Some standard content:
GB 17502—1998
This specification is formulated in accordance with the requirements of the State Council's "Regulations on the Administration of Laying Submarine Cables and Pipelines" and the State Oceanic Administration's "Implementation Measures for the Regulations on the Administration of Laying Submarine Cables and Pipelines", in order to safeguard my country's marine rights and interests, protect marine resources and environment, coordinate marine development activities, and ensure the quality of submarine cable pipeline route surveys.
The State Administration of Quality and Technical Supervision and the State Oceanic Administration have previously issued some marine survey specifications, which are not technical requirements for submarine cable pipeline route surveys, but some of the operating procedures can still be adopted. The parts quoted in this specification constitute the content of this specification. The technical requirements or specifications of some foreign companies are not directly quoted, and only the requirements applicable to my country are absorbed into this specification. This specification includes two parts: submarine cable pipeline route preselection and route survey, which can be used as the technical basis for the work of submarine cable pipeline route preselection and survey stages.
Appendix A is the appendix to the standard.
This standard is proposed by the State Oceanic Administration and is responsible for interpretation. This standard is under the jurisdiction of the National Center for Marine Standards and Metrology. This standard was drafted by the Second Institute of Oceanography, State Oceanic Administration. The main drafters of this standard are Li Quanxing, Ye Yincan, Pan Guofu, Li Qitong, Li Xiaoming, Chen Xitu and Chen Xiaoling. 829
1 Scope
National Standard of the People's Republic of China
Specifications for submarine cable and pipeline route investigation
Specifications for submarine cable and pipeline route investigationGB17502—1998
This specification specifies the pre-selection and investigation technology for submarine cable pipeline routes. The investigation technology during and after pipeline construction is not included in the scope of this specification.
2 Referenced standards
The provisions contained in the following standards constitute the provisions of this standard through reference in this standard. When this standard is published, the versions shown are valid. All standards are subject to revision, and parties using this standard should explore the possibility of using the latest versions of the following standards. GBJ11—89 Code for lightning resistance design of buildings
GBJ123—88 Standard for geotechnical test methods
GB12327-90 Code for hydrographic survey
GB/T1276391 Code for marine survey
GB/T13909-92 Code for marine survey Marine geological and geophysical survey GB/T14914—94 Code for seashore observation
GB17501—1998 Code for marine engineering topographic survey GB50021—94 Code for geotechnical engineering investigation
HY003.5—1991 Code for marine monitoring
YD5018-1996 Code for engineering design of submarine optical cable digital transmission system 3 Definitions
This standard adopts the following definitions.
Submarine cable and pipelineSubmarine cable and pipeline is a tubular facility for military and civilian submarine communication cables (including optical cables), power cables, and water (including industrial wastewater, urban sewage, etc.), gas, oil, and other substances located below the high tide level. 4 Route preselection
4.1 The task of route preselection is to select the two ends (including landing points) and the sea route location according to the overall layout of the cable pipeline. The preselected route should generally determine one plan. In areas with more complex situations, 2 to 3 comparative plans can also be selected and determined after the route survey. 4.2 The principle of route selection is technical feasibility, economic rationality, and the marine environment and development activities in the route area can meet the safe construction and operation of the cable pipeline. The requirements for selecting optical cable routes can refer to YD5018. 4.3 When pre-selecting routes, it is necessary to collect as much natural environment data as possible in the routing area, including water depth, seabed topography, landform, geology, sediment distribution, geomorphology, hydrology, meteorology, etc., especially to collect data on adverse engineering geological phenomena, such as bedrock distribution areas, scour gullies, ancient river valleys, shallow gas, turbidity current deposition areas, strong bottom currents, sand waves and their migration characteristics, seabed scouring and silting dynamics, etc. The pre-selected routes should avoid these adverse engineering geological phenomena distribution areas as much as possible. Approved by the State Administration of Quality and Technical Supervision on October 12, 1998 830
Implementation on April 1, 1999
GB17502 1998
4.4 When pre-selecting a route, it is necessary to collect as much information as possible on the marine development activities and their planning in the route area, mainly including: Fishery: including the number of fishing vessels in the route area, the main fishing method (pay special attention to whether there is sail net fishing), fishing season, shallow sea and tidal flat aquaculture areas, etc.; Mineral resource development: including the distribution of marine oil and gas fields and sand mining areas, resource exploitation status and planning, and the location of oil and gas pipelines; Transportation: including major routes and ship types (anchor types used), density, anchorages, waterways (including waterway dredging and mud dumping); Communication: distribution of submarine communication cables;
Electricity: distribution of submarine power transmission cables;
Agriculture: distribution of dams;
Municipal affairs: distribution of sewage pipelines;
Military distribution of military special zones;
Others: other marine development activities, such as tourist areas, dumping areas, marine nature reserves, scientific research and experimental areas, etc. When pre-selecting a route, it is necessary to avoid crossing with other development activities. If it cannot be avoided, it should be explained in detail to provide a basis for route coordination, design and construction.
4.5 When pre-selecting a route, attention should be paid to collecting man-made waste in the route area, such as sunken ships, containers, anchors, etc. The pre-selected route should avoid these man-made wastes.
4.6 When pre-selecting a route, a site survey of the landing point should be conducted to investigate the distribution of villages and towns near the landing point, land use, coastal properties and utilization conditions, beach (tidal flat) topography and sedimentary characteristics, the distance from the landing point to the landing station, and marine development activities near the landing point, such as fisheries, docks, and embankments. The section that is conducive to the landing of cable pipelines and close to the landing station should be selected as the landing point. 4.7 Collect the information of the cable pipelines built in the route area. If they cross the pre-selected route, the crossing point should be calculated in detail. At the same time, the failure history of the built cable pipelines should be collected, and the causes of the failures should be analyzed to provide useful experience for the design, construction and maintenance of new cable pipelines. 4.8 After the route is pre-selected, a pre-selected route report should be prepared. In addition to the detailed analysis of the relevant contents of 4.3 to 4.7, the report should also include a pre-selected route location table, which includes the turning point serial number, location (latitude and longitude), azimuth, distance between each turning point, cumulative distance, approximate water depth, etc. 5 Navigation and positioning
5.1 Basic technical requirements
5.1.1 Navigation and positioning work content
a) Onshore plane and elevation control measurement, establishment of control network, determination of navigation and positioning shore station position; b) Navigation and positioning of offshore survey vessels;
c) Positioning data collation.
