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TB 10035-2018

Chinese Standard: 'TB 10035-2018'
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BASIC DATA
Standard ID TB 10035-2018 (TB10035-2018)
Description (Translated English) Code for Design on Special Railway Earth Structure
Sector / Industry Railway & Train Industry Standard
Classification of Chinese Standard P65
Classification of International Standard 93.100
Word Count Estimation 291,244
Date of Issue 2018-10-12
Date of Implementation 2019-01-01
Older Standard (superseded by this standard) TB 10035-2006
Drafting Organization China Railway Fourth Survey and Design Institute Group Co., Ltd.
Administrative Organization National Railway Administration
Regulation (derived from) National Railways Regulations (2018) 82
Summary This standard is applicable to the special subgrade design of high-speed railway, inter-city railway, passenger and cargo line I and II railways, and heavy-duty railway.

TB 10035-2018
INDUSTRY STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
UDC
P TB 10035-2018
J 158-2018
Code for Design on Special Railway Earth Structure
铁路特殊路基设计规范
ISSUED ON: OCTOBER 12, 2018
IMPLEMENTED ON: JANUARY 1, 2019
Issued by: National Railway Administration of the PRC
Table of Contents
1 General ... 11 
2 Terms and symbols ... 13 
2.1 Terms ... 13 
2.2 Symbols ... 17 
3 Subgrade of soft soil section ... 19 
3.1 General provisions ... 19 
3.2 Stability analysis and settlement calculation ... 22 
3.3 Embankment ... 31 
3.4 Cutting ... 33 
3.5 Foundation treatment ... 35 
4 Earth structure of expansive rock and soil ... 39 
4.1 General provisions ... 39 
4.2 Embankment ... 40 
4.3 Cutting ... 41 
4.4 Slope protection and reinforcement ... 43 
4.5 Foundation treatment ... 45 
4.6 Subgrade waterproof and drainage ... 46 
5 Loess subgrade ... 48 
5.1 General provisions ... 48 
5.2 Embankment ... 49 
5.3 Cutting ... 50 
5.4 Slope protection and reinforcement ... 52 
5.5 Foundation treatment ... 52 
5.6 Subgrade waterproof and drainage ... 56 
5.7 Sinkhole treatment ... 57 
6 Saline soil and salt rock subgrade ... 58 
6.1 General provisions ... 58 
6.2 Embankment ... 58 
6.3 Side slope protection ... 61 
6.4 Foundation treatment ... 62 
6.5 Subgrade waterproof and drainage ... 63 
7 Earth structure of permafrost area ... 65 
7.1 General provisions ... 65 
7.2 Embankment ... 66 
7.3 Cutting ... 69 
7.4 Slope protection and retaining ... 70 
7.5 Transition section ... 71 
7.6 Subgrade waterproof and drainage ... 73 
7.7 Borrow pits and spoil banks ... 75 
8 Earth structure of seasonal frozen soil area ... 76 
8.1 General provisions ... 76 
8.2 Embankment ... 76 
8.3 Cutting ... 79 
8.4 Subgrade retaining and protection ... 80 
8.5 Subgrade waterproof and drainage ... 82 
9 Earth structure of granite weathered residual soil ... 83 
9.1 General provisions ... 83 
9.2 Embankment ... 84 
9.3 Cutting ... 85 
9.4 Slope protection and reinforcement ... 86 
9.5 Subgrade waterproof and drainage ... 88 
10 Subgrade of filling site ... 90 
10.1 General provisions ... 90 
10.2 Embankment ... 91 
10.3 Cutting ... 91 
10.4 Foundation treatment ... 94 
10.5 Subgrade waterproof and drainage ... 96 
11 Subgrade of landslide section ... 97 
11.1 General provisions ... 97 
11.2 Landslide stability analysis and sliding force calculation ... 97 
11.3 Prevention and control engineering ... 99 
11.4 Engineering landslide prevention... 102 
11.5 Landslide monitoring ... 103 
12 Subgrade of dangerous rock, rockfall, collapse and talus section ... 105 
12.1 General provisions ... 105 
12.2 Subgrade of dangerous rock, rockfall, and collapse section ... 105 
12.3 Subgrade of talus section ... 106 
13 Subgrade of karst and artificial pothole section ... 108 
13.1 General provisions ... 108 
13.2 Subgrade of karst section ... 109 
13.3 Subgrade of artificial pothole section ... 112 
14 Subgrade in area of sand blown by the wind ... 115 
14.1 General provisions ... 115 
14.2 Embankment ... 116 
14.3 Cutting ... 117 
14.4 Subgrade slope protection ... 117 
14.5 Plane protection of sand blown by the wind ... 118 
14.6 Windproof measures in windy areas ... 122 
15 Subgrade of snow-damaged area ... 124 
15.1 General provisions ... 124 
15.2 Subgrade section form ... 125 
15.3 Protective measures ... 125 
16 Submerged subgrade ... 128 
16.1 General provisions ... 128 
16.2 Subgrade of pond and waterlogged sections ... 131 
16.3 River beach and riverside subgrade ... 131 
16.4 Coastal subgrade ... 132 
16.5 Subgrade of reservoir section ... 135 
Appendix A Classification and relevant characteristics of special rock and soil
... 138 
Appendix B Calculation of foundation settlement and thickness of insulation
layer in permafrost ... 153 
Appendix C Calculation of load of sand blown by the wind ... 165 
Appendix D Calculation method of buried depth of sand barrier column
foundation ... 166 
Descriptions for word use of this Code ... 169 
2 Terms and symbols
2.1 Terms
2.1.1 Earth structure of special area
The general term for earth structure of special rock and soil area and earth
structure of special condition.
2.1.2 Earth structure of special rock and soil area
The earth structure located in special rock and soil sections such as soft soil,
expansive rock and soil, loess, saline soil.
2.1.3 Earth structure of special condition
The earth structure located in bad geological sections, as well as the earth
structure strongly affected by natural factors such as water and climate.
2.1.4 Soft soil
The cohesive soil deposited in still water or slow flowing water environment and
characterized by large water content (w≥wL), large void ratio (e≥1.0), high
compressibility (a0.1~0.2≥0.5 MPa-1), and low strength (Ps<0.8 MPa).
2.1.5 Loose-soft soil
The strata such as cohesive soil, silt, and sandy soil that cannot reach the soft
soil index in the earth structure engineering, which are characterized by larger
water content or void ratio, higher compressibility (a0.1~0.2≥0.25 MPa-1), and
lower strength or bearing capacity (σ0≤150 kPa).
2.1.6 Expansive soil
The cohesive soil in which clay minerals are mainly composed of hydrophilic
minerals and which has the characteristics of water swelling, softening,
disintegration, and rapid shrinkage and cracking from water loss, and can
produce reciprocating deformation.
2.1.7 Loess
The soil, formed under arid and semi-arid climatic conditions since the
Quaternary, whose particles are mainly composed of powder particles and
contain calcium carbonate and a small amount of soluble salts, and which has
the engineering geological characteristics such as macro-void and vertical
joints, poor water resistance, easy disintegration and subsurface erosion, and
3 Subgrade of soft soil section
3.1 General provisions
3.1.1 Soft soil can be classified according to its physical and mechanical
properties in accordance with Appendix A.0.1 of this Code. Subgrade shall
consider its following engineering characteristics and effects:
1 Soft soil has the characteristics of low natural strength and high
compressibility, resulting in poor subgrade stability and large foundation
settlement deformation.
2 Soft soil has the characteristics of low permeability and slow consolidation.
The consolidation of the foundation lasts a long time. The consolidation
time and its settlement amount vary greatly with the consolidation
conditions, which affects the post-construction settlement of subgrade and
construction period control of deep thick soft soil foundation.
