A red sandstone high fill road subgrade structure and construction method

Abstract

The present invention discloses a red sandstone high-fill road subgrade structure and construction method, which belongs to the field of civil engineering and solves the problem that the red sandstone fill roadbed is prone to uneven settlement and cracking. The present invention comprises an original soil base treatment layer, a base composite geotextile, a high-fill roadbed backfill layer, a roadbed reinforced anti-seepage layer, an embankment backfill layer, a roadbed backfill layer and a pavement structure layer arranged in sequence from bottom to top; a plurality of strong tamping reinforcement layers are arranged in intervals in the high-fill roadbed backfill layer, and a three-way geogrid in the roadbed is arranged on the top of each strong tamping reinforcement layer. Construction method: sequentially construct the original soil base treatment layer, the base composite geotextile, the high-fill roadbed backfill layer, the roadbed reinforced anti-seepage layer, the embankment backfill layer, the roadbed backfill layer and the pavement structure layer. The present invention has a good control effect on the settlement and deformation of the red sandstone high-fill road subgrade, thereby preventing the roadbed from sinking, solving the problem of red sandstone softening in water, and ensuring the roadbed's own bearing capacity.

Description

Technical Field

[0001] The invention belongs to the field of civil engineering, and in particular relates to a red sandstone high-fill road subgrade structure and a construction method. Background Art

[0002] Red sandstone is one of the widely distributed rocks in my country. The particle composition, mineral composition, chemical composition and microstructure of red sandstone in different regions are different, and its physical and mechanical properties and engineering mechanics properties are also different.

[0003] Paleogene and Neogene strata are widely distributed in Northwest my country. The deposition age of red sandstone is relatively new. The red sandstone bedrock under the loess layer is weak in lithology, loose in structure, easy to soften and disintegrate when exposed to water, has strong plasticity, and is easily weathered when exposed to the surface. The red sandstone in this area is prone to expansion, disintegration, crushing, softening or mudification under the action of dry-wet cycles, and the engineering stability is poor, making it difficult to control its construction quality. It is a poor roadbed filler. Various diseases often occur in existing roads, railways, slopes, tunnels and other projects. Diseases such as uneven settlement and cracking have always been common and prominent problems in red sandstone fill roadbeds, which have had a very adverse impact on driving safety, comfort and safe operation of underground pipelines. The main reason for these diseases is that the red sandstone filler was not effectively treated before filling (for example, the red sandstone was not completely disintegrated), or was not compacted enough during the filling construction project, or the roadbed subsided under the combined action of load, rainwater, pipeline leakage and other factors after opening to traffic. Therefore, efficient and safe red sandstone high fill road subgrade treatment structure and construction method urgently need to be proposed by researchers in the field of engineering technology. Summary of the invention

[0004] The purpose of the present invention is to provide a red sandstone high-fill roadbed structure to solve the problem that the red sandstone fill roadbed is prone to uneven settlement and cracking.

[0005] Another object of the present invention is to provide a red sandstone high fill road subgrade construction method.

[0006] The technical solution of the present invention is a red sandstone high-fill road subgrade structure, which is characterized by comprising an original soil base treatment layer, a base composite geotextile, a high-fill subgrade backfill layer, a subgrade reinforced anti-seepage layer, an embankment backfill layer, a roadbed backfill layer and a pavement structure layer arranged in sequence from bottom to top; multiple layers of strong compaction reinforcement layers are arranged at intervals in the high-fill subgrade backfill layer, and a three-way geogrid in the subgrade is arranged on the top of each strong compaction reinforcement layer.

[0007] As a further improvement of the present invention, a soil base strong compaction treatment layer is provided at the bottom of the original soil base treatment layer.

[0008] As a further improvement of the present invention, a roadbed bottom composite geotextile is provided at the bottom of the roadbed backfill layer, and a roadbed top three-way geogrid is provided at the top of the roadbed backfill layer.

[0009] As a further improvement of the present invention, a municipal pipeline is buried in the embankment backfill layer.

