Red layer high fill foundation PS-C double grouting micro pile settlement control method

Abstract

The present application belongs to the technical field of red layer area reinforcement, and discloses a PS-C double grouting micro pile settlement control method for red layer high fill foundation, in order to solve the problem that the red layer high fill cannot accurately obtain the grouting amount in the micro steel pipe pile, resulting in poor pouring quality and settlement exceeding the reasonable range. The present application comprises the following steps: measuring and releasing, drilling and forming a hole, cleaning the pile hole, and implanting a micro steel pipe, wherein the micro steel pipe is provided with a grouting pipe; further comprising the following steps: (1) filling gravel; (2) injecting slurry through the grouting pipe. The present application can accurately obtain the underground grouting condition, thereby improving the grouting pipe to improve the pouring quality, on the one hand, and on the other hand, the double pipe grouting mode can increase the permeability of the slurry, thereby improving the bonding and fastening of the red layer around the steel pipe pile, further reducing the settlement and improving the reinforcement quality.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of red layer area reinforcement, and particularly relates to a red layer high fill foundation PS-C double grouting micro pile settlement control method for reinforcing a red layer high fill area. BACKGROUND

[0002] With the rapid development of social economy, infrastructure construction gradually extends to mountainous areas. Due to the limitation of topography and geomorphology conditions, especially under the premise of farmland area guarantee, land resource saving becomes an important basic principle. However, in the process of construction in mountainous areas, it is inevitable to "cut mountains and fill valleys" and "deeply dig and high fill", and large-area, large-scale and large-thickness filling engineering has become common, which brings about major engineering geological problems such as high fill foundation stability, deformation and settlement, and foundation treatment.

[0003] The development of Cheng-Yu region is in full swing, especially the Cheng-Yu region double-city economic circle construction is accelerating, and the modern infrastructure network is being improved, and large-scale infrastructure construction is accelerating. The region is mainly in the Sichuan Basin, and the topography and geomorphology are hilly and mountainous areas, which belong to the core area of the southwest red layer. A large number of red layer high fill engineering is involved in the construction, in order to improve economic efficiency, save land resources and prevent environmental pollution, red layer mixed soil and stone materials are often used as filling materials. The red layer is a kind of special rock and soil with complex mechanical properties, strong water sensitivity, easy disintegration and easy softening, and the red layer soil and stone mixture as a C-type filler makes the problem of uneven settlement of the filling site more serious.

[0004] The red layer area high fill engineering has the characteristics of high fill height, large fill amount, short construction period, rapid loading and poor uniformity of fillers, and the red layer soil and stone mixture high fill foundation treatment has become a key problem in construction.

[0005] However, in the prior art, when the deep thick backfill foundation in the red layer area is treated, high-energy level dynamic compaction, anchor static pressure pile, cast-in-place pile, high-pressure jet grouting and other methods are often used, but these measures have the disadvantages of long construction period, complex process, high cost and environmental pollution.

[0006] Micro steel pipe piles have the characteristics of short construction period and low construction cost, so they have been widely used in foundation reinforcement. The construction process (or process flow) of micro steel pipe piles includes: site leveling-steel pipe pile fabrication and welding-measuring and laying out- hole spacing positioning-drill rig positioning (connecting drill rod every 2m)-cleaning the drill hole-installing the grouting machine-lowering the steel pipe to the designed elevation-installing the grouting pipe-filling with fine stones-sealing the top- mixing cement slurry-grouting cement slurry-secondary pressure grouting. During the grouting process of the micro steel pipe pile, the grouting pipe needs to be gradually raised upwards, and orderly pipe raising and continuous grouting are the key to ensuring the quality of the pile.

[0007] But for red layer high fill, even if the uniform upward to the pipe way to lift the grouting pipe, but due to the red layer land uniformity poor caused by red layer high fill area at different height position of the cement slurry dosage of penetration, so the prior art using uniform lifting grouting pipe way will still appear red layer high fill due to the cement slurry injection is not enough to cause poor quality and appear beyond the reasonable range of settlement.

