Construction method of initial dam suitable for upstream type tailing pond
Technical Field
The invention relates to a tailing discharging and stockpiling facility, in particular to an initial dam of a tailing pond, which is particularly suitable for being applied to the construction of an upstream tailing pond under the conditions that stone resources are insufficient at the place where the tailing pond is planned to be constructed, a permeable rock-fill dam is difficult to construct and the traffic is inconvenient, and can effectively reduce the seepage line of a dam body.
Background
The initial dam is built by non-tailing materials, and the main function of the initial dam is to lay a foundation for the later tailing accumulation dam, namely the foundation dam. Two types of non-permeable dams and permeable dams can be classified according to whether water is drained or not.
In the process of the upstream type tailing pond operation, the initial dam type generally adopts a permeable rock-fill dam in consideration of stable permeation at the initial stage and the later stage of the tailing pond operation. The permeable dam is a dam type which performs organized drainage in a dam body and allows organized and planned water seepage. The drainage system of the utility model has different functions and functions from the drainage system of the impermeable dam. A drainage system is also arranged in the impervious dam, and the purpose of the drainage system is to discharge seepage water in the impervious body organically, protect the impervious body and the initial dam and prevent seepage deformation. The water draining system of permeable dam is to eliminate the water leakage from the dam in organized mode and has the main function of controlling the position of the infiltration line inside the accumulated dam. The main dam type of the permeable dam is that reverse filtering bodies are additionally arranged on the upstream slope of various rockfill dams, and drainage facilities can also be additionally arranged in the impermeable dam, so that the infiltration line of a tailing fill dam can be reduced. The permeable dam is the most basic dam type in the initial dam, and is also an ideal dam type.
The dam shape of the initial dam is selected according to the specific conditions of the body, the local conditions are thoroughly met, the materials are locally obtained, and the principle of material design is adopted. The earth-rock dam has the lowest requirement on the topographic and geological conditions and has the strongest adaptability. If the local stone is not enough to build the permeable rock-fill dam, a drainage facility can be added on the basis of the homogeneous dam to realize water permeability.
In the article of 'the upstream type tailing pond is a new initial dam type seepage calculation analysis' published in 2 months 2020 of science and technology wind of Chinese journal, a new initial dam type is provided, and a part of soil and rock mixture (about 1/4 initial dam height) is filled in an upstream side partition of a conventional rockfill dam, so that tailing 'muddy' at the initial operation stage of the tailing pond is reduced, and the stable seepage of the rockfill dam is ensured. However, the initial dam belongs to a permeable dam, a large amount of stone resources are needed in construction, and the construction cost is high; moreover, after a part of soil and stone mixture is filled in the upstream side of the conventional rockfill dam in a partition mode, the water permeability is greatly reduced.
The invention discloses a design method for enabling an earth dam to meet the requirements of a permeable dam according to site conditions of a tailing pond and characteristics of dam building materials.
Disclosure of Invention
The method for constructing the initial dam of the upstream type tailing pond is low in construction cost, small in stone usage amount and good in water permeability, the designed initial dam can meet the water permeability requirement of the permeable dam, and when the site stone is not enough to construct the initial rock-fill dam and the cost for transporting stone is high, the cost can be effectively reduced, and the initial dam can meet the use requirement of the permeable dam.
In order to achieve the purpose, the construction method of the initial dam suitable for the upstream type tailing pond is realized by adopting the following technical scheme:
the invention relates to a construction method of an initial dam suitable for an upstream tailing pond, which is characterized in that dam abutment intercepting ditches are arranged on hills on two sides of the initial dam, dam foot drainage ditches are arranged at dam feet of the initial dam, the water outlet ends of the dam abutment intercepting ditches are communicated with the dam foot drainage ditches, and the following technical scheme is adopted:
1) impermeable layer at bottom of dam body at initial laying stage
Clearing the foundation of the initial dam, and paving a fine soil layer, a composite geomembrane, a coarse sand layer, a rock block layer and a sand-gravel layer from bottom to top respectively to form an impermeable layer at the bottom of the initial dam body after clearing the foundation;
the mass percentage of 0-0.1 mm grain fraction in the fine grain soil layer is more than or equal to 95%, the mass percentage of 2-13 mm grain fraction in the coarse sand layer is more than or equal to 95%, the mass percentage of 76-200 mm grain fraction in the stone layer is more than or equal to 95%, and the mass percentage of 13-76 mm grain fraction in the sand gravel layer is more than or equal to 95%; wherein: the thickness of the fine-grain soil layer is 0.17-0.23 m, the thickness of the coarse sand layer is 0.18-0.24 m, the thickness of the lump stone layer is 1.3-1.8 m, and the thickness of the sand gravel layer is 0.18-0.25 m.
