Winter soaking test pit test method for self-weight collapsible loess site

Abstract

The invention belongs to the technical field of soaking test pit tests, and provides a winter soaking test pit test method for a self-weight collapsible loess site, which avoids the problems of difficulty and potential safety hazards brought to the field soaking test pit test of loess collapsibility by severe weather conditions such as low temperature, wind and snow, freezing and the like in winter through physical thermal insulation equipment. The preset correction coefficient is used for correcting the self-weight collapsibility, the problem that due to physical heat preservation, the environment temperature and humidity in the test pit are different from the actual environment temperature and humidity, errors between test data and test data in the actual winter environment are large is solved, and meanwhile the water injection rate and the water injection duration are adjusted according to the test requirements. And the temperature in the physical thermal insulation equipment is adjusted, so that the influence of the water injection rate, time and the like on the test pit structure is reduced, and the actual test pit condition can be truly reflected.

Description

Technical Field

[0001] The invention belongs to the technical field of water immersion test pit tests, and in particular relates to a winter water immersion test pit test method for a deadweight collapsible loess site. Background Art

[0002] The loess region has special requirements for engineering construction due to its unique geological characteristics. Among them, self-weight collapsibility is one of the issues that need to be focused on in engineering construction in this region, which is directly related to the stability and safety of buildings. On-site test pit immersion tests are usually used to obtain loess collapsibility and determine the collapsibility level, which can provide key data support for engineering design and construction.

[0003] For severely cold regions, the harsh climatic conditions such as low temperature, snow and ice in winter bring great difficulties and safety hazards to the on-site immersion test pit test of loess collapsibility. The ice and snow in the immersion test pit bring technical difficulties to the settlement deformation monitoring. Physical insulation and anti-freezing measures can prevent the ice in the test pit. However, after taking physical insulation and anti-freezing measures, the temperature and humidity of the test pit environment are affected. Different from the temperature and humidity of the actual environment, the test data collected in this environment have large errors with the test data in the actual winter environment, which affects the accuracy of the test results. In addition, the water injection rate, time and water injection volume of the immersion test have a great influence on the test pit structure. The current test method cannot effectively adjust the water injection rate and time, resulting in errors in the collected test pit test data, which cannot truly reflect the actual test pit situation. Summary of the invention

[0004] In order to solve the above problems, the present invention proposes a winter immersion test pit test method for a loess site with self-weight collapsible soil. Through physical insulation equipment, the difficulties and potential safety hazards caused by adverse climatic conditions such as low temperature, wind, snow and freezing in winter to the on-site immersion test pit test of loess collapsible soil are avoided. On this basis, the self-weight collapsible amount is corrected using a preset correction coefficient, which avoids the problem that the physical insulation makes the environmental temperature and humidity in the test pit different from the actual environmental temperature and humidity, resulting in a large error between the test data and the test data in the actual winter environment. At the same time, the water injection rate and water injection duration are adjusted according to the test requirements and the temperature in the physical insulation equipment, which reduces the influence of the water injection rate and time on the test pit structure, and can truly reflect the actual test pit situation.

[0005] In order to achieve the above-mentioned object, the present invention provides a winter immersion test pit test method for a self-weight collapsible loess site, which adopts the following technical scheme:

[0006] A winter immersion test pit test method for a self-weight collapsible loess site, comprising:

[0007] Build physical insulation equipment on the excavated on-site test pit; drill holes and deploy monitoring equipment in the test pit;

[0008] Water injection; the water injection rate and duration are adjusted according to the test requirements and the temperature in the physical insulation equipment;

[0009] Acquire the detection data on the monitoring equipment, and determine the deadweight collapsibility based on the detection data; use a preset correction coefficient to correct the deadweight collapsibility to obtain a corrected deadweight collapsibility; wherein the correction coefficient is adjusted in real time based on the difference between the temperature and humidity after physical insulation and the actual ambient temperature and humidity;

[0010] The collapsibility grade is determined based on the corrected deadweight collapsibility.

[0011] Furthermore, the boreholes include seepage holes, settlement monitoring holes, moisture monitoring holes, water level monitoring holes and inclinometer monitoring holes.

