A method for distinguishing the components of surface settlement during shield construction in underconsolidated soft soil areas

Abstract

The present invention provides a method for distinguishing the composition of surface settlement caused by shield construction in underconsolidated soft soil areas. The method first selects a monitoring section containing an underconsolidated soft soil layer in the shield line, and then obtains, through monitoring, a settlement change curve over time, a section settlement curve, and a settlement rate change curve for a long period of time after the shield machine passes through the section. Then, based on the morphology of the three curves, it is judged whether the settlement caused by shield construction has been gradually completed, while underconsolidation settlement continues. The present invention provides a method for judging whether the settlement caused by shield construction is completed based only on the long-term settlement monitoring curve of the monitoring section during shield construction without studying the settlement law of the underconsolidated soft soil area itself in advance. This greatly improves the accuracy and reliability of calculating the surface settlement value caused by shield construction, and reduces the manpower, material resources and time required to study the relationship between surface settlement caused by shield construction and settlement of the underconsolidated stratum itself.

Description

Technical Field

[0001] The invention belongs to the field of settlement analysis of shield construction in civil engineering, and in particular relates to a method for distinguishing surface settlement components of shield construction in underconsolidated soft soil areas. Background Art

[0002] With the continuous development of urbanization, underground space construction has received more and more attention. As a major focus of underground space construction, subway construction is facing the problem of increasingly tight urban land resources, which inevitably leads to poor geological conditions such as soft soil when planning the route. Shield tunnel construction technology is widely used in subway tunnel construction in soft soil areas due to its many advantages such as high degree of mechanization, fast and safe construction, and little interference with the surrounding environment. [1] .

[0003] Although shield construction causes less disturbance to the surrounding strata than other tunnel construction methods, it will inevitably cause surface subsidence in soft soil areas. At the same time, due to factors such as engineering construction, transportation, groundwater extraction, or the recent filling of the site during urban development, the soft soil area itself may experience continuous large-scale subsidence, which is also manifested as the characteristics of underconsolidated soft soil strata. Many scholars at home and abroad have conducted relevant research on shield construction, most of which focus on surface subsidence caused by shield tunnel construction alone, and few have analyzed the underconsolidation characteristics of the soft soil area itself. [1～4] Related research shows that shield construction in underconsolidated soft soil areas will cause long-term consolidation settlement, and there will also be large-scale settlement of the stratum itself. [5-7] .

[0004] In existing research, surface settlement during shield construction is generally considered to be caused by shield construction, which can be divided into two parts: instantaneous settlement caused by stratum loss and consolidation settlement caused by the growth and dissipation of excess pore water pressure due to construction disturbance.

[0005] However, these two major components do not include any analysis of the possible incomplete consolidation settlement of the construction site itself. That is, when shield construction is used in underconsolidated soft soil areas, the surface settlement obtained from actual tests should also include a third part - the large-scale consolidation settlement of the underconsolidated soft soil itself. Therefore, when shield construction is used in underconsolidated soft soil areas, the total surface settlement can be divided into two parts according to the cause: the first part is the settlement caused by shield construction, including instantaneous settlement and consolidation settlement; the second part is the settlement caused by underconsolidation of the stratum. That is:

[0006] S 总 =S 施工 +S 地层 =S 瞬时 +S 固结 +S 地层

[0007] Where: S 总 is the total soil settlement in the field test; S 施工 is the soil settlement caused by shield construction, which is divided into instantaneous settlement S caused by stratum loss 瞬时 and consolidation settlement S caused by disturbance 固结 ;S 地层 It is the large-scale soil settlement of the stratum itself caused by underconsolidation in soft soil areas. The settlement rate for the entire site should be basically consistent or close.

