CN105604065A - Foundation fit support and peat-soil deep-foundation-pit-support high-pressure jet grouting anchoring method - Google Patents

Abstract

The invention provides a foundation pit support, comprising a slope top, one side of the slope top is obliquely provided with a slope, the bottom of the slope is provided with a foundation pit, the top of the slope is provided with a drainage ditch, the slope is provided with soil nails, the foundation pit There are vertically adjacent pile-hole piles and water-stop curtain piles, the bottom of the pile-hole piles and water-stop curtain piles are set below the bottom line of the foundation pit, and the anchor cables cross the pile hole piles and water-stop curtain piles, passing through The anchor cable anchor plate and the anchor cable anchor lock are fixed on one side of the pile hole pile and the water-stop curtain pile. Several anchor cable drill holes and supporting rings are set on the anchor cable, and high-pressure grouting pipes are set on the anchor cable. . The present invention also provides a peat soil deep foundation pit support high-pressure rotary jet grouting anchorage method, the anchorage section is first subjected to high-pressure rotary jetting to consolidate the soil to ensure that the axis of the anchor cable hole and the high-pressure rotary jetting consolidation soil in the anchorage section The body construction axis remains concentric. Compared with the support form of the internal support type, this foundation pit support design not only saves the construction period and saves the cost.

Description

A foundation pit support and peat soil deep foundation pit support high-pressure rotary grouting anchoring method

technical field

The invention belongs to the technical field of construction engineering, and in particular relates to a foundation pit support, and also relates to a peat soil deep foundation pit support high-pressure rotary grouting and anchoring method.

Background technique

Due to the base soil layer of peat soil in the Yunnan Plateau Basin, peat soil, as a special soil, has relatively large void ratio and water content, and has high compressibility, high sensitivity, strong creep, and poor physical and mechanical properties. , The physical characteristics of low bearing capacity, as the foundation of the structure, it will have the characteristics of long-term deformation and instability. For buildings built on such foundations, it is not uncommon for foundation pits to be excavated or subjected to dynamic loads (urban roads and subways), and it is not uncommon for damage accidents to occur due to uneven settlement and different functions.

Contents of the invention

The purpose of the present invention is to provide a foundation pit support.

Another object of the present invention is to provide a method for peat soil deep foundation pit support high-pressure rotary grouting and anchoring, which solves the problem of insufficient anchoring force in the original construction process of plateau basin peat soil in the prior art, so that the surrounding ground level and The vertical settlement was alleviated and kept within the allowable value of the code displacement.

The first technical solution adopted by the present invention is a foundation pit support, which is characterized in that it includes a slope top, one side of the slope top is inclined to be provided with a slope, the bottom of the slope is provided with a foundation pit, and the top of the slope is provided with drainage ditch, soil nails are set on the slope, vertically adjacent pile hole piles and water-stop curtain piles are set on the foundation pit, the bottom of the pile hole piles and water-stop curtain piles are set below the bottom line of the foundation pit, Crossing the pile hole pile and the water stop curtain pile, the anchor cable anchor pad and the anchor cable anchor lock are fixed on one side of the pile hole pile and the water stop curtain pile. The anchor cable is covered with a high-pressure grouting pipe.

In the above technical solution, at least two anchor cables are provided.

Another object of the present invention is to provide a method for peat soil deep foundation pit support high-pressure rotary grouting anchorage, making the above-mentioned foundation pit support, comprising the following steps:

Step 1. After excavating the foundation pit to 2 meters below the designed first crown beam, make anchor cables and high-pressure grouting pipes, and use water drilling and follow-up casing hole forming processes to perform hole forming operations;

Step 2. After the hole is formed, the follow-up casing is temporarily placed in the hole, and the manufactured anchor cable and high-pressure grouting pipe are put into the hole successively. The high-pressure grouting pipe is made of 2cm steel pipe, and the high-pressure grouting pipe is The diameter of the grout nozzle is 1.8㎜, and the high-pressure grouting pipe is installed to the bottom of the hole along with the anchor cable, and the hole is filled with a normal pressure of 5-10 MPa for one grouting, and the second high-pressure grouting is performed after initial setting for about 5-10 minutes;

