Process for treating strong karst foundation through micro steel pipe lead hole high-pressure grouting

Abstract

The invention discloses a process for treating a strong karst foundation through micro steel pipe lead hole high-pressure grouting in the technical field of engineering construction, and the process comprises the following steps: S1, pre-burying a steel pipe and filling the steel pipe with high-grade concrete according to mud sources of the bottom and the side wall of a pile hole; s2, drilling holes in the embedded steel pipe, washing the drilled holes in the steel pipe with high-pressure clear water, and then performing high-pressure grouting treatment on karst fissures and broken rocks; and S3, after high-pressure grouting is finished and before initial setting of concrete, third-level steel is inserted to serve as a shear-resistant component and welded into a steel bar bundle to stretch into the bearing platform, and it is ensured that stress is transmitted to a complete rock layer. The stability of the foundation of the adjacent building is not affected in the treatment construction process, and good effects are achieved in the aspects of saving the project construction period, reducing the economic input, effectively treating strong karst holes and the like under the condition that the column position and the upper structure of the high-rise building cannot be adjusted.

Description

Technical Field

[0001] The invention relates to the technical field of engineering construction, and in particular to a process for treating a strong karst foundation by micro steel pipe hole-leading high-pressure grouting. Background Art

[0002] Strong karst foundation refers to a foundation with strong karst development, a large number of karst forms such as caves, karst grooves, and stone buds, and these karst forms have a significant impact on the stability of the foundation. It has the following characteristics: Diverse karst forms: In strong karst foundations, karst forms such as caves, karst grooves, and stone buds are strongly developed, with different forms and sizes. Poor foundation stability: Due to the existence of karst forms such as caves and karst grooves, the stability of the foundation is seriously affected, and it is prone to collapse, uneven settlement and other problems. Difficult to handle: The treatment of strong karst foundations requires comprehensive consideration of multiple factors, such as the size of the cave, burial depth, filling conditions, etc., which makes it difficult to handle.

[0003] In one of the karst areas with complex geological conditions, more than 90% of the buildings in the urban area use pile foundations. The construction of pile foundations is restricted by geotechnical engineering geological conditions, karst development conditions, groundwater burial and bedrock weathering degree, as well as site environmental conditions. In dealing with deep and large karst caves and karst fracture zones in karst foundations, there are high risks, construction difficulties, and high economic investment. Especially in the case of narrow site conditions and a single construction plan, the foundation construction is extremely difficult. Summary of the invention

[0004] The present invention aims to provide a process for treating strong karst foundation by micro steel pipe hole high pressure grouting, which adopts micro steel pipe hole high pressure grouting to treat strong karst development foundation, strengthen the bearing layer at the pile end, and do not affect the stability of the foundation of adjacent buildings during the treatment construction process, solve the problem of high-rise buildings unable to adjust the column position and the upper structure, save the project time, reduce the economic investment, effectively treat the strong karst caves, and achieve good results.

[0005] In order to achieve the above object, the present invention provides the following technical solutions: A process for treating strong karst foundation by micro steel pipe hole high pressure grouting comprises the following steps: S1. According to the source of mud at the bottom and side wall of the pile hole, pre-buried steel pipes and filled with high-grade concrete; S2. Drill holes in the embedded steel pipe, wash the holes with high-pressure water, and then perform high-pressure grouting to treat karst fissures and broken rocks; S3. After high-pressure grouting is completed and before the initial setting of concrete, grade 3 steel is inserted as a shear member and welded into a steel bar bundle and extended into the cap to ensure that the stress is transferred to the intact rock layer.

[0006] Working principle and beneficial effects of the present invention: Through the inspection of engineering examples, high-pressure grouting has achieved good results in dealing with complex karst foundations, especially in narrow sections of construction sites, using micro steel pipes to lead holes for high-pressure grouting to deal with strong karst development foundations and enhance the bearing layer at the pile end. In addition, the stability of the foundation of adjacent buildings has not been affected during the construction process, and the problem of high-rise buildings being unable to adjust the column position and superstructure has been solved, saving engineering time, reducing economic investment, and effectively dealing with strong karst caves.

[0007] For optimization, the water-cement ratio can be 0.5:1 or 1:1. If the amount of slurry absorbed during pouring is too large, 3-5% water glass can be infiltrated into the slurry to shorten the initial setting time.

[0008] The optimized, high-grade concrete grade is C35.

[0009] Optimally, the drilling depth is controlled to be below 20.1 m, that is, to enter the intact rock more than 3d (d is the pile diameter).

