CN113982022A - Construction method for eliminating collapsibility of cement stirring insertion pile in collapsible loess area - Google Patents
Construction method for eliminating collapsibility of cement stirring insertion pile in collapsible loess area Download PDFInfo
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- CN113982022A CN113982022A CN202111218682.XA CN202111218682A CN113982022A CN 113982022 A CN113982022 A CN 113982022A CN 202111218682 A CN202111218682 A CN 202111218682A CN 113982022 A CN113982022 A CN 113982022A
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- E—FIXED CONSTRUCTIONS
- E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
- E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
- E02D27/00—Foundations as substructures
- E02D27/32—Foundations for special purposes
- E02D27/34—Foundations for sinking or earthquake territories
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- E—FIXED CONSTRUCTIONS
- E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
- E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
- E02D15/00—Handling building or like materials for hydraulic engineering or foundations
- E02D15/02—Handling of bulk concrete specially for foundation or hydraulic engineering purposes
- E02D15/04—Placing concrete in mould-pipes, pile tubes, bore-holes or narrow shafts
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- E—FIXED CONSTRUCTIONS
- E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
- E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
- E02D5/00—Bulkheads, piles, or other structural elements specially adapted to foundation engineering
- E02D5/22—Piles
- E02D5/34—Concrete or concrete-like piles cast in position ; Apparatus for making same
- E02D5/46—Concrete or concrete-like piles cast in position ; Apparatus for making same making in situ by forcing bonding agents into gravel fillings or the soil
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- E—FIXED CONSTRUCTIONS
- E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
- E02D—FOUNDATIONS; EXCAVATIONS; EMBANKMENTS; UNDERGROUND OR UNDERWATER STRUCTURES
- E02D2250/00—Production methods
- E02D2250/0023—Cast, i.e. in situ or in a mold or other formwork
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Abstract
The invention discloses a construction method for eliminating collapsible property of a cement stirring inserted pile in a collapsible loess area, which comprises the following steps of stirring for three times during construction of the cement stirring inserted pile, stirring for one time: in the depth of the bearing stratum and the non-collapsible soil stratum, the stirring pile is mechanically stirred and ascended by spraying cement slurry; in the depth of the collapsible loess layer, the stirring pile rises mechanically by spraying water, and the stirring pile rises to the ground and stops; and (3) secondary stirring: performing secondary stirring and sinking on the stirred soil layer, spraying water on the collapsible loess layer while stirring and sinking, and spraying cement slurry on the bearing layer and the non-collapsible soil layer while sinking; stirring for three times: stirring and rising the stirred soil layer for three times, spraying cement slurry and rising the soil layer while spraying water on the bearing layer and the non-collapsible soil layer, spraying water and stirring and rising the soil layer while spraying water on the collapsible loess layer, wherein the stirring soil around the pile needs to reach the saturated water content, and the construction of the stirring pile is finished.
Description
Technical Field
The invention belongs to the technical field of construction, and particularly relates to a construction method for eliminating collapsibility of cement stirring inserted piles in collapsible loess areas.
Background
The loess coverage area in China is wide, and is as high as 60 square kilometers, wherein the collapsible loess coverage area accounts for about three quarters of the total area of the loess, and is mainly distributed in Shanxi, Shaanxi, Gansu and other areas. The loess coverage depth in the areas can reach more than 100m, wherein the thickness of the collapsible loess can reach 20-30 m. The collapsible loess has a collapsible deformation with a large deformation amount and a high deformation speed after being soaked by water under a certain pressure, and has an abrupt property and non-uniformity. If a building or a structure is directly constructed on the collapsible loess natural foundation, an engineering accident which is difficult to predict is often generated.
