A test and calculation method for loess roadbed settlement

Abstract

The present invention specifically provides a method for testing and calculating the settlement of loess roadbed, which overcomes the shortcomings of existing technologies and design methods. A method for testing and calculating the settlement of loess roadbed, the method is implemented by the following steps: S1: using a static penetration test device to conduct an in-situ test on the loess roadbed, thereby obtaining the static penetration index at different depths, the static penetration index including the cone tip resistance q c , side wall friction f c ; S2: dig a test well around the in-situ test hole in step S1 and take several consolidation samples at different depths; S3: measure the compression modulus E of each consolidation sample under a specified load s , S4: Establish the static penetration index and compression modulus E s Mapping relationship; S5: Calculation of total loess roadbed settlement S. The present invention utilizes the high accuracy of in-situ testing and the large number of test samples, combined with indoor compression testing, to provide clear and feasible testing methods and calculation principles, making the test highly operable, convenient, fast, and low-cost.

Description

Technical Field

[0001] The invention relates to the field of civil engineering road and railway subgrade engineering, and in particular to a method for testing and calculating loess subgrade settlement. Background Art

[0002] Roadbed settlement is a common natural hazard in highway and railway projects. my country's highway construction has developed rapidly, and highway and railway construction in the Loess Plateau has played a good role in opening up and communicating. However, under the influence of various factors (load and rain), the roadbed in the Loess Plateau is prone to various defects, such as transverse and longitudinal cracks in the pavement, uneven roadbed settlement, roadbed subsidence, and even cavities. During the construction and operation of projects in the Loess Plateau, roadbed settlement is a common and destructive hazard, seriously affecting the normal use of highways. Summarizing current experience, loess properties, natural environmental factors, construction factors, and exploration factors are all causes of roadbed defects in the Loess Plateau, among which exploration factors account for a considerable proportion.

[0003] During the exploration, field drilling sampling, in-situ testing, indoor testing and calculation methods were generally adopted. However, due to funding and time constraints, linear projects with wide ranges such as highways and railways generally have problems such as inadequate exploration. (1) The quality of drilling during the survey period is poor. Water drilling and core tube sampling are generally used during the exploration, resulting in unclear analysis of the cause of settlement and inability to accurately judge the difference between diseases such as excessive moisture content and lack of density. Since the soil layer division of the drilling data is relatively rough, the sampling is small and not representative enough, and it is not possible to prepare to reflect the changes in the mechanical properties of the stratum, and it is impossible to accurately grasp the characteristics of thin weak layers and thin water-soaked layers. The standard penetration test in the field in-situ test is simple to operate, but the data obtained from the test are highly discrete and intermittent, and the flat plate load test cycle is long and the cost is high. (2) The soil is disturbed during soil collection, transportation, and testing, and the compressibility of the soil is overestimated. In addition, the disturbance in the indoor test is large, and the role of the permeable interlayer is not reflected when cutting small soil samples, resulting in the solidification of the test. The consolidation rate is low, the test results are often quite different from the actual results, and the test period required is very long; however, due to the disturbance of sampling in indoor conventional consolidation tests, the test results are often low; the GDS consolidation test of unsaturated soil is relatively complex and time-consuming; (3) Due to the presence of air in the pores, the properties of loess are very complex. At present, the saturated soil consolidation theory is mostly used for the calculation of loess foundation settlement. So far, a mature loess settlement calculation theory and calculation method have not yet been formed. Therefore, it is particularly important to determine reasonable settlement calculation parameters; (4) Using settlement observation data to estimate the later settlement (including the final settlement) has become a necessary means to calculate roadbed settlement. However, the settlement estimation method requires certain previous settlement data. In the absence of data, it cannot achieve the purpose of predicting foundation settlement.

[0004] At present, there are various limitations in the testing and calculation methods of loess roadbed and foundation settlement. Based on this, it is necessary to invent a testing and calculation method for loess roadbed settlement that can use existing methods to perform reasonable testing and calculation of settlement values. Summary of the Invention

[0005] In view of the problems existing in the above exploration technology, the present invention provides a method for testing and calculating the settlement of loess roadbed.

[0006] The present invention is achieved by adopting the following technical solutions:

[0007] A method for testing and calculating loess roadbed settlement is implemented by the following steps:

[0008] S1: Use the static penetration test device to conduct in-situ testing on the loess roadbed, thereby obtaining the static penetration index at different depths. The static penetration index includes the cone tip resistance q c , side wall friction f c ;

[0009] S2: digging a test well around the in-situ test hole in step S1 and taking several consolidation samples at different depths;

[0010] S3: Measure the compression modulus E of each consolidated specimen under a specified load s , the compression modulus E s It is obtained by formula (1);

[0011]

[0012] Where, P i is the specified load, kPa; P i+1 is the next level load, kPa; L is the height of the ring cutter, mm; I i is the settlement under the specified load, mm; I i+1 is the settlement under the next level of load, mm;

[0013] S4: Establishing the static penetration index and compression modulus E s Mapping relationship: The cone tip resistance q in step S1 is c , side wall friction f c and the compression modulus E in step S3 s Substituting into formula (2),

[0014] E s =a×q c +b×f c +c(2)

[0015] Calculate the fitting proportional coefficients a, b, and c; where the compression modulus E s, cone tip resistance q c , side wall friction f c The unit is MPa;

[0016] S5: Calculation of total loess roadbed settlement S:

[0017] a) When the loess roadbed settlement is caused by the overburden load uniformly loaded over a large area, the total loess roadbed settlement S is calculated by formula (3);

[0018]

[0019] Where, the total settlement of loess roadbed S is in mm; N is the upper uniform load, in kPa; the compression modulus E is si Obtained from formula (2), unit is MPa; h i is the thickness of the i-th soil layer, in m, and n is the number of soil layers;

[0020] b) When the loess roadbed settlement is caused by waterlogging, the total loess roadbed settlement S is calculated using formula (4);

[0021]

[0022] Where, the total settlement of loess roadbed S is in mm; N is the upper load of the submerged roadbed, in kPa; the compression modulus E is si Obtained from formula (2), unit is MPa; E' si is the compression modulus of soil before immersion settlement, in MPa; h i is the thickness of the i-th soil layer, in m, and n is the number of soil layers.

