CN112144514A - Simple method for forming hole and pile in sand and pebble stratum easy to collapse during rotary drilling machine - Google Patents

Abstract

A simple method for forming a pile by drilling a hole in a sand and pebble stratum which is easy to collapse in a rotary drilling machine comprises the following steps: (1) burying an orifice protecting cylinder; (2) drilling: drilling a hole in the casing; (3) drilling into the pile hole to the depth of the single drilling hole; (4) forming a wall protecting layer in the pile hole: pouring the mixed mud material into a pile hole drilled at a single time, and extruding the mixed mud material into the sand-gravel gap of the hole wall by rotating a rotary drilling machine bucket to form a wall protecting layer; (5) repeating the steps (3) to (4) until the whole pile hole is completed, and lifting out the drilling tool; (6) and hoisting the reinforcement cage into the pile hole, pouring concrete, and pulling out the orifice casing after solidification. The beneficial effects are that: the method for backfilling mixed mud materials in the drill hole in the sand-gravel layer with relatively low underground water phase forms a compact mud-skin supporting system, saves a mud pit, reduces the discharge of slurry, and greatly shortens the concrete pouring time and obviously improves the concrete quality because the pile body concrete does not use an underwater conduit pouring process.

Description

Simple method for forming hole and pile in sand and pebble stratum easy to collapse during rotary drilling machine

Technical Field

The invention relates to a simple method for forming a pile by drilling a hole in a sand-gravel stratum which is easy to collapse in a rotary drilling machine, belongs to pile forming in building foundation construction, and can be used for construction of slope protection piles, pressure-resistant piles, uplift and floating-resistant piles and the like.

Background

At present, the commonly selected process method for forming the pile in the hole of the easily collapsed sandy gravel stratum at home and abroad comprises the following steps: (1) and (3) construction of a forward circulation drilling machine and a reverse circulation drilling machine: the construction process is to drill hole, slag and protect wall by mud circulation, the two modes are small in slag discharging sandstone grain size, the drilling time of the project is long, the hole cleaning time after pile forming is long, and meanwhile, the deep water pump is easy to be blocked and damaged by mud stone, and the timeliness is poor. The mud pit needs to be cleared in time and transported and discharged outside, which causes secondary environmental pollution. When the diameter D of the pebbles in the pebble layer is more than or equal to 18cm, the content of the pebbles is 50-70 percent, and the content of the pebbles D is more than or equal to 20cm, the content of the pebbles is 70-80 percent, the process cannot pass the large particle size out of the slurry slag discharge hole, so the process is not feasible. (2) Construction of the Ukas impact drilling machine: the Ukas percussion drill adopts the action of gravity to creep into the pore-forming, and rig construction noise is big, and the difficult up to standard of noise is fallen in the environmental protection, and the rig can frequently tremble simultaneously in the sand cobble, and nearby stratum structure can receive the disturbance, and efficiency is very low moreover, does not reach the fourth of digging the rig soon. Considering these factors, the process cannot be selected. (3) And (3) manual hole digging construction: because the sand and gravel layer structure is loose, if the artificial hole digging is adopted, collapse is possible, particularly when the hole depth exceeds 16m, the artificial hole digging is further classified as a project with high risk, the construction safety cannot be guaranteed, and the risky technological method should not be adopted. (4) Construction of the rotary drilling rig: the rotary drilling rig is novel equipment researched and developed in recent years, has the characteristics of high drilling speed, low construction noise, small environmental pollution and the like, is suitable for construction of most strata, adopts a hydraulic system, can better control the hole position, the verticality and the like of a pile body, and can preferentially adopt the construction process. (5) And (3) carrying out full-pile casing follow-up rotary excavating construction: the process is a rotary drilling construction with sleeve follow-up in the whole process, is a new process developed aiming at the problem of difficult wall protection in a large-particle-size pebble layer and a complex stratum, can effectively solve the quality defects of pile bodies such as necking and hole collapse, and has the advantages of high construction requirement precision, more supporting equipment and high construction cost, and the selection of the expensive process method is not considered for the moment.

The construction process of the rotary drilling rig comprises the following steps: a reasonable rotary drilling hole forming construction process is selected in an easily collapsed thick sandy gravel stratum, and a common process method comprises the following steps: (1) a hole-forming construction process for maintaining the stability of hole wall by using slurry without circulation stability. (2) The sleeve protects the wall to form the hole, utilize the quill to keep a pore wall steady a pore-forming construction process, namely the above-mentioned whole casing follows up and dig the construction process soon. (3) The dry operation pore-forming is carried out, and the construction process of directly taking earth and forming pores by a rotary drilling rig is not needed to adopt a wall protection measure.