[0008] In the existing research on surface settlement caused by shield construction, the Peck formula [3] It is recognized as one of the more effective methods. Peck collected a large amount of tunnel settlement data and conducted statistical analysis, and concluded that the cross-sectional undrained surface settlement caused by stratum loss during tunnel construction (the plane perpendicular to the shield axis) conforms to the Gaussian distribution. The prediction formula is as follows:

[0009]

[0010] Where i is the distance from the tunnel axis to the inflection point, y is the horizontal distance from the surface settlement calculation point to the axis, S max is the maximum displacement of the axis corresponding to the ground surface.

[0011] Qu Jili et al. [8-9] Based on the Peck formula, the equivalent settlement tank method was adopted to comprehensively consider the consolidation settlement; Zhang Zhongmiao et al. [10-11] Through field measurements and analysis, it is believed that consolidation settlement occurs during slurry shield construction, but the cross-section also has a trough-shaped distribution or a nearly trough-shaped distribution (the maximum value may slightly deviate from the axis). The Peck formula can still be used for a good fit, and the turning point of the curve of the change in settlement velocity with the time of shield tail departure is taken as the dividing time point between stratum loss settlement and consolidation settlement, which is recommended to be 4 to 8 days after the shield tail leaves. Liang Rongzhu et al.

[12] Zhang Zhongmiao further proposed the “v i Using the "velocity method" and "fitting straight line method" analysis, the settlement rate is used to divide the instantaneous settlement caused by shield construction into consolidation settlement, and the time boundary is determined to be 8.5 to 12 days after the shield tail leaves. However, existing technologies cannot distinguish between surface settlement caused by construction and settlement of underconsolidated soft soil strata themselves.

[0012] [1]Mair R J.Tunnelling and geotechnics:new horizons[J].Géotechnique,2008,58(9):695-736.

[0013] [2]Vu MN, Broere W, Bosch J.Volume loss in shallow tunnelling[J].Tunnelling&Underground Space Technology Incorporating Trenchless TechnologyResearch,2016,59:77-90.

[0014] [3]Peck R B.Deep excavation and tunneling in soft ground[C] / / State of the Art Report.Proceedings of 7th International Conference on Soil Mechanicsand Foundation Engineering Mexico City:[sn], 1969

[0015] [4]Lee KM,Ji HW,Shen CK,et al.Ground Response to the Construction of Shanghai Metro Tunnel-Line 2.[J].Soils&Foundations,1999,39(3):113-134.

[0016] [5] Liu Songqiao. Reconsolidation of disturbed soft soil strata and its impact on subway tunnels[D]. Tongji University, 2007.

[0017] [6] Xiao Qin, Liu Songqiao. Analysis of reconsolidation settlement of disturbed strata during shield construction[J]. Underground Engineering and Tunneling, 2007, (03): 40-43+61.

[0018] [7] Xu Yeshuang, Ma Lei, Shen Shuilong. Analysis of surface settlement factors caused by urbanization in Shanghai [J]. Rock and Soil Mechanics, 2011, (S1): 578-582.

[0019] [8] Qu Jili, Xu Yingzi, Analysis of surface transverse settlement trough caused by shield construction [J]. Rock and Soil Mechanics, 2006(02): pp. 313-316+322

[0020] [9] Qu Jili. Study on long-term ground settlement caused by shield construction[D]. Tongji University, 2002.

[0021]

[10] Lin Cungang, Wu Shiming, Zhang Zhongmiao, et al. Analysis and prediction of ground settlement caused by slurry shield tunnel construction [J]. Civil Engineering, Architecture and Environmental Engineering, 2012, (05): 25-32.

[0022]

[11] Zhang Zhongmiao, Lin Cungang, Wu Shiming, et al. Case study of ground consolidation settlement caused by slurry shield construction [J]. Journal of Zhejiang University (Engineering Edition), 2012, (03): 431-440.