[0023] Furthermore, the calculation of the total loess roadbed settlement S in step S5 can be achieved by a numerical analysis method, which includes the following steps:

[0024] ① Based on the curve of the static penetration index versus depth measured in step S1, the roadbed soil is divided into original loess and artificially filled loess;

[0025] ② According to the depth distribution of original loess and artificial landfill loess, the boundary conditions were input into the numerical analysis software to establish a numerical analysis model;

[0026] ③ Fitting compression modulus E si The curve between the depth and the compression modulus E is obtained when fitting the relationship function between the two. si Obtained from formula (2);

[0027] ④ Calculation parameters are input into the numerical analysis model, including the stratum density, and then the calculation is performed to obtain the total loess roadbed settlement S.

[0028] Furthermore, the division of the original loess and the artificial landfill loess in step ① is carried out by analyzing the cone tip resistance q c Curve of variation with depth and sidewall friction f c The depth is changed by the depth curve. When the following conditions are met, the depth range is artificial landfill loess;

[0029] Condition 1: When the cone tip resistance q is within 1m depth c The curve of the change with depth at the cone tip resistance q c The number of peaks appearing in the range of 7MPa-25MPa is N, N≥2;

[0030] Condition 2: Within the 1m depth range described in Condition 1, the sidewall friction f c The variation curve of side wall friction f with depth c The number of peaks appearing in the range of 0.1 MPa-0.6 MPa is equal to N;

[0031] Condition 3: Cone tip resistance q c The curve of the change with depth and the side wall friction f c The depth values ​​when the i-th peak appears in the depth variation curve are h i1 With h i2 , and |h i1 -h i2 |<0.2,i=1,……N。

[0032] Furthermore, between step S4 and step S3, first the cone tip resistance q c Curve of change with depth, side wall friction resistance f c Abnormal fluctuation points in the depth variation curve are eliminated. The elimination basis is that the cone tip resistance q appears within the depth interval of 10cm-20cm. c It suddenly increases and then suddenly decreases, thereby excluding the abnormal conditions of lens anomalies and stone anomalies; then the static penetration index of the abnormal point is replaced by the average value within the set depth interval, and the set depth interval is a depth interval with the abnormal point as the center and an interval length of 40 cm.

[0033] Furthermore, the static penetration test device in step S1 includes a penetration power device, a measuring system, a probe rod, and a probe head; the probe head includes a frustum portion, a cylindrical portion, and an inverted cone portion arranged in sequence from top to bottom and coaxially arranged, and the vertical length of the frustum portion is greater than or equal to 50 mm, and the cone tip angle of the inverted cone portion is 40°-50°; the probe rod and the probe head are coaxially arranged, the diameter of the probe rod is 5mm-8mm smaller than the diameter of the cylindrical portion of the probe head, and the diameter of the probe rod is the same as the diameter of the small mouth end of the frustum portion of the probe head.

[0034] Furthermore, the step S1 is implemented by the following steps: S1.1: assembling the static penetration test device; S1.2: leveling the penetration equipment, which includes a probe rod and a probe; S1.3: penetrating the probe rod and obtaining the cone tip resistance q using the measurement system. c Curve of change with depth, side wall friction resistance f c Curve of change with depth; S1.4: When the required depth is reached, the test ends.

[0035] Furthermore, when excavating an exploration well around the in-situ test hole in step S2, if the in-situ test hole is located in the center of a plain or terrace, the distance between the exploration well and the in-situ test hole is less than or equal to 5m; if the in-situ test hole is located at the interface of a loess gully and a terrace, the distance between the exploration well and the in-situ test hole is less than or equal to 1m; the sampling depth of the consolidation sample is greater than or equal to 1m, the soil sampling interval is 10cm-20cm, the sampling depth distribution is greater than or equal to 10 layers, and M parallel samples are set for each sampling layer, where M is a positive integer greater than or equal to 6.

[0036] Furthermore, the compression modulus E under the specified load range in step S3 is s The measurement is achieved by the following steps: S3.1: Sample processing; S3.2: Sample installation; S3.3: If the sample is a saturated sample, add water to the compression container until it is full and let it stand for 12 hours. If the water level in the compression container drops during this period, add water to the compression container again until it is full, restart the timing, and let it stand for 12 hours; If the sample is an unsaturated sample, use wet cotton yarn to surround the upper and lower permeable surfaces to prevent water evaporation; S3.4: Load, and end the test after loading to the target load; S3.5: Calculate the compression modulus E using formula (1) s .

[0037] This patented method uses static penetration tests on loess roadbeds, obtaining continuous static penetration mechanical parameters for the loess roadbed. Field sampling and laboratory testing of shallow roadbed loess yielded the loess compression modulus. A correlation between shallow static penetration indices and the compression modulus was established, allowing the compression modulus of deeper loess to be derived, resulting in loess settlement values ​​based on static penetration tests. Based on different compression modulus values ​​and calculated loess roadbed settlement values, appropriate treatment measures are implemented to target weak layers at different depths, guiding roadbed engineering design and construction.

[0038] The advantages of the present invention are: utilizing the high accuracy of in-situ tests and the large number of test specimens, combined with indoor test compression tests, the shortcomings of existing technologies and design methods are overcome, the test methods and calculation principles are clear and feasible, the test operability is extremely strong, the test is convenient, the speed is fast, and the cost is low. A method for effectively and accurately calculating the settlement of loess roadbed is provided. The principle of this method is clear. Through on-site in-situ tests and indoor tests (multiple measurements, which can be omitted after gaining experience, and empirical formulas can be directly used), the settlement of loess roadbed can be directly calculated. The settlement can be predicted in advance, providing an accurate and reliable basis for correctly judging road operations, and guiding the investigation and design of loess roadbed projects. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 is a schematic structural diagram of the probe used in step S1 of the present invention;

[0040] Figure 2 is a curve showing the relationship between the cone tip resistance and the depth measured in Example 4 of the present invention;

[0041] Figure 3 is a curve showing the relationship between the sidewall friction and the depth measured in Example 4 of the present invention;

[0042] Figure 4 is a curve showing the relationship between the friction ratio and the depth measured in Example 4 of the present invention;

[0043] Figure 5 is a curve showing the relationship between compression modulus and depth in Example 4 of the present invention;

[0044] Figure 6 The subgrade settlement calculation model including subgrade vehicle load in Example 5 of the present invention;

[0045] Figure 7 is a curve showing the relationship between the compression modulus and depth obtained by fitting the collapsible waterlogged loess data in Example 5 of the present invention;

[0046] Figure 8 is a curve showing the relationship between the compression modulus and depth obtained by fitting the roadbed fill data in Example 5 of the present invention;

[0047] Figure 9 This is a settlement diagram without vehicle load after the roadbed is flooded in Example 5 of the present invention;

[0048] Figure 10 This is a diagram of vehicle load settlement after the roadbed is flooded in Example 5 of the present invention.