[0010] Optimized, three third-grade steel bars with a diameter of 32 are used and welded into a steel bar bundle.

[0011] Optimized, high-pressure grouting pump for mortar pump, the allowable working pressure is 1.5 times the maximum grouting volume, the maximum pressure is required to reach 8.0Mpa, the slurry discharge volume is 50m3 / h, and the working stability performance (pressure swing range) is less than 20%.

[0012] Optimized, water glass: modulus is 2.4 ~ 3.0, concentration is 30 ~ 45 Baume.

[0013] Optimized, the grouting hole pressure is controlled at 0.5 ~ 1.5Mpa. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 This is a schematic diagram of the bottom plane of pile 9#; Figure 2 This is the AA' section view of 9# pile. DETAILED DESCRIPTION

[0015] The following is further described in detail through specific implementation methods: Building 2 of a garden in Liupanshui City is located on the south side of Zhongshan Avenue in Shuichengpandi, at the roundabout of Zhongshan West Road. To its east are the completed buildings 1# and 5#, to its west is building 3#, and to its south is building 4#. The building is 14 stories high, with shopping malls from 1 to 4 floors. It has a full frame shear wall structure with a complex structure and a large single pile load. The design adopts an impact bored cast-in-place pile foundation. According to geotechnical engineering survey data, the geological conditions of the site are complex, karst caves are well developed, the bedrock rock mass is highly fragmented, and the groundwater level is high.

[0016] Since the west side of Building 2# is adjacent to Building 3# (Building 3# is 7 stories high, completed, and residents have moved in), the center of Building 2#'s 9# pile is only 0.8m away from the side wall of Building 3#. Building 3# uses a pipe-sinking cast-in-place pile group foundation (3-pile cap foundation) with a pile diameter of Φ550mm. There is one pipe-sinking cast-in-place pile of Building 3# on the west side within the diameter of the 9# pile. Therefore, the 9# pile cannot be constructed using an impact-bored cast-in-place foundation. When using a bored cast-in-place pile foundation and a rotary bored cast-in-place pile foundation, the construction machinery is limited by the site and cannot reach the pile position. The design unit considers the structural load and cannot make design changes. After calculation, the load of the 9# pile reaches 9400KN.

[0017] Therefore, the construction unit used artificial bored foundation to construct 9# pile. The reference pile length was 16.1m and the pile diameter was Φ1800mm. When 9# pile was constructed to 11.9m, the groundwater level was high, calculated as -2.2m based on the hole mouth. The rock at the bottom of the hole was broken, and there were sunken piles of the pile cap foundation of the 3# building sunken pipe cast-in-place pile group in the pile hole. Karst fissures were developed at the bottom of the hole, so blasting operations could not be carried out, and a large amount of groundwater could not be pumped out for construction. If the bored piles were continued to be constructed, the stability of the 3# building foundation would definitely be affected. The bottom of the 9# pile is shown in the figure. <1> .

[0018] Due to the special location of the 9# pile, the geological data show that the geological conditions of the 9# pile are as follows: Pile No. Soil layer (m) Broken and karst fissure development location A1 (mm) Complete rock layer A2(mm) Remark 9# pile 0～8.60 8.6~15.60 (9.00~10.9; 14.00~15.60 are cracks filled with soft plastic clay, 10.9~14.00 are broken rock layers) 15.6～23.6 Since the investigation report gives the characteristic bearing capacity value of the broken rock A1 in the 9# pile as 2500kPa, and the characteristic bearing capacity value of the relatively intact moderately weathered rock A2 as 4500kPa, combined with a comprehensive analysis of the load test data of high-pressure grouting of broken rocks in the construction site area, the characteristic bearing capacity value of the broken rock A1 at the bottom of the hole after high-pressure grouting treatment is 3800kPa. Considering the weak surface of the bonding between the cement slurry filling entity and the rock mass in the karst fissure, three 32-diameter grade 3 steels are inserted into the steel pipe and the borehole to enhance its shear resistance and serve as a safety reserve.

