CN113235603A

CN113235603A - Civil air defense engineering foundation pit earthwork construction method

Info

Publication number: CN113235603A
Application number: CN202110556411.9A
Authority: CN
Inventors: 牛敬森; 华林林; 李康; 张征; 朱国斌; 申祥峰; 张彦涛; 上鹏; 杨鸿智
Original assignee: China Construction Seventh Engineering Bureau Installation Engineering Co Ltd
Current assignee: China Construction Seventh Engineering Bureau Installation Engineering Co Ltd
Priority date: 2021-05-21
Filing date: 2021-05-21
Publication date: 2021-08-10

Abstract

The invention relates to a civil air defense engineering foundation pit earthwork construction method, and belongs to the technical field of civil air defense engineering construction. The civil air defense engineering foundation pit earthwork construction method comprises the following steps: the method comprises the following steps: after the deep foundation pit is measured and payed off is finished, the deep foundation pit is divided into M parts from south to north_pThe number of the regions is one,divide each region into N from west to east_qEach construction section is defined with a corresponding mark number M_pN_q（p>2，q>4, and p and q are positive integers); step two: before the corresponding construction section is excavated, the construction of a dewatering pipe well is carried out on the construction section; step three: according to a foundation pit design drawing, excavating in a partitioned, segmented and layered mode according to a retreating sequence from west to east; when the (q-1) th foundation pit is excavated, the foundation pit is excavated from the west to the east in layers, and the excavation working section is M₁N_q‑1、M₂N_q‑1……M_pN_q‑1A working section, wherein the q th foundation pit excavation working section is M₁N_q、M₂N_q……M_pN_qWorking section, and excavating from south to north in layers at the same time₁N_qSetting a street in a workshop section; step four: and D, according to the mode of the third step, until the foundation pit excavation is finished. The construction efficiency can be improved, and the construction quality can be ensured.

Description

Civil air defense engineering foundation pit earthwork construction method

Technical Field

The invention relates to the technical field of civil air defense engineering construction, in particular to a civil air defense engineering foundation pit earthwork construction method.

Background

Civil air defense engineering, abbreviated as civil air defense engineering, refers to underground protective buildings which are independently built for guaranteeing concealment of personnel and materials in wartime, civil air defense command and medical aid, and basements which are built by combining ground buildings and can be used for air defense in wartime.

The foundation of civil air defense engineering is often a deep foundation pit, which refers to an engineering with excavation depth of more than 5 meters (including 5 meters) or more than three layers (including three layers) of a basement, or with depth of less than 5 meters, but with particularly complex geological conditions, surrounding environment and underground pipelines. The construction of deep foundation pit engineering has the characteristics of uncertainty, complexity, variability, concealment and the like. The Chinese patent application with application publication number CN109914419A discloses a deep foundation pit construction method, which comprises the following steps: firstly, constructing an impervious wall along the periphery of a foundation pit; excavating earthwork on the excavation surface of the foundation pit, and constructing a first reinforced concrete support; excavating a first layer of earthwork from the middle to two sides, and arranging a first layer of foundation pit support; after a working surface of the excavator is excavated on the first layer of earthwork, continuously excavating a second layer of earthwork to two sides at the middle position of the first layer of earthwork, and arranging a second layer of foundation pit support; fifthly, after the first layer of earthwork is completely excavated, removing the second layer of foundation pit support; step six, after the working surface of the excavator is excavated on the second layer of earthwork, continuously excavating a third layer of earthwork to two sides at the middle position of the second layer of earthwork, and arranging a third layer of foundation pit support; and seventhly, repeating the steps until the foundation pit excavation is finished.

Because directly excavate the earthwork among the above-mentioned construction scheme, when being under construction on the great complexity ground of some water contents, because foundation ditch groundwater does not obtain effective treatment, so cause the ground to subside easily, can cause serious incident even, the construction is safe inadequately, above-mentioned construction scheme is that successive layer excavation earthwork and successive layer build foundation ditch bearing structure simultaneously, the foundation ditch bearing structure of this kind of scheme builds work and needs many times, dismouting repeatedly, construction period is also than longer.

Disclosure of Invention

In view of the above, the invention aims to provide a civil air defense engineering foundation pit earthwork construction method, which not only ensures the construction quality of a deep foundation pit, but also improves the construction efficiency of the deep foundation pit.