5.1.2 Navigation positioning accuracy
a) The plane and elevation control measurement accuracy shall be implemented in accordance with GB17501-1998 4.4.1 and 4.4.2 respectively; b) When the mapping scale is greater than 1:2000, the error in offshore positioning shall not be greater than 2.0mm on the map; when the scale is between 1:2000 and 1:10000, the error in offshore positioning shall not be greater than 1.0mm on the map; when the scale is less than (or equal to) 1:10000, the error in offshore positioning shall not be greater than 0.5mm on the map.
5.1.3 Coordinate system and projection
The plane coordinate adopts the national coordinate system, and the WGS-84 geodetic coordinate system or independent coordinate system can also be adopted according to the requirements of the task entruster. The Gauss-Kruger projection is adopted, and the Mercator projection can also be adopted according to the requirements of the task entruster. 5.2 Plane and elevation control measurement
According to Chapter 6 and 7 of GB17501-1998. 5.3 Navigation and positioning of survey vessels
5.3.1 Navigation and positioning requirements
5.3.1.1 Navigation and positioning of underway geophysical exploration shall meet the following requirements:831
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a) When all geophysical exploration equipment is in normal working condition, the survey vessel shall enter the extension line of the survey line 10 minutes in advance and sail normally at the speed specified for geophysical exploration; b) The deviation between the track and the designed survey line shall not exceed 20% of the survey line spacing. If it exceeds this value, the navigation personnel shall promptly notify the geophysical department to arrange for re-measurement;
c) When encountering ships or obstacles in the water, they shall be avoided to ensure the safety of the survey vessel. After bypassing the obstacle, navigate to the original design survey line and continue working;
d) The spacing between positioning points on the map should not exceed 1cm;e) The duty record should record in detail the first and last point numbers of the survey line and the interference, interruption and treatment opinions of the navigation positioning signal during the work process, and check the point number with the relevant investigators every 20 points;f) The aiming center or antenna center of the survey vessel positioning instrument should coincide with the geophysical detection positioning center as much as possible, and the horizontal distance between the two should not exceed 1mm on the map, otherwise the point eccentricity correction should be performed. 5.3.1.2 Fixed-point survey navigation positioning should meet the following requirements: a) When the survey instrument reaches the seabed, the positioning data is recorded. The deviation between the actual survey station and the designed station is no more than 2 cm on the result map; b) The navigation personnel should place the ship operating the sampling instrument on the upwind side as much as possible. 5.3.2 Navigation positioning method
The navigation positioning methods for survey vessels mainly include microwave ranging positioning method, GPS positioning method, and hydroacoustic positioning method. 5.3.2.1 Microwave ranging positioning is implemented in accordance with 8.2 of GB17501-1998. 5.3.2.2 GPS dynamic positioning, which can be used in real-time single-point positioning and differential positioning. Real-time single-point positioning is only applicable to surveys with a scale of less than (or equal to) 1:100,000 in the far sea area where differential positioning is not possible; differential positioning is applicable to surveys of all scales and is implemented in accordance with 8.3 of GB17501-1998.
5.3.2.3 The hydroacoustic positioning system includes long baseline, short baseline and ultra-short baseline hydroacoustic positioning systems. The long baseline hydroacoustic positioning system is suitable for local sea area measurement and positioning, and is implemented in accordance with 6.6.7.2 of GB12327-90. The short baseline hydroacoustic positioning system is suitable for measurement and positioning very close to the top of the underwater target, and is implemented in accordance with 6.6.7.3 of GB12327-90. The ultra-short baseline hydroacoustic positioning system is generally used to establish navigation positioning of ocean joint survey points and positioning of underwater geophysical transducers (such as side-scan sonar towfish). When used to establish navigation positioning of ocean joint survey points, it is implemented in accordance with 6.6.7.4 of GB12327-90. When used for positioning of underwater geophysical transducers, the underwater sound mark is installed in the transducer, and the three-dimensional positioning of the transducer is performed in combination with the positioning information of the survey ship. 5.3.3 Positioning data collation
5.3.3.1 Field data collation and inspection shall be carried out in accordance with 9.4.2 of GB17501-1998. 5.3.3.2 According to the positioning data, the navigation detection track map and the fixed-point survey operation location map shall be compiled. They can be compiled together or separately, and can be made by computer-assisted mapping or manually recorded in the working drawing plate for drawing; when making computer-assisted mapping, it is required to be carried out in accordance with 9.8.2 of GB17501-1998, and when drawing manually, it is required to be carried out in accordance with 9.5.2 of GB17501-1998. 6 Engineering geophysical exploration
Engineering geophysical exploration includes water depth measurement, side-scan sonar detection, surface layer detection and magnetic detection to identify the seabed topography, seabed surface conditions, seabed obstacles, shallow seabed geological features and adverse geological phenomena. Magnetic detection can be carried out as needed. 6.1 Mapping scale and survey network layout
6.1.1 Mapping scale
The scale of engineering geophysical surveying is determined according to actual needs and the complexity of the shallow geological landforms of the seabed. It is generally stipulated as follows: a) offshore and island areas are surveyed at a scale greater than (or equal to) 1:5000; b) continental shelf areas are surveyed at a scale of 1:5000 to 1:50000; c) continental slope and deep sea basin areas are surveyed at a scale of 1:25000 to 1:100000. The mapping scale can also be selected according to the client's requirements.
6.1.2 Mapping framing
GB 17502—1998
The mapping framing adopts free framing, with the principle of covering the entire survey area with fewer framing sheets. There should be a certain overlap between adjacent framing sheets and in the route turning point area.
6.1.3 Map size
Standard map size is: 50cm×70cm; 70cm×100cm; 80cm×110cm. 6.1.4 Survey line layout
The main survey line should be laid out in parallel with the pre-selected route, with a total of no less than 3 lines, one of which should be along the pre-selected route, and the other survey lines should be arranged on both sides of the center line. The survey line spacing is generally 100m~300m. The detection line should be perpendicular to the main survey line, and the spacing between them is 1km~2km when the water depth is less than 20m, and 5km~10km when it is greater than 20m. In the nearshore section and complex seabed area, the survey line spacing should be appropriately reduced, and in the deep sea basin area, the survey line spacing can be appropriately increased.