[0012] Furthermore, 50 seepage holes with a hole diameter of 110mm-130mm were arranged in the test pit, of which 36 holes were 25m deep and 16 holes were 9m deep; gravel was filled into the seepage holes.

[0013] Furthermore, with the center of the test pit as the center, three shallow marking measuring lines with an angle of 120° are arranged radially from the inside to the outside along the radius direction, which are used to observe the total deadweight wetting deformation at different positions inside and outside the test pit; in the test pit, starting from the center of the test pit, the shallow markings are arranged at equal intervals of 2m; within the range of 1 times the diameter of the test pit from the edge of the test pit, 4 shallow markings with a spacing of 2m, 3 with a spacing of 3m and 2 with a spacing of 4m, and 1 shallow marking in the center of the test pit are arranged.

[0014] Furthermore, a total of 6 survey lines were arranged on the plane with deep marks to observe the stratified self-weight collapsibility and capture the stratified settlement of the lower limit depth of self-weight collapsible loess; in the depth direction, starting from 1.5m below the test pit, one group was arranged at intervals of 1.5m-2.0m, with a maximum depth of 25.5m; each group was set with 2 deep marks of the same depth, respectively arranged in the central area and outer edge area of ​​the test pit.

[0015] Furthermore, a leveling reference network was established at the immersion test site, including 3 elevation reference points and 2 working reference points. The elevation reference points were set 100m away from the edge of the test pit, and the working reference points were 30m away from the edge of the test pit.

[0016] Furthermore, 4 soil moisture measurement lines were symmetrically arranged in the test pit, with 4 moisture monitoring holes arranged at a distance of 3.5m on each measurement line; 2 soil moisture measurement lines were symmetrically arranged outside the test pit, with 5 moisture monitoring holes arranged at a distance of 5m on each measurement line;

[0017] In the test pit, each group of test holes starts from 1.5m below the bottom of the test pit, is arranged at equal intervals of 3m, and has a maximum depth of 28.5m. Outside the test pit, the vertical direction ends at the edge of the test pit, starts 3m above the line at a 45° angle to the vertical direction, and is arranged at equal vertical intervals of 3m, with a maximum depth greater than the depth of collapsible loess.

[0018] Furthermore, when the water seepage rate is greater than the water injection rate, the water injection frequency or the water injection rate is increased; when the water seepage rate is less than the water injection rate, the water injection frequency or the water injection rate is increased; during the immersion process, the water head height in the test pit is maintained within a preset height range until the soil layer deformation stabilizes and the water injection is stopped.

[0019] Furthermore, as the temperature inside the physical insulation device increases, the water injection frequency or water injection rate increases, and as the temperature inside the physical insulation device decreases; as the temperature inside the physical insulation device increases, the water injection duration increases, and as the temperature inside the physical insulation device decreases, the water injection duration decreases.

[0020] Furthermore, the correction factor is adjusted as follows:

[0021] C = C0 + α (T1-T2) + β (H1-H2);

[0022] Among them, C is the adjusted correction coefficient; C0 is the initial correction coefficient; T1 is the temperature in the test pit after physical insulation; T2 is the ambient temperature of the test scene outside the physical insulation equipment; H1 is the humidity in the test pit after physical insulation; H2 is the ambient humidity of the test scene outside the physical insulation equipment; α and β are adjustment coefficients.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] The present invention avoids the difficulties and potential safety hazards caused by adverse climatic conditions such as low temperature, wind, snow and freezing in winter to the on-site water immersion test pit test of loess collapsibility, by building physical insulation equipment on the excavated on-site test pit. On this basis, the self-weight collapsibility is corrected by using a preset correction coefficient to obtain the corrected self-weight collapsibility, wherein the correction coefficient is adjusted in real time according to the difference between the temperature and humidity after physical insulation and the actual environmental temperature and humidity, thereby avoiding the problem that the environmental temperature and humidity in the test pit is different from the actual environmental temperature and humidity due to physical insulation, resulting in a large error between the test data and the test data in the actual winter environment, thereby ensuring the test accuracy; at the same time, the water injection rate and the water injection duration are adjusted according to the test requirements and the temperature in the physical insulation equipment, thereby reducing the influence of the water injection rate and time on the test pit structure, being able to truly reflect the actual test pit situation, and further improving the test accuracy.

