Well field hydrogeology
The coal seam 21 of the Shanxi Group in Jingtian is the main mineable coal seam, while the coal 53 is only partially recoverable. Based on the relationship between groundwater filling and water supply to the mine, as well as the distribution characteristics of the water layer in space, 7 aquifers and 5 aquifers are completely divided. Among them, the direct aquifer on the roof and floor of the 21 coal seam and the indirect aquifer on the floor are the main aquifers. The description is as follows:
(1) Aquifer (Group)
1. Upper Cambrian and Middle Ordovician limestone aquifer group (I)
Composed of the Gushan Formation to the Majiagou Formation, the main lithology is dolomitic limestone, which is exposed south of the well field. In the middle part of the thick-bedded dolomitic limestone of the Gushan Formation, karst landforms such as karst ditches, karst troughs, and stone buds are found in the area from Caocun to Dujiamen, forming a nearly east-west karst development zone (2.7km long, 0.05-0.10km wide ); near Baiping Cement Plant, there are large karst gaps (0.8-2m wide) and large karst caves (4-5m high), both of which are filled with clay and gravel. In the thin-bedded dolomitic limestone of the Changshan Formation, there are caves on the south bank of the Baijiang River in Xibaiping (the two caves are 7 to 8m apart and connected to each other). The cave is 0.8 to 1.2m high, runs southeast and is several 10m long. The exploration area revealed 65 boreholes in the aquifer, including 12 holes with a thickness greater than 50m, with a maximum thickness of 111.14m (Hole Shui 9204 found 17.59m in the Changshan Formation and 93.55m in the Xiagushan Formation). Among them, there are 7 holes in the karst caves, accounting for 10.8%. The highest karst cave is 3.22m (the middle and lower part of the Changshan Formation in hole 10309). There are many fillings in the caves. The karst cave drilling holes are distributed between the 89 and 103 exploration lines, with an elevation of 411.55 to 163.30m. The Majiagou Formation limestone is distributed in the southeastern part of the well field and east of the 113 exploration line. It is exposed in 8 holes and is 2.59-38.22m thick (38.22m in Hole 11706). The chemical composition of the aquifer limestone and electrical data show that the burial depth between Dongbaiping and Nandi is 100-250m, which is the Upper Cambrian karst development zone.
There are a few descending springs in the west of the exposed area of karst strata, with a flow rate of 0.325~2.30L/S, (elevation 461.64~382.78m). There are 7 holes leaking in the water-bearing group, with a leakage loss of 1.02m3/h~all. Leakage, unit water inflow volume 0.00962~1.863L/S·m, permeability coefficient 0.1567~5.85m/d, elevation 428.62~229.25m, it is karst fissure pressurized water. The water-bearing group is controlled by lithology, ancient weathering zones, fault zones and burial conditions, and its water richness is extremely uneven (weak to strong). The water chemical types are HCO3-Ca and HCO3-Ca·Mg water, the water temperature is 14~16.5℃, and the salinity is 0.256~0.371g/L. The average distance from the top of the aquifer group to the floor of No. 2 Coal is 72.60m, which is the indirect aquifer of the floor.
2. Limestone aquifer group (II) in the lower section of Taiyuan Formation
The aquifer is L14 limestone. There are 83 holes exposed. The average thickness of the limestone is 13.63m (the thickness of a single layer is generally 2 to 4m). It is generally 10 to 18m thick to the east of the 103 exploration line and 9 to 16m to the west. There is a trend of thickening in the east and thinning in the west. There are 4 karst cave boreholes (accounting for 4.8% of the exposed boreholes), located east of the Sub-98 exploration line, with an elevation of 299.76~128.09m. Among them, hole No. 9903 contains 7 layers of karst caves with a height of 0.20-3.13m and a karst rate of 55.2%, all filled with clay. The chemical composition of limestone, limestone mud content (SiO2, A12O3, Fe2O3) becomes lower from top to bottom, CaO content increases, and the ratio of CaO and MgO increases. The limestone is pure in quality, has high solubility, and the easily karstified water-bearing formation is sporadically exposed in the south of the well field. There is very little spring water with a flow rate of 0.100L/s. There are 7 leakage boreholes with leakage volume of 1.80~13.20m3/h, unit water inflow volume of 0.0021~0.00491L/s·m (unit water inflow volume of hole 11904 on the east side of the well field is 0.374L/s·m), and permeability coefficient of 0.0362~0.222m/ d, the water level elevation is 407.31~263.01m, which is the pressurized water of karst fissures. Water richness increases from west to east, and is weak to moderate. The water chemical type is HCO3-Ca water, the water temperature is 14.5~16℃, the salinity is 0.316~0.470g/L, and the average distance from the top of the aqueous group to the floor of the 21 coal seam is 45.60m, which is an indirect aquifer on the floor.
