阅读说明：本技术 一种沉井卡桩破除的施工方法 (Construction method for breaking pile blocking of open caisson ) 是由 赵保森 赵亚军 吕朋 王彦明 苏东黎 刘伟 李海新 韩志强 高云飞 焦道伟 周佩 于 2021-05-17 设计创作，主要内容包括：一种沉井卡桩破除的施工方法,包括制定沉井下沉方案、地质钻机取芯探明水泥加固体深度范围、沉井下沉开挖、搭设沉井钻孔平台、气动潜孔钻机冲击破碎帷幕突出桩体、振动锤提拔钢板桩切削帷幕突出桩体和沉井下沉共七个步骤。本发明不受场地狭小的制约,施工操作简单,机械设备市场保有量大,可快速投入人员机械实施清除工作,工人操作性强,能快速进场设备,处理效率及工期得到保证,且进出场费用低,经济性好。(A construction method for breaking pile sticking in an open caisson comprises the seven steps of establishing an open caisson sinking scheme, coring and finding out the depth range of a cement reinforced body by a geological drilling rig, sinking and excavating the open caisson, building an open caisson drilling platform, impacting a broken curtain to protrude a pile body by a pneumatic down-the-hole drilling rig, lifting a steel sheet pile by a vibration hammer, cutting the curtain to protrude the pile body and sinking the open caisson. The invention is not limited by narrow field, has simple construction operation, large market holding amount of mechanical equipment, can be quickly put into personnel and machinery to carry out cleaning work, has strong operability of workers, can quickly enter the equipment, ensures the treatment efficiency and the construction period, and has low cost for entering and leaving the field and good economical efficiency.)

1. A construction method for breaking a stuck pile of an open caisson is characterized by comprising the following construction steps:

step one, a sinking scheme of the open caisson (3) is formulated;

a, acquiring a stratum permeability coefficient, a stratum penetration number and a side friction resistance value according to a geotechnical investigation report;

b, calculating the sinking safety coefficient of the open caisson through an open caisson sinking checking formula;

and step c, adopting two open caisson sinking schemes according to the step a and the step b:

the first method comprises the following steps: the upper sludge layer adopts a drainage and sedimentation scheme, and the second scheme is as follows: the lower sand layer adopts a non-drainage sinking scheme;

then determining the number of sections of the wall of the open caisson, the timing and the sections of the wall of the open caisson for heightening according to the two excavation schemes, the sinking safety factor of the open caisson and the design positions of the plane and the depth of the water-stop curtain (1) of the jet grouting piles around the open caisson;

secondly, coring by a geological drilling machine to find the invasion range of the cement block protrusion;

d, constructing a waterproof curtain of the jet grouting pile;

e, after finishing the jet grouting pile water-stop curtain and before excavating the open caisson, coring by using a geological drilling rig (5) to find the area position of a cement block protrusion in the depth range of the open caisson, wherein the coring position is positioned outside an open caisson cutting edge and is arranged along the periphery of the open caisson, the coring depth is up to the base elevation (202) of the open caisson, and a long coring drill rod is used for guiding holes to core, so that an actual stratum core sample is obtained;

step three, sinking and excavating the open caisson, and adopting two open caisson sinking schemes in the step one according to the stratum condition of the open caisson;

step f: when water is drained and sunk in a sludge stratum, a digging machine is adopted to symmetrically and uniformly dig soil from the middle part to the periphery of the open caisson, and the open caisson is sunk by soil cutting of the open caisson cutting edge foot under the dead weight;

step g: observing the sinking rate of the open caisson when the open caisson sinks to the depth of the cement block protrusion; when the sinking rate of the open caisson is reduced to the suspension of the open caisson, the pile blocking of the open caisson cannot sink;

step h: digging a soil body of a cutting edge around the open caisson, removing the soil body in a gap between the well wall and a water-stop curtain of the jet grouting pile, and observing the sinking amount of the open caisson;

step i: a diver goes into the well to explore the sunk well blade, confirms the suspension height of the sunk well, and then draws a sunk well blade relative height map according to the relative position relation around the sunk well blade; a gap (601) with an annular cross section is formed between the open caisson (3) and the jet grouting pile waterproof curtain (1) and above the position of the cement block protrusion (4); a breaking device is designed and inserted in the gap (601), and comprises starting equipment positioned above the ground elevation (201) and a breaking vertical piece vertically inserted into the gap (601) and penetrating through the cement block protrusion (4);