[0025] In the present invention, the seepage holes, sedimentation monitoring holes, moisture monitoring holes, water level monitoring holes and inclinometer monitoring holes are reasonably designed, which significantly changes the moisture diffusion path, presenting a diffusion path dominated by radial seepage of the holes and upward migration of bottom water-rich water, and can obtain more comprehensive and accurate monitoring data. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The drawings in the specification that constitute a part of this embodiment are used to provide a further understanding of this embodiment. The schematic embodiments of this embodiment and their descriptions are used to explain this embodiment and do not constitute improper limitations on this embodiment.

[0027] Figure 1 This is a plan view of various hole positions in Example 1 of the present invention;

[0028] Figure 2 This is a longitudinal cross-sectional view of the buried moisture meter of Example 1 of the present invention. DETAILED DESCRIPTION

[0029] The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

[0030] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present application belongs.

[0031] Embodiment 1:

[0032] like Figure 1 As shown, this embodiment provides a winter flooding test pit test method for a loess site with self-weight collapsible soil. By building physical insulation equipment on the excavated on-site test pit, the difficulties and safety hazards caused by severe weather conditions such as low temperature, wind, snow and freezing in winter to the on-site flooding test pit test of loess collapsible soil are avoided. On this basis, the self-weight collapsible soil is corrected by using a preset correction coefficient to obtain a corrected self-weight collapsible soil. The correction coefficient is adjusted in real time according to the difference between the temperature and humidity after physical insulation and the actual environmental temperature and humidity, thereby avoiding the problem that the environmental temperature and humidity in the test pit are different from the actual environmental temperature and humidity due to physical insulation, resulting in a large error between the test data and the test data in the actual winter environment, thereby ensuring the test accuracy. At the same time, the water injection rate during water injection is adjusted according to the test purpose and the characteristics of the loess, and the water injection duration is determined according to the test requirements and the collapsible soil layer, thereby reducing the influence of the water injection rate and time on the test pit structure, and can truly reflect the actual test pit situation, further improving the test accuracy. The optional implementation steps of the method of this embodiment are:

[0033] S1. Test preparation:

[0034] Optionally, prepare an electronic level and a barcode ruler for leveling observations for loess subsidence settlement observations. Prepare a soil moisture meter and a meteorological monitoring host to monitor the changes in soil moisture over time in each soil layer during the immersion test. Prepare a sliding inclinometer to monitor the horizontal displacement of the test pit during the immersion test. Prepare steel frames, thermal insulation cotton, rainproof cloth, and heating equipment to physically insulate the test pit to prevent the water in the test immersion pool from freezing; it is understandable that a greenhouse structure is formed by setting a steel frame on the test pit and laying thermal insulation cotton and rainproof cloth on the steel frame, and electric heating, water heating and other heating equipment are installed in the greenhouse. Prepare colored strips of cloth and plastic film for anti-seepage treatment of the side walls of the test pit and the reservoir.

[0035] S2. Excavation of on-site test pit:

[0036] In order to simulate the actual collapse of loess under water conditions, the plane of the on-site test pit is circular; optionally, according to the geological survey data, the diameter of the test pit is determined to be 25m, the depth is 0.5m, and the bottom of the pit is paved with 10-15cm thick sand and gravel.

[0037] S3. Drilling rig drilling and monitoring equipment layout:

[0038] Among them, the types of holes include seepage holes, settlement monitoring holes, moisture monitoring holes, water level monitoring holes and inclinometer monitoring holes, etc. The optional operating machinery is the survey drill. The surveying technicians will carry out the location layout and provide sufficient drilling information to the on-site drilling rig staff, mainly including the number, depth and function of each borehole, and provide standardized drilling construction record forms to ensure that the daily workload can be counted and the conditions of each borehole can be checked.

