In-situ monitoring method for loess fill foundation soil consolidation compression process

Abstract

The invention discloses an in-situ monitoring method for the soil consolidation and compression process of a loess fill foundation. The in-situ monitoring method comprises the following steps: 1, calibrating a TDR (Time Domain Reflectometer) probe; 2, excavating an embedding pit, a wire groove and a wire conduit embedding groove; 3, a soil pressure meter and a TDR probe are installed, and soil is taken; 4, arranging the cables; 5, backfilling the burying pit, the wiring trough and the wiring tube burying groove; 6, measuring data of the installed soil pressure gauges and the TDR probes, and installing the soil pressure gauges and the TDR probes on the upper layer in the newly backfilled soil layer; seventhly, the sixth step is repeated for multiple times till the designed elevation is achieved through backfilling; 8, data are collected and recorded at fixed time intervals, the water content and the dry density of each layer of filling soil of the filling body are calculated, and then the compression coefficient, the compression modulus and the settling volume of the layer of filling soil are calculated. According to the method, the process that the soil volume is reduced and the density is increased due to the fact that the arrangement compactness degree between soil particles is increased and the porosity is reduced when the filled foundation soil is subjected to the external load effect is reflected from the angle of soil mechanics.

Description

Technical Field

[0001] The invention belongs to the technical field of geotechnical engineering monitoring and detection, and in particular relates to an in-situ monitoring method for the consolidation and compression process of loess fill foundation soil. Background Art

[0002] In recent years, in order to increase construction land, cities in the loess hilly and gully areas have mostly used low hills and gentle slopes around the city to create land by "cutting hills and filling ditches", forming loess fill foundations with loess as filler and layered compaction. The foundation soil will undergo consolidation compression deformation under the pressure of its own weight. The current research on the consolidation compression characteristics of loess fill foundation soil at various stages is mainly carried out through indoor consolidation compression tests or on-site settlement measurement. The above methods have the following shortcomings: (1) Indoor consolidation compression test: After sampling on-site, it is transported to indoor sample preparation. This method will cause great disturbance to the soil body. The sample size is small and is separated from the original geological environment and stress state. It cannot fully and truly reflect the consolidation compression of the foundation soil; (2) On-site settlement measurement: By installing monitoring devices inside the foundation soil, observing surface settlement or internal settlement, and analyzing the settlement change trend of the foundation soil as a whole or a certain layer of soil, it cannot directly reflect the consolidation compression of the in-situ foundation soil. In addition, for loess fill foundation, creep deformation will occur under the action of self-weight load in the later stage of construction, and humidification deformation will occur when it encounters water. When the foundation settles and deforms, the existing methods cannot distinguish the causes of deformation of the foundation soil, resulting in the inability to provide targeted engineering response measures. For this reason, an in-situ monitoring method for the consolidation and compression process of loess fill foundation soil is urgently needed in engineering to accurately evaluate the consolidation state of loess fill foundation soil. Summary of the invention

[0003] The technical problem to be solved by the present invention is to provide an in-situ monitoring method for the consolidation and compression process of loess fill foundation soil in view of the deficiencies in the above-mentioned prior art, while monitoring the changes in moisture content and dry density of the fill foundation soil. From the perspective of soil mechanics, it reflects the process in which the fill foundation soil is subjected to external loads, the arrangement density of soil particles increases, the porosity decreases, the soil volume decreases, and the density increases, so as to facilitate its promotion and use.

[0004] In order to solve the above technical problems, the technical solution adopted by the present invention is: an in-situ monitoring method for the consolidation and compression process of loess fill foundation soil, characterized in that the method comprises the following steps:

[0005] Step 1: Calibrate the TDR probe: When the backfill thickness is set and does not exceed the minimum burial elevation, select an area in the backfill site and level it. Use the one-step method to test the TDR probe to obtain the apparent dielectric constant K. a and electrical conductivity EC bThen, the moisture content and dry density of the experimental soil are obtained through indoor tests, a scatter plot is drawn, the coefficient is calculated, and the apparent dielectric constant K is obtained. a and electrical conductivity EC b Relationship with the moisture content and dry density of the experimental soil;

[0006] Step 2: Excavate the buried pit, wire trough and buried groove for wire pipe: excavate the buried pit, wire trough and buried groove for wire pipe on the existing ground filled with loess, and mark them. The buried pit is in the shape of an inverted trapezoid with a large top and a small bottom. The angle between the pit wall and the horizontal plane is less than 45°. The side length of the pit bottom should be no less than 3 times the diameter of the earth pressure gauge. The pit bottom is leveled to the buried elevation and forms a horizontal plane. Excavate the wire trough on one side of the buried pit. The length of the wire trough should be greater than twice the side length of the top of the buried pit, and the depth should be half the depth of the buried pit. Excavate the buried groove for wire pipe at the end of the wire trough. The pit bottom depth of the buried groove for wire pipe is lower than the depth of the wire trough, and the pit bottom radius is greater than the radius of the wire pipe.