fourthly, setting up an open caisson drilling operation platform;

erecting a drilling platform (7) on the top of the open caisson, wherein the drilling platform (7) is erected on the ground and is positioned right above the open caisson, comprises a group of profile steel joists (701) which are erected at intervals in parallel, then fully laying a steel plate (702), and then hoisting a breaking device, namely a down-the-hole drill (8), to the drilling platform (7);

fifthly, the pneumatic down-the-hole drill impacts and breaks the cement block protrusion of the curtain;

each down-the-hole drill (8) is provided with a vertical first breaking vertical piece, the first breaking vertical piece is a rod body with a spherical tooth drill bit (801), the first breaking vertical pieces are distributed along the periphery of a sunk well blade foot, the first breaking vertical pieces densely arrange holes on the cement block protrusion (4) along the periphery of the sunk well blade foot according to the diameter of the spherical tooth drill bit (801), and then the down-the-hole drill (8) is adopted to drive the spherical tooth drill bit (801) to impact along the periphery of the sunk well blade foot and penetrate through the cement block protrusion (4) until the base elevation (202);

sixthly, lifting the cement block protrusion of the steel sheet pile cutting curtain by a vibration hammer;

the breaking device further comprises a steel sheet pile device (9) located on the ground outside the open caisson, the steel sheet pile device (9) comprises a lifting device and a vertical second breaking vertical piece controlled by the lifting device, the second breaking vertical piece is a steel sheet pile (901), the steel sheet pile device (9) lifts the steel sheet pile to sink, the steel sheet pile device vibrates and breaks a cement block protrusion (4) which loses integrity, the steel sheet pile is symmetrically, cut in a staggered mode along the open caisson for a circle, blocks of cement falling into the water are cut, the steel sheet pile is lifted and sunk repeatedly, and the pile bottom of the steel sheet pile reaches the elevation of a substrate (202);

step seven, sinking the open caisson; when the weight of the open caisson is greater than the frictional resistance of the cement block protrusions, the open caisson sinks instantaneously, the suspended height of the open caisson from the substrate elevation (202) is controlled not to be greater than 1m, then the open caisson is symmetrically and uniformly excavated to the substrate elevation, and the open caisson is prevented from inclining until the open caisson sinks completely.

2. The open caisson pile stuck construction method according to claim 1, wherein: in the step d, the jet grouting pile waterproof curtain (1) is applied in soil in the scope of the open caisson stratum (2), the soil in the open caisson (3) is excavated, the underground water level (203) is lower than the water level (204) in the open caisson,

in the step e, the cement block protrusion (4) is a block body which is formed in the middle of the inner wall of the jet grouting pile waterproof curtain (1) and protrudes inwards in the circumferential direction, and the inner diameter of the cement block protrusion (4) is larger than the outer diameter of the open caisson (3).

3. The open caisson pile stuck construction method according to claim 2, wherein: in the fourth step, the bending deformation resistance of the section steel joist (701) at least meets the construction stress requirements of two down-the-hole drills (8), and the down-the-hole drills (8) are symmetrically distributed on the drilling platform (7).

4. The open caisson pile stuck construction method according to claim 1, wherein: in the third step, a sectional sinking method is adopted, the height of the well wall is considered before the open caisson sinks to the cement block protrusion (4), and the construction of the residual well wall of the open caisson is completed before the open caisson reaches the cement block protrusion (4).

5. The open caisson pile stuck construction method according to claim 1, wherein: in the step e, the number of coring holes is arranged according to eight holes, four holes are vertically crossed, and four holes are obliquely crossed; and the coring point position is controlled to be 100mm outside the edge foot of the open caisson for drilling and coring.

6. The open caisson pile stuck construction method according to claim 1, wherein: and f, excavating the soil body in the middle of the open caisson, symmetrically excavating the soil body below the blade foot and the soil body outside the blade foot, excavating the soil body in the gap between the blade foot and the isolation pile, and sinking the open caisson by means of self weight.

7. The open caisson pile stuck construction method according to claim 1, wherein: and fifthly, adopting two crawler-type pneumatic down-the-hole drills, drilling by using a 2m drill rod connecting rod, and configuring a spherical tooth drill bit with the diameter of 100 mm.