[0023]

[12] Liang Rongzhu et al., Settlement limit of shield construction in soft soil area[J]. Journal of Zhejiang University (Engineering Edition), 2014(07): pp. 1148-1154+1201. Summary of the Invention

[0024] The purpose of the present invention is to solve the technical defect in engineering practice that the monitoring data during shield construction cannot be used to distinguish between surface settlement caused by construction and settlement of underconsolidated soft soil layers themselves. A method with practical value and rationality for distinguishing the composition of surface settlement during shield construction in underconsolidated soft soil areas is proposed. The method is suitable for underconsolidated soft soil areas and can distinguish the composition of total surface settlement during shield construction by using only three curves.

[0025] To achieve the purpose of the present invention, the present invention provides a method for distinguishing the composition of surface settlement during shield construction in underconsolidated soft soil areas. The method distinguishes the composition of surface settlement based on three curves obtained during the construction phase: a settlement change curve of a measuring point over time, a settlement trough, and a settlement rate trough. The method comprises the following steps:

[0026] Determine the soil distribution of the site where the shield excavation project is located;

[0027] Arrange monitoring sections to obtain the time-varying settlement curve and surface settlement curve of the section during the excavation process. According to existing theories, the shape of the surface settlement curve should conform to the Gaussian distribution, also known as the trough distribution. Therefore, the settlement curve is referred to as the settlement trough in this invention.

[0028] Based on the above steps, after the cutterhead reaches the monitoring section, the section is monitored for a long time. According to the measured data of each measuring point, a curve of the settlement change of each measuring point over time is drawn;

[0029] Based on the measured data, draw the sedimentation trough at each time node and place it in the same coordinate system;

[0030] The sedimentation rate is defined as the sedimentation increment between two adjacent tests divided by the time interval. Based on the measured data, a "sedimentation rate tank" is drawn in the same way as a sedimentation tank.

[0031] Based on the series of graphs obtained in the above steps, the settlement caused by shield construction and the settlement of underconsolidated soft soil strata themselves can be distinguished by analyzing the characteristics of the graphs.

[0032] The method of the present invention can utilize the settlement curves of each measuring point measured by the shield monitoring section to distinguish the settlement caused by shield construction from the settlement of underconsolidated soft soil itself.

[0033] As a further solution of the present invention:

[0034] Because this method is suitable for distinguishing the surface settlement caused by shield construction from the settlement of underconsolidated soft soil strata themselves, the distribution of underconsolidated soft soil strata during shield tunneling should be ascertained before using this method. (Draw a stratum distribution profile, see Figure 1 )

[0035] As a further solution of the present invention: when arranging monitoring sections, the number of monitoring sections can be determined according to the actual situation of the engineering site, and its purpose is to fully obtain the settlement of the underconsolidated soft soil layer. When arranging the measuring points, starting from the central axis of the shield tunnel, arrange them on both sides (such as Figure 2 The number of measuring points for a single section is determined by the accuracy requirements, and the sedimentation tank can be drawn based on the measuring point data.

[0036] As a further solution of the present invention: because surface settlement is a process with a long time span, the monitoring of the monitoring section needs to be carried out for a long time. Generally, monitoring starts when the shield machine excavation face is about to be reached, and stops when the surface settlement is basically completed, that is, the settlement rate is close to "0".

[0037] During shield construction, the total settlement should include two parts: ① surface settlement caused by construction and ② settlement of the underconsolidated soft soil layer itself. The calculation formula is as follows:

[0038] S 总 =S 施工 +S 地层 =S 瞬时 +S 固结 +S 地层

[0039] Where: Stotal is the total soil settlement during the field test; Sconstruction is the soil settlement caused by shield construction, which is divided into instantaneous settlement due to stratum loss (Sinstantaneous) and consolidation settlement due to disturbance (Sconsolidation); Sstratum is the large-scale soil settlement of the stratum itself caused by underconsolidation in soft soil areas. The settlement rates should be basically consistent or similar for the entire site.

[0040] The present invention believes that the settlement of the underconsolidated soft soil stratum itself is a kind of overall settlement. Therefore, after the settlement caused by construction is completed, only the stratum itself settles. The three curves should have the following characteristics: the settlement change curve with time is a straight line with an approximately constant slope; the position of the settlement trough moves downward as a whole in the coordinate system over time, while the shape remains unchanged; the settlement rate trough is a straight line, and the settlement rate value gradually approaches "0".