[0008] There is also in the prior art according to the grouting quantity to lift the grouting pipe, this way is according to the size of the borehole to calculate the dosage (i.e. design grouting quantity), lifting grouting pipe is also in accordance with the actual grouting quantity and design grouting quantity to judge whether to lift the grouting pipe. This way is the same as the uniform lifting grouting pipe way described above, due to the poor uniformity of red layer high fill soil, resulting in the actual grouting quantity can not be accurately calculated, so also appear to cement slurry injection is not enough to cause poor quality and appear beyond the reasonable range of settlement. SUMMARY

[0009] In order to solve the problem of poor quality and excessive settlement of red layer high fill due to the inability to accurately obtain the grouting quantity in the micro steel pipe pile, a PS-C double grouting micro pile settlement control method for red layer high fill foundation is provided. On the one hand, it can accurately obtain the underground grouting condition and improve the grouting pipe to improve the pouring quality. On the other hand, the double pipe grouting method can increase the permeability of the slurry, thereby improving the bonding and fastening of the red layer around the steel pipe pile, further reducing the settlement and improving the quality of reinforcement.

[0010] To solve the technical problem, the technical solution adopted by the present application is:

[0011] A PS-C double grouting micro pile settlement control method for red layer high fill foundation, comprising the steps of measuring and laying out, drilling and forming a hole, cleaning the pile hole, and implanting a micro steel pipe into the pile hole, characterized in that a grouting pipe is installed in the micro steel pipe, and the grouting pipe is implanted into the pile hole together with the micro steel pipe; the step of implanting the micro steel pipe into the pile hole is followed by the following steps:

[0012] (1) filling the space between the outer wall of the grouting pipe and the inner wall of the micro steel pipe, and the space between the micro steel pipe and the inner wall of the pile hole with gravel;

[0013] (2) injecting slurry through the grouting pipe;

[0014] The grouting pipe comprises an outer grouting pipe and an inner grouting pipe, a plurality of grouting holes are arranged on the circumferential wall of the outer grouting pipe, and two strip-shaped slits are arranged on the outer grouting pipe along the length direction of the outer grouting pipe; the inner grouting pipe is sleeved in the outer grouting pipe and can move up and down in the outer grouting pipe; a casing is arranged at the lower end of the inner grouting pipe, the casing is in sliding sealing with the outer grouting pipe, the upper end of the casing extends upward to form a sealed annular cavity between the inner wall of the casing and the outer wall of the inner grouting pipe, a plurality of through holes are arranged on the lower end surface of the casing and are in communication with the annular cavity, the upper end of the casing is connected with a first input pipe for injecting PS solution, and a pressure sensor is arranged on the outer circumferential wall of the casing and corresponds to the position of the strip-shaped slit.

[0015] In some embodiments, in the process of grouting by using the grouting pipe in step (2), when the monitoring value monitored by the pressure sensor exceeds the set value, the inner grouting pipe and the casing are uniformly lifted upward by a distance and stay until the monitoring value of the pressure sensor exceeds the set value again; the process is repeated until the grouting is completed.

[0016] In some embodiments, when grouting by using the through holes on the casing and the inner grouting pipe, the cement slurry injected by the inner grouting pipe is synchronized with the PS solution injected by the through holes, and the volume ratio of the PS solution to the cement slurry is 0.2:1.

[0017] In some embodiments, the lower end of the inner grouting pipe extends out of the lower end surface of the casing, a grouting hole is arranged on the side wall of the inner grouting pipe extending out of the lower end surface of the casing and is arranged along the radial direction of the inner grouting pipe, and the grouting hole corresponds to the position of the through hole of the casing. Thus, the cement slurry sprayed from the inner grouting pipe can directly impact and mix with the PS solution flowing out of the through hole, further ensuring the uniformity of the mixing of the cement slurry and the PS solution.

