CN102277867B - A construction method of collapsible loess foundation - Google Patents

Abstract

The invention discloses a construction method of collapsible loess foundation. In the method, SDDC piles are firstly used to treat the foundation of the collapsible loess site; Intersoil compaction coefficient, SDDC pile body compaction coefficient, and evaluation of collapsibility. If any of the three indicators do not meet the design requirements, the SDDC pile filling construction will be carried out until the design requirements are met; finally, pouring Post-pile grouting construction. This method has the advantages of economy and environmental protection, large treatment depth, good treatment effect, large bearing potential and strong ability to resist complex loads. Using this method can eliminate various negative effects caused by the collapsibility of the deep collapsible loess site, and can meet the requirements of the upper high-rise buildings on the bearing capacity and settlement of the foundation.

Description

A construction method of collapsible loess foundation

technical field

The invention relates to the field of building foundation treatment, in particular to a construction method for jointly treating loess foundation collapsibility by adopting SDDC piles and cast-in-situ pile post-grouting technology.

Background technique

Loess foundation treatment problems are often encountered in Northwest and North China, usually including low-humidity collapsible loess with the main purpose of eliminating or reducing the damage of collapsible deformation, and at the same time need to improve foundation bearing capacity, and high-humidity soft loess (Especially saturated loess, which is mostly transformed from collapsible loess saturated with water, and the saturation degree S _r ﹥80%) is a foundation treatment problem aimed at improving the bearing capacity of the foundation and reducing harmful compression deformation. Since the engineering characteristics of the latter are mostly similar to those of ordinary cohesive soils, the compression deformation of the foundation should be mainly considered, and can be treated as weak cohesive soils, while the former should mainly consider the subsidence deformation of the foundation after being soaked by water.

The traditional treatment methods for collapsible loess foundation mainly include the following methods:

(1) cushion layer, (2) heavy hammer surface compaction, (3) dynamic compaction, (4) compaction pile, (5) chemical reinforcement, (6) pre-soaked water, (7) pile foundation.

Among the above treatment methods for collapsible loess foundations, method (1) and method (2) have shallow treatment depths and are not suitable for sites with deep collapsible loess; method (3) has a large negative impact on the environment and is not suitable for existing It is used around buildings and urban areas; method (4) uses a single filler, and the compaction effect on the soil between piles is not ideal, and can only eliminate the subsidence of the foundation to a limited extent; method (5) is expensive to deal with, and is generally not accepted Adopted; method (6) when the ground around the site sinks and cracks when flooded, it is easy to cause "running water" to penetrate holes and affect the safety of surrounding buildings; method (7) deal with deep collapsible loess areas, especially in self-weight collapsible loess areas In loess field, in order to overcome the adverse effects of negative friction, the required piles are long and the economy is poor.

Among the above traditional treatment methods for collapsible loess foundations, especially for sites with deep self-weight collapsible loess, there is no economical and effective foundation treatment method that can meet the requirements of high-rise buildings (tall structures) for foundation bearing capacity and settlement , Therefore, finding a new treatment method for collapsible loess foundation is a hotspot that those skilled in the art pay attention to.

Contents of the invention

In view of the shortcomings or deficiencies in the above-mentioned prior art, the object of the present invention is to provide a construction method for joint treatment of collapsible loess foundations using SDDC piles and post-grouting technology for cast-in-place piles.

In order to achieve the above tasks, the present invention is achieved through the following technical solutions:

A construction method for a collapsible loess foundation, characterized in that the method first adopts the SDDC pile method to carry out foundation treatment on a collapsible loess site; then, collect undisturbed soil on site, conduct indoor tests according to specifications, and measure Soil compaction coefficient between piles, SDDC pile body compaction coefficient, and collapsibility evaluation. If any of the three indicators do not meet the design specifications, the SDDC pile will be repaired until the design requirements are met; then carry out Grouting construction after pouring piles.