Step 3. When the normal-pressure grouting begins to solidify, start the hole-forming machine to move back and follow the casing, and start the rotary nozzle to perform rotary spraying at the anchorage section. The grouting pressure increases at a rate of 20-25cm per minute, and the diameter of the hole is 500mm. ～600㎜; pure cement slurry with water-cement ratio 0.40～0.50, grouting volume ≥ 120kg/m, until the anchorage section is completely sprayed.

In the above technical scheme, the excavation process of the foundation pit is specifically: making a slope top, setting a slope on one side of the slope top, setting a foundation pit at the bottom of the slope, setting a drainage ditch on the top of the slope, and setting soil nails on the slope.

The beneficial effects of the present invention are as follows: firstly, the method first performs high-pressure rotary spraying on the anchorage section to consolidate the soil body for soft peat soil, and then carries out anchor cable hole-forming construction, and the bearing capacity can meet the design requirements. Second, the anchorage section is firstly subjected to high-pressure rotary grouting to consolidate the soil to ensure that the axis of the hole-forming construction of the anchor cable is concentric with the construction axis of the high-pressure rotary spraying-consolidated soil in the anchorage section, which is the key process for the construction of the anchor cable hole. Third, compared with the internal support type, this foundation pit support design not only saves the construction period and cost, but also makes the subsequent construction organization more flexible. It is a technology suitable for soft peat soil foundation pit protection engineering.

Description of drawings

Fig. 1 is the structural representation of foundation pit support of the present invention;

Fig. 2 is a schematic structural view of foundation pit support high-pressure rotary grouting anchorage of the present invention;

Fig. 3 is a load-displacement curve diagram of an ordinary anchor cable test;

Fig. 4 is the load-elastic-plastic displacement curve diagram of common anchor cable test;

Figure 5 is the load-displacement curve of the high-pressure jet grouting anchor cable test;

Figure 6 is the test load-elastic-plastic displacement curve of the high-pressure jet grouting anchor cable.

In the figure, 1. drainage ditches, 2. grading, 3. soil nails, 4. pile hole piles, 5. water stop curtain piles, 6. anchor cable drilling, 7. anchor cable, 8. high pressure grouting pipe, 9. Support ring, 10. Anchor cable anchor pad, 11. Anchor cable anchor lock, 12. Bottom line of foundation pit, 13., 14.

detailed description

The present invention will be described in detail below in combination with specific embodiments.

The present invention provides a kind of foundation pit support, its structure is shown in Figure 1 and Figure 2, comprises slope crest 13, and one side of slope crest 13 is obliquely provided with slope 2, and foundation pit 14 is arranged at the bottom of slope 2, and slope crest 13 is provided with drainage ditches 1, soil nails 3 are provided on the slope 2, vertically adjacent pile hole piles 4 and water stop curtain piles 5 are arranged on the foundation pit 14, pile hole piles 4 and water stop curtain piles 5 The bottom of the foundation pit is arranged below the bottom line 12 of the foundation pit, the anchor cable 7 is set across the pile hole pile 4 and the water-stop curtain pile 5, and the anchor cable anchor pad 10 and the anchor cable anchor lock 11 are fixedly arranged on the pile hole pile 4 and the water-stop curtain pile 5. On one side of the water-stop curtain pile 5, several anchor cable boreholes 6 and supporting rings 9 are arranged on the anchor cable 7, and a high-pressure grouting pipe 8 is set on the anchor cable 7; at least two anchor cables 7 are provided.