[0039] S3.1. Seepage hole formation:

[0040] By setting up seepage holes, water infiltration can be accelerated, which can shorten the construction period and reduce construction costs to a certain extent. Optionally, 50 seepage holes are arranged in the test pit randomly or according to the preset position, with a hole size of 110mm-130mm, of which 36 holes are 25m deep and 16 are 9m deep. In view of the small area of ​​the on-site test pit and complex conditions such as earthwork, the surveying technician's layout mark is very easy to be moved or even destroyed. Therefore, if the construction progress allows, ensure the position confirmation before the drilling rig opens the hole.

[0041] The depth of the seepage holes has penetrated the collapsible loess layer in the area. After the holes are formed, they are promptly filled with gravel with a particle size of 5mm-10mm and a mud content of less than 1%.

[0042] S3.2, Settlement monitoring hole:

[0043] S3.2.1. Arrangement of shallow points: Surface settlement observation points are arranged at different locations inside and outside the test pit to observe the total deadweight collapsible deformation at different locations inside and outside the test pit.

[0044] Optionally, on the plane, with the center of the test pit as the center, three shallow marking lines A, B and C are arranged radially from the inside to the outside along the radius direction, with an angle of 120° between them. In the test pit, starting from the center of the test pit, the shallow markings are arranged at an equal interval of 2m; within the range of 1 times the diameter of the test pit from the edge of the test pit, 4 shallow markings are arranged with a spacing of 2m, 3 spacings of 3m and 2 spacings of 4m, and 1 shallow marking in the center of the test pit, a total of 46 shallow markings, the plane layout of the shallow markings is as follows Figure 1 The measuring points are numbered A1-A15, B1-B15 and C1-C15.

[0045] Optional, shallow marking is mechanical marking, using galvanized steel pipe with a diameter of 25mm, the pipe length is set according to the natural ground height difference, and a piece of The circular steel plate with a thickness of 15mm and perpendicular to the steel pipe is buried at a depth of 0.5m. The shallow pit of the shallow base is excavated manually with a diameter of 50cm. After the loose soil at the bottom of the pit is cleaned and leveled, the base steel plate is placed on the original soil layer, and then backfilled with plain soil and compacted lightly.

[0046] S3.2.2. Arrangement of deep points: set up stratified settlement observation points in the test pit to observe the self-weight collapsibility of the stratified layers and capture the lower limit depth of the self-weight collapsible loess.

[0047] Optionally, a total of 6 measuring lines are arranged on the plane for deep marking points; in the depth direction, starting from 1.5m below the test pit, one group is arranged at intervals of 1.5m-2.0m, with a maximum depth of 25.5m. Each group is set with 2 deep marking points of the same depth, which are arranged in the center area and the outer edge area of ​​the test pit respectively to eliminate the difference between the inside and outside of the test pit. The depth of the measuring hole is shown in Table 1.

[0048] Table 1 Layered observation hole depth table

[0049]

[0050] Optionally, the deep marking device consists of an inner tube and an outer tube. The inner tube is used to measure the shrinkage deformation of each layer of soil. A galvanized steel pipe with a diameter of 25 mm is threadedly connected to a predetermined length. The base of the inner tube is a 3 mm thick tube vertically welded to the steel pipe. The inner tube length of each deep mark is 2.5m above the corresponding drilling depth, that is, the inner tube is 2.0m above the ground outside the test pit. The outer tube of the deep mark is a PVC tube (whose weight can be ignored) with a diameter of 50mm. Its function is to prevent the inner tube from contacting the soil when moving. When the soil layer at the bottom plate settles, it will be directly displayed by the sinking of the inner tube. A stainless steel ruler is fixed on the top of each deep and shallow mark steel pipe, and the minimum scale of the steel ruler is 1mm.