3 When the high-sensitivity soft soil has thixotropy, construction vibration and
disturbance will cause the strength of the soft soil to be seriously reduced,
affecting the stability, deformation, or safe use of existing projects around
the construction period.
4 High-plasticity or over-consolidated soft soil has rheological properties.
Under undrained shear conditions, it will lead to more long-term strength
reduction and continuous increase of deformation of soft soil, affecting
long-term stability, deformation control, and surrounding environment
safety of the subgrade.
3.1.2 Loose-soft soil can be classified according to its physical and mechanical
properties in accordance with Appendix A.0.1 of this Code. Subgrade stability,
post-construction settlement control shall consider its engineering
characteristics such as low strength, high compressibility or easy liquefaction
and influences.
3.1.3 The subgrade of the soft soil section should be in the form of embankment.
Its height should not be less than the thickness of the foundation bed. The
choice of subgrade location shall meet the following requirements:
1 It is advisable to choose a section with narrow area and thin thickness of
soft soil.
2 In low hilly areas, closed or semi-closed depressions should be avoided.
3 In the valley between mountains, it is advisable to avoid being located in
φi - The internal friction angle of the bottom of the ith soil strip (°);
Ei-1 - Sliding force of the i-1-th soil strip transferring the ith soil strip (kN);
φi-1 - Transfer coefficient of remaining sliding force.
5 When the embankment base is reinforced with geosynthetics, the tensile
force it bears shall be calculated as the slide-resisting force.
3.2.3 When using composite foundation treatment, the overall sliding stability
analysis of the embankment and the foundation shall be based on geological
conditions, composite foundation type, and possible failure modes; adopt
appropriate methods; and, shall meet the following requirements:
1 The composite foundation of discrete material piles and of reinforced soil
piles in general sections can, in accordance with subclause 3.2.2 of this
Code, be checked and computed by the arc method or the unbalanced
thrust transfer coefficient method. According to the stratum and range of
the slip circle cutting, the composite foundation shall respectively adopt the
shear strength index of the composite or natural foundation soil. When
using discrete material piles, the drainage consolidation effect on the
foundation can be considered; the shear resistance of the soil between the
piles, increased by consolidation under the load of the embankment, can
be considered.
2 Rigid pile composite foundation, and reinforced soil pile composite
foundation in sections with complex conditions such as high embankment,
soft soil characteristics, or environmental sensitivity shall be analyzed
according to the possible failure modes of the composite foundation, using
appropriate methods or combining numerical methods. When the arc
method is used for analysis, the influencing factors such as soft soil
characteristics and pile-soil modulus ratio shall be fully considered; the
form and effect of pile-soil load sharing shall be reasonably determined;
and, the sliding surface force shall be calculated. If necessary, the
horizontal bearing capacity of the pile should be calculated, to check the
lateral stability of the pile.
3.2.4 When using rigid pile foundation treatment, the stability of the
embankment shall be analyzed according to the rigid pile foundation of the pile-
supported embankment; and, shall meet the following requirements:
1 The vertical bearing capacity of the rigid pile foundation of the pile-
supported embankment shall meet the vertical load requirements of the
embankment above the pile top. The vertical allowable bearing capacity of
a single pile shall be determined according to the following formula:
3.3.4 The boundary between embankment and other structures, the section
with large strata change, and the junction of different foundation treatment
measures shall adopt gradual transition foundation treatment measures, to
reduce uneven settlement.
3.3.5 Embankment design using drainage consolidation method for foundation
treatment shall comply with the following provisions:
1 Through the stability check analysis during the construction period, the
construction instructional design shall be conducted on the filling
parameters, such as the critical height of rapid filling, embankment filling
loading form, stepped height and loading time (including precompression).
The critical height of filling can also be determined by empirical formula
calculation.
2 When constructing a new embankment and reserving the second line, it is
advisable to design a double-line embankment at a time.
3 In accordance with the construction organization arrangement and the
construction period requirements, the construction shall be arranged in
advance. After the embankment filling construction is completed, it shall
be placed for a period of time. If necessary, the load can be increased for
precompression.
3.3.6 The subgrade of ballasted track railway with design speed of 200 km/h
and below shall be reserved for post-construction settlement widening of the
subgrade. The widening value on each side shall be calculated and determined
according to the post-construction settlement and the slope ratio of the track
bed slope.
3.3.7 Embankment shoulders should be made of dry masonry stones or precast
concrete blocks. When using mortar masonry stones or precast concrete blocks
or cast-in-place concrete, it shall strengthen measures to prevent longitudinal
uneven settlement and ensure smooth transverse drainage of foundation bed.
When the post-construction settlement is large, the road camber or its
transverse drainage slope should be enlarged. If necessary, on the top or
bottom surface of the foundation bed surface layer, an impermeable layer may
be set.
3.3.8 When the subgrade base on the subgrade on the soft soil foundation in
the earthquake area adopts sand and gravel cushion, the cushion material shall
be gravel (pebble) or coarse gravel (pebble). Fine sand must not be used. It is
not suitable to use medium and coarse sand for the embankment base cushion
in earthquake areas of 9 degrees and above.
3.3.9 Based on conditions such as embankment filler properties, slope height,
3.4.3 According to the nature of the weak soil, thickness, bottom lateral slope,
hydrogeological conditions, and types of reinforcement measures, etc., using
the circular sliding method or the unbalanced thrust method, the cutting slope
shall be subjected to stability analysis according to the relevant provisions of
section 3.2 of this Code. Combined with factors such as slope height,
environmental conditions, construction methods, it shall comprehensively
determine the slope form, slope ratio, and the load size and distribution
characteristics of rock-soil pressure or sliding force acting on the retaining
structure.
3.4.4 Slope reinforcement protection and retaining measures shall be
determined according to the engineering geological and hydrogeological
conditions of the slope, the height of the slope, the external environmental
conditions and other factors, combined with the stability analysis of the slope,
and according to the following provisions:
1 When the weak layer of the slope is thick, composite foundation treatment
measures such as cement-soil mixing piles and rotary jet piles can be used,
to reinforce the slope. The slope surface can be protected by ecological
bag flexible protection, mortar masonry stone or skeleton slope protection.
2 When the slope is not high, the slope toe should be reinforced by a low
retaining wall or a rubble stack. When the slope is high or the weak layer
is thick, the slope toe should be retained using reinforced concrete row
piles, L-shaped retaining wall, U-shaped groove structure, or
comprehensive measures, etc.
3 According to the safety and stability needs of the construction excavation
process, combined with the construction conditions, necessary water stop,
precipitation, and temporary reinforcement protection measures may be
taken.
3.4.5 The cutting shall be set with side ditch platform. The width should not be
less than 2.0 m. When the height of the cutting slope is large, or for the interface
between the soft and hard layers, the slope platform should be set. The width
should not be less than 3.0 m.
3.4.6 The cutting slope shall, in accordance with factors such as topography,
hydrological characteristics, and surrounding environment, take reasonable
waterproof and drainage measures. If necessary, support seepage ditches or
upward inclined drainage holes may be provided, to strengthen the removal of
groundwater in the slope.
3.4.7 When the back of the retaining structure wall adopts sand-pebble inverted
layer, its thickness must not be less than 0.5 m.
3.5.9 When adopting rigid pile foundation treatment measures, the following
requirements shall be met:
1 It shall comprehensively consider factors such as the embankment height,
the nature of foundation soil, the topography, and the environmental
conditions; and, combine the suitability of the pile board, pile raft, and pile-
net structure, to reasonably determine the appropriate structural form.
