A soft foundation replacement construction method

Abstract

The present invention relates to the technical field of foundation construction, and in particular to a soft foundation replacement construction method, comprising: S1, construction preparation; S2, vacuum preloading primary reinforcement; S3, unloading vacuum preloading; S4, replacement area layout; S5, excavation replacement area; S6, backfilling; the present invention aims at a soft foundation with slow drainage and long consolidation time, firstly uses a vacuum preloading reinforcement method to accelerate the discharge of water in the foundation, and performs preliminary reinforcement on the foundation, and when a roller is used to compact the original soil after vacuum preloading, spring soil appears due to the return of water from a drainage board, and the surface soil cannot be compacted, resulting in the inability to compact the upper graded gravel. The scheme adopts replacement reinforcement, and no drying is required after replacement, and the construction efficiency is high, the construction time is short, and the soil compaction degree is high, which can meet the compaction degree requirement of 90%.

Description

Technical Field

[0001] The invention relates to the technical field of foundation construction, and in particular to a soft foundation replacement construction method. Background Art

[0002] For port projects whose foundation is dredged soil from the harbor area, the dredged soil is mainly silty silty clay, silt and silty clay. After the dredged soil is blown by a suction dredger, if the blown fill soil is silty silty clay, the foundation after blowing is extremely weak, the drainage is slow, and the consolidation time is very long, so reinforcement treatment is required; if the blown fill soil is silt and silty clay, it is generally in an unconsolidated state after blowing, and the consolidation time is long.

[0003] In order to make the bearing capacity of the extremely soft foundation meet the design requirements, it needs to be reinforced. Chinese patent CN111268951A discloses an improved low liquid limit silt roadbed material and its preparation method and application. For the extremely soft foundation in the severe cold area, alkali-activated materials are used to improve the low liquid limit silt roadbed. The A liquid is doped with steel slag, and the B liquid is a NaOH solution. Since the cost of steel slag is high and the NaOH solution is corrosive and pollutes the ecological environment, it is only suitable for extremely cold areas. For offshore projects where the construction area is located in the Yellow River alluvial and marine-continental interactive sedimentary strata, especially port yards and road structure layers with high bearing capacity requirements, it is necessary to develop a pollution-free replacement construction method suitable for soft foundations with slow drainage and long consolidation time. Summary of the invention

[0004] In view of the above-mentioned deficiencies in the prior art, the present invention provides a soft foundation replacement construction method which can save construction time and reduce costs.

[0005] The present invention provides a soft foundation replacement construction method, comprising the following steps:

[0006] S1. Construction preparation:

[0007] Use amphibious excavators to level the construction area, remove debris and garbage from the site, and drain the surface water;

[0008] S2, vacuum preloading primary reinforcement:

[0009] Lay a sand cushion layer on the surface, then use a plate inserter to install a drainage board, bury a filter pipe on the sand cushion layer, install a detection instrument, dig a film pressing trench, lay a textile cloth and a sealing film, install a vacuum jet device, use a vacuum pump to vacuum pre-press the vacuum pre-pressing area, and monitor the vacuum degree and settlement amount;

[0010] S3, unloading vacuum preloading:

[0011] When the vacuum preloading reaches the design requirements, the vacuum preloading is unloaded, the water on the sealing membrane is discharged, the surface of the site is cleaned, and after unloading, the settlement area is backfilled with medium-coarse sand in layers and compacted;

[0012] S4. Laying out the replacement area:

[0013] Lay out the site that needs to be replaced and reinforced according to the control pile points and confirm the construction area;

[0014] S5. Excavation and filling area:

[0015] Use an excavator to dig the replacement area under the original mud surface in the construction area to the designed depth, cut off the drainage board retained by the above vacuum preloading in the construction area to block the vertical drainage channel, and transport the excavated original soil and drainage board to the storage area;

[0016] S6. Backfill:

[0017] After the filling material is mixed evenly, a certain thickness of the filling material is backfilled into the replacement construction area, and paving and rolling are performed. When the compaction degree reaches 90%, a first backfill layer is formed;

[0018] Continue to backfill the filling material on top of the first backfill layer until the replacement area is filled, spread and roll, and after the compaction degree reaches 90%, form a second backfill layer to complete the replacement of the soft foundation.