And (3) forming a hole for the test pile: the construction method is characterized in that the drilling operation is carried out by selecting any process at a construction site, meanwhile, the construction process of full pile casing follow-up is not considered due to the factors of manufacturing cost and construction period, and in order to ensure that the requirements of designed pile aperture, depth, verticality and the like are met, the construction of a test pile is carried out on the site, a TR200D rotary drilling rig manufactured by south China locomotive company adopted by the construction is 200KN.m in maximum torque of equipment, 187KW in engine power, 1800mm in maximum drilling diameter and 60m in maximum drilling depth. Dry operation pore-forming test pile digs earlier at the building site and digs dry operation test pile 3, and it is big to appear the drilling rod shake during the construction, phenomenon such as sticking a drill, gear grinding, when digging to 3~5m carry and bore sediment soil in the gang tube, hole collapse and undergauge phenomenon appear in the hole, can't satisfy the design requirement, shut down and carry and bore backfill pile hole, this single dry operation pore-forming test pile is unsuccessful. A mud pool is excavated near site test piles, waterproof layer treatment is done to the pool bottom and the pool wall, and the prepared mud liquid is bentonite: caustic soda =2000:25 (mass ratio), the mud proportion is controlled to be 1.1-1.15, and the colloid rate is not lower than 95%; the sand content is not more than 4%. After the rotary drilling construction, slurry is injected into the hole and does not reach the orifice and has stable liquid, the slurry permeates and flows out of the sandstone layer to cause serious loss, so the process cannot be adopted.

The above various processes do not appear to meet the construction requirements and it should be possible to invent a more economical and efficient process.

Disclosure of Invention

The invention provides a simple method for forming a pile by drilling a hole in a sand and gravel stratum which is easy to collapse in a rotary drilling machine, and aims to solve the problems in the prior art.

In order to solve the problems, the invention adopts the technical scheme that: 1. a simple method for forming a hole and a pile in a sand and gravel stratum which is easy to collapse in a rotary drilling machine is characterized by comprising the following steps:

(1) burying an orifice protection cylinder: burying an orifice pile casing at the pile position;

(2) drilling: drilling holes in the protective cylinder, and determining the depth of a single drilling hole on the basis of the principle that the hole wall does not collapse; the length of the orifice casing is equal to or close to the single drilling depth;

(3) drilling into the pile hole to the depth of the single drilling hole;

(4) forming a wall protecting layer in the pile hole: pouring the mixed mud material into a pile hole drilled at a single time, extruding the mixed mud material into a sand-gravel gap on the hole wall by rotating a rotary drilling machine bucket, bonding the sand-gravel together, and forming a viscous mud material mixed wall protection layer in the hole wall to play a wall protection role;

(5) repeating the steps (3) to (4) until the whole pile hole is completed, and lifting out the drilling tool;

(6) hoisting a reinforcement cage into the pile hole, and centering and fixing;

(7) slowly putting the string cylinder into the pile hole, wherein the distance between the string cylinder and the bottom of the pile hole is 1 m;

(8) pouring concrete, and pulling out the orifice protecting cylinder after solidification.

The mixed pug is prepared from clay and bentonite according to the weight ratio of 10:1, if the water content of the clay is high, water is not required to be sprayed, the clay can be directly blended and stirred, and if the water content of the clay is low, the water is sprayed and stirred to enable the water content to reach 20-30%, the water content is slightly higher than the optimal water content, and the user can feel wet when grasping the clay by hand; meanwhile, the aim of dust fall is also achieved.

The single drilling depth is 2 m; the length of the orifice protecting cylinder is 2m, and the bottom of the protecting cylinder is guaranteed to be seated on an original soil layer.

The embedding and fixing method of the orifice casing comprises the following steps: after the hole mouth pile casing is fixed at the pile hole position, clay is used for backfilling and tamping around the hole mouth pile casing layer by layer so as to ensure the verticality and prevent the displacement of the pile casing; if the bottom soil layer of the orifice pile casing is not cohesive soil, deep digging or soil replacement is required, after the clay with the thickness of 200-300 mm is tamped in the backfill of the pit bottom, the orifice pile casing is arranged so as to prevent the bottom opening of the pile casing from leakage and collapse; the outer side of the upper opening of the orifice protecting cylinder is bound with battens or steel pipes and is symmetrically arranged and hung tightly to prevent downward movement.

In the step (8), before concrete is poured, the slump and the workability must be checked and recorded; the concrete can not be isolated when being transported to a pouring point; the opening of the concrete pouring hole is tightly covered to prevent foreign matters from falling into the hole; in the concrete pouring process, the position of the string cylinder is always kept in the middle; and (3) pouring 0.5m more concrete after the concrete is poured to the pile top so as to ensure the strength of the pile top concrete after the laitance is chiseled off.