The specific construction steps are as follows:

Step 1: Check the geological data, combine with the design parameters, and select the appropriate hole-forming construction equipment;

Step 2: Level the site, remove obstacles on the ground, mark and deal with underground structures and pipelines within the scope of the site, and keep the site level;

Step 3: Measure and set out the line, determine the control axis and the sideline of the piling site and mark it;

Step 4, use the construction machine tool selected in Step 1 to impact and form holes. The hole-forming construction equipment generally adopts a pile driver with a pile frame, and the impact hammer adopts an olive-shaped overweight hammer. After the pile driver is in place, aligned and leveled, the hoisting hammer reaches the design height (generally it can be lifted to 10m~18m), the olive-shaped overweight hammer is automatically unhooked, and the kinetic energy of the olive-shaped overweight hammer is used to rush into the soil, and the above-mentioned steps are repeated. Operate until the hole depth meets the design requirements;

Step five, layered filling, compacted into piles:

Use a standard hopper or a transport truck to fill the pile hole with the quantitative filler mixed according to the design layer by layer, and then use the olive-shaped overweight hammer when forming the hole to tamp the filler layer by layer until the SDDC pile is formed. And each pile hole should be rammed and filled to at least 0.5m above the design elevation of the pile top; among them, the construction sequence of hole forming and filling tamping is carried out at intervals;

Step 6, the construction machinery moves to the next pile position, and repeats steps 4 and 5 until all SDDC piles are completed;

Step 7: Excavate exploratory wells to collect pile body filler samples and soil samples between piles of SDDC piles, and do indoor routine geotechnical tests. The specific requirements are as follows:

(1) According to the specifications, take some samples of the soil between the piles and the pile body filler of the SDDC pile, and do indoor routine geotechnical tests. The results should meet the compaction coefficient of the soil between the piles not less than 0.93, and the compaction coefficient of the pile body of the SDDC pile Not less than 0.97;

(2) Collapsibility evaluation. In order to further determine the elimination degree of collapsibility, excavate exploratory wells on the site to collect undisturbed soil samples of the soil between the three SDDC piles at the centroid, conduct indoor routine geotechnical tests, and determine the degree of collapsibility elimination according to the indoor test results Whether it meets the design requirements.

If the above indicators have met the design requirements, carry out the construction of grouting after pouring piles; otherwise, carry out the construction of supplementary piles of SDDC piles;

Step 8, before the construction of cast-in-situ piles, use 100mm thick C15 concrete to harden the ground that has been treated with SDDC piles;

Step 9: Use the total station to use the specified axis intersection as the control point to stake out and position the cast-in-place piles. The distance error of the pile position direction of the cast-in-place piles is not less than 5mm, and mark the pile positions one by one with spikes;

Step 10, make the reinforcement cage, check and accept it for use. The pile body pre-buried pipe grouting method is used, that is, the grouting pipe is fixed on the steel cage according to the designed grouting depth, and the grouting device is lowered together with the steel cage. Screw connections are used between grouting pipes to avoid welding;

Step 11, the hole-forming machine is in place, and the hole-forming machine is kept stable without tilting or displacement;

Step 12, adjust the hole forming machine, use the alignment ring to align the pile position of the cast-in-situ pile, start the hole forming machine, and perform hole cleaning after reaching the controlled depth;

Step 13, move the hole forming machine to the next cast-in-situ pile position, repeat step 11 and step 12, until the hole-forming operation of all cast-in-situ piles is completed;

Step 14: Hoist and lower the pre-fabricated reinforcement cage with grouting pipes installed. Before placing the reinforcement cage, tie mortar pads or plastic cards. Sink to avoid colliding with the hole wall; when the steel cage is placed in the design position, it should be fixed immediately; weld the joint between the two steel cages to ensure that the position of the steel cage is correct and the thickness of the protective layer meets the requirements;

Step fifteen, test the water of the grouting pipe. When each section of the grouting pipe is lowered with the steel cage, a water test should be done. If the water column is found to drop or disappear, check whether the grouting pipe has sand holes and whether the screw connection is sealed.