[0041] The graph of the stratum self-subsidence has the above characteristics. Therefore, according to the time nodes when these graph characteristics appear, it is possible to judge whether the settlement caused by construction is completed and only the stratum self-subsidence occurs.

[0042] As a further solution of the present invention: based on the results obtained from long-term monitoring, three curve graphs used for analysis are drawn, namely the sedimentation change curve over time, the sedimentation tank, and the sedimentation rate tank.

[0043] Among them, when drawing the curve of settlement changing with time, the horizontal axis is time and the vertical axis is the settlement of the measuring point. A curve is drawn for each measuring point and placed in the same rectangular coordinate system; according to the engineering geological characteristics of underconsolidated soft soil areas, after the settlement caused by shield construction is completed, the settlement of the underconsolidated soft soil layer itself continues. The growth rate of the first settlement will gradually decrease, while the second settlement is an approximately uniform settlement. According to the above characteristics, in the stable settlement stage, the shape of the settlement changing with time curve should be: the first section is a curve with a gradually decreasing absolute value of the slope, and after a certain time node, it becomes an approximate straight line with a slope that is almost constant.

[0044] When the settlement variation curve of a certain measuring point becomes a straight line with a slope close to constant at a certain time node, it is considered that the settlement caused by construction is basically completed, and the subsequent settlement is mainly caused by the overall settlement of the underconsolidated stratum itself. Before it becomes an approximate straight line, the settlement is mainly caused by shield construction, and the proportion of settlement caused by the stratum itself is small and can be ignored.

[0045] When plotting the settlement troughs at each time point, the horizontal axis of the trough represents the distance from the measuring point to the tunnel axis, and the vertical axis represents the amount of settlement. Its shape conforms to a trough-shaped distribution, with the data from each measuring point on a single broken line. Settlement troughs measured at different times represent different broken lines, plotted in the same coordinate system. Based on the characteristics of surface settlement, settlement increases with time during the stable settlement phase. Therefore, the position of the settlement trough in the coordinate system shifts downward over time. Furthermore, because the settlement rate of construction-induced settlement increases with proximity to the tunnel axis, the trough curve gradually deepens in the early and middle stages of monitoring. Furthermore, the increment between settlement readings at the middle measuring point of each settlement trough is larger than that at the left and right measuring points, indicating that the settlement rate at the middle measuring point is greater than that at the left and right measuring points during this stage. In the late stages of monitoring, construction-induced surface settlement is complete, and settlement of the underconsolidated stratum continues. This type of settlement is considered global, so the position of the settlement trough in the coordinate system should shift downward over time, while its shape remains unchanged. The settlement rates at each measuring point are virtually identical.

[0046] In the drawing of the settlement rate curve, the horizontal axis is the "distance from the tunnel axis" of the measuring point, and the vertical axis is the "settlement rate". The settlement rate of surface settlement caused by construction has the characteristic that the closer to the tunnel axis, the greater its value. Therefore, in the early stage of monitoring, the settlement rate curve drawn also has a trough-shaped distribution. As time goes by, the settlement rate gradually decreases, the position of the settlement rate curve moves upward, and the trough shape gradually becomes shallower until the construction and settlement are completed. The settlement curve becomes a horizontal straight line or a straight line with a slight slope. The position of this straight line will slowly move upward with time until the settlement rate is "0".

[0047] In the early stage of monitoring, the rate of settlement caused by construction shows a pattern that the middle measuring point is large and decreases as the measuring point moves away from the tunnel axis. Therefore, the settlement rate curve (also called "settlement rate trough") also presents a trough-shaped distribution at this stage. However, as the settlement rate gradually decreases, the trough shape will gradually become shallower, and the rate difference between the middle measuring point and the measuring points on both sides will also gradually decrease, and finally become a straight line. When it becomes a straight line, it means that the stratum is settling as a whole. At this stage, it is believed that only the underconsolidated stratum itself is settling.