The invention provides a peat soil deep foundation pit supporting method for high-pressure rotary grouting and anchoring. The above-mentioned foundation pit support is adopted, and the method includes the following steps:

Step 1. After the foundation pit is excavated to 2 meters below the designed first crown beam (the crown beam in the conventional technology), the anchor cable 7 and the high-pressure grouting pipe 8 are made, and the drilling process is carried out by using water drilling and following the casing hole forming process. hole operation;

Step 2. After the hole is formed, the follow-up casing is temporarily placed in the hole, and the manufactured anchor cable 7 and high-pressure grouting pipe 8 are put into the hole successively. The high-pressure grouting pipe 8 is made of 2cm steel pipe. The diameter of the grouting nozzle of the grouting pipe 8 is 1.8㎜, and the high-pressure grouting pipe 8 is installed to the bottom of the hole along with the anchor cable 7, and the hole is filled with a normal pressure of 5 to 10 MPa for one grouting, and the second high pressure is performed after the initial setting for about 5 to 10 minutes grouting;

Step 3. When the normal-pressure grouting begins to solidify, start the hole-forming machine to move back and follow the casing, and start the rotary nozzle to perform rotary spraying at the anchorage section. The grouting pressure increases at a rate of 20-25cm per minute, and the diameter of the hole is 500mm. ～600㎜; pure cement slurry with water-cement ratio 0.40～0.50, grouting volume ≥ 120kg/m, until the anchorage section is completely sprayed.

Among them, the foundation pit excavation process is specifically: making the slope top 13, setting the slope 2 on one side of the slope top 13 obliquely, setting the foundation pit 14 at the bottom of the slope 2, setting the drainage ditch 1 on the slope top 13, and setting the soil on the slope 2. Nail 3.

Example 1

1. Project overview

The proposed site is located in the High-tech Zone of Kunming City, adjacent to Haiyuan North Road in the south and Shangyuan Road in the west (Gaoxin No. 1 Haiyuan Campus). The planned total land area of the project is about 31933.49m ² , and the total construction area is 202579.98㎡. The overall planning of the project consists of 4 buildings It consists of a tower (building height 100-130m) and a podium of 1-4 floors. The foundation pit of this project covers an area of about 27,500 square meters, with 2 floors of basement. The perimeter of foundation pit excavation and support is about 785m, and the excavation depth is between 7.9m and 9.2m.

2. Geological conditions of the site

The Quaternary artificial accumulation (Q _ml ) layer is distributed on the surface of the field, and the Quaternary alluvial and diluvial (Q _al+pl ) layer is located below it, and the lithology is silty clay; the Quaternary alluvial and lacustrine (Q _{al +l} ) layer, the lithology is silty clay, clay, silty clay, peaty soil, cohesive gravel sand, silt, etc. Within the excavation depth of the foundation pit, it is mainly filled with soil, silty clay and peaty soil.

Table 1 The soil mechanical properties of the foundation pit

3. Main structural forms of foundation pit support design

As shown in Fig. 1 and Fig. 2, soil nailing wall is the main part of grading excavation from 0 to -3.5m, piles and prestressed anchor cables are the main part of vertical excavation below -3.5m, and deep mixing is used for water stop of foundation pit. Cement-soil piles and high-pressure rotary grouting piles are mainly used. There are 3 rows of prestressed anchor cables, the anchor cable aperture is 300mm, and it is made of 3Φ15.2 (or 4Φ15.2) steel strands. The design anchoring force is 410kN～720kN. Clay, clay layer. Compared with the support form of the internal support type, this foundation pit support design not only saves the construction period and cost, but also makes the subsequent construction organization more flexible. It is a technology suitable for foundation pit enclosure engineering.

4. Construction ideas of prestressed anchor cables

Based on the geological conditions of the site, how to ensure that the prestressed anchor cable can provide sufficient pullout resistance in the muddy soil and peaty soil layer to achieve the design required bearing capacity, ensure the effectiveness of the prestressed anchor cable and the support of the foundation pit? The reliability of the protection structure system is a key technical problem that needs to be solved before the implementation of the foundation pit support project.

