CN104929146B - A construction method for multi-layer karst developed foundation with piles - Google Patents

Abstract

The present invention relates to the technical field of pile foundation engineering, in particular to a construction method for multi-layer karst-developed pile foundation engineering, including first establishing a calculation model and calculation formula through structural mechanics and geological theories to obtain the investigation depth of pile foundation construction in karst areas Determine the survey depth and survey ideas, and form the survey results based on the survey ideas to investigate the characteristics of the bedrock. Based on the survey results, draw the distribution map of the geological fault zone and the relative position relationship between the proposed building and the karst development zone, and then use each proposed building as a unit Determine the construction sequence of the pile foundation on the site, and on this basis, divide the construction sequence of the pile foundation for each building to be built, and carry out different grouting pretreatments on the pile foundation in batches and layers, and then analyze the karst development zone of each building The pile foundation is subjected to grouting construction, and the construction according to the multi-layer karst development pile foundation engineering construction method disclosed by the present invention can effectively avoid ground subsidence, casualties and property losses caused by construction.

Description

A construction method for multi-layer karst developed foundation with piles

technical field

The invention relates to the technical field of pile foundation engineering, in particular to a construction method for multilayer karst-developed pile foundation engineering.

Background technique

Basement karst is prone to form soil caves due to seasonal changes in groundwater level, latent erosion, vacuum suction, etc., and develops into collapse, or the roof of the karst cave collapses due to the increase of load due to new construction loads and other reasons. The collapse endangers the stability of the building and affects driving safety, so karst grouting is required for reinforcement. Before formulating treatment measures and construction, targeted drilling and geophysical prospecting work should be carried out on the basis of careful ground investigation, and then feasible treatment measures should be formulated according to the survey results. Failure to do so may result in personal injury or property damage.

Contents of the invention

The purpose of the present invention is to provide a comprehensive treatment construction method for multi-layer karst development with pile foundation engineering, which can effectively avoid casualties and property losses caused by ground subsidence caused by construction.

Above-mentioned technical purpose of the present invention is achieved through the following technical solutions:

A construction method for multi-layer karst developed foundation engineering with piles, characterized in that the specific construction steps are as follows:

(1) Comprehensively establish calculation models and calculation formulas to form the survey depth and survey ideas of pile foundation construction in karst areas;

(2) Investigate the lithology, structure, rock surface change and weathering degree of the bedrock according to the survey ideas described in step (1), determine its hardness, integrity and basic quality level, and determine whether there are caves, free surfaces, Broken rock mass or weak rock formations to form survey results;

(3) Draw a distribution map of geological fault zones and a map of the relative position relationship between the proposed building and the karst development zone according to the survey results described in step (2);

(4) According to the distribution map of the geological fault zone and the relative position relationship map mentioned in step (3), the construction sequence of the pile foundation of the construction site is formulated on the basis of each building to be built;

According to the general first, then the partial, the construction sequence of the building is selected first with the single building as the unit. Under normal circumstances, for the pile foundations exposed with unfavorable conditions such as karst caves and fissures, it is also based on the principle of first easy and then difficult, and relatively small risky areas are selected for preliminary construction, and those with poorly developed fissures, small karst caves, and There are fewer layers of karst caves; then pile foundations with large karst caves and more layers of karst caves are constructed. For the foundation construction of each building, the principles of batching and advance pretreatment should be followed to ensure the construction progress and construction period.

(5) According to the construction sequence described in step (4), the karst development zone is divided into four grades according to the location, development situation and the possible ground collapse risk level caused by the construction of the karst pile foundation:

Level 1: Advance drilling does not encounter karst caves or the cumulative thickness of karst caves is less than or equal to 1 meter, and the construction of karst pile foundations does not cause ground subsidence or the depth of ground subsidence is less than 0.5 meters;

Level 2: The accumulative total thickness of karst caves revealed by advanced drilling is greater than 1 meter and less than or equal to 3 meters, and the depth of ground subsidence caused by karst pile foundation construction is less than 1.5 meters;

Level 3: The accumulative total thickness of karst caves revealed by advanced drilling is greater than 3 meters and less than or equal to 5 meters, and the depth of ground subsidence caused by karst pile foundation construction is less than 2.5 meters;