When necessary, vibrating when pouring the concrete at the pile head part; when the elevation of the pile top is low, the concrete can not be poured into the ground, and after the concrete is initially set, the hole is backfilled by soil, so that people or equipment and the like are prevented from falling into the hole.

The method has the advantages that: the method for backfilling mixed mud material in the drilled hole in the sand-gravel layer with relatively low underground water phase is characterized by that the plasticity and ductility of the mud material are good, and the mud material can be inserted into sand-gravel gap of pile hole wall by means of rotary extrusion of drill bit to form compact mud-skin supporting system, so that the arrangement of mud-slurry pool can be saved, the discharge of slurry liquor can be reduced, at the same time the pile body concrete can be poured into the pile body by means of water-pipe, so that the concrete pouring time can be greatly shortened, the concrete quality also can be obviously raised, and the comprehensive economic benefit index is obviously superior to that of circulating-slurry wall-protecting and full-casing follow-up hole-forming, and more superior to that of forward-backward circulating and impact drilling.

Drawings

FIG. 1 is a process flow of the present invention.

Detailed Description

Referring to fig. 1, the basic process flow of the present invention is shown in fig. 1, and the process flow of the present invention is detailed below with reference to specific examples:

1. firstly, measuring the paying-off and pile positioning position on a flat field, adding protective piles at two ends of the pile position, and making positioning piles at the two ends by using a measuring instrument to prevent the pile position from rechecking at any time when deviation occurs; the pile location is usually drilled with a deep hole on the ground by a drill rod or a puncher, white lime powder is poured in, and obvious marks such as wood sticks or steel sticks are inserted at the pile location. When necessary, the control line is projected to a remote wall for rechecking at any time.

2. The clay bentonite mixed pug is prepared by utilizing the bentonite purchased on the spot and the clay pulled nearby according to the proportion of 1: blending at a ratio of 10, if the water content of the clay is high, sprinkling is not needed, blending and stirring can be directly conducted, and if the water content of the clay is low, sprinkling is conducted, blending and stirring are conducted to enable the water content to reach 20-30%, the water content is slightly higher than the optimal water content, and a user can feel wet when grasping the clay by hand; meanwhile, the aim of dust fall is also achieved.

3. The opening pile casing is buried and fixed, the pile casing is accurately buried at the determined pile position before drilling, the length of the pile casing is at least 1.0m, preferably 2.0m, and the bottom end of the pile casing is ensured to be seated in an original soil layer. The drilling position is accurately fixed, the surface accumulated water is isolated, the orifice soil body is stabilized, and the hole wall is protected from collapse, so that the drilling work is facilitated. The orifice protecting cylinder is made of steel, the inner diameter of the protecting cylinder is 200mm larger than the diameter of the next-stage drill bit, the top mark of the protecting cylinder is 10-20cm higher than the construction surface, and the cylinder wall is ensured to be vertical to the horizontal plane. When the pile casing is positioned, the pile position is rechecked, then cross control pile lines which are mutually perpendicular are defined by taking the pile position as the center, cross bolt point control is carried out, the hole position of the pile casing is dug, the pile casing is hung and placed, clay is filled into the holes around the pile casing and tamped, meanwhile, the center of the pile casing and the center of the pile position are corrected by using the cross lines to ensure that the centers of the pile casing and the pile position are coincided with each other, and the deviation between the center position of the pile casing and the center of the pile is less than 2 cm. When the pile casing is buried, the central axis of the pile casing is aligned with the measured pile position center, and the verticality of the pile casing is strictly maintained. After the pile casing is fixed at the correct position, clay is used for backfill and tamping in a layered mode to guarantee the verticality of the pile casing and prevent slurry loss and pile casing displacement. If the bottom soil layer of the pile casing is not cohesive soil, digging deep or replacing soil, backfilling and tamping clay with the thickness of 200-300 mm at the bottom of the pit, and then placing the pile casing to prevent the bottom opening of the pile casing from leaking and collapsing. The upper opening of the protective cylinder is bound with battens or steel pipes and symmetrically hung tightly to prevent downward movement.

4. Drilling a hole, wherein the hole can not collapse after being drilled for 2m at one time through a test, filling the mixed mud material which is well mixed into the hole by using a forklift until the mixed mud material is filled to a point on the lower end of the protective cylinder, and rotationally extruding the mixed mud material into the hole wall by using a rotary drilling rig bucket to form an artificial mud material skin with viscosity, thereby achieving the wall protection effect. Then, drilling the next section for 2m, taking out the drilling tool, filling the mixed mud, and rotationally extruding the hole inlet wall by using a rotary drilling rig bucket to form a second section of artificial retaining wall; and circulating until the bottom of the hole, and lifting the drilling tool.

