The general survey and exploration of natural building materials-gravel plays a very important role in the geological exploration of water conservancy construction projects, because the cost of hydraulic concrete buildings depends to some extent on the quality, reserves and mining and transportation conditions of building materials, as well as the distance between the origin of building materials and the construction site; At the same time, the location of railway, highway, concrete mixing building and other ancillary buildings, and the auxiliary setting of traffic routes also depend on the origin of sand and gravel.

First, the selection of natural building materials origin

The natural building materials needed to build hydraulic structures usually include hard stony rocks and loose and bonded rocks that meet certain technical requirements. This paper only introduces the origin selection of aggregate gravel needed to build concrete dams.

First of all, the survey should be carried out near the designed layout area of hydraulic structures. If there is a lack of gravel material near the building, the survey can be carried out in a far area. The reserves of the selected place of origin shall meet the design requirements and the quality shall meet the requirements of technical specifications (see below for specific requirements). In addition, traffic conditions should also be considered, and it is best to be close to the traffic trunk line.

Gravel producing areas are generally distributed on the low floodplain of Gao Man beaches and rivers or on the first-class terraces covered with thin gravel layers. Hydrogeological work should be carried out at the same time as geological exploration in these areas, so as to understand the thickness of the local aquifer, as well as the water inflow and permeability coefficient of this layer, so as to consider the water supply conditions and mining methods of the origin. If the producing area is suitable for mechanized mining, it is necessary to ensure that the number of producing areas is enough for continuous mechanized mining for several months. The soil stripping layer should not be too thick, which will increase unnecessary workload. The volume of soil stripping layer should not exceed 15% ~ 20% of the volume of useful rock stratum (gravel stratum), and the above conditions may not be observed in special circumstances.

II. Contents and requirements of gravel material exploration in different design stages.

In the stage of river technical and economic report, the special investigation of building materials is generally not carried out, and the problems related to building materials are mainly solved according to published or unpublished case data, reconnaissance data and interviews with local residents. The investigation of natural building materials is usually divided into two stages-preliminary design and technical design. The exploration results in each stage should be clear as follows: (1) the position of gravel; (2) Mineral reserves corresponding to the design stage; (3) the occurrence and quality of gravel layer and the necessity of flushing; (4) Hydrogeological conditions of the place of origin; (5) The thickness and properties of the stripped soil layer; (six) the distance between the place of origin and the dam site and the transportation conditions; (7) Mining conditions of the place of origin.

(1) Preliminary design stage

According to the results of the general survey, select the promising producing areas close to the construction site, and conduct B-level exploration according to the producing areas of solid minerals. In order to obtain Grade B reserves and evaluate their quality, the topography, stratum and geological structure, hydrogeological conditions, rock occurrence and gravel quality should be preliminarily determined. Therefore, according to the requirements of concrete aggregate, the quality of crushed stone should be studied by sampling in the laboratory. 1: 5000 or 1: 10000 geological mapping, to find out the development history of rivers, as the basis for laying exploration lines to find gravel. Exploration lines are generally based on the principle that the riverbed is vertical, and the spacing between exploration lines is generally not more than 400m·m m. Each exploration line is equipped with two or more exploration pits and holes, and the distribution of pits and holes is best separated from each other in the vertical and horizontal directions (as shown in Figure 1). Pit exploration is the best exploration method, followed by impact drilling. All the pits must pass through all the useful rock layers (gravel layers) and can only be stopped when the lower part is determined to be the underlying layer.

The work results should meet the requirements of Grade B, so it should be stated that: (1) the average thickness and properties of the stripped soil layer; (2) The layered nature, distribution area and thickness of the gravel, whether there are any suitable interlayers, and whether the gravel needs cleaning; (3) Gravel quality can be analyzed by visual inspection and laboratory research results; (4) The most suitable route to the construction site; (5) Annual variation of hydrogeological conditions and surface water; (6) The most favorable mining method.

Figure 1 Schematic diagram of spacing arrangement of drilling holes and exploratory pits

(2) Technical design stage

The exploration work in the technical design stage is carried out in one or more optimal production areas selected after the exploration work in the preliminary design stage. The calculation of sand and gravel reserves in the technical design stage should reach A2 accuracy.

