Non-destructive detection mold and method for rammed earth wall

Abstract

The invention discloses a lossless detection mold and method for a rammed earth wall, and relates to the technical field of civil engineering and cultural relic protection. In order to solve the problem that in a traditional rammed earth wall nondestructive detection method, it is difficult to establish an effective corresponding relation between signal features and physical and mechanical parameters, the rammed earth wall nondestructive detection mold and method comprise the steps that rammed earth materials are prepared with reference to the soil texture of an ancient wall, and the rammed earth materials are filled into the rammed earth mold in a layered mode to prepare a wall-like test piece; carrying out nondestructive detection on the city-wall-like test piece by adopting a geological radar to obtain an oscillogram and a grey-scale map, and extracting a detection signal; sampling the city-wall-like test piece, carrying out a physical and mechanical test, and establishing a parameter database in which detection signal parameters are associated with physical and mechanical parameters; and finally, carrying out field detection on the ancient city wall, carrying out geological radar detection to obtain an actual detection signal, and matching the actual detection signal with the parameter database to obtain physical and mechanical parameter information of the ancient city wall. The method can effectively improve the accuracy of lossless detection of the rammed earth structure, and provides a scientific basis for ancient city wall protection.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of civil engineering and cultural heritage protection, and particularly relates to a rammed earth city wall non-destructive detection mold and method. BACKGROUND

[0002] As important historical and cultural heritage and civil engineering remains in China, ancient city walls are widely distributed in various places, which are mainly composed of rammed earth materials and have high historical and scientific value. However, due to the combined effects of natural environment (such as rain erosion, freeze-thaw cycle) and human factors (such as surrounding construction activities), the internal structure of ancient city walls often appears defects such as water content change, density decrease, and cavities, cracks, etc., which seriously threaten the stability and integrity of the ancient city walls. In order to protect these cultural relics, it is urgent to develop efficient and non-destructive detection technology to evaluate the physical and mechanical properties and internal defect state of the ancient city walls.

[0003] Traditional detection methods, such as excavation sampling or manual visual inspection, have the problems of strong destructiveness, low efficiency, limited coverage, etc., and cannot meet the needs of large-scale and non-destructive detection. In recent years, due to the advantages of non-destructiveness, penetration ability and high resolution, geological radar technology has been gradually applied to the detection of ancient buildings and soil structures. By emitting electromagnetic waves and analyzing the reflected signals, the geological radar can identify the water distribution, density and defect characteristics in the soil. However, the existing geological radar detection technology faces the following challenges when applied to rammed earth city walls: first, the complexity of the materials of the ancient city walls (such as the difference in water content and density) makes it difficult to interpret the signals; second, there is a lack of targeted test models, making it difficult to establish a reliable correspondence between the signals and the physical parameters and defects; third, the model preparation and ramming process is time-consuming and laborious, making it difficult to quickly realize the test of multiple parameter combinations.

[0004] In view of the above problems, although there are some rammed earth models and detection methods in the prior art, they are mostly focused on the study of single density or water content, and cannot systematically analyze the interaction between the two. In addition, the traditional mold design is complex, inconvenient to disassemble, and difficult to simulate the diversified defect state of the ancient city walls, which limits the accuracy and practicality of the detection data. Therefore, developing a rammed earth city wall non-destructive detection mold with reasonable structure and easy operation, as well as a scientific detection method matched therewith, to reduce the test workload, improve the representativeness of the model and the reliability of the detection results, has become a technical problem to be solved in the field of cultural heritage protection and civil engineering. SUMMARY

[0005] The present application provides a rammed earth city wall nondestructive detection mold and method to solve the defects in the prior art. It has the advantages of simple structure, convenient operation, high test efficiency, strong controllability, etc., and aims to quickly build the corresponding relationship between the physical and mechanical parameters of the rammed earth city wall and the geological radar signal through the laboratory model, and to provide reliable basis for the on-site nondestructive detection of the ancient city wall.

[0006] To achieve the above object, the technical idea of the present application is:

[0007] (1) A detachable wooden frame mold is designed to divide the model into dense, medium and under-dense areas to simulate the density difference of the ancient city wall. By controlling the variable method, different water content and density combinations are set to reduce the model ramming workload and systematically analyze the influence of water content and density on the geological radar signal.

[0008] (2) Artificial defects (such as cavities) are introduced during the model ramming process to ensure the authenticity of the model structure using the layered ramming process. Using a multi-frequency antenna for detection, combined with signal processing technology, the propagation time, amplitude and waveform characteristics are extracted to establish a quantitative correspondence between the signal and the physical and mechanical parameters and defects.

[0009] (3) The physical and mechanical parameters (such as density, moisture content, and compressive strength) of the model are determined through laboratory tests, combined with signal feature analysis, to form a reliable signal-parameter-defect database. The corresponding relationship is applied to on-site detection of ancient city walls to deduce their internal state, providing scientific support for cultural relic protection and safety evaluation.

[0010] To achieve the above object, the technical solution adopted by the present application is:

[0011] A rammed earth city wall nondestructive detection method, comprising: preparing rammed earth materials according to the soil quality and physical properties of the ancient city wall; making and assembling a rammed earth mold, layering and ramming the soil in the mold to make a city wall-like test piece; using a geological radar to nondestructively detect the city wall-like test piece to obtain a waveform graph and a grayscale graph, and analyzing the waveform graph and the grayscale graph to obtain the detection signal of the city wall-like test piece; sampling the city wall-like test piece after nondestructive detection and conducting indoor mechanical experiments to determine the physical and mechanical parameters of the sample, and establishing a parameter database associating the detection signal with the physical and mechanical parameters; detecting the ancient city wall using a geological radar to obtain an actual detection signal, matching the actual detection signal with the parameter database, and obtaining the physical and mechanical parameter information of the ancient city wall.

[0012] Further limitation of the above technical solution, the specific process of preparing the rammed earth material is as follows:

[0013] (1) According to the physical properties of the ancient city wall material, Xi'an local Malan loess is selected as the rammed earth material, and the volume ratio of Malan loess when compressed and loose is about 0.8;

[0014] (2) Pretreatment of Malan loess;

[0015] (3) The pretreated Malan loess is mixed with water to obtain a rammed earth material with a water content of 10-20% according to the water content range of the ancient city wall rammed earth, the dry soil mass is determined by step-by-step weighing, and 1-2% of water is added based on the designed water amount to compensate for water evaporation and infiltration.

[0016] In further limitation of the above technical solution, the rammed earth mold comprises a baffle 1 and a hoop 2, and the baffle 1 and the hoop 2 cooperate to form an open mold frame without a cover and a bottom. The rammed earth material is continuously rammed in the mold box as a whole without physical separation. The inside of the model is divided into multiple regional units according to the density by controlling the number of ramming, and the transition regions of the multiple regional units are formed at the intersections of the multiple regional units.