8. The open caisson pile stuck construction method according to claim 1, wherein: in the sixth step, when the open caisson depth is increased and the total length of the steel sheet pile is smaller than the open caisson depth, the extension bar is welded on the top of the steel sheet pile (901) to extend the steel sheet pile.

Technical Field

The invention belongs to the technical field of open caisson construction, and particularly relates to a construction method for breaking pile sticking of an open caisson.

Background

The open caisson is used as an important construction of municipal engineering and underground structures and is widely applied to urban construction. The open caisson is a shaft-shaped structure, soil and stones in the open caisson are removed manually or mechanically, and the open caisson gradually sinks to a designed elevation by overcoming the frictional resistance outside the open caisson wall by means of self gravity or other sinking assisting modes; a deep and large open caisson is constructed in a weak water-rich stratum city, and a vertical cement reinforced curtain is usually adopted to isolate the open caisson from external water-soil connection, so that the surface settlement deformation in the open caisson excavation process is reduced.

However, the construction of the open caisson in the city faces the limitation of the construction site, the design scheme, the construction scheme and the mechanical selection cannot be developed under ideal conditions, at this time, the construction can only be carried out, then, the jet grouting pile is used as a vertical curtain scheme, the jet grouting pile is a process for cutting and stirring the soil body by means of high-pressure water and high-pressure slurry jet, the slurry pressure can reach 35-40MPa, the construction site is limited, when the distance between the well wall and the constructed pile body is small, the high-pressure cement slurry is diffused and agglomerated in a stratum with good permeability, and pile blocking and stopping sinking are caused when the open caisson sinks.

Disclosure of Invention

The invention aims to provide a construction method for breaking a pile of an open caisson, and aims to solve the technical problem that the open caisson sinks to stop sinking after a cement reinforcing curtain at the periphery of the open caisson invades into an excavation surface of the open caisson to be solidified and agglomerated.

In order to achieve the purpose, the invention adopts the following technical scheme:

a construction method for breaking a stuck pile of an open caisson comprises the following construction steps:

step one, an open caisson sinking scheme is formulated;

a, acquiring a stratum permeability coefficient, a stratum penetration number and a side friction resistance value according to a geotechnical investigation report;

b, calculating the sinking safety coefficient of the open caisson through an open caisson sinking checking formula;

and step c, adopting two open caisson sinking schemes according to the step a and the step b:

the first method comprises the following steps: the upper sludge layer adopts a drainage and sedimentation scheme, and the second scheme is as follows: the lower sand layer adopts a non-drainage sinking scheme;

then determining the number of sections of the wall of the open caisson, the timing and the sections of the wall of the open caisson for heightening according to the two excavation schemes, the sinking safety factor of the open caisson and the design positions of the plane and the depth of the water-stop curtain of the jet grouting piles around the open caisson;

secondly, coring by a geological drilling machine to find the invasion range of the cement block protrusion;

d, constructing a waterproof curtain of the jet grouting pile;

e, after finishing the jet grouting pile water-stop curtain and before excavating the open caisson, coring by using a geological drilling rig to find the area position of the cement block protrusion in the depth range of the open caisson, wherein the coring position is positioned outside the edge foot of the open caisson and is arranged along the periphery of the open caisson, the coring depth is up to the base elevation of the open caisson, and a long coring drill rod is used for guiding holes to core, so that an actual stratum core sample is obtained;

step three, sinking and excavating the open caisson, and adopting two open caisson sinking schemes in the step one according to the stratum condition of the open caisson;

step f: when water is drained and sunk in a sludge stratum, a digging machine is adopted to symmetrically and uniformly dig soil from the middle part to the periphery of the open caisson, and the open caisson is sunk by soil cutting of the open caisson cutting edge foot under the dead weight;

step g: observing the sinking rate of the open caisson when the open caisson sinks to the depth of the cement block protrusion; when the sinking rate of the open caisson is reduced to the suspension of the open caisson, the pile blocking of the open caisson cannot sink;

step h: digging a soil body of a cutting edge around the open caisson, removing the soil body in a gap between the well wall and a water-stop curtain of the jet grouting pile, and observing the sinking amount of the open caisson;