[0007] Step 3: Install the earth pressure gauge, TDR probe and take soil: Place the earth pressure gauge at the center of the bottom of the burial pit, take soil from the vertical plane and take protective measures for the soil sample, take soil from the vertical plane on the side of the burial pit close to the wire trough and horizontally install the TDR probe, align the center height of the TDR probe with the top of the earth pressure gauge, tap the probe gently with a wooden hammer until the probe is completely inserted into the soil, then lay the coaxial cable and the earth pressure gauge data cable in an "S" shape at the bottom of the wire trough and lead it to the wire pipe burial trough, and send the soil sample to the laboratory;

[0008] Step 4: Arrange the cables: introduce the coaxial cable and the earth pressure gauge data cable into the conduit, place the conduit horizontally on the existing ground, pass the coaxial cable and the earth pressure gauge data cable into the conduit from the side with the notch and out from the other side, then stand the conduit upright and place it in the conduit buried groove, pass the coaxial cable and the earth pressure gauge data cable into the conduit from the bottom notch and out from the top of the conduit; then mark the cables on the top side of the conduit, store them in a waterproof bag and hang them on the top of the conduit;

[0009] Step 5: Backfill the buried pit, wire trough and wire pipe buried trough: The buried pit is manually backfilled and compacted in layers according to the original moisture content and dry density. When the layered compaction method is used for construction, in order to prevent the impact load from damaging the installed earth pressure gauge and TDR probe, rolling construction can only be carried out when the backfill thickness of the upper part of the earth pressure gauge exceeds 1.2m. After the buried pit is backfilled to the current ground, the wire trough and wire pipe buried trough are backfilled to the current ground with the original soil;

[0010] Step 6. Measure the data of the installed earth pressure gauge and TDR probe and install the upper earth pressure gauge and TDR probe in the newly backfilled layer of backfill: When the existing ground is backfilled to a height of 0.5m higher than the buried elevation of the next layer, use the TDR tester to read and record the data of the installed TDR probe, and use the earth pressure gauge reader to read and record the data of the installed earth pressure gauge;

[0011] Repeat steps 1 and 2, cut off the existing wire pipe to the bottom of the newly excavated wire trough, and fill the wire pipe to the upper part of the pipe with fine sand or bentonite, install the wire pipe interface on the top of the wire pipe, insert the newly buried earth pressure gauge, earth pressure gauge data line and coaxial cable of the TDR probe together with the installed earth pressure gauge, earth pressure gauge data line and coaxial cable of the TDR probe from the notched end of a new wire pipe, and then insert the new wire pipe into the wire pipe interface, after marking the earth pressure gauge data line and coaxial cable on the top of the new wire pipe, store them in a waterproof bag and hang them on the top of the new wire pipe, repeat step 5;

[0012] Step 7: Repeat step 6 several times until backfilling reaches the designed elevation;

[0013] Step 8: After filling in the design elevation, collect and record data at fixed intervals, and convert the measured apparent dielectric constant K a and electrical conductivity EC b Substitute the calibrated relationship to obtain the moisture content and dry density of each layer of fill in the compacted body. Then use the moisture content and dry density of each layer of fill in the compacted body to calculate the compression coefficient, compression modulus and settlement of the fill layer. The process is as follows:

[0014] Step 801: Assume that the dry density of the jth layer of soil measured from the bottom upwards for the i-th time is ρ di,j , the earth pressure data is P i,j , the laboratory can obtain the specific gravity data ds of the jth layer of soil measured for the i-th time through indoor geotechnical tests i,j , where i is the number of measurements and j is the number of fill layers from bottom to top;

[0015] Step 802: According to the formula The porosity ratio of the j-th layer of soil measured for the i-th time is e i,j The overburden pressure of each fill layer is

[0016] Step 803: Since the high fill sites in the loess region are all valley terrains, the sites can be considered to have lateral constraints. According to the formula Calculate the compression coefficient a of the j-th layer of soil measured for the i-th time i,j , according to the formula Calculate the compression modulus Es of the j-th layer of soil measured for the i-th time i,j ;

[0017] Step 804: According to the formula Calculate the settlement Δs of the jth layer of soil from the bottom to the top of the fill body during the period from the i-1th time to the ith time i,j , where H i-1,j is the thickness of the jth fill layer from bottom to top during the i-1th measurement;

[0018] According to the formula Calculate the total settlement Δs of the fill body from the i-1th time to the ith time i , where J is the total number of backfill layers;

[0019] According to the formula Calculate the settlement ΔS of the fill body at the i-th measurement of the j-th layer of soil from the bottom to the top i,j , where H 0,j is the initial thickness of the jth fill layer from bottom to top;

[0020] According to the formula Calculate the total settlement of the fill body at the i-th measurement ΔS i ;

[0021] Step 805, sort out and summarize the calculation results of each time, and judge the cause of deformation of the compact according to whether the moisture content of each layer of fill in the compact increases and whether the settlement rate of the compact increases sharply during the increase of moisture content. When the settlement deformation of the compact is relatively stable and the moisture content of each layer of fill is relatively stable, it is determined that the settlement deformation of the compact is caused by creep deformation; when the moisture content in the compact increases, the settlement deformation rate of the compact after a node increases sharply, and it is determined that the settlement deformation of the compact before the node is caused by creep deformation, and the settlement deformation of the compact after the node is caused by humidification deformation.