The most economical and safe method for building buildings and structures on the fields with large loess thickness is to adopt medium-long piles, long piles and even ultra-long pile foundations to enable pile foundations to penetrate through collapsible loess layers and directly support the collapsed loess layers on bearing layers meeting design requirements. The cement mixing inserting pile technology is just in time suitable for the large-thickness loess area, and the prestress high-strength pipe pile is inserted into the cement mixing soil, so that the pile body is surrounded by the cement mixing soil, the bearing capacity of the pile body is improved, and the prestress high-strength pipe pile has the effect of compacting the surrounding soil body in the inserting process, so that the collapsibility of partial collapsible loess can be eliminated. In addition, the cement stirring pile inserting technology can avoid the condition that the pile body bearing is influenced by over-thick sediment at the pile bottom in the construction process. However, in the heavy-thickness self-weight collapsible loess area, particularly in the loess field with the foundation collapse grade of III grade or IV grade, when the pile body passes through the collapsible loess layer, when the collapsible loess is collapsed and deformed, the pile side can be subjected to larger negative friction resistance, the bearing capacity of the pile body is influenced, and even the pile body is changed from being pressed into being pulled, and the pile body is damaged by being pulled. In addition, the side frictional resistance of the cement mixing inserted pile and the soil around the pile is larger than that of a common concrete pile, and the tensile strength of the cement mixing soil is lower, so that the influence of the negative frictional resistance on the cement mixing inserted pile is aggravated.
According to collapsible loess area building standard GB50025-2018, a common treatment method for collapsible loess foundation comprises the following steps: bedding method, dynamic compaction method, compaction method and pre-soaking method. Wherein, the cushion method can only treat the collapsibility of shallow loess above the ground water level, and the dynamic compaction method and the compaction method can only treat the collapsibility of loess with the thickness of 12-15 m above the ground water level. The presoaking method can eliminate the self-weight collapsibility and the collapsibility of the loess field with grade III or grade IV below 6 m. However, the traditional pre-soaking method has long construction time, the depth of a water injection hole is limited, and the bearing capacity of the treated foundation is low.
Disclosure of Invention
The invention provides a construction method for eliminating collapsibility of cement mixing insertion piles in collapsible loess areas, and aims to solve the technical problems.
Therefore, the invention adopts the following technical scheme:
a construction method for eliminating collapsibility of a cement mixing insertion pile in a collapsible loess area specifically comprises the following steps:
1) leveling the site before construction, measuring and lofting according to a design drawing, and calibrating the position of each cement mixing pile;
2) determining the range and degree of elimination of negative friction resistance at the pile side of the cement stirring inserted pile according to a geological survey report and upper structure requirements, thereby determining the collapsible treatment area, depth and residual collapsible amount of the collapsible loess layer around the pile;
3) according to the position calibrated by the cement mixing pile in the step 1), mechanically feeding and positioning the mixing pile, and starting the mechanical pre-mixing of the mixing pile to sink to the designed depth;
4) primary stirring: in the depth of the bearing stratum and the non-collapsible soil stratum, the stirring pile is mechanically stirred and ascended by spraying cement slurry; in the depth of the collapsible loess layer, the stirring pile rises mechanically by spraying water, and the stirring pile rises to the ground and stops;
5) and (3) secondary stirring: performing secondary stirring and sinking on the stirred soil layer, spraying water on the collapsible loess layer while stirring and sinking, and spraying cement slurry on the bearing layer and the non-collapsible soil layer while sinking;
6) stirring for three times: stirring and rising the stirred soil layer for three times, spraying cement slurry and rising at the same time on a bearing layer and a non-collapsible soil layer, spraying water and stirring and rising at the same time on a collapsible loess layer, and finishing the construction of a stirring pile;
7) pipe pile construction: positioning the prestressed high-strength concrete pipe pile, and inserting the prestressed high-strength concrete pipe pile into the stirring pile drilled in the step 6); when the pile is inserted, the prestressed high-strength concrete pipe pile is required to be kept upright, the axis of the pile is overlapped with the axis of the mixing pile until the pile is inserted into the bearing layer, and then concrete is poured into the prestressed high-strength concrete pipe pile;
8) repeating the steps 3) -7), and constructing the cement mixing piles at other positions;
9) after the collapsible deformation and the consolidation deformation of the soil layer around the pile are stable, a sandy soil cushion is laid at the collapsible deformation position around the pile, and the thickness of the sandy soil cushion is required to reach the height of the top of the pile inserted by cement stirring so as to meet the requirements of constructing a raft or other foundation forms, and the construction is finished.