Level 4: The accumulative total thickness of karst caves revealed by advanced drilling is greater than 5 meters, and the depth of ground subsidence caused by karst pile foundation construction is greater than or equal to 2.5 meters;

(6) For the karst development zone of each building pile, the pile foundation shall be grouted in batches and layers according to the grade mentioned in step (5):

(I) For the first grade, the first batch of construction is carried out, and no prevention and control is required for direct construction;

(II) For the second grade, the second batch of construction shall be carried out, and the hole-forming part shall be impacted. According to calculations, the slabs shall be thrown and compacted horizontally with the clay blocks 2 meters before entering the bedrock, and lightly hit when entering the rock;

(III) For the third grade, carry out the third batch of construction, impact the hole-forming part, fill the whole length of the rubble with the clay block for lateral compaction, and hit lightly when entering the rock;

(iv) for the fourth grade, the fourth batch of construction;

(7) Before the construction of the first batch of pile foundations, the following pretreatment methods are used to pretreat the karst caves in advance: small-diameter holes are drilled, and mortar is injected. The cement mortar ratio is: water: cement: sand = 0.8: 1.0: 1.0. According to the calculation, the hole-forming part of the impact should be filled 2 meters before entering the bedrock and compacted horizontally with the clay block, and lightly hit when entering the rock.

According to the statistics and calculation analysis of the advanced drilling survey data, combined with the practical experience of ground subsidence prevention and control engineering caused by the construction of a large number of karst pile foundations, it is divided into four grades according to the risk level of ground subsidence that may be caused by the construction of karst pile foundations. The construction of karst pile foundations Divided into four batches, and corresponding to different control measures.

Preferably, the exploration of the lithology and structure of the bedrock described in step (2) adopts the drilling and coring method, and the specific method is determined according to the rock and soil category, rock and soil drillability classification, and drilling technical requirements. For drilling requiring cores, rotary drilling should be used; for cohesive soil, auger drilling or hammer drilling can be used according to regional experience; for gravel soil, plant glue can be used to protect the wall diamond single-action double-pipe Drilling tools drilled. The drilling method will not be repeated.

Special karst survey during construction. Analyze and sort out the data on site geophysical prospecting, engineering detailed survey, advanced drilling construction and other data that have been carried out in the early stage. In addition to the development of surface karst zones, there are still deep karst zones distributed, and the elevation position of karst development is found out. When drilling ahead of time, the "corner point method" should be used. According to the axis position of each building, control survey holes should be arranged according to the survey depth around and in the middle of the building. According to the building area of each building, the ultra-deep control holes It should be controlled between 6 and 8, not less than 4, and the depth of the control holes is determined according to step (1).

As a preference, for karst and fault fracture zone areas, the exploration hole should pass through the cave or fault fracture zone and enter the stable formation, and the depth of the pile bottom entering the intact rock should not be less than 5.0m.

As a preference, for landslide loose soil and strongly weathered bedrock layer, drilling with casing protection wall or mud protection wall drilling is adopted; double-pipe single-action core drilling is used for the 5m section below the pile bottom; mud is used for the lower complete bedrock Drilling into the wall.

As a preference, the grouting construction sequence described in step (6) is as follows:

(a) preparation for construction;

(b) Pilot hole drilling;

(c) Water injection test before grouting;

(d) grouting;

(e) sealing holes;

(f) general grouting hole drilling;

(g) grouting for general grouting holes;

(h) Detection of grouting effect.

As a preference, in the step (b), when the karst is found to be large in geological drilling, and two adjacent holes may be connected, the grouting hole should be skipped and drilled, and the grouting should not be done after all the holes are drilled.

Preferably, in the step (b), the position deviation of the grouting holes does not exceed 50 cm.

Preferably, during the grouting process of the step (d), observation piles are buried in the grouting area, and the surface settlement is observed before and after the grouting, and ground observation records are carried out.

As a preference, the observation piles are arranged in the center of the line, embankments on both sides of the roadbed or the toe of the cutting slope, and 10m outside the toe of the slope (or outside the top of the cutting), and the vertical distance is not more than 50m. The range of the transition section and the heterogeneous area The observation profile should be intensified.

As a preference, when the grouting process in step (d) reaches one of the following criteria, the hole grouting is ended:

① The pressure at the grouting orifice is maintained at about 0.5MPa for 10 minutes.