[0022] The above-mentioned in-situ monitoring method for the consolidation and compression process of loess fill foundation soil is characterized in that: in step 1, the apparent dielectric constant K is obtained by testing the TDR probe using a one-step method a and electrical conductivity EC b Then, the moisture content and dry density of the experimental soil are obtained through indoor tests, a scatter plot is drawn, the coefficient is calculated, and the apparent dielectric constant K is obtained. a and electrical conductivity EC b The relationship between the moisture content and dry density of the experimental soil is as follows:

[0023] Establish the apparent dielectric constant K a and electrical conductivity EC b and the moisture content ω and dry density ρ of the fill d The relationship is: Among them, ρ wis the water density, a is the first calibration constant, b is the second calibration constant, c is the third calibration constant, d is the fourth calibration constant, f is the fifth calibration constant, and g is the sixth calibration constant; by solving the above equations together, we can get the expression of water content and soil dry density:

[0024]

[0025] One-step calibration process: Select a piece of ground in the center of the backfill area and level it. Place the guide plate on the leveled plane so that the guide plate is in full contact with the soil surface. Then, hammer four probes into the backfill soil through the circular holes on the guide plate with a wooden hammer so that the tops of the four probes are at the same height. Remove the guide plate and place the coaxial probe on the probe so that each probe is in good contact with the fulcrum on the coaxial probe. Then perform TDR testing to obtain the apparent dielectric constant K of the soil. a and electrical conductivity EC b Then, the moisture content and dry density of several groups of fill soils were obtained through indoor tests, and the constant value was obtained by drawing a scatter plot and fitting.

[0026] The above-mentioned in-situ monitoring method for the consolidation and compression process of loess fill foundation soil is characterized in that: the lower notch of the wire pipe is used to introduce the soil pressure gauge data line and the coaxial cable into the wire pipe. Since the wire pipe interface at the interface will wrap a part of the upper and lower wire pipes respectively, the notch height is 1cm to 2cm higher than half the height of the wire pipe interface to leave space for introducing the cable.

[0027] The above-mentioned in-situ monitoring method for the consolidation and compression process of loess fill foundation soil is characterized in that the probe is a stainless steel needle, the diameter of the stainless steel needle is not greater than 6 mm, and the length of the stainless steel needle is 150 mm to 200 mm.

[0028] The above-mentioned in-situ monitoring method for the consolidation and compression process of loess fill foundation soil is characterized in that: the probe is connected to the probe head through a connecting wire, and the TDR tester is connected to the data recording instrument through a data line.

[0029] Compared with the prior art, the present invention has the following advantages:

[0030] 1. The present invention measures data through TDR probes and earth pressure gauges, and can obtain the moisture content, dry density, compression index and settlement of each layer of fill in the compacted body through calculation. It can monitor the internal settlement of the compacted body and analyze the consolidation compression of the compacted body through the compression index.

[0031] 2. The present invention can calculate the moisture content of each layer of fill in the compacted body through the data measured by the TDR probe, and can judge the cause of the deformation of the compacted body according to whether the moisture content increases and whether the settlement rate of the compacted body increases sharply during the increase of the moisture content.

[0032] 3. In the present invention, the TDR probe and the earth pressure gauge are buried along with the backfill height during the backfill process, and the instrument cable is led out of the ground through the wire pipe, which reduces the work of cable burying, excavating the exploration well to take out the cable in the traditional earth pressure gauge burying method, reduces the burden on the staff, and reduces the disturbance to the backfill foundation;

[0033] 4. After the instrument cable is led out of the ground from the conduit, the conduit is backfilled with fine sand or bentonite, which can prevent the conduit from being crushed by the backfill soil and also prevent the cable from falling from the conduit during subsequent work, thereby losing the measurement data, reducing subsequent maintenance work and ensuring the integrity of the data and the accuracy of the results;

[0034] 5. During the backfilling process, the present invention lifts the coaxial cables and soil pressure gauge data lines of the lower layer upward layer by layer, so that the dry density, moisture content and soil pressure changes of the loess in the backfilling area can be measured periodically during the backfilling process, and the data of the entire construction period and the post-construction period can be obtained.