Furthermore, the cement soil mixing pile is constructed by adopting a triaxial cement soil slurry mixing method, the mixing pile with the construction depth larger than 30m adopts a rod connecting process, and the verticality deviation of the guide frame is not larger than 1/250.
Further, the water cement ratio of the cement slurry of the triaxial cement mixing pile is 1.5-2.0.
Furthermore, a flow pump for controlling the slurry conveying speed is arranged on the stirring pile machinery, and the outlet pressure of the grouting pump of the cement stirring machine in the steps 4), 5) and 6) is 0.4-0.6 Mpa.
Further, when the cement mixer is stirred and sinks, namely in the steps 3) and 5), the sinking speed is 0.5-1.0 m/min; when the cement mixer is stirred and ascended, namely in the steps 4) and 6), the ascending speed is 1.0-2.0 m/min, and the cement mixer is kept sinking or ascending at a constant speed.
Furthermore, the rotating speed of the drill bit of the cement mixer is 23-26 r/min.
The invention has the beneficial effects that:
1. according to the invention, the collapsible loess layer around the pile is fully stirred to a saturated state, so that the collapsible loess layer is subjected to collapsible deformation in advance, and the cement stirring pile is prevented from generating large negative friction resistance due to the collapsible loess collapsible deformation around the pile in the normal use process; therefore, the effect of the positive frictional resistance around the pile on the vertical bearing force can be properly improved, the situation that cement mixing soil around the pile is pulled to crack is avoided, the bearing force of the pile body is improved, and the application situation of the cement mixing inserted pile in a large-thickness self-weight collapsible loess area is improved;
2. the invention can eliminate the collapsibility of the self-weight collapsible loess below 6m and weaken the collapsibility of the part above 6m, thereby eliminating the negative friction force generated on the pile body when the self-weight collapsible loess is collapsed and deformed, increasing the positive friction force on the pile side in the collapsible loess soil layer range, improving the bearing capacity of the pile body and avoiding the condition that the cement mixing soil around the pile is pulled to crack;
3. compared with the traditional pre-soaking method, the method omits the process of transferring moisture to the deep collapsible loess layer through the reservoir or the sand well, greatly shortens the construction period, and is economic, safe and simple to operate.
Drawings
FIG. 1 is a schematic view of the arrangement of a cement mixing insert according to the present invention;
FIG. 2 is a schematic view of the construction process of the present invention 1;
FIG. 3 is a schematic illustration of the construction process of the present invention 2;
FIG. 4 is a schematic illustration of an insertion section of a prestressed concrete pipe pile according to the present invention;
FIG. 5 is a schematic cross-sectional view of a cement mixing insert pile of the present invention after construction;
Detailed Description
The invention will be further described with reference to the following drawings and specific embodiments:
a construction method for eliminating collapsibility of a cement mixing insertion pile in a collapsible loess area specifically comprises the following steps:
1) the site is leveled before construction, and the positions of the cement mixing piles are calibrated according to the measurement and lofting of a design drawing (as shown in figure 1).
2) According to the geological survey report and the upper structure requirement, determining the range and the degree of eliminating the negative friction resistance at the pile side of the cement stirring inserted pile according to the technical Specification of building pile foundations (JGJ 94-2008) and the building Standard of collapsible loess areas (GB 50025-2018), thereby determining the collapsible processing area, depth and residual collapsible amount of the collapsible loess layer around the pile.