[0010] A red sandstone high fill road subgrade construction method comprises the following steps:

[0011] S1. Construction of original soil base treatment layer: Use a dynamic tamping machine to perform dynamic tamping treatment on the soil base after clearing the surface to form a soil base dynamic tamping treatment layer. After the dynamic tamping is completed, use a roller to level the soil base, and then backfill the cleared surface area. The terrain soil base uses crushed red sandstone mixed with 30% to 40% of plain soil by mass, and adopts a layered backfilling and rolling process. The thickness of each backfill layer does not exceed 30cm; the compaction degree of the original soil base treatment layer is ≥92%;

[0012] S2. Construction of base composite geotextile: Spread the base composite geotextile flat and lay it on top of the original soil base treatment layer;

[0013] S3. Construction of high fill roadbed backfill layer: The high fill roadbed backfill layer is paved on top of the composite geotextile of the construction base, and the crushed red sandstone mixed with 30% to 40% of the mass fraction of the plain soil is used for layered backfill and rolling, and the thickness of each backfill layer does not exceed 30cm; every 4m to 6m of filling, the tamping energy level is 1000KN·m to 2000KN·m to form a strong tamping reinforcement layer, and then the three-way geogrid in the roadbed is flattened and paved. After flattening and paving the three-way geogrid, the overall mechanical properties of the red sandstone high fill roadbed are improved, and the uneven settlement of the red sandstone high fill roadbed is controlled;

[0014] S4. Construction of roadbed reinforcement and anti-seepage layer: The roadbed reinforcement and anti-seepage layer is laid on top of the high fill roadbed backfill layer, using cement gravel backfill with a thickness of 30 to 50 cm; the compaction degree of the roadbed reinforcement and anti-seepage layer is ≥95%, and the 7-day unconfined compressive strength is ≥0.8MPa;

[0015] S5. Construction of embankment backfill layer: The embankment backfill layer is laid on top of the roadbed reinforced anti-seepage layer. It is made of crushed red sandstone mixed with 30% to 40% of soil by mass and backfilled and compacted in layers. The particle size of the crushed red sandstone ranges from 0.075mm to 100mm. The compacted thickness of each backfill layer does not exceed 30cm. The compaction degree of the embankment backfill layer (5) is ≥93%, and the bearing capacity should be ≥150Kpa. Then, the trench is reversed and the municipal pipeline is buried.

[0016] S6. Construction of roadbed backfill layer and pavement structure layer: flatten and lay the roadbed bottom composite geotextile on the embankment backfill layer; the roadbed backfill layer is laid on top of the roadbed bottom composite geotextile, and crushed red sandstone mixed with 70% to 80% of plain soil by mass fraction is used for layered backfill and rolling. The particle size range of crushed red sandstone is 0.075mm to 100mm, and the compacted thickness of each backfill layer does not exceed 30cm; the compaction degree of the roadbed backfill layer is ≥95%, and the bearing capacity should be ≥160Kpa; flatten and lay the roadbed top three-way geogrid on the top of the roadbed backfill layer, and then lay the pavement structure layer.

[0017] As a further improvement of the present invention, in step S1, the strong compaction treatment method is: the point compaction energy level is 4000KN·m~6000KN·m, the point compaction is 10 times, and the full compaction energy level is 1500KN·m~2000kN·m; the point compaction is at least twice, and the full compaction is at least once.

[0018] As a further improvement of the present invention, in step S1, during point tamping, the distance between adjacent main tamping points is 5 to 6 m, and the distance between adjacent auxiliary tamping points is 5 to 6 m.

[0019] As a further improvement of the present invention, the base composite geotextile and the roadbed bottom composite geotextile both use two fabrics and one film, with a specification of 400g / ㎡ to 500g / ㎡.

[0020] As a further improvement of the present invention, in step S3, the three-way geogrid in the roadbed is overlapped by 20 cm horizontally and 30 cm vertically, and the overlapped parts are anchored in the roadbed soil of the backfill layer of the high fill roadbed with U-shaped steel nails.

[0021] As a further improvement of the present invention, in step S6, the three-way geogrid on the top of the roadbed is overlapped by 20 cm horizontally and 30 cm vertically, and the overlapped parts are anchored in the roadbed backfill layer with U-shaped steel nails.