[0035] 6. The present invention buries the instrument below the current backfill surface, reducing the mutual influence between the backfill construction work and the instrument burying work. In addition, after a layer of backfill is completed, the instruments of that layer are arranged at the same time, and each point has no influence on each other, thereby ensuring the accuracy of the test results.

[0036] In summary, the present invention simultaneously monitors the changes in moisture content and dry density of fill foundation soil, and reflects from the perspective of soil mechanics that when the fill foundation soil is subjected to external load, the arrangement density between soil particles increases, the porosity decreases, the soil volume decreases, and the density increases, which is convenient for promotion and use.

[0037] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 It is a side view of the positional relationship of the burying pit, the wire trough, and the wire pipe burying trough of the present invention, and the arrangement of the earth pressure gauge and the three-needle probe;

[0039] Figure 2 It is a top view of the positional relationship of the burying pit, the wire trough, and the wire pipe burying trough of the present invention, and the arrangement of the earth pressure gauge and the three-needle probe;

[0040] Figure 3 This is a diagram showing the effect of using the present invention to measure the data of the earth pressure gauge and the TDR probe;

[0041] Figure 4 It is a structural schematic diagram of the coaxial cable and the earth pressure gauge data line introduced into the wire pipe of the present invention;

[0042] Figure 5It is a schematic diagram of the internal structure of the three-needle probe of the present invention;

[0043] Figure 6 It is a schematic flow chart of the method of the present invention.

[0044] Description of reference numerals:

[0045] 1—existing ground; 2—burying pit; 3—conductor duct;

[0046] 4—conductor; 4-1—conductor interface; 5—conductor buried groove;

[0047] 6—soil pressure gauge; 7—TDR probe; 7-1—probe;

[0048] 7-2—connecting wire; 7-3—probe; 8—fill;

[0049] 9—soil pressure gauge data line; 10—coaxial cable; 11—soil pressure gauge reading instrument;

[0050] 12—TDR tester; 13—data line; 14—data recording instrument. DETAILED DESCRIPTION

[0051] The following describes the implementation of the present invention through specific embodiments. Those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification.

[0052] The exemplary embodiments of the present invention are now described with reference to the accompanying drawings. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. These embodiments are provided to disclose the present invention in detail and completely and to fully convey the scope of the present invention to those skilled in the art. The terms used in the exemplary embodiments shown in the accompanying drawings are not intended to limit the present invention. In the accompanying drawings, the same units / elements are marked with the same reference numerals.

[0053] Unless otherwise specified, the terms (including technical terms) used herein have the commonly understood meanings to those skilled in the art. In addition, it is understood that the terms defined in commonly used dictionaries should be understood to have the same meanings as those in the context of the relevant fields, and should not be understood as idealized or overly formal meanings.

[0054] like Figures 1 to 6 As shown, an in-situ monitoring method for the consolidation and compression process of loess fill foundation soil of the present invention comprises the following steps:

[0055] Step 1: Calibrate the TDR probe: When the backfill thickness is set and does not exceed the minimum buried elevation, select an area in the backfill site and level it. Use the one-step method to test the TDR probe 7 to obtain the apparent dielectric constant K. a and electrical conductivity EC b Then, the moisture content and dry density of the experimental soil are obtained through indoor tests, a scatter plot is drawn, the coefficient is calculated, and the apparent dielectric constant K is obtained. a and electrical conductivity EC b Relationship with the moisture content and dry density of the experimental soil;

[0056] Step 2, excavate the buried pit, wire trough and buried groove for wire pipe: excavate the buried pit 2, wire trough 3 and buried groove 5 for wire pipe on the existing ground 1 filled with loess, and mark them. The buried pit 2 is in the shape of an inverted trapezoid with a large top and a small bottom. The angle between the pit wall and the horizontal plane is less than 45°. The side length of the pit bottom should be no less than 3 times the diameter of the earth pressure gauge 6. The pit bottom is leveled to the buried elevation and forms a horizontal plane. Excavate the wire trough 3 on one side of the buried pit 2. The length of the wire trough 3 should be greater than twice the side length of the top of the buried pit 2, and the depth is half the depth of the buried pit 2. Excavate the buried groove 5 for wire pipe at the end of the wire trough 3. The pit bottom depth of the buried groove 5 for wire pipe is lower than the depth of the wire trough 3, and the pit bottom radius is greater than the radius of the wire pipe 4.