[0017] In further limitation of the above technical solution, the multiple regional units comprise a first regional unit, a second regional unit and a third regional unit which are sequentially divided along the length direction of the inner cavity of the open mold frame. There is no physical separation between the regional units, and there is a transition region between the regional units.

[0018] In further limitation of the above technical solution, the first regional unit, the second regional unit and the third regional unit are respectively prepared into a dense type city wall test piece, a medium density type city wall test piece and an under-dense type city wall test piece. The three types of test pieces control different ramming times in the preparation process, and the specific process of layered ramming of the three types of test pieces is as follows:

[0019] Row ramming, which is performed in three steps. The first ramming is used to compact the backfill soil, the interval between each ramming nest is about 0.2m, the second ramming is used to ram the gap between the first ramming, and the remaining ramming is used to ram the gap between the first two times, so that the backfill soil is compacted as a whole.

[0020] Leveling, which is performed by milling the surface of the rammed earth and repeating 1-3 times as needed.

[0021] Watering, which is performed by evenly sprinkling water first and then watering in pieces. The crawling plow is used to rake the water as it falls to avoid local water accumulation.

[0022] Among them, the number of row ramming of the dense type city wall test piece, the medium density type city wall test piece and the under-dense type city wall test piece in the layered ramming process is 25 times, 15 times and 5 times, respectively.

[0023] In further limitation of the above technical solution, model A and model B are respectively arranged in the two open mold frames, and each of model A and model B comprises a first regional unit, a second regional unit and a third regional unit.

[0024] Among them, model A is a defect-free model, no artificial defect is arranged in the test piece, only the top is temporarily stacked with blocks to assist the standing, and the blocks are removed after standing for one week;

[0025] Model B is provided with a masonry on the top of the test piece, and an artificial defect is introduced in the test piece, and detection is carried out after standing for one week;

[0026] Among them, the artificial defect includes a cavity.

[0027] Further limitation of the above technical solution, the parameter database is:

[0028]

[0029]

[0030] Another object of the present application is to provide a rammed earth mold for preparing the city wall-like test piece, the rammed earth mold comprising: a baffle 1 and a hoop 2; wherein a plurality of baffles 1 are used to form an open mold frame without cover and bottom, and a plurality of hoops 2 are arranged outside the baffles 1, used to connect the baffles 1 and realize the detachable assembly of the open mold frame.

[0031] Further limitation of the above technical solution, the size of the open mold frame ranges from 3-5m*0.8-1m*0.8-1.2m.

[0032] Compared with the prior art, the present application has the following advantages:

[0033] 1. The present application designs a detachable wooden frame mold, which is divided into dense, medium and under-dense areas by arranging blocks inside the mold, and combines with the control variable method to adjust the water content (12%-17%) and the density (by 25 times, 15 times and 5 times ramming), forming 2 large models with 6 parameter combinations, which significantly reduces the workload of preparing different density and water content models one by one in the traditional method. The mold structure is simple, convenient to operate and easy to disassemble, and by setting artificial defects such as cavities and cracks, the internal state of the ancient city wall is simulated, which overcomes the problems of complex model preparation and insufficient defect simulation in the prior art, and provides an efficient platform for the research on the corresponding relationship between the geological radar signal and the physical and mechanical parameters and the defect characteristics.

[0034] 2.The application adopts geological radar multi-frequency detection (400MHz deep layer and 900MHz shallow layer), combines signal processing technologies such as denoising, filtering and time-depth conversion, accurately extracts propagation time, amplitude and waveform characteristics, and establishes a reliable signal-parameter-defect correspondence. Compared with the signal interpretation difficulty caused by single frequency band detection in the prior art, the application analyzes the interaction of water content and density by the control variable method, enhances the accuracy and reliability of the detection results, provides a scientific basis for fine evaluation of the internal state of the ancient city wall, and significantly improves the practicability of nondestructive testing.

[0035] 3.The application constructs a signal-parameter-defect database by indoor sampling determination of the physical and mechanical parameters (such as density, water content and compressive strength) of the model, combined with geological radar signal analysis, and successfully applies it to the on-site detection of the ancient city wall, deduces the physical and mechanical properties and defect information. Compared with the on-site application limitations caused by the lack of targeted database in the prior art, the method of the application reduces the test time, improves the data consistency and prediction accuracy, provides a quantitative basis for cultural relic protection and structure safety evaluation, has significant economic benefits and protection value, and meets the detection needs of various ancient city wall materials. BRIEF DESCRIPTION OF DRAWINGS

[0036] The application will be further described below in combination with the drawings and examples.

[0037] Figure 1 is a flowchart of a rammed earth city wall nondestructive detection method of the application;

[0038] Figure 2 is a structural diagram of a rammed earth city wall nondestructive detection mold of the application;

[0039] Figure 3 is a structural exploded view of Figure 2 ;

[0040] Figure 4 is a construction size diagram of the rammed earth city wall nondestructive detection mold;

[0041] Figure 5 is a sectional view of the hoop end connection mode;

[0042] Figure 6 is a nondestructive detection model size and density division diagram of model A (water content 11%);

[0043] Figure 7 is a nondestructive detection model size and density division diagram of model B (water content 13%);

[0044] Figure 8 is a row ramming sequence diagram of the application;

[0045] Figure 9is a ground penetrating radar signal post-processing flowchart of the present application;

[0046] Figure 10 is a first time scanning graph of model A ground penetrating radar of the present application, wherein, figure (a) is a model A1 scanning graph, figure (b) is a model A2 scanning graph, figure (c) is a model A3 scanning graph;

[0047] Figure 11 is a second time scanning graph of model A ground penetrating radar of the present application, wherein, figure (a) is a model A1 scanning graph, figure (b) is a model A2 scanning graph, figure (c) is a model A3 scanning graph;

[0048] Figure 12 is a model B ground penetrating radar scanning graph of the present application, wherein, figure (a) is a first time scanning graph of model B ground penetrating radar, figure (b) is a second time scanning graph of model B ground penetrating radar, figure (c) is a third time scanning graph of model B ground penetrating radar, figure (d) is a fourth time scanning graph of model B ground penetrating radar;

[0049] Figure 13 is a first time scanning partial waveform graph of model A ground penetrating radar of the present application, wherein, figure (a) is a model A1 waveform graph, figure (b) is a model A1-2 waveform graph, figure (c) is a model A2 waveform graph, figure (d) is a model A1-3 waveform graph, figure (e) is a model A3 waveform graph;