[0051] The deep mark placement holes are drilled by drilling rigs, and the specific operations are the same as above. According to the designed burial depth of each deep mark, the spiral drill is used to drill the holes dry, and the diameter of the hole is 127mm. When the hole is 0.3m above the designed depth, the loess soil sampler is used to statically press the soil. After the loose soil at the bottom of the hole is cleaned, the inner tube of the deep mark is lowered. After the base contacts the bottom of the hole, it is lightly pressed to make it in close contact with the soil at the bottom of the hole, and then the PVC outer tube is lowered. The PVC tube is exposed 1.0m above the ground of the test pit. After the inner and outer tubes are lowered, the verticality of the inner and outer tubes is adjusted with a plumb bob. After the adjustment is completed, the gap between the PVC outer tube and the drilled hole is filled with medium-coarse sand until the hole mouth. During the immersion process, the deep mark also serves as a seepage hole.

[0052] S3.2.3. According to the relevant building deformation measurement specifications, the layout requirements of the secondary deformation measurement elevation reference points, a leveling measurement reference network is established at the immersion test site. The reference network includes three elevation reference points BM1, BM2 and BM3, and two working reference points GJ1 and GJ2. The elevation reference points are set 100m away from the edge of the test pit, and the working reference points are 30m away from the edge of the test pit. The elevation reference points and working reference points are buried by manually excavating a foundation pit with a depth of 1.0m and pouring concrete.

[0053] The local elevation of benchmark point BM1 is set to 100m, and other elevations and working benchmark points are measured together with BM1 according to the second-class leveling specifications.

[0054] Two working reference points are designed in the observation reference network to avoid that all digital barcodes are in the same direction. If 76 settlement monitoring poles are observed from one direction, there will inevitably be problems such as obstruction of the survey line and large difference in sight distance. Therefore, it is necessary to set up 2 or 3 working reference points.

[0055] S3.3, moisture monitoring hole:

[0056] like Figure 2 As shown, 4 soil moisture measurement lines are arranged symmetrically in the test pit, and 4 test holes are arranged at a distance of 3.5m on each measurement line; 2 soil moisture measurement lines are arranged symmetrically outside the test pit, and 5 test holes are arranged at a distance of 5m on each measurement line. It is used to observe the vertical infiltration process of water, and the drilling method adopts drilling, and the specific operation is the same as above.

[0057] In the test pit, each group of test holes is arranged at an equal interval of 3m starting from 1.5m below the bottom of the test pit, with a maximum depth of 28.5m. Outside the test pit, the vertical arrangement is: starting from the edge of the test pit as the endpoint, 3m above the 45° angle line with the vertical direction, and arranged at an equal vertical interval of 3m, with a maximum depth greater than the depth of collapsible loess.

[0058] A total of 26 test holes were arranged this time, with a total of 224. The moisture meter was buried in the pre-drilling method. When the design depth was reached, the moisture meter and air pressure sensor were buried, and then the soil was backfilled and compacted, and the hole was sealed with concrete.

[0059] After the moisture meters are buried, the initial readings of each moisture meter are measured for 5 consecutive days to monitor whether they are working properly. During the immersion process, the buried moisture meters are observed and recorded every 8 hours, and the data are sorted and summarized to draw a curve of the change of observation data over time.

[0060] S3.4, water level monitoring hole

[0061] Optionally, in order to timely and accurately grasp the groundwater level during the test immersion process, three water level observation holes are set near the test piles, with the hole depths set to 15m, 8m and 21m respectively, and the drilling method is drilling. After the formal water injection, the 9-meter method is used for observation once a day.

[0062] S3.5, Inclinometer monitoring hole:

[0063] Optionally, in order to study the horizontal displacement of the soil outside the test pit during the immersion test as the water moves, three groups of horizontal displacement monitoring holes are arranged at intervals of 5 meters from 1 meter outside the edge of the test pit. The hole depth is 27 meters and the hole drilling method is to use a drilling rig. The horizontal displacement deformation monitoring is measured by an inclinometer. During the immersion period, the horizontal displacement is observed once a day.

[0064] S4. Water immersion test work:

[0065] Before releasing water, the settlement observation rod, soil moisture sensor and inclinometer hole should be observed three times, and the average value should be taken as the initial value of the test pit test. The determination of the initial value provides important reference value for the subsequent settlement analysis, soil moisture change analysis and test pit horizontal displacement analysis.

