Technological method for repairing heavy metal polluted soft soil through bottom vacuum leaching and reinforcing through dynamic compaction

Abstract

The invention relates to a process method for repairing heavy metal polluted soft soil through bottom vacuum leaching and reinforcing through dynamic compaction. Aiming at the problems of incapability of repairing soil for a long time, too high repairing cost, slow repairing, poor repairing effect and the like in various existing heavy metal polluted soft soil repairing methods, the polluted soil is treated through a bottom vacuum leaching method, so that the soil repairing efficiency is greatly improved; and then the soft soil repaired through the bottom vacuum method is reinforced through a dynamic compaction method, and finally the two purposes of repairing and reinforcing are achieved. Compared with the prior art, the heavy metal polluted soft soil remediation technology is low in cost and can be applied on a large scale.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of contaminated soil remediation, in particular to a process method for remediation of heavy metal contaminated soft soil by bottom vacuum leaching and dynamic compaction reinforcement. BACKGROUND

[0002] Soft soil is widely distributed, but at the same time, the continuous development of industry exacerbates the generation of heavy metal pollutants. Due to the shortcomings in the emission and resource utilization process of heavy metal pollutants, it is inevitable for heavy metal pollutants to flow to soft soil areas. The heavy metal contaminated soft soil has the following characteristics: 1) fine particles and large specific surface area, which increases the adsorption capacity of heavy metals, thereby significantly increasing the removal difficulty. 2) The permeability is extremely low, and the permeability coefficient is generally in the order of 10 -6 cm / s, so it is difficult for water or solution to penetrate the soil to flush out the pollutants. 3) The soft soil has low strength, and after remediation, it cannot be directly used as a foundation, and needs to be reinforced by geotechnical engineering methods.

[0003] At present, the remediation methods for heavy metal contaminated soil mainly include in-situ fixation, phytoremediation, bioremediation and electrokinetic remediation.

[0004] In-situ fixation is to add amendments to the soil, and to fix heavy metals in the soil by adsorption, precipitation or complexation, thereby reducing their mobility and bioavailability. It has the advantages of high cost-effectiveness, suitable for large-area application, and can utilize the natural adsorption capacity in soft soil. However, it does not remove heavy metals, and the long-term effect may be weakened due to environmental changes. Phytoremediation uses plants to absorb heavy metals through roots, stabilize metals in soil or remove them through volatilization to achieve remediation. Phytoremediation has the advantages of environmental protection, low cost, aesthetics and improvement of soil ecology, and is particularly suitable for long-term remediation. However, the process is slow, usually taking several years, and the removal efficiency for high concentration pollution is low. In addition, the biomass of treated contaminated plants may cause secondary pollution. For soft soil environment, plants that can tolerate flooding or dense conditions need to be selected, and plant adaptability is a key factor. Bioremediation uses microorganisms to change the form of heavy metals through biotransformation, precipitation or adsorption, thereby reducing their toxicity or mobility. This technology has the advantages of natural process, little interference, low cost, suitable for long-term application, and can be combined with phytoremediation. However, the remediation efficiency is affected by microbial activity and soil conditions (such as pH and humidity), and the process may be slow, which is not suitable for sites that require urgent remediation. In soft soil, anaerobic conditions are common, so suitable microorganisms need to be selected. Electrokinetic remediation makes charged particles move towards the electrode by electroosmosis and electromigration through the application of an electric field, and then removes them. Electrokinetic remediation is effective for soft soil, as its low permeability limits other methods, and in-situ application can reduce site disturbance. However, the technology is not yet mature, and needs to improve efficiency, has high energy consumption, may need pH control, and long-term effect needs to be verified.

[0005] Vacuum preloading is an effective method for rapidly consolidating soft soil by applying a vacuum negative pressure load to the foundation soil. This method rapidly drains water from the soft soil, increases the effective stress within the soil, and promotes rapid consolidation. It has been widely used in civil engineering. However, it is generally suitable for treating soft soils at greater depths and is costly for treating soft soils with thin surface layers. Heaped load preloading applies a piled load to the foundation soil, increasing the total stress within the soil and allowing water to drain to the surface through vertical drainage channels within the foundation, achieving rapid consolidation. However, this method requires a large amount of heaped material and storage space after treatment, resulting in high costs and a lengthy construction period. Dynamic compaction involves lifting a rammer to a certain height and allowing it to fall freely, converting the rammer's potential energy into kinetic energy to compact the foundation soil. It is effective for consolidating shallow surface soils and is widely used in various types of soft and gravelly soils.

[0006] Currently, various heavy metal contaminated soft soil remediation methods have many problems such as being unable to repair the soil in the long term, or having high remediation costs, slow remediation, and poor remediation effects. Therefore, there is an urgent need for a low-cost and large-scale heavy metal contaminated soft soil remediation technology. Summary of the Invention

[0007] The purpose of the present invention is to overcome the defects of the above-mentioned prior art and provide a process method for bottom vacuum leaching to repair heavy metal contaminated soft soil and dynamic compaction reinforcement. The present invention proposes a combined method of bottom vacuum leaching to repair heavy metal contaminated soft soil and dynamic compaction to reinforce foundation soil. The contaminated soil is treated by the bottom vacuum leaching method, which greatly improves the efficiency of soil remediation. Afterwards, the dynamic compaction method is used to reinforce the soft soil that has been repaired by the bottom vacuum method, and finally achieves the two purposes of repair and reinforcement. The present invention proposes a new approach from the two perspectives of soil remediation and foundation reinforcement. It is a low-cost and large-scale heavy metal contaminated soft soil remediation technology with broad application prospects and good social and economic benefits.