2) An upstream drainage ridge and a downstream drainage ridge of the initial dam are respectively arranged at the upstream and the downstream of the initial dam, an initial dam drainage mattress is paved on an impermeable layer at the bottom of the initial dam between the upstream drainage ridge and the downstream drainage ridge of the initial dam, and the upstream drainage ridge and the downstream drainage ridge of the initial dam are communicated with the initial dam drainage mattress; the stone material for stacking the seepage drainage arrises is required to be a good permeable material, the content of the stone material with the granularity smaller than 2mm is not more than 5 percent, the maximum diameter of the stone material is not more than 0.5m, the stone material is required to be fresh, hard, weather-resistant and abrasion-resistant, weatherproof stone is not used, the wet compressive strength is not less than 40Mpa, and the softening coefficient is not less than 0.80; the seepage drainage prism and the seepage drainage mattress are both wrapped by double-layer geotextile.
3) Pre-burying a vertical drainage blind ditch pipe on a drainage mattress of the initial dam in the initial dam, wherein the lower end of the vertical drainage blind ditch pipe is communicated with the drainage mattress of the initial dam; the vertical seepage elimination blind ditch pipe is wrapped by geotextile and is symmetrically arranged in the initial dam.
4) Embedding an inclined drainage blind ditch at the contact part of the initial dam and the mountain, embedding a transverse drainage blind ditch at the contact part of the initial dam and the mountain, wherein the upper water inlet of the inclined drainage blind ditch is communicated with the transverse drainage blind ditch, and the lower water outlet of the inclined drainage blind ditch is communicated with the drainage mattress of the initial dam; the blind ditch is formed by wrapping rubble stones by double-layer geotextile, the rubble stones are compact and have good water permeability, and the aim is to increase the drainage capacity of the contact part of the initial dam and a mountain and further reduce the seepage line of the dam.
5) Initial dam construction
In the space formed between the upstream seepage drainage arris body of the initial dam, the downstream seepage drainage arris body of the initial dam and the mountain bodies at two sides of the initial dam, the initial dam is built layer by layer from bottom to top and is compacted in a layering way, and after the upstream seepage drainage arris body height of the initial dam is compacted, the method is implemented according to the following steps:
step 1: adopting cohesive soil to pile and compact the first layer of the initial dam, and constructing an anti-seepage slope protection layer on the upstream slope of the first layer of the initial dam;
step 2: adopting cohesive soil to pile and compact the second layer of the initial dam above the first layer of the initial dam, and constructing an anti-seepage slope protection layer on the upstream slope of the second layer of the initial dam;
section 3: adopting cohesive soil to pile and compact the third layer of the initial dam on the second layer of the initial dam, and constructing an anti-seepage slope protection layer on the upstream slope of the third layer of the initial dam;
and 4, step n: and the rest can be done by analogy until the building height reaches the design height.
And paving a geomembrane on the surface of the dam crest of the initial dam, and paving a broken stone protective layer and a dry block stone protective layer on the geomembrane. The dry stone has a specification, the ratio of long to short sides is not more than 4, the content of the dry stone is less than 5 percent and the dry stone has proper gradation.
Furthermore, the anti-seepage slope protection layer is respectively a sand-gravel layer, a rock block layer, a sand-gravel layer, a coarse sand layer, a composite geomembrane and a coarse sand layer from inside to outside; the composite geomembrane is formed by sandwiching a geomembrane between two layers of geotextiles; in the anti-seepage slope protection layer, the mass of 13-76 mm grain size fraction in the sand-gravel layer is more than or equal to 95%, the mass of 76-200 mm grain size fraction in the rock block layer is more than or equal to 95%, and the mass of 2-13 mm grain size fraction in the coarse sand layer is more than or equal to 95%; in the anti-seepage slope protection layer, the thickness of the coarse sand layer is 0.18-0.24 m, the thickness of the stone layer is 1.3-1.8 m, and the thickness of the sand gravel layer is 0.18-0.25 m.