The layout of exploration lines in the technical design stage is generally to insert a new exploration line in parallel between the exploration lines in the previous stage, so that the distance between the old and new exploration lines does not exceed 200m, thus forming an exploration network with A2 reserves.

In the exploration work, in addition to the test sampling of concrete aggregate, semi-productive washing test and concrete compressive strength test should also be carried out in the place of origin. According to the results of laboratory research, the applicability of building materials is finally determined; And calculate the reserves and exploitable quantity of the producing area in detail. Finally, the most reasonable and economical mining method is put forward.

(3) Detailed construction stage

The exploration of natural building materials is generally not carried out in the detailed exploration stage of construction. Only in the previous survey work, due to a series of reasons, the reserves required for the design of natural building materials (A2 level) were not determined within the scope of the water control project, and exploration work and sampling were carried out at the stage of compiling the construction details. In this case, the gravel reserves are also increased from Grade B to Grade A2.

Three. Exploration method

After the exploration team receives the design task book and determines the layout of exploration pits and holes, it will be handed over to surveyors for on-site positioning, and technicians will conduct on-site inspection before excavation. If the arranged pit location is not suitable for excavation, the pit can be changed to drilling or its location can be moved slightly. When moving the pit location, it must be considered that the new pit location should be as close as possible to the exploration line, otherwise it will destroy the whole exploration network and bring unnecessary trouble to the reserve calculation.

The exploration method is manual percussion drilling and pit excavation.

(1) Trial pit excavation work

In general, the sand and gravel production areas are mostly distributed on the floodplain, so the excavation of exploration test pits will probably be mostly carried out below the groundwater level. Due to the loose formation and flowing erosion of groundwater, all the fine particles in the gravel layer will be washed away, resulting in the collapse of gravel, which directly affects the safety of workers. Therefore, it is impossible to work without support. In this case, we generally use "inverted tower" support.

Fig. 2 Side view and top view of "inverted tower" bracket

The "inverted tower" bracket consists of several square wooden frames, which contract from top to bottom and from large to small (Figure 2). It is shaped like the reflection of a pagoda. This support is generally reduced by 0.20~0.25m every 0.5m. The final cross section of the test pit should not be less than1.0m×1.0m. Therefore, the selection of the opening cross section of the test pit should be calculated according to the depth of the test pit and the number of support reductions.

The groundwater in the pit should be pumped by pumps with different horsepower according to the groundwater level and water inflow.

In uniform gravel layer, the excavation of test pit is generally smooth. In case of quicksand layer and boulder, special treatment should be carried out. When the quicksand layer is 0.3~0.5m thick (it can be tested by steel bar or hand drill), it can be made into small rolls as long as the test pit with rod plants such as straw and reed, so as to be connected with the support and prevent the quicksand from upwelling.

If the water content is low and the quicksand layer is thick (1.0~2.0m ~ 2.0m), piles can be arranged with 5mm wooden boards (the pile head of sheet pile must be wrapped with iron sheet), and the inner and outer sides of the test pit can be supported by drying (depending on the actual situation), and the frame can be lowered while digging until it passes through the quicksand layer.

If the treatment of boulder is limited to the poor equipment in the construction site, a tripod can be set up at the pit mouth and a pulley hinge can be set up. Stones can be tied with ropes, twisted with hinges, and then pulled out of the pit with horizontal pulley hinges. For boulders that have exceeded the pit diameter, blasting can be used (generally this situation is rare).

The advantages of excavation with exploratory pit are: (1) the section is large, and the geologist on duty can enter the exploratory pit, directly observe the general situation of gravel from the pit wall, and accurately measure the position, thickness and natural occurrence of harmful interlayer or convex lens. This provides accurate data for the correct evaluation of gravel layer quality and sampling; (2) The excavation work will not destroy the natural particle gradation of gravel. These advantages cannot be realized by drilling.

(2) human impact training

The minimum diameter (inner diameter) of exploration drilling hole for gravel material shall not be less than 150mm. This is because it can ensure that the coarsest gravel is taken out of the hole. Drilling methods for exploring gravels are generally divided into:

1) rotary drilling of drill pipe (usually called push grinding drilling). The commonly used bits for this kind of drilling are: spoon bit and disc bit.

2) Hammer drilling, and it is most appropriate to use circlip drill when drilling. This method is most suitable for production areas with gravel size less than150 mm.