[0008] The purpose of the present invention can be achieved by the following technical solutions:

[0009] The object of the present invention is to provide a process for repairing heavy metal contaminated soft soil by bottom vacuum leaching and dynamic tamping reinforcement, the process comprising the following steps:

[0010] 1) Analyze the contaminated soft soil to be remediated, select a leaching site based on the soil characteristics of the contaminated soft soil, excavate a leaching pool, and arrange the leaching pool;

[0011] 2) arranging a bottom vacuum leaching assembly in the leaching pool, the bottom vacuum leaching assembly comprising a drainage plate, a woven cloth or geotextile cloth, and a vacuum device, the woven cloth or geotextile cloth being arranged above the drainage plate, and the drainage plate being connected with the vacuum device;

[0012] 3) performing bottom vacuum leaching, continuously applying vacuum and supplementing leaching liquid until the heavy metal content of the soil reaches a standard value and below, obtaining the remediated soil and removing the woven cloth or geotextile cloth;

[0013] 4) after removing the woven cloth or geotextile cloth, starting the vacuum device of the bottom vacuum leaching assembly to perform bottom vacuum pumping, reducing the water content of the soil to an optimal water content (the optimal water content is a key physical parameter in soil mechanics representing the compaction characteristics of cohesive soil, and is defined as the water content corresponding to the maximum dry density of the soil under standard compaction conditions);

[0014] 5) after reducing the water content of the soil to the optimal water content, determining optimal dynamic compaction parameters, performing different numbers of point ramming to meet the requirements of foundation bearing capacity and compression characteristics, and then performing full ramming to achieve reinforcement.

[0015] Further, step 1) specifically includes the following processes:

[0016] 1-1) performing indoor test analysis on the heavy metal contaminated soft soil to be remediated to obtain the pollution degree, permeability, and grading parameters, and selecting the vacuum pressure, reagent concentration, and treatment thickness based on the above parameters;

[0017] 1-2) selecting a leaching site according to the soil characteristics;

[0018] 1-3) excavating a leaching pool in the selected leaching site and setting up an impermeable barrier wall to form a water-impermeable contaminated soft soil storage site.

[0019] Further, in step 1-2), the leaching site can be an in-situ site or an off-site site, and the leaching site is an artificially selected cool and humid area.

[0020] Further, in step 1-3), the depth of the leaching pool is 0.8-1.2 m.

[0021] Further preferably, in step 1-3), the depth of the leaching pool is 1 m.

[0022] Further, in step 1-3), the impermeable barrier wall is arranged at the bottom and around the leaching pool, the impermeable barrier wall is higher than the ground surface of the leaching site, a cofferdam is arranged around the leaching pool, and a waterproof lining is laid at the bottom and the sidewall of the leaching pool.

[0023] Further, in step 2), the bottom vacuum leaching assembly further comprises a sensor probe, and the sensor probe is arranged in the leaching pool.

[0024] Further, the sensor probe comprises one or more of a sensor for testing humidity, a sensor for testing temperature, a sensor for testing pH.

[0025] Further, in step 2), after selecting the leaching site, a suitable device is used to lay the drainage plate at the bottom of the contaminated soft soil.

[0026] Further, in step 2), a single-layer or multi-layer drainage plate is arranged. The laying of the drainage plate is not limited to the bottom of the leaching tank. When the soil layer is thick, multiple layers of drainage plates can also be arranged in the soil layer, and the time of alternating extraction of leaching liquid is determined by experimental tests.

[0027] Further, in step 2), the width and spacing of the drainage plate are both 100-500 mm.

[0028] Further preferably, in step 2), the width and spacing of the drainage plate are both 100 mm, and the specific size is determined by laboratory experiments.

[0029] Further, in step 2), to reduce the extrusion deformation of the drainage plate, a protective tool made of perforated steel can be fixed above the drainage plate.

[0030] Further, the drainage plate can also be used for water supply.

[0031] Further, in step 2), the bottom vacuum leaching assembly further comprises a drain pipe.

[0032] Further, the vacuum device is connected to the head of the drainage plate through the drain pipe.

[0033] Further, the vacuum device is an air compressor.

[0034] Further, step 3) specifically comprises the following steps:

[0035] 3-1) crushing, screening and pretreating the heavy metal contaminated soft soil to be repaired, mixing with the leaching liquid after removing impurities, increasing the initial moisture content, and obtaining the pretreated contaminated soft soil;

[0036] 3-2) injecting the leaching liquid into the leaching tank and filling the pretreated contaminated soft soil in layers, after filling each layer of soil, standing the contaminated soft soil to a stable state, and leveling and supplementing the leaching liquid to a liquid surface 2-3 cm from the surface of the contaminated soft soil;

[0037] 3-3) starting the vacuum device to extract the vacuum, monitoring the settlement, pore water pressure and deep displacement changes, and extracting the leaching liquid through the drainage plate;

[0038] 3-4) continuously extracting the vacuum and supplementing the leaching liquid until the amount of leaching liquid reaches the preset value;

[0039] 3-5) judge whether the soil heavy metal content reaches the standard value and below, if not, return to step 3-3), if yes, obtain the repaired soil;

[0040] 3-6) after obtaining the repaired soil, remove the woven cloth or geotextile.

[0041] Further, in step 3-3), the vacuum refers to: control the vacuum degree ≥ 60 kPa.

[0042] Further, in step 3-4), the vacuum is continuously extracted and the leaching liquid is supplemented according to the solid-liquid ratio of 1:2-3, and the preset value of the leaching liquid amount is 2-3 times the weight of the soil.

[0043] Further preferably, in step 3-4), the vacuum is continuously extracted and the leaching liquid is supplemented according to the solid-liquid ratio of 1:2, and the preset value of the leaching liquid amount is 2 times the weight of the soil. For example, when the solid-liquid ratio is 1:2, 1 kg of contaminated soft soil (dry soil) requires 2 L of leaching liquid. During the leaching process, the leaching liquid needs to be continuously supplemented above the contaminated soil, but not higher than the cofferdam.

[0044] Further, in step 3-4), during the vacuum extraction process, draw the time history curves of settlement, pore water pressure and deep displacement, and adjust the vacuum pressure according to the changes of the time history curves.

[0045] Further, in step 3-5), the source of the standard value of the soil heavy metal content is: "Soil Environmental Quality Construction Land Soil Pollution Risk Control Standard (Trial)", number: GB 3600-2018, applicable scope: residential, commercial, industrial and other construction land. According to "first type of land" and "second type of land", the screening values and control values of heavy metals such as arsenic, cadmium, lead, mercury and nickel are given.