3. The limestone aquifer group in the upper section of the Taiyuan Formation (III)
The average thickness of the L7 limestone and above in the Taiyuan Formation is 16m, and the L7-9 limestone is the aquifer. 96 holes were exposed (115 holes were exposed in the L8-9 limestone). The thickness of the limestone ranged from 0 to 16.86m, with an average thickness of 9.41m. The west part of 99 exploration line is generally 5-10m thick, and the L7 limestone phase-changed sandstone section is 2-5m thick; the east part is generally 8-12m thick, with a changing pattern of thicker in the east and thinner in the west. There are 73 holes in the L9 limestone whose lithology is siliceous siderite mudstone, accounting for 63.5% of the exposed boreholes, with an average thickness of 0.59m. The western part of the L8 limestone is mostly marl, with an average thickness of 2.34m. The L7 limestone is a thick layered cryptocrystalline chert-containing nodule limestone, 0 to 13.94m thick, with an average thickness of 8.26m. The eastern part of the well field is thicker and the layers are stable, while the western part becomes thinner and part of the phase changes to sandstone. L9 and L8 limestone have high mud content, with average contents of 45.6% and 27.5% respectively. L7 limestone has high CaO content, with an average of 45.84%. The CaO and MgO ratios of L8 and L7 limestone are more than 20 times. The chemical characteristics of the limestone are consistent with the above lithology. There are 7 holes in the L7 limestone, accounting for 7.3% of the exposed boreholes, and 16 holes in the L7-8 limestone, accounting for 16.7%. The karst fissure leakage holes are distributed between the 99 and 108 exploration lines, with an altitude of 79.24 to 340.48m, forming a karst fissure development area. Karst develops above 150m, and below it is mainly dissolved fissures.
Bounded by the Ji F31 fault, a small number of descending springs are exposed in the west, with a flow rate of 0.014~0.615L/s, a unit water inflow of 0.00487~0.164L/s·m, and a permeability coefficient of 0.080~1.90m/d. The water level elevation is 305.295~412.80m; the unit water inflow volume in the east is 0.353~0.664L/s·m, the single-hole pumping permeability coefficient is 2.93~9.44m/d, and the water level elevation is 268.989~299.86m. The east and south lines have stronger hydraulic conductivity, followed by the north line. The chemical characteristics of groundwater include pH value of 7.40-8.30, salinity of 0.307-0.471g/L, water temperature of 15-17℃, and water quality types of HCO3-Ca and HCO3-Ca·Mg water. Based on the above, west of the Ji F31 fault is the weakly water-rich limestone fissure water-bearing water, and to the east is the karst fissure water-bearing water with moderate water-richness. The spatial distribution and water richness of karst fissures are heterogeneous. The average distance from the top of the L8 limestone to the floor of the 21 coal seam is 17.28m, which is the direct aquifer of the floor.
Characteristics of groundwater flow field in the limestone aquifer in the upper section of Taiyuan Formation:
(1) Natural flow field of groundwater
Before the porous pumping test, long-term groundwater observation was obtained Natural flow field. The eastern and western parts of the Ji F31 fault have completely different characteristics, mainly in the following aspects:
1) The groundwater isolines in the eastern part are sparse, with a hydraulic gradient of 1% to 12.4%, and a south-west-north direction is formed along the fault zone. Strong groundwater runoff zone in the east direction;
2) The groundwater isolines in the west are dense, with a hydraulic gradient of 8.4% to 16.7%, and the groundwater level is about 60m higher than in the east;
3) The direction of groundwater flow reflected by the flow field is from south to north and from east to west in the east; from west to east in the west. Groundwater collects in the fault zone and flows northeastward.
(2) Groundwater Artificial Flow Field
Porous water pumping test site, with the main hole of Sub-10211 as the center to form an elliptical falling funnel in the east (the long axis is consistent with the direction of the Ji F31 fault) ; The natural flow field characteristics of groundwater are basically maintained in the west. As the pumping time increases, the falling funnel continues to expand (the dynamic water level shows a slow downward trend), and the recovery water level lasts for 37 to 84 days, indicating that the groundwater recharge conditions are poor.
4. Shanxi Formation Sandstone Water-bearing Formation (IV)
There are 4 to 5 layers of fine-coarse sandstone (commonly known as Dazhan Sandstone, Xiangtan Sandstone and Fengtan Sandstone) above the 21 coal seam. Jiagou Sandstone) is an aquifer. 204 holes were drilled, and the sandstone thickness ranged from 2.45 to 58.23m, with an average of 20.11m. The aquifer is exposed in the low hilly area of the shallow part of the well field, with few springs and a flow rate of 0.014-0.155L/s.
According to statistics from the 93-hole engineering geological catalogue, 58 holes, accounting for 62.4%, have broken cores. The sandstone fissures are relatively developed. There are 10 leaking holes, accounting for 4.9% of the exposed holes. The leakage amount is 1.00-12.00m3/h, unit The water inflow volume is 0.0062~0.0181L/s·m, the permeability coefficient is 0.0141~0.2974m/d (there are 3 holes for draining), and the water level elevation is 320.86~371.81m. The water temperature is 14~16℃, the salinity is 0.242~0.382g/L, and the water quality types are HCO3-Ca·Mg·K+Na and HCO3-Ca water. The water-bearing group is weakly water-rich and belongs to the confined water of sandstone pores and fissures. It is the direct aquifer of the roof of the 21 coal seam.