3) Drill pipes are used for percussive drilling, including cross bit, I-bit, I-bit, valve bit, etc.

4) Wire rope impact drilling, using valve (commonly used valve in sand layer).

Drilling structure is the most important thing in exploration. Whether the structure selection is correct and the equipment is suitable plays a decisive role in reaching the depth to ensure normal drilling and correctly taking rock samples and samples. If the formation is simple and dense, there is no need to run casing to protect the borehole wall or prevent borehole collapse, and the borehole structure is simple, otherwise it will be more complicated.

The selection of drilling structure is generally based on: ideal geological histogram, planned drilling depth, sample quality requirements, drilling method, drilling tool type and drilling method.

Drilling can be used for exploration, it can be drilled deep, and it can be explored on water, which is its advantage. However, the natural gradation of rock samples taken from borehole is easy to be destroyed, and the understanding of its quality is not as comprehensive as that of exploration pit.

Four. Geological recording and sampling

Geological recording and sampling is the most basic and skilled work in geological work.

Recording is a meticulous and complicated work, and the quality of original records in the work is often not high, which causes many difficulties for indoor finishing. At this time, although many problems were found, it was not easy to solve them, because the loopholes had been filled or collapsed, and it was no longer possible to proofread and check. Therefore, the geological comrades who make records must fully understand the geological requirements in the exploration of building materials and describe the situation in the pits in detail in their work.

Taking the geological record of No.425 exploration pit (after indoor arrangement) as an example, this paper explains the format and content of the geological record (Figure 3) in A2-level exploration of a gravel producing area in Sanmenxia Project.

Figure 3 Histogram

From the geological description of the histogram, we can not only know the names of each layer, but also clearly understand the details of each layer, as well as some hydrogeological data, which can provide correct information for indoor consolidation work and help consolidation comrades to understand the specific conditions of each pit more clearly.

There are two kinds of sampling from the pit: take rock samples every 0.5m or when changing layers, and put a small bag at a time, indicating the sampling position, depth, number, sampling date, etc. As a specimen to test the geological conditions of the mine, rock samples are equivalent to cores and are only used by geologists and inspectors.

The sample was sent to the laboratory for analysis. Sampling work is generally carried out in gravel layer, and ineffective rock layers under overburden and gravel layer are not sampled. Gravel and sand layer are sampled in the whole tunnel, that is, a certain weight is taken from the effective rock stratum-gravel from top to bottom as a sample. This method can dig a vertical trench with a width of 0.4~0.5m and a depth of 0.25~0.5m on the pit wall, and the gravel taken from the trench is taken as a sample. If it is difficult to carve grooves on the pit wall below the groundwater or the rock stratum is loose, the multi-bucket method is adopted, that is, one bucket is selected from five buckets of gravel, or one shovel is selected from five shovels as a sample. Of course, other multiples can also be used for sampling. If the sample taken exceeds the amount required for the screening test, it can be reduced by quartering. The general sample is 1000kg, and then the gravel sample of 1000kg is screened on site. The purpose of this field screening is to find a more representative natural particle gradation that is closer to the natural form, which is much more accurate than the results screened from dozens of kilograms of samples sent to the laboratory. The percentages of maximum particle size 150 ~ 80~40mm, 80 ~ 40~20mm, 40 ~ 20~5mm and 20~5mm can be obtained after field screening (sand is carried out in the laboratory). After screening, 3 ~ 4 kg samples with different particle sizes should be selected for rock composition, surface properties and gravel particle shape test (see Table 1 and Table 2).

Table 1 Identification of surface properties and shapes of gravel particles

Table 2 Identification of Rock Composition of Gravel

The work of the above simple field test is closely coordinated with the work of the laboratory. Therefore, the data obtained in the field should be submitted to the laboratory and classified together with the samples in order to present a complete test result.

The weight of the samples sent to the laboratory for aggregate requirement test is generally 150kg, and the samples of 150kg must maintain their natural particle gradation.

In the process of sampling, a very important problem is the treatment of harmful interlayer and harmful particles (such as coal and clay blocks). Generally speaking, when there is a thin clay interlayer or silt layer in the effective rock layer (sand layer and gravel layer), samples should be taken according to the normal sampling method, and harmful substances such as clay should not be selected. Because it is impossible to select those harmful substances layer by layer during formal mining, but the harmful interlayer should be mixed with gravel for mining. Therefore, the samples collected during exploration should be as close as possible to the quality of gravel during mining.

