3.4　Engineering Geology of Hydraulic Structures

3.4.1　The investigation into the site of an earth-rock dam shall include:

1　Stratigraphic texture，layering thickness，distribution features of riverbed overburden and terrace deposit，distribution of sludge，fine sand layer，collapsible loess，suspended and solitary boulder layers in both the present and the ancient riverbeds，and assessment of the bearing capacity，deformation，shearing strength，seismic liquefaction of soil layer and other dam building conditions.

2　Proposal of permeability coefficient of rock（or soil）mass，allowable permeability gradient，physical-mechanical parameters，and advices on treatment of unfavorable geological issues.

3　Distribution，width，filling condition of any fractured fault zone and zones with concentration fissures located at anti-seepage structures，and assessment of their seepage stability.

4　Weathering，unloading thickness and properties of rock mass at dam foundation（abutment）.

5　Distribution elevation of relative confining beds at dam foundation（or abutment）and buried depth of groundwater on both banks，and proposal regarding anti-seepage scope and depth of dam foundation（or abutment）.

3.4.2　The investigation into the site of a concrete dam shall include:

1　Topography and landform of the dam site，thickness and permeability feature of overburden，scope and depth of riverbed channel.

2　Lithologic characteristics and physical-mechanical properties of dam foundation（abutment）；distribution and properties of weak intercalations.

3　Weathering and unloading characteristics of rock mass at dam foundation（abutment）；positions of fractured fault zone，fissure-concentrated zone，fault along the river and low-dip structure plane，and properties and extension status of filling materials.Categorization of quality of rock mass on dam foundation，identification of position of usable rock surface and proposal for physical-mechanical parameters of rock（soil）mass.

4　Distribution，scale，filling condition and connectivity of Karst cave and passages in the dam foundation（abutment）of soluble rock dam site；distribution and flow of Karstic springs，and the characteristics of replenishment，runoff and discharge.

5　Hydrological and geological conditions of dam site，permeability and zoning of rock mass in dam foundation（abutment）and the buried depth of any relatively impervious layer，and to propose the antiseepage scope and depth for the dam foundation（abutment）.

6　Assessment of anti-slide stability，deformation and seepage stability of the dam foundation（abutment），and proposal of treatment measures for unfavorable engineering geological issues.

7　Investigation into the site of a concrete dam（gate）to be built on overburden may refer to the relevant requirements for the site of an earth-rock fill dam.

3.4.3　The investigation into water release structures shall include:

1　Topography and landform，stratigraphic lithology，geological structure，weathering and unloading characteristics of rock mass，groundwater table，and physical-mechanical properties of rock（or soil）mass.

2　Stability of slopes on both banks and anti-scour characteristics of rock mass in scouring area.

3　Suggestions on physical-mechanical parameters of rock（or soil）mass and treatment measures.

3.4.4　The investigation into underground structures including tunnels，underground powerhouse，surge chamber and embedded pipes shall include:

1　Topography and landform，stratigraphic lithology，geological structure，groundwater table，thickness of overlaying rock mass，thickness of weathering and unloading zones of rock mass at intake and outlet，properties and extension length of structural plane of major faults and weak layers and their combination relationship with axes of tunnels or chambers.Categorization of the surrounding rocks by their engineering geological properties and proposal for physical-mechanical parameters of rock（or soil）mass.

2　Assessment of tunneling condition and stability of slopes at intake and outlet；investigation of danger of poisonous and explosive gases at any tunnel sections that pass through coal-bearing strata；assessment of stability of surrounding rocks in goaf chambers and rock burst in deep tunnels；and analysis and assessment of the impact of karst caves and underground river systems in soluble rock area on the tunneling condition.

3　Assessment of the stability of rock mass at cave roof，high sidewall and conjunction sections with consideration of crustal stress for underground powerhouse and surge chamber，and proposal of treatment measures and suggestions.

4　Identification of the relationship between dip angle，inclination of rock strata with dip angle of pipes that are embedded in stratified strata，and assessment of stability conditions of rock mass.

3.4.5　The investigation into channels shall include:

1　Topography and landform，stratigraphic lithology，geological structure，and distribution of landslide and debris flow.

2　Segmentation of channels into engineering geological sections according to slope height，properties of rock（or soil）mass and strata attitude，and assessment of channel seepage and stability of channel foundation and slopes.

3　Proposal of corresponding physical-mechanical parameters of rock（or soil）mass and suggested value of stable slope，and advices on treatment measures.

3.4.6　The investigation into penstocks and fore bay shall include:

1　Topography and landform，thickness of overburden，slope of bedrock surface，geological structure，stability conditions of mountain，physical-mechanical properties of rock（or soil）mass at fore bay and anchorage block foundation.

2　Assessment of stability of slopes along the penstock and the fore bay，bearing capacity of foundation and differential deformation，and proposal of physical-mechanical parameters of rock（or soil）mass.

3.4.7　The investigation into the sites of main and auxiliary powerhouses shall include:

1　Topography and landform，characteristics of rock（or soil）mass，bearing capacity，deformation properties，permeability and slope stability.

2　Identification of-distribution and properties of weathering zone，unloading zone and weak intercalation of rock mass for structures on rock foundation，and proposal of the physical-mechanical parameters of rock mass.

3　Identification of thickness，properties，stratified characteristics and permeability of overburden，the bury of groundwater，and distribution，properties and seismic liquefaction condition of any mud and fine sand layer for structures on soft foundation，and assessment of deformation and permeability stability；and proposal of various physical-mechanical parameters and suggestions on treatment measures.