[0050] Figure 14 is a second time scanning partial waveform graph of model A ground penetrating radar of the present application, wherein, figure (a) is a model A1 waveform graph, figure (b) is a model A1-2 waveform graph, figure (c) is a model A2 waveform graph, figure (d) is a model A1-3 waveform graph, figure (e) is a model A3 waveform graph;

[0051] Figure 15 is a first time scanning partial waveform graph of model B ground penetrating radar of the present application, wherein, figure (a) is a model B1 waveform graph, figure (b) is a model B1-2 waveform graph, figure (c) is a model B2 waveform graph, figure (d) is a model B1-3 waveform graph, figure (e) is a model B3 waveform graph;

[0052] Figure 16 is a fourth time scanning partial waveform graph of model B ground penetrating radar of the present application, wherein, figure (a) is a model B1 waveform graph, figure (b) is a model B1-2 waveform graph, figure (c) is a model B2 waveform graph, figure (d) is a model B1-3 waveform graph, figure (e) is a model B3 waveform graph;

[0053] Figure 17are stress-strain relationship curves of the model A and B of the present application under different confining pressures, wherein, the figure (a), the figure (b), the figure (c) are stress-strain relationship curves of the model A1, A2, A3 respectively, the figure (d), the figure (e), the figure (f) are stress-strain relationship curves of the model B1, B2, B3 respectively;

[0054] Figure 18 are shear strength parameters of the model soil sample of the present application, wherein, the figure (a), the figure (b), the figure (c) are shear strength parameters of the model A1, A2, A3 respectively, the figure (d), the figure (e), the figure (f) are shear strength parameters of the model B1, B2, B3 respectively;

[0055] Figure 19 are stress-strain relationship curves of the model A and B of the present application under different confining pressures, wherein, the figure (a), the figure (b), the figure (c) are stress-strain relationship curves of the model A1, A2, A3 respectively, the figure (d), the figure (e), the figure (f) are stress-strain relationship curves of the model B1, B2, B3 respectively; Figure 1 Corresponding relationship between shear strength parameters and physical parameters of rammed earth;

[0056] Figure 20 are stress-strain relationship curves of the model A and B of the present application under different confining pressures, wherein, the figure (a), the figure (b), the figure (c) are stress-strain relationship curves of the model A1, A2, A3 respectively, the figure (d), the figure (e), the figure (f) are stress-strain relationship curves of the model B1, B2, B3 respectively;

[0057] In the figure: 1, baffle; 2, hoop; 21, first hoop; 22, second hoop; 23, first cross brace; 24, first vertical brace; 25, second vertical brace; 26, second cross brace. DETAILED DESCRIPTION

[0058] In order to make the above objectives, features and advantages of the present application more apparent, the specific embodiments of the present application are described in detail below with reference to the accompanying drawings.

[0059] In the following description, a lot of specific details are set forth in order to provide a thorough understanding of the present application, however, the present application can also be implemented in other ways different from the description herein, and those skilled in the art can make similar generalization without departing from the connotation of the present application, therefore, the present application is not limited by the specific embodiments disclosed below.

[0060] Secondly, the "one embodiment" or "embodiment" referred to herein means that the specific features, structures or characteristics can be included in at least one implementation of the present application. "In one embodiment" appearing in different places in the specification does not mean the same embodiment, nor is the embodiment alone or selectively mutually exclusive with other embodiments.

[0061] Embodiment one

[0062] In combination Figures 1 to 20 The present application discloses a kind of rammed earth mould, comprising: baffle 1 and hoop 2, multiple baffles 1 are used to form the open type mould frame of no cover no bottom, multiple hoops 2 are arranged in baffle 1 outside, for connecting each baffle 1 and realizing the detachable assembly of the open type mould frame.

[0063] Specifically, the baffle 1 is provided with five, respectively, in the four around the mold, forming an open mold frame, for containing ramming material and supporting model forming. Specifically, the overall size of the mold is 300-500 cm long x 80-100 cm wide x 100-150 cm high, the baffle is made of pine board with a thickness of 5 cm, the surface is polished and waterproofed to prevent water leakage and deformation of the wood during ramming. The baffle is connected by a clamping groove and a bolt to ensure that the structure is stable and can be disassembled, facilitating sampling operation after model forming.

[0064] Specifically, the hoop 2 is provided with a plurality of circumferential arrangements outside the baffle, for detachable connection of the baffle, and enhancement of the overall stability of the mold structure. The hoop 2 is composed of the following sub-components:

[0065] Specifically, the first hoop 21 is provided with 4, arranged in parallel along the upper and lower edges of the front and rear side baffles outside. The first hoop 21 is an integral reinforcing member that transversely penetrates the full length of the baffle, enhancing the overall rigidity and anti-deformation ability of the baffle. Each first hoop 21 is provided with a limiting protrusion at both ends. The length of the main section of the first hoop 21 is 20 cm longer than the length of the front and rear side baffles, and the length of the limiting protrusions at both ends is 10 to 15 cm. This structure design not only facilitates assembly and disassembly, but also significantly improves the overall stability and front and rear side constraint strength of the mold under stress, effectively preventing warping and loosening of the baffle during work.

[0066] Specifically, the second hoop 22 is provided with 8, symmetrically and parallelly arranged along the top and bottom of the mold, with 4 on the top and 4 on the bottom. Among them, the second hoop 22 on the left and right sides of the top and bottom is used to fix the baffle 1, and the two second hoops 22 in the middle of the top and bottom are used to divide the open mold frame into three area units along the length direction, namely the first area unit, the second area unit and the third area unit, which facilitates the partitioned research and non-destructive testing of the ramming material in different areas.

[0067] The second hoop 22 is also made of a wooden strip, with the same width and thickness as the first hoop 21, and each second hoop 22 is also provided with a limiting protrusion at both ends. The length of the main section of the second hoop 22 is 20 cm longer than the length of the front and rear side baffles, and the length of the limiting protrusions at both ends is 10 to 15 cm.

[0068] Specifically, the first cross brace 23 is an integrally formed strip-shaped member, and is linear as a whole. Four first cross braces 23 are provided, are parallel to the first hoop 21, are evenly distributed along the outer sides of the front and rear side plates, and are located in the gaps between the upper and lower first hoops 21. The first cross brace 23 is a wooden strip with a width of 5 cm and a thickness of 2 cm, and has a length that is 10 cm longer than the length of the front and rear side plates, that is, each end of the length of the front and rear side plates extends by 5 cm. The first cross brace 23 and the first hoop 21 jointly form a frame support structure of the front and rear sides, and are fixed to the outer sides of the side plates by bolts.

[0069] In the present embodiment, eight first vertical braces 24 are provided, are arranged vertically along the outer sides of the front and rear side plates, and are four on each side. Each first vertical brace 24 is a wooden strip with a width of 4 cm and a thickness of 2 cm, and has a length equal to that of the left and right side plates 1, so as to achieve full coverage support in the length direction of the entire mold.