In order to achieve the purpose, the technical scheme adopted by the invention is as follows:

a civil air defense engineering foundation pit earthwork construction method comprises the following steps:

the method comprises the following steps: after the deep foundation pit measurement and setting-out are finished, on a plane, dividing the deep foundation pit into Mp (p >2 and p is a positive integer) areas from south to north, dividing each area into Nq (q >4 and q is a positive integer) construction sections from west to east, and defining the corresponding label of each construction section as MpNq (p >2 and q >4 and both p and q are positive integers);

step two: before the corresponding construction section is excavated, the construction of a dewatering pipe well is carried out on the construction section;

step three: excavating according to foundation pit design drawing and according to the sequence of retreating from west to east in a partitioning and layering way, namely M₁The region excavation sequence is M₁N₁Section → M₁N₂Section → … … → M₁N_qSection, M₂The region excavation sequence is M₂N₁Section → M₂N₂Section → … … → M₂N_qSection No. … …, M_pThe region excavation sequence is M_pN₁Section → M_pN₂Section → … … → M_pN_qWorking section, simultaneously excavating all areas, excavating from west to east in a layering way when the 1 st foundation pit is excavated, wherein the excavation working section is M₁N₁、M₂N₁……M_pN₁The working sections are used for carrying out layered excavation from the west to the east in the (q-1) th foundation pit excavation according to the sequence of the foundation pit excavation working sections at each time, and the excavation working sections are M₁N_q-1、M₂N_q-1……M_pN_q-1A working section, wherein the q th foundation pit excavation working section is M₁N_q、M₂N_q……M_pN_qWorkshop section, with separate excavation from south to north, and at M₁N_qSetting a berm with a set gradient at the middle part of the workshop section, backward digging out a berm soil body by adopting an excavator when the berm is closed, digging and supporting the slope side of the foundation pit in the excavation process of the foundation pit, adopting a soil nailing wall supporting mode for supporting, pushing the construction of a downcomer well from the west to the east, arranging monitoring points of the foundation pit, and constructing a support pile at the north side from the west to the east;

step four: and D, according to the mode of the third step, until the foundation pit excavation is finished.

Furthermore, the earth excavation is carried out from top to bottom in vertical layering, and each layer of excavation surface of the earth nail support is located 50cm below each layer of earth nails.

Further, the construction sections of each zone are divided into an even number.

Furthermore, from the west to the east, two adjacent construction sections are constructed simultaneously in each area.

Furthermore, when the foundation pit is excavated, when two construction sections corresponding to each region and constructed simultaneously are excavated to the bottom of the foundation pit, the construction of the dewatering pipe well is carried out on the positions of the subsequent adjacent construction sections.

Furthermore, the projection area of each construction section in the up-down direction is equal.

Further, when the downcomer well is constructed, the steps of well point measurement positioning → well completion → hole cleaning → well hoisting and releasing → backfill gravel filter layer → sealing → well washing → installation of a water pump and a control circuit → trial water pumping → normal work of the downcomer well → well pulling after the completion of dewatering → well sealing are carried out.

The beneficial effects of the above technical scheme are that: according to the civil air defense engineering foundation pit earthwork construction method, before excavation, downcast pipe well construction is carried out, underground water of the foundation pit is treated, and the safety of excavation is guaranteed; before excavation, the deep foundation pit is divided into a plurality of areas on the plane, each area is divided into a plurality of construction sections, partitioned, segmented and layered construction is carried out, the foundation pit is excavated and supported simultaneously, construction is orderly, collapse is not prone to occurring, construction efficiency is improved, partitioned, segmented and layered construction is carried out, and excavation and supporting quality of each construction section can be guaranteed. In addition, the construction of the downcast wells is orderly carried along with the excavation of each construction section, the traditional mode that all construction is completed before excavation is not adopted, on one hand, the condition that the downcast wells are damaged during foundation pit excavation and the necessary time is needed for repairing can be avoided, and in addition, the position accuracy of the downcast wells can be ensured, so that the earthwork excavation and the foundation pit downcast wells can be operated in a crossed mode, the construction compatibility of each work type is improved, the contradiction conflict possibly caused when the two wells are constructed independently is avoided, and the construction efficiency is improved under the condition of ensuring the construction quality.

Drawings

FIG. 1 is a process flow diagram of the civil air defense construction foundation pit earthwork construction method of the present invention;

FIG. 2 is a plan sectional view of foundation pit earthwork in the civil air defense construction foundation pit earthwork construction method of the present invention;

FIG. 3 is a plan sequence view of excavation of foundation pit earthwork in the civil air defense construction method of the present invention;

fig. 4(a) to 4(h) are schematic views showing a construction sequence of foundation pit earthwork construction in an area a in the civil air defense construction method of the present invention.

Detailed Description

The invention is described in further detail below with reference to the drawings and the detailed description.

The concrete embodiment of the civil air defense engineering foundation pit earthwork construction method of the invention is as follows:

the construction process of the civil air defense engineering foundation pit earthwork construction method is shown in figure 1, namely foundation pit dewatering → first layer of foundation pit excavation → first layer of slope support → next layer of foundation pit excavation → excavation to above the basement according to the steps → manual cleaning of basement soil → basement treatment → end of foundation pit excavation, detection and layout are carried out simultaneously before the first layer of slope support and the manual cleaning of basement soil, namely, monitoring points are set, normal and abnormal conditions of the monitoring points are judged, and the abnormal conditions are treated.

