Deep sea rare earth sediment foundation preparation method based on supergravity centrifugal physical simulation

Abstract

The invention provides a deep sea rare earth sediment foundation preparation method based on supergravity centrifugal physical simulation. The deep sea rare earth sediment foundation preparation method comprises the steps of similarity ratio design, solid phase formula design, initial layered filling in a model box, pore solution preparation, supergravity centrifugal accelerated consolidation and similarity evaluation of a model sample and a deep sea original sample. According to the technical scheme, deep sea stress and temperature boundaries can be reproduced at the same time in a laboratory scale, and the consolidation steady-state time is greatly shortened; the solid phase formula aligns the original sample mineral composition and the rare earth element REE spectrum, and pore water chemical alignment actually measures the seawater main ion strength and pH / Eh value; stable batch preparation can be achieved without open sea sampling, the cost and risk of going out of sea, salvaging and transporting are remarkably reduced, indoor low-cost large-scale preparation of deep sea rare earth sediment sea water samples is achieved, and large-scale indoor mechanics, seepage and process evaluation tests are supported; physical property / chemical / microcosmic / mechanical quantitative thresholds are provided, consistency acceptance and engineering application are facilitated, and batch-to-batch consistency and controllability are high.

Description

Technical Field

[0001] This invention relates to the field of marine geotechnical engineering and hypergravity physics simulation technology, and more particularly to a method for preparing a deep-sea rare earth sediment foundation based on hypergravity centrifugal physics simulation. Background Technology

[0002] The rare earth resources in deep-sea sediments of the Pacific Ocean are approximately 800–1000 times greater than those on land. Deep-sea rare earth-rich sediments (REY-rich sediments) are characterized by fine grain size, high porosity, and significant enrichment of medium to heavy rare earth elements (REEs), and have been considered an important potential strategic resource carrier by numerous surveys and research efforts. REY-rich sediments are found in low-temperature (approximately 0–4 °C) and high hydrostatic pressure (increasing linearly with depth, reaching tens of MPa at depths of several thousand meters) seabed environments, exhibiting fine grains, high porosity, and significant REE enrichment. Obtaining in-situ samples typically relies on a "sea-mining-salvage-pressure / cryore transport" chain, including ocean voyages, deep-sea drilling / coring, and ROV / AUV operations. This presents challenges such as difficulties in voyage organization, limited weather windows, extremely high costs for sampling equipment and vessels at sea, and limitations in the success rate and integrity of pressure-holding sampling. Samples are prone to irreversible changes during salvage and long-distance transport, including unloading, desorption, oxidation, and ion exchange, leading to deviations in pore water chemistry and microstructure from their in-situ state. Current supply of standard materials and experimental materials is insufficient to cover the complex conditions of "rare earth richness—cryore temperature and high pressure—high saturation," hindering systematic and large-scale indoor mechanism and engineering evaluation.

[0003] While traditional gravity-based laboratory methods can perform sample preparation and loading under normal temperature and pressure, they struggle to simultaneously reproduce the stress and temperature boundaries of the deep sea, and also find it difficult to achieve equivalent long-term consolidation-seepage-chemical equilibrium within a controllable period. This leads to problems such as insufficient stress levels, consolidation history mismatch, and distortion of pore structure and pore water states in the model soil, resulting in systematic deviations from in-situ strength, permeability, and microscopic characterization. Therefore, relying solely on gravity-based sample preparation and testing is insufficient to support the comparability, reproducibility, and large-scale research requirements of deep-sea rare earth sediments.

[0004] Centrifugal physics simulations offer an equivalent path to reproduce extreme environments for addressing the aforementioned challenges: applying n·g of hypergravity to a 1 / n scaled model allows for the realization of hydrostatic and effective stress fields of the same magnitude as the prototype on a small scale (scaled effect); simultaneously, the timescale of multiphase migration / convective diffusion and other time-consuming processes is approximately shortened by n², meaning that one day in the model under 100g conditions is equivalent to approximately 27.4 years in the prototype (time-shortening effect), significantly expanding the simulable range of large-scale, long-duration problems. Therefore, by accelerating saturation / consolidation effects under the combined control of "ng-level hypergravity environment + isothermal field," samples with higher consistency with in-situ mechanics, properties, and microstructure can be reproducibly obtained in the laboratory.