②When the grouting point is 3-5m out of the grouting range.

(1) In the karst development area of the first terrace of the Yangtze River, use the comprehensive application analysis of geological structure, structural mechanics, engineering geology, engineering survey and other theories to guide the comprehensive treatment of pile foundation construction in the karst development area, and establish calculations through structural mechanics and geological theories The investigation depth of pile foundation construction in the karst area is obtained from the model and calculation formula; (2) When performing advanced drilling investigation, the "corner point method" should be used to survey the surrounding and middle positions of each building according to the axis position of each building. Depth arrangement of control reconnaissance holes; (3) According to the first overall and then partial, based on the idea of combining qualitative and quantitative, use the results of geophysical prospecting and construction survey to draw the distribution map of geological fault zones and the relative position relationship between the proposed building and karst development, and the planned The construction sequence of the overall pile foundation based on the building body is proposed in the site; (4) On the basis of the distribution map of the overall geological fault zone and the local relative position map, the "corner point control method" is proposed, and according to the location and development of the karst , according to the pile foundation construction sequence of each building, it is divided into batches and layers, and at the same time, different construction pretreatment measures are targeted to prevent large-scale deep construction subsidence; (5) The pile foundation construction sequence of each building in the karst development area is proposed And draw the construction sequence diagram to guide the construction. (6) Through the above steps, avoid large-scale deep subsidence during pile foundation construction, avoid construction machinery and personnel casualties, and ensure that the construction meets the requirements and standards of design specifications.

To sum up, construction according to the multi-layer karst-developed foundation engineering construction method with piles disclosed in the present invention can effectively avoid ground subsidence, casualties and property losses caused by construction.

Description of drawings

Fig. 1 is a construction sequence diagram of a field pile foundation in a specific embodiment.

Fig. 2 is a construction sequence diagram of multi-layer karst-developed foundation with piles in a specific embodiment.

detailed description

A construction method for multi-layered karst-developed foundation engineering with piles, the specific construction steps are as follows:

(1) Comprehensively establish calculation models and calculation formulas to form the survey depth and survey ideas of pile foundation construction in karst areas.

(2) According to the survey idea described in step (1), use drilling and coring methods to survey the lithology, structure, rock surface change and weathering degree of the bedrock, determine its hardness, integrity and basic quality level, and determine whether there are caves , air surface, broken rock mass or weak rock formation, forming survey results.

For karst and fault fracture zone areas, the exploration hole should pass through the karst cave or fault fracture zone and enter the stable stratum, and the depth of the pile bottom entering the intact rock should not be less than 5.0m.

For landslide loose soil and strongly weathered bedrock layer, use casing retaining wall drilling or mud retaining wall drilling; use double-pipe single-action core drilling for the 5m section below the pile bottom; use mud retaining wall drilling for the lower complete bedrock .

(3) Draw the distribution map of geological fault zones and the relative position relationship between the proposed building and the karst development zone according to the survey results mentioned in step (2).

(4) According to the distribution diagram of the geological fault zone and the relative position relationship diagram mentioned in step (3), the construction sequence of the pile foundation on the site is formulated on the basis of each building to be built. See attached drawing 1 for details, and the number 5 represents the first The number 6 represents the second step of construction, the number 7 represents the third step of construction, the number 8 represents the fourth step of construction, and the number 9 represents the fifth step of construction.

(5) According to the construction sequence described in step (4), the karst development zone is divided into four grades according to the location, development situation and the possible ground collapse risk level caused by the construction of the karst pile foundation. See attached drawing 2 for details ,

The first grade 1: No karst cave is encountered in the advanced drilling or the cumulative thickness of the karst cave is less than or equal to 1 meter, and the construction of karst pile foundation does not cause ground subsidence or the ground subsidence depth is less than 0.5 meters;

The second level 2: The accumulative total thickness of karst caves revealed by advanced drilling is greater than 1 meter and less than or equal to 3 meters, and the ground subsidence depth caused by karst pile foundation construction is less than 1.5 meters;

The third level 3: The cumulative thickness of karst caves revealed by advanced drilling is greater than 3 meters and less than or equal to 5 meters, and the depth of ground subsidence caused by karst pile foundation construction is less than 2.5 meters;