[0049] In the figure, 501 is the inverted cone portion of the probe, 502 is the cylindrical portion of the probe, 503 is the frustum portion of the probe, and 504 is the probe rod. DETAILED DESCRIPTION

[0050] Example 1

[0051] A method for testing and calculating loess roadbed settlement is implemented by the following steps:

[0052] S1: Use the static penetration test device to conduct in-situ testing on the loess roadbed, thereby obtaining the static penetration index at different depths. The static penetration index includes the cone tip resistance q c , side wall friction f c ;

[0053] S2: digging a test well around the in-situ test hole in step S1 and taking several consolidation samples at different depths;

[0054] S3: Measure the compression modulus E of each consolidated specimen under a specified load s , the compression modulus E s It is obtained by formula (1);

[0055]

[0056] Where, P i is the specified load, kPa; P i+1 is the next level load, kPa; L is the height of the ring cutter, mm, for the standard consolidation test L is 20; I i is the settlement under the specified load, mm; I i+1 is the settlement under the next level of load, mm;

[0057] S4: Establishing the static penetration index and compression modulus E s Mapping relationship: The cone tip resistance q in step S1 is c , side wall friction f c and the compression modulus E in step S3 s Substituting into formula (2),

[0058] E s =a×q c +b×f c +c (2)

[0059] The fitting proportional coefficients a, b, and c are obtained, which are dimensionless; where the compression modulus E s , cone tip resistance q c , side wall friction f c The unit is MPa;

[0060] S5: Calculation of total loess roadbed settlement S:

[0061] a) When the loess roadbed settlement is caused by the overburden load uniformly loaded over a large area, the total loess roadbed settlement S is calculated by formula (3);

[0062]

[0063] Where, the total settlement of loess roadbed S is in mm; N is the upper uniform load, in kPa; the compression modulus E is si Obtained from formula (2), unit is MPa; h i is the thickness of the i-th soil layer, in m, and n is the number of soil layers;

[0064] b) When the loess roadbed settlement is caused by waterlogging, the total loess roadbed settlement S is calculated using formula (4);

[0065]

[0066] Where, the total settlement of loess roadbed S is in mm; N is the upper load of the submerged roadbed, in kPa; the compression modulus E is si Obtained from formula (2), unit is MPa; E' si is the compression modulus of soil before immersion settlement, in MPa; h i is the thickness of the i-th soil layer, in m, and n is the number of soil layers.

[0067] In step S4 of the present invention, a mathematical correlation analysis is performed based on the CPT test hole test parameters (depth, cone tip resistance, sidewall friction) and the curve graph, and the compression modulus obtained from the indoor compression modulus test, matching a corresponding algorithm, such as the least squares method, to establish a relationship between the compression modulus, the cone tip resistance, and the sidewall friction. Due to the large differences in soil properties at different sites, the calculated relationship parameters of the fitting proportional coefficients a, b, and c vary, and the specific experimental fitting shall prevail. Using this fitting formula, the compression modulus of the site is calculated using the test data (cone tip resistance, sidewall friction).

[0068] The calculation of formula (3) and formula (4) in step S5 of the present invention adopts manual calculation, which is applicable to simple working conditions. Among them, formula (3) is applicable to the situation where the overlying load is uniformly loaded over a large area and the thickness of the settlement compression layer is small; formula (4) is applicable to the situation where a large area of ​​loess undergoes relatively uniform settlement due to immersion in water. When a large area of ​​loess settles due to immersion in water, the load on it remains unchanged.

[0069] The calculation of the total loess roadbed settlement S in step S5 can be achieved by numerical analysis, which includes the following steps:

[0070] ① Based on the curve of the static penetration index versus depth measured in step S1, the roadbed soil is divided into original loess and artificially filled loess. The division of the roadbed soil can also be determined in combination with the construction site conditions;

[0071] ② According to the depth distribution of original loess and artificial landfill loess, the boundary conditions were input into the numerical analysis software to establish a numerical analysis model;

[0072] ③ Fitting compression modulus E si The curve between the depth and the compression modulus E is obtained when fitting the relationship function between the two. si Obtained from formula (2);

[0073] ④ Calculation parameters are input into the numerical analysis model, including the stratum density, and then the calculation is performed to obtain the total loess roadbed settlement S.

[0074] Numerical analysis is applicable to complex working conditions, including those involving changes in groundwater levels, overburden loads, and layered backfill in loess roadbeds. The relationship function in step ③ is a parameter affected by the loess consolidation history and requires a function derived from field measurements obtained through static penetration testing.

[0075] The division of original loess and artificial landfill loess in step ① is achieved by analyzing the cone tip resistance q c Curve of variation with depth and sidewall friction f c The depth is changed by the depth curve. When the following conditions are met, the depth range is artificial landfill loess;

[0076] Condition 1: When the cone tip resistance q is within 1m depth c The curve of the change with depth at the cone tip resistance q c The number of peaks appearing in the range of 7MPa-25MPa is N, N≥2;

[0077] Condition 2: Within the 1m depth range described in Condition 1, the sidewall friction f c The variation curve of side wall friction f with depth c The number of peaks appearing in the range of 0.1 MPa-0.6 MPa is equal to N;

[0078] Condition 3: Cone tip resistance q c The curve of the change with depth and the side wall friction f c The depth values ​​when the i-th peak appears in the depth variation curve are h i1 With h i2 , and |h i1 -h i2 |<0.2,i=1,……N。

[0079] The properties of natural loess and artificial landfill loess are quite different. Natural loess is relatively homogeneous, while most artificial fills are compacted loess, which generally shows a relatively anisotropic property (the mechanical index in the vertical direction is much greater than that in the horizontal direction). Within a depth of 1m, affected by construction, the cone tip resistance and side wall resistance show irregular periodic up and down fluctuations along the depth direction, and the peak and trough values ​​of the cone tip resistance and side wall resistance are basically the same within a depth of 0.2m. The values ​​of the cone tip resistance and side wall resistance vary greatly. The peak values ​​of the cone tip resistance and side wall resistance within a depth of 1m appear at least twice, and the number of peak values ​​of the two are the same. The cone tip resistance is generally between 7-25Mpa, and the side wall resistance is generally between 0.1-0.6Mpa.