[0005] This invention is based on the hypergravity scaling / time-reduction technology approach to reproduce the high-pressure and low-temperature occurrence environment of deep-sea rare earth sediments, achieving the goal of stable batch preparation without relying on sea sampling. It significantly reduces sample acquisition costs, shortens the sample acquisition cycle, and improves repeatability, providing a unified and traceable sample basis for carrying out large-scale indoor mechanical and seepage tests and green mineral collection technology process evaluation. Summary of the Invention

[0006] To overcome the shortcomings of existing technologies, this invention provides a method for preparing deep-sea rare earth sediment foundations based on centrifugal physics simulation. This invention addresses the challenges of equivalent reproduction and mass production of low-temperature (0–4 °C) to high hydrostatic pressure (tens of MPa) samples from deep-sea rare earth-rich sediments under these conditions. It solves the problem of systematic deviations in "mechanical-physical-microstructure" caused by the difficulty in simultaneously replicating measured stress and temperature boundaries in normal gravity experiments, and the difficulty in achieving consolidation-seepage-chemical steady state within a controllable period. A complete set of methods for foundation sample preparation and pore solution configuration under centrifugal physics simulation is established, enabling the obtained samples to serve as stable support for large-scale indoor experiments using "deep-sea rare earth sediment foundation seawater samples."

[0007] This invention is achieved through the following technical solution: a method for preparing deep-sea rare earth sediment foundations based on hypergravity centrifugal physics simulation, characterized by comprising the following steps: Step S1, Similarity Ratio Design: Geometric similarity is established between the actual water depth H of the target sea area and the designed water depth h inside the model box: the scaling ratio is taken as 1 / n = h / H, and the centrifugal acceleration ng is determined accordingly; Step S2, Solid-phase formulation design: Based on the mineral composition, particle size distribution, and REE analysis spectrum of the collected deep-sea rare earth sediments, the approximate ratio of fine-grained clay to silty framework minerals in the target formulation was determined to ensure that the clay mineral-silty framework-rare earth element content of the raw materials was identical to that of the deep-sea rare earth sediments. Fine-grained clay and silty framework were selected as the sample preparation base materials, with rare earth-rich fine particles as the additive phase. During the preparation process, the porosity e, liquid limit, plasticity index, and mineral analysis spectrum of the sample base materials were finely adjusted to ensure that the initial percentage deviations from the porosity e, liquid limit, plasticity index, and mineral analysis spectrum of the deep-sea original samples did not exceed ±10%. The soil sample mixing, grinding, and homogenization processes were carried out under an inert nitrogen atmosphere, and the final powder particle size was controlled within 1 / 2 oz. 99 ≤74m; Step S3: Initial layered filling within the model box: The prepared solid phase was layered in layers approximately 20–100 mm thick to form a solid phase filling layer, with the thickness error of each layer controlled within ±2 mm. The initial void ratio e0≈1.15e was obtained by light compaction using 20% ​​of the standard compaction energy. * , where e * The target porosity; During the filling process, temperature sensors were buried in the upper, middle and lower layers respectively, at depths of approximately 0.15h1, 0.50h1 and 0.85h1 of the sample height h1; pore pressure sensors and soil pressure sensors were set at 0.3h1 and 0.5h1; for temperature boundary control, the initial pre-cooling and constant temperature of the model box were set within the range of seabed temperature T0-2℃. Step S4, Pore solution preparation: The pore solution was prepared based on field measurement data of deep-sea water in the target area. The ionic strength and ionic ratio were replicated by matching the concentrations of Na⁺, Mg²⁺, Ca²⁺, K⁺, Cl⁻, SO₄²⁻ and HCO₃⁻ ions. The salinity error was allowed to be no more than ±2‰. The pH and Eh values ​​of the prepared pore solution should be close to the original properties of the seawater, with the pH deviation limited to ±0.2 and the Eh deviation limited to ±20 mV. After batch preparation of the pore solution and pre-cooling it to the target temperature T0, it is injected into the model box; Step S5: Centrifugal Acceleration and Consolidation The model box was placed in a large geotechnical centrifuge to create a hypergravity environment of n·g. After reaching the target centrifugal acceleration, saturation was determined based on S. r ≥ 0.95, the consolidation judgment criteria are that under ng and T0 conditions, the consolidation reaches U≥ 90% and the pore water pressure dissipates; Step S6: Similarity evaluation between model specimen and deep-sea original sample At the physical property level, the relative errors of porosity and density are both required to be less than 10%, where the void ratio can be obtained by the mass-volume method and the density can be converted by the maximum-minimum dry density method. At the chemical level, the relative error between the liquid phase conductivity at 24 h steady state and the original seawater sample should not exceed 15% as the chemical steady-state criterion, and the conductivity fluctuation during the steady state should be controlled within ±2%. At the microscopic level, the pore size distribution obtained by MIP should show that the relative difference of the main peak position is less than 20%, and the distribution similarity coefficient is not less than 0.85. At least five representative fields of view should be collected by SEM to conduct semi-quantitative comparison of the neck / cavity ratio, floc size and sheet / floc orientation. At the mechanical level, the relative error between the T-bar tester and the original sample should be controlled within 20% using the rebound strength or its equivalent characteristic value as a reference.