2 For low embankment, slope or non-crusted silt, muddy soil foundation, and
when settlement deformation is strictly controlled, pile board or pile raft
structure should be adopted. When using a pile-net structure, appropriate
treatment measures shall be taken to ensure lateral stability.
3 Driven and pressed prefabricated reinforced concrete piles should be used.
When the foundation soil is sandwiched with stones, boulders or is uneven
in hardness, reinforced concrete cast-in-situ bored piles may be used.
4 When the top of rigid pile is above the ground and buried in the filling
embankment, the filling embankment under the pile top shall be stable.
After its settlement is basically completed, a rigid pile foundation shall be
set.
3.5.10 Grouting, micro piles, etc. can be used for soft soil and loose-soft soil
foundation treatment under special conditions or reinforcement of existing
subgrade foundation. The design shall comply with the relevant provisions of
the current "Technical code for improvement of soil and foundation of existing
buildings" JGJ 123.
3.5.11 When there is a soft layer beneath the composite foundation and the
bearing layer at the bottom of the rigid pile, the bearing capacity of the
foundation shall be verified; and, shall meet the corresponding requirements.
3.5.12 For composite foundations and rigid pile pile-net (pile raft) structures, a
reinforced cushion of sand gravel or rubble with a thickness of not less than 0.4
m shall be placed on the top of the pile (cap). The reinforcement should be a
geogrid. The ultimate tensile strength shall not be less than 50 kN/m.
3.5.13 For sections reinforced using composite foundation or rigid piles, before
construction, according to the design, technical test piles shall be carried out,
to confirm that the design and construction related parameters are technically
feasible.
3.5.14 The upper subgrade project can be constructed only after the foundation
reinforcement quality test is passed.
top of the cutting should not be less than 5 m.
4.6.2 For medium and strong expansive rock and soil cutting slopes, slope
seepage ditches or upward inclined drainage holes should be set, to strengthen
the drainage of groundwater.
4.6.3 The sealing and water isolation treatment OF the top surface of the bottom
layer of foundation bed or the bottom surface of the replacement SHALL be
strengthened. The embankment and the cutting foundation bed with developed
groundwater should adopt waterproof materials, which can be laid continuously
on site. When geosynthetics are used for sealing and water isolation, they
should not be overlapped along the cross-sectional direction; and, along the
line direction, the overlapping shall be reduced. For the cutting foundation bed
with developed groundwater, it shall take measures for prevention and drainage
of groundwater, such as lowering or deepening the side ditch, setting necessary
vertical and horizontal drainage seepage ditches and seepage pipes, etc.
4.6.4 For the cutting where groundwater is developed, underground drainage
measures such as upward inclined drainage holes, slope seepage ditches, and
longitudinal blind ditches should be adopted.
4.6.5 The slope toe of embankment shall be provided with measures such as
drainage ditches, elevated berms, or retaining walls, to prevent water
immersion.
4.6.6 The basement of the low embankment and low-lying section shall be filled
with permeable soil filler. The bottom is provided with an anti-seepage sealing
layer. If necessary, measures such as vertical and horizontal drainage seepage
ditches and seepage pipes can be added, to prevent and eliminate surface
water accumulation.
4.6.7 The gutters, intercepting ditches, side ditches, drainage ditches, and
platforms shall be reinforced by anti-scouring and anti-seepage measures. For
the side ditches of cuttings, it shall strengthen the treatment measures to
prevent accumulation and seepage. The structural design of the side ditch shall
consider the influence of horizontal expansion force.
Note: 1 The listed slope ratio refers to the comprehensive slope ratio of a single soil layer.
If there are multiple soil layers, it can be determined by comprehensive
consideration, according to the differences in the nature of the soil layers at
different times and genesis and their proportion in the slope.
2 For the graded slope ratio of stepped slopes, the same slope ratio value can be
taken for homogeneous soil layers; different slope ratio values can be selected for
heterogeneous soil layers.
3 When the ground lateral slope of the top of the cutting is less than 20°, its influence
on slope ratio is not considered. When it is 20°~35°, the height of Q4 loess slope
is greater than 12 m; the height of ଷୟ୪,୮୪ loess slope is greater than 15 m. The
slope ratio can be slowed down by one level (calculated as 0.25). When greater
than 35°, it shall be determined through stability checking.
4 For Q2 and Q1 loess, it shall consider the influence of structural fissures on slope
stability.
5.3.5 The stability checking of the cutting slope should adopt the arc method.
The stability safety factor shall not be less than 1.25.
5.4 Slope protection and reinforcement
5.4.1 For slope protection and reinforcement, based on conditions such as soil
quality, precipitation, slope height, slope ratio, it shall take reinforcement
measures to prevent spalling, erosion, and deformation.
5.4.2 When the embankment height is greater than 3 m, the geogrid should be
laid horizontally in layers on both sides of the slope. The vertical spacing shall
not be greater than 0.6 m. Embankment slopes can be protected by geonet
cushion, hollow bricks, and water intercepting skeleton slope protection, etc.
5.4.3 For the cutting slope, it is advisable to adopt hollow brick, water
intercepting skeleton slope protection, anchor frame beam slope protection,
hole-window retaining wall, slope toe wall or comprehensive measures for
protection and reinforcement and waterproof and drainage treatment.
5.5 Foundation treatment
5.5.1 For subgrades in loess areas, according to settlement calculations or
stability checks, appropriate foundation treatment measures shall be taken, to
ensure that the subgrade is stable and the post-construction settlement is
controlled.
5.5.2 For non-collapsible loess foundations, treatment measures shall be taken
in accordance with the current "Code for design of railway earth structure" TB
to the top surface of the non-collapsible loess layer, take 1.0 for I and II
regions of non-self-weight collapsible loess site; and, for the remaining
areas, take the β0 value of the area where the project is located;
αi - The coefficient of submergence probability of foundations at different
depths, which is based on regional experience. When there is no regional
experience, within the depth of 0~10 m below the basement, take 1.0.
Within a depth of 10 m~20 m below the basement, take 0.9. Within a depth
of 20 m~25 m below the basement, take 0.6. Below 25 m below the
basement, take 0.5. If the groundwater is likely to rise into the collapsible
soil layer, or the section where the influence of lateral flooding is inevitable,
take 1.0.
2 The calculated depth of collapse ΔS shall be calculated from the basement
(the excavation section shall be from the road shoulder), and at the non-
self-weight collapsible loess site, accumulate to 10 m below the basement
and the depth of the foundation compression layer; at the self-weight
collapsible loess site, accumulate to the top surface of the non-collapsible
loess layer. The soil layer with collapsibility coefficient (δs) less than 0.015
is not accumulated.
5.5.5 At non-self-weight collapsible loess sites, when the sum of the additional
stress and the saturated self-weight pressure of the overlying soil is greater
than the initial collapse pressure of each soil layer, the collapse is calculated.
5.5.6 The post-construction settlement of subgrade of collapsible loess
foundation shall be determined according to the following provisions:
1 When adopting treatment measures that penetrate the collapsible
foundation to prevent the influence of collapsible deformation or
completely eliminate the collapsibility of the foundation, the post-
construction settlement shall be determined according to the calculation of
compressive deformation settlement of the foundation after treatment.
2 When the treatment measures to partially eliminate the collapsibility of the
foundation are adopted, the post-construction settlement shall be
calculated and determined according to the remnant collapse of the treated
foundation and the settlement of the foundation compressive deformation.
3 The calculation of compressive deformation settlement of the foundation
shall comply with the relevant provisions of the current national standard
"Standard for building construction in collapsible loess regions" GB 50025.