[0022] The beneficial effects of the present invention are:

[0023] 1. The red sandstone high-fill road subgrade structure of the present invention improves the overall mechanical properties of the red sandstone high-fill road subgrade. At the same time, by setting a soil base tamping treatment layer in the original soil base treatment layer, a multi-layer tamping reinforcement layer in the high-fill road subgrade backfill layer, and a three-way geogrid in the subgrade, and a cement-gravel soil paved construction subgrade reinforced anti-seepage layer, it has a good control effect on the settlement and deformation of the red sandstone high-fill road subgrade, thereby preventing the roadbed from sinking. The multi-layer tamping reinforcement layer is set in the high-fill road subgrade backfill layer to ensure the compaction of the backfill soil and reduce the void ratio of the backfill soil; the multi-layer three-way geogrid in the subgrade can avoid the uneven settlement of the high-fill soil as much as possible.

[0024] 2. The present invention reasonably controls the particle size of red sandstone in each structural layer and reasonably designs the backfill compaction process of each structural layer, thereby ensuring the compaction degree of the roadbed and preventing the roadbed from sinking.

[0025] 3. The present invention arranges a layer of composite geotextile on the top of the original soil base treatment layer and the bottom of the roadbed backfill layer, and arranges a roadbed reinforcement anti-seepage layer under the municipal pipeline, which has a good waterproof effect, solves the problem of red sandstone softening when it encounters water, ensures the bearing capacity of the roadbed itself, and eliminates the post-construction settlement of the filling area and the original red sandstone foundation.

[0026] 4. The construction method of the present invention is simple, which avoids the large-scale transportation and abandonment of red sandstone, saves project investment, is simple to construct, has a short construction period, and has little impact on the natural environment and social environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 This is a schematic structural diagram of a red sandstone high fill road subgrade structure of the present invention;

[0028] Figure 2 This is a flow chart of a red sandstone high fill road subgrade construction method of the present invention;

[0029] Figure 3 The present invention provides a layout diagram of the main tamping points and the auxiliary tamping points in step S1 of a red sandstone high fill road subgrade construction method.

[0030] In the figure: 1 is the original soil base treatment layer; 1-1 is the soil base dynamic compaction treatment layer; 2 is the base composite geotextile; 3 is the high fill roadbed backfill layer; 3-1 is the dynamic compaction reinforcement layer; 3-2 is the three-way geogrid in the roadbed; 4 is the roadbed reinforced anti-seepage layer; 5 is the embankment backfill layer; 5-1 is the municipal pipeline; 6 is the roadbed backfill layer; 6-1 is the composite geotextile at the bottom of the roadbed; 6-2 is the three-way geogrid on the top of the roadbed; 7 is the pavement structure layer; 8 is the secondary compaction point; 9 is the main compaction point. DETAILED DESCRIPTION

[0031] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0032] like Figure 1 As shown, a red sandstone high embankment road subgrade structure comprises an original soil base treatment layer 1, a base composite geotextile 2, a high embankment subgrade backfill layer 3, a subgrade reinforcement anti-seepage layer 4, an embankment backfill layer 5, a roadbed backfill layer 6 and a pavement structure layer 7 which are arranged in sequence from bottom to top; a plurality of strong compaction reinforcement layers 3-1 are arranged at intervals in the high embankment subgrade backfill layer 3, and a three-way geogrid 3-2 is arranged in the subgrade on the top of each strong compaction reinforcement layer 3-1.

[0033] A soil base strong compaction treatment layer 1-1 is provided at the bottom of the original soil base treatment layer 1.

[0034] A roadbed bottom composite geotextile 6 - 1 is provided at the bottom of the roadbed backfill layer 6 , and a roadbed top three-dimensional geogrid 6 - 2 is provided at the top of the roadbed backfill layer 6 .

[0035] A municipal pipeline 5 - 1 is buried in the embankment backfill layer 5 .

[0036] Embodiment 1,

[0037] Figure 2 The operating flow of the method of the present invention is shown.