[0018] In some embodiments, after the grouting by using the inner grouting pipe and the casing is completed, the inner grouting pipe and the casing are pulled upward, and then the top of the micro steel pipe is sealed, and then the outer grouting pipe is used for pressurized grouting, and the slurry pressure during the pressurized grouting is greater than the pressure during the grouting by using the inner grouting pipe and the casing.

[0019] In some embodiments, during the pressurized grouting by using the outer grouting pipe (i.e., the second grouting), the slurry during the grouting is a mixed slurry of the cement slurry and the PS solution.

[0020] In some embodiments, the outer grouting pipe is fixed in the micro steel pipe by connecting steel bars. Thus, the micro steel pipe and the outer grouting pipe are connected to form an integral whole by the connecting steel bars, further improving the bending strength of the pile foundation.

[0021] Compared with the prior art, the present application has the following beneficial effects:

[0022] The red layer high fill foundation PS-C double grouting micro pile settlement control method of the present application obtains the liquid level position of the slurry in the pile hole through the pressure sensor on the casing, and judges whether to lift the inner grouting pipe according to the same. It has the advantages of simple and reliable distinguishing method. At the same time, since the pressure sensor and the inner grouting pipe move synchronously, the pressure sensor can monitor at all times until the grouting is completed. Compared with the prior art which calculates the grouting amount in advance and lifts the grouting pipe, the present application controls the lifting of the inner grouting pipe through the pressure sensor, so as to ensure that the gaps at different height positions of the red layer high fill (due to the poor uniformity of the red layer, the gaps are different) can be fully filled with slurry, thereby improving the grouting quality of the red layer high fill, and ultimately reducing the amount of settlement of the red layer high fill, so that the amount of settlement of the red layer high fill is within a reasonable range.

[0023] At the same time, the present application uses the double grouting method of PS solution and cement slurry, which can improve the strength after grouting, and further improve the bonding strength between the red layer high fill (i.e. the soil around the pile) and the steel pipe pile, and further improve the pile quality. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 It is a structure schematic view when the outer grouting pipe and the inner grouting pipe of the present application are sleeved in the micro steel pipe;

[0025] Figure 2 It is a structure schematic view when the outer grouting pipe and the inner grouting pipe of the present application are sleeved in the micro steel pipe; Figure 1 It is a local enlarged view schematic view of A;

[0026] Figure 3 It is a transverse cross-sectional view schematic view after pouring of the present application;

[0027] Figure 4 It is another transverse cross-sectional view schematic view after pouring of the present application;

[0028] Markings in the figure: 1, pile hole, 2, micro steel pipe, 3, outer grouting pipe, 31, strip-shaped joint, 4, inner grouting pipe, 41, grouting hole, 5, casing, 51, through hole, 6, annular cavity, 7, pressure sensor, 8, first input pipe, 9, second input pipe, 10, connecting steel bar, 11, set stone. DETAILED DESCRIPTION

[0029] The present application will be further described below in conjunction with the embodiments, and the described embodiments are only a part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, other embodiments obtained by those skilled in the art without creative labor also belong to the protection scope of the present application.

[0030] In the description of the present application, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application; the terms "first", "second", "third" are only for the purpose of description, and cannot be understood as indicating or implying relative importance; in addition, unless otherwise explicitly specified and limited, the terms "mounting", "connecting", "connecting" should be understood in a broad sense, for example, it can be fixedly connected, or it can be detachably connected, or integrally connected; it can be directly connected, or indirectly connected through an intermediate medium. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0031] The PS-C double grouting micro pile settlement control method for red layer high fill foundation of the present application in combination with the drawings comprises the following steps: a measuring and releasing procedure, a drilling and hole forming procedure, a pile hole cleaning procedure, and a procedure of implanting a micro steel pipe 2 into the pile hole 1, wherein a grouting pipe is installed in the micro steel pipe 2, and the grouting pipe is implanted into the pile hole 1 together with the micro steel pipe 2; the procedure of implanting the micro steel pipe 2 into the pile hole 1 is followed by the following steps in sequence:

[0032] (1) filling gravel 11 between the outer wall of the grouting pipe and the inner wall of the micro steel pipe 2, and between the micro steel pipe 2 and the inner wall of the pile hole 1;

[0033] (2) injecting slurry through the grouting pipe;

[0034] The grouting pipe comprises an outer grouting pipe 3 and an inner grouting pipe 4, a plurality of grouting holes are formed on the circumferential wall of the outer grouting pipe 3, and two strip-shaped slits 31 are formed on the outer grouting pipe 3 along the length direction of the outer grouting pipe 3; the inner grouting pipe 4 is sleeved on the inside of the outer grouting pipe 3 and can move up and down in the outer grouting pipe 3; a casing 5 is installed on the lower end of the inner grouting pipe 3, and the casing 5 is in sliding sealing contact with the outer grouting pipe 3, wherein a sealing ring is installed on the outer circumferential wall of the casing 5 to realize sealing contact with the outer grouting pipe 3; the upper end of the casing 5 extends upward so that a sealed annular cavity 6 is formed between the inner wall of the casing 5 and the outer wall of the inner grouting pipe 4; a plurality of through holes 51 are formed on the lower end face of the casing 5 and are in communication with the annular cavity 6; a first input pipe 8 for injecting PS solution is connected to the upper end of the casing 5; a pressure sensor 7 is installed on the outer circumferential wall of the casing 5 corresponding to the position of the strip-shaped slits 31; and a second input pipe 9 for injecting cement slurry is connected to the upper end of the inner grouting pipe 4.

[0035] In the implementation process, the sealing ring is arranged on the casing 51 on the upper side and the lower side of the pressure sensor 7, which is used for protecting the pressure sensor 7, and prevents the slurry from contacting the pressure sensor through the gap between the casing 5 and the outer grouting pipe 3, so as to ensure that the slurry contacted by the pressure sensor is only the slurry passing through the strip-shaped joint 31 along with the rising of the slurry surface. Even if it is said that the pressure sensor contacts the slurry pressure, it means that the slurry surface has been higher than the lower end surface of the casing 5. That is, the installation position of the pressure sensor 7 is higher than the position of the upper end surface of the through hole 5 on the casing 5.

[0036] Among them, the process of measuring the pay-off, the process of drilling into the hole, the process of cleaning the pile hole, and the process of implanting the micro steel pipe into the pile hole all belong to the prior art, and those skilled in the art can understand and understand; At the same time, it is not the improvement point of the present application, so it will not be repeated.

[0037] In the construction process of the present application, firstly, the space between the outer wall of the micro steel pipe and the outer wall of the grouting pipe (the outer wall of the grouting pipe is the outer wall of the outer grouting pipe), and the space between the outer wall of the micro steel pipe and the pile hole are filled with rice stones, and then the cement slurry is input through the inner grouting pipe, and the cement slurry is poured out from the lower end of the inner grouting pipe and fills and extrudes the gap between the rice stones, and at the same time passes through the flower hole on the steel pipe pile and impacts and extrudes the pile hole, so that the cement slurry enters the gap in the red layer and fills and extrudes the gap in the red layer; At the same time, the PS solution input through the first input pipe is poured out from the through hole at the lower end of the casing, and together with the cement slurry, it extrudes and fills the red layer, so as to realize the pouring of the micro steel pipe pile. When the cement slurry and the PS solution are poured into the space between the rice stones and the space in the red layer at the same time by the inner grouting pipe and the casing, the slurry surface formed by the cement slurry and the PS solution together will gradually rise and be in contact and extrusion with the pressure sensor through the strip-shaped joint, and the installation of the pressure sensor is slightly higher than the lower end surface of the casing, so that the liquid level position of the slurry (that is, the distance between the slurry surface and the lower end surface of the casing) can be directly obtained by using the pressure sensor. That is to say, when the pressure sensor detects the pressure (or when the pressure changes, the pressure applied to the pressure sensor by the slurry will change, and the higher the height difference between the slurry surface and the pressure sensor, the greater the pressure value applied to the pressure sensor by the slurry), it means that the grouting of this section has been completed (the slurry (that is, the cement slurry and the PS solution) has filled the gap in the red layer of this section) and the inner grouting pipe needs to be lifted upward, and the casing is lifted upward synchronously when the inner grouting pipe is lifted upward, and the operation is repeated to complete the PS (that is, the PS solution)-C (cement slurry) double grouting operation.