6.2 Depth measurement
6.2.1 Technical requirements
6.2.1.1 The accuracy of depth measurement is measured by the difference between the depth measurement values at the intersection of the main survey line and the detection line. The root mean square error should not be greater than 0.20m when the water depth is less than 20m, and should not be greater than 1% of the actual water depth when the water depth is greater than (or equal to) 20m. 6.2.1.2 The layout of survey lines shall be carried out in accordance with 6.1.4. When using a multi-beam sounding system for full coverage depth measurement, a reasonable survey line spacing should be selected based on the water depth and instrument performance to ensure that there is no less than 10% overlap between adjacent survey lines. If there is a lack of sound velocity or hydrological data in the survey area, an appropriate number of sound velocity or hydrological observation points should be arranged to obtain sound velocity profile data for sound velocity correction of the sounding data. 6.2.1.3 The datum of the water depth map is the "1985 National Height Datum". Other datums may be used according to the requirements of the survey task entrusting party. 6.2.2 Implementation of water depth measurement
According to 9.2.6, 9.2.7 and 9.2.8 of GB17501-1998. 6.2.3 Data collation
6.2.3.1 Depth measurement shall be carried out in accordance with 9.5.4 of GB17501-1998. 6.2.3.2 Depth correction shall be carried out in accordance with 9.5.5 of GB17501-1998. 6.2.3.3 The result map of water depth measurement shall include water depth map and water depth profile map. The map shall be drawn by computer according to the data file, and the report can also be printed according to the water depth data. The depth map should be based on the track map, and the depth contour interval is generally 0.5m, 1m, 2m, 5m, 10m, 20m, 50m, 100m or 200m, depending on the map scale and terrain slope. The depth contours are divided into the head curve and the counting curve. The legend should indicate the depth sounder model and depth reference plane. The horizontal scale of the depth profile is generally 1:5000, 1:10000, 1:100000, and the vertical scale is generally 1:100, 1:200, 1:500, 1:1000 or 1:5000.6.3 Side-scan sonar detection
6.3.1 Technical requirements
6.3.1.1 Choose a reasonable sonar according to the survey line spacing Scanning range requires 100% coverage within the route survey corridor, and adjacent survey lines must have 20% to 30% repeated coverage. When the water depth is too small, the repeated coverage rate can be appropriately reduced. 6.3.1.2 The operating frequency of the side scan sonar is 50kHz~~500kHz, the horizontal beam angle is less than (or equal to) 1°, the pulse length is less than (or equal to) 0.2ms, and the effective range is greater than (or equal to) 200m; it has functions such as water removal, speed correction, and tilt distance correction. 6.3.1.3 Supplementary detection should be carried out for the following situations: missed survey line segments, track deviation from the designed survey line greater than 20% of the survey line spacing, and unqualified recorded map quality resulting in inability to make correct interpretations. 6.3.2 Implementation of marine detection||tt ||6.3.2.1 Before the start of the survey, a representative sea area should be selected in or near the survey area for instrument debugging to determine the best working parameters. 6.3.2.2 After the sonar towfish enters the water, the survey vessel shall not stop or reverse, and shall keep the heading stable as much as possible, and shall not use a large rudder angle to correct the heading; a small rudder angle and a large turn should be used to change the survey line. 6.3.2.3 The height of the sonar towfish from the seabed should be 10% to 20% of the scanning range. In waters with large seabed undulations, the height of the towfish from the seabed can be appropriately increased.
6.3.2.4 When the sonar spectrum is recorded as a spectrum record after water body removal, speed correction and tilt distance correction, the uncorrected original data should be recorded in electronic media at the same time.
GB 17502—1998
6.3.2.5 The sonar towfish can be automatically positioned by using water acoustic positioning equipment, and the position of the sonar towfish can also be corrected by manual calculation. 6.3.2.6 Conduct a preliminary interpretation of the sonar map records on site, and arrange additional survey lines in different directions around suspicious targets for further detection.
6.3.3 Interpretation of detection data
Combined with the results of seabed sampling and shallow layer profile detection, interpret the seabed surface conditions; identify interference signals, noise and echo signals that have no engineering significance on the sonar map records; identify the types of seabed sediments, determine the distribution range of various types of sediments and exposed bedrock on the seabed; analyze the seabed micro-topography; identify and locate seabed obstacles. For the identified seabed surface features and seabed obstacles, the speed, tilt distance and transducer position should be corrected to determine their true position, distribution range, size and shape, and plot them on the track map. For seabed surface features with vertical undulations, their near-sighted height and depth should be determined based on the length of the acoustic shadow on the sonar record map. The obviously concave and convex irregular terrain morphology of the interpreted seabed surface should be added to the water depth map. 6.3.4 Results Maps
Based on the side-scan sonar detection results, a seafloor status map is drawn. The map uses the track map as the base map, and includes geological data on seafloor sampling, coastlines, surrounding land areas, and major land features. According to the requirements of the task entruster, the sonar mosaic map of the survey area is completed based on the sonar detection data, using computer automatic digital mosaic or manual mosaic.
6.4 Stratum Surface Detection
6.4.1 Technical Requirements
6.4.1.1 Shallow stratigraphic profile detection obtains stratigraphic changes and adverse geological phenomena within a depth of 30m below the seafloor, with a stratigraphic resolution of no less than 30cm. When surveying the pipeline route, a mid-stratum profile detection is carried out as needed to obtain acoustic profile records within a depth of 100m below the seafloor surface, identify stratigraphic distribution characteristics and disastrous geological phenomena, and have a stratigraphic resolution of no less than 1m. 6.4.1.2 The recorded surface image is clear, without strong noise interference and image blur, blank, interruption, etc. 6.4.2 Implementation of marine exploration
6.4.2.1 Shallow stratum profile detection uses shallow penetration stratigraphic profiler, and the transducer should be immersed in water at a depth of not less than 0.5m. Medium stratum profile detection uses medium penetration stratigraphic profiler, and its lightning source and hydrophone array must be towed outside the stern vortex area and float at a certain depth. 6.4.2.2 Before the start of marine exploration, tests should be carried out in the survey area to determine the instrument working parameters to obtain the best stratum penetration depth and resolution, and to suppress noise and interference to the minimum. 6.4.2.3 The requirements for the navigation of survey vessels during marine exploration are the same as those in 6.3.2.2. 6.4.2.4 The recorded profile image should be complete, with the missed or missing part in the middle not exceeding 250m, and the cumulative missed section less than 2% of the total length of the survey line. Otherwise, supplementary surveys should be conducted.