The fourth grade 4: The cumulative thickness of karst caves revealed by advanced drilling is greater than 5 meters, and the depth of ground subsidence caused by karst pile foundation construction is greater than or equal to 2.5 meters;

(6) For the karst-developed pile foundation of each building pile, carry out grouting construction in batches and layers according to the grade described in step (5):

(I) For the first grade 1, the first batch of construction is carried out, and no prevention and control is required for direct construction;

(II) For the second level 2, the second batch of construction will be carried out, and the hole-forming part will be impacted. According to calculation, the rubble and clay block will be compacted horizontally 2 meters before entering the bedrock, and the volume of the filling will be about 18.84m ³ . tap when

(III) For the third grade 3, carry out the third batch of construction, impact the hole-forming part, fill the whole length of the rubble and clay block laterally compacted (volume about 18.84m ³ ), lightly hit when entering the rock, the volume of the above thrown fill It can be calculated and determined according to the actual situation;

(IV) For the fourth level 4, carry out the fourth batch of construction, the specific sequence is as follows:

(a) Construction preparation

(1) Familiar with the general situation of each karst grouting site project, prepare the construction plan, karst grouting hole layout plan, construction technology disclosure and other technical work in advance.

(2) Measure and set out, according to the plan layout of karst grouting holes, stake out each grouting hole, and measure and record the ground elevation of the corresponding grouting hole.

According to the requirements of the design drawings, the settlement observation piles shall be buried, and the settlement observation shall be carried out during the construction period.

(3) Connect the construction water and electricity, and test the drilling rig to ensure that the equipment can be drilled normally.

(4) Prepare cement, sand, water glass, fly ash for grouting, and inspect the incoming raw materials.

(5) Detect the status of all grouting equipment to ensure that the equipment can operate normally, and reasonably set up cement sheds, mixing stations and ancillary facilities.

(b) Pilot hole drilling;

According to the principle of combining exploration and irrigation, the drilling is divided into pilot holes and general grouting holes. First, the pilot holes are drilled. After the pilot holes are completed, the data is sorted out and reported to the supervision and design unit to determine the relevant grouting depth and range.

(1) Drilling: The soil layer and the rock layer are all drilled with water drills, and the hole position deviation of the grouting hole does not exceed 50cm.

The grouting hole spacing is 5m; the thickness of the soil layer is ≥3m, the thickness of the grouting layer is not less than 10m, the depth of the soil layer is not less than 5m, the thickness of the soil layer is less than 3m, and the depth of the karst treatment is not less than 10m.

① Soil layer drilling: Drill with a φ108mm drill bit to ensure that the hole diameter is ≮110mm. After each drilling cycle is completed, take out the soil cores, place them neatly, and record the depths of different soil layers with labels. All the holes adopt φ108mm casing, and the wall casing is 0.2 to 0.5 meters above the ground.

②Drilling in rock formations: φ91mm drill bits are used below the bedrock surface. During the drilling process, cores are taken out and placed neatly. Small labels are used to record different lithologies and depths of caves. After drilling to the designed depth, clean the drilled holes, and the cleaning time should not be less than 20 minutes.

When geological drilling finds that the karst is large and two adjacent holes may be connected, the grouting hole should be skipped and drilled, and the grouting should not be done after all the holes are drilled.

(2) After the drilling is completed, the geological recorder will record the core in time, and record the depth of different soil and rock layers, the development of karst and the depth of the groundwater level. During the drilling process, the supervisory engineer stood by to record the geological changes.

(3) Fix the grouting casing with cement mortar.

(c) Water injection test before grouting;

(d) Grouting: (1) Install a disc mixer (flange) on the casing, debug the grouting machine, test the pressure of the pipeline, check the connection and sealing quality of the pipeline and joints, and connect the pressure gauge , ready for grouting.

(2) After the water injection test is completed, start grouting. In case of karst passages, large caves and fissures, fill medium-coarse sand and cement mortar, etc. as appropriate. If there is karst development but the amount of grout suction is small or no grout is injected, first use high-pressure clean water to clean the hole or drill the hole, and then dredge the karst fissure channel before grouting.