[0080] According to the test parameters obtained by static penetration, the cone tip resistance q is analyzed. c , side wall resistance f s The changes of the two parameters can be combined with the friction ratio R if necessary. f According to the parameter changes, geological stratification of fill and original soil in the engineering site is carried out.

[0081] The calculation accuracy of foundation settlement can be improved by stratifying and subdividing the soil layer mechanically according to indicators such as cone tip resistance, side wall friction resistance and friction resistance ratio.

[0082] Between step S4 and step S3, first the cone tip resistance q c Curve of change with depth, side wall friction resistance f c Abnormal fluctuation points in the depth variation curve are eliminated. The elimination basis is that the cone tip resistance q appears within the depth interval of 10cm-20cm. c It suddenly increases and then suddenly decreases, thereby excluding the abnormal conditions of lens anomalies and stone anomalies; then the static penetration index of the abnormal point is replaced by the average value within the set depth interval, and the set depth interval is a depth interval with the abnormal point as the center and an interval length of 40 cm.

[0083] In the analysis of abnormal data, the curve of friction ratio changing with depth and the curve of pore water pressure changing with depth can also be combined.

[0084] The static penetration test device in step S1 includes a penetration power device, a measuring system, a probe rod 504, and a probe; Figure 1 As shown, the probe includes a frustum portion 503, a cylindrical portion 502, and an inverted cone portion 501, which are arranged in sequence from top to bottom and coaxially, and the vertical length of the frustum portion 503 is equal to 50 mm, and the cone tip angle of the inverted cone portion 501 is 40°; the probe rod 504 is coaxially arranged with the probe, and the diameter of the probe rod 504 is 5 mm smaller than the diameter of the cylindrical portion of the probe, and the diameter of the probe rod 504 is the same as the diameter of the small mouth end of the frustum portion 503 of the probe.

[0085] During measurement, other necessary reaction force measures may be used as needed. Penetration power equipment can be divided into two types: deadweight type that utilizes its own weight and ground anchor type that utilizes reaction force. With the help of engines, hydraulic systems and other devices, vertical downward force is provided to press the static penetration probe into the loess at a uniform speed.

[0086] The measurement system is generally a static resistance strain gauge or a static penetration digital force gauge, which includes a depth measurement element and a probe inclination measurement element.

[0087] The standard shape of the probe is cylindrical, with a conical base and a top connected to the probe rod. In this method, the tip angle of the inverted cone is 40°-50°, which is significantly different from the cone angle of ordinary probes. Due to the large variation in the strength of loess strata, especially thin layers of silty clay, dynamic compaction and other methods are often used in roadbed fill. This results in interbedded hard and soft layers in the compacted loess. The purpose of reducing the cone angle is to increase the tip pressure during penetration by reducing the angle, making it easier to penetrate harder loess strata and thus detect parameters of deeper loess layers. Table 1 lists the dimensions of currently commonly used static penetration probes.

[0088] Table 1: Commonly used static penetration probe dimensions

[0089] <![CDATA[Probe cross-sectional area (cm 2 )]]> Probe diameter (mm) Effective side wall length (mm) <![CDATA[Frictional cylinder side wall area (cm 2 )]]> 10 35.7 133.7 150 15 43.7 218.5 300 20 50.4 189.5 300

[0090] The probe rod material should be seamless alloy steel formed in one step. The wall thickness of the probe rod should be greater than 2 / 3 of the cone head radius. Solid probe rods can be used when drilling ultra-deep holes or soil layers with dense hard layers and high strength. Each probe rod has the same length of 1m, with tight shoulders and good interchangeability. During the test, the static penetration cone tip squeezes the surrounding soil and it is difficult to recover in a short time. The lateral deformation of the loess layer is generally small. The probe rod diameter is 5-8mm smaller than the cone head diameter in the above table, which can effectively reduce the side wall friction resistance, increase the total penetration depth, and save costs;

[0091] The connection between the probe and the probe rod adopts a smooth transition connection, and the length of the connection piece (i.e. the vertical length of the frustum) should not be less than 50mm to ensure a sufficiently small curve transition.

[0092] Other unmentioned parts of the probe and the probe rod in the present invention adopt existing structures.

[0093] The step S1 is implemented by the following steps: S1.1: assembling the static penetration test device; S1.2: leveling the penetration equipment, which includes a probe rod and a probe; S1.3: penetrating the probe rod and obtaining the cone tip resistance q using a measurement system. c Curve of change with depth, side wall friction resistance f c Curve of change with depth; S1.4: When the required depth is reached, the test ends.

[0094] The specific operation process of static penetration testing is as follows:

[0095] S1.1: Assemble the static penetration test apparatus;

[0096] S1.2.1: Align the penetration probe with the hole and adjust the static penetration equipment to keep the level bubble of the penetration equipment centered.

[0097] S1.2.2: Before penetration, test the probe to ensure proper function of the jack, cone, friction cylinder, and other components. Insert the probe rod into the guide, adjust the vertical position, and tighten the guide to ensure that the probe penetrates vertically into the soil. Start the power equipment and adjust it to normal working condition.

[0098] S1.3.1: Penetrate the probe into the loess at a constant speed of 1.2 ± 0.3 m / min (above the freezing line in winter). Raise the probe above the ground surface so that the probe sensor is free of stress. Once the probe temperature has reached equilibrium with the ground temperature (the instrument zero point is stable), adjust the instrument to zero or record the initial reading. Then, proceed with normal penetration. The measuring instrument will automatically record and process the data.

[0099] S1.3.2: Penetration should be stopped when the predetermined depth is reached or one of the following situations occurs: the penetration force of the probe main unit reaches the rated penetration force; the probe resistance reaches the maximum pressure, generally 20-30MPa; the reaction device fails; it is found that the bending of the probe rod has reached an unacceptable degree; the total inclination of the probe rod reaches 15°-20°.