[0048] Compared with the existing analysis methods, the present invention can at least achieve the following beneficial effects:

[0049] The method described in the present invention can distinguish the surface settlement components of shield construction in underconsolidated soft soil areas. Without pre-determining the settlement laws and values ​​of the earth at the engineering site, it can distinguish the settlement caused by shield construction and the settlement of the underconsolidated soft soil layer itself based solely on the settlement monitoring results by reasonably specifying a monitoring plan, and obtain parameters such as the settlement amount and settlement rate of the two types of settlement respectively.

[0050] The present invention can identify the differences in settlement rates caused by different factors to determine whether the surface settlement caused by shield construction is complete, and further distinguish between under-consolidation settlement of the stratum itself and settlement caused by shield construction. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 It is the longitudinal geological profile of the test section (unit: m).

[0052] Figure 2 Distribution map of surface settlement measurement points in the test section (unit: m).

[0053] Figure 3 This is a graph showing the change of surface settlement of the test section over time.

[0054] Figure 4 This is the surface settlement trough diagram of the test section.

[0055] Figure 5 This is the surface settlement rate trough diagram of the test section.

[0056] Figure 6 A flowchart of a method provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0057] To further clarify the objectives, technical solutions, and advantages of the present invention, the example analysis of the present invention is clearly and completely described in conjunction with the accompanying drawings. It is obvious that the described embodiments are only a portion of the embodiments of the present invention, not all of them. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0058] In actual engineering, shield construction excavation may pass through under-consolidated soft soil areas. In this special stratum, surface settlement is caused by two factors: shield construction and settlement of the stratum itself. In response to this situation, the present invention provides a method for distinguishing the composition of surface settlement caused by shield construction in under-consolidated soft soil areas.

[0059] The method of the present invention has been applied in actual projects and has achieved expected results. However, in order to more clearly illustrate the implementation of the present invention, an example will be used to illustrate the implementation steps. The stratum of the shield construction site in this example is as follows: Figure 1 As shown, the bottom of the silt is completely weathered granite and the top is plain fill. Shield construction is carried out in the silt. The tunnel location and measurement point distribution are shown in Figure 2 As shown, assuming that the following graph of settlement variation with time ( Figure 3 )、Sedimentation Tanks( Figure 4 )、Sedimentation rate tank( Figure 5 ) are obtained from long-term measurements of the monitoring sections arranged in the example. The following are the specific steps of the analysis.

[0060] Taking the above project as an example, the analysis steps are as follows:

[0061] Step 1: Determine the soil layer distribution of the project site and draw a longitudinal geological profile, such as Figure 1 shown.

[0062] Step 2: Set up the monitoring section and set up measuring points on the monitoring section.

[0063] In some embodiments of the present invention, the arrangement of the monitoring sections is as follows: Figure 1 As shown in the figure, a cross section is selected along the shield tunneling path, and monitoring begins when the shield cutterhead is about to reach the cross section. During the construction process, the settlement information of this cross section can reflect the surface settlement caused by the shield construction and the settlement of the underconsolidated stratum itself.

[0064] In some embodiments of the present invention, the specific arrangement of measuring points on the monitoring section is as follows:

[0065] The arrangement of measuring points on the monitoring section is as follows: Figure 2 As shown in the figure, multiple measuring points are set at the corresponding surface positions of the monitoring section. Measuring point 1 (abbreviated as DB1) is located on the left side of the tunnel axis, 8m away from the central axis. A measuring point is arranged every 4m from left to right, with a total of 5 measuring points (DB1~DB5). Based on the surface settlement data measured at these 5 measuring points, the settlement trough and settlement rate trough can be obtained.