[0066] S4.1, water injection rate control:

[0067] The injection rate should be adjusted according to the test purpose and the characteristics of loess to ensure that water can penetrate evenly into the soil layer.

[0068] In arid areas, water is drawn by water trucks or injected through motor wells. The capacity of the water truck is fixed, and its injection rate can be determined by the number of times the water truck transports water every day; the injection rate of motor wells is determined by a metering water meter; during the injection process, the water level in the pit is monitored in real time to ensure that the head height is maintained within the set range of 25cm-35cm. When the water level drops, that is, the water seepage rate is greater than the injection rate, the injection rate of the test pit can be increased by increasing the frequency of water trucks transporting water and extending the injection time of the motor well. On the contrary, when the water level in the test pit rises, the water immersion rate of the test pit is less than the injection rate, and the water level in the pit is stabilized by reducing the injection rate.

[0069] When the temperature in the physical insulation equipment is high, the degree of thawing of frozen soil in the stratum is better. Based on this, in order to reduce the injection time, as the temperature in the physical insulation equipment increases, the injection frequency or injection rate increases, which improves the test efficiency while ensuring the seepage effect; when the temperature in the physical insulation equipment is low, the degree of thawing of frozen soil in the stratum is worse, and rapid water injection will affect the seepage effect. Therefore, as the temperature in the physical insulation equipment decreases, the injection frequency or injection rate decreases to avoid the problem of reduced test accuracy caused by the influence on the seepage effect. The relationship between the injection frequency or injection rate and the temperature change can be set to a linear change relationship, etc.

[0070] S4.2. Water injection duration:

[0071] The duration of water injection should be determined according to the test requirements and the collapsibility of the loess layer. During the immersion process, the water head height in the test pit should be maintained at about 30 cm. Water injection can be stopped until the deformation of the soil layer stabilizes. The deformation stability standard is that the average deformation in the last 5 days is less than 1 mm / d, which means that collapsibility has been fully induced without destroying the soil structure.

[0072] Similarly, when the temperature in the physical insulation equipment is high, the degree of thawing of the frozen soil in the stratum is better, and the water seepage effect is good. Based on this, in order to reduce the injection time, as the temperature in the physical insulation equipment increases, the injection time increases to ensure the water seepage effect and test accuracy; and when the temperature in the physical insulation equipment is low, the degree of thawing of the frozen soil in the stratum is worse, and the water seepage effect is poor. Therefore, as the temperature in the physical insulation equipment decreases, the injection time decreases to avoid the problem of excessive water injection caused by poor water seepage effect. The relationship between the injection time and temperature change can be set to a linear change relationship, etc.

[0073] S4.3. Data Recording:

[0074] All parameter changes during the entire water injection process should be recorded in detail, including injection volume, time, water level changes, etc., to facilitate subsequent analysis.

[0075] S5. Data collection and analysis:

[0076] S.5.1. Settlement observation:

[0077] Settlement observation is to obtain the settlement of each observation hole by regularly observing the digital barcode ruler on the upper part of the settlement monitoring rod. The focus of settlement observation is the relative amount of settlement of the monitoring rod during the test. Therefore, it is very important to determine the initial value of each monitoring rod before officially carrying out the test, to ensure that the observed value of the monitoring rod remains stable for nearly 3 days, and to start water injection after taking this as the initial value. In this embodiment, optionally, the settlement observation cycle is set to twice a day. In order to avoid the influence of atmospheric refraction on leveling observation, the effective observation time period is 8:30-10:30 in the morning and 3:00-5:00 in the afternoon. In addition, since the working reference point is relatively close to the immersion test pit, it may be affected by the collapsibility of loess. Therefore, according to the on-site work arrangement, the working reference point should be re-measured and checked at least once a week.

[0078] Daily observation data can be tabulated on the same day to timely discover and solve problems. Weekly observation reports are prepared to analyze the trend of settlement by drawing settlement and time curves; settlement rates in different time periods are calculated to evaluate the stability of loess structure.