step i: a diver goes into the well to explore the sunk well blade, confirms the suspension height of the sunk well, and then draws a sunk well blade relative height map according to the relative position relation around the sunk well blade; a gap with an annular cross section is formed between the open caisson and the water-stop curtain of the jet grouting pile and above the position of the cement block protrusion; a breaking device is designed and inserted in the gap and comprises starting equipment positioned above the ground elevation and a breaking vertical piece vertically inserted into the gap and penetrating through the cement block protrusion;

fourthly, setting up an open caisson drilling operation platform;

erecting a drilling platform on the top of the open caisson, wherein the drilling platform is erected on the ground and is positioned right above the open caisson, comprises a group of profile steel joists which are erected at intervals in parallel, is fully paved with steel plates, and then a breaking device, namely a down-the-hole drilling machine is hung on the drilling platform;

fifthly, the pneumatic down-the-hole drill impacts and breaks the cement block protrusion of the curtain;

the first breaking vertical pieces are rod bodies with spherical tooth drill bits, the first breaking vertical pieces are distributed along the periphery of the sunk well blade foot, the first breaking vertical pieces drill holes on the cement block protruding body in a close-packed mode according to the diameter of the spherical tooth drill bits along the periphery of the sunk well blade foot, and then the spherical tooth drill bits are driven by the down-the-hole drill to impact along the periphery of the sunk well blade foot to penetrate through the cement block protruding body until the elevation of the substrate is reached;

sixthly, lifting the cement block protrusion of the steel sheet pile cutting curtain by a vibration hammer;

the breaking device further comprises a steel sheet pile device located on the ground outside the open caisson, the steel sheet pile device comprises a lifting device and a vertical second breaking vertical piece controlled by the lifting device, the second breaking vertical piece is a steel sheet pile, the steel sheet pile device lifts the steel sheet pile to sink, the integrity of the cement block protrusion is broken by vibration, the steel sheet pile is symmetrical along the open caisson in a circle during cutting, the cutting is staggered, the cement block blocks falling into the water are cut, the lifting and the sinking are repeated, and the pile bottom of the steel sheet pile reaches the elevation of the substrate;

step seven, sinking the open caisson; when the weight of the open caisson is greater than the frictional resistance of the cement block protrusions, the open caisson sinks instantaneously, the suspended height of the open caisson from the height of the substrate is controlled to be not more than 1m, then the open caisson is symmetrically and uniformly excavated to the height of the substrate, and the open caisson is prevented from inclining until the open caisson sinks completely.

In the step d, the water-stop curtain of the jet grouting pile is applied in soil in the stratum range of the sinking well, the soil in the sinking well is excavated, the underground water level is lower than the water level in the sinking well,

in the step e, the cement block protrusion is a block body which is provided with a circumferential inward protrusion in the middle of the inner wall of the jet grouting pile waterproof curtain, and the inner diameter of the cement block protrusion is larger than the outer diameter of the open caisson.

In the fourth step, the bending deformation resistance of the profile steel joist at least meets the construction stress requirements of two down-the-hole drills, and the down-the-hole drills are symmetrically distributed on the drilling platform.

And in the third step, a sectional sinking method is adopted, the height of the well wall is considered before the open caisson sinks to the cement block protrusion, and the construction of the residual well wall of the open caisson is completed before the open caisson reaches the cement block protrusion.

In the step e, the number of coring holes is arranged according to eight holes, four holes are vertically crossed, and four holes are obliquely crossed; and the coring point position is controlled to be 100mm outside the edge foot of the open caisson for drilling and coring.

And f, excavating the soil body in the middle of the open caisson, symmetrically excavating the soil body below the blade foot and the soil body outside the blade foot, excavating the soil body in the gap between the blade foot and the isolation pile, and sinking the open caisson by means of self weight.

And fifthly, adopting two crawler-type pneumatic down-the-hole drills, drilling by using a 2m drill rod connecting rod, and configuring a spherical tooth drill bit with the diameter of 100 mm.

And step six, when the open caisson depth is increased and the total length of the steel sheet pile is smaller than the open caisson depth, welding an extension bar on the top of the steel sheet pile and lengthening the steel sheet pile.