6.4.2.5 Preliminary analysis of the recorded profile image, if a suspicious target is found, additional survey lines should be laid to determine its nature. 6.4.3 Stratigraphic surface data interpretation
Data interpretation is carried out using replicated stratigraphic surface records, mainly including the following contents: a) Identify interference waves on profile records and remove geological illusions; b) Divide the profile seismic (acoustic) sequence and compare it with the geological drilling stratification data in the survey area; analyze the spatial morphology of each sequence and the contact relationship between each sequence, and determine the geological characteristics and engineering properties of each sequence; the layers at the intersection of the main survey line and the detection line must be closed; c) Perform seismic phase analysis based on seismic (acoustic) parameters such as reflection structure, amplitude, continuity, frequency, etc. recorded in the profile, and infer the sedimentary environment, sedimentary phase, sediment type and its engineering properties, etc.; d) Identify the following adverse geological phenomena: shallow gas, ancient river valley, landslide, collapse, fault, mud mound, bedrock, turbidity current deposits, salt dome, submarine soft soil interlayer, erosion groove, etc., and determine their nature, size, shape and distribution range. 6.4.4 Results Maps
Compile stratigraphic profiles and shallow geological feature maps based on the results of stratigraphic layer detection and geological data of the survey area. 6.4.4.1 Stratigraphic profiles should generally be compiled using the route centerline; the horizontal scale is the same as that specified in 6.1.1, and the vertical scale is reasonably selected. Generally, the ratio of the vertical and horizontal scales is not greater than 10:1. The map includes important features such as the seabed interface, stratigraphic interface, lithology of each layer, shallow gas distribution interface, faults, etc., and marks the main landforms passed, the locations of seabed sampling and drilling, and the layered description and test results of seabed sedimentary columns or cores.
6.4.4.2 The shallow geological characteristic map mainly includes the following contents: a) thickness contour lines or top surface burial depth contour lines of important stratigraphic layers; b) important topography, landforms and shallow geological phenomena; c) distribution of major adverse geological phenomena and their morphology, nature, scale, genesis, etc. The shallow gas zone should mark the top burial depth of the gas-bearing stratum and the possible distribution range;
d) main landforms in the survey area, seabed sampling station and drilling position and core test results. When the content of the shallow geological characteristic map is relatively small, it can be compiled together with the seabed surface status map. 6.4.4.3 When drawing the stratigraphic profile, time-depth conversion is required. The time-depth conversion should be based on the sound velocity logging data or other sound velocity data in the sea area within and near the survey area. When there is no actual sound velocity data, the assumed sound velocity of 1500m/s can be used for time-depth conversion. The sound velocity data used for time-depth conversion must be indicated in the legend column. 6.5 Marine magnetic detection
6.5.1 Technical requirements
6.5.1.1 The mean square error of magnetic detection should not be greater than 2nT, and the mean square error calculation shall be carried out in accordance with 36.2.5 of GB/T13909-92. 6.5.1.2 The survey line layout is consistent with other geophysical survey lines. Supplementary survey lines are added to the abnormal areas that may be caused by magnetic objects according to the survey data; supplementary survey lines are added to the areas marked as magnetic objects (pipelines, cables, wellheads, bombs, sunken ships, etc.) by historical data. 6.5.1.3 When the survey data is used for geological condition analysis in the survey area, a geomagnetic diurnal variation observation station should be established at the same time as the marine survey. The requirements for geomagnetic diurnal variation observation shall be carried out in accordance with 35.3 of GB/T13909-92. 6.5.2 Implementation of marine survey
6.5.2.1 When the water depth is greater than 100m, the sensor should be deep-towed. 6.5.2.2 The requirements for the navigation of survey vessels in marine magnetic survey are the same as those in 6.3.2.2. 6.5.2.3 Before the survey begins, a ship magnetic orientation influence test should be carried out in the survey area in accordance with 34.2 of GB/T13909-92. 6.5.3 Interpretation of survey data
6.5.3.1 According to the magnetic anomaly, the seabed magnetic objects are identified, and the properties, plane positions, shapes, sizes, occurrences and burial depths of these objects are calculated and determined. The interpretation should be combined with the results of side-scan sonar and stratigraphic profile survey. 6.5.3.2 The measured geomagnetic data are corrected for the geomagnetic normal field, daily variation and ship magnetic field, and the geomagnetic anomaly is calculated; the geological interpretation is carried out to obtain geological information such as the bedrock lithology and morphology, basement fracture characteristics, and igneous rock activities in the route area. The calculation of geomagnetic anomaly is carried out in accordance with 36.2 of GB/T13909-92, and the geological interpretation is carried out in accordance with 37.3 of GB/T13909--92. 6.5.4 Results Maps
Detected ferromagnetic objects on the seabed should be marked on the seabed surface map, and some of the more important parts should be separately mapped and explained as needed.
The results of the geological interpretation of geomagnetic anomalies shall be marked on the geological feature map. 7 Sediment sampling and geotechnical tests
7.1 The main task of sediment sampling and geotechnical tests is to understand the plane and vertical distribution characteristics of the sediment in the submarine cable and pipeline routing area and its engineering properties. Sediment sampling stations should be arranged in different sediment locations preliminarily determined by the interpretation of engineering geophysical data. The interval of sediment sampling along the route is 2km when the water depth is less than 20m, 5km when it is 20-200m, and 20km when it is greater than 200m. Sampling can be reduced or not in non-buried areas. Sampling stations should be arranged in potential submarine engineering geological disaster areas, such as faults, landslides, sand waves, shallow gas (gas-bearing sediments), buried ancient river channels, irregular bedrock surfaces, etc.
7.2 Seabed sampling generally uses gravity samplers, which are divided into surface sampling and column sampling. The column sampling depth should be greater than 2m for muddy seabed and greater than 0.3m for sandy seabed. When column sampling is difficult, surface sampling can be used instead. 835
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7.3 When implementing column sampling of seabed sediments, there should be a liner in the sampling tube. After obtaining the sample, it should be numbered and properly kept. After the on-site analysis test, it should be sent to the laboratory as soon as possible. During storage and transportation, it should be prevented and avoided to be subjected to dynamic or impact loads that cause disturbance and water loss of the soil sample structure. 7.4 Record the sampling location, water depth, sample, and length in detail. The sample should be described in detail, and the soil sample or soil sample photos should be kept. The description shall include at least the following:
a) color;
b) smell;
c) soil classification name;
d) particle size composition;
e) soil state and disturbance degree;
f) soil layer structure and texture;
g) biological content.