5.5.7 Collapsible loess foundation shall be analyzed according to factors such
as post-construction settlement requirements, foundation characteristics,
treatment depth, construction equipment, material sources, and impact on the
6 Saline soil and salt rock subgrade
6.1 General provisions
6.1.1 Saline soil can be classified based on the chemical composition and
content of salt and the degree of collapse and salt expansion according to
Appendix A.0.4 of this Code. The subgrade in the saline soil area shall consider
the influence of the following characteristics:
1 After the soluble salt in the saline soil is soaked and dissolved in water, the
soil structure is loosened and collapse occurs.
2 Saline soil is swellable and hygroscopic. The soil is prone to salt expansion
or softening.
3 Saline soil is highly corrosive.
6.1.2 According to the main mineral composition, salt rock can be divided into
gypsum rock, potash rock, and mirabilite rock. The subgrade in salt rock area
shall consider the influence of the following characteristics:
1 The salt rock in the dry state has high strength and low compressibility;
and, after immersion in water, is prone to latent erosion and collapse.
2 When temperature and moisture change, salt rock will swell.
3 Salt rock is highly corrosive.
6.1.3 The location of the subgrade in the saline soil area shall be selected in
the section with high terrain, deep groundwater level, smooth drainage, low salt
content in the soil, low salinity of groundwater, and small distribution range of
saline soil; and, it shall pass as an embankment.
6.1.4 The subgrade in the salt rock area shall avoid the section with abundant
surface water and groundwater and concentrated development of salting-in. It
shall choose to pass through the section with thicker salt layer and higher
strength. In the salting-in area, it shall choose to pass in a section with a small
range, few dark holes, a thick roof, and a small possibility of further
development of salting-in.
6.2 Embankment
6.2.1 Embankment filler shall be comprehensively determined based on factors
such as railway grade, rainfall. It shall also meet the following requirements:
1 High-speed railway and inter-city railway subgrade shall not use saline soil
6.4.4 When the stability of the subgrade does not meet the requirements, the
sum of the collapse of the foundation and the amount of compression
settlement is greater than the allowable value of the post-construction
settlement of subgrade, or the salt expansion and deformation of the foundation
exceeds the track adjustment range, the foundation shall be treated, to prevent,
reduce, or eliminate the influence of foundation collapse and salt expansion.
6.4.5 For foundation treatment, according to factors such as the engineering
impact characteristics of saline soil and environmental conditions, it shall take
measures, such as replacement, precompression, dynamic compaction,
dynamic compaction replacement, gravel piles, water immersion pre-
dissolution, salinization, and partition methods; and, use engineering materials
with strong corrosion resistance.
6.4.6 When the salt content of the topsoil of foundation and natural berm is
greater than the allowable value specified in Table 6.2.1 of this Code, it shall be
eradicated. When a partition is set up, it may not be eradicated.
6.4.7 When the surface soil of the foundation is loose, it shall be compacted by
rolling or compacted by digging and backfilling in layers. When the loose soil
layer is thick, reinforcement measures such as replacement and dynamic
compaction can be taken.
6.4.8 When the foundation soil is a weak soil layer, according to the weak soil
layer’s nature, thickness, water content, depth of surface water accumulation,
etc., according to the relevant provisions of clause 3 of this Code, the foundation
treatment shall be carried out. The treatment measures shall meet the anti-
corrosion requirements.
6.4.9 For salt crust layer with dissolution pores, the basement can be rolled by
heavy machinery. For loose salt rock with thickness less than 3 m, excavation
and replacement measures may be adopted. The caves and gaps in the salt
rock shall be compacted by gravel-cobble packing or backfilled with brine
cement slurry.
6.5 Subgrade waterproof and drainage
6.5.1 For the subgrade in the saline soil area, it shall take anti-seepage
measures. The inner edge of the drainage ditch (gutter) must not be less than
5 m away from the slope toe (cutting roof). The drainage outlet shall be far from
the line.
6.5.2 In the sloping plain area of the piedmont, intercepting ditches shall be set
up 10 m away from the slope toe upstream of the subgrade.
6.5.3 In order to prevent secondary salinization, in saline soil area, drainage
7 Earth structure of permafrost area
7.1 General provisions
7.1.1 The classification of permafrost and the ground temperature zoning of
permafrost on the Qinghai-Tibet Plateau shall comply with the provisions of
Appendix A.0.5 of this Code.
7.1.2 The permafrost subgrade shall consider the following characteristics and
effects:
1 The natural or artificial table depth range of permafrost may produce
seasonal freeze-thaw alternations, resulting in thaw collapse or frost
heaving deformation of subgrade engineering. The ice content of the soil
is the key factor for thaw collapse.
2 The thermal stability of permafrost varies with the mean average ground
temperature. The lower the mean average ground temperature, the greater
the cold storage capacity, and the better the stability of frozen soil
foundation.
3 The permafrost near the natural table is more sensitive to environmental
changes. The boundary between the frozen soil and the thawing area is
prone to uneven deformation.
4 The frozen soil with high ice content in areas I and II of the Qinghai-Tibet
Plateau is very sensitive to environmental changes and surface
disturbances; and, likely to cause or exacerbate poor frozen soil geological
problems.
7.1.3 When the line is located in the following bad frozen soil area, it is not
suitable to pass through as a subgrade.
1 The sections where the spring eyes are concentrated in exposure, the
amount of ice is large, it is easy to form frost heaving mound, ice cones,
and ice mantles in winter, and it is difficult to control the subgrade
engineering.
2 The junction of high-ice content frozen soil and thawing area.
3 Developmental hot-melt lakes and ponds, a wide range of swamps, or
swamps with steep lateral slopes.
4 High-temperature highly unstable high-ice content sections or island-
shaped frozen soil area which is not easy to keep warm.
anti-seepage measures are taken.
3 The distance FROM the inner side of the drainage ditch, gutter, and water
retaining dike of frozen soil section with low ice content TO the toe of the
embankment slope or the top of the cutting shall not be less than 5 m. The
form of the ditch section is designed according to the general area.
7.6.4 In thick-underground ice and permafrost swamp sections, earth retaining
dikes or water retaining dikes can be used in combination with drainage ditches. 
The distance between the edge of the drainage ditch and the slope toe of the
water retaining dike shall not be less than 1.0 m.
7.6.5 In the frozen soil area with high ice content in the Qinghai-Tibet Plateau,
when the longitudinal drainage conditions of the line are smooth, water retaining
dikes should be used. The artificial permafrost table at the bottom of the water
retaining dike shall not drop; and shall meet the following requirements:
1 When the ground cross slope is obvious, it should be set above the
subgrade. The distance between the slope toe of the water retaining dike
and the top of the cutting or embankment slope toe should not be less than
5 m.
2 The cross section of the water retaining dike shall be trapezoidal. The
height should not be greater than 1.0 m. The top width shall not be less
than 1.0 m. The slope ratio shall be 1 : 1.5~1 : 1.75.
7.6.6 For the groundwater that is harmful to the subgrade, according to the type
of groundwater, water volume, accumulated water and stratum conditions,
measures such as freezing ditch, ice accretion pit, or seepage ditch shall be
selected; and shall meet the following requirements:
1 When seepage ditches are used to exclude groundwater, thermal
insulation measures shall be taken for seepage ditches and inspection
wells. The location of the water outlet shall be selected in sunny and wind-
sheltered places with open terrain, large height difference, steep
longitudinal slope, etc. It shall adopt buried cone or other forms of thermal
insulation measures.
2 When groundwater is exposed on the cutting slope, the water must be
drained. Thermal insulation measures shall be taken on the slope.