[0046] Further, in step 3-6), after obtaining the repaired soil, the mineral composition and pollutant residue of the repaired soil are analyzed, and the environmental risk is evaluated. After the foundation is reinforced, the woven cloth or geotextile is removed for foundation reinforcement.

[0047] Further, in step 3-6), the gradation, particle morphology and pH value of the repaired soil are detected to evaluate its safety for reuse.

[0048] Further, in step 3-6), the recovery liquid of mixed pollutants is collected to facilitate subsequent separation of the heavy metals of the medicament for resource recycling and reuse.

[0049] Further, step 5) specifically includes the following processes:

[0050] 5-1) confirm the dynamic compaction construction parameters by trial ramming;

[0051] 5-2) According to the construction parameters determined by the trial ramming, the ramming is carried out according to a certain ramming interval, ramming energy and number of hits;

[0052] 5-3) The bottom vacuum water pumping continues, and when the dissipation amount of the excess pore water pressure generated by the ramming is greater than or equal to the preset value, the bottom vacuum water pumping is stopped;

[0053] 5-4) It is judged whether the soil body reaches the requirements of foundation bearing capacity and compression characteristics, if not, the ramming pit is pushed flat and returns to step 5-2), if yes, the ramming is stopped, the ramming pit is pushed flat, and step 5-5) is executed;

[0054] 5-5) Full ramming is carried out to realize reinforcement.

[0055] Further, in step 5-3), the vacuum equipment of the bottom vacuum leaching assembly is continuously used to reduce the water content of the foundation soil (soil after repair) to approach the optimal water content, so as to obtain the optimal compaction degree.

[0056] Further, the preset value of the dissipation amount of the excess pore water pressure generated by the ramming is 70-80%.

[0057] Further preferably, the preset value of the dissipation amount of the excess pore water pressure generated by the ramming is 75%.

[0058] Further, the detection items of the foundation bearing capacity and the compression characteristics are selected from one or more of the soil water content, the void ratio, the compression modulus, the compression coefficient, the single bridge or double bridge static sounding, the vane shear strength, and the plate load test.

[0059] Further, in step 5), the foundation soil (soil after repair) is reinforced by the ramming method to further improve the foundation bearing capacity and reduce the compression characteristics to meet the requirements of engineering construction.

[0060] The technical concept of the application is as follows: The ordinary leaching method is to set vertical well points, and the leaching liquid flows horizontally from the injection well to the soil to be repaired, and then is pumped out from the water pump well. During the flow process, it is subjected to the combined action of downward gravity and horizontal vacuum load, and the direction is inclined downward, it is difficult to ensure that the leaching liquid flows through the contaminated soil, and the leaching efficiency is low. In the bottom vacuum leaching, the leaching liquid flows vertically downward from the top of the soil to be repaired, which can ensure that the leaching liquid flows through the soil to be repaired without dead angle, greatly improving the leaching efficiency. The method of bottom vacuum leaching greatly solves the problems of low permeability of soft soil and injection of leaching liquid on site. The bottom vacuum action can make the leaching liquid flow uniformly through the entire soil area while controlling the pumping rate of the leaching liquid, without the need to lay other complex injection equipment, and has the advantage of low cost.

[0061] After repair, dynamic compaction, particularly low-energy dynamic compaction, is highly effective for reinforcing thin, soft soils on the surface. Bottom vacuum leaching typically involves thin layers of repaired soil, effectively covering this area and achieving optimal foundation reinforcement. Furthermore, because the bottom vacuum leaching assembly continues to operate during the dynamic compaction process, the soil's moisture content can be reduced to a very low level, achieving even better dynamic compaction results, especially for fine-grained soils with high moisture content.

[0062] The remediation of heavy metal-contaminated soft soils is significant not only in pollution control but also in its potential for resource recovery and a circular economy. For example, in the Pearl River Delta, treating 100 square kilometers of contaminated soft soil (1 meter deep) could remove approximately 64,000 tons of lead, valued at approximately US$128 million, while also making the land usable again to support urbanization and agricultural development. This not only reduces the threat of heavy metals to ecosystems but also promotes efficient resource utilization.

[0063] Compared with the prior art, the present invention has the following beneficial effects:

[0064] 1) This technical solution provides a process for bottom vacuum leaching to repair heavy metal contaminated soft soil and dynamic compaction reinforcement. It is mainly aimed at various heavy metal contaminated soft soils such as ordinary soft soil, super soft soil, dredged mud, etc., and uses bottom vacuum filtration to utilize the mutual superposition and promotion effect between gravity and vacuum load to efficiently and quickly remove pollutants from these contaminated soft soils and reduce the pollution level. After the repair is completed, the vacuum equipment of the bottom vacuum leaching mechanism is directly used to pump out groundwater to reduce the moisture content of the soil. Then, the dynamic compaction method is used to reinforce the low-strength soft soil, improve the bearing capacity of the foundation, reduce the compression characteristics, and make it meet the requirements of engineering construction land.

[0065] 2) The process method of the bottom vacuum leaching for repairing heavy metal contaminated soft soil and dynamic compaction reinforcement provided by the technical solution has the advantages of high heavy metal removal rate and fast repair speed compared with the ordinary well point leaching method, greatly improves the repair efficiency of heavy metal contaminated soil, and can greatly reduce the repair cost. Compared with the in-situ repair method such as solidification and stabilization landfill, the application introduces the concept of bottom vacuum leaching, and has the function of long-term repair of contaminated soil. At the same time, unlike most existing methods, the method is easier to popularize to engineering practice, and has the advantages of high efficiency and low cost. Compared with the conventional leaching method, the application has two differences: whether it is suitable for soft soil with extremely low permeability, the application further accelerates the leaching rate through the action of bottom vacuum, so as to achieve the purpose of fast and efficient repair of soil; and the required equipment is different: compared with the traditional off-site leaching, the application does not need large washing equipment, only needs to place the leaching and soil in the leaching pool paved with drainage board, and then uses vacuum equipment (air compressor) to filter to complete the leaching. The process of treating contaminated soft soil is greatly simplified, more contaminated soft soil can be treated, and the effect is better.