[0057] Step 3, install the soil pressure gauge, TDR probe and take soil: place the soil pressure gauge 6 at the center of the bottom of the burial pit 2, take soil from the vertical plane and take protective measures for the soil sample, take soil from the vertical plane on the side of the burial pit 2 close to the wire trough 3 and horizontally install the TDR probe 7, align the center height of the TDR probe 7 with the top of the soil pressure gauge 6, gently tap the probe 7-1 with a wooden hammer until the probe 7-3 completely enters the soil, then lay the coaxial cable 10 and the soil pressure gauge data line 9 in an "S" shape at the bottom of the wire trough 3 and lead them to the wire pipe burial trough 5, and send the soil sample to the laboratory;

[0058] Step 4: Arrange the cables: introduce the coaxial cable 10 and the earth pressure gauge data line 9 into the wire tube 4, place the wire tube 4 horizontally on the existing ground 1, pass the coaxial cable 10 and the earth pressure gauge data line 9 into the wire tube 4 from the side with the notch of the wire tube and pass it out from the other side, then stand the wire tube 4 upright and place it in the wire tube burying groove 5, so that the coaxial cable 10 and the earth pressure gauge data line 9 pass into the wire tube 4 from the bottom notch and pass it out from the top of the wire tube 4; then mark the cables on the top side of the wire tube 4, store them in a waterproof bag and hang them on the top of the wire tube 4;

[0059] Step 5: Backfilling of the buried pit, wire duct and buried wire pipe duct: The buried pit 2 is backfilled and compacted in layers according to the original moisture content and dry density. When the layered compaction method is used for construction, the earth pressure gauge 6 and TDR probe 7 are installed to prevent the impact load from damaging them. The rolling construction can only be carried out when the backfill thickness of the upper part of the earth pressure gauge 6 exceeds 1.2m. After the buried pit 2 is backfilled to the current ground, the wire duct 3 and the buried wire pipe duct 5 are backfilled to the current ground 1 with the original soil;

[0060] Step 6: Measure the data of the installed earth pressure gauge and TDR probe and install the upper earth pressure gauge and TDR probe in the newly backfilled layer of backfill: When the existing ground is backfilled to a height of 0.5m higher than the buried elevation of the next layer, use the TDR tester 12 to read and record the data of the installed TDR probe 7, and use the earth pressure gauge reader 11 to read and record the data of the installed earth pressure gauge 6;

[0061] Repeat steps 1 and 2, cut off the existing wire pipe 4 to the bottom of the newly excavated wire trough 3, and fill the wire pipe 4 to the upper part of the pipe with fine sand or bentonite, install the wire pipe interface 4-1 on the top of the wire pipe 4, insert the newly buried earth pressure gauge 6, earth pressure gauge data line 9 and coaxial cable 10 of TDR probe 7 together with the installed earth pressure gauge 6, earth pressure gauge data line 9 and coaxial cable 10 of TDR probe 7 from the end with the gap of a new wire pipe 4, and then insert the new wire pipe 4 into the wire pipe interface 4-1, after marking the earth pressure gauge data line 9 and coaxial cable 10 on the top of the new wire pipe 4, store them in a waterproof bag and hang them on the top of the new wire pipe 4, and repeat step 5;

[0062] Step 7: Repeat step 6 several times until backfilling reaches the designed elevation;

[0063] Step 8: After filling in the design elevation, collect and record data at fixed intervals, and convert the measured apparent dielectric constant K a and electrical conductivity EC b Substituting into the calibrated relationship, the moisture content and dry density of each layer of fill in the compacted body 8 are obtained, and then the compression coefficient, compression modulus and settlement of each layer of fill in the compacted body 8 are calculated using the moisture content and dry density of each layer of fill in the compacted body 8. The process is as follows:

[0064] Step 801: Assume that the dry density of the jth layer of soil measured from the bottom upwards for the i-th time is ρ di,j , the earth pressure data is P i,j , the laboratory can obtain the specific gravity data ds of the jth layer of soil measured for the i-th time through indoor geotechnical tests i,j , where i is the number of measurements and j is the number of fill layers from bottom to top;

[0065] Step 802: According to the formula The porosity ratio of the j-th layer of soil measured for the i-th time is ei,j The overburden pressure of each fill layer is

[0066] Step 803: Since the high fill sites in the loess region are all valley terrains, the sites can be considered to have lateral constraints. According to the formula Calculate the compression coefficient a of the j-th layer of soil measured for the i-th time i,j , according to the formula Calculate the compression modulus Es of the j-th layer of soil measured for the i-th time i,j ;

[0067] Step 804: According to the formula Calculate the settlement Δs of the jth layer of soil from the bottom to the top of the fill body during the period from the i-1th time to the ith time i,j , where H i-1,j is the thickness of the jth fill layer from bottom to top during the i-1th measurement;

[0068] According to the formula Calculate the total settlement Δs of the fill body from the i-1th time to the ith time i , where J is the total number of backfill layers;

[0069] According to the formula Calculate the settlement ΔS of the fill body at the i-th measurement of the j-th layer of soil from the bottom to the top i,j , where H 0,j is the initial thickness of the jth fill layer from bottom to top;

[0070] According to the formula Calculate the total settlement of the fill body at the i-th measurement ΔS i ;

[0071] Step 805, sort out and summarize the calculation results of each time, and judge the cause of deformation of the compact according to whether the moisture content of each layer of fill in the compact increases and whether the settlement rate of the compact increases sharply during the increase of moisture content. When the settlement deformation of the compact is relatively stable and the moisture content of each layer of fill is relatively stable, it is determined that the settlement deformation of the compact is caused by creep deformation; when the moisture content in the compact increases, the settlement deformation rate of the compact after a node increases sharply, and it is determined that the settlement deformation of the compact before the node is caused by creep deformation, and the settlement deformation of the compact after the node is caused by humidification deformation.