3 In the section where the water over frozen layer is developed, it shall treat
the water over frozen layer.
replacement filler shall meet the technical requirements of the antifreeze layer.
8.3.2 When the foundation bed is hard rock that is not easy to weather, it may
not be replaced. The over-excavation part shall be filled with concrete. When
ballasted track is used, the subgrade surface shall be provided with a lateral
drainage slope with a slope of not less than 4%.
8.3.3 When the frost heaving grade of the foundation bed soil is grade I, or the
bed is soft rock and hard rock easy to be weathered, based on comprehensive
analysis of the soil quality, lithology, joint fissure development degree, and frost
heaving deformation control requirements, the antifreeze performance shall be
determined. When necessary, it shall take replacement measures.
8.3.4 The slope ratio of cutting slope shall be determined based on
comprehensive analysis of slope height, geotechnical properties, climate,
hydrological conditions, etc. When the frost heaving grade of the slope soil
quality is III, IV, V, the slope ratio shall be slowed down properly.
8.4 Subgrade retaining and protection
8.4.1 When the design thawing depth is less than or equal to 1.0 m, the buried
depth of the retaining wall foundation shall not be less than 0.25 m below the
design thawing depth and shall not be less than 1.0 m. When the design
thawing depth is greater than 1.0 m, the buried depth of the retaining wall
foundation shall not be less than 1.25 m. The foundation soil from the basement
to the depth range of 0.25 m below the design thawing depth shall be replaced
with slightly-frozen heaving soil.
8.4.2 The thermal insulation layer can be set on the back of the retaining wall
and the ground on the top of the wall. Or the slightly-frozen heaving coarse-
grained soil can be used to replace the frost heaving soil on the slope of the
back of the wall. The thickness of the thermal insulation layer and the
replacement thickness can be determined by heat engineering calculation.
8.4.3 The slide-resisting and anti-overturning stability check of the retaining wall
in seasonal frozen soil area shall be conducted according to the warm season
and the cold season, respectively. The horizontal frost heaving force and earth
pressure shall not be combined at the same time when the load effect is
combined. The design load effect combination in the cold season shall consider
the freezing force acting on the foundation and the horizontal frost heaving force
on the back of the wall.
8.4.4 The size and distribution of horizontal frost heaving stress acting on the
back of the wall shall be determined by on-site tests. When the test cannot be
carried out, the distribution pattern can be selected according to Figure 8.4.4.
σHk in the figure shall be taken according to Table 8.4.4. It shall also meet the
9 Earth structure of granite weathered residual soil
9.1 General provisions
9.1.1 The engineering classification of granite weathered residual soil can be
divided according to the provisions of Appendix A.0.7 of this Code. The
following engineering characteristics and impacts shall be considered for the
subgrade:
1 The composition and structure of weathered residual soil of granite are
quite different. As a subgrade filler, it shall fully consider the influence of
soil type, particle composition, particle size grading, and water stability.
2 When the weathered residual soil of granite is cohesive soil, it has the
characteristics of disintegration, softening, or swelling with water. When it
is sandy soil, it has poor anti-erosion ability. The slope is prone to shallow
collapse, erosion, or collapse damage.
3 In sections with severely differential weathering of granite, the weathered
residual soil is prone to produce weak interlayers. The deep thick residual
soil slope is prone to engineering landslides. The slope is prone to develop
dangerous rocks and boulders, which affects the stability of the cutting
slope and subgrade safety.
4 The weathered residual soil of granite and its underlying strong and weakly
weathered rock are quite different in properties such as rock-soil structure,
strength, water stability. When the contact interface forms a weak zone,
engineering landslides are likely to occur.
9.1.2 The subgrade should avoid the sections where the natural slope of granite
weathered residual soil is severely eroded and collapsed, or the dangerous
rocks and boulders on slopes are developed and large in scale, and where
engineering landslides are likely to occur. When it is difficult to circumvent, it
shall choose to pass in a short distance at a position that is easy to handle; and
take reliable treatment measures.
9.1.3 The subgrade of granite weathered residual soil shall avoid high-fill deep-
excavation and long cuttings. It shall strengthen the measures for stability of
slopes, preventing erosion, and drainage interception. The embankment slope
height should not be greater than 15 m. The cutting slope height should not be
greater than 20 m.
9.1.4 In the deep and thick layer of granite weathered residual soil section with
steep cross slope of weak interlayer or contact zone and with groundwater
development, the cutting slope height shall be strictly controlled; the necessary
groundwater is developed, for the ballasted track railway with a speed of 200 km/h,
the treatment depth should be the thickness of the bottom layer of the bed.
9.3.3 When the residual layer group C and D soil with poor water stability is
below the bed surface,  the bottom surface of the bed surface or the bottom
surface of the replacement should be treated with geosynthetics sealing and
waterproof measures.
9.3.4 For the cutting bed of the groundwater development section, measures
for lowering the groundwater level or setting up "embankment-type" cutting
structure and "U" groove structure should be adopted. If necessary, measures
such as rotary jet and grouting can be used.
9.3.5 The slope ratio of the granite weathered residual soil cutting slope shall
be comprehensively determined according to the geotechnical characteristics,
the nature of weak layer, the combination of structural planes, climatic
characteristics, hydrogeological conditions, and the stable slope of natural
mountain slopes and artificial side slopes, etc.
9.3.6 When the slope height does not exceed 15 m, and the slope soil is more
homogeneous and well cemented, without adverse structural planes, and the
natural slope is stable, the slope ratio and form can be designed in accordance
with the current "Code for design of railway earth structure" TB 10001. When
the slope height is greater than 15 m, or the engineering geological and
hydrogeological conditions are complex, the slope ratio and form shall be
designed by engineering analogy combined with slope stability analysis.
9.3.7 The method of slope stability analysis and calculation shall be determined
according to the possible damage form. The circular arc method should be
adopted for the overall sliding of homogeneous soil slope; the stability safety
factor shall not be less than 1.25. When the slope slides along the weak layer
or structural plane, the transfer coefficient method should be adopted; the
stability safety factor shall not be less than 1.15.
9.3.8 The cutting spoil shall be far away from the cutting top. Appropriate
protection and reinforcement, and drainage interception measures shall be
taken, to prevent soil erosion or geological disasters.
9.4 Slope protection and reinforcement
9.4.1 Slope protection and reinforcement shall follow the principle of
strengthening slope surface protection, intercepting drainage, and combing
suitable retaining reinforcement; and meet the following requirements:
1 When the slope is high, or the engineering geological and hydrogeological
conditions are complex, the slope stability analysis shall be combined, to
1 For embankments filled with granite weathered residual sandy soil, it is
appropriate to take measures such as slope protection by out-soil grass
and shrub planting in three-dimensional vegetation net, geonet cushion, or
hollow brick, slope protection by planting bag or ecological bag, slope
protection by out-soil grass and shrub planting in water interception
skeleton and comprehensive slope protection.
2 For embankments filled with granite weathered residual cohesive soil, it is
appropriate to take measures such as slope protection by grass and shrub
planting, slope protection by grass and shrub planting in water interception
skeleton.
3 When the embankment slope is high, during the filling process, the geogrid
should be laid horizontally in layers on both sides of the slope.
9.4.5 The size of the slope protection and reinforcement structure shall be
determined by comprehensive consideration of different railway grades,
engineering geological conditions, and climatic characteristics, etc.
9.4.6 For dangerous rock, boulder, and thin layer of weathered residual soil on
steep slope, which endanger the stability of the subgrade or the safety of
operation, it shall take treatment measures such as removal, interception, or
reinforcement.