5. Wu 3 coal roof and floor sandstone aquifer group (V)
According to the statistics of 29 holes within the mineable range of the coal seam, the roof aquifer is 1 to 3 layers of fine to medium-grained sandstone , thickness 0~15.8m, average 4.94m. There is little spring water and the flow rate is less than 0.5L/s. There are 7 holes leaking, with a leakage amount of 0.84m3/h, and they are all leaking (3 holes are leaking from structural fissures, with a water leakage amount of 0.84-2.40m3/h, and the remaining 4 holes are leaking from the weathered zone of the old kiln). The floor aquifer has 1 to 2 layers of fine to medium-grained sandstone, mostly lenses, generally 1.00 to 17.76m thick, with an average thickness of 2.92m. The leakage amount in hole 10802 is 2.40m3/h, and the old kiln in hole 10503 leaks water, and the leakage amount is greater than 9m3/h. The aquifer is confined water in sandstone pores and fissures.
6. Pingdingshan Sandstone Aquifer (VI)
The lithology is mainly thick to extremely thick layered medium-coarse-grained sandstone, with an average thickness of 69m. Exposed in the single-sided mountain peak area, there are more descending springs exposed, with a flow rate of 0.091~2.883L/s. There are 12 fully exposed boreholes. The aquifer structure and weathered fissures are developed. Water gushed from 2 holes with a flow rate of 0.28-0.35L/s. Water leaked from 1 hole with a leakage loss of 4.00m3/h. It is a sandstone fissure confined water aquifer. The water temperature is 13~17℃, the salinity is 0.212~0.326g/L, and the water quality type is HCO3-Ca and HCO3-Ca·K+Na water. The aquifer has nothing to do with coal mining and can be used as a source of local small-volume water supply.
7. Quaternary aquifer (VII)
Distributed in the valleys of low mountains and hills, it is slope-diluvial and alluvial-diluvial material, with an average thickness of 7.10m. Among them, the first-level terrace deposits in the Baijiang River Valley are generally 3 to 6 meters thick. The aquifer has a binary structure. The upper part is sub-sandy soil containing small gravels, and the lower part is composed of sub-sandy soil and sub-clay. The gravel diameter is 50 to 500 mm, sub-round to sub-angular, and poorly sorted. The spring water flow rate is 0.10~1.192L/s, the water level is 3~5m deep, the aquifer is pore phreatic, and the water richness is weak to moderate. The water temperature is 12~17℃, the salinity is 0.262~0.422g/L, and the water quality type is HCO3-Ca water. The aquifer covers the Upper Cambrian in part of the section between the 92 exploration line in the south of the well field and the Ji F31 fault. It is above the upper Carboniferous Taiyuan Formation limestone and the Lower Permian Shanxi Formation sandstone aquifer, which is recharged.
(2) Aquifer
1. Benxi Formation aluminous mudstone aquifer
There are 69 holes exposed in the well field, with a thickness of 2.26m and an average of 10.0m . The layer is stable and is the aquifer between the Upper Cambrian and Middle Ordovician limestone aquifers and the lower Taiyuan Formation limestone aquifers.
2. Sand and mudstone aquifer in the middle section of Taiyuan Formation
The stratum between the top of L4 rock and the bottom of L7 rock is exposed by 101 holes, with a thickness of 14.0-54.0m and an average thickness of 24.00m. m, and the thickness of mudstone accounts for 65.8%. It is the aquifer between the upper and lower limestone aquifers of the Taiyuan Formation.
3. The water-proof layer of the floor of the 21 coal seam
The strata between the top of the L8 limestone and the bottom of the 21 coal seam are exposed in 137 holes. The lithology is mainly mudstone with thin layers. There are layers of marl, fine sandstone and coal seams, with thickness ranging from 2.60 to 37.61m, with an average of 17.28m. To the west of Ji F31, the shallow part is generally thicker than 10m, and the middle and deep part is 5-10m; in the east it becomes thinner, generally 5-10m thick. The average rock tensile strength is 2.1MPa. The layers are stable, the thickness changes greatly, and the water barrier is poor.
4. The mudstone aquifer of the Lower Shihezi Formation
The stratum below the Wu-3 coal floor aquifer is about 160m thick, and its lithology is mainly mudstone and sandy mudstone. Interbedded with thin layers of sandstone and thin coal seams. The thickness is large, the layer is stable, and it is a good water-proof layer.
5. The upper Shihezi Formation mudstone aquifer
The stratum between the bottom of Pingdingshan sandstone and the Wu3 coal roof aquifer (including the upper strata of the Lower Shihezi Formation), thick About 320m, the lithology is mainly mudstone, with large thickness and stable layers, making it a good water-proof layer. Among the above-mentioned water-proof layers, the water-proof layer between the aquifers below the 21 coal seam has relatively good water-proof properties in the western part of the mine field under natural conditions, while the eastern part has poor water-proof properties due to damage by faults.