5. And (4) manufacturing a steel reinforcement cage, and leveling a steel reinforcement cage processing field. The labels are kept after the reinforcing steel bars enter the yard and are respectively stacked in order according to specifications, so that pollution and corrosion are prevented.

According to the design, calculating the length of the material used by the stirrups and the length of the distribution section of the main reinforcements, straightening the required reinforcements, and cutting the reinforcements in batches by using a cutting machine for later use. Because the specifications and sizes of the main reinforcement, the stirrup and the winding reinforcement to be welded are different, the main reinforcement, the stirrup and the winding reinforcement are respectively placed to prevent misuse. The joints of the vertical steel bars of the pile body steel reinforcement cage are mechanically connected or welded. The welding length is single-side 10d, and the length of the two sides is 5d (d is the diameter of the steel bar). The positions of the welding joints need to be staggered, the joint rate is less than or equal to 50%, the staggered distance is more than 35d (d is the diameter of the steel bar) and is not less than 500 mm.

And (5) manufacturing the stirrup on a reinforcing steel bar ring manufacturing table and welding the stirrup according to requirements. The support frames are placed on the same horizontal plane at intervals of 2m and aligned with the central line, and then the main ribs with fixed length are placed on the welding support frames in a straight mode. And (3) sleeving the stirrups into the main reinforcements according to the design requirements (or sleeving the main reinforcements into the stirrups) and keeping the stirrups to be vertical to the main reinforcements, and performing spot welding or binding. After the stirrups and the main reinforcements are welded or bound, the winding reinforcements are wound on the stirrups according to a specified interval, bound by binding wires and fixed by spot welding at intervals.

The steel reinforcement cage made by sections should take proper measures to prevent torsion and bending when being carried.

According to the actual situation on site, after the reinforcement cage is formed, self-checking, hidden checking and cross-over checking are carried out according to the standard requirements, wherein the contents comprise the reinforcement (appearance, variety, model and specification), the welding line (length, width, thickness, seaming, surface leveling and the like), the reinforcement cage allowable deviation (main reinforcement interval, stiffening reinforcement interval, reinforcement cage diameter, length and the like), and the records are made. After the product is qualified, the product can be hoisted.

The steel reinforcement cage after the inspection is qualified should be laid on the level ground according to specification number layering, prevents to warp.

6. The steel reinforcement cage and the string barrel are hoisted, the hoisting steel reinforcement cage adopts a shoulder pole hoisting method, hoisting points are arranged at the connecting positions of the hooping and the main reinforcement of the steel reinforcement cage, and the hoisting points are symmetrical and are hoisted at one time.

The steel reinforcement cage sets up reasonable hoisting point to guarantee that the steel reinforcement cage does not warp when lifting by crane. The steel bar cage hanging holes are adapted to the hole positions, vertical, light and slow to be placed in the holes. If the descent is obstructed, the descent should be stopped, the reason is found out and the descent is processed, and the promotion of the descent and the forced descent are strictly forbidden. And measuring the elevation of the top of the protective cylinder on site, and accurately calculating the length of the hanging rib so as to control the elevation of the pile top of the steel reinforcement cage, the upward floating of the steel reinforcement cage and the like.

4-6 lifting points with a crane with proper tonnage are selected for lifting the steel reinforcement cage, so that the steel reinforcement cage is not deformed during lifting. Before the steel reinforcement cage is transferred, a cushion block of the steel reinforcement protection layer is installed firstly to ensure the thickness of the concrete protection layer. After the reinforcement cage is installed in place, the top elevation of the pile casing is measured by a level gauge, the top end of the reinforcement cage is ensured to reach the designed elevation, and then the reinforcement cage is fixed immediately. And controlling the pile top elevation of the reinforcement cage by using the phi 14 or phi 16 hanging bars.

After the steel reinforcement cage is hoisted in place and fixed in the middle, the string barrel can be hoisted and fixed, and the funnel is assembled at the upper part.

7. The poured concrete forms a pile, and before the concrete is poured, the slump and the workability must be checked and recorded. The concrete can not be isolated when being transported to the pouring point. The orifice should be covered tightly before pouring concrete, prevent that the foreign matter from falling into downthehole.

In the concrete pouring process, the position of the string cylinder is always kept in the middle, a specially-assigned person should command the string cylinder to be lifted, and the pile top must be filled with more than 0.5m after the pile top is filled with the concrete, so that the strength of the pile top concrete after the laitance is chiseled off is ensured. If necessary, the pile head is vibrated.

