CN114961751B - Method for predicting soil body displacement caused by shield tunneling in soil-rock composite stratum - Google Patents
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Abstract
The invention discloses a method for predicting soil body displacement caused by shield tunneling in a soil-rock composite stratum, which comprises the following steps: establishing a calculation model according to the stratum characteristics and the tunnel characteristics, and determining a calculation surface, a calculation depth and a calculation range; according to the characteristic that the shield penetrates through the upper soft and lower hard soil-rock composite stratum, an excavation face convergence mode is represented by an excavation face convergence mode parameter gamma; the equivalent soil loss parameter G is used to represent the soil loss, and G can be represented by the geometric clearance G p Soil body three-dimensional elastic-plastic deformation U * 3d And the radial clearance omega generated by correcting the shield construction and overexcavating is considered to be obtained by accumulation; the influence of the layered stratum above the excavation surface on deformation transmission is considered, and the main influence tangent value tan beta of the calculated depth is deduced i '; based on a random medium theory, a small amount of ground surface measured data of known sections are used for repeatedly fitting and determining calculation parameters, and then the displacement values of soil bodies of more sections of the same engineering are estimated in a mode of adjusting the eccentricity kappa of the shield, so that the risk is prejudged, and the construction is guided.
Description
Technical Field
The invention belongs to the field of geotechnical engineering, and particularly relates to a soil displacement prediction method caused by shield tunneling in a soil-rock composite stratum, which is suitable for soil-rock composite strata with soft top and hard bottom and is used for calculating earth surface and underground soil displacement values caused by shield tunnel construction.
Background
The shield is widely applied in China and is developing towards more complex projects such as large diameter, large burial depth, composite stratum and the like. In recent years, more and more shield projects tunneling in upper soft and lower hard soil-rock composite strata appear domestically, and shield tunneling in the strata is easy to cause upper soft soil overexcavation and cause larger ground surface settlement. Therefore, the method has engineering significance for developing research on the problems of soil displacement and surface subsidence caused by tunneling of the shield in the upper soft and lower hard soil-rock composite stratum.
Aiming at the problem of soil deformation caused by tunneling in a stratum with a soft upper part and a hard lower part, the conventional methods comprise an empirical method, an analytical (semi-analytical) method, numerical simulation and an indoor model test, wherein the numerical simulation is taken as a main method. Most of work mainly focuses on inverse analysis according to actually measured data aiming at an empirical method, so that a classic Peck formula is corrected, and the purpose of predicting the surface settlement is achieved. The accuracy of the numerical simulation method depends on the modeling level, the boundary conditions and the selection of parameters to a great extent, and the accuracy cannot be effectively guaranteed. The influence of the scale effect can't be avoided in the indoor model test, and comparatively sensitive to external disturbance, and the precision can't be ensured, and on the other hand, the model test needs to customize the test model according to the experimental requirement, needs to spend a large amount of time, energy and cost. The analytic method (semi-analytic) method adopts the concept of equivalent soil mass loss parameter g, can effectively analyze the ground surface settlement rule caused by tunnel construction in different projects, and has a wide application range, but most of the prior methods aim at homogeneous strata and less research on soil-rock composite strata, so that a soil mass displacement prediction method suitable for tunnel construction in upper-soft and lower-hard soil-rock composite strata needs to be provided.
In summary, the three methods of empirical method, numerical simulation and indoor model test have many disadvantages, and most of the analytical (semi-analytical) methods are directed at homogeneous strata at present, and there is no method for predicting soil displacement caused by shield construction in composite strata at present, so an effective research method needs to be provided.
Disclosure of Invention
The invention aims to provide a method for predicting soil body displacement caused by shield tunneling in a soil-rock composite stratum, and aims to solve the problems that the existing empirical method is low in applicability, difficult to control numerical simulation precision, and large amount of time, energy and cost are needed for indoor model tests.