[0066] 4) The process method of the bottom vacuum leaching for repairing heavy metal contaminated soft soil and dynamic compaction reinforcement provided by the technical solution has the advantages of relatively low treatment cost, good surface treatment effect, short treatment period, no addition of any external agent, and environmental protection and low carbon.

[0067] 5) The process method of the bottom vacuum leaching for repairing heavy metal contaminated soft soil and dynamic compaction reinforcement provided by the technical solution has the advantages of wide application prospect from the aspects of environmental governance and resource recycling if the method is used to repair heavy metal contaminated soft soil.

[0068] 6) The process method of the bottom vacuum leaching for repairing heavy metal contaminated soft soil and dynamic compaction reinforcement provided by the technical solution has three differences compared with the vacuum preloading method and the stack preloading method: first, it does not need to additionally set up a drainage system, but directly uses the existing bottom vacuum system to pump water and reduce the water content of the soil; second, it does not need additional stack material and treatment of the stack material, but uses the strong impact force generated by the rammer to compact the foundation soil, which is short in construction period and good in effect; and third, it is convenient to realize information construction, and adjusts the subsequent dynamic compaction parameters including the number of times, the number of hits, the energy and all other parameters according to the treatment effect of the foundation soil after each dynamic compaction. BRIEF DESCRIPTION OF DRAWINGS

[0069] Figure 1 The process flow chart of the process method of the bottom vacuum leaching for repairing heavy metal contaminated soft soil and dynamic compaction reinforcement in the embodiments of the application.

[0070] Figure 2The longitudinal section view of the leaching field of the system for repairing heavy metal contaminated soft soil and dynamic compaction reinforcement by bottom vacuum leaching in the embodiment of the present application.

[0071] Figure 3 The drainage board arrangement form of the bottom vacuum leaching assembly for repairing heavy metal contaminated soft soil and dynamic compaction reinforcement by bottom vacuum leaching in the embodiment of the present application.

[0072] Figure 4 The dynamic compaction ramming point arrangement mode of the system for repairing heavy metal contaminated soft soil and dynamic compaction reinforcement by bottom vacuum leaching in the embodiment of the present application. Figure 4 The numbers 1 and 2 in the middle circle represent the first pass and the second pass, respectively.

[0073] Figure 5 The dynamic compaction ramming point arrangement mode of the system for repairing heavy metal contaminated soft soil and dynamic compaction reinforcement by bottom vacuum leaching in the embodiment of the present application.

[0074] The figure label:

[0075] 1, air compressor, 2, drain pipe, 3, leaching liquid, 4, contaminated soft soil, 5, cofferdam, 6, drainage board, 7, woven cloth or geotextile, 8, first pass ramming point, 9, second pass ramming point, 10, full compaction ramming point. DETAILED DESCRIPTION

[0076] The present application will be described in detail below with reference to the accompanying drawings and specific embodiments. In the technical solution, if the component model, material name, connection structure, control method, algorithm and other features are not explicitly stated, they are considered as common technical features disclosed in the prior art.

[0077] In the present application, unless otherwise explicitly specified and limited, the terms "mounting", "connection", "connection", "fixing" and other terms should be understood broadly, for example, it can be fixed connection, or detachable connection, or integrated; it can be mechanical connection, or electrical connection; it can be directly connected, or indirectly connected through an intermediate medium, or the internal communication of two elements or the interaction relationship between two elements. For ordinary skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0078] It is to be noted that the relative terms such as first and second and the like in the present disclosure are only used to differentiate one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between such entities or operations. Moreover, the terms "comprises", "comprising", or any other variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by "comprises... a" does not, without more constraints, exclude the existence of additional identical elements in the process, method, article, or apparatus that comprises the element.

[0079] The present disclosure provides a process for remediation of heavy metal contaminated soft soil 4 by bottom vacuum leaching and dynamic compaction, which comprises the following steps:

[0080] 1) Analyzing the contaminated soft soil 4 to be remediated, and selecting a leaching site based on the soil properties of the contaminated soft soil 4 to excavate and arrange leaching pools;

[0081] 2) Arranging a bottom vacuum leaching assembly in the leaching pool, which comprises a drainage plate 6, a woven cloth or geotextile 7, and a vacuum device, the woven cloth or geotextile 7 is arranged above the drainage plate 6, and the drainage plate 6 is connected with the vacuum device;

[0082] 3) Performing bottom vacuum leaching, continuously vacuuming and supplementing leaching liquid 3 until the heavy metal content of the soil reaches a standard value or below, obtaining the remediated soil and removing the woven cloth or geotextile 7;

[0083] 4) After removing the woven cloth or geotextile 7, starting the vacuum device of the bottom vacuum leaching assembly to perform bottom vacuum pumping to reduce the water content of the soil to an optimal water content;

[0084] 5) After reducing the water content of the soil to an optimal water content, determining the optimal dynamic compaction parameters, and performing different numbers of point compaction to meet the requirements of foundation bearing capacity and compression characteristics, and then performing full compaction to achieve reinforcement.

[0085] In some embodiments of the present disclosure, step 1) specifically comprises the following process:

[0086] 1-1) Performing indoor test analysis on the heavy metal contaminated soft soil 4 to be remediated to obtain the degree of contamination, permeability, and grading parameters, and selecting the vacuum pressure, reagent concentration, and treatment thickness based thereon;

[0087] 1-2) Selecting a leaching site based on the soil properties;

[0088] 1-3) Select a leaching site to excavate a leaching pool, and set up a seepage-proof barrier wall to form a non-permeable contaminated soft soil 4 storage site.

