(2) Regional hydrogeological conditions
① Water-bearing formations
According to the characteristics of groundwater occurrence, the types of groundwater
occurred in the project site are: massive volcanic rock fissure water, massive intrusive
rock fissure water, and a small amount of weathered residual pore-fissure water.
Massive volcanic rock fissure water and massive intrusive rock fissure water
occur in weathered residual pores and fissures as well as structural fissures of tuff
and intrusive rock, with uneven water abundance and a shortage of water (spring
flow
0.1 m
3 /L s).
Weathered eluvial pore-fissure water mainly occurs in the fully weathered zone
in the upper part of bedrock. The bedrock structural fissure water occurs in the
structural fissures in the lower part of the bedrock, and the structural fissures are
unevenly developed. The water abundance of the structural fissures is generally
poor and the burial depth is relatively large.
According to the site investigation data, the site exploratory holes has a depth of
13.7–33.9 m and expose moderately weathered tuff. No groundwater level is found
in most holes, such as ZK4 with a depth of 33.8 m, a bottom elevation of 538.34 m,
and no groundwater level. This indicates that the depth of groundwater table in the
area is large. Most of the exploratory holes in the site have water leakage, which
reveal that the pores and fissures are relatively developed in the fully weathered
zone above the bedrock, and the fissures in the moderately weathered tuff are
relatively developed, with good water permeability. However, because the site is
located at the level ground in low mountains, with relatively high terrain, the
weathered zone of bedrock is permeable to water to a certain degree, but most of it
is not water-bearing.
② Groundwater recharge, runoff and discharge
At this project site, the fissure water of bedrock mainly receives recharge by vertical
infiltration of atmospheric precipitation. Because the terrain in the area is steep, the
terrain fluctuates greatly, and the groundwater runoff speed is fast, the atmospheric
precipitation infiltrates into the ground and flows along the slope. There is no
obvious dividing line between the recharge area and the discharge area. Generally,
relatively high terrain is the relative recharge area, while relatively low terrain, the
gully at the toe, is the relative discharge area, where water is mainly discharged in
the form of sheet water seepage and spring water into the gully and the toe of slope
with low terrain, or discharged along the terrain to the downstream stream in the
form of runoff.
Phreatic water in the network of cracks in the weathered zone is only sporadically distributed in the hollow places around the project site, and mostly receives
recharge by atmospheric precipitation and lateral recharge by fissure water of
bedrock. It is discharged to the gully or a certain stream at the hollow places in the
form of spring water. The recharge relationship between groundwater and surface
water of stream and gully is greatly affected by season. Generally, in the wet season,
232
5 Application Cases
① Water-bearing formations
According to the characteristics of groundwater occurrence, the types of groundwater
occurred in the project site are: massive volcanic rock fissure water, massive intrusive
rock fissure water, and a small amount of weathered residual pore-fissure water.
Massive volcanic rock fissure water and massive intrusive rock fissure water
occur in weathered residual pores and fissures as well as structural fissures of tuff
and intrusive rock, with uneven water abundance and a shortage of water (spring
flow
0.1 m
3 /L s).
Weathered eluvial pore-fissure water mainly occurs in the fully weathered zone
in the upper part of bedrock. The bedrock structural fissure water occurs in the
structural fissures in the lower part of the bedrock, and the structural fissures are
unevenly developed. The water abundance of the structural fissures is generally
poor and the burial depth is relatively large.
According to the site investigation data, the site exploratory holes has a depth of
13.7–33.9 m and expose moderately weathered tuff. No groundwater level is found
in most holes, such as ZK4 with a depth of 33.8 m, a bottom elevation of 538.34 m,
and no groundwater level. This indicates that the depth of groundwater table in the
area is large. Most of the exploratory holes in the site have water leakage, which
reveal that the pores and fissures are relatively developed in the fully weathered
zone above the bedrock, and the fissures in the moderately weathered tuff are
relatively developed, with good water permeability. However, because the site is
located at the level ground in low mountains, with relatively high terrain, the
weathered zone of bedrock is permeable to water to a certain degree, but most of it
is not water-bearing.
② Groundwater recharge, runoff and discharge
At this project site, the fissure water of bedrock mainly receives recharge by vertical
infiltration of atmospheric precipitation. Because the terrain in the area is steep, the
terrain fluctuates greatly, and the groundwater runoff speed is fast, the atmospheric
precipitation infiltrates into the ground and flows along the slope. There is no
obvious dividing line between the recharge area and the discharge area. Generally,
relatively high terrain is the relative recharge area, while relatively low terrain, the
gully at the toe, is the relative discharge area, where water is mainly discharged in
the form of sheet water seepage and spring water into the gully and the toe of slope
with low terrain, or discharged along the terrain to the downstream stream in the
form of runoff.
Phreatic water in the network of cracks in the weathered zone is only sporadically distributed in the hollow places around the project site, and mostly receives
recharge by atmospheric precipitation and lateral recharge by fissure water of
bedrock. It is discharged to the gully or a certain stream at the hollow places in the
form of spring water. The recharge relationship between groundwater and surface
water of stream and gully is greatly affected by season. Generally, in the wet season,
232
5 Application Cases