[0008] As a preferred option, the model box is a supergravity static model box with a combination structure of aluminum alloy box body and steel base plate, 1.2 m×0.95 m×1.0 m; the inner wall of the box is treated with sandblasting and fluorocarbon transparent coating, and a laser displacement meter is installed under the cover of the model box, and the corresponding reflector needs to be placed on the filled solid phase surface.

[0009] As a preferred embodiment, the fine-grained clay in step S2 includes kaolinite, illite, sodium montmorillonite, and chlorite, and the silty skeleton includes quartz and feldspar.

[0010] As a preferred option, in step S3, six to seven layers are laid, with a single layer thickness of 20–100 mm. After laying, the layers are allowed to stand and pre-cool to T0 ± 2℃ before centrifugal loading.

[0011] As a preferred embodiment, the model pore solution prepared in step S4 is filtered through a 0.22–0.45 μm filter and circulated in an inert material pipeline, with a pH deviation ≤ ±0.2.

[0012] As a preferred option, in step S5, the model box is placed in a large geotechnical centrifuge to construct an n·g hypergravity environment. A segmented g-increasing strategy is adopted, with the g value gradually increased and maintained at a stable pore pressure: 0 → 20 g steady state for 1 min → 40 g steady state for 10 min → 60 g steady state for 10 min → 80 g steady state for 10 min → 100 g. Formal hypergravity accelerated consolidation is carried out at 100 g, and then maintained at 100 g until the equivalent degree of consolidation U ≥ 90%, with the pore water pressure change approaching zero and the volumetric rate of change < 10⁻⁻⁻⁶. 7 s⁻¹ is the termination criterion.

[0013] By employing the above technical solutions, this invention has the following beneficial effects compared to existing technologies: (1) Equivalent reproduction of the extreme environment of high pressure, low temperature and high salinity in the deep sea: Simultaneously reproduce the stress and temperature boundary of the deep sea on a laboratory scale and significantly shorten the consolidation steady state time.

[0014] (2) Consistency of solid-liquid two-phase preparation of the sample: the solid phase formulation is aligned with the original sample mineral composition and rare earth element REE spectrum, and the pore water chemistry is aligned with the measured seawater main ion strength and pH / Eh value.

[0015] (3) The preparation process is standardized, batch-produced, and repeatable: Through mature processes such as layered filling, preliminary compaction, pre-cooling of the model box, and accelerated saturation / consolidation in a hypergravity field, the test of the obtained samples is standardized.

[0016] (4) Significantly reduce costs and improve efficiency: Stable batch preparation can be achieved without offshore sampling, significantly reducing the cost and risk of "going to sea-salvaging-transportation", enabling low-cost large-scale indoor preparation of "deep-sea rare earth sediment seawater samples", supporting large-scale indoor mechanical, seepage and process evaluation tests.