[0100] S1.4: After the test, the probe should be promptly removed and the instrument zeroed. The instrument should be calibrated to the initial value and the penetration index should be corrected during the penetration process. The probe should be properly stored after removal to prevent damage from vibration.

[0101] When excavating an exploration well around the in-situ test hole in step S2, if the in-situ test hole is located in the center of a plain or terrace, the distance between the exploration well and the in-situ test hole is equal to 4m; if the in-situ test hole is located at the interface of a loess gully and a terrace, the distance between the exploration well and the in-situ test hole is equal to 0.5m; the sampling depth of the consolidation sample is equal to 1m, the soil sampling interval is 10cm, the sampling depth distribution is equal to 10 layers, and 6 parallel samples are set for each layer.

[0102] When sampling, appropriate deviations can be made for flooded sites based on the geological conditions.

[0103] The compression modulus E under the specified load range in step S3 sThe measurement is achieved by the following steps: S3.1: Sample processing; S3.2: Sample installation; S3.3: If the sample is a saturated sample, add water to the compression container until it is full and let it stand for 12 hours. If the water level in the compression container drops during this period, add water to the compression container again until it is full, restart the timing, and let it stand for 12 hours; If the sample is an unsaturated sample, use wet cotton yarn to surround the upper and lower permeable surfaces to prevent water evaporation; S3.4: Load, and end the test after loading to the target load; S3.5: Calculate the compression modulus E using formula (1) s .

[0104] The test equipment includes consolidation instrument, ring knife, permeable stone and deformation measuring equipment. The consolidation sample area is 30cm 2 or 50cm 2 , 20mm high, with a certain rigidity, the inner wall should maintain a high degree of smoothness, it is advisable to apply a thin layer of silicone grease or polytetrafluoroethylene.

[0105] The specific steps of the test are as follows:

[0106] S3.1: Shape the sample, place the lower permeable stone and filter paper on the bottom plate of the consolidation test container, place the retaining ring and the sample into the container, cover the soil sample with filter paper and permeable stone, and then lower the pressure guide ring and pressure transmission piston to ensure close contact between the components in the consolidation instrument container.

[0107] S3.2: Place the compression vessel in the center of the pressure frame, close the pressure transmission piston and beam, pre-apply 1kPa pressure, make all parts of the oedometer in close contact, install the dial indicator, and adjust the reading to zero.

[0108] S3.3: If the specimen is saturated, fill the container with water until it is full before applying the load and allow it to stand for 12 hours. After the water level in the compression container drops, fill the container with water again and allow it to stand for another 12 hours before commencing the test. If the specimen is unsaturated, surround the upper and lower permeable surfaces with wet cotton yarn to prevent evaporation.

[0109] S3.4: Remove the preload and apply the first level of load. Avoid shock and shaking when adding the weight. Immediately start the stopwatch as the weight is added. Load levels are generally specified as 50 kPa, 100 kPa, 200 kPa, 300 kPa, and 400 kPa. The loading level can be adjusted based on soil hardness and specific requirements. The final level of pressure should be 100 kPa-200 kPa greater than the calculated pressure of the overburden.

[0110] S3.5: After the test, dismantle the instrument, take out the intact soil sample, weigh its mass, and determine its final moisture content (if the saturation after the test does not need to be determined, the final moisture content does not need to be determined), and clean the instrument.

[0111] Example 2

[0112] The static penetration test device in step S1 includes a penetration power device, a measuring system, a probe rod 504, and a probe; the probe includes a frustum portion 503, a cylindrical portion 502, and an inverted cone portion 501 arranged in sequence from top to bottom and coaxially arranged, and the vertical length of the frustum portion 503 is equal to 85 mm, and the cone tip angle of the inverted cone portion 501 is 46°; the probe rod 504 is coaxially arranged with the probe, the diameter of the probe rod 504 is 6 mm smaller than the diameter of the cylindrical portion of the probe, and the diameter of the probe rod 504 is the same as the diameter of the small mouth end of the frustum portion 503 of the probe.

[0113] When excavating an exploration well around the in-situ test hole in step S2, if the in-situ test hole is located in the center of a plain or terrace, the distance between the exploration well and the in-situ test hole is equal to 4.3m; if the in-situ test hole is located at the interface of a loess gully and a terrace, the distance between the exploration well and the in-situ test hole is equal to 0.7m; the sampling depth of the consolidation sample is equal to 1.3m, the soil sampling interval is 17cm, the sampling depth distribution is equal to 12 layers, and 7 parallel samples are set for each layer.

[0114] Example 3

[0115] The static penetration test device in step S1 includes a penetration power device, a measuring system, a probe rod 504, and a probe; the probe includes a frustum portion 503, a cylindrical portion 502, and an inverted cone portion 501 arranged in sequence from top to bottom and coaxially arranged, and the vertical length of the frustum portion 503 is equal to 100 mm, and the cone tip angle of the inverted cone portion 501 is 50°; the probe rod 504 is coaxially arranged with the probe, the diameter of the probe rod 504 is 8 mm smaller than the diameter of the cylindrical portion of the probe, and the diameter of the probe rod 504 is the same as the diameter of the small mouth end of the frustum portion 503 of the probe.

[0116] When excavating an exploration well around the in-situ test hole in step S2, if the in-situ test hole is located in the center of a plain or terrace, the distance between the exploration well and the in-situ test hole is equal to 5m; if the in-situ test hole is located at the interface of a loess gully and a terrace, the distance between the exploration well and the in-situ test hole is equal to 1m; the sampling depth of the consolidation sample is equal to 1.5m, the soil sampling interval is 20cm, the sampling depth distribution is equal to 15 layers, and 9 parallel samples are set for each layer.

[0117] Example 4

[0118] The working condition of this embodiment is that the roadbed fill is dense, but the underlying collapsible loess is soaked in water.

[0119] A loess roadbed is a fill roadbed with a length of about 400m, a width of about 30m, and a fill height of 7m (the total thickness of the road surface and roadbed is about 2m, and the load is about 24kN / m3 The following 5 meters are compacted loess with a weight of about 21kN / m 3 ), the geological conditions below are as follows: the original ground surface is composed of collapsible Q3 loess, silt, with a thickness of about 5m; Q2 loess, silty clay.