[0066] Step 3: Draw the following graph based on the measured data over a longer period of time: Figure 3 The settlement variation curve of each monitoring section is shown as follows: Figure 4 The settlement trough shown (the distance between the measuring point and the tunnel axis is the horizontal coordinate, and the settlement amount is the vertical coordinate), Figure 5 The settlement rate trough shown (with the distance of the measuring point from the tunnel axis as the horizontal coordinate and the settlement rate as the vertical coordinate).

[0067] According to existing theories, the shape of the surface settlement curve conforms to the Gaussian distribution, also known as the trough distribution. Therefore, the settlement curve is referred to as the settlement trough in the present invention.

[0068] Step 4: Based on the drawn curve, distinguish between the settlement caused by shield construction and the settlement of the underconsolidated soft soil layer itself by analyzing the characteristics of the graph.

[0069] In some embodiments of the present invention, the curve formed in step 3 is analyzed as follows:

[0070] The curve of surface settlement measurement points of monitoring section changing with time is as follows Figure 3As shown in the figure (where the horizontal axis test duration is zero when the shield cutter head reaches the monitoring section). It can be seen that after the shield machine has passed for a long time, the overall trend of settlement is shown.

[0071] In the later stage of the 350-day settlement test, surface settlement at each measuring point continued to occur, and the curves finally approached inclined straight lines with basically the same slope, that is, each measuring point showed a similar settlement rate, indicating that all measuring points still had a similar stable rate of settlement in the later stage, which is more in line with the law of large-scale settlement of the site, that is, large-scale settlement of the underconsolidated stratum itself.

[0072] The sedimentation tank of the monitoring section is as follows Figure 4 As shown in the figure, the surface settlement curve of the monitored cross section exhibits a distinct trough-shaped distribution, consistent with the existing distribution pattern of surface settlement caused by shield construction. After the shield machine passed through, the settlement trough curve continued to shift downward, and settlement continued to occur. The trough shape gradually deepened, and the settlement amount and settlement rate at the measuring point at the axis were greater than those at the measuring points on either side. However, after 175 days, the shape of the cross-sectional settlement trough curve gradually stabilized and remained unchanged, showing an overall downward shift, and settlement continued at a certain rate. Analysis shows that within about 5 to 6 months after the shield leaves the test section, the settlement caused by shield construction accounts for a larger proportion of the total settlement, while the settlement caused by the site's own underconsolidation accounts for a smaller proportion of the total settlement, or even can be ignored, which is manifested in the gradual development and deepening of the cross-sectional settlement trough; as time goes by, the settlement caused by shield construction gradually completes to the point where it can be ignored, while the settlement caused by the site's own underconsolidation accounts for an increasing proportion of the total settlement, which is manifested in the fact that each measuring point sinks at the same rate, the shape of the settlement trough remains unchanged, and it moves downward as a whole.

[0073] The settlement rate of the monitoring section is as follows: Figure 5 Based on existing experience and theory, the settlement rate caused by construction also conforms to a trough distribution, that is, the settlement rate at measuring points close to the axis is higher, while the settlement rate at measuring points far from the axis is lower. When construction settlement is completed and only stratum settlement occurs, the settlement rate at each measuring point remains consistent, showing an overall settlement trend.

[0074] according to Figure 5 It can be seen intuitively and obviously that the incremental sedimentation rate trough curve gradually changes from a trough curve to a straight line, and the curve value gradually decreases and approaches 0, and finally reaches relative stability.

[0075] For the monitoring section, the maximum incremental sedimentation rate trough occurs at measuring point DB3, closest to the axis, and gradually decreases from 1.1 mm / d to 0.02 mm / d 25 days after the shield tail passed through the monitoring section. Meanwhile, the sedimentation rate at measuring point DB5, farthest from the axis, decreases from 0.60 mm / d to 0.02 mm / d, and the difference between the two decreases from 0.5 mm / d to 0 mm / d, corresponding to the gradual loss of the trough shape in the rate curve. It is clear that as time passes, the surface settlement rate at the measuring point on the axis becomes increasingly close to that of the measuring points on either side, and the surface settlement rate curve gradually loses its trough shape.