Compared with the prior art, the invention has the following characteristics and beneficial effects:

the invention can rapidly treat limit-invasion cement lumps to make the open caisson sink. The invention is particularly suitable for arranging a cement reinforcing curtain at the periphery of the wall of the open caisson, the cement reinforcing body invades the sinking range of the open caisson to cause the problems of pile blocking, suspension and stopping sinking of the open caisson, and cement mortar caking invading the excavation range of the open caisson is quickly removed to make the open caisson sink.

The invention adopts the method of drilling mechanical crushing and sheet pile cutting to remove hard cement agglomeration protrusions around the wall of the open caisson. The method of mechanical crushing and sheet pile cutting refers to that the sinking excavation of the open caisson hollows out the vertical soil body in the gap between the well wall and the cement reinforced curtain, the blade foot and the substrate are suspended and still can not sink, and the method of crushing by using a pneumatic down-the-hole drilling machine and sheet pile cutting is combined, so that the well wall of the open caisson is separated from constraint, and the sinking purpose is achieved.

The invention provides a structure for impacting and crushing cement agglomerates, cutting sheet piles and cutting falling mud agglomerates through a pneumatic down-the-hole drill, which is not limited by narrow places, is simple in construction operation, large in mechanical equipment market holding amount, capable of being quickly put into personnel and machines to carry out cleaning work, strong in worker operability, capable of quickly entering equipment, low in-out cost and good in economical efficiency, and ensures treatment efficiency and construction period.

Drawings

The present invention will be described in further detail with reference to the accompanying drawings.

FIG. 1 is a schematic diagram of the invasion limit of a cement reinforced curtain around a sunk well.

Fig. 2 is a schematic diagram of open caisson perimeter drilling coring.

Fig. 3 is a schematic view of a caisson pile.

Fig. 4 is a schematic cross-sectional view of fig. 3.

Fig. 5 is a schematic diagram of the setting up of the open caisson pile clamping platform and the drilling and crushing.

Fig. 6 is a schematic top view of fig. 5.

Fig. 7 is a schematic diagram of the cutting of the open caisson pile clamping steel plate.

Reference numerals: 1-jet grouting pile waterproof curtain, 2-open caisson stratum, 201-ground elevation, 202-substrate elevation, 203-underground water level, 204-water level in the open caisson, 3-open caisson, 301-well wall height connection, 4-cement block protrusion, 5-geological drilling rig, 6-open caisson excavation surface, 601-gap, 7-drilling platform, 701-section steel joist, 702-steel plate, 8-down-the-hole drilling rig, 801-spherical tooth drill bit, 9-steel plate pile equipment and 901-steel plate pile.

Detailed Description

The embodiment is shown in figures 1-7, and the construction method for breaking the pile sticking of the open caisson comprises the following construction steps:

step one, referring to fig. 1, a sinking scheme of an open caisson 3 is formulated; and (4) prejudging the plane and vertical range and depth of the cement block protrusion according to the geotechnical engineering characteristics and the stratum permeability coefficient in the geotechnical investigation report.

Step a, understanding geotechnical engineering characteristics, stratum permeability coefficients and checking stratum penetration number and side frictional resistance values according to the frictional resistance of each soil layer and each section depth of the open caisson reported by geotechnical investigation; and calculating to obtain the sinking coefficient of the open caisson, and formulating a scheme for sinking the open caisson with water drainage and sinking without water drainage.

And b, calculating a sinking safety system of the well section by using a sinking checking formula of the open caisson in the building construction handbook 6.14.3. And judging the plane and depth range of the cement reinforced curtain invading the open caisson according to the vertical and horizontal permeability coefficients of the stratum reported by the geotechnical investigation.

And c, setting the well wall joining height before the open caisson sinks to the cement block area in advance. Two open caisson sinking schemes are adopted according to the step a and the step b: combining open caisson geotechnical engineering characteristics, stratum permeability coefficient and open caisson sinking safety factor, the comprehensive factor adopts two different sinking schemes, the first: the upper sludge layer adopts a drainage and sedimentation scheme, and the second scheme is as follows: the lower sand layer adopts a non-drainage sinking scheme; and then determining the number of sections of the wall of the open caisson, the timing and the sections of the wall of the open caisson 301 for heightening according to the two excavation schemes, the sinking safety coefficient of the open caisson and the design positions of the plane and the depth of the water-stop curtain 1 of the jet grouting piles around the open caisson.