[0079] 2.5.2. Water infiltration monitoring:

[0080] Optionally, after the moisture meter is buried, measure the initial reading of each moisture meter for 5 consecutive days to monitor whether it is working properly. During the immersion process, observe and record the buried moisture meters every 8 hours, organize and summarize the data, and draw a curve of the change of observation data over time.

[0081] Before and after water injection, a 25.0m deep borehole is arranged inside and outside the test pit. A soil sample is taken every 1 meter to measure the moisture content and saturation of each layer of soil to understand the wetting range and water saturation status of the foundation soil.

[0082] 2.5.3. Horizontal displacement monitoring:

[0083] The horizontal displacement of the foundation pit is monitored by an inclinometer. Optionally, the deformation of the inclinometer hole can be observed by a numerical vertical movable inclinometer probe, a control cable, a pulley device and a readout instrument.

[0084] Optionally, observations are made once a day, during which the probe is moved from the bottom of the inclinometer casing to the top, and is temporarily stopped at a set interval (1m) to measure the inclination. The inclination of the probe is measured by two force-balanced servo accelerometers, one of which measures the inclination of the longitudinal position of the inclinometer casing groove and the other measures the inclination perpendicular to the plane of the measuring wheel. The inclination can be converted into lateral displacement. By comparing the current and initial observation data, the change in lateral offset can be determined, thereby obtaining the movement displacement of the formation.

[0085] S6. Evaluation of loess collapsibility:

[0086] According to the results of the on-site pit immersion test, combined with the regional correction coefficient, the collapsibility of loess can be accurately evaluated. According to the analysis of the indoor immersion compression test data and the on-site test data, there may be differences between the measured and calculated values ​​of the self-weight collapsibility, and this difference may be related to the region where the site is located. The correction coefficient between the measured and calculated values ​​of the self-weight collapsibility of the site where the on-site pit immersion test was carried out was 1.2. The maximum measured self-weight collapsibility was 133.43 mm, and the calculated value obtained by conversion with the correction coefficient was 111.19 mm. According to the collapsibility classification of collapsible loess foundations in the building standards for collapsible loess areas, it was judged that the area belongs to Grade II.

[0087] Optionally, when determining the correction coefficient, in addition to considering the area where the site is located, it is also necessary to consider the difference between the temperature and humidity after physical insulation and the actual ambient temperature and humidity, because the higher the temperature and humidity, the worse the hardness of the frozen soil in the actual bottom layer, and the actual deadweight shrinkage is greater than the actual value. Optionally, the correction coefficient can be adjusted as follows:

[0088] C=C0+α(T1-T2)+β(H1-H2)

[0089] Among them, C is the adjusted correction coefficient; C0 is the initial correction coefficient, which can be selected as 1.2; T1 is the temperature in the test pit after physical insulation; T2 is the ambient temperature of the test scene outside the physical insulation equipment; H1 is the humidity in the test pit after physical insulation; H2 is the ambient humidity of the test scene outside the physical insulation equipment; α and β are adjustment coefficients. Since temperature has a greater impact on the test than humidity, α is greater than β. Specifically, it can be determined and adjusted based on historical data.

[0090] The above description is only a preferred embodiment of the present embodiment and is not intended to limit the present embodiment. For those skilled in the art, the present embodiment may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present embodiment shall be included in the protection scope of the present embodiment.

Claims

1. A winter immersion test pit test method for a self-weight collapsible loess site, characterized in that: include: Set up physical insulation equipment on the excavated on-site test pit; and drilling and deployment of monitoring equipment in the test pit; Water injection; the water injection rate and duration are adjusted according to the test requirements and the temperature in the physical insulation equipment; Acquire the detection data on the monitoring equipment, and determine the deadweight collapsibility based on the detection data; use a preset correction coefficient to correct the deadweight collapsibility to obtain a corrected deadweight collapsibility; wherein the correction coefficient is adjusted in real time based on the difference between the temperature and humidity after physical insulation and the actual ambient temperature and humidity; The collapsibility grade is determined based on the corrected deadweight collapsibility.