[0089] In some embodiments of the present application, step 3) specifically comprises the following process:

[0090] 3-1) The contaminated soft soil 4 to be repaired is pretreated by crushing and screening, and after removing impurities, it is mixed with the leaching solution 3 to increase the initial moisture content, and the pretreated contaminated soft soil 4 is obtained;

[0091] 3-2) The leaching solution 3 is injected into the leaching pool, and the pretreated contaminated soft soil 4 is filled layer by layer. After filling each layer, the contaminated soft soil 4 is left to stabilize, and after leveling, the leaching solution 3 is supplemented to be 2-3 cm away from the surface of the contaminated soft soil 4;

[0092] 3-3) Start the vacuum equipment to extract vacuum, monitor the settlement, pore water pressure and deep displacement changes, and extract the leaching solution 3 through the drain board 6;

[0093] 3-4) Continue to extract vacuum and supplement the leaching solution 3 until the amount of the leaching solution 3 reaches the preset value;

[0094] 3-5) Determine whether the soil heavy metal content reaches the standard value and below. If not, return to step 3-3). If yes, the repaired soil is obtained;

[0095] 3-6) After obtaining the repaired soil, the woven cloth or geotextile 7 is removed.

[0096] In some embodiments of the present application, step 5) specifically comprises the following process:

[0097] 5-1) Determine the dynamic compaction construction parameters by trial ramming;

[0098] 5-2) According to the construction parameters determined by trial ramming, dynamic compaction is carried out at a certain dynamic compaction interval, dynamic compaction energy and number of blows;

[0099] 5-3) Continue bottom vacuum water extraction, and stop the bottom vacuum water extraction when the dissipation amount of the excess pore water pressure generated by the dynamic compaction is greater than or equal to the preset value;

[0100] 5-4) Determine whether the soil body meets the requirements of foundation bearing capacity and compression characteristics. If not, push the ramming pit and return to step 5-2). If yes, stop dynamic compaction, push the ramming pit, and execute step 5-5);

[0101] 5-5) Perform full compaction to achieve reinforcement.

[0102] The content of the present application will be further described in detail below in combination with specific embodiments.

[0103] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, it does not require further definition or explanation in subsequent drawings.

[0104] The following describes some embodiments of the present invention in detail with reference to the accompanying drawings. In the absence of conflict, the following embodiments and features in the embodiments may be combined with each other.

[0105] In the following embodiments, unless otherwise specified, raw materials or processing techniques are conventionally available in the market or conventional processing techniques are used. Unless otherwise specified, functional components or structures are conventional components or structures used in the art to achieve the corresponding functions.

[0106] Example 1

[0107] like Figures 1-3 As shown, this embodiment provides a process for bottom vacuum leaching to repair heavy metal contaminated soft soil and dynamic compaction reinforcement, the main steps of which include:

[0108] 1) Conduct indoor test analysis on the heavy metal contaminated soft soil 4 to be repaired to obtain the pollution degree, permeability, and gradation parameters, and use them to select the vacuum pressure, reagent concentration, and treatment thickness;

[0109] 2) Selecting a leaching site based on soil characteristics. The leaching site can be either an in-situ site or an off-site site. The leaching site is a manually selected cool and humid area;

[0110] 3) Select a leaching site and excavate a leaching pool. The pit depth of the leaching pool is about 1m, and an anti-seepage barrier wall is set to form an impermeable storage place for contaminated soft soil 4. The anti-seepage barrier wall is set at the bottom and around the leaching pool. The anti-seepage barrier wall is higher than the ground of the leaching site. Cofferdams 5 are set around it, and waterproof pads are laid on the bottom and side walls.

[0111] 4) Arrange a bottom vacuum elution assembly in the elution tank. The bottom vacuum elution assembly includes a drain board 6, a woven cloth or geotextile 7, a vacuum device, and a drain pipe 2. The drain board 6 is arranged in a single layer or multiple layers, and its size is determined according to the vacuum pressure. The woven cloth or geotextile 7 is set above the drain board 6. The drain board 6 is connected to the vacuum device. The vacuum device is connected to the board head of the drain board 6 through the drain pipe 2. The vacuum device is an air compressor 1. The width and spacing of the drain board 6 are both 100 to 500 mm. To reduce the extrusion deformation of the drain board 6, a protective device made of porous steel can be fixed above the drain board 6;

[0112] 5) setting a sensor probe for testing humidity, temperature, pH, etc. in the leaching tank to monitor the soil state in real time, the bottom vacuum leaching assembly further comprising a sensor probe disposed in the leaching tank, the sensor probe comprising one or more of a sensor for testing humidity, a sensor for testing temperature, a sensor for testing pH;

[0113] 6) crushing, screening and pretreating the soft soil 4 to be repaired, mixing the pretreated soft soil 4 with the leaching solution 3 after removing impurities, and increasing the initial water content to obtain the pretreated contaminated soft soil 4;

[0114] 7) injecting the leaching solution 3 into the leaching tank and filling the pretreated contaminated soft soil 4 layer by layer, after filling each layer of soil, the contaminated soft soil 4 is left to a stable state, and after leveling, the leaching solution 3 is supplemented to be 2-3 cm away from the surface of the contaminated soft soil 4;

[0115] 8) starting the vacuum equipment to draw vacuum, controlling the vacuum degree to be greater than or equal to 60 kPa, monitoring the settlement, pore water pressure and deep displacement changes, and drawing the leaching solution 3 through the drain board 6;

[0116] 9) continuously drawing vacuum at a solid-liquid ratio of 1:2 (during the vacuum drawing process, the time history curves of settlement, pore water pressure and deep displacement are drawn, and the vacuum pressure is adjusted appropriately according to the changes in the time history curves) and supplementing the leaching solution 3 until the amount of the leaching solution 3 reaches a preset value, the preset value of the amount of the leaching solution 3 being twice the weight of the soil, for example, 1 kg of contaminated soft soil 4 (dry soil) requires 2 L of leaching solution 3 when the solid-liquid ratio is 1:2, and during the leaching process, the leaching solution 3 needs to be continuously supplemented above the contaminated soft soil 4, but not higher than the cofferdam 5;

[0117] 10) judging whether the heavy metal content of the soil reaches a standard value or not, if not, returning to step 8), and if yes, obtaining the repaired soil, wherein the source of the standard value of the heavy metal content of the soil is: “Soil Environmental Quality Construction Land Soil Pollution Risk Control Standard (Trial)”, GB 3600-2018, applicable to residential, commercial, industrial and other construction land. The screening value and control value of arsenic, cadmium, lead, mercury, nickel and other heavy metals are given according to “first type of land” and “second type of land” respectively;