(3) For the grouting holes with fillings in the cave or the grouting holes with doubts about the quality of the grouting, use a drilling rig to clean the holes and re-grouting after 1 to 2 hours of grouting to ensure that the grout has reached the lower limit of the cave or meets the design Grouting amount and grouting end condition. When the grouting process reaches one of the following standards, end the grouting of the hole:

① The pressure at the grouting orifice is maintained at about 0.5MPa for 10 minutes.

②When the grouting point is 3-5m out of the grouting range.

Set observation piles at the center of the line in the grouting area, the embankment on both sides of the subgrade or the toe of the cutting slope, and 10m outside the toe of the slope (or outside the top of the cutting), and the longitudinal spacing is not greater than 50m. The transition section and the heterogeneous area should be densely observed , Observing the surface settlement before and after grouting, and making ground observation records. During the construction period, surface deformation monitoring must be carried out every day. The actual measurement of surface deformation shall not be greater than 1mm, and detailed records shall be made. The grouting pressure shall be controlled according to the observation data, so as not to affect the stability of the cutting slope or nearby structures. At the same time, the monitoring data shall be Submit to relevant departments for roadbed settlement analysis.

(e) Hole sealing: After the grouting is finished, the quality inspection engineer will inspect and notify the supervisory engineer to check and confirm the final hole conditions. Remove the flange, pull out the casing, backfill the hole with M7.5 cement mortar, beat it tightly, and mark the hole.

(f) Drilling of general grouting holes and grouting of general grouting holes: after the construction of pilot exploration holes, drilling, grouting construction and sealing of general grouting holes shall be carried out.

(g) Detection of grouting effect: After grouting, the treatment effect is detected by geophysical prospecting, core drilling and hydraulic test.

(1) Water injection test. Before the water injection test, after measuring the stable water level in the hole, carry out quantitative water injection in the hole, and observe the change range of water absorption per unit length. The water absorption per unit length of the test after grouting should be less than the water absorption before grouting. 3 to 5%, it can be judged that the grouting effect has been achieved.

(2) Drilling inspection, the number of inspection holes is 5%, and the grouting effect can be visually judged according to the filling of the coring slurry.

(7) Before the construction of the first batch of pile foundations, the following pretreatment methods should be used to pretreat the karst caves in advance: drilling holes with small diameters, injecting mortar, and the ratio of cement mortar is: water: cement: sand = 0.8: 1.0: 1.0. For the hole forming part by impact, it is calculated that 2 meters before entering the bedrock, the rubble and clay block will be compacted horizontally, and the volume of the filling will be about 18.84m ³ , and it will be hit lightly when entering the rock.

This specific embodiment is only an explanation of the present invention, and it is not a limitation of the present invention. Those skilled in the art can make modifications to this embodiment without creative contribution as required after reading this specification, but as long as they are within the rights of the present invention All claims are protected by patent law.

Claims (10)