After the reinforcement cage is placed, carry out the second cleaning in the hole, and then check the water surface in the hole again, and seal the upper opening of the grouting pipe with a plug if there is no abnormality;

Step sixteen, pouring concrete pouring piles. Concrete cast-in-situ piles are poured with a release tube, and the thickness of the virtual soil in the drilled hole is checked and measured again before the release of the tube. When the design requirements are met, the concrete pouring is carried out continuously. When pouring concrete to the top of the cast-in-place pile, proper Exceed the design elevation of the pile top of the cast-in-situ pile to ensure that the pile top elevation of the cast-in-place pile meets the design requirements after the laitance is removed. At the same time, make no less than one group of test blocks with the same mix ratio;

Step seventeen, pressurized water test, the pressurized water test is carried out within 24 hours after pile formation. Before formal grouting, a water pressure test must be carried out to check the smoothness of the pipeline and check valve.

If hole expansion, hole collapse or large filling coefficient occurs on the pile side or pile end, special attention should be paid to the pressure water test in advance, and it should be carried out within 5 hours after the concrete is poured to ensure that the thicker concrete cover can be washed away layer.

During the test, a special person shall record the breakthrough pressure value and the smoothness of the pipeline;

Step 18, repeat step 14, step 15, step 16, and step 17 to complete the pile-forming work of each cast-in-place pile and prepare for post-grouting construction at the same time;

Step nineteen, post grouting construction. The method of secondary grouting is adopted to give full play to the effect of grouting and obtain better results.

(1) Initial injection: After 3 to 5 days of concrete curing for cast-in-situ piles, grouting will start, and the cement slurry configured according to the design will be injected into the bottom of the pile or the soil layer on the side of the pile through a high-pressure pump and a pre-embedded grouting pipe. For compound grouting, the pile side grouting is generally carried out first, and the pile bottom grouting is carried out after 12 hours. The pressure at the initial injection should be small, and the slurry will be thin to thick. During the initial injection, pay close attention to the changes of the grouting pressure and the amount of grouting, and pay attention to the grouting rhythm. When grouting at the bottom of the pile, a dial indicator should be set to detect the lifting amount of the pile to avoid excessive.

(2) Secondary grouting: The grouting pipes for the second grouting should preferably be distributed symmetrically with the grouting pipes for the first grouting. The amount of grouting for the second time is generally 1/3~1/4 of the first time, and the water-cement ratio can be increased appropriately.

(3) The grouting sequence of the same pile: grouting the upper pipe first, then the lower pipe, and finally the end pipe; the grouting sequence of the same pile cap: first the surrounding piles and then the central pile.

Step 20, stop grouting. The general control principle of terminating grouting is mainly based on grouting volume, supplemented by pressure control. However, the grouting parameters should also be reasonably selected according to the geological conditions. For example, if the pile end is a dense gravel and pebble layer, the grouting amount should be the main control index; if the pile side is a dense loess layer, the grouting pressure should be the main control index. index.

Immediately after the grouting is completed, screw the plug on the grouting pipe to avoid reducing the grouting effect due to grouting back.

In step 21, repeat steps 19 and 20 to continuously complete the post-grouting construction work of each cast-in-place pile.

The method of the invention can effectively solve the problem that high-rise buildings (tall structures) on the deep collapsible loess site have strict requirements on foundation bearing capacity, settlement, environmental impact and the like. And because the pile length can be effectively shortened after adopting this method, the economic benefit brought by it is more significant than other methods.

Description of drawings

Figure 1 is a schematic diagram of the layout of SDDC piles;

Fig. 2 is a schematic sectional view of foundation treatment;

Figure 3 is a schematic diagram of the embedding of the grouting pipe.

The marks in the figure represent respectively: 1. soil between piles, 2. SDDC pile, 3. natural soil layer without collapsibility in the lower part of the foundation , 4. cast-in-place pile, 5. grouting pipe.

The present invention will be described in detail below with reference to the accompanying drawings and embodiments.

Detailed ways

Super Down-hole Dynamic Compaction (Super Down-hole Dynamic Compaction, referred to as SDDC), which uses the mechanism of high kinetic energy, super pressure, and strong compaction to form holes through impact, from deep to shallow, and form piles layer by layer. , In the process of overpressure kinetic energy dynamic compaction, a large dynamic passive earth pressure is generated on the side of the soil between the piles, forcing the filler to compact and extrude downward and around, so that the physical and mechanical indicators of the soil between the piles are fully improved. It can be widely used in the treatment of various special foundations such as miscellaneous filling, liquefaction, weak subsidence, and expansion. This method has the advantages of strong adaptability, large treatment depth, good treatment effect, environmental protection, little impact on the environment, and good economic benefits. It has been gradually recognized by people in recent years, and the treatment effect is good. The invention introduces the in-hole deep ultra-strong compaction method into the pile foundation method to treat the collapsibility of the loess foundation, and it is proved by practice that a satisfactory effect is obtained.