The stratum engineering characteristics and mechanical property indexes in an investigation report are grasped and understood before specific construction, the table is looked up to obtain the standard penetration number and the side friction resistance value of each soil layer, the height of a first section of well wall of the open caisson is controlled to be 3-5m, the height of a multilayer board is taken to be 1.8m as a modulus on site, a high well wall structure of 3.6m is constructed, and the phenomenon that after the well wall is poured, the contact surface of a 250mm blade foot and a foundation is small, so that the blade foot concentrated stress structure is deformed and cracked is prevented; according to the height of the open caisson structure of 18.4m, a method of manufacturing and sinking by sections is adopted, the open caisson is manufactured by five sections and sinks for three times, and each section of the structure construction section with the height of 3.6m is divided; the method comprises the steps of preliminarily determining the height of the open caisson, calculating a weighted average frictional resistance standard value of comprehensive multilayer soil within the height range of each section of well wall by utilizing a building construction calculation manual 6.14.3 open caisson sinking checking calculation, bringing the standard value into a sinking force system balance formula according to the dead weight of the open caisson and peripheral constraint conditions, calculating the sinking coefficient of each section to be larger than the sinking safety coefficient of 1.2, enabling the open caisson to sink smoothly, obtaining the sinking coefficient, determining to adopt a drainage sinking scheme and a non-drainage sinking scheme according to the stratum soil permeability coefficient of the sinking position of each section of well wall, performing drainage sinking excavation on watertight silt soil at the depth of more than 11.07m, accelerating the sinking speed, performing non-drainage sinking on a strongly-permeable sand layer below 11.07m, and preventing the water level in the open caisson from leaking water and sand at the seam of a water-stop curtain to cause the subsidence of the outer surface of the open caisson.

Specifically, the method comprises the steps of judging the range of a curtain cement paste invading the open caisson according to the permeability coefficient of each stratum at the sinking depth position of the open caisson, wherein the horizontal and vertical permeability coefficients of a sand layer in the sinking depth stratum of the open caisson are 25m/d, and forming a water-stop curtain by using a high-pressure jet grouting pile, wherein the jet pressure of the pile is usually 30-40 Mpa, so that the sprayed cement paste is further expanded and permeated to the outside of the reinforced stratum under the pushing of water pressure and slurry pressure.

The open caisson sinking to the cement caking district before considers the height that the open caisson meets the height in advance, will open caisson surplus 2 sections wall of a well before arriving the cement caking district construction completion, firstly can make the open caisson increase the dead weight, and the second prevents that cement mortar caking from driving the back, and the open caisson sinks fast, and the wall of a well top soil body does not have the backstop, exists and meets the safe risk of high wall of a well collapse.

Step two, referring to fig. 2, a geological drilling rig 5 cores to ascertain the invasion range of the cement block protrusion; after the construction of the water-stop curtain of the jet grouting pile is completed, drilling holes along the periphery of the outer wall of the open caisson to core and find out the plane, the vertical range and the depth of the cement block protrusion.

And d, constructing a waterproof curtain of the jet grouting pile. The jet grouting pile waterproof curtain 1 is applied in soil in the scope of the open caisson stratum 2, the soil in the open caisson 3 is excavated, the height of the top of the open caisson does not exceed the water level 204 in the open caisson, and the underground water level 203 is lower than the water level 204 in the open caisson.

And e, after the jet grouting pile water-stop curtain is finished and before the open caisson is excavated, coring by using a geological drilling rig 5 to find the region position of the cement block protrusion in the depth range of the open caisson, wherein the cement block protrusion 4 is a block body which protrudes inwards in the circumferential direction and is arranged in the middle of the inner wall of the jet grouting pile water-stop curtain 1, and the inner diameter of the cement block protrusion 4 is larger than the outer diameter of the open caisson 3.

The coring position is positioned outside the edge foot of the open caisson and arranged along the circumference of the open caisson, the coring depth reaches the base elevation 202 of the open caisson, and a long coring drill rod is adopted to guide holes to core, so that the actual stratum core sample is obtained to the maximum extent.