[0070] Specifically, the first vertical brace 24 is vertically arranged on the outer sides of the front and rear side plates, and is sequentially embedded in the gaps between the first hoop 21 and the second hoop 22. That is, one end of each first vertical brace 24 is lapped on the outer side of the first hoop 21, and the other end is tightly fitted with the inner surface of the limiting protrusion of the second hoop 22, so as to achieve effective limiting and positioning in the vertical direction. In addition, the longitudinal outer surface of the first vertical brace 24 also cooperates with the outer side of the first cross brace 23, and as a whole, plays a role of strengthening the structural rigidity of the mold, preventing displacement and deformation of the front and rear side plates.

[0071] Specifically, the second vertical brace 25 is provided with four second vertical braces 25, which are vertically arranged along the upper and lower edges of the outer sides of the left and right side plates, and are two on each side. The length of each second vertical brace 25 is 20 cm longer than the height of the left and right side plates, that is, each end of the height of the left and right side plates extends by 10 cm. The second vertical brace 25 is a wooden strip with a width of 4 cm and a thickness of 2 cm, and is fixed to the outer sides of the side plates by bolts, for enhancing the vertical support of the left and right side plates.

[0072] Specifically, the second cross brace 26 is provided with four second cross braces 26, which are horizontally arranged along the outer sides of the left and right side plates. Each second cross brace 26 is an integrally formed long strip-shaped member, and has a length that is 10 cm longer than the length of the left and right side plates 1, so as to ensure effective lapping and limiting with adjacent members during structural assembly.

[0073] Specifically, the second cross brace 26 is horizontally embedded in the gap between the second vertical brace 25 and the first hoop 21, that is, one end of each cross brace is fitted with the outer side of the second vertical brace 25, and the other end is opposite to the first hoop 21. Through this structural arrangement, the second cross brace 26 can firmly connect the vertical and horizontal components, and further improve the overall rigidity and structural stability of the left and right side plates of the mold.

[0074] II. An embodiment of a non-destructive detection method for rammed earth city walls

[0075] In combination Figures 1 to 20 A rammed earth city wall nondestructive detection method first needs to prepare rammed earth materials according to the soil quality and physical characteristics of the ancient city wall, and specifically, the preparation of the rammed earth materials needs to take the following steps:

[0076] (1) Prepare test materials

[0077] In order to meet the ground penetrating radar detection of rammed earth, the size of the model box should not be too small, and considering the large amount of earthwork for rammed earth, the size of the ancient city wall rammed earth model (such as shown in FIG. Figure 4 The rammed earth material uses Malan loess in Xi'an, and the loess compression coefficient is 0.8. Considering the waste in the transportation, water mixing and ramming process, 2% of the soil quantity is added to the soil for ramming. The standard specification of the blue bricks is 240mmx115mmx53mm (lengthxwidthxheight), and 2-3 layers of bricks are laid on the surface of the model by rolling. In order to facilitate subsequent sampling, a detachable wooden frame is used as a rammed earth mold. The main test materials used in the present application are shown in Table 1.

[0078] Table 1 Nondestructive detection model test materials, tools and equipment

[0079]

[0080]

[0081] (2) Loess airing and impurity removal

[0082] The obtained original soil is crushed, and the soil is gathered into small soil piles and then the soil is poured onto the top of the soil pile by using an iron mill. The calcium nodule, brick and stone around the bottom of the soil pile are removed by spading. This method uses gravity to remove impurities layer by layer, and the soil can be obtained quickly. The impurity removal step is repeated 1-2 times as needed. The soil after removing impurities is flattened and aired until dry.

[0083] (3) Water content ratio (taking Xi'an city wall as an example)

[0084] It is known that the water content of the rammed earth of Xi'an city wall is mainly between 12% and 17%. Before the test, the water content of the dry soil with a unit weight (1 kg) is pre-allocated. The wet soil meets the requirement of "hand holding into a ball and falling to the ground" to meet the ramming requirement ("hand holding into a ball and falling to the ground" specifically refers to the optimal water content of the soil, that is, the soil can be held into a ball in the hand, and can be freely scattered after falling to the ground. Such soil quality is suitable for backfilling and ramming).

[0085] The water content pre-allocation result shows that the water content of the Malan loess in Xi'an region after airing and impurity removal is between 10% and 20%, which can better meet the ramming requirement.

[0086] Before ramming, the loess material is mixed with water according to the designed water content. Considering the evaporation and infiltration of water caused by weather and other factors, 1% to 2% more water should be added to the designed water content.

[0087] Because the amount of soil used in model ramming is large, in order to make the actual water content of the rammed soil consistent with the designed water content, the weight of the soil should be determined before the dry soil is mixed with water. The dry soil mass can be calculated by using the method of step-by-step weighing and summation. After the dry soil is mixed with water, the wet soil with the pre-mixed water content should be compared to ensure that the actual water content of the rammed soil is close to the designed water content.

[0088] In order to facilitate non-destructive testing, the rammed soil mold includes a baffle 1 and a hoop 2, which cooperate to form an open mold frame without a cover and a bottom. The rammed soil material is continuously rammed in the mold frame as a whole, and by controlling the number of ramming times, the inside of the model is divided into multiple regional units according to the density, and the multiple regional units form transition regions with varying densities at their intersections. The inside of the open mold frame is not physically separated, and the division of the regional units is mainly realized by the second hoop 22 symmetrically arranged at the top and bottom.

[0089] The multiple regional units include a first regional unit, a second regional unit, and a third regional unit sequentially divided along the length direction of the inner cavity of the open mold frame. There is no physical division between each regional unit, and there is a transition region between each regional unit. The first regional unit, the second regional unit, and the third regional unit respectively prepare a dense type city wall test piece, a medium density type city wall test piece, and an under-dense type city wall test piece. In the preparation process of the three types of test pieces, the density is adjusted by controlling the different number of ramming times of each layer (such as 24 times, 12 times, and 8 times of ramming for each ramming nest corresponding to dense, medium dense, and under-dense). The prepared rammed soil material is uniformly placed in each regional unit of the mold according to the predetermined layer thickness, and ramming is carried out according to the layer ramming method to ensure that each region obtains the designed density.

[0090] Combined with the actual measurement results of Xi'an city wall, the average water content of the soil body is about 13%. To simulate the actual project, the water content of the test model rammed soil material is set to three schemes of 11%, 13%, and 15%. Before the test starts, a certain amount of dry soil is taken and mixed with water in proportion to make the wet soil meet the traditional ramming requirement of "holding together in hand and scattering on the ground". After actual operation, the rammed soil material with a water content of 15% has too much water, which shows that the soil is muddy and the strength decreases significantly, which is not suitable for ramming, and finally this water content scheme is not adopted.

