Basic working methods of hydrogeologic surveying and mapping

(1) Preparation and field investigation

The main work contents are as follows: ① Collect and study the existing physical geography, geological landform and hydrogeological data in the work area, get a preliminary understanding of the hydrogeological conditions in the study area, understand the degree of hydrogeological research and existing problems, so as to carry out the surveying and mapping work in a targeted manner; (2) Where there are aerial and satellite films, we must make full use of them and carefully interpret and translate them; (3) According to the needs, select representative routes and conduct field reconnaissance; (4) Geology and equipment preparation.

(2) Study or actually measure the controlled (representative) profile.

Field hydrogeological surveying and mapping should start from the research or actual measurement of control (representative) profile. Its purpose is to find out the sequence, lithology, structure, structure and lithofacies characteristics of all kinds of rocks in the area, the development characteristics, thickness and contact relationship of cracks and karst, determine the indicator layer or stratigraphic group, and study the water-bearing and other hydrogeological characteristics of all kinds of rocks.

A representative profile should be selected and arranged along the dip direction of strata. Sketch mapping should be carried out on site to find problems in time and supplement them in time. According to the needs, samples such as strata, structures and fossils, and samples such as water, soil and rocks are taken for analysis and identification. In areas with complex hydrogeological conditions, it is best to measure more 1 ~ 2 profiles for comparison. If some key parts of the control profile cannot be covered clearly, a certain amount of stripping or pit exploration will be carried out.

(3) Layout of field observation lines and observation points

1. Layout principle of observation line

According to the principle of using the shortest route to observe the most contents, the observation lines are arranged along the direction where the geological and hydrogeological conditions change the most, and cross natural outcrops (springs, underground river outlets, etc.) as much as possible. ) and artificial outcrops (wells, holes, etc.). ) of groundwater and key hydrogeological section. In practical work, there are three main methods for laying observation lines:

(1) crossing method: that is, the observation line is arranged in the direction perpendicular or nearly perpendicular to the geological boundary, geological structure line, landform unit and aquifer strike of the working area. This method has high efficiency and can get the most results with the least workload, and is often used in bedrock areas or small and medium-scale surveying and mapping.

(2) Tracing method: tracing along geological boundaries, geological structural lines, geological unit boundaries and adverse geological phenomena (bedding tracing). This method can find out the distribution law of geological boundaries and geological phenomena in detail, but the workload is large. This method is mainly used for large-scale hydrogeological mapping.

(3) Comprehensive method (also known as uniform distribution method and comprehensive exploration method): that is, in the work area, the observation lines are arranged by combining crossing method and recourse method. For example, in the loose layer distribution area, the observation line is arranged perpendicular to the maximum direction of modern river valley or parallel to the direction of landform change, and it is required to cross the watershed, and if necessary, it can be pursued along the river valley, and the neotectonic phenomenon can be carefully studied; In the piedmont inclined plain area, it should be arranged along the piedmont to the plain, from the top of alluvial fan to the fan edge (or overflow zone), and the observation line should also be arranged parallel to the direction where the lithology of the mountain changes obviously; In areas with poor outcrops, sometimes comprehensive exploration can be used to find strata and groundwater outcrops; In the plain area where Quaternary strata are widely distributed, there are few outcrops of bedrock, so the surveying and mapping network can be formed by evenly distributing points at equal intervals to control the area.

2. Layout principle of observation points

The layout of observation points should not only control the whole area, but also take care of key areas. Observation points should generally be arranged in representative areas with geological and hydrogeological significance. Geological points can generally be arranged at stratigraphic interfaces, fault zones, places where folds change dramatically, places where cracks and karst develop and various contact zones. Geomorphological points are arranged in topographic control points, geomorphological genetic type control points, various geomorphological boundaries and physical geological phenomenon development points; Hydrogeological points are arranged in springs, wells, boreholes and surface water bodies, outcrops of main aquifers or water-bearing fault zones, surface water leakage areas, hydrogeological boundaries and signs that can reflect the existence and activities of groundwater. Existing water intake and drainage projects should also be equipped with observation points. See relevant specifications for the technical quota of observation lines and observation points. For example, see Table 2- 1 for Code for Hydrogeological Investigation of Water Supply (GB50027-200 1).