7.5 Important pipeline projects, add mud temperature test. In the absence of geothermal probes in China, mud temperature can be measured immediately when sediment is taken on board. Or measure the bottom water temperature and mud temperature at the same time, establish the relationship between the two, and then collect the bottom water temperature data to calculate the mud temperature. 7.6 Geotechnical test items should include:
a) Water content (ui);
b) Natural gravity (7);
c) Specific gravity (Gs);
d) Liquid limit (WL);
e) Plastic limit (Wp);
f) Particle analysis;
g) Undrained shear strength (small penetration test, small cross-plate shear test). When conditions permit, unconfined compressive strength test, direct shear test, or triaxial undrained shear test can be carried out: h) For important pipeline projects, dynamic triaxial shear test shall be added according to the requirements for sand liquefaction identification. 7.7 Geotechnical analysis test methods and technical requirements shall be implemented in accordance with Chapter 3.4.5.6.7 of GBJ123-88. 7.8 Soil test data collation, soil classification method according to Appendix A (Standard Appendix). Domestic projects can also be implemented according to relevant industry standards or specifications.
7.9 The results of the bottom survey should be shown on the geological characteristic map and the comprehensive profile map. 8 Engineering geological drilling
For important pipeline projects, engineering geological drilling is required during route survey. 8.1 Hole layout
Engineering geological drilling is generally determined after the interpretation of geophysical exploration data. A certain number of engineering geological drilling holes should be arranged in different landforms, geological units and distribution areas of adverse geological phenomena. The spacing of boreholes along the pipeline route is generally 5km when the water depth is less than 20m, and 20km when the water depth is 20~~200m. Engineering geological drilling can be reduced or not carried out in non-buried areas of pipelines. 8.2 Drilling technical requirements
8.2.1 The distance between the actual drilling hole position and the designed hole position must be less than 30m, otherwise it should be re-positioned. 8.2.2 The depth of the borehole varies according to the buried depth of the pipeline, generally 8 to 10 meters or 5 times the buried depth of the pipeline. 8.2.3 The diameter of the core shall not be less than 69 mm.
8.2.4 For cohesive soil, the core shall be taken by the hydraulic method of a thin-walled corer, and for sandy soil, the core shall be taken by hammering. 8.2.5 Before drilling, the water depth shall be measured and corrected by the drill rod reading. After obtaining the first core sample, the water depth shall be measured again for further correction.
8.2.6 The core sampling rate: not less than 80% for cohesive soil; not less than 70% for bedrock (using diamond drill bit), not less than 60% for sandy soil, and not less than 50% for weathered and broken zone and pebble layer (using biological glue sampling). 836
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8.2.7 The interval between no cores shall not exceed 1m for cohesive soil and 2m for other soils. 8.2.8 The sampling interval of the undisturbed soil layer is generally less than 2m. When the soil layer thickness is greater than 3m, the maximum sampling interval shall not exceed 3m. 8.3 Borehole Logging
8.3.1 Borehole logging is carried out simultaneously with offshore drilling operations. Contents of the log: a) Lithology description;
b) Color photography;
c) Sampling records;
d) Field test records;
e) Borehole structure;
) Construction operation conditions.
8.3.2 On-site sample processing includes:
a) The samples obtained by drilling are stored in a special core box in order and in a timely manner. Each core is separated from the next core by a core card. The core card is painted with paint to indicate the start and end depths of drilling. The missing parts of the core should be marked and filled with fillers; b) All samples are wrapped with cling paper and tin foil; c) The original samples are wrapped with cling paper and tin foil, placed in a plastic tube and sealed with wax, marked with depth, top and bottom, numbered, and placed vertically in a box, and kept warm.
8.4 Drilling results and completion report
8.4.1 The materials to be submitted after the drilling is completed include: a) Drilling completion report;
b) Compilation book;
c) Sample distribution and sample delivery list;
d) Drilling engineering geological comprehensive column chart,
e) Field test chart;
f) Core transfer and storage table.
8.4.2 Main contents of drilling completion report:
a) Drilling purpose and task;
b) Borehole coordinates, elevation, water depth; bzxz.net
c) Construction time;
d) Drilling and coring methods,
e) Abnormal conditions during drilling,
f) Drilling quality acceptance.
8.5 Sample indoor test
Test items and methods shall be carried out in accordance with 7.5 to 7.7 of this standard. 9 Landing section survey
9.1 The landing point of the cable pipeline refers to the sea-land interface point of the cable pipeline route, which is generally on the landward side of the sand bank or artificial dam slightly higher than the high tide level of the spring tide. The scope of the landing section survey should include the vicinity of the landing point, the intertidal zone crossed by the route, and the adjacent shallow sea (usually to a water depth of about 5m).
9.2 The scale of the landing section survey shall not be less than 1:5000. 9.3 The requirements for the landing point survey include:
a) Accurately determine the geographical coordinates and elevation of the landing point. The accuracy of the geographical coordinate measurement should meet the requirements of third-order triangulation points; the accuracy of the elevation measurement should meet the requirements of fourth-order leveling;
b) 0.5km of the coastline on both sides of the landing point should be measured, and the rest can be transferred from large-scale maps; 837
GB17502—1998
c) The landforms or artificial buildings (such as dams, houses, electric poles, sluices, etc.) within 0.5km on both sides of the landing point should be measured, and the landforms and buildings should be photographed.
9.4 The survey of intertidal zone includes:
a) Topographic mapping of intertidal zone, which is spliced with beach and water survey methods; b) Bottom survey of intertidal zone, which can be done by beach sampling (surface, columnar or hand-drilled) and water sampling methods, and detailed description of bottom distribution; c) Landing point and intertidal zone topography survey shall be carried out in accordance with 10 of GB17501-1998. 9.6 Nearshore waters refer to the intertidal zone to the shallow sea with a depth of about 5m. Since the route survey vessel cannot enter, the survey is conducted by a shallow draft vessel. The survey requirements refer to Chapters 5, 6, 7 and 8 of this specification. When columnar sampling is difficult, surface sampling can be carried out. 10 Observation of marine hydrological and meteorological elements
Marine hydrological and meteorological elements include meteorology, waves, tide level, ocean current, water temperature, sea ice and other items. 10.1 Marine Meteorology
10.1.1 Collect and organize the meteorological conditions of the route area, point out the best climate window throughout the year, and provide a basis for the selection of the cable pipeline construction period. 10.1.2 Sources of meteorological data: Meteorological observations on board during route survey; collection of meteorological station data near the route area; ship survey and reporting data of the route area over the years.
10.1.3 The collected and organized meteorological parameters are: a) Wind, including the frequency of wind in each direction in each month for many years, average wind speed and maximum wind speed (10m above the sea surface) and the number of strong wind days in each month for many years; b) Temperature, including the extreme highest, lowest and average temperature in each month for many years; c) Humidity, refers to the average relative humidity in each month for many years; d) Fog, refers to the average foggy days in each month for many years.
