TB 10025-2019Code for design of retaining structures of railway earthworks (English PDF)

2.1 Terms

2.1.1 geosynthetics

Generic term of the synthetic materials products applied in the geotechnical engineering

2.1.2 geotextile

Permeable cloth geosynthetics made of polymer fibers as the raw material

2.1.3 woven geotextile

Geotextile woven with fiber yarn or filament yarn along a certain direction

2.1.8 composite geodrain

Geodrain made of geotextile wrapping the core materials of different shapes and materials

2.1.9 strip geodrain

Vertical drain material made of plastic strip drain core materials in different shapes externally wrapped with nonwoven geotextile; strip geodrain is a kind of composite geodrain

2.1.10 special geosynthetic

Geosynthetic made by special processes and with special purposes

2.1.15 geocell

Three-dimensional geosynthetics products, with honeycomb structures, welded or assembled by the geosynthetics pieces

2.1.16 geomat

Three-dimensional net-shaped geosynthetics made of thread-line synthetic materials through a certain process treatment and by fusing on the nodes

2.1.17 three-dimensional vegetation grids

A kind of cell-shaped (similar to prismatic shape) vegetation geonet, made of plastic fiber through textile processing

2.1.18 expanded polystyrene

Light-duty geomaterials made of polystyrene by expanding after added with foaming agent and through moulding or extrusion process

2.1.31 creep

The phenomenon of material gradually increasing deformation with time under the action of constant force

2.2 Symbols

A - Dimensionless coefficient irrelevant to the filler property

Bs - Empirical coefficient relevant to the type and gradation of the protected

4.1 General requirements

4.1.1 Geosynthetics may be adopted for the seepage prevention, filtration and drainage of constructed railway bed.

4.2 Design

4.2.1 The laying positions of geosynthetics and cushion layer arrangement

shall meet the following requirements.

4.2.3 During the treatment for the existing railway subgrade bed problems, the geosynthetics shall be selected according to the following requirements.

4.2.4 The technical performance of geosynthetics shall meet the following requirements.

4.3 Key point of construction

4.3.1 Excavated section of bed must meet the design requirements. The subgrade surface under the sand cushion shall be made into the drainage slope not less than 4 % leaning to the outside of subgrade, and the subgrade surface and sand cushion shall not free from sharp sundries and crushed stone.

4.3.5 The problem treatment construction for the existing railway subgrade

bed must ensure the travel safety. Blockade line, by-pass or overhead track, speed-limiting traveling crane, and section construction methods may be adopted in the construction according to the construction conditions.

5.1 General requirements

5.1.1 Integrated protection measures of geosynthetics and other

engineering materials and engineering measures shall be adopted for the subgrade side slope.

5.2 Slope surface protection

5.2.1 Cut slope with soil, weathered rock, soft rock easy of weathering and

underground water seepage on the slope surface as well as embankment slope with slope surface subject to the rainfall erosion should adopt three-dimensional vegetation grids, geomat and geonet in combination with green protective measures such as planting vegetations and vegetation zone.

5.3 Scour protection

5.3.1 When the geosynthetics are used to the scour protection engineering, their applicable conditions may be determined according to Table 5.3.1.

5.3.3 Geofabriform scour protection engineering design shall meet the following requirements.

5.4 Sandstorm protection

5.4.1 Subgrade protection design in the sandstorm zone shall meet the following requirements.

5.5 Severe cold zone protection

5.5.1 When the insulation treatment is required for the side slope of cut in the severe cold zone, on the cut top, below the subgrade surface and in the embankment foundation, the composite geomembrane, expanded polystyrene or polyurethane insulation materials should be adopted as the protective layer.

5.6 Key points of construction

5.6.1 The geosynthetics protection engineering construction shall meet the following requirements.

5.6.2 The geosynthetic rock cage and sinking pillow scour protection

engineering construction shall meet the following requirements.

6.1 General requirements

6.1.1 Geosynthetics, which are used in the intercepting and draining of surface and underground water for subgrade or for supporting and blocking protective structures, may be regarded as materials for filtration layer, impermeable layer and drainage pipe.

6.2 Design

6.2.1 Geotextile, or geotextile and sand gravel may be regarded as filtration materials in the following cases.

6.2.5 When the subgrade top or bottom is required to be water exclusive and impermeable or to drain transversely, sand cushions with geomembrane or composite geomembrane installed in between should be adopted, and the gradient of transverse drainage should not be less than 4%.

6.2.6 The seepage ditches which adopt geosynthetics shall meet the following requirements.

6.2.9 The plastic permeable pipe diameter as well as the seep hole size

and layout shall be determined according to the pipe material type, seepage and drainage requirements, and protected soil conditions. Geotextiles should be adopted to envelop outside the plastic permeable pipe as a filtration layer.

6.2.10 The calculation of discharge capacity and seepage amount for

flexible permeable hoses, plastic permeable pipes and seepage ditch made of geotextile-enveloped sand and stone may comply with relevant specifications and provisions.

6.3.3 The overlapping width of filtration geotextile should not be less than

20 cm. Permeable geomembrane and composite geomembrane should adopt bonding method, and the adhesion width shall not be less than 10 cm, the bonding strength shall not be less than the design strength of the material, and there shall be free of sundries like sand and stone between the bonding faces.

6.3.4 The permeable pipe behind seepage ditches and retaining walls shall be laid and fixed according to the design position. The joints between the inclined pipe and longitudinal pipe behind retaining walls may adopt "T" shaped ones, and the permeable pipe joints shall be firm and difficult to be loosened so as to keep soil and crushed stone from falling into the pipes.

7.1 General requirements

7.1.1 In the case that the embankment filler is fine-grained soil or soft rock, the stability of the widened subgrade from a reconstructed or extended secondary line is poor, and steepening embankment slope is required due to the limit of topography, geosynthetics reinforcement may be adopted for strengthening.

7.2 Reinforcement soil embankment

7.2.1 Geosynthetics in embankment may adopt the following structural types.

7.2.2 When the embankment adopts multi-layer geosynthetics

reinforcement, the spacing between each layer of geosynthetics should neither be less than the minimum thickness of each filling layers nor be greater than 1m and the minimum laying width of the reinforcement materials shall not be less than 2.5m.

7.3 Reinforcement soil retaining wall

7.3.1 Reinforcement soil retaining wall may adopt structural types like the enveloped type and plate-suspended type.

7.4 Key points of construction

7.4.1 The construction of reinforcement soil embankment shall meet the following requirements.

8.1 General requirements

8.1.1 Geosynthetics may be used for strengthening the reinforcement, accelerating drainage consolidation and separating capillary water in the cases of soft soil, loose-soft soil and salty soil foundations. Reinforcement strengthening for foundations should select geogrids, geotextiles or geocells which are of a high strength and small elongation rate.

8.1.2 The measures for soft soil foundation treatment by using

geosynthetics shall be determined according to the foundation conditions, embankment height and stability, post-work sedimentation, construction period, etc.

8.2 Design

8.2.1 The design of reinforcement strengthening for soft soil foundation

shall meet the following requirements.

8.2.5 The technical performances of composite geomembrane shall meet the following requirements.

8.3 Key points of construction

8.3.1 The construction of reinforcement strengthening for soft soil

foundation shall meet the following requirements.

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