[0019] For the reasons stated above, it was decided to stop the construction of bored pile foundation and use high-pressure grouting to treat the karst fissures and broken rocks at the base to reduce the rock embedding depth of the whole pile. The treated pile bottom is the foundation bearing layer, forming the following construction plan: (1) Block the mud source at the bottom and side wall of the 9# pile hole, and then try to remove the mud at the bottom of the hole and the clay in the cracks. First, pre-embed Ø108mm steel pipes. No less than 6 Ø108mm steel pipes should be pre-embedded in the entire bottom of the hole. The position of the pre-embedded Ø108mm steel pipes is as shown in the figure. <1> The hole bottom plane diagram is used for layout. Then the cracks are filled with high-grade concrete C35, and then the concrete is poured to 2.00m below the hole mouth with the designed strength C30. The pre-buried Ф108mm steel pipe should be higher than the concrete surface by more than 0.5m. During the construction process, measures are taken to make the pre-buried Ф108mm steel pipe vertical so that the Ф91mm drill hole can be constructed in the Ф108mm steel pipe later.

[0020] (2) After the concrete reaches the setting period, according to the karst fissure position in the investigation report, a hole is drilled in the pre-buried 108mm steel pipe, and the drilling depth is controlled to be less than 20.1m, that is, more than 3d (d is the pile diameter) into the intact rock. Then, the hole is washed with high-pressure clean water in the 108mm steel pipe, and then high-pressure grouting is carried out to treat the karst fissure and A1 broken rock. It is required that the high-pressure water washing hole and high-pressure grouting should be constructed in accordance with the current relevant specifications.

[0021] (3) After high-pressure grouting is completed and before the initial setting of concrete, three grade 3 steel bars with a diameter of 32 are welded into a steel bar bundle and inserted into the bottom of the high-pressure grouting hole. The steel bar bundle extends into the 9# pile cap, so that part of the stress at the bottom of the pile is transferred along the track steel to the A2 intact rock.

[0022] (4) The results of high-pressure grouting treatment for fractured areas and broken rock are shown in Figure <1> An inspection borehole is set up at the plane position of the hole bottom to test the quality of high-pressure grouting. The next process can be carried out only when the cracks are filled, the broken rock mass is well cemented, and the high-pressure grouting stone body meets the design strength requirements.

[0023] The above treatment plan is detailed in the attached Figure 1 , Attachment Figure 2 .

[0024] The specific process is as follows: 1. Drilling: Use XJ-100 engineering drilling rig, calibrate the drilling rig, and drill in the Φ108mm steel pipe buried in advance. Drill to the designed depth and complete the hole. No rock core should remain in the hole. During the drilling process, keep records of each time's footage and rock integrity.

[0025] Borehole washing: According to the drilling data, a steel pipe with a closed bottom and holes on the side is placed along the borehole. A borehole washer that uses compressed air to cause water to produce a lateral jet. According to the development of rock karst in the irrigation area, the lateral flow pressure should be controlled, and the karst fissures should be washed with high-pressure water. The borehole washing pressure should be controlled at around 1Mpa. The fillings in the karst fissures are repeatedly washed and cut section by section to turn them into mud. Then, two branch pipes are placed (without a borehole washer). The high-pressure pump is opened to gear II to make the borehole washing water flow rate reach 1000L / min, so that clay and sand can be discharged from the orifice. The washing is repeated section by section until the water is clear.

[0026] Grouting (initial grouting): According to the consolidation grouting and backfill grouting in the "Technical Specifications for Hydraulic Construction and Cement Grouting Construction" SL62-94, this grouting is for 6 holes. After flushing the 6 holes in turn, grouting begins. Each grouting point uses a drilling rig to spray from bottom to top. The drilling rig speed is controlled at 72r / min and the displacement reaches 50m3 / h. If the grouting is too large, water glass can be added appropriately, or low-pressure, thick slurry, flow limiting, limited quantity, and intermittent grouting can be used according to the specific situation.

[0027] Blocking holes: After the initial grouting is completed, wait for the cement to form a stone body and reach a certain age, then use a drilling rig to sweep holes at each grouting point, and the sweeping holes are all more than 0.5m beyond the karst cave section.

[0028] High-pressure grouting (re-grouting): After the hole is swept and flushed, double pipes are placed in each hole, and the grouting section is blocked with grouting plugs. The remaining 8 holes are blocked with grouting plugs, and then high-pressure grouting is carried out. After the grouting starts, the pressure is gradually increased to the design pressure. After the thick slurry is discharged from the slurry outlet, the stop holes are blocked. In this way, high-pressure grouting is carried out for the other holes respectively.

[0029] If the amount of grouting absorption is too large during the grouting process, water glass can be added appropriately, or low-pressure, thick slurry, flow limiting, quantity limiting, and intermittent grouting can be used according to the specific situation.