When concrete is poured, not less than 1 group of concrete test pieces are manufactured for each group.

After pouring, the steel casing is pulled out before concrete is initially set, and the verticality of the steel casing is maintained when the steel casing is lifted.

When the elevation of the pile top is low, the concrete can not be poured into the ground, and after the concrete is initially set, the hole is backfilled by soil, so that people or equipment and the like are prevented from falling into the hole.

Engineering implementation case

1. Overview of the engineering

1.1 Foundation pit support design

1.1.1 brief description of Foundation pit support design

The scientific experimental building project is located in the Beijing area, the site is located above the first-level terrace of the white river, the elevation of the natural ground is 58.79-60.26 m, the elevation of the bottom plate of the building structure is-10.60 m, and +/-0.00 is 61.85 m. The foundation pit adopts a pile anchor supporting system, the slope protection pile phi is 800mm, the pile length is 11.4 m-12.0 m, the pile distance is 1.5m, the concrete strength of the pile body and the crown beam is C25, and 2 pre-stressed anchor rods are vertically arranged.

1.1.2 expert demonstration brief description

The engineering foundation pit excavation depth exceeds 5 meters, according to the requirements of the ministry of construction and Ministry of safety management of the highly dangerous subsection project, the expert argumentation of the special project of foundation pit supporting and earthwork excavation engineering safety is organized in 3, 3 and 27 days of 2020, and aiming at the geological rock and soil condition of the engineering, the foundation pit depth and the surrounding construction condition, the safety of the design scheme and the close coordination matters in the construction are proved in detail.

1.2 overview of the stratigraphic soil texture

According to the detailed geotechnical engineering survey report (10 months in 2018) of the project, the geotechnical soil layer conditions are counted as follows:

the strata in the exploration depth range (deepest 35.0 m) of the geotechnical engineering investigation can be divided into three categories of a modern artificial accumulation layer, a recent sediment layer and a quaternary sediment layer according to the cause type and the deposition age, and further divided into 6 large layers according to the lithology and engineering characteristics, and the categories are as follows:

modern manual accumulation of layers:

the surface layer of the proposed site is an artificial accumulation layer with the thickness of 0.30-1.20 m.

Filling clay silt and sandy silt with a layer I: brown yellow, slightly dense and slightly wet, mica and iron oxide, containing a large number of plant roots and local pebbles.

Filling soil with fine sand, namely 1 layer: brown yellow, slightly wet and dense, feldspar and quartz being the main components, and containing a small amount of brick slag, ash and gravel.

Filling soil with pebbles in a layer I2: mottle, slightly wet, loose, with a small amount of ploughing soil on the surface layer, generally =3-6cm for D, =12cm for D, round, medium grade, medium fine sand and silt filled, and a small amount of construction waste locally.

The artificially accumulated layers are the newly deposited layers as follows:

the elevation is 58.16-59.74 m below:

pebble layer II: mottle, slightly dense and slightly wet, generally =4-8cm for D, =15cm for D, 60-70% of content, sub-circular, better gradation, mainly filled with medium fine sand and sandwiched with thin fine sand layers.

Fine medium sand 2 1 layer: grey white, slightly wet and dense, feldspar and quartz being the main components, and mica sheets.

Sandy silt-clay silt 2 layers: brown yellow, dense, wet, mica, iron oxide.

The next generation of layers is the quaternary deposit layer:

the elevation is 53.14-54.58 m below:

pebble layer III: variegated, dense in middle, slightly wet, D is generally =5-8cm, D is big =18cm, the content is 50-70%, round, the gradation is better, the middle coarse sand is the main filling;

medium and fine sand layer III 1: grey white, slightly wet, dense, feldspar and quartz being the main, containing mica sheets.

The elevation is 47.14-48.43 m below:

pebble layer iv: variegated, dense and slightly wet, D is generally =5-8cm, D is large =20cm, the content is 70-80%, the product is round and has good gradation, and medium coarse sand is mainly filled.

Silty clay, heavy silty clay (1 layer): brown yellow, very wet, plastic to hard plastic, mica, iron oxide.

The elevation is 38.99-40.85 m below:

layer five of pebbles: variegated, dense and wet, D is generally =6-10cm, D is big =20cm, the content is 70-80%, the round shape is better in gradation, and medium coarse sand is mainly filled.

1 layer of coarse sand is gray, dense and wet, and contains feldspar and quartz mainly and mica sheets.

The elevation is 30.79-32.25 m below:

pebble layer: variegated, dense and wet, D is generally =6-12cm, D is big =20cm, the content is 70-80%, the round shape is better in gradation, and medium coarse sand is mainly filled.

