Method for constructing pumping-injection well of groundwater reservoir in dump of open-pit mine

A method for constructing a pumping-injection well of a groundwater reservoir in a dump of an open-pit mine, wherein the pumping-injection well comprises a bottom pipe, a plurality of intermediate pipes, and a top pipe in sequence from bottom to top;

• concrete straight pipes each having an identical diameter and permeable to water are respectively arranged on an outer side of the bottom pipe, an outer side of each of the intermediate pipes, and an outer side of the top pipe;
• an equal-diameter steel pipe having circular holes distributed on a surface thereof is fixedly nested in each of the concrete straight pipes;
• a bottom of the steel pipe nested in the bottom pipe is flush with a bottom of one of the concrete straight pipes which is located on the outer side of the bottom pipe, a top of the steel pipe nested in the bottom pipe is 1 m higher than a top of the one of the concrete straight pipes which is located on the outer side of the bottom pipe, and an exposed region at the top of the steel pipe nested in the bottom pipe is provided with the circular holes;
• a horizontal position of a bottom of the steel pipe nested in each of the intermediate pipes is 1 m higher than a horizontal position of a bottom of a respective one of the concrete straight pipes which is located on the outer side of each of the intermediate pipes, a top of the steel pipe nested in each of the intermediate pipes is 1 m higher than a top of the respective one of the concrete straight pipes which is located on the outer side of each of the intermediate pipes, and an exposed region at the top of the steel pipe nested in each of the intermediate pipes is provided with the circular holes;
• similar to the intermediate pipes, a horizontal position of a bottom of the steel pipe nested in the top pipe is 1 m higher than a horizontal position of a bottom of one of the concrete straight pipes which is located on the outer side of the top pipe, a top of the steel pipe nested in the top pipe is higher than a top of the one of the concrete straight pipes which is located on the outer side of the top pipe, and an exposed region at the top of the steel pipe nested in the top pipe is provided with the circular holes;
• a well cover is arranged above the top pipe;
• the steel pipe at the bottom of each of the intermediate pipes is configured to engage with the steel pipe at the top of a respective one of the intermediate pipes therebelow or the bottom pipe through a groove-protrusion technique, so as to connect the pipes as a whole from bottom to top by gravity;
• the method comprises following steps:
• S1:
• using a designed position of the pumping-injection well as a center of circle, arranging a radially radiating rubble barrier circumferentially around the pumping-injection well, installing the bottom pipe of the pumping-injection well at the center of the circle, fixing a bottom of the bottom pipe with concrete, and piling up a rubble pile which is slightly lower than a top of the bottom pipe around the bottom pipe, to further fix the bottom pipe;
• S2:
• continuing to install an intermediate pipe of the intermediate pipes on the bottom pipe, and continuing to pile up the rubble pile to a height which is 2 m to 3 m lower than a top of the intermediate pipe;
• S3:
• continuing to stack multiple intermediate pipes of the intermediate pipes to a design height of the groundwater reservoir, and discarding sandstone and gravel materials as reservoir materials for constructing the groundwater reservoir, wherein water is stored in gaps of the sandstone and gravel materials, and stones of the groundwater reservoir bury the intermediate pipes which are already installed to maintain stability thereof;
• S4:
• after the intermediate pipes are installed to a height more than a construction height of the groundwater reservoir, continuing to install the intermediate pipes;
• starting to normally discard stripped materials of the open-pit mine from an upper surface of the groundwater reservoir, forming steps in the dump;
• when continuing to discard the stripped materials upward, reserving a pit on an upper layer of each of the steps in the dump along a periphery of the pumping-injection well, filling the pit with the sandstone and gravel materials to form a sump;
• continuing to discard the stripped materials, burying the already installed pumping-injection well and the sump, wherein a wellbore installation status is monitored in real time during the installation of the intermediate pipes to perform a correction in a timely manner to ensure that the intermediate pipes are upright;
• S5:
• continuing to stack and install the intermediate pipes;
• when reaching a height which is 15 m lower than a final height of the dump, starting to construct an inverted cone-shaped surface sump within 30 m around the pumping-injection well;
• and
• S6:
• when a design height of the dump is reached, installing the top pipe and the well cover to form the complete pumping-injection well.