[0120] During the operation of a highway, irregular cracks appear on the asphalt pavement, and the operation and maintenance unit urgently needs to analyze the cause of the disease. The test and calculation method of loess roadbed settlement described in the present invention is adopted during the survey and design.

[0121] Instruments and equipment: (1) Penetration equipment: static penetration vehicle; (2) The measuring instrument is a static penetration digital force gauge, which includes a depth measuring element and a probe inclination measuring device; (3) The standard shape of the probe is a cylinder with a cone at the bottom and the top connected to the probe rod, with a cone tip angle of 40 degrees and a cone head cross-sectional area of ​​15 cm 2 The friction tube length is 218.5mm. (4) The probe rod material is made of seamless manganese steel alloy steel that allows for retraction and minimizes side wall friction. Each probe rod is the same length, 1m, with tight fitting threads and good interchangeability. The probe rod diameter is 36mm and the probe rod wall thickness is 24mm. (5) The connection between the probe and the probe rod adopts a smooth transition connection, and the connecting piece (i.e., the cone portion of the probe) is 80mm long.

[0122] step:

[0123] (1) In-situ test of loess roadbed settlement:

[0124] (1) Align the penetration probe with the hole position and adjust the static penetration equipment to keep the level bubble of the penetration equipment in the center.

[0125] (2) Before penetration, test the probe pressure to check if the top column, cone head, friction cylinder and other components are functioning properly. Insert the probe rod connected to the probe into the guide, adjust the verticality and tighten the guide device to ensure that the probe penetrates vertically into the soil. Start the power equipment and adjust it to normal working condition.

[0126] (3) Insert the probe into the loess at an average speed of 1.2 ± 0.3 m / min (above the freezing line in winter), then lift it out of the ground so that the probe sensor is in a stress-free state. Zero the instrument or record the initial reading, and then proceed with normal penetration. The measuring instrument automatically records and processes the data.

[0127] (4) The test depth reached 22.8m. Preliminary analysis of the data showed that the fill loess had good compaction properties at 0-5m, the original loess at 5-10.7m was obviously saturated with water, and the original loess at 10.7-22.8m was relatively normal. The cone tip resistance and side wall resistance at the deepest point were normal and not saturated with water. The test was completed. The curves of the relationship between the cone tip resistance and depth, the relationship between the side wall friction resistance and depth, and the relationship between the friction resistance ratio and depth are shown in the attached figure. Figure 2 , Attachment Figure 3 , Attachment Figure 4 shown.

[0128] (5) After the test, the probe should be promptly removed, the instrument zeroing status should be recorded, and the initial value should be calibrated to correct the penetration index during the penetration process. After the probe is removed, it should be cleaned and oiled immediately and properly stored to prevent damage to the probe due to vibration.

[0129] (2) Indoor compression modulus test of loess roadbed settlement

[0130] The test equipment includes a consolidation tester, a ring cutter, a permeable stone, and a deformation measuring device. The consolidation specimen has an area of ​​50 cm2 and a height of 20 mm. It has a certain rigidity, a smooth inner wall, and is coated with a thin layer of silicone grease.

[0131] Test steps:

[0132] (1) As the in-situ test site was soaked in water, soil samples could not be taken. Soil samples were taken from the same geological location around the roadbed of the in-situ test site. Generally, soil was taken from 1m below the surface with a sampling interval of 10cm. A total of 10 layers were sampled, with 6 samples taken from each layer.

[0133] (2) Processing the sample;

[0134] (3) Place the compression container in the center of the pressure frame, close the pressure transmission piston and the crossbeam, pre-apply 1kPa pressure to make the various parts of the consolidator in close contact, install the dial indicator, and adjust the reading to zero.

[0135] (4) Before applying the load, fill the container with water until it is full and keep it still for 12 hours. After the water level in the compression container drops, fill the container with water again until it is full and keep it still for another 12 hours before starting the test.

[0136] (5) Remove the preload and immediately apply the first level of load. Avoid shock and shaking when adding the weight. Start the stopwatch immediately after adding the weight. The loads are 100 kPa and 200 kPa.

[0137] (6) After the test, dismantle the instrument, carefully take out the intact soil sample, weigh it, and measure its final moisture content (if the saturation after the test does not need to be measured, it is not necessary to measure the final moisture content), and clean the instrument.

[0138] (7) The specific test data are shown in Table 2. The compression modulus under a pressure of 100-200 kPa was calculated according to the formula (1) described in the present invention.

[0139] Table 2: Indoor compression test calculations

[0140]

[0141]

[0142] (3) Calculation and analysis method of loess roadbed settlement

[0143] (1) Analysis of abnormal data of static penetration test

[0144] Based on the test parameters (depth / cone tip resistance / side wall friction resistance / friction resistance ratio / pore water pressure, etc.) and curve graphs of static penetration test holes obtained using an in-situ testing device and in-situ testing process for loess roadbed settlement, the rationality of the test data was analyzed. The loess of the roadbed was obviously stratified, and it was preliminarily judged that there were no abnormal data points.

[0145] (2) Stratification of undisturbed loess and artificially filled loess based on the static penetration index

[0146] Based on the test parameters obtained from the static penetration test, and by analyzing the changes in the three parameters of cone tip resistance qc, sidewall resistance fs, and friction ratio Rf, it was determined that the roadbed soil within the 0-5m range was artificial fill, with natural, undisturbed loess beneath. Comparison with the on-site topography confirmed that this was consistent with the test data. Due to the abnormally low static penetration test data within the 5-10.5m range and the normal data indicators for the underlying loess, the project team initially analyzed the cause of the project's problems: Due to inadequate on-site topography and drainage facilities, drainage was poorly maintained over a large area of ​​the original roadbed surface at the project site, resulting in water infiltration of the loess below the original ground line at the construction site, which in turn caused settlement.

[0147] (3) Mapping relationship between static penetration index and settlement calculation parameters

[0148] Based on the CPT test hole test parameters (depth / cone tip resistance / side wall friction resistance) and curve diagram obtained from an in-situ test device and in-situ test process of loess roadbed settlement, and the compression modulus obtained from an indoor compression modulus test of loess roadbed settlement, mathematical correlation analysis is performed to match the corresponding algorithm (such as the least squares method, etc.) to establish the correlation relationship between the compression modulus and the cone tip resistance and side wall friction resistance. Generally, there is a relationship as shown in formula (2). Using the above fitting formula, the compression modulus of the site is calculated using the test data (cone tip resistance, side wall friction resistance).