3) The cement mixing pile is preferably constructed by adopting a triaxial cement slurry mixing method, the mixing pile with the construction depth of more than 30m is preferably constructed by adopting a rod connecting process, and the verticality deviation of the guide frame is not more than 1/250; the water-cement ratio of cement slurry of the triaxial cement mixing pile is preferably 1.5-2.0, the prepared slurry cannot be separated, the pumping is continuous, and an automatic pressure flow recorder is adopted; and then mechanically entering and positioning the mixing pile according to the position calibrated by the cement mixing pile in the step 1), and starting the mechanical pre-mixing of the mixing pile to sink to the designed depth.
4) Primary stirring: in the depth of the bearing stratum and the non-collapsible soil stratum, the stirring pile is mechanically stirred and ascended by spraying cement slurry; within the depth of the collapsible loess layer, the stirring pile is lifted up by spraying water mechanically and stopped when the stirring pile is lifted to the ground (as shown in fig. 2).
5) And (3) secondary stirring: the stirred soil layer is stirred for the second time and sinks, the collapsible loess layer is sprayed with water while being stirred, and the bearing layer and the non-collapsible soil layer are sprayed with cement paste while being sunk (as shown in figure 2).
6) Stirring for three times: stirring and rising the stirred soil layer for three times, spraying cement slurry and rising the soil layer while spraying water on the bearing layer and the non-collapsible soil layer, spraying water and stirring and rising the soil layer while spraying water on the collapsible loess layer, wherein the stirring soil around the pile needs to reach the saturated water content, and the construction of the stirring pile is finished (as shown in figure 3);
wherein, the outlet pressure of the grouting pump of the cement mixer in the steps 4), 5) and 6) is 0.4-0.6 Mpa; when the cement mixer is stirred and sinks, namely in the steps 3) and 5), the sinking speed is 0.5-1.0 m/min; when the cement mixer is stirred and ascended, namely in the steps 4) and 6), the ascending speed is 1.0-2.0 m/min, and the uniform sinking or ascending is kept; the rotating speed of the drill bit of the cement mixer is 23-26 r/min.
7) Pipe pile construction: positioning the prestressed high-strength concrete pipe pile, and inserting the prestressed high-strength concrete pipe pile into the stirring pile drilled in the step 6); when the pile is inserted, the prestressed high-strength concrete pipe pile needs to be kept upright, the axis of the pile is overlapped with the axis of the mixing pile until the pile is inserted into the supporting layer, then concrete is poured into the prestressed high-strength concrete pipe pile, and the filling needs to be compact (as shown in fig. 4);
the type of the pile pressing machine and the selection of the balance weight are determined according to factors such as geological conditions, pile types, pile density, vertical bearing capacity of a single pile, existing construction conditions and the like, the designed pile pressing force is not more than 0.9 time of the weight of the frame and the balance weight, and the pile pressing force is driven into a pile core of the cement mixing pile and inserted into a bearing layer for a certain distance; the final pressure control standard of the static pressure pile is mainly elevation, pressure is auxiliary, the number of continuous final pressure re-pressing times can be 2-3, the pressure stabilizing pile pressing force is not less than the final pressure, and the pile stabilizing time is preferably 5-10 s.
8) And repeating the steps 3) to 7) to construct the cement mixing piles at other positions.
9) Observing collapsible deformation and consolidation deformation of a soil layer around the pile, and according to collapsible loess area building standards, the standard of collapsible deformation stability is that the average collapsible amount of the last 5 days is less than 1mm/d, which indicates that the pile body is qualified; after the collapsible deformation and the consolidation deformation of the soil layer around the pile are stable, a sandy soil cushion is laid at the collapsible deformation position around the pile, and the thickness of the sandy soil cushion is required to reach the height of the top of the pile inserted with cement stirring so as to meet the requirements of constructing a raft or other foundation forms, and the construction is finished (as shown in figure 5).