[0076] Further analysis shows that the rate curve of the monitoring section begins to lose its trough shape after 225 days, and the rate curve appears and remains as a straight line; combined with Figure 4 and Figure 5 Analysis shows that 5 to 6 months after the shield machine cutterhead passed through the section, the surface showed an overall sinking trend, the settlement rates at each measuring point were basically similar, and the trough-shaped settlement caused by the shield construction had basically ended; the continued settlement increment and settlement rate at this time should be caused by the underconsolidation of the site itself, and were distributed in a linear manner in the cross section.

[0077] The present invention is applicable only when the shield construction project is located in an underconsolidated soft soil area, the shield tunnel passes through an underconsolidated soil layer, and there is both settlement caused by the shield construction and settlement of the underconsolidated soil layer itself. In such cases, the present invention can effectively distinguish the components of surface settlement.

[0078] At present, in actual shield construction projects, when measuring the surface settlement caused by shield construction, the settlement of the underconsolidated stratum itself is often ignored, or the settlement of the stratum itself is directly deducted based on the pre-determined ground settlement law and value of the area. However, in general engineering practice, it is rare to study and determine the settlement law of the area itself in advance, which easily leads to two adverse effects: first, in engineering practice, the degree of disturbance of the surrounding strata by shield construction obtained from construction tests is greater than the actual degree, and the actual settlement should exclude the underconsolidation settlement of the stratum itself; second, in scientific research, a true and reliable study of the impact of shield construction on the surrounding strata should be based on accurate field test data, so it is necessary to accurately identify and exclude the underconsolidation settlement of the stratum itself. The method of the present invention is of great significance whether in analyzing the impact of shield construction on the surrounding environment to formulate countermeasures or in scientific research on shield-induced settlement, and provides ideas and effective methods for analyzing surface settlement caused by shield construction in underconsolidated soft soil areas.

[0079] Finally, it should be noted that the present invention is not limited to the details of the exemplary embodiments described above and that the invention may be embodied in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, those skilled in the art should regard the embodiments as illustrative and non-limiting. The scope of the present invention is defined by the appended claims, not the foregoing description, and all variations within the meaning and range of equivalents of the claims are intended to be encompassed therein. Any reference sign in a claim should not be construed as limiting the claim to which it relates.

[0080] In addition, it should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A method for distinguishing the components of surface settlement during shield construction in underconsolidated soft soil areas, characterized in that: The following steps are involved: Determine the soil layer distribution at the shield excavation site; Arrange monitoring sections and set measuring points on them; When the cutterhead is about to reach the monitoring section, the monitoring section will be monitored. Based on the measured surface settlement data of each measuring point, a curve of the settlement amount of each measuring point over time will be drawn. Based on the measured data, draw the sedimentation trough at each time node and place it in the same coordinate system; Define the sedimentation rate by dividing the sedimentation increment between two adjacent tests by the time interval. Based on the measured data, draw a "sedimentation rate tank" in the same way as drawing a sedimentation tank. Based on the drawn curves, the settlement caused by shield construction and the settlement of underconsolidated soft soil strata themselves are distinguished; In the plotting of the settlement rate curve, the horizontal axis is the "distance from the tunnel axis" of the measuring point, and the vertical axis is the "settlement rate". In the early stage of monitoring, the settlement rate curve is distributed in a trough shape. As time goes by, the settlement rate gradually decreases, the position of the settlement rate curve moves upward, and the trough shape gradually becomes shallower. Until the construction and settlement are completed, the settlement curve becomes a horizontal straight line or a straight line with a slight slope. The position of this straight line will slowly move upward over time until the settlement rate reaches 0. In the early stage of monitoring, the rate of settlement caused by construction shows a pattern that the middle measuring point is large and decreases as the measuring point moves away from the tunnel axis. Therefore, the settlement rate curve in this stage also presents a trough-shaped distribution. However, as the settlement rate gradually decreases, the trough will gradually become shallower, and the rate difference between the middle measuring point and the measuring points on both sides will also gradually decrease, and finally become a straight line. When it becomes a straight line, it means that the stratum is settling as a whole. At this stage, it is believed that only the underconsolidated stratum itself is settling.