The type of pile foundation in the present invention depends on specific requirements, and can adopt pile-column foundation, pile-beam foundation, pile-wall foundation, pile-raft foundation, pile-box foundation, etc. Bottom piles, full house piles, partial full house piles and other methods.

Referring to Fig. 1, Fig. 2 and Fig. 3, the construction method of the collapsible loess foundation of the present invention uses SDDC piles and cast-in-situ piles (taking bored cast-in-situ piles as an example) post-grouting technology to jointly treat the wetness of collapsible loess foundations. Trapped, specifically include the following steps:

1. Construction of SDDC pile 2.

Step 1: Check the geological data, combine with the design parameters, and select the appropriate hole-forming construction equipment;

Step 2: Level the site, remove obstacles on the ground, mark and deal with underground structures and pipelines within the scope of the site, and keep the site level;

Step 3: Measure and set out the line, determine the control axis and the sideline of the piling site and mark it;

Step 4, use the construction machine tool selected in Step 1 to impact and form holes. The hole-forming construction equipment generally adopts a pile driver with a pile frame, and the impact hammer adopts an olive-shaped overweight hammer. After the pile driver is in place, aligned and leveled, the hoisting hammer reaches the design height (generally it can be lifted to 10m~18m), the olive-shaped overweight hammer is automatically unhooked, and the kinetic energy of the olive-shaped overweight hammer is used to rush into the soil, and the above-mentioned steps are repeated. Operate until the hole depth meets the design requirements;

Step 5: fill in layers and ram them into piles. Use a standard hopper or a transport truck to fill the quantitative filler mixed according to the design (bricks, rough stones, concrete blocks and other large hard materials cannot be used as fillers) into the pile holes in layers, and then use the olive-shaped overweight when the holes are formed. The hammer tamps the filler layer by layer until it becomes SDDC pile 2. Each pile hole should be tamped to at least 0.5m above the design elevation of the pile top; among them, the construction sequence of hole formation and filling tamping is carried out at intervals;

Step six, shifting the construction machinery. Repeat steps 4 and 5 until all SDDC piles 2 are completed;

Step 7: Excavate exploratory wells to collect pile body filler samples of SDDC pile 2 and soil between piles 1 (soil with collapsibility in the upper part) samples, and do indoor routine geotechnical tests. The specific requirements are as follows:

(1) According to the specifications, take a number of filling samples of soil between piles 1 and pile body of SDDC pile 2, and do indoor routine geotechnical tests. The results should satisfy that the compaction coefficient of soil between piles 1 and The compaction coefficient is not less than 0.97;

(2) Collapsibility evaluation. In order to further determine the degree of collapsibility elimination, exploratory wells were excavated on the site to collect undisturbed soil samples of the soil 1 between the piles at the centroid of the three SDDC piles 2, and the indoor routine geotechnical test was carried out. According to the indoor test results, the collapsibility was determined Whether the degree of elimination meets the design requirements.

If the above indicators have met the design requirements, carry out the construction of grouting after the bored pile; otherwise, carry out the construction of SDDC pile 2;

Step eight, before carrying out the construction of the bored pile 4, use 100mm thick C15 concrete to harden the ground that has been treated with the SDDC pile 2;

2. Post grouting construction of bored pile 4

Step 9: Use the total station to use the designated axis intersection as the control point to stake out and position the 4 pile positions of the bored piles. mark one by one;

Step 10, production and acceptance of reinforcement cage:

The pile body pre-buried pipe grouting method is used, that is, the grouting pipe 5 is fixed on the steel cage according to the designed grouting depth, and the grouting device is lowered together with the steel cage. The grouting pipes 5 are connected by screw to avoid welding;