9.5 Subgrade waterproof and drainage
9.5.1 According to the terrain conditions, the cutting top shall be provided with
single-side or double-side gutters. The slope toe of the embankment shall be
protected from water immersion and erosion. If necessary, reinforcement
measures to prevent erosion and seepage should be taken. Drainage ditch
should be provided outside the slope toe.
9.5.2 For the subgrade slope of granite weathered residual soil, combined with
slope protection, it is advisable to take comprehensive waterproof and drainage
measures such as anti-scouring, anti-slip. If necessary, drainage interception
measures such as slope platform intercepting ditches, drainage interception
channels, and slope seepage ditches may be taken.
9.5.3 For cuttings in areas where groundwater is developed, measures, such
as lowering or deepening side ditches or setting longitudinal blind ditches, slope
upward inclined drainage holes, and slope seepage ditches, should be taken to
prevent, control, and drain groundwater.
9.5.4 For the basement of low embankments and low-lying sections, it is
advisable to fill with seepage soil fillers, or take measures such as vertical and
horizontal drainage seepage ditches and seepage pipes, to prevent and
10 Subgrade of filling site
10.1 General provisions
10.1.1 Based on the material composition, landfill method, and engineering
properties, according to Appendix A.0.8 of this Code, the filling can be divided
into four types: fill soil, plain fill, dredger (jetting) fill, and miscellaneous fill.
Subgrade shall consider the following engineering characteristics and impact:
1 The material composition of the fill soil is relatively uniform. It has a certain
degree of compaction. As the foundation, with different degrees of
compaction and upper load, it has under-consolidation, normal
homojunction, or over-consolidation. The foundation treatment shall
distinguish the influence of its consolidation state.
2 Plain fill is under-consolidated, with low bearing capacity and large
settlement deformation.
3 Dredger (jetting) fill and miscellaneous fill have the characteristics of under-
consolidation, high compressibility, low bearing capacity, etc., which can
easily lead to instability of the subgrade or large settlement deformation of
the foundation.
4 When the miscellaneous soil has high organic matter content or chemical
erosion, it shall consider its impact on subgrade structure and environment.
5 When the filling has the characteristics of uneven material composition,
compactness, or thickness, it is easy to form a weak interlayer, which is
not conducive to the stability of the slope and the control of the differential
settlement of the foundation. When it has collapsibility or thixotropy, the
foundation treatment shall fully consider its impact.
10.1.2 The subgrade of the filling site shall avoid the large-scale, thick, and
poor-quality dredger (jetting) and miscellaneous fill sections. It should pass
through the sections where the distribution of the filling is narrow, the thickness
is thin, the composition and properties are more uniform, and the base cross
slope is gentle.
10.1.3 For the subgrade of the filling site, it shall avoid deep long cuttings,
strictly control the height of cutting slopes, and strengthen the slope stability
measures. The height of cutting slope should not exceed 15 m for the fill soil
section; 10 m for the plain fill section; and 6 m for the dredger (jetting) fill and
miscellaneous fill section.
10.1.4 The foundation treatment of the filling site shall consider the negative
11 Subgrade of landslide section
11.1 General provisions
11.1.1 The line shall avoid huge, large, and complex landslide sections or
groups. When it is difficult to avoid the medium and small landslides, it shall
choose to pass in a position, which is conducive to the stability of the landslide
and the safety of the line; and adopt reliable engineering treatment measures.
11.1.2 For the subgrade of landslide section, according to the type and scale of
the landslide, the geotechnical properties of the landslide body, the
hydrogeological conditions, the conditions of landslide formation and
development, the degree of its damage to the project shall be analyzed.
Effective remedial measures shall be taken in time, to ensure the stability of the
subgrade and the safety of construction and operation.
11.1.3 Landslide prevention and control shall follow the principle of “one-time
cure and no future troubles”. It shall adopt engineering measures, which
combine drainage interception with load reduction or backpressure and
retaining, to comprehensively control.
11.1.4 Large and complex landslides should be monitored for stability.
11.1.5 In sections with thick loose accumulations, fractured crushed zones,
weathered fractured zones, bedding of rock masses, rocks of uneven hardness,
weak foundations on slopes, and special rock-soil, engineering geological line
selection shall be strengthened and reliable preventive measures taken, to
prevent engineering landslides.
11.2 Landslide stability analysis and sliding force calculation
11.2.1 In addition to considering the weight of sliding mass, building load, sliding
surface resistance, and buoyancy of the design water level as permanent loads,
the landslide stability analysis shall also consider the effect of the temporary
construction load, earthquake horizontal force, penetration force, and other
temporary loads acting on the sliding mass.
11.2.2 The stability of the landslide can be comprehensively analyzed according
to the engineering geological analogy and mechanical balance calculation. For
broken-line sliding surface, the transfer coefficient method should be used for
calculation.
11.2.3 According to factors such as landslide characteristics, hydrogeological
conditions and engineering experience, the remaining sliding force of the
landslide should be calculated by the transfer coefficient method. The bar force
1 For shallow landslides, at the front edge of the landslide, supporting
seepage ditches can be adopted, to eliminate or dry groundwater or
shallow stagnant water of the landslide body; and also serve as a support
for the landslide body. When necessary, the supporting seepage ditch can
be combined with the slide-resisting retaining structure. The bottom of the
supporting seepage ditch shall be placed no less than 0.5 m below the
sliding surface.
2 The shallow groundwater of the landslide body or the shallow stagnant
water of the soil body can, by an intercepting seepage ditch perpendicular
to the direction of groundwater flow, be led out of the sliding mass. The
ditch bottom shall be placed in an impervious layer or bedrock. The
longitudinal drainage slope shall not be less than 2%.
3 The deep groundwater in the landslide should be drained by the upward
inclined drainage holes. The length of the upward inclined hole shall pass
through the sliding surface, with built-in soft permeable pipe or plastic
seepage pipe. If necessary, the pipe can be filled with medium coarse sand
or sand-gravel. The upward inclined drainage slope shall not be less than
5%.
4 When it is difficult to remove deep groundwater from thick landslides, in the
stable stratum, drainage tunnels can be used for drainage. The clearance
height of the discharge tunnel section should be 2.0 m~2.5 m. The width
should be 1.0 m~1.5 m. The lining of the water collecting section can be a
lace wall. Vertical or radial water collecting holes can be set on the top of
the drainage tunnel. The longitudinal drainage slope at the bottom of the
tunnel shall not be less than 1%.
5 When the landslide body is a complex stratum with multiple aquifers or has
a large water content, a combination of water collection wells (groups),
upward inclined holes, and drainage tunnels can be used, to form a three-
dimensional underground drainage system.
11.3.3 When taking load reduction and backpressure measures, it shall meet
the following requirements:
1 When the sliding bed of the main slide section of the landslide is steep, the
load can be reduced in the middle and rear of the sliding body. But the
stability of the rear part of the landslide and the mountains on both sides
after earth removal shall be ensured, to prevent the rear edge from
generating new slips.
2 When conditions permit, measures can be taken to backfill the front edge
of the landslide. Filling and backpressure shall prevent clogging the
12 Subgrade of dangerous rock, rockfall, collapse and
talus section
12.1 General provisions
12.1.1 The line shall avoid large-scale dangerous rock, rockfall-developed
section or large-scale collapse section. For the local dangerous rock, rockfall,
and small and medium-sized collapse sections, when it is difficult to avoid,
according to the type of disease and the degree of damage, etc., it shall
reasonably select the location of the line and the prevention and control
measures.
12.1.2 In dangerous rock, rockfall, and collapse sections, the subgrade should
be located at a location with a small influence range, a relatively short and
gentle slope, and easy to control and treat. It shall also take safe and reliable
engineering measures, such as sheltering, interception, removal, reinforcement,
or comprehensive treatment.