(four) the necessary lighting and pumping.

Light exploration means using Luoyang shovel, small thread drill, awl and other light tools for exploration.

Table 2- 1 Hydrogeological Surveying and Mapping Observation Points and Observation Route Length

Note: ① When geological and hydrogeological mapping are carried out simultaneously, the number of geological observation points in the table should be multiplied by 2.5; When rechecking hydrogeological surveying and mapping, the number of observation points is 40% ~ 50% of the specified number; (2) Use small values when hydrogeological conditions are simple, large values when complex, and intermediate values when conditions are medium.

(1) Luoyang shovel exploration: it can complete a round hole with smaller diameter and deeper depth and take out disturbed soil samples. General soil erosion depth 10m, loess erosion depth 30m. Shovel heads with different shapes can be used in different soil layers (Figure 2- 1). Arc shovel head is suitable for loess and cohesive soil layer; The circular shovel head can be equipped with iron cross or movable blade, which can not only rush in but also take out sand samples; The shovel head can crush larger gravel and pebbles in the hole.

(2) Exploration with small auger: The small auger (Figure 2-2) is a manual rotary drilling with pressure, which can take out disturbed soil samples, and is suitable for cohesive soil and sandy soil layers, with a general exploration depth of less than 6m.

Figure 2- 1 Luoyang shovel (unit: cm)

Figure 2-2 Small Thread Drill (unit: cm)

(3) Cone detection: use a cone tool to rush down into the soil, and find out the thickness of loose overburden by feeling. The exploration depth can reach more than 10m. The most effective thing is to find out the thickness of swamp, soft soil and loess cave.

In hydrogeological surveying and mapping, in addition to comprehensively collecting the data of existing wells and caves (mines) in the survey area, some light exploration and pumping are needed. For example, some pits, grooves, shallow boreholes or geophysical exploration can be arranged to obtain the accurate location of buried strata, faults, cracks or karst development areas, and expose groundwater outcrops. In order to obtain the water-rich data of aquifer, it is necessary to arrange some pumping tests by mechanical wells, and some geophysical exploration work can be arranged to obtain the thickness of loose layer and the overlying bedrock structure.

(5) Do a good job in the field and indoors.

During the field surveying and mapping, the original field data of that day should be catalogued and sorted every day, mainly including the sorting of original records, the cleaning of field sketches, the sorting of data such as springs, wells and caves, and the cataloguing and registration of water, soil and rock samples, so as to gradually sum up the regular understanding. Field work should be systematically sorted out in stages over a period of time, and once problems or deficiencies are found, they should be checked or supplemented immediately.

In addition, in order to avoid some phenomena or some boundaries between groups or between adjacent sheets during surveying and mapping, it is required that the surveying and mapping scope of each surveying and mapping group should go deep into adjacent areas (groups) for a certain distance, and often carry out field surveying and mapping with adjacent groups.

The main contents of indoor work are as follows: ① Carefully, meticulously and systematically sort out surveying and mapping data, and if errors or deficiencies are found, supplementary work should be carried out; ② Complete the analysis, experiment and identification of water, soil and rock samples in the laboratory, and sort out relevant data; (3) Do a good job in sorting out data such as exploration and field test; ④ Prepare hydrogeological maps (including representative hydrogeological profiles) and hydrogeological mapping reports (or sheet descriptions). Hydrogeological surveying and mapping results are usually included in the general report of hydrogeological investigation.

Traditional geological and hydrogeological mapping is generally carried out on paper maps. Because paper maps are often used in the field, the filled geological map must be clearly drawn and then colored with watercolor. The main defects of this method are the lack of geological attribute data in geological maps, as well as the difficulty in modification, uneven coloring, low efficiency, difficult preservation and poor data appreciation. Computer-aided geological mapping based on GPS, RS and GIS (referred to as "3 S" technology) has the characteristics of attaching geological attribute data to graphics, completely changing the traditional way of expressing information in geological maps, and also has the advantages of being able to modify at any time, enjoying data, and being easy to save and transmit. Therefore, the hydrogeological survey should adopt digital geological mapping based on "3S" technology as far as possible.