The specific subdivision can be divided into the following main steps:

the method comprises the following steps: after the deep foundation pit is measured and payed off is finished, the deep foundation pit is divided into M parts from south to north on the plane_p（p>2, and p is a positive integer) of regions, each region being divided into N from west to east_q（q >4) Each construction section is defined with a corresponding mark number M_pN_q（p>2，q >4, and p and q are positive integers);

In this embodiment, the earth excavation plane is divided into 3 areas, 6 construction sections in each area, and 18 construction sections in total, according to the principle of plane partition segmentation, vertical layering and limited quantity balanced excavation. As shown in FIG. 2, for convenience of describing the code of each construction section, the letters A, B, C represent three zones, A-1, A-2, A-3, A-4, A-5 and A-6 represent six construction sections in the A zone, B-1, B-2, B-3, B-4, B-5 and B-6 represent six construction sections in the B zone, and C-1, C-2, C-3, C-4, C-5 and C-6 represent six construction sections in the C zone. In this embodiment, the projection areas of the construction segments in the up-down direction are not equal, but in other embodiments, the areas may be equally divided, that is, the projection areas of the construction segments in the up-down direction are equal.

According to the actual situation of a construction site and in combination with a foundation pit design drawing, the earthwork plan of the engineering foundation pit retreats from west to east sequentially, sectionally and hierarchically excavates. As shown in fig. 3, the excavation sequence of the area a: a-1 construction section → A-2 construction section → A-3 construction section → A-4 construction section → A-6 construction section; and B area excavation sequence: b-1 construction section → B-2 construction section → B-3 construction section → B-4 construction section → B-5 construction section → B-6 construction section; c area excavation sequence: c-1 construction section → C-2 construction section → C-3 construction section → C-4 construction section → C-5 construction section → C-6 construction section. A. B, C excavating three areas simultaneously, excavating a first foundation pit section: excavating from west to east in layers, and simultaneously excavating an A-1 construction section, a B-1 construction section and a C-1 construction section; and excavating a section of the foundation pit for the second time: excavating from west to east in layers, and simultaneously excavating an A-2 construction section, a B-2 construction section and a C-2 construction section; excavation sections of the foundation pit for the third time: excavating from west to east in layers, and simultaneously excavating an A-3 construction section, a B-3 construction section and a C-3 construction section; fourth foundation pit excavation section: excavating from west to east in layers, and simultaneously excavating an A-4 construction section, a B-4 construction section and a C-4 construction section; fifth foundation pit excavation section: excavating from west to east in layers, and simultaneously excavating an A-5 construction section, a B-5 construction section and a C-5 construction section; and excavating a section of the sixth foundation pit: excavating layer by layer from south to north, excavating the A-6 construction section, the B-6 construction section and the C-6 construction section simultaneously, arranging a berm at the middle part of the A-6 construction section, wherein the width is 4m, the gradient is 1:6, and excavating the soil body of the berm backwards by adopting an excavator when the berm is closed.

The earth excavation is carried out from top to bottom in vertical layering according to sections, and each layer of excavation surface of the earth nail support is located 50cm below each layer of earth nails. The excavation heights of the layers are shown in the following table:

earth excavation vertical layering altimeter (1-1)

Serial number	Item	Position of excavated elevation	Height of excavation
				1	Ground elevation	50.43
2	Layer 1 of foundation pit	48.53	1.9m
				3	Foundation pit layer 2	47.13	1.4m
4	Foundation pit layer 3	45.73	1.4m
				5	Foundation pit layer 4	44.33	1.4m
6	Layer 5 of foundation pit	42.93	1.4m
				7	6 th layer of foundation pit	41.63	1.3m

Earth excavation vertical layering altimeter (2-2)

Serial number	Item	Position of excavated elevation	Height of excavation
				1	Ground elevation	50.43
2	Layer 1 of foundation pit	48.63	1.8m
				3	Foundation pit layer 2	46.83	1.8m
4	Foundation pit layer 3	45.43	1.4m
				5	Foundation pit layer 4	42.93	2.5m
6	Layer 5 of foundation pit	41.43	1.5m