[0017] (5) Clear detection criteria and high controllability: Four types of quantitative thresholds are proposed, namely physical property, chemical, microscopic and mechanical properties, which facilitates consistency acceptance and engineering application, and ensures high consistency and controllability between batches.

[0018] Additional aspects and advantages of the invention will become apparent in the following description or may be learned by practice of the invention. Attached Figure Description

[0019] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which: Figure 1 This is a schematic diagram of the process of the present invention; Figure 2 This is a diagram showing the layout of the hypergravity model box and sensors of the present invention; Figure 3 This is a schematic diagram of the sample microstructure preparation and detection method of the present invention. Detailed Implementation

[0020] To better understand the above-mentioned objectives, features, and advantages of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in these embodiments can be combined with each other.

[0021] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and therefore the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0022] The following is combined with Figures 1 to 3 The present invention provides a detailed description of the method for preparing deep-sea rare earth sediment foundations based on hypergravity centrifugal physics simulation.

[0023] like Figure 1 As shown, this invention proposes a method for preparing deep-sea rare earth sediment foundations based on hypergravity centrifugation physical simulation. The method comprises two parts: foundation preparation and pore solution preparation, and is implemented on a large geotechnical centrifuge under hypergravity-accelerated equivalent consolidation. Specifically, it includes the following steps: Step S1, Similarity Ratio Design: Geometric similarity is established based on the actual water depth H of the target sea area and the designed water depth h in the model box: the scaling ratio is taken as 1 / n = h / H (h is based on the static water depth from the top of the sample at the centrifugal radius to the water surface, with an accuracy of ±0.5 mm), thereby determining the centrifugal acceleration ng (n>100 is usually used to simulate the deep sea environment), so that the gravitational volume force and hydrostatic pressure in the model meet the prototype order of magnitude. The principle for obtaining the effective stress equivalence criterion is: for any model depth h and target depth H, the following conditions must be met. By setting a reasonable centrifugal acceleration, the difference between the in-situ stress level in the deep sea and the stress level of the scaled model under hypergravity is made less than 5%.

[0024] The model box is a hydrostatic model box with a combined structure of aluminum alloy body and steel base plate, measuring 1.2 m × 0.95 m × 1.0 m. The inner wall of the box is treated with sandblasting and a fluorocarbon transparent coating. A laser displacement meter needs to be installed under the model box cover, and the corresponding reflector needs to be placed on the filled solid surface to record the descent of the solid top height under the hypergravity field, reflecting its consolidation degree. All sensor cables need to be connected to the data acquisition panel of a large geocentrifuge for real-time data transmission. This embodiment simulates rare earth samples at a water depth of 130 m. The hypergravity centrifugation acceleration will be 100 g, the water depth inside the model box will be set to 650 mm, the simulated sediment thickness will be set to 200 mm, and a 150 mm space will be left at the top to prevent overflow.