Claims (6)
1. A construction method for eliminating collapsibility of a cement mixing insertion pile in a collapsible loess area is characterized by comprising the following steps of:
1) leveling the site before construction, measuring and lofting according to a design drawing, and calibrating the position of each cement mixing pile;
2) determining the range and degree of elimination of negative friction resistance at the pile side of the cement stirring inserted pile according to a geological survey report and upper structure requirements, thereby determining the collapsible treatment area, depth and residual collapsible amount of the collapsible loess layer around the pile;
3) according to the position calibrated by the cement mixing pile in the step 1), mechanically feeding and positioning the mixing pile, and starting the mechanical pre-mixing of the mixing pile to sink to the designed depth;
4) primary stirring: in the depth of the bearing stratum and the non-collapsible soil stratum, the stirring pile is mechanically stirred and ascended by spraying cement slurry; in the depth of the collapsible loess layer, the stirring pile rises mechanically by spraying water, and the stirring pile rises to the ground and stops;
5) and (3) secondary stirring: performing secondary stirring and sinking on the stirred soil layer, spraying water on the collapsible loess layer while stirring and sinking, and spraying cement slurry on the bearing layer and the non-collapsible soil layer while sinking;
6) stirring for three times: stirring and rising the stirred soil layer for three times, spraying cement slurry and rising at the same time on a bearing layer and a non-collapsible soil layer, spraying water and stirring and rising at the same time on a collapsible loess layer, and finishing the construction of a stirring pile;
7) pipe pile construction: positioning the prestressed high-strength concrete pipe pile, and inserting the prestressed high-strength concrete pipe pile into the stirring pile drilled in the step 6); when the pile is inserted, the prestressed high-strength concrete pipe pile is required to be kept upright, the axis of the pile is overlapped with the axis of the mixing pile until the pile is inserted into the bearing layer, and then concrete is poured into the prestressed high-strength concrete pipe pile;
8) repeating the steps 3) -7), and constructing the cement mixing piles at other positions;
9) after the collapsible deformation and the consolidation deformation of the soil layer around the pile are stable, a sandy soil cushion is laid at the collapsible deformation position around the pile, and the thickness of the sandy soil cushion is required to reach the height of the top of the pile inserted by cement stirring so as to meet the requirements of constructing a raft or other foundation forms, and the construction is finished.
2. The construction method for eliminating collapsibility of a cement mixing inserted pile in a collapsible loess area as claimed in claim 1, wherein the cement mixing pile is constructed by a triaxial cement slurry mixing method, the mixing pile with a construction depth of more than 30m is constructed by a rod connecting process, and the verticality deviation of the guide frame is not more than 1/250.
3. The collapsible loess area cement mixing insert pile construction method as set forth in claim 2, wherein the cement paste ratio of the triaxial cement mixing pile is 1.5-2.0.
4. The collapsible loess area cement mixing inserting pile construction method for eliminating the collapsible property as claimed in claim 1, wherein a flow pump for controlling the slurry conveying speed is provided on the mixing pile mechanism, and the outlet pressure of the slurry pump of the cement mixer in steps 4), 5) and 6) is 0.4-0.6 Mpa.
5. The collapsible loess area cement mixing and inserting pile construction method as set forth in claim 1, wherein the sinking speed of the cement mixer is 0.5-1.0 m/min during the mixing sinking, i.e., in steps 3) and 5); when the cement mixer is stirred and ascended, namely in the steps 4) and 6), the ascending speed is 1.0-2.0 m/min, and the cement mixer is kept sinking or ascending at a constant speed.
6. The collapsible loess area cement mixing inserted pile construction method as set forth in claim 1, wherein the rotation speed of the drill of the cement mixer is 23-26 r/min.
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| CN202111218682.XA CN113982022A (en) | 2021-10-20 | 2021-10-20 | Construction method for eliminating collapsibility of cement stirring insertion pile in collapsible loess area |
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2021
- 2021-10-20 CN CN202111218682.XA patent/CN113982022A/en active Pending
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| WO2020244123A1 (en) * | 2019-06-04 | 2020-12-10 | 东南大学 | Method for treating collapsible loess foundation with vibration rod compaction |
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