1.3 site hydrogeological conditions

During the engineering investigation, no groundwater was found in the depth range of 35.00 m. The highest water level elevation is about 38.0 meters (about 22.0 meters buried depth) in nearly 3-5 years, the deepest part of the engineering foundation pit is 11.80 meters, and the lowest elevation of the bottom of the engineering foundation pit is 50.35 meters and is far higher than the underground water level.

2. Selection of construction scheme

According to geological conditions and engineering requirements, a reasonable construction scheme is selected under the condition of ensuring the construction period and economic construction cost, and operability demonstration of various schemes is as follows:

2.1 direct and reverse circulation rig construction

The construction process of the positive and negative circulation drilling machine for constructing the pile hole comprises the steps of drilling a hole, discharging slag and protecting a wall through mud circulation, wherein the two modes are small in slag discharging sandstone particle size, long in drilling time and long in hole cleaning time after pile forming, and meanwhile, a deep water pump is easy to be blocked and damaged by mudstones, so that the timeliness is poor. The mud pit needs to be cleared in time and transported and discharged outside, which causes secondary environmental pollution. The process can not pass the particle size of the stratum of the item from a pebble layer III to the outside of a slurry residue discharge hole, so that the process cannot be selected.

2.2 Ucas percussive drill construction

The Ukas percussion drill adopts gravity action to drill a hole, the construction noise of the drill is large, the environmental protection and noise reduction are difficult to reach the standard, meanwhile, the drill frequently shakes in sand and pebbles, the structure of the adjacent stratum is disturbed, and the process method cannot be selected by considering the factors.

2.3 construction of manual hole digging

Because the sand and gravel layer is loose in structure, if manual hole digging is adopted, collapse is possible, the construction safety cannot be guaranteed, and the process method is not adopted.

2.4 construction of Rotary drilling rig

The rotary drilling rig is novel equipment researched and developed in recent years, has the characteristics of high drilling speed, low construction noise, small environmental pollution and the like, is suitable for construction of most strata, adopts a hydraulic system, can better control quality requirements such as hole positions, verticality and the like of a pile body, and can preferably adopt the construction scheme.

2.5 full casing follow-up rotary digging construction

The process is a rotary drilling construction with sleeve follow-up in the whole process, is a new process developed aiming at the problem of difficult wall protection in a large-particle-size pebble layer and a complex stratum, can effectively solve the quality defects of pile bodies such as necking and hole collapse, and has the advantages of high construction requirement precision, more supporting equipment, high economic cost and no consideration for selecting the process method.

3. Selection of construction technique

3.1 selection of construction Process

Selecting a reasonable rotary drilling hole-forming construction process according to engineering requirements of a thick sand pebble layer and a slope protection pile, wherein the common process method comprises the following steps:

3.1.1 non-circulating mud dado pore-forming

A pore-forming construction process using non-circulation stable slurry to keep pore wall stable.

3.1.2 Sleeve Protect wall pore-forming

A hole forming construction process for keeping the hole wall stable by utilizing a sleeve is a full pile casing follow-up rotary excavating construction process mentioned in the above.

3.1.3 Dry working to form holes

The construction process of directly taking earth and forming holes by a rotary drilling rig does not need to adopt a wall protection measure.

3.2 pore-forming construction of test pile

The method is characterized in that a drilling operation is carried out by selecting any process at a construction site, and meanwhile, the construction process of adopting a full casing follow-up is not considered due to the factors of manufacturing cost and construction period, so that the requirements of designed pile aperture, depth, verticality and the like are met, and the construction of the test pile is carried out in 24 days, 4 months and 2020.

3.2.1 Main parameters of the rig installation

The rotary drilling rig is a TR200D rotary drilling rig manufactured by south China vehicle company, the maximum torque of the rotary drilling rig is 200KN.m, the engine power is 187KW, the drilling diameter is 1800mm at most, and the drilling depth is 60m at most.

3.2.2 Dry-working hole-forming test pile

When the construction of rotary drilling dry operation test piles (3) is carried out on a construction site, the phenomena of drill rod shaking, drill jamming and gear grinding are caused, when the slag soil in a lifting drill row barrel is dug to 3-5 m, hole collapse and hole shrinkage are caused in the hole, the design requirements cannot be met, the machine is stopped to lift the drill and backfill the pile hole, and the single dry operation hole forming test pile is unsuccessful.

3.2.3 circulating-free slurry dado pore-forming test pile

Digging a slurry tank near the site test pile, processing the waterproof layer on the bottom and wall of the tank, and blending the slurry to bentonite: caustic soda =2000:25 (mass ratio kg), mud proportion is controlled to be 1.1-1.15, and colloid rate is not lower than 95%; the sand content is not more than 4%. After the rotary drilling construction, slurry is injected into the hole and does not reach the orifice and has stable liquid, the slurry permeates and flows out of the sandstone layer to cause serious loss, so the process cannot be adopted.