[0025] Step S2, Solid-phase formulation design: Based on the mineral composition (XRD), grain size distribution, and REE analysis spectrum of the collected deep-sea rare earth sediments, the approximate ratio of fine-grained clay to silty framework minerals in the target formulation was determined to ensure that the clay mineral-silty framework-rare earth element content of the raw materials was identical to that of the original deep-sea rare earth sediments. Fine-grained clay and silty framework were selected as the sample preparation base materials, with rare earth-rich fine particles as the additive phase. The fine-grained clay included kaolinite, illite, sodium montmorillonite, and chlorite, while the silty framework included quartz and feldspar. During the preparation process, the porosity e, liquid limit, plasticity index, and mineral analysis spectrum of the sample base materials were finely adjusted to ensure that the initial percentage deviations from the porosity e, liquid limit, plasticity index, and mineral analysis spectrum of the original deep-sea samples did not exceed ±10%. The soil sample mixing, grinding, and homogenization processes were carried out under an inert nitrogen atmosphere to avoid additional reactions and rare earth element loss. The final powder particle size was controlled within 1 / 2 mm. 99 ≤74 μm (meets the conventional requirements for the preparation of rare earth standard materials); Step S3: Initial layered filling within the model box: The prepared base material is laid in six to seven layers, each layer being 20–100 mm thick. This layering of approximately 20–100 mm thick forms a solid-phase filling layer, with each layer's thickness controlled within ±2 mm. After laying, the material is allowed to pre-cool to T0 ± 2℃ before centrifugal loading. An initial porosity ratio e0≈1.15e is obtained using a light compaction method with 20% of the standard compaction energy. * , where e * The target porosity; During the filling process, temperature sensors were buried in the upper, middle, and lower layers at depths of approximately 0.15h1, 0.50h1, and 0.85h1 of the sample height h1, respectively. Pore pressure sensors and soil pressure sensors were installed at 0.3h1 and 0.5h1 (vertical placement was avoided to ensure no interference). Before installation, all sensors required reinforcement and waterproofing measures at the wiring and joints, and were arranged parallel to the bottom plane of the model box to prevent damage caused by tensile forces during accelerated consolidation under hypergravity. For temperature boundary control, the initial pre-cooling and constant temperature of the model box were set within the range of seabed temperature T0-2℃. Initial cooling was performed under constant gravity. The circulating thermostatic bath was filled with a 30–40% (v / v) ethylene glycol-water mixture. Freezing coils were tightly attached to the outer wall and bottom plate of the bath, and the contact surfaces were coated with high thermal conductivity silicone grease. The cooling process was implemented in stages: from room temperature to 10 °C, 5 °C, and then to T0−0.2 °C, with a cooling rate controlled at ≤1 °C / h. Each platform was held for 30–60 min to dissipate the temperature gradient. The return / outflow liquid temperature difference and the rate of change of the three soil layers were used as criteria for determining the adequacy of heat transfer.

[0026] Once the temperature difference between the three layers is ≤0.5 ℃ and remains stable for ≥60 min, the thermostatic bath is stopped, the refrigerant is released, and the bath is purged with dry nitrogen until no residual liquid is sprayed out. Subsequently, the model box is tightly wrapped with a double-layer aerogel composite insulation material and an aluminized reflective film, and all overlaps are sealed with low-temperature resistant tape.

[0027] Step S4, Pore solution preparation: The pore solution was prepared based on field measurement data of deep-sea water in the target area. The ionic strength and ionic ratio were replicated by matching the concentrations of Na⁺, Mg²⁺, Ca²⁺, K⁺, Cl⁻, SO₄²⁻, and HCO₃⁻ ions, with a salinity tolerance of no more than ±2‰. Regarding pH and redox environment, a carbonate buffer system and deoxygenation / oxygenation strategy were used to ensure that the pH and Eh values ​​of the prepared pore solution closely approximate the properties of the original seawater, with pH deviation limited to ±0.2 and Eh deviation limited to ±20 mV. The prepared model pore solution was filtered through 0.22–0.45 μm and circulated in an inert material pipeline, with a pH deviation ≤ ±0.2.

[0028] Pre-cooling is typically performed under constant gravity. A circulating thermostatic bath is filled with a 30–40% (v / v) ethylene glycol-water mixture. Freezing coils are tightly attached to the outer wall and bottom plate of the bath, and the contact surfaces are coated with high thermal conductivity silicone grease. The cooling path is implemented in stages: from room temperature to 10℃, 5℃, and then to T0−0.2℃, with a cooling rate controlled at ≤1℃ / h. Each platform is held for 30–60 min to dissipate the gradient. The return / outlet liquid temperature difference and the temperature change rate of the three soil layers are used as criteria for heat exchange adequacy. When the temperature difference between the three layers is ≤0.5℃ and remains stable for ≥60 min, the thermostatic bath is stopped, the refrigerant is vented, and the bath is purged with dry nitrogen until no residual liquid is ejected. Subsequently, the model box is tightly wrapped with a double-layer aerogel composite insulation material and an aluminized reflective film, and all overlaps are sealed with low-temperature resistant tape. Pore solution is prepared in batches and pre-cooled to the target temperature T0 before being injected into the model box. Step S5: Centrifugal Acceleration and Consolidation Since simulations of deep-sea working conditions typically operate under high centrifugal acceleration and heavy load conditions, to optimize consolidation efficiency and ensure the safety and stability of the preparation process, the target centrifugal acceleration needs to be increased in segments, with each segment's increase not exceeding 20g. The model chamber is placed in a large geotechnical centrifuge to construct a hypergravity environment of n·g. Once the target centrifugal acceleration is reached, saturation is determined based on S. r ≥ 0.95, the consolidation criterion is that under ng and T0 conditions, consolidation is carried out until U ≥ 90% and pore water pressure dissipates; at the end of consolidation, it is also necessary to confirm that the pore pressure change tends to zero and the axial volumetric rate of change drops to 10. −7 s −1Only then can unloading and sampling be carried out. The above criteria can be calculated from pore pressure gauge monitoring data and laser displacement gauge records of changes in the surface height of the foundation soil.