[0038] The present application obtains the liquid level position of the slurry in the pile hole through the pressure sensor on the protection cylinder, and judges whether to lift the inner grouting pipe according to the liquid level position, and has the advantages of simple and reliable distinguishing mode. At the same time, since the pressure sensor and the inner grouting pipe move synchronously, the pressure sensor can be monitored until the grouting is completed. Compared with the prior art which calculates the grouting amount in advance and lifts the grouting pipe, the present application controls the lifting of the inner grouting pipe through the pressure sensor, so that the gaps at different height positions of the red layer high fill (due to the poor uniformity of the red layer, the gaps are different) can be fully filled with slurry, thereby improving the grouting quality of the red layer high fill, and finally reducing the settlement amount of the red layer high fill, so that the settlement amount of the red layer high fill is within a reasonable range.

[0039] At the same time, the present application uses the double grouting mode of PS solution and cement slurry to improve the strength after grouting, thereby improving the bonding strength between the red layer high fill (i.e. the soil around the pile) and the steel pipe pile, and further improving the pile quality.

[0040] The mechanism of the PS-C double slurry formed by the PS solution (i.e. potassium silicate solution, also known as potassium water glass) and the cement slurry to improve the strength is as follows.

[0041] The main mineral components of the cement in the cement slurry are as follows:

[0042] Dicalcium silicate: 2(2CaO·SiO2)+4H2O→3CaO·2SiO2·3H2O+Ca(OH)2;

[0043] Tricalcium silicate: 3CaO·SiO2+nH2O→2CaO·SiO2·(n-1)H2O+Ca(OH)2;

[0044] Tricalcium aluminate: 3CaO·Al2O3+6H2O→3CaO·Al2O3·6H2O, etc.

[0045] The dicalcium silicate and tricalcium silicate in the cement undergo hydrolysis and hydration reaction to produce calcium hydroxide. The calcium hydroxide reacts with the PS solution to form a gel body—hydrated calcium silicate in a finely dispersed state, and the hydrated calcium silicate has early strength and is a relatively strong skeleton.

[0046] Ca(OH)2+K2O·nSiO2+mH2O→CaO·nSiO2·mH2O+2KOH;

[0047] At the same time, the simultaneous double slurry (i.e. cement slurry (C) and PS solution (PS) also reacts with the substances in the soil to form new solidified bodies, such as hydrated magnesium silicate, hydrated barium silicate, etc., which can also enhance the strength of the soil. After final setting, a stone body with high strength and good water stability is formed, causing the stone body and the soil to be in close and rough contact, and the stone body and the compacted foundation soil (soil around the pile) and the steel pipe pile to form a composite foundation, which combines the advantages of steel pipe piles and grouting technology. Under load, the micro steel pipe plays a dual role, longitudinally bearing load under compression, and circumferentially restraining the cement slurry pile body under tension. The lateral deformation of the pile body is prevented under lateral restraint, forming a three-dimensional stress state. The compressive strength of the cement slurry pile body is greatly improved, and the bearing capacity of the cement slurry pile body is also correspondingly improved.