[0091] In order to improve the test efficiency and facilitate subsequent comparison, two representative city wall type rammed soil test pieces, model A and model B, are set up.

[0092] Model A: water content is 11%.

[0093] Region A1, A2, A3 represent dense (24 times), medium dense (12 times), and under dense (8 times) respectively (see Figure 6 ).

[0094] Model B: water content is 13%.

[0095] Region B1, B2, B3 are also dense, medium dense and under dense respectively (see Figure 7 ).

[0096] In Model B, to further simulate the actual city wall internal structure changes, two hollows are arranged at the junction of different density regions using bricks (the hollows are both 14 cm from the bottom of the model, and the sizes are 48 cm x 13.4 cm x 11.5 cm and 24 cm x 13.4 cm x 11.5 cm respectively). In addition, Model B also uses rolling brick method to build two layers of blue bricks, with a total masonry height of about 25 cm (i.e. 11.5 x 2 + 1 x 2).

[0097] In each model, the regions of different densities are numbered as follows: A1 / B1 (dense), A2 / B2 (medium dense), A3 / B3 (under dense), to facilitate subsequent detection and data comparison.

[0098] The specific process of layering ramming of the three types of specimens is as follows:

[0099] The rammed earth model is prepared according to the traditional method of ancient buildings, taking three steps of row ramming, taking flat, and falling water. Different ramming times are used for different ramming, medium and under dense parts in each ramming pit, but the actual ramming effect specified by the number of times is easily affected by human factors, so the thickness of the soil layer before and after ramming can be used to determine whether to continue ramming. The rammed earth is layered rammed, and the thickness of each layer of virtual soil is about 18 cm, which is suitable for ramming with a hammer after stepping flat. The ramming diagram is shown in Figure 8 .

[0100] The specific steps of layering ramming are as follows:

[0101] 1) Row ramming: row ramming is divided into three steps: head ramming (commonly known as "charging sea pit"), second ramming (commonly known as "building silver ingot"), and residual ramming (commonly known as "filling ditch" and "cutting stem"). Head ramming is the first time to ram the backfill soil, as shown by mark ① in the figure. The distance of each ramming pit is about 0.2 m. On this basis, the gap of the head ramming pit is selected for the second time of ramming, as shown by mark ② in Figure 8 . Subsequently, the third time of ramming is carried out on the gap of the previous two ramming pits, as shown by mark ③ in Figure 8 . The position of the third time of ramming is the gap of the previous two ramming pits, and after ramming, the entire foundation backfill soil is basically filled (see Figure 8 ).

[0102] 2) Taking flat: use a mill to smooth the surface of the rammed soil, and repeat 1 to 3 times as appropriate.

[0103] 3) Water: After the rammed earth surface is taken, water is sprayed on the surface. The water should not be sprayed too quickly. First, water is sprayed in a flower shape, then water is sprayed in a piece, and a crawling plow is used to gather the water. This avoids local water accumulation and subsequent soil compaction.

[0104] Specifically, each ramming nest can be hit 25 times, 15 times and 5 times, respectively, for different compaction models. It should be noted that the soil in the compacted area should be as compacted as possible, and the soil in the under-compacted area should be as loose as possible, so as to distinguish the compaction degree of different parts of the soil. At the same time, the under-compacted part of the rammed earth should maintain good integrity to meet the subsequent sampling and sample preparation requirements, so the soil in this part should strictly follow the three-step requirements of the ramming during the ramming. Subsequently, the top of the rammed earth can be built with green bricks, and the soil is allowed to consolidate for 3 days before being detected by a geological radar.

[0105] In addition, artificial defects are introduced in the model during the layered ramming process, including cavities and cracks. The cavity is formed by an internal closed space formed by stacking green bricks or welding steel plates, and the crack is formed by cutting or leaving a gap to simulate the structural characteristics of the ancient city wall.

[0106] After the ramming is completed, consolidation treatment is also required. The specific steps are as follows: 2-3 layers of green bricks are built on the top of the rammed earth, the green bricks are built in a rolling brick manner, and the soil is allowed to consolidate for 3 days before being detected by a geological radar. This is mainly because: under the surrounding protection of the hoop and support, the stiffness of the model box is large, and no obvious deformation occurs during the ramming process. The size of the model is mainly to meet the detection needs of the ground penetrating radar. The upper part of the rammed earth is built with blocks, which on one hand consolidates the soil using the weight of the blocks, and on the other hand simulates the outer brick of the rammed earth city wall.

[0107] After the preparation of the city wall-like test piece with water content and compaction degree zoning and the completion of the consolidation treatment, the test piece is subjected to non-destructive detection using a geological radar (GPR) after being left for one week. The non-destructive detection includes the following steps:

[0108] 1. Non-destructive detection method for city wall-like rammed earth test piece characteristics

[0109] The geological radar antenna can be used in combination with 400MHz and 900MHz (both frequencies are widely used). The 400MHz antenna has a deeper detection depth and relatively smaller accuracy; the 900MHz antenna has a smaller detection depth and relatively larger accuracy. Therefore, the use of both antennas is more conducive to analyzing the detection signals of the rammed earth model. The detection of the rammed earth city wall can use an antenna with a lower frequency (preferably 100MHz, 200MHz, 270MHz, 350MHz, and 400MHz). During the model test, the antenna is placed on the upper part of the rammed earth or the block, and a line measurement method is used to slowly and smoothly pull the antenna along the long side of the model.

[0110] 1.1 Radar signal processing

[0111] After the completion of the model ramming, the uniform load of 20 kPa is applied on the top by using bricks, and the soil is consolidated after standing for a week, wherein the model A is pure soil, and the model B is internally arranged with a cavity and overlying masonry. In the case of known rammed soil size, the material electrical parameters are obtained by continuous adjustment through continuous measurement of 400 MHz antenna, 1024 sampling points per channel, and time window setting of 30 ns. The model A and model B are nondestructively detected by ground penetrating radar, and the radar scan map is obtained, which is post-processed (see Figure 9 ).

[0112] 1.2 Gray scale image analysis of nondestructive testing of the model

[0113] The continuity of the gray scale image of the rammed soil density has a certain influence. The gray scale imaging effect of the model A3 is the worst, which is caused by poor density, but it cannot be ruled out that there is an accidental factor, so the model is detected for many times.

[0114] The poor density of the rammed soil will reduce the imaging effect of the ground penetrating radar, and the gray scale image mainly presents point distribution, while the gray scale image of the rammed soil in the dense state has good continuity. At the site where the density of the rammed soil changes, the gray scale image will be obviously bent, wherein the first scan image and the second scan image of the model A ground penetrating radar are shown in Figure 10 and Figure 11 .