If such harmful substances or particles are concentrated or form a thick layer, and the layer is above or below the gravel layer (as shown in Figure 4). Samples should be taken separately, otherwise the level is listed as invalid, so sampling is not necessary. Then it can be mined without mining, or it can be mined when the ineffective layer is excavated, which has no effect on the gravel quality.

Fig. 4 schematic diagram of different sampling according to different geological conditions.

Five, the general provisions of hydraulic concrete on the physical properties of gravel

Natural building materials, whether named in the field or indoors, should be named according to the classification of engineering geology and different particle sizes. There is a difference between engineering geology classification and building materials classification. Therefore, when sorting out and analyzing data in the office, the name of gravel layer that meets the quality requirements, that is, the name originally classified according to engineering geology, should be converted into the classification standard of building materials. Gravel layers that do not meet the quality requirements should be named and described according to their original engineering geological classification if they do not need to be converted. If there is only one effective layer, for the convenience of work, it can also be directly named and described by building materials classification (see Table 3).

According to the composition of loose rock particles, its constituent particles can be divided into the following groups:

Engineering geological survey history of Sanmenxia water control project on the Yellow River

Classification of building materials:

Table 3

When evaluating the quality of gravel, it is mainly based on the provisions of the Soviet Technical Specification for Natural Building Materials for Hydraulic Buildings.

1. Quality inspection of gravel mixing

The percentage of sand and gravel shall be determined according to the following different particle sizes:

Natural particle gradation (mixed in mm): > 150, 150 ~ 80, 80 ~ 40, 40 ~ 20, 20 ~ 10, 10 ~ 5, 5 ~ 2.5 ~ 60.

The maximum particle size d in the gravel should be found, and the so-called maximum particle size d means that the gravel passing through the sieve is not less than 95% of the whole sample.

2. Gravel quality

Table 4

3. Quality of sand

Table 5

The evaluation of crushed stone quality (physical properties) is mainly to compare the test data with national standards, analyze and study the quality of crushed stone from various producing areas, and finally draw a conclusion according to the compressive strength of concrete.

Calculation of intransitive verb reserves

Reserve calculation is an integral part of geological data collation of sand and gravel origin. Through the calculation of reserves, the amount of gravel suitable for the exploration stage in the producing area can be obtained as the basis for design.

Reserves calculation can be divided into two types: geological reserves calculation and exploration reserves calculation. In the stage of technical and economic investigation and report, according to geological data, the distribution area and depth of gravel are estimated to get a rough reserve, or a few pits and holes are calculated to get a "C" level reserve. In the preliminary design and technical design stage, the calculation should be based on the geological data of the exploration pit. The calculation results within the scope of exploration network belong to "B" or "A2" level, and the calculation amount outside the scope of exploration network is secondary reserves. For example, "A2" level, the reserves in the exploration network belong to "A2" level, and the reserves outside the exploration network belong to "B" level. In this way, A2+B reserves or B+C reserves can be obtained.

Generally, the calculation accuracy of reserves in the preliminary design stage does not exceed 20% ~ 40% of the total reserves in the place of origin, and the error in the technical design stage does not exceed 10% ~ 15%. To calculate the number of digits, you only need to reach the equivalent number of digits required by the design. Other bits can be replaced by zeros (according to the regulation и- 13).

The calculation methods of reserves are: arithmetic average method; Parallel section method; Triangulation; Isogram method, etc. When calculating, two or more methods can be used to correct each other. The choice of specific methods depends on the specific conditions of the exploration area, and the first three methods are generally used.

In the case of uneven distribution of rock thickness, pit spacing and exploration lines, the arithmetic average method can be used. This method is very simple, and the result is correct, that is, the calculation range of reserves is delineated on the plan, the area is calculated, and then the average thickness is calculated according to the exploration data in the area.

Calculation formula:

Q=FH (volumetric method) Q=FHD (gravimetric method)

Q—— reserves (m3/t); F- area; D- specific gravity; H—— average thickness.

Parallel section method: make a vertical section of pits and holes arranged along or near parallel lines in this area (Figure 5).

