7.2 Underground Pipeline
7.2.1 Underground pipeline of the same category and with similar burial depth shall be arranged in a proper and centralized way，however，shall not be laid overlapped.
7.2.2 Underground pipeline and pipe trench shall not be arranged in the lateral pressure influential zone of foundation of the buildings and structures，and it shall be avoided to affect the foundation of the buildings and structures by excavation work at the time of construction and maintenance of the pipeline/pipe trench.
7.2.3 Underground pipeline and pipe trench shall neither be arranged parallel and under the railway，nor the main road.
7.2.4 Underground pipeline and pipe trench should not pass through the throat area of the railway station（yard）and the area where the handling operation frequently takes place.
7.2.5 The minimum horizontal clearance between the underground pipelines shall meet the following requirements:
1 The clearance shall not be less than those specified in Table 7.2.5；when the elevation difference of burial depth of the adjacent pipelines is larger than 0.5m，values in the table shall also be subject to checking calculation according to soil property.
2 If the water supply pipe is laid below the sewage pipe，the water supply pipe must be made of metal，and the minimum horizontal clearance shall be properly determined according to the permeability of soil and conditions of groundwater under the premise that the requirements in Table 7.2.5 are fulfilled.
3 Where the water supply pipe and drainage pipe are buried together in the sand soil and the water supply pipe is not made of metal or synthetic plastic，the horizontal clearance between the supply pipe and the drainage pipe shall not be less than 1.5m.
4 When oxygen pipe and acetylene pipe and gas pipe which serve the same purpose are laid at the same level，the minimum horizontal clearance between pipes may be reduced to 0.25m，but loose soil or sand shall be filled in the space from bottom of the trench up to 300mm above the top of pipe before backfilling is performed.
7.2.6 The minimum horizontal clearance between underground pipeline and buildings and structures shall not be less than those specified in Table 7.2.6 and shall meet the following requirements:
1 If the railway and road are on the embankment or in the cutting，the clearance from water supply pipe to toe of slope of the railway embankment shall not be less than 5.0m，and to top of slope of the cutting shall not be less than 10.0m.The clearance from the water drainage pipe to toe of slope of railway embankment and to top of slope of the cutting shall not be less than 5.0m.
2 Horizontal clearance from the liquid and liquefied petroleum gas pipe to special buildings，structures（incl.military facilities，inflammable/explosive article storages，important cultural relic sites under state-level protection，airports，railway stations，wharfs，etc.）shall not be less than 100.0m；the horizontal clearance to residential district，villages，towns and important public buildings shall not be less than 50.0m if the pipe pressure is higher than 4.0MPa，not less than 40.0m if the pipe pressure is in the range of 1.6MPa-4.0MPa，and not less than 25.0m if the pipe pressure is below 1.6MPa.
3 If the pipeline burial depth is larger than the foundation bottom depth of of the buildings and structures，the minimum horizontal clearance from the pipeline to edge of the foundation of buildings and structures shall be subject to calculation according to soil property，but under no circumstance shall be less than those specified in Table 7.2.6.
4 The horizontal clearance from underground fuel gas pipe to the foundation of electric pole（tower）shall also meet the requirements for clearance between underground fuel gas pipe and earthing body of AC electric power transmission line as specified in current national standard GB 50028 Codefor Design of City Gas Engineering.
7.2.7 Horizontal clearance from the underground pipeline to the boundary of yard storing or handling corrosive materials shall not be less than 2.0m.
7.2.8 Underground pipeline must be arranged outside the surface subsidence limitation of the mine，keeping the distance in between no less than 15m.
7.2.9 The following requirements shall be complied with when the underground pipeline or pipe trench crosses the railway or road:
1 Vertical clearance from top of the pipe to bottom of the tracks of the railway shall not be less than 1.5m.
2 Vertical clearance from top of the pipe to bottom of the pavement layer of the road shall not be less than 0.7m.
Table 7.2.5 Minimum Horizontal Clearance between the Underground Pipelines（m）
Note:the values in the table refer to the horizontal clearance between outer walls of the pipeline，pipe trench，pipe，pipe insulation layer，and the outside most cable，etc.
Table 7.2.6 Minimum horizontal clearance between underrgound pipeline and buildings and structures （m）
Table 7.2.6 （continued ）
Table 7.2.6 （continued ）
Table 7.2.6 （continued）
Note：unless otherwise indicated，all values in the table refer to those counted from outside wall of the pipe，pipe trench and pipe insulation layer，or from the outside edge of the outside most cable.
7.2.10 In case the pipeline or pipe trench crossing the railway or road cannot meet the requirements of Article 7.2.9 herein，protection sleeve shall be used.The length of protection sleeve shall comply with the following requirements:
1 If the subgrade of railway or road is embankment，the protection sleeve shall extend out of the toe of slope of the embankment at both ends for no less than 1.0m.
2 If the subgrade of railway or road is not embankment，the protection sleeve shall extend out of the railway shoulder，highway road shoulder or urban road pavement at both ends for no less than 1.0m.
3 If water drainage side ditch is provided at the side of railway and road，the protection sleeve shall extend out of the ditch for 1.0m.
7.2.11 Arrangement at interception of the underground pipelines shall meet the following requirements:
1 Water supply pipe shall be arranged above the water drainage pipe.
2 Combustible gas pipe shall be arranged above other pipes（except for thermal power pipe）.
3 Thermal power pipe shall be arranged above the combustible gas pipe and water supply pipe.
4 Electric cables shall be arranged below the thermal power pipe and above other pipes.
5 Oxygen pipe shall be arranged below the combustible gas pipe and above other pipes.
6 Corrosive media pipe and acid/alkali-bearing water drainage pipe shall be arranged below other pipes.
7.2.12 Arrangement of the comprehensive pipe trench should meet the following requirements:
1 Pipe trench through which people can pass may be arranged under the green belt；if there are difficulties in doing so，it may be arranged under the road shoulder or sidewalk.
2 Ancillary structures of the pipe trench，such as trench entrance，ventilation shaft，etc.，shall be kept away from the pavement and shall not affect the road sight distance.
7.2.13 The following requiremens shall be complied with when laying the pipelines in the same trench:
1 Thermal power pipe shall not be laid in the same trench with electric power cable and telecommunication cable.
2 Oxygen pipe shall not be laid in the same trench with the fuel oil pipe，corrosive media pipe，electric cable and wire.Power cable shall not be laid together with combustible gas/combustion air pipe and fuel oil pipe in the same trench.
3 Water drainage pipe shall be arranged at bottom of the trench；if there are corrosive media pipes inside the trench，the water drainage pipe shall be arranged above them.
4 Elevation of the corrosive media pipe shall be lower than that of other pipes in the same trench.5 The pipes，which may cause unfavorable effect to each other，shall not be laid in the same trench.