During actual excavation, the original miniature ground is mechanically transported to the designed elevation 50.43m, then pipe well construction, support pile construction and foundation pit earthwork excavation are carried out. And (3) rolling the outer side of the foundation pit within 9 meters by using a road roller, and arranging and constructing temporary facilities, as shown in fig. 4 (a). A-1 construction section, an A-2 construction section, a B-1 construction section, a B-2 construction section, a C-1 construction section and a C-2 construction section are used for excavating foundation pits layer by layer from west to east and supporting layer by layer. The first excavation depth of the south side foundation pit is 1.9m, the second excavation depth is 1.4m, the third excavation depth is 1.4m, the fourth excavation depth is 1.4m, the fifth excavation depth is 1.4m, and the sixth excavation depth is 1.3 m. The first excavation depth of the north side foundation pit is 1.8m, the second excavation depth is 1.8m, the third excavation depth is 1.4m, the fourth excavation depth is 2.5m, and the fifth excavation depth is 1.5 m. Construction of a support pile on the north side, construction of a pipe well, manual side slope repair, construction of soil nails, guniting and net hanging and arrangement of monitoring points of a foundation pit are shown in fig. 4 (b). Then, the A-1 construction section, the A-2 construction section, the B-1 construction section, the B-2 construction section, the C-1 construction section and the C-2 construction section excavate the next layer of earthwork, the well is dug to reduce the water, the foundation pit side slope is excavated while being supported, the pipe well construction is pushed from west to east, and meanwhile, the north support piles are constructed from west to east, as shown in fig. 4 (C). Then, an A-3 construction section, an A-4 construction section, a B3-construction section, a B-4 construction section, a C-3 construction section and a C-4 construction section are constructed in a soil subsection layering mode, well digging and water lowering are carried out, a foundation pit side slope is excavated and supported at the same time, pipe well construction is pushed from west to east, monitoring points of the foundation pit are arranged, and a north side support pile is constructed from west to east as shown in a figure 4 (d). Then, earthwork layering and subsection excavation is carried out on the A-1 construction section, the A-2 construction section, the B-1 construction section and the B-2 construction section, the C-1 construction section and the C-2 construction section to a foundation pit, the foundation pit is excavated while being supported, a support pile on the north side is constructed from west to east, the integrity of the support pile is detected before the earthwork excavation is carried out under the support pile on the north side, and after the acceptance is passed, the lower-layer earthwork excavation, the foundation pit well digging and the water lowering are carried out, and the foundation groove testing is carried out, as shown in fig. 4 (e). A-3 construction section, A-4 construction section, B-3 construction section, B-4 construction section, C-3 construction section and C-4 construction section, earthwork is excavated to the bottom of the foundation pit in a layered and segmented manner, and the foundation pit is excavated while being supported. The north supporting pile is constructed from west to east, the integrity of the supporting pile is detected before the earthwork excavation under the north supporting pile is carried out, the lower-layer earthwork excavation, the pit digging and the precipitation and the foundation groove inspection are carried out after the acceptance is qualified, and the steps are shown in fig. 4 (f). Then, an A-5 construction section, an A-6 construction section, a B5 construction section, a B-6 construction section, a C-5 construction section and a C-6 construction section are constructed in a soil subsection and layering mode, well digging and water lowering are carried out, a foundation pit is excavated while supporting is carried out on the side slope of the foundation pit, pipe well construction is propelled from west to east, monitoring points of the foundation pit are arranged, and a support pile on the north side is constructed from west to east as shown in a figure 4 (g). A-5 construction section, A-6 construction section, B-5 construction section, B-6 construction section, C-5 construction section and C-6 construction section are excavated to the bottom of the foundation pit, excavated, finally closed at A-6 construction section, foundation pit precipitation, side slope support and foundation pit groove inspection are carried out, as shown in figure 4 (h).

Before excavation, all the earth piled on the original ground is removed, the piling load is strictly forbidden within the range of 3m of the top of the foundation pit, the piling load requirement on the ground beyond 3m is not more than 20kpa, and the height is less than 1.5 m. And after the first layer of excavation is finished, carrying out slope support, and after the soil nails, the support piles and the anchor shotcrete reach the allowable strength, starting the second layer of excavation. And the excavator returns to the initial point of the first layer excavation to perform the second layer excavation according to the walking direction of the first layer, and constructors simultaneously finish the slope trimming and the slope anchor-spraying support construction. And when the groove is dug to the height of 20cm from the groove bottom, manually digging to the designed groove bottom height. And after the earthwork excavation is finished, informing the owner and the supervisor to carry out groove inspection in time, and immediately carrying out cushion layer construction after the groove inspection is qualified. Because the area of the foundation pit is large, a berm needs to be built in the foundation pit during the earth moving outside, the slope of the berm is 1:6, the transportation safety of a large heavy-duty truck is met, the top of the berm is higher than the bottom of the periphery by 23-30cm, and the situation that the peripheral rainwater flows backward into the foundation pit is prevented.

In the construction of the downcast pipe well, the steps of well point measurement and positioning → well completion → hole cleaning → hanging and releasing well pipe → backfill gravel filter layer → sealing → well washing → installation of a water pump and a control circuit → trial pumping → normal work of the downcast well → well pulling after the completion of the downcast operation → well sealing are carried out. And the tube well is positioned by a total station according to the measurement control point. And in the well formation, a mud wall-protecting rotary drilling machine is adopted to drill a hole, after the hole is formed, a well is washed to clean sediment at the bottom of the hole, and a well pipe and a filter material are continuously put into the well. When the well pipe is lowered, the well pipe is made of sand-free concrete water filter pipe, nylon net is wrapped below water level, and the well pipe is vertically fixed by bamboo strips and iron wires. The filter material is coarse sand filter material of 2.5-5 mm, and is slowly filled with spade along the circumference of well pipe until it is filled to ground, and the filter material is promptly sealed with clay after well washing. The well washing adopts a sewage pump to wash the well, sewage flowing out of the well washing is discharged into a water interception ditch outside a foundation pit, and is discharged to a nearby municipal pipe network after being precipitated, and a submersible pump can be put into the well washing to test the water pumping operation after the well washing is finished and water is cleaned. After the well is washed for 12-24 hours, clear water flows out, and then water can be continuously pumped. When the water is turbid and contains a large amount of powder and particle components, the particle size of the filter material is adjusted to be fine. And paying attention to underground water level observation in the precipitation process, starting strong precipitation for all wells in the excavation area before and in the excavation process of the foundation pit, and then properly adjusting the number of precipitation wells in the pit according to the water level observation condition and the weather condition. And (3) backfilling the pipe well by using medium coarse sand after the pump is stopped, and when the pipe well is backfilled to 1m below the ground, filling the pipe well to the ground elevation by using C15 concrete after the pipe well is naturally stabilized for 3-5 days in a water-containing saturated state, thereby completing well sealing.