[0030] Sealing the hole: Without waiting for the initial setting of cement, add the prefabricated track steel and use cement slurry with a water-cement ratio of 0.5:1 to grout from the bottom of the hole upward to seal the hole. Fine sand can be added to the cement slurry appropriately to increase the strength of the cement slurry stone body and ensure the integrity of the bearing layer.

[0031] 2. High-pressure grouting control Arrangement of grouting points and placement of grouting plugs: Each hole is grouting point based on the drilled hole, and the grouting plug at each grouting point should be placed more than 0.5m away from the bottom of the Φ108㎜ steel pipe.

[0032] Standard value of compressive strength of stone body: In order to ensure that the compressive strength value of stone body is permanently similar to that of rock in site area, chemical grouting should not be used in site area. According to the load characteristics of the building, pure cement grouting should be used for grouting area. The cement grade should not be lower than PO.42.5 ordinary Portland cement. The average compressive strength of intact limestone in the proposed site is 34.77Mpa (original survey report). Therefore, the optimal ratio of grouting in site area is a water-cement ratio of 1:1, which ensures that the compressive strength value of stone body is greater than or close to 34.77Mpa.

[0033] Initial consolidation grouting pressure control: prevent excessive pressure from causing ground lifting or damaging rocks or poured pile foundations. Instant high pressure will also cause harmful splitting in the bedrock. If the pressure is insufficient, the slurry penetration range will not meet the design requirements. The correct selection of grouting pressure is closely related to the engineering effect. According to the geological conditions of the site, this grouting takes into account various factors such as the hydrostatic pressure of groundwater, the depth of the stop plug, the grouting depth, the total length of the grouting section, the weight of the grouting liquid, the height from the grouting section to the groundwater level, the weight of the water, the weight of the covering layer, and the development of karst fissures. Through calculation, it is concluded that the control pressure of each grouting hole is 0.5~1.5Mpa.

[0034] Control of final seepage consolidation pressure: After the initial grouting, since cement slurry is prone to shrinkage cracks, and the groundwater permeability coefficient in the site is large and the geological conditions are complex, in order to ensure the consolidation quality of cement slurry in the rock, each grouting point adopts hole sweeping, and the grouting pressure is increased before grouting (re-grouting). It is advisable to grout in sections from top to bottom, and the grouting pressure is controlled at 3.0~4.0Mpa, and the peak value can reach 6.0~8.0Mpa, which is appropriately adjusted according to the amount of grouting suction.

[0035] 3. High-pressure grouting quality inspection After the grouting is completed, when the curing age is reached, the quality inspection of the reinforced pile bottom bearing layer is carried out. The inspection method adopts the drilling method. Two boreholes are arranged along the middle of the pile to check the penetration of cement slurry in the pile bottom bearing layer, the crushing of broken rocks and the filling of cement slurry in the cracks, etc., and the taken cement stone body is tested for compressive strength. At the same time, the bearing layer is inspected by the acoustic wave transmission method. The indoor saturated compressive strength test results of the cement stone body have reached 35.2Mpa, and the results of the acoustic wave transmission method for the bearing layer show that the pile bottom bearing layer is complete, the wave velocity is stable and continuous, and the construction results meet the design requirements. The building has been completed and has been in use for nearly 15 years without any adverse conditions.

[0036] 4. Grouting equipment and tool performance requirements Mixer: Its speed and stirring capacity are adapted to the type of liquid being mixed and the displacement of grouting, and can ensure uniform and continuous mixing of slurry. High-pressure grouting pump: It is advisable to use a mortar pump, with an allowable working pressure of 1.5 times the maximum grouting volume, a maximum pressure of 8.0Mpa, a slurry displacement of 50m3 / h, and a working stability performance (pressure swing range) of less than 20%. Grouting pipeline: Steel wire braided hose, that is, a special high-pressure grouting pipe, which requires smooth flow of slurry and can withstand a grouting pressure of 10Mpa. High-pressure grouting plug (ball): It has good expansion and pressure resistance, and can reliably close the grouting hole section under the design pressure. Pressure gauge: A large-range pressure gauge, the maximum value of which should be 2.0 to 2.5 times the maximum grouting pressure, and a pressure gauge is required to be set at the grouting orifice. Double pipe (steel pipe): The outer pipe is a 2-branch pipe, and the inner pipe is a 1 / 4-branch pipe. The outer pipe is used to discharge water and return slurry, and the inner pipe is used for grouting.

[0037] Drilling rig: To ensure the quality of grouting, it is used for segmented hole sweeping or rotary jet grouting.

