soil in contact with the structure.

Claims

1. A method for wedging crushed stone composite backfill soil to prevent seepage damage to earth dam structure in cold regions, characterized in that: The following steps are involved: (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 composite backfill soil on the upper surface of the backfill soil layer and the upper surface of the foundation concrete cushion layer, and compacting the laid composite backfill soil; (3) Sporadically lay a layer of crushed stone or pebbles on the surface of the compacted composite backfill soil, and tamp the entire layer of crushed stone or pebbles into the composite backfill soil; (4) Compact the composite backfill soil containing gravel or pebbles at the junction with the dam-penetrating structure with a hammer, and use a fan to dry the wet layer; (5) Repeat steps (2) to (4) to fill the composite backfill soil to the designed height.

2. The method of wedging crushed stone composite backfill soil to prevent seepage damage to earth dam structure in cold regions by using a method according to claim 1, characterized in that: The compaction degree of the backfill soil layer in step (1) is 93-97%.

3. The method of wedging crushed stone composite backfill soil to prevent seepage damage to earth dam structure in cold regions by using a method according to claim 1, characterized in that: The composite backfill soil in step (2) is composed of the following raw materials in parts by weight: Sandy loam or loam or dispersed soil, soil moisture content is 17-25%, 1000 parts; Grade Ⅰ or Ⅱ fly ash, 0 to 200 parts; Grade I or II slaked lime, 20 to 200 parts.

4. The method of wedging crushed stone composite backfill soil to prevent seepage damage to earth dam structure in cold regions by using a method 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 composite backfill soil to prevent seepage damage to earth dam structure in cold regions by using a method 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 composite backfill soil to prevent seepage damage to earth dam structure in cold regions by using a method 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 95%.

7. The method of wedging crushed stone composite backfill soil to prevent seepage damage to earth dam structure in cold regions according to claim 1 is 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 stone composite backfill soil to prevent seepage damage to earth dam structure in cold regions by using a method as claimed in claim 1, characterized in that: The coverage of the scattered gravel or pebbles in step (3) is 30-80%.

9. The method of wedging crushed stone composite backfill soil to prevent seepage damage to earth dam structure in cold regions according to claim 1, characterized in that: In the step (4), the compaction degree at the junction with the dam-penetrating structure is greater than 97%.

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