According to the design requirements and geological conditions of the site, the prestressed anchor cable construction is divided into two stages. The first stage is the experimental stage, and the anchor cable is constructed and tested; the second stage is the implementation stage. According to the experimental results, the best construction technology is selected and the project is implemented. Anchor cable.

5. Construction anchor cable test

Through field experiments, verify the bonded anchorage strength of the anchor cable body in the designed anchorage soil layer (mainly peaty soil, silty clay and clay), so as to determine the rationality of the design bearing capacity of the anchor cable in the local layer; The construction technology (drilling technology, grouting technology) that should be adopted for the anchor cable construction under the geological conditions of the site; through the analysis of the test results, it is determined whether the safety factor of the anchor cable and the deformation of the anchor cable are within the effective control range.

5.1. Experimental process and equipment

In the test, water drilling, full channel and pipe technology were used for the hole forming process, and two different processes were used for the grouting process: the conventional grouting process (2 times grouting) and the high-pressure rotary grouting expansion grouting process in the anchorage section. The equipment used is Wuxi Amman MDL-135D crawler drilling rig, Tianjin GPB-90 high pressure pump and prestressed anchor cable tensioning equipment. Materials (1) Steel strands: high-strength, low-relaxation Φ15.20 steel strands produced by Tianjin Gaoli; (2) Unbonded pressure plates and P anchors: both are shaped products; (3) Cement for grouting : P.O42.5 ordinary Portland cement.

The anchor cable drilling adopts water drilling and full casing follow-up water flushing method to form a hole once; the grouting method of the anchorage section adopts the high-pressure rotary jet grouting expansion grouting process, the grouting equipment adopts high-pressure pump and high-pressure rotary jet machine, and the grouting pipe adopts The diameter of the spray nozzle is 1.8mm, and the high-pressure grouting pipe is installed to the bottom of the hole with the anchor cable. After the casing is removed, the hole will be expanded by rotary spraying. The grouting pressure is 25MPa, and the lifting speed is 25cm per minute. Reaming diameter 500 ~ 600 mm (demonstration value). For pure cement slurry with a water-cement ratio of 0.40-0.50, the grouting volume is ≥120kg/m.

comparative example

In this comparative example, the anchor cable is drilled using water drilling and the full casing follow-up water flushing method to form a hole once; in this embodiment, the anchor section grouting method adopts the conventional grouting process, and the grouting pipe is installed in the middle of the anchor cable body when weaving the anchor cable , the grouting direction is from the bottom of the hole to the orifice until the orifice returns to the thickened grout to ensure that the grout is full. The grouting adopts two grouting methods. The first grouting starts before the anchor cable is installed and the casing is removed. , The grouting pressure is 0.5MPa. After the first grouting, the casing is removed, and the second grouting is performed at an interval of about 2 hours. The pressure is 5MPa and the water-cement ratio is 0.40-0.50. The grouting volume is ≥120kg/m.

Result analysis:

1. Test anchor cable arrangement:

According to the geological conditions of the site and the actual situation of the site, two sets of comparative experiments were carried out at different positions of the 2nd section, 5th section, and 6th section in the foundation pit support design scheme, with 2 anchor cables in each group. The basic experimental parameters of the anchor cables are as follows:

Table 2 Test anchor cable parameter list

2. Results of anchor cable tensioning

7 days after the experimental anchor cable is installed, use the calibrated jack (YCW100G) and high-pressure oil pump (ZB4500) to carry out the pulling test. The test was carried out in strict accordance with the provisions of the bolt acceptance test in the "Technical Regulations for Building Foundation Pit Support" (JGJ120-2012). During the test, the initial load is taken as 0.1 times the design value Tw of the axial tensile bearing capacity of the anchor rod. The test adopts the method of multi-cycle loading. The loading classification and anchor head displacement observation time should be determined according to Table 2. The loading level observation time , measure and read the displacement of the anchor head 3 times, and the maximum displacement is observed for 10 minutes. The termination test conditions are: ① the displacement does not converge, the anchor is pulled out from the rock and soil layer or the anchor is pulled out from the anchor; ② the test load value meets the design requirements; The resulting displacement increment at the end of the ① anchor exceeds 2 times the incremental test load of the previous stage.