[0118] 11) after obtaining the repaired soil, analyzing the mineral composition and pollutant residue of the repaired soil, evaluating the environmental risk, and then carrying out foundation reinforcement, and removing the woven cloth or geotextile 7;

[0119] 12) after removing the woven cloth or geotextile 7, starting the vacuum equipment of the bottom vacuum leaching assembly to draw water, and reducing the water content of the soil to the optimal water content;

[0120] 13) confirming the construction parameters of the dynamic compaction by trial ramming;

[0121] 14) Carry out dynamic compaction according to the construction parameters determined by the test compaction, with a certain dynamic compaction spacing, dynamic compaction energy and number of blows;

[0122] 15) Continue bottom vacuum pumping. When the excess pore water pressure dissipated by dynamic compaction is greater than or equal to a preset value (the preset value of the excess pore water pressure dissipated by dynamic compaction is 75%), stop bottom vacuum pumping.

[0123] 16) Determine whether the soil meets the foundation bearing capacity and compression characteristics requirements (the test items for the foundation bearing capacity and compression characteristics are selected from one or more of the following: soil moisture content, void ratio, compression modulus, compression coefficient, single-bridge or double-bridge static penetration test, cross-plate shear strength, flat plate load test, etc.); if not, flatten the tamping pit and return to step 14); if so, stop dynamic compaction, flatten the tamping pit, and execute step 15);

[0124] 17) Carry out full tamping to achieve reinforcement, level the full tamping pit, conduct foundation bearing capacity and compression characteristics testing, and verify the reinforcement effect of the foundation soil;

[0125] 18) Completion acceptance.

[0126] Example 2

[0127] like Figures 1-5 As shown, this embodiment provides a process for bottom vacuum leaching to repair heavy metal contaminated soft soil and dynamic compaction reinforcement, the main steps of which include:

[0128] (1) Conduct indoor tests to analyze the characteristics of the contaminated soft soil 4 to be repaired, and obtain the contamination degree, permeability, and gradation parameters of the contaminated soft soil 4, so as to determine the required vacuum pressure, reagent concentration, and corresponding treatment thickness of the contaminated soft soil 4.

[0129] (2) According to the soil properties of the contaminated soft soil 4, an off-site leaching site is selected. The site can be selected in a nearby location with good address conditions and a cool and humid environment.

[0130] (3) At the selected site, dig a pit for treating contaminated soft soil 4 in the same way as the foundation pit. The pit is about 1m deep and serves as a leaching pool. After the excavation is completed, support is provided and an anti-seepage barrier wall is built at the bottom and around the perimeter to form an impermeable soil storage area. The anti-seepage barrier wall is higher than the site, and a cofferdam is built around the raised part. To ensure that the risk of filtrate leakage is eliminated, a waterproof liner or bentonite material can be laid at the bottom and around the anti-seepage barrier wall to enhance the anti-seepage performance.

[0131] (4) According to the soil area and thickness, the drainage plate 6 is laid, which can be laid in single layer or multiple layers. The width and length of the drainage plate 6 are determined according to the vacuum pressure generated by the air compressor 1, and the appropriate size can be determined by laboratory experiments (the spacing of the drainage plate 6 is shown in FIG. 6, and the width and spacing of the drainage plate 6 are usually 100-500 mm, which is set as a horizontal drainage plate). In order to reduce the extrusion deformation of the drainage plate 6, a protective tool made of perforated steel can be fixed above the drainage plate 6. After the drainage plate 6 is laid, the head of the drainage plate 6 is connected to the air compressor 1 through the drainage pipe 2, as shown in FIG. 7, and the woven cloth or geotextile 7 is laid on the area above the drainage plate 6. Figure 3 Figure 2

[0132] (5) The temperature, humidity, pH, and conductivity sensors are laid in the leaching tank to monitor the changes of various parameters in real time during the leaching process, so as to adjust in time. The sensor probe includes a sensor for testing humidity, a sensor for testing temperature, a sensor for testing pH, and a pore water pressure gauge.

[0133] (6) The contaminated soft soil 4 needs to be excavated by excavating equipment, and then the contaminated soft soil 4 is subjected to coarse screening, crushing, and removal of large impurities, etc. In the process of treatment, the leaching liquid 3 is soaked as much as possible to increase the initial moisture content, and the pretreated contaminated soft soil 4 is obtained.

[0134] (7) Before filling the soil, a certain amount of leaching liquid 3 is continuously injected into the leaching tank, and then the pretreated contaminated soft soil 4 is slowly filled. When the soil layer is thick, the layer-by-layer filling method is adopted. When the flow of the upper layer of the contaminated soft soil 4 reaches a stable state, the second layer of the drainage plate 6 can be laid (in this embodiment, multiple layers of the drainage plate 6 are not set). After the laying is completed, the remaining pretreated contaminated soft soil 4 is continuously injected.

[0135] (8) The contaminated soft soil 4 is static for a period of time to reach stability, and then a certain amount of leaching liquid 3 is added to the surface of the soil after being appropriately leveled. The distance between the liquid surface of the leaching liquid 3 and the soft soil surface is kept within the range of 2-3 cm.

[0136] (9) The vacuum equipment air compressor 1 is used for vacuumizing. During the vacuumizing process, the vacuum degree should be ensured to reach a certain level, which is generally above 60 kPa. The changes of the settlement, pore water pressure, and deep lateral displacement are monitored, and the corresponding time curve is drawn to monitor the change law of various indexes, and the vacuum pressure is adjusted according to the change of the time curve.

[0137] ​​(10) If multi-layer drainage plate 6 is used for leaching, the order and duration of vacuum extraction of each layer need to be adjusted to ensure that the leaching liquid 3 can fully wash out the heavy metal pollutants. The specific order can be obtained from laboratory experiments (multi-layer drainage plate 6 is not provided in this embodiment).