Step eleven, the drilling machine is in place, and the drilling machine is kept stable without tilting or displacement;

Step 12: Straighten the tappets of the drilling frame, use the alignment ring to align the 4 pile positions of the bored piles, start the drilling machine to drill and excavate, and after reaching the control depth, perform idling at the bottom of the hole to clear the soil Drilling stops and drilling; hole quality assurance measures are:

1) The depth of the hole measured with the sounding rope/hammer and the thickness of the virtual soil should not exceed 100mm;

2) Keep the height of the mud liquid level in the hole to prevent shrinkage and collapse;

Step 13, move the drilling machine to the next bored pile 4 pile position, repeat step 11 and step 12, until the hole-forming operation of all bored piles 4 is completed;

Step 14: Hoist and lower the prefabricated reinforcement cage installed with the grouting pipe 5. Before placing the reinforcement cage, tie the mortar block or plastic card. Slowly sink to avoid collision with the hole wall; when the steel cage is placed in the design position, it should be fixed immediately; weld the joint between the two steel cages to ensure that the position of the steel cage is correct and the thickness of the protective layer meets the requirements;

Step fifteen, the grouting pipe 5 tests the water. When each section of the grouting pipe 5 is lowered with the steel cage, a water test should be done. If the water column is found to drop or disappear, check whether the grouting pipe 5 has sand holes and whether the screw connection is sealed.

After the reinforcement cage is placed, carry out the second cleaning in the hole, and then check the water surface in the hole again. If there is no abnormality, seal the upper opening of the grouting pipe 5 with a plug;

Step sixteen, pouring concrete. Concrete is poured with a chute, and the thickness of the virtual soil in the borehole is checked and measured again before the chute is released, and it is carried out when the design requirements are met. The concrete pouring is carried out continuously. When the concrete is poured to the top of the bored pile 4, the Appropriately exceed the design elevation of the pile top of the bored pile 4 to ensure that the pile top elevation of the bored pile 4 meets the design requirements after the laitance is removed. At the same time, make no less than one group of test blocks with the same mix ratio;

Step seventeen, water pressure test: the water pressure test is carried out within 24 hours after the pile is formed. Before formal grouting, a water pressure test must be carried out to check the smoothness of the pipeline and check valve.

If hole expansion, hole collapse or large filling coefficient occurs on the pile side or pile end, special attention should be paid to the pressure water test in advance, and it should be carried out within 5 hours after the concrete is poured to ensure that the thicker concrete cover can be washed away layer.

During the test, a special person shall record the breakthrough pressure value and the smoothness of the pipeline;

Step 18, repeat step 14, step 15, step 16, and step 17, complete the pile-forming work of each bored pile 4, and prepare for post-grouting construction at the same time;

Step nineteen, post grouting construction. The method of secondary grouting is adopted to give full play to the effect of grouting and obtain better results.

(1) Preliminary injection: After 3 to 5 days of concrete curing for the bored cast-in-place pile 4, grouting will start, and the cement slurry configured according to the design will be injected into the bottom of the pile or the soil layer on the side of the pile through the high-pressure pump and the pre-embedded grouting pipe 5 In the middle, if it is compound grouting, the pile side grouting is generally carried out first, and the pile bottom grouting is carried out after 12 hours. The pressure at the initial injection should be small, and the slurry will be thin to thick. During the initial injection, pay close attention to the changes of the grouting pressure and the amount of grouting, and pay attention to the grouting rhythm. When grouting at the bottom of the pile, a dial indicator should be set to detect the lifting amount of the pile to avoid excessive.

(2) Secondary grouting: the grouting pipes 5 for the second grouting are preferably distributed symmetrically with the grouting pipes 5 for the first grouting. The amount of grouting for the second time is generally 1/3~1/4 of the first time, and the water-cement ratio can be increased appropriately.

(3) The grouting sequence of the same pile: grouting the upper pipe first, then the lower pipe, and finally the end pipe; the grouting sequence of the same pile cap: first the surrounding piles and then the central pile.