The foundation pit support is supported by a soil nailing wall, and the construction sequence from excavation of earth to 50cm below the soil nail → slope cleaning → line laying and hole positioning → hole forming → soil nail installation → grouting → steel bar mesh laying → concrete surface spraying → maintenance → circulation of the next layer of soil nail construction to the base is carried out. The specific construction method comprises the following steps: firstly, adopting a mode of digging soil and loading the soil by an excavator and transporting the soil by a dump truck, and reserving a manual slope repairing with the thickness of 5-10 cm; the excavator makes the side wall on the operation depth into a slope to ensure the working surface of the soil nail hole-forming mechanical drilling machine. Secondly, after mechanical excavation, the slope surface is finished manually, in order to ensure the smoothness of the sprayed concrete surface layer, the slope surface needs to be repaired by hanging wires, and the deficient soil of the slope surface needs to be removed before the slope surface is sprayed with concrete for supporting. And thirdly, adopting an anchor rod drilling machine to form holes, wherein the depth of the formed holes is 100mm larger than the length of the anchor rod. Fourthly, the soil nailing reinforcing steel bars are phi 20 reinforcing steel bars, the transverse spacing is 1.5 meters, the vertical spacing is 1.4 meters, the inclination angle is 10 degrees, L-shaped hooks are arranged at the outer ends, centering brackets are welded at intervals of 2.0m, the height of each centering bracket is not less than 2.5cm, the soil nailing reinforcing steel bars are formed by bending phi 6 smooth circles, and 3 brackets are fixed on each section; when placing the soil nail reinforcing steel bars, the grouting pipes are bound with the soil nail reinforcing steel bars, and the distance between the grouting pipes and the bottom of the hole is about 0.2 m. Fifthly, grouting by a hole bottom grouting method, namely inserting a grouting pipe into the hole bottom, pulling the grouting pipe outwards while grouting, ensuring that the bottom of the grouting pipe is deep below the grouting surface, placing a grout stop valve at an orifice when grouting is carried out until grout flows out of the orifice, and grouting under pressure, wherein the grouting pressure is 0.2 MPa. Sixthly, binding the reinforcing steel bars on the slope surface manually by using a phi 6.5@250 reinforcing steel bar net, turning up the slope top by 1.0m, overlapping the adjacent meshes by 300mm in length, and using a concrete cushion block with the thickness of 3cm for the gap between the meshes and the slope surface. The soil nails and the reinforcing mesh are connected by phi 14 reinforcing ribs through long, the reinforcing ribs are welded with the soil nail main ribs, and the transverse spacing and the vertical spacing of the reinforcing ribs are 300cm and 280cm respectively. Seventhly, arranging a water drain pipe on the soil nail wall with the elevation below-3.50 meters, placing the water drain pipe with the diameter of 20mmUVC at a distance of 4m x 4m, wherein the length of the water drain pipe is 800mm, and taking a reverse filtration measure for preventing soil particles from losing. After the working procedures are finished, spraying concrete, wherein the concrete is commercial concrete, spraying concrete is carried out gradually upwards from the bottom of the wall excavation layer by adopting 2 air compressors of KVF12-7 and 2 sets of PT5 concrete spraying machines, but the concrete is not sprayed within the overlapping length range of the reinforcing steel bar meshes at the bottom, and the concrete is sprayed with the wall surface of the lower layer simultaneously after the concrete is overlapped and bound with the reinforcing steel bar meshes of the lower layer; the spray head and the spray receiving surface are vertical, the distance between the spray head and the operation surface is preferably 0.6-1.0 m, and the spray thickness is 80 mm. In order to ensure that the thickness of the sprayed concrete during construction reaches a specified value, a short steel bar section can be vertically driven into the wall surface of the side wall to serve as a mark, water spraying maintenance is started after the sprayed concrete is finally set for 2 hours, and the maintenance time is preferably 3-7 d; when the next concrete spraying operation is continued, the grout layer and loose debris on the joint surface of the construction joint are carefully removed and water is sprayed to make it moist. The sprayed concrete should be obliquely overlapped, the overlapping length is 20cm, and for the low-lying part caused by local over digging, the low-lying part can be firstly sprayed flat and then sprayed from bottom to top.