[0072] It should be noted that the TDR (Time domain reflectometry) tester can emit voltage pulses in the form of electromagnetic waves to propagate and reflect in the probe and fill soil. The reflected signal is transmitted back to the TDR tester, and the reflected waveform is displayed on the oscilloscope through the data line. The apparent dielectric constant K of the fill soil can be obtained through the time difference between the reflection start point and the end point in the reflection waveform and the final stable voltage.a and electrical conductivity EC b , and then the moisture content ω and dry density ρ of the fill can be obtained through calibration d .

[0073] In this embodiment, in step 1, the TDR probe 7 is tested using a one-step method to obtain the apparent dielectric constant K a and electrical conductivity EC b Then, the moisture content and dry density of the experimental soil are obtained through indoor tests, a scatter plot is drawn, the coefficient is calculated, and the apparent dielectric constant K is obtained. a and electrical conductivity EC b The relationship between the moisture content and dry density of the experimental soil is as follows:

[0074] Establish the apparent dielectric constant K a and electrical conductivity EC b and the moisture content ω and dry density ρ of the fill d The relationship is: Among them, ρ w is the water density, a is the first calibration constant, b is the second calibration constant, c is the third calibration constant, d is the fourth calibration constant, f is the fifth calibration constant, and g is the sixth calibration constant; solving equations 1 to 3 simultaneously, we can get the expressions of water content and soil dry density:

[0075]

[0076] One-step calibration process: Select a piece of ground in the center of the backfill area and level it. Place the guide plate on the leveled plane so that the guide plate is in full contact with the soil surface. Then, hammer four probes into the backfill soil through the circular holes on the guide plate with a wooden hammer so that the tops of the four probes are at the same height. Remove the guide plate and place the coaxial probe on the probe so that each probe is in good contact with the fulcrum on the coaxial probe. Then perform TDR testing to obtain the apparent dielectric constant K of the soil. a and electrical conductivity EC b Then, the moisture content and dry density of several groups of fill soils were obtained through indoor tests, and the constant value was obtained by drawing a scatter plot and fitting.

[0077] In this embodiment, the notch at the bottom of the wire tube is used to introduce the soil pressure gauge data line 9 and the coaxial cable 10 into the wire tube 4. Since the wire tube interface at the interface will wrap a part of the upper and lower wire tubes, the notch height is 1cm to 2cm higher than half the height of the wire tube interface to leave space for introducing the cables.

[0078] In this embodiment, the probe 7 - 3 is a stainless steel needle, the diameter of the stainless steel needle is no more than 6 mm, and the length of the stainless steel needle is 150 mm to 200 mm.

[0079] In this embodiment, the probe 7 - 3 is connected to the probe head 7 - 1 via a connecting wire 7 - 2 , and the TDR tester 12 is connected to the data recording instrument 14 via a data line 13 .

[0080] When the present invention is used, the wire pipe can be made of PVC, PE, PB, ABS and other materials. The wire pipe should have a certain rigidity to prevent damage during the backfilling process.

[0081] The interfaces between conduits can be connected by socket, gluing, thread or flange. Hot melt, electric melt and other methods should not be used to prevent damage to the cables during pipeline connection.

[0082] When excavating the wire conduit burying groove in step 2, the depth of the bottom of the wire conduit burying groove should be slightly lower than the wire groove, but should not be greater than the height of the notch at the bottom of the wire conduit. A certain thickness of concrete can be replaced at the bottom of the wire conduit burying groove to prevent the wire conduit from crushing the cable due to excessive upper pressure in the subsequent process.

[0083] When excavating the burial pit in step 2, if a weak layer is found, it should be cleaned and replaced in time, and the soil pressure gauge should be placed on a solid soil layer. If the soft layer is too large to be cleaned, a point equal to the distance from the wire conduit burial groove can be selected around the wire conduit burial groove to re-excavate the burial pit.

[0084] In step six, the buried wire pipe is filled with fine sand or bentonite. The purpose is to prevent the pressure on the outside of the wire pipe from being too high, causing the wire pipe to deform and thus damaging the coaxial cable and soil pressure gauge data cable in the pipe; it can also prevent the cables in the pipe from being pulled back into the wire pipe due to gravity during subsequent work.