[0115] The imaging effect of the model B is poorer than that of the model A, which indicates that the water in the soil will affect the imaging effect of the ground penetrating radar scan. The first to fourth scan images of the model B are shown in FIG. 12, and it can be seen from Figure 12 that the second scan imaging effect is the best, and the overlying masonry and internal defects of the rammed soil can be clearly seen.

[0116] Overall, at the site where the density changes, the gray scale image will produce relatively obvious point distribution or turning. The size of the left cavity (with masonry) is 586 mm x 240 mm x 168 mm (length x width x height), and the size of the right cavity (with masonry) is 346 mm x 240 mm x 168 mm (length x width x height), and the cavity presents a parabola with the opening downward in the gray scale image, wherein the opening of the left parabola is large, and the opening of the right parabola is small.

[0117] In summary, the 400 MHz ground penetrating radar meets the depth requirements of the rammed earth model. Model A and Model B have different scanning image effects due to the difference in water content, which shows that water in the soil can reduce the imaging effect of the scanning image. The continuity of the gray scale image is better in areas with high compaction than in areas with low compaction. In areas with low compaction or changing compaction, the gray scale image fluctuates or presents a punctate distribution. The imaging effect of rammed earth scanning is greatly affected by other factors such as operation or environment, so when using ground penetrating radar to detect rammed earth, repeated scanning is needed until a more ideal effect is achieved. During the field detection of the city wall, the measurement lines should be densified in key areas, and multiple measurements should be taken to obtain sufficient effective scanning images.

[0118] 1.3 Waveform analysis of non-destructive testing of models

[0119] Model A1-2 is located at the transition between Model A1 and A2, and Model A1-3 is located at the transition between Model A2 and A3. The first scan waveform ( Figure 13 ) and the second waveform ( Figure 14 ) are basically the same.

[0120] When the compaction of the rammed earth is large, the size of each group of positive and negative in the waveform is basically the same, showing a sinusoidal wave with gradually decreasing energy. When the compaction of the rammed earth is large, the energy decay of the waveform is relatively fast, i.e., the compaction of the rammed earth is inversely proportional to the energy decay of the electromagnetic wave, and the detection depth of the electromagnetic wave decreases with the increase of the compaction of the rammed earth. This law is more obvious when the frequency of the electromagnetic wave is smaller (see Figure 15 、 16 ).

[0121] According to the physical and mechanical parameters of the model, the compaction of Model B is lower than that of Model A, and the water content is higher. When there is a masonry on the upper part of the model, the positive and negative of the waveform at the corresponding position significantly increase. When there is a cavity inside the rammed earth, the negative of the waveform at the corresponding position on the top of the cavity significantly increases. The waveforms obtained by multiple scans at the same part of the model may have a large difference, so based on the actual situation, ground penetrating radar should be used for multiple scans, and appropriate and effective waveforms should be selected. The scanning waveforms of different parts of the rammed earth are clearly distinguished, and the signal strength decays faster in areas with high compaction. In addition to the compaction and water content of the rammed earth, the waveform amplitude is also affected by the internal defects of the rammed earth.

[0122] After completing the non-destructive detection of the ground penetrating radar, representative samples are selected from different areas of the city wall-like test piece (such as compact, medium compact, under-compact, and cavity periphery, etc.). The samples are sent to the laboratory for physical and mechanical performance testing according to the standard test procedures, including but not limited to: water content (ω), specific gravity (γ), Poisson's ratio, pore water pressure, and other mechanical parameters, and a parameter database is established.

[0123] 2. Indoor test of rammed earth sample properties

[0124] During sampling, the size of the sample was a 18cm cube to ensure that the sample reflected the true density and moisture of the rammed earth. Four samples were taken from each model at different density areas, for a total of 24 samples from both models. The samples were immediately transported to the laboratory for indoor testing to measure sample density, moisture content, elastic modulus, and shear strength. According to the Standard for Soil Test Methods (GB / T 50123-2019), the density and moisture content of the rammed earth sample were measured using the ring method and alcohol burning method, respectively. The ring had a mass of m = 43g and a volume of V = 50cm 3 ; the alcohol had a concentration of 95%.

[0125] After obtaining the test soil blocks from the non-destructive detection model, the samples were processed in the laboratory into triaxial test specimens, which were cylindrical with a diameter of D = 39.1mm and a height of H = 8.0mm. The confining pressures for the test were 100kPa, 200kPa, 300kPa, and 400kPa.

[0126] The specific steps of the indoor test are as follows:

[0127] 2.1 Soil sample preparation

[0128] The target size of the block sample was 18cm, and the actual sample size ranged from 15 to 25cm, with an average size of about 18cm.

[0129] 2.2 Physical and mechanical parameter testing

[0130] According to the Standard for Soil Test Methods (GB / T 50123-2019), the maximum deviatoric stress, Poisson's ratio, and pore water pressure of the soil sample under different confining pressures were obtained through alcohol burning, ring method, and triaxial compression test. The density of the soil was obtained through the ring method, and the moisture content was measured through the alcohol burning method. The parameter database established is shown in Table 2.

[0131] Table 2 Physical and mechanical parameters of non-destructive detection model samples

[0132]

[0133]

[0134] From the comparison test scheme, it can be seen that the actual moisture content is greater than the designed moisture content, and the moisture content range of the two models is significantly different. Overall, the density and moisture content of the lower samples are greater than those of the upper samples, and the density and moisture content of Model A have greater dispersion.

[0135] The main reasons for the actual average moisture content being greater than the designed moisture content are that the moisture of the dried loess is not fully evaporated, and the large soil blocks are still moist inside; and the test period was mostly rainy, and the moisture of the loess was inevitably infiltrated.

[0136] However, the model test is based on the Xi'an city wall, and the parameters of the rammed loess of the Xi'an city wall are not uniform and continuous. The measured moisture content is mainly in the range of 14% to 20%, which basically covers the moisture content range of the city wall, and the test results meet the requirements.

[0137] 2.2.1 UU triaxial test

[0138] Based on the data obtained from the UU triaxial test with the confining pressure as the variable, the ε1=16% is taken as the standard for the triaxial shear failure of the soil sample, the axial strain ε1 is taken as the horizontal axis, and the axial deviatoric stress (σ1-σ3) is taken as the vertical axis, and the (σ1-σ3)ε1 curve is plotted.

[0139] The trends of the curves are basically the same. In the initial compression stage, the strength of the soil sample is unstable, and the stress-strain curve is irregular or wavy, so the initial compression stage is removed (the strain is about 2%) when the curve is smooth and rising, and the obtained curve conforms to the first two stages of the curve shear three-stage.