[0038] Grouting materials and slurry preparation Cement: The cement grade used for grouting should not be lower than PO.42.5 ordinary Portland cement.

[0039] Sand: It should be natural sand or artificial sand with hard texture, particle size should not be greater than 2.5 mm, mud content should not be greater than 3%, and organic matter content should not be greater than 3%.

[0040] Water glass: The modulus should be 2.4-3.0, and the concentration should be 30-45 degrees Baume.

[0041] Water: According to the water quality analysis of the site, it has no corrosive effect on reinforced concrete and can be obtained locally.

[0042] Due to the abundant groundwater in the site, the water-cement ratio can be 0.5:1 or 1:1. If the amount of grouting is too large during grouting, 3-5% water glass can be infiltrated into the slurry to shorten the initial setting time. The time from preparation to the end of the slurry should be less than 4 hours. After adding admixtures, the time from preparation to the end of the slurry should be less than 2 hours. Grouting pressure control: Install a grouting plug between the grouting pipe and the borehole to prevent the slurry from surging and overflowing. Grouting is performed in the inner pipe, and the pressure is controlled by the pressure control gauge connected to the grouting machine. In order to ensure the compressive and tensile strength of the stone body in the reinforced part and ensure the quality of grouting, the grouting pressure and the water-cement ratio of the slurry are strictly controlled during the grouting construction.

[0043] The quality of karst foundation treatment directly affects the use or service life of the building. This embodiment summarizes the construction technical requirements, construction process flow, high-pressure grouting control, and high-pressure grouting quality inspection of high-pressure grouting in the treatment of karst foundation construction through the treatment of the karst foundation of the 9# pile of the 2# building in a garden in Liupanshui City. After the inspection of the engineering example, high-pressure grouting is used to treat the strong karst development foundation in the treatment of complex karst foundations, especially the narrow section of the construction site, and the micro steel pipe lead hole high-pressure grouting is used to treat the strong karst development foundation to enhance the bearing layer at the pile end. And the stability of the foundation of the adjacent building is not affected during the treatment construction process, which solves the problem that the column position of the high-rise building cannot be adjusted, and the upper structure cannot be adjusted, and the project period is saved, the economic investment is reduced, and the strong karst caves are effectively treated. The gap has achieved good results.

Claims

1. A process for treating strong karst foundation by micro steel pipe hole high pressure grouting, characterized in that: The following steps are included: S1. According to the source of mud at the bottom and side wall of the pile hole, pre-buried steel pipes and filled with high-grade concrete; S2. Drill holes in the embedded steel pipe, wash the holes with high-pressure water, and then perform high-pressure grouting to treat karst fissures and broken rocks; S3. After high-pressure grouting is completed and before the initial setting of concrete, grade 3 steel is inserted as a shear member and welded into a steel bar bundle and extended into the cap to ensure that the stress is transferred to the intact rock layer.

2. The process for treating strong karst foundation by micro steel pipe hole high pressure grouting according to claim 1 is characterized in that: The water-cement ratio can be 0.5:1 or 1:

1. If the amount of slurry absorbed during pouring is too large, 3-5% water glass can be infiltrated into the slurry to shorten the initial setting time.

3. The process for treating strong karst foundation by micro steel pipe hole-drawing high pressure grouting according to claim 2 is characterized in that: The high-grade concrete grade is C35.

4. The process for treating strong karst foundation by micro steel pipe hole high pressure grouting according to claim 3 is characterized in that: The drilling depth is controlled to be below 20.1 m, that is, to enter the intact rock more than 3d (d is the pile diameter).

5. The process for treating strong karst foundation by micro steel pipe hole high pressure grouting according to claim 4 is characterized in that: Three third-grade steel bars with a diameter of 32 are used and welded into a steel bar bundle.

6. The process for treating strong karst foundation by micro steel pipe hole high pressure grouting according to claim 5 is characterized in that: The mortar pump used for high-pressure grouting pump has an allowable working pressure of 1.5 times the maximum grouting volume, requires a maximum pressure of 8.0Mpa, a slurry discharge volume of 50m3 / h, and a working stability performance (pressure swing range) of less than 20%.

7. The process for treating strong karst foundation by micro steel pipe hole high pressure grouting according to claim 6 is characterized in that: Water glass: modulus is 2.4~3.0, concentration is 30~45 degrees Baume.

8. The process for treating strong karst foundation by micro steel pipe hole high pressure grouting according to claim 7 is characterized in that: The pressure of the grouting holes is controlled at 0.5~1.5Mpa.

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