The pile diameter of the supporting pile is 800mm, the pile spacing is 1600mm, the pile length is 10.50m, and the pile end enters the 5 th layer. The pile body concrete strength grade is C30, and the thickness of the main reinforcement protective layer is 50 mm. And (3) constructing according to the sequence of cast-in-place pile construction of a support system → crown beam construction → earth excavation to 50cm below the position of the 1 st anchor cable → application of the 1 st anchor cable → inter-pile net hanging and concrete spraying → earth excavation to 50cm below the position of the 2 nd anchor cable → application of the 2 nd anchor cable → inter-pile net hanging and concrete spraying → excavation to the designed elevation of the foundation → inter-pile net hanging and concrete spraying. And (3) measuring and setting the pile core of the drilled pile by using a total station during pile position lofting, vertically driving a steel bar with the diameter of 6mm to the pile core for positioning, re-measuring the pile core before construction after the pile driver is in place, and starting hole forming construction after the re-measurement is correct. And (3) pre-embedding a pile casing according to the pile position, wherein the inner diameter of the pile casing is about 100mm larger than the designed pile diameter, and the height of the pile casing is 1.5 m. The embedding error between the center of the pile casing and the center of the pile position is not more than 50mm, and the embedding of the pile casing is kept vertical; the diameter of the opening for embedding the pile casing is more than 200mm, cohesive soil is filled around the opening from bottom to top, and the drill can be drilled after the position is checked by a measurer accurately. When the drilling machine is in place, the pile position is aligned and rechecked, so that the pile machine is ensured to be vertical and stable, no inclination and movement occur in construction, and after the centering and in-place adjustment of the pile machine is completed, the machine is locked, and the centering and horizontal deviation is ensured not to occur. The drilling machine is adopted for dry operation hole forming, when drilling and soil taking are carried out, the soil layer is cut into by means of the dead weight of the drill rod and the drill bit, the oblique bucket teeth cut soil blocks when the drilling bucket rotates and push the soil blocks into the bucket to complete the soil taking, after the drilling bucket is filled with soil, the drill rod and the drilling bucket are lifted to the ground by the crane, the bottom door is opened by pulling a switch on the drilling bucket, and the soil in the drilling bucket is automatically discharged by means of the dead weight. The drill rod is lowered down to close the hopper door, and then the drill rod is rotated into the hole to dig the next hopper, and after the hole is formed to the designed depth, the hole opening is protected and is checked. After the final hole is finished, the slurry is precipitated for half an hour, a drilling machine is used for primary hole cleaning, after a supervision engineer checks that the thickness, the aperture, the hole depth and the verticality of the settled slag are qualified, the drilling machine is removed, a steel reinforcement cage is installed, a hole sealing guide pipe is installed, and then secondary hole cleaning is carried out. And (3) cleaning the holes by adopting a slurry changing method for the secondary hole cleaning, taking a conduit for pouring the underwater concrete as a pipeline, pressing high-quality slurry into the holes by using a slurry pump until all indexes of returned fresh slurry are up to the standard, measuring that the thickness of sediments at the bottom of the holes meets the design and specification, and installing a large hopper after the thickness of the sediments at the bottom of the holes is up to the standard and is checked by a supervision engineer to be approved to prepare for pouring the underwater concrete. The reinforcement cage is manufactured in a centralized manner in the processing shed, and is transported to each pile position by a flat car to be bound and molded, in order to prevent the reinforcement cage from deforming in the hoisting and transporting process, reinforcing steel bar welding anti-deformation supports are used at the end of each section and the reinforcing ring in the reinforcement cage, and the supports are cut off when the reinforcement cage is hoisted to the orifice; the steel reinforcement cage is laid and is adopted the crane to hoist the steel reinforcement cage and slowly put into downthehole down, and steel reinforcement cage owner muscle outer fringe is 50mm to design pile diameter concrete surface net protective layer thickness, and the symmetry sets up four ear muscle around the steel reinforcement cage, and the interval is equal with the strengthening rib basically, ensures steel reinforcement cage protective layer thickness. The conduit is connected by screw threads, the inner diameter of the conduit is phi 250 to phi 280, the length of the bottom tube is 4m, and the length of each section in the middle is generally 2.5 m. Before the pipe uses, must carry out outward appearance inspection, butt joint inspection to the pipe, qualified rear can be put into use, pipe length should be equipped with according to the hole depth, satisfy the needs of clear hole and concrete placement under water, the pipe should be firm in the drill way junction, set up the sealing washer, when hanging, should make the position placed in the middle, the axis is straight, stable heavy, avoid card hanging steel reinforcement cage and scrape and hit the pore wall, after transferring the pipe to the hole bottom, through the inspection after error-free, mention the pipe gently, control end opening is apart from 0.5m at the hole bottom to be located drilling central authorities. The concrete adopts commercial concrete, the concrete label is C30, and the concrete vehicle is used for stirring and transporting; transporting the concrete to the site by using a concrete stirring transport vehicle, and conducting underwater concrete pouring by using a guide pipe, wherein the slump is controlled to be 18-22 cm; the concrete water-stop plug with the same label is adopted for water stop, the concrete pouring amount of the hopper is accurately calculated, and the height of the first batch of concrete embedded guide pipes is ensured to be 1.0 m; during pouring, the rising speed of concrete pouring is not more than 2m/h, the guide pipe is guaranteed to be buried in the concrete for 2-6 m, the concrete pouring needs to be finished at one step without interruption, pouring is controlled to be finished within 4-6 h to guarantee the uniformity of the concrete, the concrete amount of the last car is poured to the designed elevation of the top of the crown beam, the concrete pouring is finished, 0.3-0.4 m is removed immediately, and chiseling is carried out when the remaining crown beam to be constructed is left to combine new and old concrete and guarantee the quality of the concrete.