[0149] Table 3 Static penetration index and compression modulus at different depths

[0150]

[0151] A linear regression analysis was performed with the tip resistance and sidewall resistance as independent variables and the compression modulus as the dependent variable. As can be seen from Table 3, the simulation formula is: compression modulus = 0.316 + 1.114 * tip resistance + 17.146 * sidewall resistance. The model R-square value is 0.891, which means that the tip resistance and sidewall resistance can explain 89.1% of the variation in the compression modulus.

[0152] When the model was subjected to the F test, it was found that the model passed the F test (F=28.476, p=0.000<0.05), which means that at least one of the cone tip resistance and side wall resistance will have an impact on the compression modulus. The regression coefficient value of the cone tip resistance is 1.114 (t=7.304, p=0.000<0.01), which means that the cone tip resistance will have a significant positive impact on the compression modulus.

[0153] The regression coefficient of sidewall resistance is 17.146 (t=3.968, p=0.005<0.01), which means that sidewall resistance has a significant positive impact on compression modulus.

[0154] Therefore, both the cone tip resistance and the side wall resistance have a significant positive impact on the compression modulus.

[0155] Table 4 Correlation analysis between static penetration index and compression modulus at different depths

[0156]

[0157]

[0158] Using the above formula, the compression modulus of the site is obtained. Since the table is too large, it is expressed in the form of a curve as shown in the attached figure. Figure 5 shown.

[0159] (3) Settlement calculation and analysis based on static penetration index

[0160] The survey unit provides the loess compression modulus E' of the roadbed subsidence caused by waterlogging s =8MPa, the overlying load N

[0161] N = 24 × 2 + 21 × 5 = 153 kPa

[0162] The total thickness of the soil layer is 0.1m, and the layering parameter E of the soil obtained after layering is s The total settlement of the roadbed before and after flooding can be calculated according to the following formula:

[0163]

[0164] The settlement of the loess roadbed was calculated to a depth of 22.9 meters below the roadbed. The compacted roadbed section from 0 to 5 meters exhibited good compaction, with most settlement values ​​being negative, indicating no settlement. The loess roadbed from 5 to 11.3 meters experienced settlement. The Q2 loess roadbed settlement difference from 11.3 to 22.9 meters exhibited alternating positive and negative values, indicating no settlement in this section. Therefore, settlement occurred only in the Q3 collapsible loess section from 5 to 11.3 meters. The specific calculation results are shown in Tables 5 and 6.

[0165] Table 5: Calculation of settlement of loess roadbed after filling and compaction

[0166]

[0167]

[0168] Table 6 Calculation of water-soaked settlement of collapsible loess roadbed

[0169]

[0170]

[0171] It is estimated that the total settlement of the roadbed in the later period will be 364mm. As of the survey period, the maximum settlement of the loess roadbed on site was about 300mm, which is close to the predicted value. However, it is estimated that the loess roadbed will continue to settle, but the rate will gradually slow down.

[0172] Example 5

[0173] The working condition of this embodiment is that the roadbed is densely filled, the underlying collapsible loess is soaked in water, and the road is not closed and can be used normally.

[0174] The equipment is the same as that in Implementation Case 4

[0175] step:

[0176] (1) The in-situ test of loess roadbed settlement is the same as that in Case 4

[0177] (2) The indoor compression modulus test of loess roadbed settlement is the same as that in Case 4

[0178] (III) The three steps and results of the loess roadbed settlement calculation and analysis method are the same as those in Implementation Case 4: (1) Analysis of abnormal data in static penetration test data; (2) Stratification of undisturbed loess and artificially filled loess based on static penetration test index; and (3) Mapping relationship between static penetration test index and settlement calculation parameters.

[0179] (4) Settlement calculation based on static penetration index

[0180] All other working conditions were the same as those in Case 5. Due to the roadbed settlement, lateral cracks began to develop on some sections of the fill slope. To ensure traffic safety, the operator did not close traffic but urgently closed the heavily loaded roadbed side. The operator was required to calculate the final deformation of the loess roadbed under the effects of vehicle load and gravity after flooding. Based on on-site vehicle statistics, the vehicle load (including impact) was approximately 50 kPa.

[0181] In this embodiment, finite element software is used to perform calculations.

[0182] First, according to the project site conditions and in-situ test data, a numerical analysis model is established, the soil layers are reasonably divided, and the boundary conditions are determined according to the project. In this example, half of the roadbed width is taken for calculation and model establishment, as shown in the attached figure. Figure 6 As shown in the figure, the layers from top to bottom are roadbed, subgrade fill, collapsible loess (waterlogged), and undisturbed loess (waterlogged). Both subgrade fill and collapsible loess are artificially filled loess. Whether loess is waterlogged is determined by determining if the pore water pressure of waterlogged loess is greater than zero, while the pore water pressure of unwaterlogged loess is less than or equal to zero. The stratum weight input in the analysis is the roadbed weight.

[0183] Then, input the measured compression modulus value obtained by static penetration, fit the curve of compression modulus and vertical depth, and obtain the relationship function between the two. Figure 7 , Attachment Figure 8 As shown, the total elastic modulus E in the figure is equivalent to the compression modulus.

[0184] Input various material parameters and other parameters into the numerical analysis software, and supplement and improve other calculation parameters; finally, perform the calculation and obtain the loess roadbed settlement as shown in the figure below. The final settlement caused by immersion is 333.46mm, the final settlement caused by local loading after immersion is 391.96mm, and the settlement caused by vehicle load is 58.5mm. Figure 9 , Attachment Figure 10 shown.