[0038] Lanzhou Economic and Technological Development Zone has no relevant experience in treating the red sandstone high-fill roadbed. The method of the present invention is used for treatment, which includes the following steps:

[0039] S1. Construction of original soil base treatment layer 1: The soil base is cleared to a thickness of 40 to 60 cm, and the clearing range is 3 m outside the slope foot of the roadbed; then a dynamic compaction machine is used to compact the cleaned soil base to form a soil base dynamic compaction treatment layer 1-1. The dynamic compaction treatment method is: the point compaction energy level is 4000KN·m to 6000KN·m, the point compaction is 10 times, the full compaction energy level is 1500KN·m to 2000kN·m, the point compaction is at least twice, the full compaction is at least once, and when the point compaction is performed, if Figure 3 As shown in the figure, a row of main tamping points 9 and a row of auxiliary tamping points 8 are arranged alternately, the distance D between adjacent main tamping points 9 is 5-6m, the distance D between adjacent auxiliary tamping points 8 is 5-6m, and the corresponding tamping point spacing during full tamping adopts the tamping impressions to overlap each other by 1 / 4 (for round-bottom tamping hammers, the overlap can be made according to 1 / 4 of the tamping hammer diameter), and the standard for the end of strong tamping is that the average tamping amount between the last two blows is not more than 50mm; after the strong tamping is completed, the soil base is leveled with a roller, and then the surface clearing range is backfilled. Humus soil is removed in this layer, which enhances the bearing capacity of the soil base and improves the deformation resistance of the soil base; the terrain soil base adopts crushed red sandstone mixed with 30%-40% of plain soil by mass, and adopts a layered backfilling and rolling process, and the backfill thickness of each layer does not exceed 30cm; the compaction degree of the original soil base treatment layer 1 is ≥92%;

[0040] S2. Construction of base composite geotextile 2: Spread the base composite geotextile 2 flat and lay it on top of the original soil base treatment layer 1 to prevent groundwater from seeping into the roadbed, causing the softening of the filled red sandstone and the subsidence and deformation of the roadbed;

[0041] S3. Construction of high fill roadbed backfill layer 3: The high fill roadbed backfill layer 3 is paved on the construction base composite geotextile 2, and crushed red sandstone (particle size range is 0.075mm~150mm) is mixed with 30%~40% of the mass fraction of the plain soil for backfilling and rolling in layers. The thickness of each backfill layer shall not exceed 30cm, and the roller shall be a vibratory roller of more than 12 tons; every 4m~6m of filling, a tamping energy level of 1000KN·m~ 2000KN·m is used for tamping to form a strong tamping reinforcement layer 3-1, and the compaction degree is not less than 92% of the design and specification requirements, and then the three-dimensional geogrid 3-2 in the roadbed is flattened and laid; the three-dimensional geogrid 3-2 in the roadbed (specification is TX190L) is overlapped by 20cm in the horizontal direction and 30cm in the vertical direction, and the overlap is anchored in the high fill roadbed backfill layer 3 roadbed soil with U-shaped steel nails. The three-dimensional geogrid 3-2 in the roadbed is overlapped by 20cm in the horizontal direction and 30cm in the vertical direction. 0 ), oblique (30 0 ), oblique (60 0 ), horizontal (90 0 )Mechanical properties: quality control tensile modulus ≥150KN / m at 2% strain;

[0042] S4. Construction of roadbed reinforcement and anti-seepage layer 4: The roadbed reinforcement and anti-seepage layer 4 is laid on top of the high fill roadbed backfill layer 3. The roadbed reinforcement and anti-seepage layer 4 is located at the bottom of the municipal pipeline 5-1 with the maximum buried depth of the road, 4m to 6m away from the bottom of the pavement structure layer 7, and is backfilled with cement gravel soil (cement, gravel, soil mass ratio is 8:22:70), with a thickness of 30 to 50cm; the layered backfill compaction thickness does not exceed 30cm, and the roller is a vibrating roller of more than 12 tons; the compaction degree of the roadbed reinforcement and anti-seepage layer (4) is ≥95%, and the 7-day unconfined compressive strength is ≥0.8MPa; the setting of the construction roadbed reinforcement and anti-seepage layer 4 improves the roadbed anti-seepage effect and roadbed bearing capacity, and ensures the stability of the red sandstone high fill roadbed;