2. The method for distinguishing the surface settlement components during shield construction in underconsolidated soft soil areas according to claim 1, characterized in that: When arranging measuring points on the monitoring section, they are arranged on both sides with the central axis of the shield tunnel as the starting point.

3. The method for distinguishing the components of ground settlement during shield construction in underconsolidated soft soil areas according to claim 1, characterized in that: The monitoring points of the monitoring section are used to monitor the settlement of the section for a long time. The monitoring includes three stages: before the cutterhead reaches the section, after the cutterhead reaches the section, and after the shield tail leaves the section, until the settlement stops.

4. The method for distinguishing the components of ground settlement during shield construction in underconsolidated soft soil areas according to claim 1, characterized in that: The monitoring section is located on the shield tunneling path.

5. The method for distinguishing the components of ground settlement during shield construction in underconsolidated soft soil areas according to claim 1, characterized in that: When drawing a curve showing the change of settlement over time, the horizontal axis is time and the vertical axis is the settlement of the measuring point. A curve is drawn for each measuring point and placed in the same rectangular coordinate system. In the stable settlement stage, the shape of the curve showing the change of settlement over time should be: the first section is a curve with a gradually decreasing absolute value of the slope, and after a certain time node, it becomes an approximate straight line with a nearly constant slope.

6. The method for distinguishing the components of surface settlement during shield construction in underconsolidated soft soil areas according to claim 5, characterized in that: When the settlement-versus-time curve of a certain measuring point becomes an approximate straight line with a nearly constant slope at a certain time node, it is considered that the settlement caused by construction is basically completed, and subsequent settlement is mainly caused by the overall settlement of the underconsolidated stratum itself. Before it becomes an approximate straight line, the settlement is mainly caused by shield construction, and the proportion of settlement caused by the stratum itself is relatively small.

7. The method for distinguishing the components of ground settlement during shield construction in underconsolidated soft soil areas according to claim 1, characterized in that: When plotting the settlement troughs at each time point, the horizontal axis represents the distance from the measuring point to the tunnel axis, and the vertical axis represents the amount of settlement. The shape of the trough conforms to a trough distribution, with the data from each measuring point on a single broken line. Settlement troughs measured at different times represent different broken lines, all plotted in the same coordinate system. During the stable settlement phase, settlement increases with time, resulting in a downward shift in the coordinate system. Furthermore, because the settlement rate of construction-induced settlement increases with proximity to the tunnel axis, the trough curve gradually deepens in the early and middle stages of monitoring. Furthermore, the increment between settlement readings at the central measuring point of each trough is larger than that at the left and right measuring points, indicating that the settlement rate at the central measuring point is greater than that at the flanking measuring points during this phase. In the late stages of monitoring, construction-induced surface settlement is complete, and settlement of the underconsolidated stratum continues. This type of settlement is considered global, so the position of the trough in the coordinate system should shift downward over time, while its shape remains unchanged. The settlement rates at each measuring point are virtually identical.

8. The method for distinguishing the components of ground settlement during shield construction in underconsolidated soft soil areas according to claim 7, characterized in that: The settlement trough curve is distributed in a trough shape. During the stage when the settlement caused by construction accounts for a large proportion, because the settlement rate of the middle measuring point is greater than the settlement rate of the measuring points on both sides, the trough shape of the curve gradually deepens with the passage of time in the early and middle stages of monitoring. When the trough shape no longer deepens and shows a trend of overall downward movement and unchanged shape, it is considered that the settlement caused by construction is completed, and the continued settlement is caused by the overall settlement of the underconsolidated stratum.

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