[0019] The soft foundation replacement construction method of this technical solution is aimed at soft foundations with slow drainage and long consolidation time. The vacuum preloading reinforcement method is first used to accelerate the drainage of water in the foundation and to preliminarily reinforce the foundation. When the roller is used to compact the original soil after vacuum preloading, spring soil appears due to the return of water from the drainage board, and the surface soil cannot be compacted, resulting in the inability to compact the upper graded gravel. This solution adopts replacement reinforcement, and no drying is required after replacement, the construction efficiency is high, the construction time is short, and the soil compaction degree is high to meet the compaction degree requirement of 90%.

[0020] In some embodiments of the present application, the designed depth of the replacement area is 1-1.2 m, the depth of the first backfill layer is 0.5-0.7 m, and the depth of the second backfill layer is 0.5-0.7 m.

[0021] In some embodiments of the present application, in step S6, the filling material includes 50% fly ash and 50% silt by weight; the traditional replacement filling process uses lime soil and construction waste mixed with 5% lime in silt, which is costly, and lime and water absorb water, resulting in a decrease in the free water content in the soil and consolidation. It also requires overall drying, and the construction time is long; the construction cost of using fly ash and silt is reduced to 60~80 yuan / cubic meter, and no drying is required, saving construction time.

[0022] In some embodiments of the present application, in step S6, when constructing the first backfill layer, an excavator is used to first spread the fly ash 0.25-0.35m, spread and roll it, and then the excavator continues to spread the silt 0.25-0.35m, and a backhoe and a rotary plow are used to mix the fly ash and silt evenly, and then rolling construction is performed;

[0023] The construction process of the second backfill layer is the same as that of the first backfill layer, and the construction process of the first backfill layer is repeated to form the second backfill layer.

[0024] In some embodiments of the present application, when a roller is used to compact the first backfill layer and the second backfill layer, the driving speed does not exceed 2 km / h, and the rolling direction is gradually from both sides to the middle for multiple rolling to avoid missing pressure.

[0025] In some embodiments of the present application, in step S2, the sand cushion layer is a medium-coarse sand cushion layer, and the thickness of the medium-coarse sand cushion layer is 40 cm.

[0026] In some embodiments of the present application, in step S2, the insertion depth of the drain board is such that the lower end of the drain board needs to pass through the silt layer and enter the silty clay for more than 1.0 meter without entering the lower permeable layer.

[0027] In some embodiments of the present application, in step S3, when the vacuum full load preloading exceeds 90 days, and the consolidation degree of the foundation soil under the preloading load is not less than 80%, and the measured surface settlement rate is not more than 2.5 mm / d for 5 consecutive days, vacuum preloading unloading is performed.

[0028] Based on the above technical scheme, the soft foundation replacement construction method of the present invention is aimed at the soft foundation with slow drainage and long consolidation time. The vacuum preloading reinforcement method is first used to accelerate the drainage of water in the foundation and preliminarily reinforce the foundation. When the roller is used to compact the original soil after vacuum preloading, the drainage board returns water, resulting in spring soil. The surface soil cannot be compacted, resulting in the inability to compact the upper graded gravel. This scheme adopts replacement reinforcement, and no drying is required after replacement, the construction efficiency is high, the construction time is short, and the soil compaction degree is high, which can meet the compaction degree requirement of 90%;

[0029] The invention adopts fly ash and powdered soil, reduces the construction cost to 60-80 yuan / m3, does not need to be air-dried, and saves construction time. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of this application. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0031] Figure 1The present invention is a flowchart of a soft foundation replacement construction method according to an embodiment of the present invention. DETAILED DESCRIPTION

[0032] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0033] In the description of the present invention, it should be understood that the terms "center", "lateral", "longitudinal", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside" and "outside" etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0034] The terms "first", "second", and "third" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the technical features indicated. Thus, a feature defined as "first", "second", and "third" may explicitly or implicitly include one or more of the features.