10.1.4 The pipeline route survey can increase the calculation of the maximum wind speed in the recurrence period. Generally, it is required to calculate the maximum wind speed in the recurrence period of 3s, 1 min, 10 min, and lh for 1 year, 10 years, 50 years, and 100 years. 10.1.5 The meteorological observation method shall be implemented in accordance with 18 to 25 in GB/T12763.3--1991. 10.2 Waves
10.2.1 Collect wave data in the routing area and point out the period with better sea conditions throughout the year to provide a basis for the selection of the cable pipeline construction period. 10.2.2 Wave data mainly collects data from hydrological and meteorological stations near the routing area, as well as ship report data from previous years. If necessary, it can be calculated based on meteorological data.
10.2.3 Wave data collation requirements include the frequency of waves, maximum wave height, average wave height and corresponding period in many years, months and directions; average wave height, maximum wave height and main wave direction in many years and months. 10.2.4 Pipeline route survey can increase the calculation of wave height and period in the recurrence period. Generally, it is required to calculate the maximum wave height (Hmax), effective wave height (H.) and average zero crossing (T2) period with a recurrence period of 1 year, 10 years, 50 years and 100 years. 10.3 Tide
10.3.1 Analyze the relationship between the tidal properties of the route area and various tidal levels. 10.3.2 Tidal observation stations can be set up in nearshore or island areas, and tidal data can be collected in farshore areas, or predicted tide levels can be used. 10.3.3 The relationship between the base surface and each tidal surface includes the 1985 National Height Datum, the theoretical depth datum, the local customary base surface, the local mean sea level, the theoretical highest tide level and the lowest tide level. 10.3.4 Pipeline route survey can increase the extreme tide level of the recurrence period, that is, the highest and lowest tide levels that occur once in 50 years and 100 years. 10.3.5 Tidal station observation requirements shall be implemented in accordance with 7 to 10 of GB/T14914--1994. 10.4 Ocean Current
10.4.1 Source of ocean current data: collect previous measured data in the route area, or use predicted ocean current data. The pipeline route survey should arrange enough measuring stations and buoy stations with a monthly cycle in the route area according to the terrain conditions to obtain ocean current data. 10.4.2 Ocean current data should include three layers: surface, middle and bottom. The analysis items are mainly the flow conditions in the route area, the measured maximum tidal velocity, the average large tidal velocity, the average small tidal velocity, the maximum possible tidal velocity and the mainstream direction, and numerical simulation when necessary. The pipeline route survey can increase the calculation of the maximum tidal velocity with a recurrence period (1 year, 10 years, 50 years, 100 years). As an option, the continuous time intervals with a flow velocity of less than 3 knots are counted. 10.4.3 The requirements for ocean current observation shall be implemented in accordance with 2124 of GB/T12763.2-1991. 10.5 Water temperature
10.5.1 Water temperature observation and ocean current observation are carried out simultaneously, and the existing water temperature observation data in the route area should also be collected. 10.5.2 Water temperature parameters mainly describe the spatial distribution of water temperature and the temporal variation of water temperature. 10.5.3 Water temperature observation requirements shall be implemented in accordance with 13~16 of GB/T12763.2-1991. 10.6 Sea ice
10.6.1 Collect existing sea ice observation data in the route area, and set up observation stations when necessary. 10.6.2 Sea ice data collection and observation requirements shall be implemented in accordance with 32~35 of GB/T12763.2-1991. 11 Determination of corrosion environment parameters of submarine cables and pipelines Corrosion environment parameters include bottom water chemistry, sediment chemistry, sediment resistivity, sulfate-reducing bacteria and fouling organisms in sediments, etc. 11.1 Bottom water chemistry
11.1.1 The bottom water chemistry sampling station is generally the same as the bottom sediment sampling station, and water samples are collected 1m above the seabed. 11.1.2 The bottom water chemistry test shall not be less than the following parameters: pH, Eh, dissolved oxygen and oxygen saturation. 11.1.3 The technical requirements for bottom water chemistry determination shall be in accordance with GB/T12763.4-1991, 9~~20. 11.2 Sediment Chemistry
11.2.1 The sampling station for sediment chemistry is generally the same as that for bottom sediment. The sampling layers of sediment chemistry in columnar samples can be divided into three layers: surface, middle and bottom.
11.2.2 Sediment chemistry tests shall include no less than the following parameters: pH, Eh, Fe3+/Fe2+, salinity, carbonate, and organic matter. Cable route surveys shall include the determination of sulfide.
11.2.3 The technical requirements for sediment chemistry determination shall be in accordance with GB/T13909--1992, 18, and the determination technology for sulfide shall be in accordance with HY003.5-1991, 14.
11.3 Sediment resistivity
11.3.1 Sediment resistivity measurement is mainly used for submarine pipeline route survey. The measurement station is consistent with the bottom sampling station. The measurement level can be divided into three layers: surface, middle and bottom.
11.3.2 A microcomputer induced polarization instrument can be used for resistivity measurement, and the observation error should be less than 1m·2.11.4 Sulfate-reducing bacteria in sediments
Use a sterile tongue depressor to collect sediment samples from the surface, middle and bottom of the columnar sample to detect the number of sulfate-reducing bacteria. The technical requirements for sulfate-reducing bacteria detection shall be implemented in accordance with 15 to 18 of GB/T12763.6--1991. 11.5 Fouling organisms
11.5.1 Generally, it should include attached organisms and drilling organisms. 11.5.2 The technical requirements for investigation shall be implemented in accordance with 31 to 34 of GB/T12763.6--1991. 12 Seismic Hazard Analysis
Seismic work for submarine cable and pipeline routing includes seismic hazard analysis, ground motion parameter estimation, sand liquefaction identification, and landslide and collapse assessment.
12.1 Ground Hazard Analysis
The probability analysis of ground hazard requires the probability of the project site encountering a ground motion exceeding a given value in the future, or the exceedance probability P, which is usually represented by an earthquake exceedance probability curve.
The probabilistic method of ground hazard analysis takes into account the uncertainty of the time, location, and propagation path of earthquakes affecting the project site. The ground motion parameters given have probabilistic meanings, which can optimize the design between economic investment and risk level. 839
GB 17502—1998
Seismic hazard analysis includes regional (200km on both sides of the route) and near-field (25km on both sides of the route) seismic structures, seismic activity, potential source area division, and probability calculation of seismic hazard. Finally, the earthquake intensity value and bedrock ground motion horizontal peak acceleration value with a probability of exceeding 10% in 50 years for the project site are given.