Further, in the step 5), the height of each layer of stacking from bottom to top is 2.2-2.8 m, the thickness of the layered compaction is not more than 0.8m, after the layers are rolled by a vibratory roller, each layer of sampling is used for measuring the porosity, the number of the sampling and the technical requirement of the porosity measurement are implemented according to the specification requirement, and the porosity of the dam body after the compaction is required to be not more than 22%. The cautions and technical requirements of the cohesive soil pile must comply with the technical Specification for construction of rolled earth-rock dam DL/5129-2001 and GBJ201-83 Specification for construction and acceptance of earthwork and blasting engineering, so as to achieve the expected filling quality.
Further, the stability of the tailing dam is analyzed by a Bishop method; and analyzing the seepage field of the tailing dam by using a finite element method, calculating a node water head, and outputting a water level line by using a computer.
The construction method of the initial dam suitable for the upstream tailing pond has the following effects after the technical scheme is adopted:
(1) when the existing stones in the field are not enough to build a rock-fill dam and the cost for transporting stones is too high, the method can obviously reduce the cost;
(2) the drainage of the cohesive soil initial dam can be realized through a drainage facility main body formed by the upstream and downstream drainage arrises and the drainage mattress;
(3) the dam body infiltration line can be further reduced when the infiltration line in the initial dam is higher through the vertical drainage blind ditch pipe pre-buried in the initial dam;
(4) the oblique drainage blind ditch is pre-buried at the contact part of the initial dam and the mountain, and the transverse drainage blind ditch is pre-buried at the contact part of the initial dam and the mountain, so that the drainage effect can be increased, and the dam body infiltration line is further reduced;
(5) the method is simple in construction, the designed drainage facility mostly uses stones, geomembranes and geotextiles, and construction materials are convenient to obtain.
Drawings
Fig. 1 is a schematic cross-sectional structure diagram of a primary dam system suitable for an upstream tailings pond constructed by the method of the present invention;
fig. 2 is a schematic diagram of a longitudinal section structure of an initial dam system suitable for an upstream tailings pond constructed by the method of the present invention.
The reference signs are: 1-drainage prism at upstream of initial dam; 1' -drainage arrises at the downstream of the initial dam; 2-draining seepage mattress of initial dam; 3-vertical drainage blind ditch pipe; 4-a dam foot drainage ditch; 5-seepage-proofing slope protection layer; 6-late tailing dam; 7-oblique drainage blind ditches; 8-horizontal drainage blind ditches; 9-impermeable layer at the bottom of the dam body at the initial stage.
Detailed Description
The method for constructing the initial dam suitable for the upstream-type tailing pond according to the invention is further described in detail with reference to the accompanying drawings and examples.
The method for constructing the initial dam suitable for the upstream tailing pond is characterized in that dam abutment intercepting ditches are arranged on the hills on two sides of the initial dam, dam foot drainage ditches 4 are arranged at the dam feet of the initial dam, the water outlet ends of the dam abutment intercepting ditches are communicated with the dam foot drainage ditches 4, and the following technical scheme is adopted:
1) impermeable layer at bottom of dam body at initial laying stage
Clearing the foundation of the initial dam, and paving a fine soil layer, a composite geomembrane, a coarse sand layer, a rock block layer and a sand-gravel layer from bottom to top respectively to form an impermeable layer 9 at the bottom of the initial dam body after clearing the foundation; the mass percentage of 0-0.1 mm grain fraction in the fine grain soil layer is more than or equal to 95%, the mass percentage of 2-13 mm grain fraction in the coarse sand layer is more than or equal to 95%, the mass percentage of 76-200 mm grain fraction in the lump stone layer is more than or equal to 95%, and the mass percentage of 13-76 mm grain fraction in the sand gravel layer is more than or equal to 95%; the thickness of the fine-grained soil layer is 0.2m, the thickness of the coarse sand layer is 0.2m, the thickness of the stone layer is 1.5m, and the thickness of the sand-gravel layer is 0.2 m.