Concretely, an XY-180 geological drilling machine is adopted for drilling and coring; coring depth from the ground to the bottom elevation of the open caisson; the number of coring holes is arranged according to eight holes, four holes are vertically crossed, and four holes are obliquely crossed; the coring point position is controlled to be 100mm outside the edge foot of the open caisson for drilling and coring; the coring drill rod adopts a drill rod with the length of 3.3m to core, so that a core sample is collected to the maximum extent, and the strength of a cement slurry invasion limit section and a cement mortar block body within the open caisson depth range is ascertained.

Step three, referring to the figures 3-4, sinking and excavating the open caisson, and adopting two open caisson sinking schemes in the step one according to the stratum condition of the open caisson; and (5) sinking the open caisson to the depth of the cement block protrusion, and observing the sinking rate of the open caisson. The open caisson excavation face 6 is shown in the figure. And (3) adopting a sectional manufacturing and sectional sinking method, considering the height of the well wall in advance before the open caisson sinks to the cement block protrusion 4, and completing the construction of the residual well wall of the open caisson before the open caisson reaches the cement block protrusion 4.

Step f: when the drainage sinks in the silt stratum, because the sinking coefficient of the open caisson is large, in order to prevent the open caisson from sinking too fast, the digging machines are adopted to symmetrically and uniformly dig and dig soil bodies from the middle part to the periphery of the open caisson, and the open caisson is sunk by the dead weight of the soil cut by the open caisson cutting edge.

Step g: observing the sinking rate of the open caisson when the open caisson sinks to the depth range of the cement block protrusion; when the sinking rate of the open caisson is obviously reduced to the suspension of the open caisson, the pile blocking of the open caisson cannot sink.

Step h: digging soil at the edge of the sunk well, removing soil in the gap between the well wall and the water-stop curtain of the jet grouting pile, and observing the sinking amount of the sunk well.

Step i: a diver goes into the well to explore the sunk well blade, confirms the suspension height of the sunk well, and then draws a sunk well blade relative height map according to the relative position relation around the sunk well blade; a gap 601 with an annular cross section is formed between the open caisson 3 and the jet grouting pile waterproof curtain 1 and above the position of the cement block protrusion 4; a breaking device is designed and inserted in the gap 601, and comprises a starting device positioned above the ground elevation 201 and a breaking vertical member vertically inserted into the gap 601 and penetrating through the cement block protrusion 4.

The front three sections of 10.8m of the open caisson are positioned on a sludge layer, a drainage sinking excavation scheme is adopted, the middle excavation of the open caisson extends to the edge feet at the periphery, the excavation depth is 0.5m each time, and if the open caisson does not sink, the excavation depth is 0.5m, so that the open caisson can stably and uniformly cut soil and sink; when the open caisson sinks to below 11.08m and enters a fine sand layer containing mud, underground water is a pressure-bearing water layer, a non-drainage sinking scheme is adopted, the frictional resistance in the sand layer is increased, and when the open caisson sinks slowly, firstly four sections and five sections of well walls of the open caisson are manufactured on the ground, the open caisson sinks without draining, a blade foot digging scheme is adopted, firstly, soil in the middle of the open caisson is dug, then soil below the blade foot and soil outside the blade foot are dug symmetrically, soil in a 700mm gap between the blade foot and an isolation pile is dug, and the open caisson sinks by means of self weight.

When the open caisson sinks to the range of the cement agglomeration section, the elevation of the open caisson is observed, the sinking rate is 1-2cm per hour or the open caisson is suspended and stops sinking, the condition that the periphery of the wall of the open caisson is closely attached to the protruded cement agglomeration body and the open caisson is blocked and cannot sink is considered. At the moment, a diver goes into the well and explores the sunk well blade foot, confirms the hanging height of the sunk well and the relative position relation around the sunk well blade foot, and then draws a relative height map of the sunk well blade foot.

And step four, building an open caisson drilling operation platform as shown in the figures 5-6.

Erecting a drilling platform 7 on the top of the open caisson, wherein the drilling platform 7 is erected on the ground and is positioned right above the open caisson, comprises a group of profile steel joists 701 which are erected at intervals in parallel, and is fully paved with a steel plate 702, and then hoisting a breaking device, namely a down-the-hole drill 8, to the drilling platform 7; when the steel joist 701 is made of I-shaped steel, the I-shaped steel joist is placed on a concave node of a precast beam of the cover plate on the top surface of the open caisson, and then a steel plate is fully paved. The bending deformation resistance of the profile steel joist 701 at least meets the construction stress requirements of the two down-the-hole drills 8, and the down-the-hole drills 8 are symmetrically distributed on the drilling platform 7.