2. A winter immersion test pit test method for a self-weight collapsible loess site as claimed in claim 1, characterized in that: The boreholes include seepage holes, settlement monitoring holes, moisture monitoring holes, water level monitoring holes and inclinometer monitoring holes.

3. A winter immersion test pit test method for a self-weight collapsible loess site as claimed in claim 2, characterized in that: Arrange 50 seepage holes with a hole diameter of 110mm-130mm in the test pit, of which 36 holes are 25m deep and 16 holes are 9m deep; fill the seepage holes with gravel.

4. A winter immersion test pit test method for a self-weight collapsible loess site as claimed in claim 2, characterized in that: With the center of the test pit as the center of the circle, three shallow marking measuring lines with an angle of 120° are arranged radially from the inside to the outside along the radius direction, which are used to observe the total deadweight wetting deformation at different positions inside and outside the test pit; in the test pit, starting from the center of the test pit, the shallow marking points are arranged at equal intervals of 2m; within the range of 1 times the diameter of the test pit from the edge of the test pit, 4 shallow marking points with a spacing of 2m, 3 with a spacing of 3m and 2 with a spacing of 4m, and 1 shallow marking point in the center of the test pit are arranged.

5. A winter immersion test pit test method for a self-weight collapsible loess site as claimed in claim 2, characterized in that: A total of 6 survey lines are arranged on the plane with deep marks, which are used to observe the stratified self-weight collapsibility and capture the stratified settlement of the lower limit depth of self-weight collapsible loess; in the depth direction, starting from 1.5m below the test pit, one group is arranged at intervals of 1.5m-2.0m, with a maximum depth of 25.5m; each group has 2 deep marks of the same depth, which are arranged in the central area and outer edge area of ​​the test pit respectively.

6. A winter immersion test pit test method for a self-weight collapsible loess site as claimed in claim 2, characterized in that: A leveling reference network is established at the immersion test site, including 3 elevation reference points and 2 working reference points. The elevation reference points are set 100m away from the edge of the test pit, and the working reference points are 30m away from the edge of the test pit.

7. A winter immersion test pit test method for a self-weight collapsible loess site as claimed in claim 2, characterized in that: Four soil moisture measurement lines are arranged symmetrically in the test pit, with four moisture monitoring holes arranged at a distance of 3.5m on each measurement line; two soil moisture measurement lines are arranged symmetrically outside the test pit, with five moisture monitoring holes arranged at a distance of 5m on each measurement line; In the test pit, each group of test holes starts from 1.5m below the bottom of the test pit, is arranged at equal intervals of 3m, and has a maximum depth of 28.5m. Outside the test pit, the vertical direction ends at the edge of the test pit, starts 3m above the line at a 45° angle to the vertical direction, and is arranged at equal vertical intervals of 3m, with a maximum depth greater than the depth of collapsible loess.

8. A winter immersion test pit test method for a self-weight collapsible loess site as claimed in claim 1, characterized in that: When the water seepage rate is greater than the water injection rate, increase the water injection frequency or injection rate; when the water seepage rate is less than the water injection rate, increase the water injection frequency or injection rate; during the immersion process, the water head height in the test pit is maintained within the preset height range until the soil deformation stabilizes and the water injection is stopped.

9. A winter immersion test pit test method for a self-weight collapsible loess site as claimed in claim 1, characterized in that: As the temperature inside the physical insulation equipment increases, the water injection frequency or injection rate increases, and as the temperature inside the physical insulation equipment decreases; as the temperature inside the physical insulation equipment increases, the water injection duration increases, and as the temperature inside the physical insulation equipment decreases, the water injection duration decreases.

10. A winter immersion test pit test method for a self-weight collapsible loess site as claimed in claim 1, characterized in that: The correction factor is adjusted as follows: C = C0 + α (T1-T2) + β (H1-H2); Among them, C is the adjusted correction coefficient; C0 is the initial correction coefficient; T1 is the temperature in the test pit after physical insulation; T2 is the ambient temperature of the test scene outside the physical insulation equipment; H1 is the humidity in the test pit after physical insulation; H2 is the ambient humidity of the test scene outside the physical insulation equipment; α and β are adjustment coefficients.

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