[0048] In the prior art, there is also a way of adding potassium silicate solution (PS solution) to cement, but in the prior art, cement and PS solution are added simultaneously, i.e. after the cement and PS solution are uniformly mixed, pouring is carried out. This method can cause the formation of gel-like calcium silicate hydrate in advance, and because the calcium silicate hydrate is in a gel-like state, it is difficult to enter the gaps of the red layer high fill (or in other words: due to the blocking and plugging of the gaps by the gel-like calcium silicate hydrate, the amount of calcium silicate hydrate that can enter the gaps of the red layer high fill is greatly reduced), thereby reducing the consolidation effect with the soil around the pile (i.e. the red layer), and ultimately causing a large amount of settlement of the red layer high fill, and the frictional resistance applied by the soil around the pile to the pile foundation is also greatly reduced. The present application uses double grouting, and when the cement slurry and the PS solution come into contact, grouting is already in progress. The cement slurry and the PS solution are sprayed onto the soil around the pile (i.e. the pile hole wall) before the gel-like calcium silicate hydrate has a chance to form, thereby allowing more cement slurry and PS solution to enter the gaps of the red layer, thereby filling the gaps and forming gel-like calcium silicate hydrate over time, and after hardening, forming a stone body. The stone body and the soil are in close and rough contact, and the stone body and the compacted foundation soil and the steel pipe pile form a composite foundation, which together controls settlement, improves the density, strength, compression modulus and bearing capacity of the foundation soil.

[0049] At the same time, in the prior art, the micro steel pipe pile is directly filled with gravel inside the micro steel pipe (i.e. without filling gravel around the micro steel pipe). In the present application, gravel is filled in the interior and exterior regions of the micro steel pipe (i.e. between the micro steel pipe and the pile hole), and simultaneous grouting is carried out. The stone body outside the micro steel pipe can protect the micro steel pipe, increase the friction of the pile body, and improve durability, thereby improving the density, strength, compression modulus and bearing capacity of the foundation soil.

[0050] In conclusion, the application can improve the compactness, strength, compression modulus and bearing capacity of the red-layer high-fill foundation, and finally reduce the occurrence of settlement.

[0051] In some embodiments, in the process of grouting by using the grouting pipe in step (2), when the monitoring value monitored by the pressure sensor exceeds the set value, the inner grouting pipe and the casing are uniformly lifted by a distance and stay until the monitoring value of the pressure sensor exceeds the set value again; the cycle is repeated until the grouting is completed.

[0052] In some embodiments, in the process of grouting by using the through hole 51 on the casing 5 and the inner grouting pipe 4, the cement slurry injected by the inner grouting pipe 4 is synchronously injected with the PS solution injected by the through hole 51, and the volume ratio of the PS solution to the cement slurry is 0.2:1.

[0053] In the process of inputting the PS solution and the cement slurry by using the first input pipe 8 and the second input pipe 9 respectively, the PS solution and the cement slurry should be configured in advance, which is understood by those skilled in the art and will not be described here.

[0054] In fact, the configuration of the PS solution is the dilution of the high-modulus potassium silicate solution (wherein the Baumé degree of the high-modulus potassium silicate solution is 24-26, and the modulus is 3.8) to a concentration of 10%. The dilution of the high-modulus potassium silicate solution (i.e. the configuration of the PS solution) is a prior art, which is understood by those skilled in the art and will not be described here.

[0055] In order to control the gel time and slurry diffusion radius of the double slurry (for example Figure 3 and Figure 4 the outermost area in the middle), a good grouting effect is obtained, and laboratory ratio test shows that when the volume ratio of the potassium water glass solution to the cement slurry is 0.2:1, the grouting effect is the best.

[0056] The cement slurry is injected by the inner grouting pipe, and the PS solution is injected by the through hole of the casing, so that the cement slurry can impact and mix with the peripheral PS solution in the process of injection, and under the blocking action of the gravel and the micro steel pipe, the cement slurry continuously impacts and mixes with the PS solution, so that the cement slurry and the PS solution can be uniformly mixed. Especially the filled gravel, because the gap between the gravels is irregular, the cement slurry and the PS solution are uniformly mixed under the action of continuous impact and reflux, which can ensure that the cement slurry and the PS solution fully react, and finally form a high-strength stone body together with the gravel and the soil around the pile (i.e. the red layer).