[0043] S5. Construction of embankment backfill layer 5: The embankment backfill layer 5 is paved on top of the roadbed reinforced anti-seepage layer 4. It is made of crushed red sandstone mixed with 30% to 40% of plain soil in layers for backfilling and rolling. The crushed red sandstone has a particle size range of 0.075mm to 100mm and has a good gradation. The compacted thickness of each backfill layer does not exceed 30cm. The roller uses a vibrating roller of more than 12 tons, and a small machine is used to compact the top 50cm of the municipal pipeline 5-1. The compaction degree of the embankment backfill layer 5 is ≥93%, and the bearing capacity should be ≥150Kpa. Then the trench is reversed and the municipal pipeline 5-1 is buried. There are many municipal pipelines 5-1 in the embankment backfill layer 5, which makes compaction and backfilling difficult. In addition, there is additional stress in the roadbed working area. In order to ensure the compaction degree and bearing capacity of the embankment backfill layer 5, the requirements for the particle size range and compaction index of the crushed red sandstone are increased to ensure the integrity and completeness of the roadbed range as much as possible.

[0044] S6, construction of roadbed backfill layer 6 and pavement structure layer 7: flatten and lay the roadbed bottom composite geotextile 6-1 on the embankment backfill layer 5; the roadbed backfill layer 6 (thickness 1.2m) is laid on the roadbed bottom composite geotextile 6-1, and the crushed red sandstone mixed with 70% to 80% of the mass fraction of the plain soil is used for layered backfilling and rolling. The crushed red sandstone has a particle size range of 0.075mm to 100mm and has a good gradation. The compacted thickness of each layer does not exceed 3 0cm; the roller shall be a vibrating roller of more than 12 tons; the compaction degree of the roadbed backfill layer 6 shall be ≥95%, and the bearing capacity shall be ≥160Kpa; the roadbed top three-dimensional geogrid 6-2 shall be flattened and laid on the top of the roadbed backfill layer 6, and the roadbed top three-dimensional geogrid 6-2 (specification is TX190L) shall be overlapped 20cm horizontally and 30cm vertically, and the overlap shall be anchored in the roadbed backfill layer 6 with U-shaped steel nails, and the roadbed top three-dimensional geogrid 6-2 shall be overlapped in the vertical direction (0 0 ), oblique (30 0 ), oblique (60 0 ), horizontal (90 0 ) Mechanical properties: quality control tensile modulus ≥ 150KN / m at 2% strain; then pavement structure layer 7 is paved. Roadbed backfill layer 6 is the direct working area of ​​the roadbed, which further improves the requirements for the particle size range and compaction index of the broken red sandstone. The bottom of the roadbed backfill layer 6 is provided with a roadbed bottom composite geotextile 6-1 to ensure the waterproof effect. The top of the bottom of the roadbed backfill layer 6 is provided with a roadbed top three-way geogrid 6-2 to improve the bearing capacity and control the uneven settlement of the roadbed.

[0045] The base composite geotextile 2 and the roadbed bottom composite geotextile 6-1 both use two cloths and one film, with a specification of 400g / ㎡~500g / ㎡.

[0046] This embodiment has achieved good social and economic benefits.

[0047] (1) Social benefits: The excavation of red sandstone in the Gaolan Ecological Restoration and Industrial Development Demonstration Zone (Starting Area) of Lanzhou Economic and Technological Development Zone is as high as 90 million m³. If it is abandoned, a large area of ​​land will be needed, and it will have a great impact on the local ecological environment. This application can promote the on-site utilization of red sandstone in road engineering and similar engineering construction in Lanzhou, further improve the engineering quality of red sandstone high-fill roadbed in Lanzhou, reduce the abandonment of red sandstone, and protect the ecological environment.

[0048] (2) Economic benefits: The present invention provides methods and technical support for the on-site utilization of red sandstone in road engineering, reduces waste earthwork, and saves engineering investment. The filling volume of three roads, T1514# Road, T1525# Road, and T1543# Road in the Gaolan Ecological Restoration and Industrial Development Demonstration Zone (Starting Area) of Lanzhou Economic and Technological Development Zone, reached 2.1 million m³. The on-site use of red sandstone for filling can save engineering investment of about 42 million yuan compared with borrowing earthwork from outside.