1. A kind of multilayer karst development band pile foundation engineering construction method is characterized in that, concrete construction steps are as follows: (1) Comprehensively establish calculation models and calculation formulas to determine the depth of pile foundation geophysical prospecting and construction survey and survey ideas in karst areas; (2) Investigate the lithology, structure, rock surface change and weathering degree of the bedrock according to the survey ideas described in step (1), determine its hardness, integrity and basic quality level, and determine whether there are caves, free surfaces, Broken rock mass or weak rock formations to form survey results; (3) Draw a distribution map of geological fault zones and a map of the relative position relationship between the proposed building and the karst development zone according to the survey results described in step (2); (4) According to the distribution map of the geological fault zone and the relative position relationship map mentioned in step (3), the construction sequence of the pile foundation on the site is formulated with each building to be built as a unit; (5) According to the construction sequence described in step (4), the karst development zone is divided into four grades according to the location, development situation and the possible ground collapse risk level caused by the construction of the karst pile foundation: Level 1 (1): No karst caves are encountered in advance drilling, or the cumulative thickness of karst caves is less than or equal to 1 meter, and the construction of karst pile foundations does not cause ground subsidence or the depth of ground subsidence is less than 0.5 meters; The second level (2): the cumulative thickness of karst caves revealed by advanced drilling is greater than 1 meter and less than or equal to 3 meters, and the depth of ground subsidence caused by karst pile foundation construction is less than 1.5 meters; The third level (3): the cumulative thickness of karst caves revealed by advanced drilling is greater than 3 meters and less than or equal to 5 meters, and the depth of ground subsidence caused by karst pile foundation construction is less than 2.5 meters; The fourth level (4): The cumulative thickness of karst caves revealed by advanced drilling is greater than or equal to 5 meters, and the depth of ground subsidence caused by karst pile foundation construction is greater than 2.5 meters; (6) For the karst-developed pile foundation of each building pile, carry out grouting construction in batches and layers according to the grade described in step (5): (I) For the first grade (1), the first batch of construction is carried out, and no prevention and control is required for direct construction; (II) For the second level (2), carry out the second batch of construction, impact the part of the hole, and calculate the 2 meters before entering the bedrock, throw the screed and the clay block for lateral compaction, and hit lightly when entering the rock; (Ⅲ) For the third grade (3), carry out the third batch of construction, impact the hole-forming part, throw the full-length flakes and clay blocks for lateral compaction, and hit lightly when entering the rock; (IV) For the fourth grade (4), carry out the fourth batch of construction; (7) Before the construction of the first batch of pile foundations, the following pretreatment methods are used to pretreat the karst cave in advance: small-diameter drilling, injection of mortar, and the cement mortar ratio is: water: cement: sand = 0.8: 1.0: 1.0; impact For the hole-forming part, according to calculations, 2 meters before entering the bedrock, the stones and clay blocks should be thrown and compacted horizontally, and lightly hit when entering the rock. 2. A construction method for multi-layer karst-developed piled foundation engineering according to claim 1, characterized in that: the investigation of the lithology and structure of the bedrock described in step (2) adopts the method of drilling and coring. 3. A construction method for multi-layer karst development with pile foundation engineering according to claim 2, characterized in that: according to the law and degree of karst development in different areas of the site, suitable pile type and pile length are selected to stabilize the karst roof For karst and fault fracture zones, exploration holes should pass through karst caves or fault fracture zones and enter stable strata, and the depth of pile bottoms entering intact rock should not be less than 5.0m. The compressive strength, shear strength and tensile strength of the pile foundation are used to check the stability of the karst roof of the pile foundation. 4. according to claim 2 or 3 described a kind of multi-layer karst development belt pile foundation engineering construction method, it is characterized in that: adopt casing retaining wall drilling or mud retaining wall drilling for landslide loose soil and strong weathered bedrock layer Double-pipe single-action core drilling is used in the 5m section below the pile bottom; mud retaining wall drilling is used for the complete bedrock below. 5. A construction method for multi-layer karst-developed pile foundation engineering according to claim 1, characterized in that the grouting construction sequence described in step (6) is as follows: (a) preparation for construction; (b) Pilot hole drilling; (c) Water injection test before grouting; (d) grouting; (e) sealing holes; (f) general grouting hole drilling; (g) grouting for general grouting holes; (h) Detection of grouting effect. 6. A construction method for multi-layered karst-developed pile foundation engineering according to claim 5, characterized in that: in the step (b), when the geological drilling finds that the karst is relatively large, two adjacent holes may be connected When drilling, the grouting hole should be skipped and drilled, and the grouting should not be done after all the holes are drilled. 7. A construction method for a multi-layered karst developed foundation with piles according to claim 5, characterized in that: in the step (b), the position deviation of the grouting holes does not exceed 50 cm. 8. A construction method for a multi-layered karst developed foundation with piles according to claim 5, characterized in that: in the grouting process of the step (d), observation piles are buried in the grouting area, and before and after grouting Observe its surface subsidence and make ground observation records. 9. A kind of construction method of multi-layer karst development belt pile foundation engineering according to claim 8, characterized in that: the observation pile is arranged in the center of the line, the embankment on both sides of the subgrade or the foot of the cutting slope, and outside the foot of the slope or 10m outside the top of the cutting are arranged respectively, and the longitudinal spacing is not more than 50m, and the observation section should be intensified in the range of the transition section and the heterogeneous area. 10. A construction method for a multi-layered karst developed foundation with piles according to claim 5, characterized in that: when the grouting process in the step (d) reaches one of the following standards, the hole grouting is ended: ①The pressure at the grouting orifice is maintained at about 0.5MPa for 10 minutes; ②When the grouting point is 3-5m outside the grouting range.