3.2.4 dry operation and mixed mud material dado pore-forming test pile

Aiming at the fact that pebbles in an on-site stratum have larger particle sizes (D is larger than =20cm and the content is 70-80%), by means of on-site technology and flight crew according to actual conditions, the side wall of a cylinder drill bit is cut by gas welding to enlarge a slag discharge inlet, a drilling machine is used for aligning and correcting a machine body, a footage is drilled at a low rotation speed, after every 2m of drilling is carried out, a drill rod is lifted to give out a hole position, a soil shifter is matched with a backfilled clay and a bentonite mixture is placed into a pile hole, and the ratio of the backfilled: the method comprises the steps that bentonite =10:1 (volume ratio), the water content is controlled to be 20-30%, a drilling machine is used for drilling again in place, the mixture is extruded to the wall of a pile hole to form a viscous mud skin, the wall protection effect is achieved, and the method is repeatedly operated until the design elevation is drilled.

In a specific soil layer with the sandy gravel layer and a lower underground water level, the time for rotary digging of a pile with the depth of 18 meters and the diameter phi of 800mm is about 2 hours and 40 minutes, if the pile with the same depth is rotary dug in the clay layer, the time is about 30 minutes, and if the pile is constructed by a positive and negative circulation drilling machine, the time is about 4 hours to 5 hours.

After pore forming, the illumination hole wall is smooth and has no phenomena of hole collapse, hole shrinkage and the like, a reinforcement cage is hoisted, a string of cylinders are placed down, and concrete pouring is finished within one hour. After 2 piles with the length of 18 meters are tested, the length of the cast-in-place pile is 16.5 meters, the dosage of cast-in-place concrete is 9m2, and the filling coefficient is calculated (the ratio of the actual cast-in-place concrete square amount of one pile to the theoretical square amount calculated according to the outer diameter of the pile): s = V real/V theory = V real/pi. (R/2) 2. H =9/3.14 × 0.42 × 16.5=1.09>1.0 (3-1)

The filling coefficient is a basis for judging the pile-forming quality, if the filling coefficient is less than 1, the actual concrete filling amount of the pile is less than the theoretical calculation amount, the pile body quality has certain defects, and the pile can be indirectly judged to be unqualified. The filling coefficient of the engineering test pile is 1.09 larger than 1.0, so that the length of the pile body meets the requirement, necking does not occur, and the like, the filling coefficient value is not too large (generally not larger than 1.3), so that the pile body is regular in forming, holes do not collapse and the like, and the design and specification requirements are met.

4. Construction process flow with operability

The pile test on site can meet the requirements of design and engineering conditions, the pile test is determined to be successful, and the process flow of the rotary drilling rig for the project is shown in the figure 1.

And (3) formally developing construction in 5 and 1 month in 2020, and finishing 14/18 m, 47/13.5 m, 8/12.7 m, 9/12.3 m and 26/14.3 m scientific test steel pipe piles in 5 and 19 months in 2020.

5. Detection result of slope protection pile

5.1 detection method

The method belongs to the application range of elastic waves, when an instantaneous impact force is applied to the pile top, the generated elastic waves are transmitted downwards along the pile body, meet the pile bottom interface or the interface between piles (namely the change of the pile diameter, the uneven medium of the pile body, the breakage and the like) in the transmission process, generate the reflection of the elastic waves, and are transmitted upwards along the pile body. Therefore, by arranging a wave detector on the pile top and connecting a recording instrument, the propagation condition and the travel time of the elastic wave can be recorded. Because the propagation of the elastic waves in the pile body is closely related to the physical properties of the pile body, the integrity of the pile body can be analyzed and the position of the defect of the pile body can be calculated according to the travel time of the reflected waves and the dynamic characteristics of the elastic waves.

5.2 test results

The detection test is carried out before the construction of the crown beam and after the strength of the concrete reaches 50% of the designed strength. And (4) carrying out low-strain pile body integrity detection on 18 piles by a detection mechanism on site in 6/11/2020, wherein all the piles are I-type piles after the pile bodies are tested to be complete.

6. Look and feel quality of slope protection pile

After the construction of the foundation pit slope protection pile crown beam is finished in 6-13 th of 2020, earth excavation is carried out when the concrete strength reaches 70%, and the field measurement of the pile spacing and the pile diameter size meets the design requirements. The thickness of the mud cover of the exposed pile body is measured between 100 mm and 150 mm.