Claims

1. A red sandstone high fill road subgrade construction method, characterized by: The following steps are involved: S1. Construction of original soil base treatment layer (1): Use a dynamic compactor to compact the soil base after clearing to form a soil base dynamic compaction treatment layer (1-1). After the dynamic compaction, use a roller to level the soil base, and then backfill the cleared area. The terrain soil base uses crushed red sandstone mixed with 30% to 40% of plain soil by mass, and adopts a layered backfilling and rolling process. The thickness of each backfill layer does not exceed 30 cm; the compaction degree of the original soil base treatment layer (1) is ≥92%; S2, constructing the base composite geotextile (2): spreading the base composite geotextile (2) flat and laying it on top of the original soil base treatment layer (1); S3. Construction of high fill roadbed backfill layer (3): The high fill roadbed backfill layer (3) is paved on top of the construction base composite geotextile (2), and is backfilled and rolled in layers using crushed red sandstone mixed with 30% to 40% of plain soil by mass. The thickness of each backfill layer does not exceed 30 cm. Every 4 to 6 m of filling, a tamping energy level of 1000 KN·m to 2000 KN·m is used to form a strong tamping reinforcement layer (3-1), and then the three-way geogrid (3-2) in the roadbed is flattened and paved; S4. Construction of roadbed reinforcement and anti-seepage layer (4): The roadbed reinforcement and anti-seepage layer (4) is laid on top of the high fill roadbed backfill layer (3) and is backfilled with cement gravel soil with a thickness of 30 to 50 cm. The compaction degree of the roadbed reinforcement and anti-seepage layer (4) is ≥ 95% and the 7-day unconfined compressive strength is ≥ 0.8 MPa. S5. Construction of embankment backfill layer (5): The embankment backfill layer (5) is laid on top of the roadbed reinforced anti-seepage layer (4). It is made of crushed red sandstone mixed with 30% to 40% of plain soil by mass, and is backfilled and compacted in layers. The particle size of the crushed red sandstone ranges from 0.075 mm to 100 mm, and the compacted thickness of each backfill layer does not exceed 30 cm. The compaction degree of the embankment backfill layer (5) is ≥ 93%, and the bearing capacity should be ≥ 150 Kpa. Then, the trench is reversed and the municipal pipeline (5-1) is buried. S6. Construction of roadbed backfill layer (6) and pavement structure layer (7): The roadbed bottom composite geotextile (6-1) is flattened and laid on the embankment backfill layer (5); the roadbed backfill layer (6) is laid on top of the roadbed bottom composite geotextile (6-1), and crushed red sandstone mixed with 70% to 80% of plain soil by mass is used for backfilling and rolling in layers, the crushed red sandstone particle size range is 0.075 mm to 100 mm, and the backfill compaction thickness of each layer does not exceed 30 cm; the compaction degree of the roadbed backfill layer (6) is ≥95%, and the bearing capacity should be ≥160 KPa; the roadbed top three-dimensional geogrid (6-2) is flattened and laid on the top of the roadbed backfill layer (6), and then the pavement structure layer (7) is laid.

2. A red sandstone high fill road subgrade construction method according to claim 1, characterized in that: In step S1, the strong compaction treatment method is: the point compaction energy level is 4000KN·m~6000KN·m, the point compaction is 10 times, and the full compaction energy level is 1500KN·m~2000kN·m; the point compaction is at least twice, and the full compaction is at least once.

3. A red sandstone high fill road subgrade construction method according to claim 2, characterized in that: In step S1, during point tamping, the distance between adjacent main tamping points (9) is 5 to 6 m, and the distance between adjacent auxiliary tamping points (8) is 5 to 6 m.

4. A red sandstone high fill road subgrade construction method according to any one of claims 1 to 3, characterized in that: The base composite geotextile (2) and the roadbed composite geotextile (6-1) both use two fabrics and one film, with a specification of 400g / ㎡ to 500g / ㎡.

5. A red sandstone high fill road subgrade construction method according to claim 4, characterized in that: In step S3, the three-dimensional geogrid (3-2) in the roadbed is overlapped by 20 cm horizontally and 30 cm vertically, and the overlapped part is anchored in the roadbed soil of the high fill roadbed backfill layer (3) using U-shaped steel bar nails.

6. A red sandstone high fill road subgrade construction method according to claim 5, characterized in that: In step S6, the three-dimensional geogrid (6-2) on the top of the roadbed is overlapped by 20 cm in the horizontal direction and 30 cm in the vertical direction, and the overlapped part is anchored in the roadbed backfill layer (6) using U-shaped steel bar nails.

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