Fig. 5 Reserve calculation scheme for parallel section

Fig. 6 Schematic diagram of triangle reserves calculation method

Triangulation method: this method can be used when the pit spacing is unequal or the exploration line is not regular enough. Connect the exploration points into many triangles on the plan; Use the area of the triangle to calculate the reserves (Figure 6).

Engineering geological survey history of Sanmenxia water control project on the Yellow River

A, b-base and height of triangle; H—— thickness of effective rock stratum; Q 1-a triangle reserve; Q 1+Q2+Q3+…=Q is the total reserves of the producing area.

Finally, the ratio of covering layer to effective layer should be calculated.

Similarly, the volume of its covering layer is also calculated by the above method.

Table 6 Calculation Table of Parallel Section Method

Seven, organize and prepare the industry report.

(A) finishing industry

Generally divided into the following three aspects:

1. Arrangement of particle components

The effective gravel particle composition obtained in the field and laboratory is listed in the summary table, and the weighted average of gravel particle composition in each pit, each layer and the whole production area is calculated in this table. The grain components of lentil (convex lens) and thin interlayer separated from geological profile are not analyzed separately, but are contained in thicker components. Sometimes, the stratification of a single gravel layer is unknown or uncommon, so it is best to combine several rock layers into a large layer and calculate the weighted average of particle composition according to this large layer.

The weighted average value of particle composition of effective layer (gravel layer) should be included in this report in tabular form and drawn on the applicable standard curve. If the cumulative curve of weighted average particle composition does not exceed the boundary, gravel is the standard of concrete aggregate for hydraulic structures (see Figure 7 and Figure 8).

Fig. 7 Composition curve of concrete gravel particles

Note: ① The so-called maximum value of D means that the gravel passing through the screen is not less than 95% of the screen aperture of the whole sample; (2) Gravel suitable for concrete, whose particle composition does not exceed the diagonal area.

Fig. 8 Composition curve of gravel particles in concrete

Note: The grain composition of sand suitable for concrete shall not exceed the diagonal area.

Calculate the weighted average particle composition according to the following formula:

Engineering geological survey history of Sanmenxia water control project on the Yellow River

Where: b refers to the weighted average content of particles in a certain layer;

B1-the same particle content in the first test layer or the first test section;

B2—— the same particle content in the second test layer or the second test section;

M 1, m2…mn—— the thickness of test section or test layer.

In order to calculate the weighted average composition, auxiliary tables (see tables 7 and 8) can be used, and the results of multiplying the number of pits, sampling depth, test section thickness and test section thickness by the initial percentage content of particles can be written in the auxiliary tables. In any case, the total amount of all particles should be equal to the thickness of the test section multiplied by 100. The weighted average composition of each particle can be easily obtained by dividing the total thickness of the test section by the sum of multipliers.

As shown in the figure-* * meets the standard,-* * does not meet the standard, and the particles are fine.

Table 7 Reserves Calculation Table

Table 8 Auxiliary Table for Weighted Average Calculation of Particle Composition (Classification of Building Materials)

Table 9 Composition of Rock Particles (Classification of Building Materials)

Converted into the total content of gravel in the gravel mixture, the percentage content of gravel with different particle sizes can be multiplied by 100. Then divide by the total gravel content and convert the sand in the same way.

Particle conversion of sand and gravel is calculated according to the commonly used formula:—

For gravel 40: 100 = 10: x, then

(Total gravel content) (Percentage of some particles)

For Sha 60: 100 = 8: x, then

(Total sand content) (certain particle size percentage)

The conversion results of each pit and hole must be included in the summary table, and the information of each layer and the whole origin should also be included in this table.

2. Finishing of physical properties

All test results should be collected in the summary table and included in the average value in the table. Like the arithmetic average, it should be calculated according to the test value. The average value, variation range (i.e. maximum or minimum) and test time shall be listed.

Whether sand and gravel are suitable for preparing hydraulic concrete aggregate must be based on the comparison of physical properties between average index and national standards.

3. Map classification work

After the exploration of sand and gravel, the pit inspection table, vertical and horizontal section and plan shall be submitted. In areas with simple geological conditions, the geological and geomorphological map and the mine layout map can be integrated together. In the technical design stage, the isoline map of groundwater level and the isoline map of useful rock strata and overburden should be submitted.