[0138] (11) Under stable pressure conditions, vacuum extraction is continued to extract a certain amount of leaching liquid 3 as a reference. For example, when the solid-liquid ratio is 1:2, 1 kg of contaminated soft soil 4 (dry soil) requires 2 L of leaching liquid 3. During the leaching process, leaching liquid 3 needs to be continuously supplemented above the contaminated soft soil 4, but not higher than the cofferdam.

[0139] (12) Multiple rounds of leaching are performed, and the heavy metal content of the soil at different sites is detected after each round of leaching to determine whether it meets the standard value or not. If it does not meet the standard value, leaching can continue until the soil heavy metal removal rate meets the requirements. The specific leaching timing and number of times can be estimated from laboratory experimental results. The standard value of the soil heavy metal content is from “Soil Environmental Quality Construction Land Soil Pollution Risk Control Standard (Trial)”, GB3600-2018, which is applicable to residential, commercial, industrial, and other construction sites. The screening values and control values of arsenic, cadmium, lead, mercury, nickel, and other heavy metals are given for “first type of land” and “second type of land” respectively.

[0140] (13) After completion, the repaired contaminated soft soil 4 is obtained, and the mineral and pollutant residual components of the repaired contaminated soft soil 4 are analyzed. The gradation, particle change, pH, mineral composition change, and other characteristics of the treated contaminated soil are detected to analyze the repair effect of the contaminated soil and assess its risk. The soil repair situation and the risk of recontamination are evaluated, and the geotextile or geotextile 7 is removed.

[0141] (14) The vacuum equipment of the bottom vacuum leaching assembly is started to continue to extract groundwater from the repaired contaminated soft soil 4 in the leaching tank, reducing the water content of the soil.

[0142] (15) Soil (repaired contaminated soft soil 4) samples are taken in the leaching tank for indoor conventional soil test, such as water content, void ratio, liquid limit, plastic limit, particle composition, density, consolidation, and permeability characteristics, as well as on-site tests such as static sounding, vane shear strength, and plate load, to obtain the physical and mechanical parameters of the soil.

[0143] (16) The water content of the soil in the foundation is monitored, and when the water content of the soil approaches the optimal water content, dynamic compaction construction is carried out.

[0144] (17) Perform dynamic compaction construction, in this embodiment, two-point ramming and one full ramming are adopted, the rammer weight is 15T, the rammer diameter is 2.2-2.5m, with a vent, the first point ramming energy is 2000-3000kN.m, the first point 8 is arranged in a square, the first point 8 spacing is 4.0-5.0m x 4.0-5.0m, the number of hits per point is 5-8 hits, and the uplift of the ramming pit periphery is not more than 20cm.

[0145] (18) Continue to open the vacuum device of the bottom vacuum leaching assembly to pump water, at the same time, closely monitor the reading of the pore water pressure gauge, and after the dissipation amount of the excess pore water pressure generated by the dynamic compaction reaches 75%, push the ramming pit flat and perform the second point ramming.

[0146] (19) The second point ramming energy is 2000-3000kN.m, the second point 9 is arranged at the center position of the first point 8 of the first adjacent four first points 8, arranged in a square, the second point 9 spacing is 4.0-5.0m x 4.0-5.0m, the number of hits per point is 5-8 hits, and the uplift of the ramming pit periphery is not more than 20cm.

[0147] (20) Continue to open the vacuum device of the bottom vacuum leaching assembly to pump water, at the same time, closely monitor the reading of the pore water pressure gauge, and after the dissipation amount of the excess pore water pressure generated by the dynamic compaction reaches 75%, stop ramming and vacuum pumping, at this time, the soil has reached the requirements of foundation bearing capacity and compression characteristics, push the second point ramming pit flat and perform full ramming.

[0148] (21) The full ramming energy is 800-1000kN.m, the adjacent full ramming points 10 overlap by one-fourth of the diameter of the hammer mark, and the number of hits per point is 2-3 hits.

[0149] (22) Push the full ramming pit flat and perform foundation strength and compression characteristic detection, the detection items include soil moisture content, pore ratio, compression modulus, compression coefficient, single bridge or double bridge static sounding, cross shear strength, plate load test, etc.

[0150] (23) Acceptance of completion.

[0151] Example 3

[0152] As shown in Figures 1-5 , the embodiment provides a process method for repairing heavy metal contaminated soft soil by bottom vacuum leaching and dynamic compaction reinforcement, and based on the embodiment 2, the conditions in steps (17)-(21) are as follows:

[0153] (17) carry out dynamic compaction construction, in the embodiment, two passes of point ramming and one pass of full ramming are adopted, the rammer weight is 15T, the rammer diameter is 2.2m, a vent is provided, the first pass of point ramming energy is 2000kN.m, the first pass of point ramming 8 is arranged in a square, the first pass of point ramming 8 spacing is 5.0m x 5.0m, the number of hits per point is 5 hits, and the ramming pit periphery uplift is not more than 20cm.

[0154] (18) continue to open the vacuum device of the bottom vacuum rinse assembly to carry out water pumping, at the same time, closely monitor the reading of the pore water pressure gauge, after the dissipation amount of the excess pore water pressure generated by the dynamic compaction reaches 75%, push the ramming pit, and carry out the second pass of point ramming.

[0155] (19) the second pass of point ramming hit energy is 3000kN.m, the second pass of point ramming 9 is arranged at the center position of the first pass of adjacent four first pass of point ramming 8, arranged in a square, the second pass of point ramming 9 spacing is 5.0m x 5.0m, the number of hits per point is 8 hits, and the ramming pit periphery uplift is not more than 20cm.

[0156] (20) continue to open the vacuum device of the bottom vacuum rinse assembly to carry out water pumping, at the same time, closely monitor the reading of the pore water pressure gauge, after the dissipation amount of the excess pore water pressure generated by the dynamic compaction reaches 75%, stop the ramming vacuum pumping, at this time, the soil body has reached the requirements of the foundation bearing capacity and compression characteristics, push the second pass of point ramming pit, and carry out full ramming.

[0157] (21) the full ramming energy is 1000kN.m, the adjacent full ramming point 10 overlaps the diameter of the rammer imprint by one fourth, and the number of hits per point is 2-3 hits.