[0035] In the description of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a direct connection, or an indirect connection through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0036] The soft foundation replacement construction method of this embodiment is suitable for the foundation of dredged soil in the harbor area. The dredged soil within the dredging range is mainly silty silty clay, silt and silty clay. When the blown fill soil is silty silty clay, the foundation is extremely weak after blowing, the drainage is slow, and the consolidation time is very long, so reinforcement treatment is required; when the blown fill soil is silt and silty clay, it is generally in an unconsolidated state after blowing, and the consolidation time is long. Therefore, it is necessary to first perform vacuum preloading treatment on the construction area. Specifically, the following steps are included:

[0037] S1. Construction preparation:

[0038] Use amphibious excavators to level the construction area, remove debris and garbage from the site, and drain the surface water;

[0039] S2, vacuum preloading primary reinforcement:

[0040] A 40cm thick medium-coarse sand cushion layer is laid on the surface by mechanical and manual methods. Since the geology of the construction area is mainly silt and silty clay, which is generally slightly to weakly permeable, no sealing wall is temporarily set up. If it is found that the permeability is large during construction and affects the effect of vacuum preloading, a sealing wall will be added in time.

[0041] If it is found on site that a sealing wall needs to be added, clay mixing should be used to seal the three sides (east, south, and west) or all four sides of the vacuum pre-compression until the requirements for vacuum sealing performance are met.

[0042] Sealing wall construction is to mix clay into the sandy soil layer with high air and water permeability on the surface or buried deep underground, so as to reduce the permeability of the sandy soil and make it suitable for vacuum preloading construction technology. The width of the clay sealing wall (i.e. the ditch width) shall not be less than 1.2m, and the depth of entering the impermeable layer shall not be less than 1.0m. After mixing, the clay content of the wall shall be greater than 40%, and the permeability coefficient shall not be greater than 5×l0-6cm / s.

[0043] Then use the plate inserter to install the drainage board, and use the casing installation method. The verticality of the casing should be controlled during the sinking process, and the verticality of the casing should be controlled by the pitch angle of the installation frame, and its deviation should be controlled to be no more than 15mm / m. If the casing sinking speed suddenly slows down or excessive bending occurs, the sinking of the casing should be stopped immediately, and the obstacles should be analyzed and checked. If hard objects such as stones are encountered during the casing sinking process, the casing can be installed at the nearby board position to avoid obstacles;

[0044] The lower end of the casing needs to pass through the silt layer and enter the silty clay for more than 1.0 meter and ensure that it does not enter the lower permeable layer. During construction, pay attention to the ammeter reading of the plug-in machine. When the ammeter reading changes significantly, it means that it has entered the silty clay layer. During the casing sinking process, attention should be paid to controlling the verticality of the casing at all times.

[0045] After the plastic drain board is installed, the testing instrument is buried in time, and then the main pipe and filter pipe are buried on the sand cushion layer. The main pipe is made of φ63mm PVC pipe, and the filter pipe is made of φ63mm PVC pipe. After punching, it is wrapped with a layer of non-woven fabric. The strength of the PVC pipe is required to withstand a pressure of 400kPa. The filter pipe is connected into a network shape with two-way, three-way and four-way. The connection between the pipe fittings and the filter pipe and between the filter pipes is made of steel wire rubber hose; in order to prevent the sealing film from being punctured by hard objects during the vacuuming process, after the main pipe and filter pipe are buried, the exposed plastic drain board head needs to be buried below the sand surface, the holes formed when the board is inserted are filled, and the silt blocks and all angular hard objects on the surface layer are cleared to make the sand surface flat;

[0046] Use an excavator to dig the film-pressing trench. When digging the sealing trench, the debris in the trench must be removed. When excavating, ensure the cross-sectional size, cut off the permeable layer, and the slope surface should be smooth and free of hard objects. First, lay a layer of 200g / ㎡ non-woven textile fabric as a protective layer. When laying, the membrane should not be pulled too tight. A fold of about 10cm should be reserved every 10 meters to prevent the sealing membrane from being damaged by excessive tension during vacuuming. The sealing membrane should ensure good sealing performance. A special film-exit device should be used at the membrane outlet of the pipeline, and the sealing performance should be ensured. The sealing membrane should be buried at a depth of not less than 1m, and finally the soil should be excavated to bury the membrane. The backfill surface of the film-pressing trench should be 50 to 100cm lower than the membrane surface to keep the film-pressing trench moist during vacuuming. The film outlet of the filter tube is treated with a film-exit device. The film-exit device is made of a Ф5cm seamless pipe, extending 30cm outside the membrane, and there is a retractable and tight surplus film at the film outlet.