[0029] After the model box is hoisted into the centrifuge basket, a staged g-increase strategy is adopted, with the g value gradually increased while maintaining stable pore pressure. Details are as follows: 0 → 20 g (steady-state for 1 min) → 40 g (steady-state for 10 min) → 60 g (steady-state for 10 min) → 80 g (steady-state for 10 min) → 100 g. Formal accelerated consolidation under hypergravity begins at 100 g, and is subsequently maintained at 100 g until the equivalent degree of consolidation U ≥ 90%, with the pore water pressure change approaching zero and the volumetric rate of change < 10⁻⁻⁻⁶. 7 s⁻¹ is the termination criterion. It has been verified that, within a 2-hour simulation process of centrifugation under hypergravity, the average temperature rise can be controlled to ≤4 ℃, and the interlayer temperature difference to ≤1.5 ℃.

[0030] Step S6: Similarity evaluation between model specimen and deep-sea original sample The process needs to cover four levels: physical properties, chemistry, microstructure, and mechanics, with clearly defined thresholds used as the criteria for sample preparation and factory release. At the physical property level, the relative error between porosity and density should be less than 10%, where the void ratio can be obtained using the mass-volume method, and density can be calculated using the maximum-minimum dry density method. At the chemical level, the relative error between the liquid phase conductivity at 24 hours steady state and the original seawater sample should not exceed 15% as the criterion for steady-state chemical stability, and it is recommended that conductivity fluctuations during the steady-state period be controlled within ±2%. At the microstructure level, the pore size distribution obtained through MIP should show a relative difference of less than 20% in the main peak position, with a distribution similarity coefficient of not less than 0.85. At least five representative fields of view should be collected by SEM to perform semi-quantitative comparisons of the neck / cavity ratio, floc size, and sheet / floc orientation to confirm the similarity of the microstructure. At the mechanics level, using a T-bar analyzer with rebound strength or its equivalent characteristic value as a reference, the relative error with the original sample should be controlled within 20%.

[0031] When there is an unavoidable slight conflict between temperature and stress boundary conditions, priority should be given to ensuring the equivalent stress field corresponding to ng, with the temperature allowed to fluctuate slightly within the range of T0 ± 2℃. If the degree of saturation and degree of consolidation cannot be simultaneously achieved within the established time period, then S should be ensured first. r ≥0.95, and then U≥90% can be achieved by extending the centrifugation time or optimizing the confining pressure path. If the MIP main peak deviation exceeds 20%, the initial compaction energy and e0 deviation should be traced back, and the layered filling and compaction thickness should be reduced to 20–40 mm in subsequent batches to promote the convergence of the pore structure to the target distribution.

[0032] When there is an unavoidable slight conflict between temperature and stress boundaries, priority should be given to ensuring the equivalent stress field corresponding to ng, and the temperature is allowed to fluctuate slightly within the range of T0 ± 2℃. If the deviation of the MIP main peak exceeds 20%, the initial compaction energy and e0 deviation should be traced back, and the layered filling and compaction thickness should be reduced to 20–40 mm in subsequent batches to promote the convergence of the pore structure towards the target distribution.

[0033] All sensors and devices must undergo pressure resistance testing in advance to ensure long-term stable operation of the system under high-g centrifugal conditions.