12.1.3 In the talus section, according to the size and material composition of
the talus, and the topographic and geological conditions such as the nature and
slope of the underlying rock-soil and the activity of groundwater and surface
water, it shall analyze and evaluate the development stage, stability, and impact
of the talus on the project; and reasonably choose the line location and
engineering measures.
12.1.4 For large talus with large area, loose accumulation layer, steep slope of
accumulation bed, abundant replenishment sources, of which the stability is
significantly influenced by groundwater and surface water, and which may
cause slippage, the line shall avoid it. For small and medium-sized talus, when
it is difficult to avoid, the subgrade should pass through by low filling and shallow
excavation; stable reinforcement measures shall be taken.
12.2 Subgrade of dangerous rock, rockfall, and collapse section
12.2.1 When the line is close to the medium-scale dangerous rock, rockfall, or
collapse section, shielding buildings such as the open cut tunnel, shed tunnel
shall be used for treatment. The sheltering building shall be of sufficient length,
to prevent dangerous rocks, falling rocks, and collapsed rocks from falling into
the subgrade.
12.2.2 When the scale of dangerous rock and rockfall and the size of the
collapsed body are small or large, but far away from the line, it is possible to
take treatment measures such as clearing, roof support, hanging net and
anchoring-shotcreting, flexible active protection system, and anchoring; or to
checking method can use the transfer coefficient method. The safety factor can
be 1.10~1.25. When passing as an embankment, the stability of the
embankment after loading shall be checked. When passing as a cutting, the
stability of the excavated and unloaded slope shall be checked. When the
stacked bed has a downwardly-inclined rock face, or there is a weak interlayer
in the talus, its stability should be checked, respectively.
12.3.2 For the subgrade of talus section, according to the hydrogeological
conditions of the talus, it shall adopt the measures of intercepting and
discharging surface water and ground water. For talus in the gully, it shall
strengthen waterproof and drainage measures. The talus near the river shall be
well protected against erosion.
12.3.3 For the cutting slope of talus section, based on material composition,
natural angle of repose, and stability analysis, the grade of side slope should
be determined comprehensively. When the slope is high, ladder-shaped slopes
should be used.
12.3.4 When the subgrade is located in the unstable talus section,
corresponding comprehensive measures such as slide-resisting retaining shall
be taken, to ensure the stability of the subgrade. Regarding the subgrade of the
stable talus section, when cutting talus on the excavation slope may damage
the balance conditions of the talus, it is advisable to construct retaining works
on the upper or lower sides.
12.3.5 In the section of loose accumulation layer, according to the slope
lithology and compactness, etc., it shall take measures such as slope brushing,
slope protection, or base slide-resisting reinforcement. The slope shall be
controlled in height. It shall carry out the drainage interception treatment of the
top of the slope, to prevent the slope from generating diseases. When
groundwater is exposed, dredging and drainage measures shall be taken.
12.3.6 For subgrades of more complex talus sections, it shall take deformation
monitoring measures. Monitoring can be performed according to section 11.5
of this Code. According to the observation data, adjust the construction method
and improve the design measures, to ensure the safety of construction and
operation.
12.3.7 When the soil quality or compactness of the cutting bed and
embankment basement talus mass does not meet the requirements, it shall
take treatment measures, such as in-situ rolling, digging-tamping, replacement,
or grouting reinforcement.
reinforcement.
13.1.6 For subgrades of artificial pothole sections, it is advisable to set up
ground displacement observation facilities; to monitor the surface subsidence
and horizontal displacement of the basement during construction and operation
periods, and to timely take necessary treatment measures.
13.1.7 Subgrade base grouting treatment shall follow the principle of
"exploration-grouting combination, process control". According to the geological
conditions and grouting conditions revealed by the construction of the pilot
grouting (exploration) hole, adjust the design requirements such as grouting
parameters and process.
13.1.8 For grouting-reinforced foundations, it shall adopt comprehensive
methods such as water pressure test combined with geophysical prospecting,
drilling for core, to test and evaluate the grouting effect.
13.2 Subgrade of karst section
13.2.1 For karst caves in the subgrade bed range or dissolution fissures without
(half) filling, filled karst ditches, karst grooves, etc., it shall take measures such
as uncovering backfilling, excavation and replacement, or beam-slab spanning
for reinforcement treatment.
13.2.2 For the development zone of karst caves and dissolution fissures below
the foundation bed range, according to the degree of damage to the stability of
the subgrade, deformation control requirements, and environmental factors,
etc., the treatment measures shall be selected according to the following
principles:
1 When the exposed karst or covering layer thickness is not more than 5 m,
treatment measures such as backfilling, excavation and replacement,
reinforcement of supporting roof in cave or spanning of the beam-slab
structure, and grouting reinforcement should be adopted.
2 When the thickness of the covering layer is greater than 5 m, and the
closed and isolated groundwater can maintain the normal use of water
resources, grouting reinforcement should be adopted, to close the soil-
rock interface.
3 For the high-speed railway with complicated basement karst, ballastless
track inter-city railway subgrades, or the railway subgrades in the sections
with strict groundwater environmental protection requirements, pile board
structure should be adopted to span.
13.2.3 When backfilling, excavation and replacement, reinforcement of
and movement, it shall analyze and evaluate the stability and deformation trend;
and take corresponding measures to prevent collapse, reserve sufficient
settlement, widen the subgrade, control the mining boundary, and ensure a safe
distance, etc.
13.3.2 According to factors such as buried depth and size of the mined-out area,
roof thickness and geotechnical properties, surface stability and deformation
trend, by using appropriate evaluation methods, the safety distance on both
sides of the subgrade shall be determined by comprehensive analysis and
calculation.
13.3.3 For the mined-out area that affects the stability or deformation control of
the subgrade, according to its location, shape and size, tunnel direction, roof
thickness, rock-soil strength of the roof, filling conditions in the tunnel, and the
degree of compaction of the filler, etc., the reinforcement method shall be
determined. It shall also meet the following requirements:
1 The shallowly-buried mined-out area should be treated by open-cut and
backfill.
2 The deep-buried mined-out area with unobstructed tunnels should be
treated by flake backfill, roof support, and grouting, etc.
3 Deep-buried, multi-layer overlapping and staggered, inaccessible mined-
out areas should be treated by grouting and sand grouting, etc.
4 For high-speed railway and ballastless track inter-city railway embankment,
when the base tunnel is buried deep or overlapped and staggered, pile
board structure spanning measures can be adopted.
13.3.4 The treatment width of the subgrade base shall ensure that, the safety
distance of untreated mined-out area meets the requirements of subclause
13.3.2 of this Code.
13.3.5 When grouting reinforcement is used, according to the length, shape,
size, and filling of the tunnel in the reinforcement area, according to the
provisions of subclause 13.2.7 of this Code, the concealed mined-out area can
be designed for grouting reinforcement. When the extension direction of the
tunnel exceeds the reinforcement range of the subgrade, drill holes can be set
at the reinforced boundary of the tunnel; and concrete is poured to form a slurry
control dam.
13.3.6 For artificial caves such as tombs, cellars, dry wells, Karez wells
(underground canals), according to the situation, it shall take measures to
prevent collapse, such as excavation and backfilling, tamping, grouting
reinforcement, or pile board structure spanning.
14 Subgrade in area of sand blown by the wind
14.1 General provisions
14.1.1 Sand blown by the wind can be classified according to Appendix A.0.9
of this Code. Subgrades in desert, Gobi, and desertified land areas shall be
designed according to the subgrade in area of sand blown by the wind.