In order to achieve the purpose, the technical scheme adopted by the invention is as follows:
a method for predicting soil body displacement caused by shield tunneling in a soil-rock composite stratum comprises the following steps:
collecting related engineering stratum parameters and shield tunnel design parameters, establishing a three-dimensional calculation model among the shield tunnel, the upper part layer covering soil and the lower part hard rock, and determining a calculation surface x 0 Calculating the depth z 0 Calculating the radius l, calculating the plane x 0 Taking the range of each l in the front and the back as a calculation range, finding out the gradient alpha angle of the RSI surface of the soil-rock interface and the change position of the gradient theta angle of the tunnel in the calculation range, and cutting the calculation range into N sections at the change positions of the alpha angle and the theta angle to obtain tan alpha and tan theta values of each section;
utilizing the convergence mode parameter gamma of the excavation surface, the excavation section P and the burial depth H of the converged section Q 1 、H 2 Representing a convergence mode of a tunnel excavation surface in actual engineering;
calculating the geometric gap G p Three-dimensional elastic-plastic deformation U of soil body * 3d Calculating a radial gap omega generated by considering shield construction deviation correction and overexcavation based on the shield eccentricity kappa, accumulating the three parts and correcting by combining the grouting filling rate delta to obtain an equivalent soil loss parameter g;
according to the calculation plane x 0 The stratum distribution and the soil body parameters are processed to obtain the calculated depth z 0 Has a major influence on the tan beta value i ′。
Based on a random medium theory, actually measured data of the displacement of the surface soil body of a certain section are known, the displacement calculated values of any point of the surface soil body are obtained by respectively superposing the surface displacements in different directions caused by shield excavation of all sections in a calculation range according to relevant parameters of the section, then the calculated values are fitted with the actually measured data, the grouting filling rate delta, the shield eccentricity kappa and the excavation surface convergence mode parameter gamma are determined by continuously adjusting the calculation parameters and repeatedly fitting, and the shield eccentricity kappa is adjusted to position the same project on a calculation surface x 0 Calculating a depth z 0 And (6) predicting the displacement value of the soil body.
Further, collecting related engineering stratum parameters and shield tunnel design parameters, and establishing a three-dimensional calculation model among the shield tunnel, the upper part layer covering soil and the lower part hard rock, wherein the three-dimensional calculation model specifically comprises the following steps:
collecting related engineering stratum parameters and shield tunnel design parameters, and establishing a three-dimensional coordinate system, wherein the tunnel axis is positioned on the xoz plane, and the excavation section burial depth is H 1 The tunneling direction is along the positive direction of the x axis and forms an angle theta with the horizontal direction; the upper part of the tunnel is provided with a plurality of layered stratums, the tunnel penetrates through a soil-rock composite stratum with soft upper part and hard lower part in the tunneling direction, the upper part of the excavation surface is a soft soil layer, and the lower part of the excavation surface is a hard rock stratum; the RSI surface is simplified into a broken line segment which forms an angle alpha with the horizontal and has the buried depth H 3 And finishing the establishment of the three-dimensional calculation model.
Further, the excavation surface convergence mode parameter gamma, the excavation section P and the burial depth H of the converged section Q are utilized 1 、H 2 The convergence mode of the tunnel excavation surface in the actual engineering is shown as follows:
in the formula: the value range of gamma is [ -1,1], and g represents the equivalent soil loss parameter.
Further, the equivalent soil loss parameter g is expressed as follows:
further, according to the calculation plane x 0 The stratum distribution and the soil body parameters are processed to obtain the calculated depth z 0 Has a major influence on the tan beta value i ', indicated as follows:
in the formula: h is i Is to calculate the depth z 0 The height from the bottom of the formation i, the depth z is calculated 0 In the stratum i (i is more than or equal to 1 and less than or equal to n), K i 、
The coefficient of the width of a settling tank of the ith stratum from top to bottom and the internal friction angle of the soil body have->
h is the burial depth of the center of the soil damage occurring area, and n is the number of strata.
Further, the earth surface displacements in different directions caused by shield excavation of all sections in the calculation range are respectively superposed to obtain earth surface displacement calculation values, and the earth surface displacement calculation values are as follows:
in the formula: b is a mixture of 1 、a 1 And b 2 、a 2 Upper and lower limits of integral, d, along the z-axis before and after convergence, respectively 1 、c 1 And d 2 、c 2 Upper and lower limits of integral, f, along the y-axis before and after convergence, respectively j 、e j (j is more than or equal to 1 and less than or equal to N) are respectively the upper limit and the lower limit of each small section, and satisfy the following conditions: a is 1 ＝H 3 、b 1 ＝H 1 -R d 、a 2 ＝H 3 、b 2 ＝H 2 -(R d -0.5g)、
tanβ i Is a depth z 0 The main influence of (A) on the tangent, H 3 For RSI surface buried depth, H 1 For digging section buried depth H 2 Depth of penetration of converged cross section, R d For the radius of the excavated surfaceXi, zeta and eta respectively represent coordinate values of the computing unit on an x axis, a y axis and a z axis, and the value range corresponds to the boundary value of the soil loss occurrence region V; x, y, and z each represent coordinate values of an arbitrary point (x, y, z).