[0140] In the first shear stage, the curve is approximately linear, and the deviatoric stress (σ1-σ3) rapidly rises; in the second stage, the slope of the curve decreases, and the deformation of the soil sample changes from mainly elastic deformation to mainly plastic deformation. The curve basically presents strain hardening, and the curves of the soil samples A1 and A2 at the confining pressure σ3=100 kPa and the soil samples A3 and B3 at the confining pressure σ3=400 kPa present strain softening.

[0141] It can be seen from the comparison of the stress-strain curves of the models A and B that, under the same confining pressure, the greater the density and the smaller the moisture content, the greater the deviatoric stress, and the moisture content has a greater impact on the deviatoric stress (see Figure 17 ).

[0142] In the initial shear stage of the sample, the stress-strain curve presents the characteristics of an approximately straight line due to the small shear strain, the derivative value of the fitting function at x=0 is the elastic modulus of the material based on the linear variation law, and the average of the elastic modulus E values of the stress-strain relationship curves under four different confining pressures can obtain the corresponding partial elastic modulus E of the model. According to the analysis of the above stress-strain curves, formula (1) has a good fitting effect on the stress-strain curve, and the fitting accuracy of each curve is above 99%.

[0143]

[0144] The derivative of formula (1) at x = 0 is obtained as follows:

[0145]

[0146] According to Table 3, the discreteness of the elastic modulus E of the soil sample is large, and the average elastic modulus is positively correlated with the density of the soil sample, and negatively correlated with the water content, and the water content is the controlling factor affecting the elastic modulus of the soil sample.

[0147] Table 3 Stress-strain curve fitting results and elastic modulus of each part of the model A and B

[0148]

[0149]

[0150] According to the indoor mechanical experiment, the physical and mechanical parameters (such as water content, density, strength, etc.) of the model A and B of the city wall-like test piece are determined, and combined with the stress-strain curve fitting results and elastic modulus of each part of the model A and B, a parameter database (see Table 4) is established, which is associated with the detection signal and the physical and mechanical parameters, and provides a data basis for subsequent parameter inversion.

[0151] Table 4 Parameter database

[0152]

[0153]

[0154] In the above table, A represents the model A; A1 represents the unit of the model; A11 represents the sample of the unit of the model; B represents the model B; B1 represents the unit of the model; B11 represents the sample of the unit of the model.

[0155] 2.2.2 Strength parameter determination

[0156] In order to obtain the shear strength parameters of the soil sample, the Mohr circle and its envelope of the soil sample are drawn (see Figure 18 ). The intercept and slope of the Mohr circle envelope are the cohesion C and the internal friction angle, respectively.

[0157] Table 5 Shear strength index of each part of the model A and B

[0158]

[0159] According to the relationship between the rammed earth water content and density and the cohesion and internal friction angle in Table 5, the cohesion increases significantly with the increase of water content; the internal friction angle decreases significantly with the increase of water content; the change of compactness has no obvious effect on the cohesion and internal friction angle. The elastic model is more obviously affected by the cohesion of the rammed earth, which further indicates that the water content has an important influence on the elastic model.

[0160] 2.3 Analysis of the relationship between the strength parameters and the physical parameters

[0161] There is a certain internal relationship between the shear strength parameters and the physical parameters of the rammed earth. The variation trend of the unit weight is basically the same as that of the internal friction angle, and the variation trend of the water content is basically opposite to that of the cohesion. The variation amplitude of the internal friction angle is smaller, and the variation amplitude of the cohesion is larger, which indicates that the shear strength of the rammed earth is more sensitive to the change of the water content (see Figure 19 ).

[0162] 3. Method for determining the physical and mechanical properties

[0163] On the basis of establishing the "probe signal-physical and mechanical parameter" correlation database, the embodiment further utilizes the quantitative relationship between the experimental data and the ground penetrating radar (GPR) signal characteristics to realize the nondestructive inversion of the physical and mechanical properties of the rammed earth structure.

[0164] The specific steps are as follows: based on the laboratory test results of the rammed earth, the shear strength parameters (cohesion C and internal friction angle) of the rammed earth material have a significant correlation with the water content. In order to establish the mapping relationship between the electromagnetic wave propagation characteristics of the ground penetrating radar (GPR) and the shear strength parameters of the rammed earth, the quantitative correlation between the water content and the GPR signal characteristic parameters is constructed through the dielectric constant inversion model (improved Topp equation).

[0165] The water content has a controlling effect on the shear strength of the rammed earth. The relationship between the soil layer dielectric constant r and the soil water content is the main way to calculate the soil water content using the ground penetrating radar, and the relative dielectric constant of the soil layer can be obtained from the propagation speed of the electromagnetic wave in the layer:

[0166]

[0167] In the formula, c is the propagation speed of the electromagnetic wave in the air; v is the propagation speed of the electromagnetic wave in the soil; x is the relative distance between the transmitting antenna and the receiving antenna; d is the depth of the reflection interface; t is the double-path time of the electromagnetic wave incidence and reflection.

[0168] Currently, there are four formulas for calculating soil moisture using dielectric constant: the Topp formula, the Roth formula, the Herkelrath formula, and the CRIM model. The Topp formula, based on the principles of time domain reflectometry (TDR), links electrical properties with soil moisture and is widely used. The Topp formula is expressed as follows:

[0169] ε r =3.03+9.30×θ+146.00×θ 2 -76.70×θ 3 (4)

[0170] The volumetric moisture content of soil is inverted based on the Topp formula, and the expression is as follows:

[0171] θ=-5.3×10 -2 +2.92×10 -2 ε r -5.5×10 -4 ε r 2 +4.3×10 -6 ε r 3 (5)

[0172] During GPR data processing, the raw data is preprocessed. Correlation analysis between the instantaneous characteristic parameters of the image data (based on instantaneous frequency, instantaneous phase, and instantaneous amplitude) obtained via Hilbert transform and the dielectric constant shows that the product of the instantaneous frequency and the reciprocal of the instantaneous amplitude (frequency-to-amplitude ratio) has the most significant correlation with the dielectric constant, with a correlation coefficient of 0.75. The frequency-to-amplitude ratio comprehensively reflects the propagation velocity and energy attenuation of electromagnetic waves in rammed earth, and its physical meaning conforms to the description of the moisture content-dielectric relationship based on the Maxwell-Garnett mixed medium theory.