When evaluating the activity of the main hidden faults in the near field, it is necessary to fully collect and analyze relevant data such as geophysical detection and engineering geological drilling of submarine cable pipeline routing projects.
12.2 Sand liquefaction identification
When there is saturated sand or saturated silt in the routing area, the possibility of liquefaction should be identified, and the degree of liquefaction hazard should be evaluated and suggestions for anti-liquefaction measures should be put forward. When the intensity is 6, earthquake liquefaction can generally not be considered. When the intensity is greater than 6, it can be identified according to the provisions of 3.3 of GBJ11-89.
12.3 Landslide and collapse assessment
Areas with a seismic fortification intensity of 7 or greater are defined as strong earthquake areas. Sites in strong earthquake areas should consider potential landslide and collapse assessments. When evaluating the potential landslides and collapses at the strong earthquake zone site of the submarine cable pipeline routing project, it is recommended to follow the relevant provisions of GB50021--94.
Landslide is the phenomenon that the unstable soil (or rock mass) on the slope slides downward along a certain sliding surface (sliding zone) as a whole under the action of earthquake force or gravity. Underwater landslides are more likely to occur under the action of earthquake force or gravity in the steep slope section of the submarine deep water tank. Landslide investigation should be done as follows: a) The scope, scale, geological background, nature and degree of hazard of the landslide should be identified. The primary and secondary conditions and causes of the landslide should be analyzed, and the degree of stability should be determined, its development trend should be predicted, and prevention and control plan suggestions should be put forward; b) Engineering geological mapping and investigation should be carried out for the landslide area investigation, and its scope should include the landslide area and its adjacent stable areas. The scale can be selected from 1:200 to 1:2000 according to the scale of the landslide. 12.3.2 Underground features formed by geological and geochemical processes and (or) human activities may cause collapse conditions that seriously affect the safety of the project site. The following should be followed when conducting collapse assessment:
a) For sites with potential collapse hazards, when the standard value of foundation bearing capacity fk or the average shear wave velocity Usm is greater than the values listed in Table 1, the collapse impact can be ignored;
Table 1 Standard values of critical bearing capacity and average shear wave velocity values Design intensity
Standard value of bearing capacity fk, kPa
Average shear wave velocity value Usm
b) When the collapse impact needs to be considered in the submarine cable and pipeline routing project, appropriate anti-seismic measures can be taken in combination with the nature of the project and foundation conditions.
13 Evaluation of route conditions and report writing
13.1 Evaluation of route
13.1.1 Engineering geological conditions
Summarize the engineering geological conditions such as topography, geomorphology, geology, structural background, seabed surface conditions, bottom soil and its geotechnical properties in the entire route area, and pay special attention to whether the route avoids adverse engineering geological phenomena (such as scour gullies, shallow gas, seabed collapse, landslides, turbidity currents, bedrock, ancient river valleys, active sand waves, mud mounds, salt domes, soft soil interlayers, etc.). If it cannot be avoided, it should be described clearly so that corresponding engineering measures can be taken during design and construction. 13.1.2 Marine hydrometeorological environment
Analyze the weather, waves, tides, currents, water temperature, sea ice and their characteristic values in each section of the route, recommend a climate window suitable for cable pipeline construction, and conduct a detailed analysis of the marine environment (such as strong bottom currents) that may affect the construction, operation and maintenance of cable pipelines. 13.1.3 Engineering Seismic Conditions
Analyze the regional seismic structure and seismic activity of the route area, calculate the seismic activity parameters of each potential source area, including the seismic intensity value with a 50-year exceedance probability of 10% and the horizontal peak acceleration value of the bedrock seismic movement: Estimate the seismic intensity of the submarine cable pipeline route under the action of earthquakes and waves.3.2 Resistivity can be measured using a microcomputer induced polarization instrument, and the observation error should be less than 1m·2. 11.4 Sulfate-reducing bacteria in sediments
Use a sterile tongue depressor to collect sediment samples from the surface, middle and bottom of the columnar sample to detect the number of sulfate-reducing bacteria. The technical requirements for sulfate-reducing bacteria detection shall be implemented in accordance with 15 to 18 of GB/T12763.6--1991. 11.5 Fouling organisms
11.5.1 Generally, attached organisms and drilling organisms should be included. 11.5.2 The technical requirements for investigation shall be implemented in accordance with 31 to 34 of GB/T12763.6--1991. 12 Seismic hazard analysis
Seismic work for submarine cable and pipeline routes includes seismic hazard analysis, ground motion parameter estimation, sand liquefaction identification, and landslide and collapse assessment.
12.1 Seismic Hazard Analysis
The probability analysis of seismic hazard requires the probability of the project site encountering a seismic motion exceeding a given value in the future, or the exceedance probability P, which is usually expressed by the earthquake exceedance probability curve.
The probability method of seismic hazard analysis takes into account the uncertainty of the time, location and propagation path of the earthquake affecting the project site. The given seismic motion parameters have probabilistic meanings, which can optimize the design between economic investment and risk level. 839
GB 17502—1998
Seismic hazard analysis includes regional (200km on both sides of the route) and near-field (25km on both sides of the route) seismic structures, seismic activity, potential source area division and probability calculation of seismic hazard. Finally, the seismic intensity value and bedrock seismic horizontal peak acceleration value with a 50-year exceedance probability of 10% are given for the project site.
When assessing the activity of the main hidden faults in the near field, it is necessary to fully collect and analyze relevant data such as geophysical exploration and engineering geological drilling for submarine cable and pipeline routing projects.
12.2 Identification of sand liquefaction
When there is saturated sand or saturated silt in the routing area, the possibility of liquefaction should be identified, and the degree of liquefaction hazard should be evaluated and suggestions for anti-liquefaction measures should be put forward. When the earthquake intensity is 6, earthquake liquefaction can generally be ignored. When the earthquake intensity is greater than 6, it can be identified in accordance with the provisions of 3.3 of GBJ11-89.
12.3 Landslide and collapse assessment
Areas with a seismic fortification intensity of 7 or greater are defined as strong earthquake areas. Potential landslide and collapse assessment should be considered for sites in strong earthquake areas. When evaluating the potential landslide and collapse of sites in strong earthquake areas of submarine cable and pipeline routing projects, it is recommended to follow the relevant provisions in GB50021--94.