[0085] The above description is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any simple modification, change and equivalent structural change made to the above embodiment based on the technical essence of the present invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. An in-situ monitoring method for the consolidation and compression process of loess fill foundation soil, characterized in that: The method comprises the following steps: Step 1: Calibrate the TDR probe: When the backfill thickness is set and does not exceed the minimum burial elevation, select an area in the backfill site and level it. Use the one-step method to test the TDR probe (7) to obtain the apparent dielectric constant K. a and electrical conductivity EC b Then, the moisture content and dry density of the experimental soil are obtained through indoor tests, a scatter plot is drawn, the coefficient is calculated, and the apparent dielectric constant K is obtained. a and electrical conductivity EC b Relationship with the moisture content and dry density of the experimental soil; Step 2, excavating the burial pit, wire trough and wire pipe burial trough: excavating the burial pit (2), wire trough (3) and wire pipe burial trough (5) on the existing ground (1) filled with loess, and marking them well. The burial pit (2) is in the shape of an inverted trapezoid with a larger top and a smaller bottom. The angle between the pit wall and the horizontal plane is less than 45°. The side length of the pit bottom should be no less than 3 times the diameter of the earth pressure gauge (6). The pit bottom is leveled to the burial elevation and forms a horizontal plane. Excavating the wire trough (3) on one side of the burial pit (2). The length of the wire trough (3) should be greater than twice the side length of the top of the burial pit (2). The depth is half the depth of the burial pit (2). Excavating the wire pipe burial trough (5) at the end of the wire trough (3). The pit bottom depth of the wire pipe burial trough (5) is lower than the depth of the wire trough (3). The pit bottom radius is greater than the radius of the wire pipe (4); Step 3, install the soil pressure gauge, TDR probe and take soil: place the soil pressure gauge (6) at the center of the bottom of the burial pit (2), take soil from the vertical plane and take protective measures for the soil sample, take soil from the vertical plane on the side of the burial pit (2) close to the wire trough (3) and horizontally install the TDR probe (7), align the center height of the TDR probe (7) with the top of the soil pressure gauge (6), gently tap the probe (7-1) with a wooden hammer until the probe (7-3) completely enters the soil, then lay the coaxial cable (10) and the soil pressure gauge data line (9) in an "S" shape at the bottom of the wire trough (3) and lead them to the wire pipe burial trough (5), and send the soil sample to the laboratory; Step 4, arranging cables: introduce the coaxial cable (10) and the earth pressure gauge data cable (9) into the wire tube (4), place the wire tube (4) horizontally on the existing ground (1), pass the coaxial cable (10) and the earth pressure gauge data cable (9) into the wire tube (4) from the side with the notch of the wire tube and pass it out from the other side, then stand the wire tube (4) upright and place it in the wire tube buried groove (5), let the coaxial cable (10) and the earth pressure gauge data cable (9) pass into the wire tube (4) from the bottom notch and pass it out from the top of the wire tube (4); then mark the cables on the top side of the wire tube (4), store them in a waterproof bag and hang them on the top of the wire tube (4); Step 5: Backfilling of the burial pit, wire duct and wire pipe burial groove: The burial pit (2) is manually backfilled and compacted in layers according to the original moisture content and dry density. When the layered compaction method is used for construction, in order to prevent the impact load from damaging the installed earth pressure gauge (6) and TDR probe (7), rolling construction can only be carried out when the backfill thickness of the upper part of the earth pressure gauge (6) exceeds 1.2m. After the burial pit (2) is backfilled to the existing ground, the wire duct (3) and the wire pipe burial groove (5) are backfilled to the existing ground (1) with the original soil; Step 6: Measure the data of the installed earth pressure gauge and TDR probe and install the upper earth pressure gauge and TDR probe in the newly backfilled layer of backfill: When the existing ground is backfilled to a height that exceeds the buried elevation of the next layer by 0.5m, use the TDR tester (12) to read and record the data of the installed TDR probe (7), and use the earth pressure gauge reading instrument (11) to read and record the data of the installed earth pressure gauge (6); Repeat steps 1 and 2, cut the existing wire pipe (4) to the bottom of the newly excavated wire trough (3), fill the wire pipe (4) to the top of the pipe with fine sand or bentonite, install a wire pipe interface (4-1) on the top of the wire pipe (4), insert the newly buried earth pressure gauge (6), earth pressure gauge data line (9) and coaxial cable (10) of the TDR probe (7) together with the installed earth pressure gauge (6), earth pressure gauge data line (9) and coaxial cable (10) of the TDR probe (7) from the end with a notch of a new wire pipe (4), and then insert the new wire pipe (4) into the wire pipe interface (4-1), after marking the earth pressure gauge data line (9) and coaxial cable (10) on the top of the new wire pipe (4), store them in a waterproof bag and hang them on the top of the new wire pipe (4), and repeat step 5; Step 7: Repeat step 6 several times until backfilling reaches the designed elevation; Step 8: After filling in the design elevation, collect and record data at fixed intervals, and convert the measured apparent dielectric constant K a and electrical conductivity EC b Substituting into the relationship obtained by calibration, the moisture content and dry density of each layer of fill in the compacted body (8) are obtained, and then the compression coefficient, compression modulus and settlement of each layer of fill in the compacted body (8) are calculated using the moisture content and dry density of each layer of fill in the compacted body (8). The process is as follows: Step 801: Assume that the dry density of the jth layer of soil measured from the bottom upwards for the i-th time is ρ di,j , the earth pressure data is P i,j , the laboratory can obtain the specific gravity data ds of the jth layer of soil measured for the i-th time through indoor geotechnical tests i,j , where i is the number of measurements and j is the number of fill layers from bottom to top; Step 802: According to the formula The porosity ratio of the j-th layer of soil measured for the i-th time is e i,j The overburden pressure of each fill layer is Step 803: Since the high fill sites in the loess region are all valley terrains, the sites can be considered to have lateral constraints. According to the formula Calculate the compression coefficient a of the j-th layer of soil measured for the i-th time i,j , according to the formula Calculate the compression modulus Es of the j-th layer of soil measured for the i-th time i,j ; Step 804: According to the formula Calculate the settlement Δs of the jth layer of soil from the bottom to the top of the fill body during the period from the i-1th time to the ith time i,j , where H i-1,j is the thickness of the jth fill layer from bottom to top during the i-1th measurement; According to the formula Calculate the total settlement Δs of the fill body from the i-1th time to the ith time i , where J is the total number of backfill layers; According to the formula Calculate the settlement ΔS of the fill body at the i-th measurement of the j-th layer of soil from the bottom to the top i,j , where H 0,j is the initial thickness of the jth fill layer from bottom to top; According to the formula Calculate the total settlement of the fill body at the i-th measurement ΔS i ; Step 805, sort out and summarize the calculation results of each time, and judge the cause of deformation of the compact according to whether the moisture content of each layer of fill in the compact increases and whether the settlement rate of the compact increases sharply during the increase of moisture content. When the settlement deformation of the compact is relatively stable and the moisture content of each layer of fill is relatively stable, it is determined that the settlement deformation of the compact is caused by creep deformation; when the moisture content in the compact increases, the settlement deformation rate of the compact after a node increases sharply, and it is determined that the settlement deformation of the compact before the node is caused by creep deformation, and the settlement deformation of the compact after the node is caused by humidification deformation.