[0034] Abnormal operating conditions and corrective procedures. If any monitoring layer experiences a rapid temperature rise exceeding T0+4 ℃, the insulation layer thickness needs to be increased or the current hypergravity consolidation time shortened. In the next batch, the pre-cooling time should be extended and the pre-cooling temperature lowered. After the experiment, samples of the upper, middle, and lower pore solutions were taken for rapid conductivity and pH measurements. If it is necessary to retain the rare earth background content, only neutral artificial seawater was used for equal-volume dilution to avoid leaching or redeposition caused by acid / alkali treatment. The correlation between ionic strength differences and temperature curves confirmed that the impact of the salinity gradient on the temperature control strategy did not exceed expectations.

[0035] If temperature sensor drift or intermittent occurs during the centrifugation simulation, interpolation estimation should be performed based on the temperatures of other layers and the heating rate. After the experiment, the sensor's continuity and insulation should be checked. If chemical comparisons deviate (exudate conductivity or pH relative error >15%), the pore solution formulation and mixing uniformity should be reviewed; if necessary, low-shear circulating stirring and extended settling time should be introduced. If the MIP pore size distribution similarity coefficient is <0.85, the single-layer thickness should be reduced to 20–25 mm or the layer compaction energy reduced to 10–15% to weaken interlayer structural effects.

[0036] Data recording and result judgment. Temperature, pore pressure, and rotational speed data are recorded at a sampling rate of no less than 1 Hz and correspond one by one with the event log (start / stop of precooling, removal of water bath, hoisting, start and end of each g-level steady state, start / end of accelerated consolidation under hypergravity, and handling of abnormalities). The necessary conditions for batch qualification include: the average temperature rise of the observer during hypergravity centrifugal consolidation ≤2 ℃, the interlayer temperature difference ≤0.8 ℃; the relative error of chemical compatibility ≤15%; the pore size distribution similarity coefficient ≥0.85; and the deviation of small strain modulus or strength indicators from the target in-situ window ≤20%. When any indicator fails to meet the standard, it is recorded as "batch requiring adjustment," and the parameters are fine-tuned according to the correction priority order of the above two sections before being repeated.

[0037] In the description of this invention, the term "a plurality of" refers to two or more. Unless otherwise explicitly defined, the terms "upper," "lower," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. The terms "connection," "installation," "fixing," etc., should be interpreted broadly. For example, "connection" 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. For those skilled in the art, the specific meaning of the above terms in this invention can be understood according to the specific circumstances.

[0038] In the description of this specification, the terms "one embodiment," "some embodiments," "specific embodiment," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0039] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a deep-sea rare earth sediment foundation based on a high-gravity centrifugal physics simulation, characterized in that... Specifically, it includes the following steps: Step S1, Similarity Ratio Design: Geometric similarity is established between the actual water depth H of the target sea area and the designed water depth h inside the model box: the scaling ratio is taken as 1 / n = h / H, and the centrifugal acceleration ng is determined accordingly; Step S2, Solid-phase formulation design: Based on the mineral composition, particle size distribution, and REE analysis spectrum of the collected deep-sea rare earth sediments, the approximate ratio of fine-grained clay to silty framework minerals in the target formulation was determined to ensure that the clay mineral-silty framework-rare earth element content of the raw materials was identical to that of the deep-sea rare earth sediments. Fine-grained clay and silty framework were selected as the sample preparation base materials, with rare earth-rich fine particles as the additive phase. During the preparation process, the porosity e, liquid limit, plasticity index, and mineral analysis spectrum of the sample base materials were finely adjusted to ensure that the initial percentage deviations from the porosity e, liquid limit, plasticity index, and mineral analysis spectrum of the deep-sea original samples did not exceed ±10%. The soil sample mixing, grinding, and homogenization processes were carried out under an inert nitrogen atmosphere, and the final powder particle size was controlled within 1 / 2 oz. 99 ≤74m; Step S3: Initial layered filling within the model box: The prepared base material is layered in layers approximately 20–100 mm thick to form a solid-phase filling layer, with the thickness error of each layer controlled within ±2 mm. An initial porosity ratio e0≈1.15e is obtained by light compaction using 20% ​​of the standard compaction energy. * , where e * The target porosity; During the filling process, temperature sensors were buried in the upper, middle and lower layers respectively, at depths of approximately 0.15h1, 0.50h1 and 0.85h1 of the sample height h1; pore pressure sensors and soil pressure sensors were set at 0.3h1 and 0.5h1; for temperature boundary control, the initial pre-cooling and constant temperature of the model box were set within the range of seabed temperature T0-2℃. Step S4, Pore solution preparation: The pore solution was prepared based on field measurement data of deep-sea water in the target area. The ionic strength and ionic ratio were replicated by matching the concentrations of Na⁺, Mg²⁺, Ca²⁺, K⁺, Cl⁻, SO₄²⁻ and HCO₃⁻ ions. The salinity error was allowed to be no more than ±2‰. The pH and Eh values ​​of the prepared pore solution should be close to the original properties of the seawater, with the pH deviation limited to ±0.2 and the Eh deviation limited to ±20 mV. After batch preparation of the pore solution and pre-cooling it to the target temperature T0, it is injected into the model box; Step S5: Centrifugal Acceleration and Consolidation The model box was placed in a large geotechnical centrifuge to create a hypergravity environment of n·g. After reaching the target centrifugal acceleration, saturation was determined based on S. r ≥ 0.95, the consolidation judgment criteria are that under ng and T0 conditions, the consolidation reaches U≥ 90% and the pore water pressure dissipates; Step S6: Similarity evaluation between model specimen and deep-sea original sample At the physical property level, the relative errors of porosity and density are both required to be less than 10%, where the void ratio can be obtained by the mass-volume method and the density can be converted by the maximum-minimum dry density method. At the chemical level, the relative error between the liquid phase conductivity at 24 h steady state and the original seawater sample should not exceed 15% as the chemical steady-state criterion, and the conductivity fluctuation during the steady state should be controlled within ±2%. At the microscopic level, the pore size distribution obtained by MIP should show a relative difference of less than 20% in the position of the main peak, and the distribution similarity coefficient should not be less than 0.