[0057] Meanwhile, in the application process, the pipe is only driven to move upward with the inner grouting pipe 4 and the casing 5 which moves synchronously with the inner grouting pipe, while the outer grouting pipe 3 which contacts with the mortar does not move, so it will not affect the pouring quality because of lifting the pipe for grouting. In the prior art, no matter how to control the pipe for grouting, it will affect the pouring quality because of dragging the mortar which has been injected.

[0058] In some embodiments, the lower end of the inner grouting pipe 4 extends out of the lower end surface of the casing 5, the side wall of the inner grouting pipe 4 which extends out of the lower end surface of the casing 5 is provided with grouting holes 41 arranged along the radial direction of the inner grouting pipe 4, and the grouting holes 41 correspond to the through holes 51 of the casing 5. Thus, the cement mortar sprayed from the inner grouting pipe 4 can directly impact and mix with the PS solution flowing out of the through holes 51, further ensuring the uniformity of the mixing of the cement mortar and the PS solution.

[0059] In some embodiments, after the grouting with the inner grouting pipe 4 and the casing 5 is completed, the inner grouting pipe 4 and the casing 5 are pulled upward, and then the top of the micro steel pipe 2 is sealed, and then the outer grouting pipe 3 is used for pressurized grouting. The pressure of the grouting liquid during pressurized grouting is greater than the pressure during grouting with the inner grouting pipe 4 and the casing 5 (that is, the pressure of the grouting liquid during pressurized grouting is greater than the pressure of the cement mortar input by the inner grouting pipe, and the pressure of the grouting liquid during pressurized grouting is greater than the pressure of the PS solution injected by the casing). In the prior art, the top of the steel pipe is sealed before the first grouting (that is, the area except the grouting pipe is sealed) and the grouting liquid is directly injected, which can cause the air in the pile hole to flow into the soil (that is, the red layer high fill soil) under the action of the grouting liquid pressure, and part of the gas can mix into the poured grouting liquid to form a small amount of voids, thereby affecting the pouring quality. In the application process, the top of the micro steel pipe is not sealed during the first grouting (that is, during the injection of the cement mortar and the PS solution), the air in the pile hole can be discharged from the top of the micro steel pipe and the periphery of the micro steel pipe, thereby discharging the air in the pile hole and filling it with the cement mortar and the PS solution which are injected, so as to ensure the discharge of the air in the pile hole, and then the outer grouting pipe is used for pressurized grouting (that is, the second grouting). Compared with the construction process of the steel pipe pile in the prior art, the application can reduce the air flowing into the soil (that is, the red layer high fill soil) and the grouting liquid, thereby further improving the density and pouring quality of the red layer high fill soil.

[0060] In some embodiments, during the process of pressurized grouting by using the external grouting pipe (i.e. the second grouting), the grout at the time of grouting is a mixed grout of cement grout and PS solution. The main role of the second grouting is to supplement grouting (the reason for supplementing grouting is the absorption of liquid phase and the shrinkage of solidification during the first grouting), so the cement grout and the prepared PS solution are mixed uniformly before the second grouting. The mixed grout of cement grout and PS solution can improve the strength, and at the time of pressurized grouting (i.e. the second grouting), the gaps in the soil around the pile have been filled and compacted by the cement grout and PS solution injected during the first grouting, so the generated calcium silicate hydrate during the second grouting will not block the gaps in the red layer high fill soil body.

[0061] In some embodiments, the external grouting pipe 3 is fixed inside the micro steel pipe 2 by the connecting steel bars 10. Thus, the micro steel pipe 2 and the external grouting pipe 3 are connected by the connecting steel bars 10 to form a whole, further improving the bending strength of the pile foundation.