2. The in-situ monitoring method for the consolidation and compression process of loess fill foundation soil according to claim 1, characterized in that: In step 1, the TDR probe (7) is tested using the one-step method to obtain the apparent dielectric constant K a and electrical conductivity EC b Then, the moisture content and dry density of the experimental soil are obtained through indoor tests, a scatter plot is drawn, the coefficient is calculated, and the apparent dielectric constant K is obtained. a and electrical conductivity EC b The relationship between the moisture content and dry density of the experimental soil is as follows: Establish the apparent dielectric constant K a and electrical conductivity EC b and the moisture content ω and dry density ρ of the fill d The relationship is: Among them, ρ w is the water density, a is the first calibration constant, b is the second calibration constant, c is the third calibration constant, d is the fourth calibration constant, f is the fifth calibration constant, and g is the sixth calibration constant. Solving equations (1) to (3) together, we can get the expression of water content and soil dry density: One-step calibration process: Select a piece of ground in the center of the backfill area and level it. Place the guide plate on the leveled plane so that the guide plate is in full contact with the soil surface. Then, hammer four probes into the backfill soil through the circular holes on the guide plate with a wooden hammer so that the tops of the four probes are at the same height. Remove the guide plate and place the coaxial probe on the probe so that each probe is in good contact with the fulcrum on the coaxial probe. Then perform TDR testing to obtain the apparent dielectric constant K of the soil. a and electrical conductivity EC b Then, the moisture content and dry density of several groups of fill soils were obtained through indoor tests, and the constant value was obtained by drawing a scatter plot and fitting.

3. The in-situ monitoring method for the consolidation and compression process of loess fill foundation soil according to claim 1, characterized in that: The notch at the bottom of the wire tube is used to introduce the soil pressure gauge data line (9) and the coaxial cable (10) into the wire tube (4). Since the wire tube interface at the interface will wrap a part of the upper and lower wire tubes, the height of the notch is 1 cm to 2 cm higher than half the height of the wire tube interface, so as to leave a gap for introducing the cable.

4. The in-situ monitoring method for the consolidation and compression process of loess fill foundation soil according to claim 1, characterized in that: The probe (7-3) is a stainless steel needle, the diameter of the stainless steel needle is no more than 6 mm, and the length of the stainless steel needle is 150 mm to 200 mm.

5. The in-situ monitoring method for the consolidation and compression process of loess fill foundation soil according to claim 1, characterized in that: The probe (7-3) is connected to the probe head (7-1) via a connecting wire (7-2), and the TDR tester (12) is connected to a data recording instrument (14) via a data line (13).

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