Step 20, stop grouting. The general control principle of terminating grouting is mainly based on grouting volume, supplemented by pressure control. However, the grouting parameters should also be reasonably selected according to the geological conditions. For example, if the pile end is a dense gravel and pebble layer, the grouting amount should be the main control index; if the pile side is a dense loess layer, the grouting pressure should be the main control index. control indicators.

Immediately after the grouting is finished, screw the plug on the grouting pipe 5, so as not to reduce the grouting effect due to grouting back.

In step 21, repeat steps 19 and 20 to continuously complete the post-grouting construction work of each bored pile 4 .

Precautions for construction in winter and rainy seasons:

(1) In winter, when the temperature is lower than 0°C and concrete is poured, heating and heat preservation measures should be taken. When pouring, the temperature of concrete shall be carried out according to the winter construction plan. Before the pile top reaches 50% of the design strength, it must not be frozen; when the temperature is still above 30°C, the concrete should be retarded according to the specific situation.

(2) During the rainy season, strictly adhere to the regulations of pouring concrete while drilling to prevent the hole from collapsing after the hole is filled with water. There must be various drainage measures on site to prevent ground water from flowing into the tank, causing slope collapse or subsidence of foundation soil, and tilting of hole-forming machinery.

In addition, during the rainy season, when there is water on the site or the water content of the soil layer is high, the phenomenon of impacting the hole-forming suction hammer is serious. At this time, drilling rigs can be used to drill holes, but the number of times of tamping on the filler in the hole must be appropriately increased;

When adopting the method of the present invention to carry out construction, the filler of SDDC pile 2 does not select brick, rubble, concrete block or other large hard materials for use.

In the design of cast-in-situ pile foundation, the foundation treated by SDDC pile 2 is regarded as a composite foundation, and the pile position layout of SDDC pile 2 is not considered. The physical and mechanical indicators of layer 3 adopt the data provided by the geological survey report.

The present invention has been specifically described above by way of examples, but the present invention is not limited to the above specific examples.

The principle of the present invention is explained below.

In-hole deep super dynamic compaction method (SDDC) forces the undisturbed soil in the hole to extrude laterally during the hole forming process, so that the soil within a certain range around the pile is squeezed, disturbed and reshaped. When filling, the hole is forced to The inner filler squeezes the hole wall laterally again, causing the soil in a larger area around the pile to be squeezed, disturbed and reshaped again. The waves and dynamic stress generated by the huge ramming energy of dynamic compaction act repeatedly, forcing the soil skeleton to form Plastic deformation, thereby improving the compactness and shear strength of the soil, improving the deformation characteristics of the soil, and the formed beaded piles are interlocked with the soil between the piles, and the bearing capacity is high. Due to the strong compaction during hole formation, this method eliminates The effect of loess collapsibility is more effective than other methods. Its reinforcement mechanism mainly has the following four points:

(1) The dynamic compaction effect on the original during the process of hole formation and pile formation;

(2) Pile body filling and displacement (including the pile body and the aggregate squeezed into the soil between the piles);

(3) When lime soil is used, the hydration and gelation of quicklime (chemical replacement). In the collapsible loess area, the foundation treated by the SDDC method can effectively eliminate the collapsibility while improving the physical and mechanical properties of the soil. Then, on the formed SDDC pile composite foundation, the design and construction of the cast-in-place pile combined with post-grouting technology are carried out.

The reinforcement mechanism of cast-in-situ piles using compound grouting technology in post-grouting construction mainly includes:

(1) Osmotic consolidation;

(2) Compact filling effect;

(3) Splitting and reinforcing effect;

(4) The effect of expanding the bottom and expanding the diameter.

Under the action of the above mechanism, the physical and mechanical properties of the foundation soil are further improved, the collapsibility of the loess at the grouting place is further eliminated, the bearing capacity of the cast-in-situ pile is greatly improved, and the settlement of the pile foundation is greatly reduced under the same load .