[0047] Install a vacuum jet device, use a vacuum pump to evacuate the vacuum preloading area, and monitor the vacuum degree and settlement. Start timing after the vacuum degree reaches 85kpa. The full-load evacuation time of the vacuum preloading area is tentatively set at 120 days according to the design requirements. If the unloading standard is not met, continue to apply a constant load until it is met.

[0048] S3, unloading vacuum preloading:

[0049] When the vacuum full load preloading exceeds 90 days, and the consolidation degree of the foundation soil under the preloading load is not less than 80%, and the measured surface settlement rate for 5 consecutive days is not more than 2.5mm / d, vacuum preloading unloading is carried out. The vacuum preloading unloading is arranged to stop the pump and unload in sequence according to the principle of first four weeks and then the middle; the overlying water on the sealing membrane is discharged, and the surface layer of the site is cleaned. When the foundation consolidation degree can reach more than 90%, the settlement area is backfilled with medium and coarse sand in layers after unloading, and compacted by rolling. In this embodiment, the backfilling and compaction are required to the final intersection elevation of 3.4m;

[0050] S4. Laying out the replacement area:

[0051] Lay out the site that needs to be replaced and reinforced according to the control pile points and confirm the replacement construction area;

[0052] S5. Excavation and filling area:

[0053] Use an excavator to dig the replacement area under the original mud surface in the replacement construction area. Use two 260 excavators to dig 1m from east to west in sequence, cut off the drainage board retained by the above vacuum preloading in the construction area to block the vertical drainage channel, and after building a temporary road, deploy four dump trucks to transport the excavated original soil and drainage board to the original storage area;

[0054] S6. Backfill:

[0055] The fly ash is transported to the replacement construction area, and the fly ash is first spread 25 cm by an excavator, and then the silt is spread 25 cm by the excavator. The fly ash and silt are evenly mixed by a backhoe and a rotary plow, and then rolled. The weight fraction ratio of fly ash to silt is 50:50, and the first backfill layer is formed after the compaction degree reaches 90%. This further solves the problem that the surface soil cannot be compacted after the vacuum preloading is completed, and the graded gravel laid is difficult to compact.

[0056] Above the first backfill layer, continue to repeat the above operations. First, use an excavator to spread the fly ash 25 cm thick, spread and roll it, and then use the excavator to continue spreading the silt 25 cm. Use a backhoe and rotary plow to mix the fly ash and silt evenly, and then carry out rolling construction. The weight fraction ratio of fly ash to silt is 50:50. After the compaction degree reaches 90%, the second backfill layer is formed to complete the replacement of the soft foundation.

[0057] The traditional replacement filling process uses lime soil mixed with 5% lime in silt and construction waste, which is costly. Lime and water absorb water, resulting in a reduction in free water content in the soil and consolidation. It also requires overall drying, which takes a long time to construct. The construction cost of using fly ash and silt is reduced to 60-80 yuan / m3, and there is no need for drying, which saves construction time.

[0058] This embodiment uses a 22t vibratory roller for rolling and compaction, and controls the driving speed. Generally, the flat roller and the vibratory roller should not exceed 2km / h; and the number of compaction passes should be controlled; the compaction degree is required to reach 90%, and the rolling machine should maintain a certain distance from the foundation to prevent the foundation from being crushed or displaced;

[0059] Based on the above technical scheme, the soft foundation replacement construction method of the present invention is aimed at the soft foundation with slow drainage and long consolidation time. The vacuum preloading reinforcement method is first used to accelerate the drainage of water in the foundation and preliminarily reinforce the foundation. When the roller is used to compact the original soil after vacuum preloading, the drainage board returns water, resulting in spring soil. The surface soil cannot be compacted, resulting in the upper graded gravel cannot be compacted. This scheme adopts replacement reinforcement, and no drying is required after replacement, the construction efficiency is high, the construction time is short, and the soil compaction degree is high, which can meet the compaction degree requirement of 90%; it further solves the problem that the surface soil cannot be compacted after the vacuum preloading is completed, and the graded gravel laid;

[0060] The invention adopts fly ash and powdered soil, reduces the construction cost to 60-80 yuan / m3, does not need to be air-dried, and saves construction time.