Landslide is the phenomenon that unstable soil (or rock) on the slope slides downward along a certain sliding surface (sliding zone) as a whole under the action of earthquake force or gravity. Underwater landslides are more likely to occur under the action of earthquake force or gravity in the steep slope section of the deep seabed trough. Landslide investigation should do the following: a) The scope, scale, geological background, nature and degree of hazard of the landslide should be found out. The primary and secondary conditions and causes of the landslide should be analyzed, and the degree of stability should be determined, its development trend should be predicted, and suggestions for prevention and control plans should be put forward; b) Engineering geological mapping and investigation should be carried out in the landslide area investigation, and its scope should include the landslide area and its adjacent stable areas. The scale can be selected from 1:200 to 1:2000 according to the scale of the landslide. 12.3.2 Underground features formed by geological geochemical processes and (or) human activities may cause collapse conditions that seriously affect the safety of the engineering site. The following should be followed when conducting collapse assessment:
a) For sites with potential collapse hazards, when the standard value of foundation bearing capacity fk or the average shear wave velocity Usm is greater than the values listed in Table 1, the collapse impact can be ignored;
Table 1 Standard values of critical bearing capacity and average shear wave velocity values Design intensity
Standard value of bearing capacity fk, kPa
Average shear wave velocity value Usm
b) When the collapse impact needs to be considered in the submarine cable and pipeline routing project, appropriate anti-seismic measures can be taken in combination with the nature of the project and foundation conditions.
13 Evaluation of route conditions and report writing
13.1 Evaluation of route
13.1.1 Engineering geological conditions
Summarize the engineering geological conditions such as topography, geomorphology, geology, structural background, seabed surface conditions, bottom soil and its geotechnical properties in the entire route area, and pay special attention to whether the route avoids adverse engineering geological phenomena (such as scour gullies, shallow gas, seabed collapse, landslides, turbidity currents, bedrock, ancient river valleys, active sand waves, mud mounds, salt domes, soft soil interlayers, etc.). If it cannot be avoided, it should be described clearly so that corresponding engineering measures can be taken during design and construction. 13.1.2 Marine hydrometeorological environment
Analyze the weather, waves, tides, currents, water temperature, sea ice and their characteristic values in each section of the route, recommend a climate window suitable for cable pipeline construction, and conduct a detailed analysis of the marine environment (such as strong bottom currents) that may affect the construction, operation and maintenance of cable pipelines. 13.1.3 Engineering Seismic Conditions
Analyze the regional seismic structure and seismic activity of the route area, calculate the seismic activity parameters of each potential source area, including the seismic intensity value with a 50-year exceedance probability of 10% and the horizontal peak acceleration value of the bedrock seismic movement: Estimate the seismic intensity of the submarine cable pipeline route under the action of earthquakes and waves.3.2 Resistivity can be measured using a microcomputer induced polarization instrument, and the observation error should be less than 1m·2. 11.4 Sulfate-reducing bacteria in sediments
Use a sterile tongue depressor to collect sediment samples from the surface, middle and bottom of the columnar sample to detect the number of sulfate-reducing bacteria. The technical requirements for sulfate-reducing bacteria detection shall be implemented in accordance with 15 to 18 of GB/T12763.6--1991. 11.5 Fouling organisms
11.5.1 Generally, attached organisms and drilling organisms should be included. 11.5.2 The technical requirements for investigation shall be implemented in accordance with 31 to 34 of GB/T12763.6--1991. 12 Seismic hazard analysis
Seismic work for submarine cable and pipeline routes includes seismic hazard analysis, ground motion parameter estimation, sand liquefaction identification, and landslide and collapse assessment.
12.1 Seismic Hazard Analysis
The probability analysis of seismic hazard requires the probability of the project site encountering a seismic motion exceeding a given value in the future, or the exceedance probability P, which is usually expressed by the earthquake exceedance probability curve.
The probability method of seismic hazard analysis takes into account the uncertainty of the time, location and propagation path of the earthquake affecting the project site. The given seismic motion parameters have probabilistic meanings, which can optimize the design between economic investment and risk level. 839
GB 17502—1998
Seismic hazard analysis includes regional (200km on both sides of the route) and near-field (25km on both sides of the route) seismic structures, seismic activity, potential source area division and probability calculation of seismic hazard. Finally, the seismic intensity value and bedrock seismic horizontal peak acceleration value with a 50-year exceedance probability of 10% are given for the project site.
When assessing the activity of the main hidden faults in the near field, it is necessary to fully collect and analyze relevant data such as geophysical exploration and engineering geological drilling for submarine cable and pipeline routing projects.
12.2 Identification of sand liquefaction
When there is saturated sand or saturated silt in the routing area, the possibility of liquefaction should be identified, and the degree of liquefaction hazard should be evaluated and suggestions for anti-liquefaction measures should be put forward. When the earthquake intensity is 6, earthquake liquefaction can generally be ignored. When the earthquake intensity is greater than 6, it can be identified in accordance with the provisions of 3.3 of GBJ11-89.
12.3 Landslide and collapse assessment
Areas with a seismic fortification intensity of 7 or greater are defined as strong earthquake areas. Potential landslide and collapse assessment should be considered for sites in strong earthquake areas. When evaluating the potential landslide and collapse of sites in strong earthquake areas of submarine cable and pipeline routing projects, it is recommended to follow the relevant provisions in GB50021--94.
Landslide is the phenomenon that unstable soil (or rock) on the slope slides downward along a certain sliding surface (sliding zone) as a whole under the action of earthquake force or gravity. Underwater landslides are more likely to occur under the action of earthquake force or gravity in the steep slope section of the deep seabed trough. Landslide investigation should do the following: a) The scope, scale, geological background, nature and degree of hazard of the landslide should be found out. The primary and secondary conditions and causes of the landslide should be analyzed, and the degree of stability should be determined, its development trend should be predicted, and suggestions for prevention and control plans should be put forward; b) Engineering geological mapping and investigation should be carried out in the landslide area investigation, and its scope should include the landslide area and its adjacent stable areas. The scale can be selected from 1:200 to 1:2000 according to the scale of the landslide. 12.3.2 Underground features formed by geological geochemical processes and (or) human activities may cause collapse conditions that seriously affect the safety of the engineering site. The following should be followed when conducting collapse assessment:
a) For sites with potential collapse hazards, when the standard value of foundation bearing capacity fk or the average shear wave velocity Usm is greater than the values listed in Table 1, the collapse impact can be ignored;
Table 1 Standard values of critical bearing capacity and average shear wave velocity values Design intensity
Standard value of bearing capacity fk, kPa
Average shear wave velocity value
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