In summary, compared with the traditional method, the innovative contribution of the loess foundation collapsible construction method of the present invention is as follows:

(1) Under the effects of the above two aspects, the collapsibility of the loess foundation can be eliminated, and then the problem of negative friction on the pile side caused by the collapsibility of the loess foundation can be solved. pile foundation design;

(2) Because the cast-in-place piles are treated jointly with SDDC piles and the post-grouting technology of the cast-in-place piles, the bearing capacity of the piles is greatly improved, and the settlement of the pile foundation is greatly reduced under the same load. Therefore, the pile length can be effectively shortened under the premise of meeting the specification requirements, and the economic benefit can be greatly improved. And because the pile foundation has the characteristics of large bearing capacity and strong ability to resist complex loads, after reasonable design according to engineering characteristics, it can meet the stability and differential settlement requirements of the upper high-rise buildings (tall structures) on the foundation.

Claims (2)

1. the job practices of a collapsible loess foundation is characterized in that, this method at first adopts SDDC stake method that ground is carried out in the loess place with settlement by soaking and handles; Then, gather undisturbed soil at the scene, carry out laboratory test by standard, record the compacted coefficient of inter-pile soil and SDDC stake pile body coefficient of consolidation, and carry out the settlement by soaking evaluation, if having when not satisfying design specifications in three indexs, then carry out the piling construction of SDDC stake, until meeting design requirement; Carry out the construction of filling pile ' s after grouting then; Concrete job practices may further comprise the steps:

Step 1 is verified geologic information, in conjunction with design parameters, selects suitable drilling construction facility;

Step 2, obstruction is on the ground removed in smooth place, and undreground works and pipeline in the scope of mark disposal field keep levelling of the land;

Step 3 is measured unwrapping wire, makes control axis, piling site boundary and sign;

Step 4, the construction equipment of selecting in the applying step one, impact holing, drilling construction facility adopt the stake machine of band pile frame, and jump bit is selected the overweight hammer of olive shape for use, pile-forming machine perching, align, after the leveling, the lifting weight arrives design height, and the overweight hammer of olive shape is automatically-unhooked, pours in the soil by the kinetic energy of the overweight hammer of olive shape, carry out aforesaid operations repeatedly, reach designing requirement until hole depth;

Step 5, the layering filler, ram pile:

To insert a hole by the quantitative filler layering that design is mixed and stirred with standard hopper or dumper, the overweight hammer of the olive shape when using pore-forming then is with filler compaction in layers one by one, until pile; And each hole should be rammed and be filled to more than the design elevation of top 0.5m at least; Wherein, the sequence of construction of pore-forming and filling tamped is carried out at interval;

Step 6, construction machinery move to next stake position, and repeating step four, step 5 are all finished until stake;

Step 7, pile body filler sample and the inter-pile soil sample of excavation prospect pit collecting pile are done indoor conventional soil test, and specific requirement is as follows:

(1) it is some to get the pile body filler sample of inter-pile soil and stake by standard, does indoor conventional soil test, and the compacted coefficient that its result should satisfy inter-pile soil is not less than 0.93, and the coefficient of consolidation of pile body of stake is not less than 0.97;

(2) settlement by soaking evaluation: for further determining the elimination degree of settlement by soaking, the not disturbed soil sample of three stake centre of form place inter-pile soils is gathered in ground on the scene excavation prospect pit, carry out indoor conventional soil test, according to laboratory test results, judge whether the elimination degree of settlement by soaking meets design requirement;

If above each index meets design requirement, then carry out the construction of filling pile ' s after grouting; Otherwise carry out the piling construction of stake;

Step 8 before carrying out filling pile construction, adopts the thick C15 concrete of 100mm that cure process is carried out on the ground of adopting pile and handling;

Step 9 adopts total powerstation to utilize the crossing point of axes of appointment to do the control point, and to the setting-out of grout pile position, location, the stake position direction range error of castinplace pile is not less than 5mm, and with spike mark is one by one carried out in the stake position;

Step 10 adopts the pre-pipe laying mud jacking of pile body, namely by the mud jacking degree of depth requirement of design, madjack pipe is fixed on the reinforcing cage, and squeezing unit is transferred with reinforcing cage, adopts screwed connection to avoid welding between the madjack pipe;

Step 11, the pore-forming facility are in place, and keep boring machine steady, not run-off the straight, displacement;

Step 12 is adjusted boring machine, to good grout pile position, starts boring machine with the contraposition circle, reach controlling depth after, carry out hole operation clearly;