The process flow of the crown beam construction is carried out according to the sequence of excavating earthwork between piles to the designed elevation → chiseling the pile head → manufacturing and installing steel bars → installing templates → pouring concrete → maintaining concrete. The method specifically comprises the following steps: firstly, after the construction of the bored pile is finished, the construction is measured and set out to determine the earth excavation boundary of the crown beam, and the earth is removed to the designed bottom elevation of the crown beam by adopting an excavator matched with manual work. And secondly, when the elevation of the pile top is excavated, breaking the upper loose layer by using an air pick, manually beating 70mm within 100mm of the pile head, leaving 30mm to extend into the crown beam, placing crown beam reinforcing steel bars behind the high-pressure air gun for removing slag, and enabling the main reinforcing steel bars of the rotary-excavated pile to extend into the crown beam by 70 cm. And thirdly, after the crown beam steel bars are processed in a processing field, the crown beam steel bars are transported to the field for installation, and the crown beam steel bars are installed strictly according to the design size and the interval during installation. The crown beam formwork is made of plywood with the thickness of 12mm and wood keels with the thickness of 50 multiplied by 100mm, the distance between the keels is 200mm, the formwork is reinforced by steel pipes, one horizontal steel pipe is arranged at intervals of 250mm, vertical pipes and inclined struts are arranged outside the side dies of the two side beams, the inclined struts can be supported on a tamped soil body by wood squares, and the end parts of the inclined struts are stably padded by the wood squares. And fifthly, the top beam concrete is commercial concrete, is transported to a pouring place by a transport vehicle for a concrete mixing station to be matched with the chute for pouring, the pouring is horizontally layered pouring, and the plug-in vibrator is used for vibrating. Sixthly, after the construction of the crown beam concrete is finished, timely covering, watering and curing are carried out, and the die can be disassembled after the strength of the concrete reaches 2.5 MPa.

The design aperture of the anchor cable is 200mm, the inclination angle is 15 degrees, and 1860-grade steel strands are adopted; the wale is made of 20a type channel steel, the anchor plate is made of 200 multiplied by 15Q235 steel, and the batten plate is made of 150 multiplied by 75 multiplied by 10Q 235 steel. The construction process of the prestressed anchor cable comprises the following steps: drilling → installing anchor cable → grouting anchor hole → installing waist beam → installing anchor device → tensioning and locking anchor hole → checking and accepting anchor sealing. The specific construction method comprises the following steps: firstly, according to the actual slope surface, according to the design arrangement requirements, accurately measuring and placing the anchor hole position on the slope surface, and marking the anchor cable hole-opening position at the site construction position by using red paint. Secondly, accurately measuring and releasing the hole position of the anchor cable according to the slope, accurately installing a fixed drilling machine, adopting a GC-50 type anchor rod drilling machine to dry drill to form a hole, and after drilling reaches the designed depth, using high-pressure air to completely remove fine granular soil and water in the hole out of the hole. Thirdly, the single cable body of the anchor cable is produced in a reinforcing steel bar processing field, and the assembly is completed on the construction site, wherein the manufacturing procedure is as follows: blanking → braiding → assembling guide cap and corrugated pipe → cable testing → storing. The anchor cable steel strands are separated by adopting an isolation frame, the binding distance between the end parts of the isolation frame is 0.80m, and the middle part and the top part of the isolation frame are 2.0 m. The isolation frame can be made of iron plates with the thickness of 2-3 mm. And binding a secondary grouting pipe in the middle of the anchor cable, wherein the secondary grouting pipe is a PVC plastic pipe, opening 2 small holes at intervals of 1.0m below a free section, sealing the holes by using a rubber ring or an electrical tape, and keeping the end part of the grouting pipe 50cm away from the end part of the anchor cable. When the two sections are connected, the plastic pipe is sleeved into the iron pipe and bound by the iron wire. Coating butter on the free section steel strand, wrapping with a sleeve or with a double-layer glass cloth, wherein the length of the free section is as follows: MG1 and MG2 are 9m and 7.5 respectively, and the water test is carried out to the slip casting pipe to the steel strand wires that make, and the seepage phenomenon can be put into the anchor rope hole just to the leakage phenomenon does not have, after the anchor rope preparation is accomplished, utilizes the manual work to lift the anchor rope and slowly puts into the hole to the design depth, and the anchor rope exposes the part and wraps up with the rubberized fabric and prevents to rust after the bundle is worn. Adopting PO.32.5 grade pure cement slurry with water-cement ratio of 0.5, adopting primary grouting, after the slurry is solidified, the slurry volume is contracted, and the contact area of anchoring body and soil body can be reduced, so that the pulling resistance of anchor rope can be reduced, and in order to raise the pulling resistance of anchor rope, the anchor rope adopts secondary grouting technology, i.e. when the steel strand anchor rope is made, a grouting pipe (tied together with steel strand) is inserted, the primary grouting is normal-pressure grouting, and is inserted into hole bottom by means of movable primary grouting pipe, and is injected from inside to outside so as to replace the slurry in the hole, and when the slurry and impurity in the hole are all replaced by cement slurry and overflow from hole opening, the 1 st grouting can be completed; and after the 1 st grouting slurry reaches the initial setting strength, performing 2 nd grouting, wherein the grouting slurry is pure cement slurry with the water cement ratio of 0.45-0.50, the grouting pressure is 2.0-3.0 Mpa, and the grouting is stabilized for more than 10 min. Fifthly, anchor installation: the anchor backing plate is made of 200X 18 steel plates, the waist beam is made of 20a # I-steel, and a 250X 20 wedge-shaped steel plate is arranged between the waist beam and the anchor backing plate to ensure that the surface of the anchor is vertical to the stress direction of the steel strand. Stretching after the slurry reaches 80% of the designed strength, adopting an OVM anchor, using a YCW150 hydraulic jack, selecting a ZB4/5OO type oil pump as a hydraulic power source for stretching and locking, and stretching an anchor cable: 0 → 10% δ k initial stress 50KN (pre-tension) → 50% δ k (hold charge 5 minutes) → δ k (500 KN) (hold charge 30 minutes) → 250KN (300 KN) anchoring. (MG1 Anchorage line Lock value is 250KN, MG2 Anchorage line Lock value is 300 KN). Stretching to a design tension (500 KN) and keeping for 30min, measuring creep displacement of the anchor cable within 30min, and if the creep value does not exceed 1mm, determining that the anchor cable is qualified; and then unloaded to the locked value to be locked. And protecting the anchor head. And (3) sealing the anchor after the prestressed anchor cable is locked for 48 hours without obvious stress relaxation, cutting off redundant steel strands by using a hand-held sand turbine, keeping the length of the steel strands to be 5-10cm to prevent dragging and sliding, filling gaps among the anchor backing plate and the anchor head with cement paste, and sealing the gaps with 30MPa concrete to prevent corrosion.