[0061] Finally, it should be noted that: the various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0062] The above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, ordinary technicians in the field should understand that the specific implementation methods of the present invention can still be modified or some technical features can be replaced by equivalents without departing from the spirit of the technical solution of the present invention, which should be included in the scope of the technical solution for protection of the present invention.

Claims

1. A soft foundation replacement construction method, characterized by: The specific steps include: S1. Construction preparation: Use amphibious excavators to level the construction area, remove debris and garbage from the site, and drain the surface water; S2, vacuum preloading primary reinforcement: Lay a sand cushion layer on the surface, then use a plate inserter to install a drainage board, bury a filter pipe on the sand cushion layer, install a detection instrument, dig a film pressing trench, lay a textile cloth and a sealing film, install a vacuum jet device, use a vacuum pump to vacuum pre-press the vacuum pre-pressing area, and monitor the vacuum degree and settlement amount; S3, unloading vacuum preloading: When the vacuum full load preloading exceeds 90 days, and the consolidation degree of the foundation soil under the preloading load is not less than 80%, and the measured surface settlement rate is not more than 2.5mm / d for 5 consecutive days, vacuum preloading unloading is carried out. The vacuum preloading unloading is arranged to stop the pump and unload in sequence according to the principle of four weeks first and then the middle; the overlying water on the sealing membrane is discharged, and the surface of the site is cleaned. When the foundation consolidation degree reaches more than 90%, the settlement area is backfilled in layers with medium and coarse sand after unloading, and compacted by rolling; S4. Laying out the replacement area: Lay out the site that needs to be replaced and reinforced according to the control pile points and determine the replacement construction area; S5. Excavation and filling area: Use an excavator to dig the replacement area under the original mud surface in the construction area to the designed depth, cut off the drainage board retained by the above vacuum preloading in the construction area to block the vertical drainage channel, and transport the excavated original soil and drainage board to the storage area; S6. Backfill: After the filling material is mixed evenly, a certain thickness of the filling material is backfilled into the replacement construction area, and paving and rolling are performed. When the compaction degree reaches 90%, a first backfill layer is formed; Continue to backfill the filling material on top of the first backfill layer until the replacement area is filled, spread and roll, and after the compaction degree reaches 90%, form a second backfill layer to complete the replacement of the soft foundation; In step S6, the filling material includes 50% by weight of fly ash and 50% by weight of silt, and does not need to be aired after replacement; In step S6, when constructing the first backfill layer, an excavator is used to first spread the fly ash 0.25-0.35m, spread and roll it, and then the excavator continues to spread the silt 0.25-0.35m, and a backhoe and a rotary plow are used to mix the fly ash and silt evenly, and then roll it; Repeat the first backfill layer construction process to form the second backfill layer.

2. The soft foundation replacement construction method according to claim 1 is characterized in that: The designed depth of the replacement area is 1-1.2 m, the depth of the first backfill layer is 0.5-0.7 m, and the depth of the second backfill layer is 0.5-0.7 m.

3. The soft foundation replacement construction method according to claim 1 is characterized in that: When the first backfill layer and the second backfill layer are compacted by a roller, the driving speed shall not exceed 2 km / h, and the rolling direction shall be gradually rolled from both sides to the middle for multiple times to avoid missing compaction.

4. The soft foundation replacement construction method according to claim 1 is characterized in that: In step S2, the sand cushion layer is a medium-coarse sand cushion layer, and the thickness of the medium-coarse sand cushion layer is 40 cm.

5. The soft foundation replacement construction method according to claim 4 is characterized in that: In step S2, the insertion depth of the drain board is such that the lower end of the drain board needs to pass through the silt layer and enter the silty clay for more than 1.0 meter, and does not enter the lower permeable layer.

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