The scale of the histogram depends on the depth of the hole. For holes with a depth of 10m, the scale of 1: 50 is generally adopted (see Figure 2).

There is not much difference between the drawing method of gravel exploration profile and general geological profile, but for the convenience of reserves calculation, the rock boundary line is often represented by straight lines. The proportion of the profile should also be determined according to the specific situation. The general requirement is to clearly show the geological conditions, groundwater level, sampling depth and reserve calculation boundary on the map.

The scheme includes two contents: first, geological conditions, horizontal boundary line of rock strata, landform boundary line and so on. The geological requirements are relatively simple and need not be too complicated (if the geological conditions of the place of origin are indeed quite complicated, a geological map should be drawn separately). Second, the actual material drawing, the figures on the drawing must be very accurate, and there can be no contradiction or discrepancy between the histogram, section and plan. And indicate the pit number, elevation, water level, gravel layer thickness and overburden thickness on the map. For example, in order to study and analyze the quality of each pit, the indicators of some inspection items can also be expressed on the plan. According to the quality situation, it is divided into several areas.

Table10×× gravel quality in production area

Table 1 1×× quality of producing sand

(2) preparation of the report

Technical report on general survey and exploration of building materials: it is usually a part of the general report of engineering geology, and consists of the following two parts: text and chart annex. The main text should include necessary drawings and tables, and the appendix of the main text includes the summary tables of particle composition and rock physical properties, which are arranged at the back of the bibliography.

The general survey and detailed exploration report of the origin of building materials usually include: ① introduction; (2) the results of the census; ③ Exploration results; ④ General conclusion. If the building materials report is not included in the general report, but a separate report should be set up, "Regional Geological Survey" and "Regional Climate Survey" should be added.

In the first part "Introduction", it is necessary to point out the tasks of the field team (required reserves and their uses) and the proponent of the tasks, the simple information of the designed water control project (backwater elevation of the main buildings and water control project), the workload mainly completed during the field work (tabular form), the comparison between the completed workload and the plan, and the executors of the field work and indoor finishing work.

The second part "results of census work" includes all data during the census and preliminary exploration. Each place of origin should be described and the overall conclusion should be drawn. When describing the origin, it should be pointed out: the relative position of the origin from the dam site, the number of completed potholes, geological and hydrogeological conditions, the reserves with the quality of "C", and suggestions on the utilization of materials.

The third part "exploration achievements" should be classified according to their functions and then described in detail. The description of each place of origin becomes a separate chapter, and each chapter should include: ① Introduction; (2) A brief description of the geology and hydrogeology of the place of origin; ③ Exploration work and sampling test; ④ Quality evaluation; ⑤ Reserves calculation; 6 conclusion.

In the "Introduction", it should be pointed out: the geographical location of the place of origin, the distance from the place of origin to the construction site, the traffic conditions, the topographic features of the place of origin, the ground elevation, and the genetic type. The previous work should also be briefly described.

In the "Introduction to Genetic Geology and Hydrogeology", it is necessary to point out the occurrence characteristics and genesis of rock strata, the particle composition and thickness of each rock stratum, and at the same time explain the useful rock strata and water content.

"Exploration Work and Sampling Test" includes all the data of drilling, including the deepest and shallowest holes, average depth, exploration method, aperture size, drainage situation, number and quantity of inspection holes, average distance between exploration lines and online holes, etc. In addition, the sampling method and quantity should also be stated.

In the part of quality identification, there are two kinds of data: (1) small particle composition data, which describes the content and size of brucite; (2) Information on physical properties and harmful impurities. Then compare the test results with the national standards to evaluate the quality of the producing area.

In the section of "Calculation of Reserves", it should be pointed out that the area that has been explored and the area that has been calculated as reserves, as well as the reasons why a section within the exploration scope is not applicable, which belong to the soil layer? Those belong to useful rock formations? The calculation range of reserves should be marked on the plane and section. And attach the calculation results of reserves.

Conclusion: In this part, we should point out the origin position from the dam site, briefly explain the quality and quantity of gravel, suggestions for utilization or improvement and future work.

Finally, in the "general conclusion", each source investigated and each source explored during the census should be briefly explained. Then, compare and comment on all the producing areas, and put forward suggestions for using or further exploring the producing areas.

(Originally published in Hydrogeology Engineering Geology, No.8, 1957)