Table 3 Summary of test results

Through the statistics of the measured experimental data, the most representative two groups of experimental data were selected for comparative analysis. It can be seen from Table 3 and Figure 3 to Figure 6 that the ordinary anchor cable of the comparative example cannot meet the design requirements, and the high pressure of the embodiment Rotary grouting expanded body anchor cables all meet the design requirements for bearing capacity. Therefore, it is determined that the anchor cable construction process of this project is carried out by the high-pressure rotary grouting expanded body anchor cable process.

According to the determined construction technology, the construction of 250 anchor cables totaling about 2,000 meters was completed. The monitoring data showed that the horizontal displacement and vertical displacement of the foundation pit were within the 30mm range of deformation control required by the design, and no alarms occurred during construction. It can be seen that the support technology of high-pressure rotary grouting expanded body anchor cable and anchor pile has achieved good support effect.

Claims (4)

1. A kind of foundation pit support is characterized in that, comprises slope crest (13), and slope crest (13) one side is provided with slope (2), and the bottom of slope (2) is provided with foundation pit (14), Drainage ditches (1) are arranged on the top of the slope (13), soil nails (3) are arranged on the grading (2), and vertically adjacent pile hole piles (4) and water stop are arranged on the foundation pit (14). The bottom of the curtain pile (5), the pile-hole pile (4) and the water-stop curtain pile (5) are arranged below the foundation pit bottom line (12), and the anchor cable (7) traverses the pile-hole pile (4) and the water-stop The curtain pile (5) is fixed on one side of the pile hole pile (4) and the water-stop curtain pile (5) through the anchor cable anchor pad (10) and the anchor cable anchor lock (11), on the anchor cable (7) Several anchor cable boreholes (6) and support rings (9) are provided, and a high-pressure grouting pipe (8) is sheathed on the anchor cable (7). 2. The foundation pit support according to claim 1, characterized in that there are at least two anchor cables (7). 3. A method for peat soil deep foundation pit support high-pressure rotary grouting anchorage, is characterized in that, making the foundation pit support described in claim 1 may further comprise the steps: Step 1. After excavating the foundation pit to 2 meters below the designed first crown beam, make anchor cables (7) and high-pressure grouting pipes (8), and use water drilling and follow-up casing hole forming processes to perform hole forming operations; Step 2. After the hole is formed, the follow-up casing is temporarily placed in the hole, and the manufactured anchor cable (7) and high-pressure grouting pipe (8) are put into the hole successively. The high-pressure grouting pipe (8) is made of a 2cm steel pipe Processed, high-pressure grouting pipe (8) nozzle diameter 1.8mm, high-pressure grouting pipe (8) is installed to the bottom of the hole along with the anchor cable (7), and the hole is filled with a normal pressure of 5-10MPa for one grouting. After about 5 to 10 minutes of initial setting, carry out secondary high-pressure grouting; Step 3. When the normal-pressure grouting begins to solidify, start the hole-forming machine to move back and follow the casing, and start the rotary nozzle to perform rotary spraying at the anchorage section. The grouting pressure increases at a rate of 20-25cm per minute, and the diameter of the hole is 500mm. ～600㎜; pure cement slurry with water-cement ratio 0.40～0.50, grouting volume ≥ 120kg/m, until the anchorage section is completely sprayed. 4. the method for peat soil deep foundation pit support high-pressure rotary jet grouting anchorage according to claim 3, is characterized in that, described foundation pit excavation process is specifically: make slope top (13), slope top (13)- A grading (2) is arranged for side inclination, a foundation pit (14) is arranged at the bottom of the grading (2), a drainage ditch (1) is arranged on the top of the slope (13), and soil nails (3) are arranged on the grading (2).