[0158] The above description of the embodiments is for the convenience of the ordinary skilled person in the art to understand and use the invention. Those skilled in the art can easily make various modifications to these embodiments, and apply the general principles described herein to other embodiments without creative labor. Therefore, the present invention is not limited to the above embodiments, and the improvements and modifications made by those skilled in the art without departing from the scope of the invention should be within the scope of protection of the invention.

Claims

1. A process for remediation of heavy metal contaminated soft soil by bottom vacuum rinse and dynamic compaction reinforcement, characterized in that, The process method comprises the following steps: 1) selecting a leaching site to excavate a leaching pool and arranging the leaching pool; 2) arranging a bottom vacuum leaching assembly in the leaching pool, the bottom vacuum leaching assembly comprising a drainage plate, a woven cloth or geotextile cloth, and a vacuum device, the woven cloth or geotextile cloth being arranged above the drainage plate, and the drainage plate being connected with the vacuum device; 3) performing bottom vacuum leaching, continuously vacuumizing and supplementing leaching liquid until the heavy metal content of the soil reaches a standard value and below, obtaining the repaired soil, and removing the woven cloth or geotextile cloth; 4) after removing the woven cloth or geotextile cloth, starting the vacuum device of the bottom vacuum leaching assembly to perform bottom vacuum pumping to reduce the water content of the soil to an optimal water content; 5) after reducing the water content of the soil to the optimal water content, determining the parameters of dynamic compaction, performing point compaction of different passes until the soil reaches the requirements of foundation bearing capacity and compression characteristics, and then performing full compaction to achieve reinforcement.

2. The process for remediation of heavy metal contaminated soft soil and dynamic compaction reinforcement by bottom vacuum rinse according to claim 1, characterized in that, Step 1) specifically comprises the following processes: 1-1) performing indoor test analysis on the heavy metal contaminated soft soil to be repaired to obtain the pollution degree, permeability, and grading parameters, so as to select the vacuum pressure, reagent concentration, and treatment thickness; 1-2) selecting a leaching site according to the soil characteristics; 1-3) selecting the leaching site to excavate a leaching pool and arranging an impermeable barrier wall to form a water-impermeable contaminated soft soil storage site.

3. The process for remediation of heavy metal contaminated soft soil and dynamic consolidation according to claim 2, characterized in that, In step 1-2), the leaching site is an artificially selected cool and humid area; In step 1-3), the depth of the leaching pool is 0.8-1.2 m; In step 1-3), the impermeable barrier wall is arranged at the bottom and around the leaching pool, the impermeable barrier wall is higher than the ground of the leaching site, a cofferdam is arranged around, and a waterproof lining is laid at the bottom and sidewall.

4. The process for remediation of heavy metal contaminated soft soil and dynamic consolidation according to claim 1, characterized in that, In step 2), the bottom vacuum leaching assembly further comprises a sensor probe arranged in the leaching pool. The sensor probe comprises one or more of a sensor for testing humidity, a sensor for testing temperature, and a sensor for testing pH.

5. The process for remediation of heavy metal contaminated soft soil and dynamic consolidation according to claim 1, wherein, In step 2), a single layer or multiple layers of drainage plates are arranged. In step 2), the width and spacing of the drainage plates are both 100-500 mm.

6. The process for remediation of heavy metal contaminated soft soil and dynamic consolidation according to claim 1, wherein, In step 2), the bottom vacuum leaching assembly further comprises a drain pipe. The vacuum device is connected with the head of the drainage plate through the drain pipe. The vacuum device is an air compressor.

7. The process of claim 1, wherein the process is characterized in that, Step 3) specifically comprises the following steps: 3-1) crushing and screening the heavy metal contaminated soft soil to be repaired for pretreatment, mixing the contaminated soft soil after removing impurities with leaching liquid to increase the initial water content, and obtaining the pretreated contaminated soft soil; 3-2) injecting the leaching liquid into the leaching pool and filling the pretreated contaminated soft soil layer by layer, after filling each layer of soil, standing the contaminated soft soil until it reaches a stable state, and then supplementing the leaching liquid to a position 2-3 cm above the surface of the contaminated soft soil after leveling; 3-3) starting the vacuum device to vacuumize, monitoring the changes of settlement, pore water pressure, and deep displacement, and extracting the leaching liquid through the drainage plate; 3-4) continuously vacuumizing and supplementing the leaching liquid until the amount of the leaching liquid reaches a preset value; 3-5) judging whether the heavy metal content of the soil reaches a standard value and below, if not, returning to step 3-3), and if yes, obtaining the repaired soil. 3-6) After the soil is repaired, the woven cloth or geotextile is removed.

8. The process of claim 1, wherein the process is characterized in that, In step 3-4, vacuum is continuously extracted and the leaching solution is replenished at a solid-liquid ratio of 1:2-3, and the preset value of the amount of the leaching solution is 2-3 times the weight of the soil. In step 3-4, during the vacuum extraction, time history curves of settlement, pore water pressure and deep displacement are drawn, and the vacuum pressure is adjusted according to the changes of the time history curves.

9. The process of claim 1, wherein the process is characterized in that, Step 5) specifically includes the following processes: 5-1) The construction parameters of the dynamic compaction are determined by trial ramming; 5-2) According to the construction parameters determined by the trial ramming, dynamic compaction is carried out at a certain dynamic compaction interval, dynamic compaction energy and number of blows; 5-3) The bottom vacuum water extraction is continued, and when the dissipation amount of the excess pore water pressure generated by the dynamic compaction is greater than or equal to the preset value, the bottom vacuum water extraction is stopped; 5-4) It is judged whether the soil body meets the requirements of foundation bearing capacity and compression characteristics, if not, the ramming pit is pushed flat and returns to step 5-2), if yes, the dynamic compaction is stopped, the ramming pit is pushed flat, and step 5-5) is executed; 5-5) Full ramming is carried out to realize reinforcement.

10. The process of claim 9, wherein the process is characterized in that, The preset value of the dissipation amount of the excess pore water pressure generated by the dynamic compaction is 70-80%.

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