14.1.2 For lines in areas of sand blown by the wind, comprehensive
consideration shall be given to the environment of sand blown by the wind and
topography and landform conditions. It shall choose to pass in open terrain. For
sections of severe sand blown by the wind, it shall use straight lines or larger-
radius curves; and use appropriate engineering types.
14.1.3 Subgrade in area of sand blown by the wind should adopt the form of
embankment; avoid long sections of low cuttings, deep cuttings, half-
embankment and half-cutting, and high embankments; and avoid frequent
changes of embankments and cuttings. The location of the subgrade shall meet
the following requirements:
1 The subgrade in the desert section should be set in the fixed, semi-fixed,
low dune zone, shallow groundwater level, and other easily fortified
sections; and away from the dune leeward slope.
2 The subgrade engineering of the Gobi section should be set in the ground
covered with gravel, without quicksand, and with low wind force; and avoid
the gale tuyere sections.
3 The subgrade of desertified land section should not be set in the abdomen
of the land with rapid desertification and severe desertification in a large
area.
14.1.4 For subgrade in area of sand blown by the wind, based on factors such
as topography and climate along the line, hydrological characteristics, strong
wind characteristics, laws of activity of sand blown by the wind, and the degree
of impact on railway operation, in accordance with the principles of "adapting to
local conditions, combining permanence with temporariness, step-by-step
implementation, comprehensive governance", plane protection on both sides
shall be carried out in sections.
14.1.5 In the design of sand and wind protection projects, in combination with
factors such as the degree of impact of protective structures on operational
safety and protection timeliness, the basic wind pressure shall be determined;
and shall comply with the following regulations:
than 1 : 1.75. When the slope height is greater than 6 m and not more than 12
m, the side slope ratio shall not be steeper than 1 : 2. Each side of the subgrade
surface shall be widened by 0.3 m~0.5 m.
14.2.6 When the gravelly soil is used as filler in the strong wind area, and the
embankment slope has no protective measures, each side of the subgrade
surface shall be widened by 0.3 m~0.5 m.
14.3 Cutting
14.3.1 When the bottom bed of high-speed railway, ballastless track railway,
and heavy-haul railway is silt or fine sand, it shall take replacement, soil
improvement, or reinforcement measures. When the bearing capacity of the
bottom bed of other railways does not meet the requirements, it shall take
compaction measures.
14.3.2 The slope form of silty and fine sand cutting shall be linear. When the
slope height is not greater than 6 m, the side slope ratio should not be steeper
than 1 : 1.75. When the slope height is greater than 6 m and not more than 12
m, the side slope ratio should not be steeper than 1 : 2.
14.3.3 For shallow cuttings in the Gobi windy sand flow area, when the angle
between the wind direction and the line is large, the expansion type should be
adopted. The side slope ratio should not be steeper than 1 : 4.
14.3.4 In arid and extremely arid desert belts, when a single rainfall can all
penetrate into the sand layer without generating runoff, drainage facilities may
not be provided.
14.3.5 The cutting section shall be provided with a sand platform. The width of
the sand platform shall be determined according to the sand source, the
dominant wind direction, and the maximum amount of sand accumulated at one
time, etc. The width of the sand platform outside the side ditch shall not be less
than 2 m. When no side ditch is provided, the width of the sand platform shall
not be less than 3 m. The sand platform shall be covered with pebble soil, gravel
soil, coarse gravel soil, cohesive soil, or cement mortar block board, etc.
14.4 Subgrade slope protection
14.4.1 When the embankment filler or cutting slope stratum is silt, fine sand,
and silty soil that is easy to be eroded, the shoulder, slope, and the surface
within 5 m from the top of the cutting to the outside shall be protected. For other
fillers or strata, in the high wind area and the Gobi windy sand flow area with
strong wind, according to the slope height, it is advisable to take measures to
prevent wind erosion on the shoulder and slope.
2 The structural design of the permanent sand barrier shall be based on the
load of sand blown by the wind. The foundation burial depth of the sand
barrier can be calculated according to Appendix D of this Code. The safety
factor of anti-overturning stability of the sand barrier shall not be less than
1.2.
3 The high vertical sand barrier should be perpendicular to the dominant wind
direction. The distance from the embankment slope toe or the cutting top
shall be comprehensively determined based on the wind speed, the
embankment height or the cutting depth, and the topography on the
windward side; and should not be less than 50 m.
4 The height of the high vertical sand barrier shall be comprehensively
determined according to the data, such as the topography, wind speed,
sand carrying height, engineering cost. When there is no data, in the desert
area, it should not be less than 1 m; in the Gobi strong wind area, it should
not be less than 1.5 m.
5 In sections with strong winds and abundant sand sources, the number of
rows of sand barriers can be appropriately increased outward. The
distance between the rows shall be calculated and determined according
to the maximum wind speed. It should be 10~20 times the height of the
barrier. The permanent sand barrier structure should not be used at the
leading edge.
6 A single sand retaining ditch dike should be used in sections, where there
are few sand sources. When there are many sand sources, a sand-proof
fence can be used on the outside. The distance from the sand retaining
ditch dike should not be less than 20 m.
7 When crossing a gully or overflow area, based on the flood pressure and
wind force, the anti-overturning stability of the column shall be calculated,
respectively.
14.5.8 The plane protection of sand blown by the wind shall be provided with a
maintenance channel. Fire barriers shall be provided as required. Its installation
shall meet the following requirements:
1 The maintenance channel should be planned in accordance with sand
control project, bridge-culvert entrance-exit, and fire barrier.
2 The surface of the maintenance channel should be laid with pebbles or
gravel, to prevent wind erosion. The particle size should not be less than
3 cm. The thickness should not be less than 10 cm. The width should not
be less than 5 m.
15 Subgrade of snow-damaged area
15.1 General provisions
15.1.1 Railway snow damages include snow accumulation and avalanche.
15.1.2 The direction of the line should be parallel to the dominant wind direction
of the snow drift; or the intersection angle shall not be greater than 30°. The line
shall avoid the foot of the hill slope with severe snow, the section prone to
avalanches and its hazard areas. When it is difficult to circumvent, it shall
choose to pass as a reasonable prevention project in the section with a small
range and a light hazard. For subgrade engineering, according to the
characteristics of terrain, topography, accumulated snow, or avalanche, it shall
take effective protective measures.
15.1.3 Subgrades in snow-damaged sections shall avoid low-fill shallow-
excavation and deep and long cuttings. The embankment height should be
greater than 3 times the average snow depth; and must not be less than 1.5 m.
The cutting depth should be 2.0 m~6.0 m. When it is unavoidable, a section
that is not easy to accumulate snow shall be used; and appropriate protective
measures be taken.
15.1.4 The design of subgrade protection engineering in snow-damaged areas
shall meet the following requirements:
1 In sections with severe snow accumulation, comprehensive control
measures can be taken to combine snow fences, snow banks, wind
deflectors, shrubbery belts, etc., to prevent the accumulated snow from
harming the subgrade engineering.
2 When the subgrade passes through the avalanche section and its hazard
area, according to the terrain conditions, preventive measures such as
stabilizing the snow on the slope, grading blocking, dredging and
dissipating energy can be taken.
15.1.5 For existing subgrade section, when serious snow accumulation or
avalanche hazards that bury lines often occur, engineering measures such as
open cut tunnels or shed tunnels can be used for remediation.
15.1.6 The subgrade shall meet the requirements of scouring of snowmelt water
flow and waterproof and drainage.
15.1.7 For subgrades in complex snow-damaged sections, it shall monitor the
snow damage after subg......
Related standard:   TB 10025-2019  TB 10041-2018
Related PDF sample:   TB 10001-2016  TB 10106-2010
   
 
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