And (3) tensioning the anchor cable, locking and sealing the anchor, hanging a net and spraying concrete between piles, drilling holes on the support piles by using an electric drill to implant phi 20 steel bars with the depth of 20cm, leaking 5cm outside and the distance between adjacent planted bars of 3m, then installing 6.5@250 x250 steel bar net sheets, and firmly welding the steel bars with the planted bars, wherein the method for spraying concrete between piles is the same as that of a concrete-nailed wall, and the surface of sprayed concrete near the waist beam is flush with the surface of the support piles, so that the waist beam is ensured to be closely attached to the sprayed concrete and the support piles.

The civil air defense engineering foundation pit earthwork construction method has the advantages that the construction is orderly, the collapse is not easy to occur, the construction compatibility of each work type can be improved, the contradiction conflict possibly caused when the civil air defense engineering foundation pit earthwork construction method and the civil air defense engineering foundation pit are independently constructed can be avoided, and the construction efficiency is improved under the condition of ensuring the construction quality.

The above-described embodiments of the present invention do not limit the scope of the present invention. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention should be included in the scope of the claims of the present invention.

Claims

1. A civil air defense engineering foundation pit earthwork construction method is characterized by comprising the following steps:

the method comprises the following steps: after the deep foundation pit measurement line laying is finished, on the plane, from south to northDividing a deep foundation pit into M_p（p>2, and p is a positive integer) of regions, each region being divided into N from west to east_q（q >4, and q is a positive integer) construction segments, a corresponding reference number M defining each construction segment_pN_q（p>2，q >4, and p and q are positive integers);

2. The civil air defense construction foundation pit earthwork method as claimed in claim 1, wherein the earthwork excavation is performed from top to bottom in vertical layers, and each excavation surface of the earth nail support is positioned 50cm below each layer of earth nails.

3. The civil air defense construction foundation pit earthwork method of claim 1, wherein the construction segments of each zone are divided into an even number.

4. The civil air defense construction foundation pit earthwork of claim 3, wherein two adjacent construction sections are simultaneously constructed per zone from the west to the east direction.

5. The civil air defense construction foundation pit earthwork method according to claim 4, wherein when the foundation pit is excavated, and when two simultaneously constructed construction sections corresponding to each region are excavated to the bottom of the foundation pit, the construction of the downcomer well is performed at the position of the subsequent adjacent construction section.

6. The civil air defense construction foundation pit earthwork method as claimed in any one of claims 1 to 5, wherein the projected area of each construction section in the up-down direction is equal.

7. The civil air defense construction foundation pit earthwork method according to any one of claims 1 to 5, wherein the construction of the downcomer well is carried out according to the steps of well point measurement positioning → well completion → hole cleaning → hanging and releasing well pipe → gravel packing layer → sealing → well washing → installation of water pump and control circuit → trial pumping → normal operation of the downcomer well → well pipe pulling after completion of dewatering → sealing well.