[0173] Specifically, the instantaneous frequency and instantaneous amplitude eigenvalues ​​of the radar image after Hilbert transform were calculated, and the instantaneous parameter data were extracted with a sampling interval of 5 cm. To reduce the influence of random errors, the mean removal method was used to process the instantaneous parameters of different regions, and the dielectric constant was calculated based on this. Different models were selected for regression analysis of the two sets of data, and a cubic model function fitting the relationship between the frequency-amplitude ratio and the dielectric constant was obtained. The coefficient of determination R 2 The dielectric constant was calculated using the fitting formula, and the water content at each depth was inverted using the Topp water content empirical formula, as shown in Table 5 and Figure 20 As shown. Fitting model function expression

[0174] The formula is as follows:

[0175] ε r = -2.3533 + 32.7246x - 7.2462x 2 + 1.4627x 3 (6)

[0176] wherein ε r is the dielectric constant, and x is the frequency amplitude ratio.

[0177] Table 6 Comparison of the frequency amplitude ratio inversion of the water content of each part of the city wall model with the measured value (mass water content)

[0178] Sample No. Frequency Amplitude Ratio e r ]] Inversion of water content 1 Observed moisture content 0 A1 0.8725 20.4165 0.1583 0.1685 A2 1.0385 16.6255 0.2382 0.2078 A3 0.6572 15.7347 0.1436 0.1569 B1 0.8564 16.6787 0.1830 0.1930 B2 0.8735 14.5467 0.1832 0.1937 B3 0.8265 15.6734 0.1824 0.1940

[0179] In combination with Table 6 and Figure 20 It can be seen that the trend of the predicted value and the measured value is basically the same, the maximum error of the inversion value and the measured value is 3.04%, and the average error is 1.43%, indicating that the ground penetrating radar has certain accuracy in the prediction of water content. Between the frequency amplitude ratios of 0.8564 and 0.8725, the predicted value and the measured value tend to be stable, and the water content is about 0.19, indicating that the confidence of the prediction result is higher in this frequency amplitude ratio range.

[0180] The above shows and describes the basic principles and main features of the present application and the advantages of the present application, and it is obvious to those skilled in the art that the present application is not limited to the details of the above exemplary embodiments, and the present application can be implemented in other specific forms without departing from the spirit or essential characteristics of the present application; therefore, from any point of view, the embodiments should be regarded as exemplary and non-limiting, the scope of the present application is defined by the appended claims rather than the above description, therefore all changes falling within the meaning and scope of the equivalent elements of the claims are intended to be included in the present application, and any reference signs in the claims should not be regarded as limiting the claims involved.

[0181] Although embodiments of the present application have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the present application, the scope of the present application being defined by the appended claims and their equivalents.

Claims

1. A non-destructive detection method for rammed earth walls, characterized in that: include: Prepare rammed earth materials based on the soil quality and physical properties of the ancient city wall; Make rammed earth molds, tamp the rammed earth materials in layers in the molds to make city wall-like specimens; The geological radar is used to conduct non-destructive detection on the wall-like specimen, and the waveform image and grayscale image of the wall-like specimen are obtained. The waveform image and grayscale image are then analyzed to obtain the detection signal of the wall-like specimen. After non-destructive detection, samples of the wall-like specimens were taken, and indoor mechanical experiments were conducted to measure the physical and mechanical parameters of the samples, and a parameter database was established that correlated the detection signals with the physical and mechanical parameters. Conduct geological radar detection on the ancient city wall to obtain actual detection signals, match the actual detection signals with the parameter database, and obtain the physical and mechanical parameter information of the ancient city wall.

2. The non-destructive detection method for rammed earth walls according to claim 1, characterized in that: The specific process of preparing rammed earth materials is as follows: (1) Based on the physical properties of the ancient city wall materials, the local Malan loess in Xi'an was selected as the rammed earth material. The volume ratio of Malan loess when compacted to loose is about 0.8; (2) Pretreatment of Malan loess; (3) The pre-treated Malan loess was mixed according to its moisture content. According to the moisture content range of the rammed earth of the ancient city wall, the dry soil mass was determined by the step-by-step weighing method. 1% to 2% was added to the designed water consumption to compensate for water evaporation and infiltration, and the pre-mixed rammed earth material with a moisture content between 10% and 20% was obtained.

3. The non-destructive detection method for rammed earth walls according to claim 1, characterized in that: The rammed earth mold comprises a baffle (1) and a hoop bar (2), wherein the baffle (1) and the hoop bar (2) cooperate to form an open mold frame without a cover or a bottom, and the rammed earth material is continuously compacted as a whole in the mold frame without any physical partition, and by controlling the number of tamping times, the interior of the model is divided into a plurality of regional units according to the density, and a transition area with a density change is formed at the intersection of the plurality of regional units.

4. The non-destructive detection method for rammed earth walls according to claim 3, characterized in that: The plurality of area units include a first area unit, a second area unit and a third area unit which are sequentially divided along the length direction of the inner cavity of the open mold frame. There is no physical division between the area units and there are transition areas between the area units.

5. The non-destructive detection method for rammed earth walls according to claim 4, characterized in that: The first, second and third regional units were used to prepare dense, medium-dense and less-dense city wall specimens, respectively. Different tamping times were controlled during the preparation of the three types of specimens. The specific process of layered tamping of the three types of specimens was as follows: The tamping is carried out in three steps: the first tamping is to compact the backfill soil, with the spacing between each tamping hole being about 0.2m; the second tamping is done in the gap between the first tamping, and the remaining tamping is done in the gap between the first two tamping to make the backfill soil dense as a whole; Level the surface of the rammed earth with a milling machine, and repeat 1-3 times depending on the situation; When water falls, sprinkle the water evenly first and then let it fall into a large area. Use a sled to pick up the water as it falls to avoid local water accumulation. Among them, the number of tamping times for dense city wall specimens, medium-dense city wall specimens and less-dense city wall specimens during the layered tamping process were 25, 15 and 5 respectively.

6. The non-destructive detection method for rammed earth walls according to claim 4, characterized in that: A model A and a model B are respectively arranged in two open mold frames, wherein the model A and the model B each include a first area unit, a second area unit, and a third area unit; Model A is a defect-free model. No artificial defects are set inside the specimen. Only blocks are temporarily piled on the top to assist in static standing. The blocks are removed after one week of static standing. Model B has masonry on top of the specimen and artificial defects introduced inside the specimen, which is then tested after standing for a week; Among them, artificial defects include voids.

7. The non-destructive detection method for rammed earth walls according to claim 1, characterized in that: The parameter database is:

8. A rammed earth mold, characterized in that: The rammed earth mold is used to prepare the wall-like specimen in claim 1, and the rammed earth mold comprises: a baffle (1) and a hoop (2); A plurality of baffles (1) are used to enclose and form an open-type mold frame without a cover or a bottom, and a plurality of hoop strips (2) are arranged on the outside of the baffles (1) and are used to connect the baffles (1) and realize the detachable assembly of the open-type mold frame.

9. The rammed earth mold according to claim 8, characterized in that: The size range of the open mold frame is 3-5m×0.8-1m×0.8-1.2m.

Images