Claims

1. A method for testing and calculating loess roadbed settlement, characterized by: The method is implemented by the following steps: S1: Use the static penetration test device to conduct in-situ testing on the loess roadbed, thereby obtaining the static penetration index at different depths. The static penetration index includes the cone tip resistance q c , side wall friction f c ; S2: digging a test well around the in-situ test hole in step S1 and taking several consolidation samples at different depths; S3: Measure the compression modulus E of each consolidated specimen under a specified load s , the compression modulus E s It is obtained by formula (1); Where, P i is the specified load, kPa; P i+1 is the next level load, kPa; L is the height of the ring cutter, mm; I i is the settlement under the specified load, mm; I i+1 is the settlement under the next level of load, mm; S4: Establishing the static penetration index and compression modulus E s Mapping relationship: The cone tip resistance q in step S1 is c , side wall friction f c and the compression modulus E in step S3 s Substituting into formula (2), AND s =a×q c +b×f c +c(2) Calculate the fitting proportional coefficients a, b, and c; where the compression modulus E s , cone tip resistance q c , side wall friction f c The unit is MPa; S5: Calculation of total loess roadbed settlement S: a) When the loess roadbed settlement is caused by the overburden load uniformly loaded over a large area, the total loess roadbed settlement S is calculated by formula (3); Where, the total settlement of loess roadbed S is in mm; N is the upper uniform load, in kPa; the compression modulus E is si Obtained from formula (2), unit is MPa; h i is the thickness of the i-th soil layer, in m, and n is the number of soil layers; b) When the loess roadbed settlement is caused by waterlogging, the total loess roadbed settlement S is calculated using formula (4); Where, the total settlement of loess roadbed S is in mm; N is the upper load of the submerged roadbed, in kPa; the compression modulus E is si Obtained from formula (2), unit is MPa; E' si is the compression modulus of soil before immersion settlement, in MPa; h i is the thickness of the i-th soil layer, in m, and n is the number of soil layers.

2. The method for measuring and calculating loess roadbed settlement according to claim 1, wherein: The calculation of the total loess roadbed settlement S in step S5 can be achieved by numerical analysis, which includes the following steps: ① Based on the curve of the static penetration index versus depth measured in step S1, the roadbed soil is divided into original loess and artificially filled loess; ② According to the depth distribution of original loess and artificial landfill loess, the boundary conditions were input into the numerical analysis software to establish a numerical analysis model; ③ Fitting compression modulus E si The curve between the depth and the compression modulus E is obtained when fitting the relationship function between the two. si Obtained from formula (2); ④ Calculation parameters are input into the numerical analysis model, including the stratum density, and then the calculation is performed to obtain the total loess roadbed settlement S.

3. The method for testing and calculating loess roadbed settlement according to claim 2, wherein: The division of original loess and artificial landfill loess in step ① is achieved by analyzing the cone tip resistance q c Curve of variation with depth and sidewall friction f c The depth is changed by the depth curve. When the following conditions are met, the depth range is artificial landfill loess; Condition 1: When the cone tip resistance q is within 1m depth c The curve of the change with depth at the cone tip resistance q c The number of peaks appearing in the range of 7MPa-25MPa is N, N≥2; Condition 2: Within the 1m depth range described in Condition 1, the sidewall friction f c The curve of the change of side wall friction f with depth c The number of peaks appearing in the range of 0.1MPa-0.6MPa is equal to N; Condition 3: Cone tip resistance q c The curve of the change with depth and the side wall friction f c The depth values ​​when the i-th peak appears in the depth variation curve are h i1 With h i2 , and |h i1 -h i2 |<0.2,i=1,……N。 4. The method for testing and calculating loess roadbed settlement according to claim 1, wherein: Between step S4 and step S3, first the cone tip resistance q c Curve of change with depth, side wall friction resistance f c Abnormal fluctuation points in the depth variation curve are eliminated. The elimination basis is that the cone tip resistance q appears within the depth interval of 10cm-20cm. c It suddenly increases and then suddenly decreases, thereby excluding the abnormal conditions of lens anomalies and stone anomalies; then the static penetration index of the abnormal point is replaced by the average value within the set depth interval, and the set depth interval is a depth interval with the abnormal point as the center and an interval length of 40 cm.

5. The method for testing and calculating loess roadbed settlement according to claim 1, wherein: The static penetration test device in step S1 includes a penetration power device, a measuring system, a probe rod, and a probe head; the probe head includes a frustum portion, a cylindrical portion, and an inverted cone portion arranged in sequence from top to bottom and coaxially arranged, and the vertical length of the frustum portion is greater than or equal to 50 mm, and the cone tip angle of the inverted cone portion is 40°-50°; the probe rod and the probe head are coaxially arranged, the diameter of the probe rod is 5mm-8mm smaller than the diameter of the cylindrical portion of the probe head, and the diameter of the probe rod is the same as the diameter of the small mouth end of the frustum portion of the probe head.

6. The method for testing and calculating loess roadbed settlement according to claim 5, characterized in that: The step S1 is implemented by the following steps: S1.1: assembling the static penetration test device; S1.2: leveling the penetration equipment, which includes a probe rod and a probe; S1.3: penetrating the probe rod and obtaining the cone tip resistance q using a measurement system. c Curve of change with depth, side wall friction resistance f c Curve of change with depth; S1.4: When the required depth is reached, the test ends.

7. The method for testing and calculating loess roadbed settlement according to claim 1, wherein: When excavating an exploratory well around the in-situ test hole in step S2, if the in-situ test hole is located in the center of a plain or terrace, the distance between the exploratory well and the in-situ test hole is less than or equal to 5m; if the in-situ test hole is located at the interface of a loess gully and a terrace, the distance between the exploratory well and the in-situ test hole is less than or equal to 1m; the sampling depth of the consolidation sample is greater than or equal to 1m, the soil sampling interval is 10cm-20cm, the sampling depth distribution is greater than or equal to 10 layers, and M parallel samples are set for each sampling layer, where M is a positive integer greater than or equal to 6.

8. The method for testing and calculating loess roadbed settlement according to claim 1, wherein: The compression modulus E under the specified load range in step S3 s The measurement is achieved by the following steps: S3.1: Sample processing; S3.2: Sample installation; S3.3: If the sample is a saturated sample, add water to the compression container until it is full and let it stand for 12 hours. If the water level in the compression container drops during this period, add water to the compression container again until it is full, restart the timing, and let it stand for 12 hours; If the sample is an unsaturated sample, use wet cotton yarn to surround the upper and lower permeable surfaces to prevent water evaporation; S3.4: Load, and end the test after loading to the target load; S3.5: Calculate the compression modulus E using formula (1) s .

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