Specifically, three I-beams 40a are arranged in a top plate beam groove reserved in a circular open caisson top structure with the diameter of 9.2m as a supporting beam, a 10mm steel plate is fully paved on the upper portion of the top plate beam groove, two drilling machines are simultaneously constructed in the span of one I-beam according to the weight of 100KN of two down-the-hole drilling machines and the most unfavorable state, and the maximum positive stress of the middle and lower sides of the span is calculated to be 174.66KN/mm²According to the design strength index of steel products in section 4.4 of Steel Structure Standard, the bending strength of the carbon structural steel Q235 is 215KN/mm²The bending strength is 0.852 < 1, and the acceptance requirement is met.

And step five, as shown in the figures 5-6, the pneumatic down-the-hole drill impacts the cement block protrusion of the broken curtain.

Every down-the-hole drill 8 has vertical first vertical piece that breaks, first vertical piece that breaks is the body of rod of taking button bit 801, and first vertical piece that breaks distributes along open caisson sword foot periphery, and first vertical piece that breaks closely arranges the drilling on cement piece protrusion 4 according to the diameter of button bit 801 along open caisson sword foot periphery, then adopts down-the-hole drill 8 to drive button bit 801 along open caisson sword foot periphery impact and run through cement piece protrusion 4 until base elevation 202, and the impact is broken and is revealed regional 3.6m cement piece protrusion 4 of sand bed.

Specifically, two crawler-type pneumatic down-the-hole drills are adopted, a 2m drill rod connecting rod is used for drilling, spherical tooth drill bits with the diameter of 100mm are configured, and holes are drilled in a close-packed mode according to the diameter of the drill bits; the impact energy of the drilling machine is 11kg/m, the impact frequency is 80 times/minute, and the cement caking area with the depth of 3.6m of the revealed sand layer is crushed; the perimeter of the open caisson is 32m, the number of the holes is 267, 40 down-the-hole drills can be constructed in one day, and a plurality of down-the-hole drills can be arranged as required.

Step six, referring to fig. 7, the vibration hammer lifts the steel sheet pile to cut the cement block protrusion of the curtain.

Aboveground steel sheet pile equipment 9 outside the open caisson still is located, steel sheet pile equipment 9 includes by lifting equipment and by lifting equipment control's vertical second abolishes perpendicular piece, the second abolishes perpendicular piece and is steel sheet pile 901, and steel sheet pile equipment 9 lifts the steel sheet pile and sinks, and the vibration breakage has lost the cement piece protrusion 4 of integrality, and steel sheet pile during the cutting is along open caisson a week symmetry, crisscross cutting, cuts the mud caking that falls into water, promotes repeatedly and sinks, and the pile bottom of steel sheet pile is up to basement elevation 202.

Specifically, a DX500 type steel plate pile machine and a 15m Larsen IV type steel plate pile are adopted, cement mortar blocks which are drilled and broken on the periphery of the open caisson and lose integrity are removed by vibration sinking cutting of the steel plate pile, the cement blocks are collapsed to the bottom of the open caisson, and the open caisson sinks by means of self weight.

When the open caisson depth is increased and the total length of the steel sheet pile is smaller than the open caisson depth, an extension bar is welded to the top of the steel sheet pile 901 to extend the steel sheet pile. Adopting a construction process of strip welding, and welding the two sides of the web plate in a lengthening way by using a steel bar with the diameter of 25; the sequence of cutting the pile body of the steel sheet pile is to symmetrically and alternately lift and pull the steel sheet pile, so that the open caisson can sink stably and uniformly by means of dead weight, and the inclination is prevented.

Step seven, sinking the open caisson; when the weight of the open caisson is greater than the frictional resistance of the cement block protrusion, the open caisson sinks instantaneously, so that the excavation depth of the open caisson is controlled before drilling, the suspension height of the open caisson from the base elevation 202 is not greater than 1m, a long-arm excavator is adopted to dig broken slag and cement mortar blocks falling to the bottom of the open caisson after sinking, the broken slag and the cement mortar blocks are symmetrically and uniformly excavated to the base elevation, and the open caisson is prevented from inclining until the open caisson sinks completely.