[0062] In the specific implementation process, the connecting steel bars are connected with the external grouting pipe and the micro steel pipe by welding. Since the size of the micro steel pipe is small, the connecting steel bars can be welded on the outer wall of the external grouting pipe first, then the external grouting pipe and the connecting steel bars are put into the micro steel pipe, and the connecting steel bars at both ends of the external grouting pipe are connected and fixed with the micro steel pipe by welding. The remaining connecting steel bars can not need to be welded and can play a certain supporting role.

Claims

1. A PS-C double grouting micro pile settlement control method for red layer high fill foundation, comprising the steps of measuring and setting out, drilling a hole, cleaning the pile hole, and implanting a micro steel pipe into the pile hole, characterized in that, The micro steel pipe is provided with a grouting pipe which is implanted into the pile hole together with the micro steel pipe; the process of implanting the micro steel pipe into the pile hole is followed by the following steps in sequence: (1) filling the space between the outer wall of the grouting pipe and the inner wall of the micro steel pipe and the space between the micro steel pipe and the inner wall of the pile hole with gravel; (2) injecting slurry through the grouting pipe; The grouting pipe comprises an outer grouting pipe and an inner grouting pipe, a plurality of grouting holes are formed in the circumferential wall of the outer grouting pipe, two strip-shaped slits are formed in the outer grouting pipe along the length direction of the outer grouting pipe; the inner grouting pipe is sleeved in the outer grouting pipe and can move up and down in the outer grouting pipe; a casing is mounted at the lower end of the inner grouting pipe, the casing is in sliding sealing with the outer grouting pipe, the upper end of the casing extends upward so that a sealed annular cavity is formed between the inner wall of the casing and the outer wall of the inner grouting pipe, a plurality of through holes are formed in the lower end face of the casing and communicate with the annular cavity, the upper end of the casing is connected with a first input pipe for injecting PS solution, pressure sensors are mounted on the outer circumferential wall of the casing and correspond to the positions of the strip-shaped slits, the upper end of the inner grouting pipe is connected with a second input pipe for injecting cement slurry.

2. The PS-C double grouting micro pile settlement control method for red layer high fill foundation according to claim 1, characterized in that, In the process of injecting slurry through the grouting pipe in step (2), when the monitoring value monitored by the pressure sensor exceeds the set value, the inner grouting pipe and the casing are uniformly lifted upward by a distance and stay until the monitoring value of the pressure sensor exceeds the set value again; the process is repeated until the injection of slurry is completed.

3. The red layer high fill foundation PS-C double grouting micro pile settlement control method according to claim 1, characterized in that, When the cement slurry injected by the inner grouting pipe and the PS solution injected through the through holes of the casing are injected synchronously, the volume ratio of the PS solution to the cement slurry is 0.2:

1.

4. The PS-C dual-injection micro-pile settlement control method for red-layer high fill foundation according to any one of claims 1-3, characterized in that, The lower end of the inner grouting pipe extends out of the lower end face of the casing, grouting holes are formed in the side wall of the inner grouting pipe extending out of the lower end face of the casing and are arranged along the radial direction of the inner grouting pipe, and the grouting holes correspond to the positions of the through holes of the casing.

5. The red layer high fill foundation PS-C double grouting micro pile settlement control method according to claim 4, characterized in that, After the injection of slurry through the inner grouting pipe and the casing is completed, the inner grouting pipe and the casing are pulled upward, and then the top of the micro steel pipe is sealed, and then the outer grouting pipe is used for pressurized grouting, and the pressure of the slurry during pressurized grouting is greater than the pressure during the injection of slurry through the inner grouting pipe and the casing.

6. The red layer high fill foundation PS-C double grouting micro pile settlement control method according to claim 1, characterized in that, In the process of pressurized grouting through the outer grouting pipe, the slurry during grouting is a mixed slurry of cement slurry and PS solution.

7. The red layer high fill foundation PS-C double grouting micro pile settlement control method according to claim 1, characterized in that, The outer grouting pipe is fixed in the micro steel pipe through a connecting steel bar.

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