2) An upstream drainage and seepage prism 1 and a downstream drainage and seepage prism 1' of the initial dam are respectively arranged at the upstream and the downstream of the initial dam, an initial dam drainage and seepage mattress 2 is laid on an impermeable layer 9 at the bottom of the initial dam between the upstream drainage and seepage prism 1 and the downstream drainage and seepage prism 1', and the upstream drainage and seepage prism 1 and the downstream drainage and seepage prism 1' of the initial dam are communicated with the initial dam drainage and seepage mattress 2;
3) a vertical drainage blind ditch pipe 3 is pre-buried above a drainage mattress 2 of the initial dam in the initial dam, and the lower end of the vertical drainage blind ditch pipe 3 is communicated with the drainage mattress 2 of the initial dam;
4) an inclined drainage blind ditch 7 is pre-buried at the contact part of the initial dam and the mountain, a transverse drainage blind ditch 8 is pre-buried at the contact part of the initial dam and the mountain, an upper water inlet of the inclined drainage blind ditch 7 is communicated with the transverse drainage blind ditch 8, and a lower water outlet of the inclined drainage blind ditch 7 is communicated with the drainage mattress 2 of the initial dam;
5) initial dam construction
In the space formed by the upstream seepage drainage arris body 1 of the initial dam, the downstream seepage drainage arris body 1' of the initial dam and the mountains at two sides of the initial dam, the initial dam is built layer by layer from bottom to top and is compacted in layers, and after the upstream seepage drainage arris body 1 of the initial dam is compacted to the height, the method is implemented according to the following steps:
step 1: adopting cohesive soil to pile and compact the first layer of the initial dam, and constructing an anti-seepage slope protection layer 5 on the upstream slope of the first layer of the initial dam;
step 2: adopting cohesive soil to pile and compact the second layer of the initial dam above the first layer of the initial dam, and constructing an anti-seepage slope protection layer 5 on the upstream slope of the second layer of the initial dam;
section 3: adopting cohesive soil to pile and compact the third layer of the initial dam on the second layer of the initial dam, and constructing an anti-seepage slope protection layer 5 on the upstream slope of the third layer of the initial dam;
and 4, step n: and the rest can be done by analogy until the building height reaches the design height.
The anti-seepage slope protection layer 5 is respectively a sand-gravel layer, a rock block layer, a sand-gravel layer, a coarse sand layer, a composite geomembrane and a coarse sand layer from inside to outside; the mass percentage of 13-76 mm grain size fraction in the sand-gravel layer is more than or equal to 95%, the mass percentage of 76-200 mm grain size fraction in the stone layer is more than or equal to 95%, and the mass percentage of 2-13 mm grain size fraction in the coarse sand layer is more than or equal to 95%; in the anti-seepage slope protection layer 5, the thickness of the coarse sand layer is 0.2m, the thickness of the stone layer is 1.5m, and the thickness of the sand gravel layer is 0.2 m.
The composite geomembrane adopted by the invention is formed by sandwiching a layer of geomembrane between two layers of geotextile, and the specification of the geotextile is 300-600 g/m2(ii) a Wherein: the composite geomembrane in the step 1) adopts 300g/m2Geotextile, the composite geomembrane of the step 5) adopts 600g/m2The geotextile is non-woven, and the geomembrane is an HDPE film.
In the step 5), the height of each layer of pile from bottom to top is 2.5m, and the thickness of the layered compaction is not more than 0.8 m.
After the initial dam is built to the designed height, a geomembrane is laid on the surface of the top of the initial dam, and a broken stone protective layer and a dry block stone protective layer are laid on the geomembrane.
After the initial dam is built and tailings are discharged to the level, the construction of the sub-dam 6 is started, and the construction sequence of the sub-dam 6 is as follows:
firstly, leveling a foundation layer, and respectively constructing a fine soil layer, a composite geomembrane and a coarse tailings protective layer on the foundation layer from bottom to top to form a first-stage sub-dam; after the first-stage sub-dam construction is finished and tailings are discharged to the level, the second-stage sub-dam construction is carried out after the first-stage sub-dam construction is finished; the construction sequence of the second-stage sub-dam is also flat foundation layer → fine soil layer → composite geomembrane → coarse tailings protective layerAnd so on. The mass ratio of 0-0.1 mm grain fraction in the fine grain soil layer is more than or equal to 95%, the mass ratio of 2-13 mm grain fraction in the coarse sand layer is more than or equal to 95%, and the thickness of the fine grain soil layer is 0.2 m; the coarse tailings protective layer is dug and transported from an old tailings pond, and the thickness of the coarse tailings protective layer is 0.2 m; the composite geomembrane is formed by sandwiching a layer of geomembrane between two layers of geotextile, and the specification of the geotextile is 300g/m2The geomembrane is a 1.5mm HDPE membrane.
The stability of the tailing dam is analyzed by adopting a Bishop method; and analyzing the seepage field of the tailing dam by using a finite element method, calculating a node water head, and outputting a water level line by using a computer.