85. At least five representative fields of view should be collected by SEM to conduct a semi-quantitative comparison of the neck / cavity ratio, floc size, and sheet / floc orientation. At the mechanical level, the relative error between the T-bar tester and the original sample should be controlled within 20% using the rebound strength or its equivalent characteristic value as a reference.

2. The method for preparing a deep-sea rare earth sediment foundation based on centrifugal physics simulation according to claim 1, characterized in that... The model box is a supergravity static model box with a combination structure of aluminum alloy box body and steel base plate, measuring 1.2m×0.95m×1.0m; the inner wall of the box is treated with sandblasting and fluorocarbon transparent coating; a laser displacement meter is installed under the cover of the model box, and the corresponding reflector needs to be placed on the filled solid phase surface.

3. The method for preparing a deep-sea rare earth sediment foundation based on centrifugal physics simulation according to claim 1, characterized in that... The fine-grained clay in step S2 includes kaolinite, illite, sodium montmorillonite and chlorite, and the silty skeleton includes quartz and feldspar.

4. The method for preparing a deep-sea rare earth sediment foundation based on centrifugal physics simulation according to claim 1, characterized in that... In step S3, the layers are laid in six to seven layers, with a single layer thickness of 20–100 mm. After laying, the layers are allowed to cool to T0 ± 2℃ before centrifugal loading.

5. The method for preparing a deep-sea rare earth sediment foundation based on centrifugal physics simulation according to claim 1, characterized in that... The model pore solution prepared in step S4 is filtered through a 0.22–0.45 μm filter and circulated in an inert material pipeline, with a pH deviation ≤ ±0.

2.

6. The method for preparing a deep-sea rare earth sediment foundation based on centrifugal physics simulation according to claim 1, characterized in that... In step S5, the model box is placed in a large geotechnical centrifuge to construct an n·g hypergravity environment. A segmented g-increasing strategy is adopted, with the g value gradually increased and maintained at a stable pore pressure: 0 → 20 g steady state for 1 min → 40 g steady state for 10 min → 60 g steady state for 10 min → 80 g steady state for 10 min → 100 g. Formal hypergravity accelerated consolidation is carried out at 100 g, and then maintained at 100 g until the equivalent degree of consolidation U ≥ 90%, with the pore water pressure change approaching zero and the volumetric rate of change < 10⁻⁻⁻⁶. 7 s⁻¹ is the termination criterion.

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