The local external swelling concrete of the excavated exposed individual pile body is like pomegranate scab, and the defects of the existing quality defects are searched and analyzed. The first reason may be that the hole is drilled in a local pile, a mud wall protection layer is not well formed, and hole collapse is caused, and the second reason may be that concrete is not poured in time after the hole is formed, so that the delay time is long, and the mud skin of the wall protection is lost to cause falling and hole collapse. The third reason is that the backfilling mud cannot be completely and compactly filled in the pile hole because the drilling depth is over 2 meters each time, and the mud skin cut into the pebble layer after re-drilling is thinner, so that the hole wall cannot be supported to form the local small hole collapse phenomenon.

And (3) aiming at the bulge concrete part outside the pile body, chiseling by using a small machine to ensure no exposed ribs and ensuring the diameter size of the pile to be within a positive deviation.

Claims (6)

1. A simple method for forming a hole and a pile in a sand and gravel stratum which is easy to collapse in a rotary drilling machine is characterized by comprising the following steps:

burying an orifice protection cylinder: burying an orifice pile casing at the pile position;

drilling: drilling holes in the protective cylinder, and determining the depth of a single drilling hole on the basis of the principle that the hole wall does not collapse; the length of the orifice casing is equal to or close to the single drilling depth;

drilling into the pile hole to the depth of the single drilling hole;

forming a wall protecting layer in the pile hole: pouring the mixed mud material into a pile hole drilled at a single time, extruding the mixed mud material into a sand-gravel gap on the hole wall by rotating a rotary drilling machine bucket, bonding the sand-gravel together, and forming a viscous mud material mixed wall protection layer in the hole wall to play a wall protection role;

repeating the steps (3) to (4) until the whole pile hole is completed, and lifting out the drilling tool;

hoisting a reinforcement cage into the pile hole, and centering and fixing;

slowly putting the string cylinder into the pile hole, wherein the distance between the string cylinder and the bottom of the pile hole is 1 m;

pouring concrete, and pulling out the orifice protecting cylinder after solidification.

2. The simple method for forming the pile by the hole in the sand-gravel stratum which is easy to collapse of the rotary drilling machine according to claim 1, wherein the mixed mud material is prepared from clay and bentonite according to a weight ratio of 10:1, if the water content of the clay is high, water is not required to be sprayed, the clay can be directly blended and stirred, and if the water content of the clay is low, the water is sprayed and stirred to enable the water content to reach 20-30%, the water content is slightly higher than the optimal water content, and the user can feel wet when grasping the clay by hand; meanwhile, the aim of dust fall is also achieved.

3. The simple method for forming the pile by the hole in the sand-gravel stratum which is easy to collapse of the rotary drilling machine according to claim 1, wherein the single drilling depth is 2 m; the length of the orifice protecting cylinder is 2m, and the bottom of the protecting cylinder is guaranteed to be seated on an original soil layer.

4. The simple method for forming the pile by the hole in the sand-gravel stratum which is easy to collapse of the rotary drilling machine according to claim 1 is characterized in that the method for burying and fixing the orifice casing comprises the following steps: after the hole mouth pile casing is fixed at the pile hole position, clay is used for backfilling and tamping around the hole mouth pile casing layer by layer so as to ensure the verticality and prevent the displacement of the pile casing; if the bottom soil layer of the orifice pile casing is not cohesive soil, deep digging or soil replacement is required, after the clay with the thickness of 200-300 mm is tamped in the backfill of the pit bottom, the orifice pile casing is arranged so as to prevent the bottom opening of the pile casing from leakage and collapse; the outer side of the upper opening of the orifice protecting cylinder is bound with battens or steel pipes and is symmetrically arranged and hung tightly to prevent downward movement.

5. The simple method for forming the pile by the rotary drilling machine in the sand-gravel stratum prone to collapse according to claim 1, wherein in the step (8), before concrete pouring, the slump and the workability must be checked and recorded; the concrete can not be isolated when being transported to a pouring point; the opening of the concrete pouring hole is tightly covered to prevent foreign matters from falling into the hole; in the concrete pouring process, the position of the string cylinder is always kept in the middle; and (3) pouring 0.5m more concrete after the concrete is poured to the pile top so as to ensure the strength of the pile top concrete after the laitance is chiseled off.

6. The simple method for forming the pile by the hole in the sand-gravel stratum which is easy to collapse of the rotary drilling machine according to claim 5, wherein the vibration is carried out when concrete is poured into the pile head; when the elevation of the pile top is low, the concrete can not be poured into the ground, and after the concrete is initially set, the hole is backfilled by soil, so that people or equipment and the like are prevented from falling into the hole.

Images