Step 13, mobile pore-forming facility are to next castinplace pile position, and repeating step 11 and step 12 are until the pore-forming operation of finishing all castinplace piles;

Step 14 is transferred the reinforcing bar cage hoisting of making in advance that installs Grouting Pipe, ties up mortar cushion block or plastic clip before reinforcing cage is put into, and during install reinforcing cage, the mating holes position, hangs and directly holds up surely, slowly sinks, and avoids colliding hole wall; When reinforcing cage is put into design attitude, should fix immediately; Weld junction between two sections reinforcing cages, to guarantee the correct position of reinforcing cage, guarantees that protective layer thickness meets the requirements;

Step 15, madjack pipe tries the water: should do the test of trying the water when every joint madjack pipe is transferred with reinforcing cage, if find that water column descends or water column disappears, should check then whether madjack pipe has sand holes, screwed connection whether to seal;

Reinforcing cage is placed and is carried out in the metapore that finishes needing again the water surface in the inspection eye after the second time, finished in clear hole, and it is suitable for reading that no abnormal back seals madjack pipe with plug;

Step 10 six, concreting: with putting a slide tube concreting, before putting the slide tube, check and measure the thickness of loosened soil in the boring again, carry out when reaching designing requirement, concreting is adopted and is carried out continuously, when concreting is pushed up to the stake of castinplace pile, should suitably surpass the stake top design elevation of castinplace pile, to guarantee that after cutting laitance the stake top mark height of castinplace pile adheres to specification; Simultaneously, make the test block of same match ratio, per tour must not be less than one group;

Step 10 seven, packer permeability test: packer permeability test carries out in 24 hours behind pile, must carry out packer permeability test before the formal mud jacking, to check the unimpeded situation of pipeline and one way valve, if during the situation that in stake side or stake end reaming takes place, collapse hole or fullness coefficient is bigger, need pay special attention to carry out in advance packer permeability test, carry out guaranteeing to wash open thicker concrete coating in concreting in intact 5 hours; Break through force value and the unimpeded situation of pipeline by special messenger's record during test;

Step 10 eight, repeating step 14, step 15, step 10 six, step 10 seven are finished the pile work of each castinplace pile, are the ready work of back mud jacking construction simultaneously;

Step 10 nine, back mud jacking construction: take the mode of secondary grouting, comprising:

(1) just annotate: the concrete curing of castinplace pile pile body began mud jacking after 3～5 days, at the bottom of will being injected into by high-pressure pump and pre-buried madjack pipe by the good cement paste of design configurations or go in the stake side soil layer, if adopt compound mud jacking, then carry out a side pressure slurry earlier, carry out pile base grouting after 12 hours again; Pressure is little when just annotating, slurries by rare to thick; To keep a close eye on the variation of grouting pressure, grouting amount when just annotating, and note slip casting rhythm, should arrange during pile grouting dial gage detect stake on the amount of lifting, avoid excessive;

(2) secondary grouting: the Grouting Pipe of slip casting for the second time is symmetrically distributed with the Grouting Pipe of slip casting for the first time, and grouting amount is generally primary 1 ∕, 3～1 ∕ 4 for the second time, and water/binder ratio suitably improves;

(3) mud jacking of same pile order: earlier last side pipe is carried out mud jacking, descend side pipe then, hold the pipe mud jacking at last; The mud jacking order of same cushion cap stake: stake rear center stake earlier;

Step 2 ten stops mud jacking: the total control principle that stops mud jacking is that pressure is controlled to be auxilliary based on the mud jacking amount, but the mud jacking parameter is according to the geological conditions choose reasonable, if the stake end during for closely knit gravel boulder bed, should be the major control index with the mud jacking amount; The stake side should be the major control index with mud jacking pressure then when being closely knit loess formation;

After mud jacking finishes immediately to the madjack pipe plug of screwing on, in order to avoid reduce squeezing quality because of overfall;

Step 2 11, repeating step 19, step 2 ten are finished the construction working of each filling pile ' s after grouting continuously.

2. the method for claim 1 is characterized in that, the filler of described pile is not selected fragment of brick, rubble, concrete block or other bulk stiff materials for use.

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