According to the technical scheme, the invention has the beneficial effects that:
(1) The result obtained by the prediction method is matched with the actually measured data, the accuracy is high, and the method can be used for calculating the soil displacement value caused by shield construction in a soft and hard soil-rock composite stratum.
(2) When the calculation model is established, the conditions that the RSI surface fluctuates along the shield tunneling direction and the soil-rock ratio in the excavation section changes continuously are considered, the condition that a plurality of covering soil layers exist on the upper portion of the tunnel excavation surface are considered, and the condition that a certain gradient exists in the shield tunneling direction and the gradient changes is considered, so that the established mechanical model is more fit with the actual engineering condition, and the calculation result is more accurate.
(3) The method has wide applicability, can be used for different upper soft and lower hard soil and rock composite stratum engineering, can estimate the displacement values of the earth surfaces and the underground soil bodies of more sections only by acquiring related engineering data in the calculation process and performing inverse analysis and determination on the calculation parameters through the actually measured data of the earth surfaces of a few sections, is convenient for predicting the displacement values of the earth surfaces and the underground soil bodies of the sections which are not excavated in the shield construction process and performing risk prompt on the sections with larger displacement values of the soil bodies, thereby performing soil body reinforcement measures or adjusting the shield construction scheme in advance and reducing the influence of shield excavation.
(4) All calculation steps of the engineering can be realized through Matlab program programming, and when different sections, different depths and even different engineering soil body displacement values are calculated, calculation can be completed only by modifying related parameters, so that the engineering soil body displacement calculation method is convenient, practical and high in efficiency.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the invention and not to limit the invention. In the drawings:
FIG. 1 is a flow chart of a prediction method provided by an embodiment of the present invention;
FIG. 2 is a diagram of a computational model provided by an embodiment of the present invention;
FIG. 3 is a schematic diagram illustrating convergence of a shield excavation face;
FIG. 4 illustrates three exemplary tunnel excavation face convergence patterns;
FIG. 5 is a schematic view of the eccentricity of a shield tunneling machine;
FIG. 6 is a schematic diagram of shield eccentric overexcavation;
FIG. 7 is a schematic diagram of a shield over-excavation region;
FIG. 8 is a schematic representation of the propagation of the primary angle of influence (β) of the formation;
FIG. 9 is a schematic diagram of a unit excavation;
FIG. 10 is a simplified diagram of case one (Guangzhou underground pipe gallery) engineering calculation and reliability verification;
FIG. 11 is a schematic diagram of engineering calculation and reliability verification in case two (F.guan intercity railway);
fig. 12 is a simplified engineering calculation diagram and a reliability verification diagram for case three (Shenzhen subway No. 7 line).
FIG. 13 is a diagram showing a transverse surface sedimentation value under different hard rock ratio (B) conditions;
FIG. 14 is a comparison of longitudinal surface subsidence values under different hard rock ratio (B) conditions.
Description of the reference numerals: a tunnel 1; a soft soil layer 2; a hard rock layer 3; an overlying layered formation 4; designing an excavation boundary 5; actually excavating a boundary 6; an overbreak area 7.
Detailed Description
The present invention will be further described with reference to the following examples. The following examples are set forth merely to provide an understanding of the invention. It should be noted that, for those skilled in the art, it is possible to make various improvements and modifications to the present invention without departing from the principle of the present invention, and those improvements and modifications also fall within the scope of the claims of the present invention.
As shown in fig. 1, an embodiment of the present invention provides a method for predicting soil displacement caused by shield tunneling in a soil-rock composite stratum, including the following steps:
and S101, establishing a three-dimensional coordinate system according to the engineering stratum characteristics and the shield tunnel characteristics, establishing a calculation model, and obtaining stratum parameters and shield tunnel design parameters. Determining a calculation plane x according to the established calculation model 0 Calculating the depth z 0 Calculating the radius l, calculating the plane x 0 And taking the range of each l before and after the l as a calculation range, finding out the gradient alpha angle of the RSI surface and the change position of the gradient theta angle of the tunnel in the calculation range, and cutting the calculation range into N sections at the change positions of the alpha angle and the theta angle to obtain the tan alpha and tan theta values of each section.
Step S102, utilizing the convergence mode parameter gamma of the excavation surface, the excavation section P and the buried depth H of the converged section Q 1 、H 2 To show the convergence pattern of the tunnel excavation face in the actual project.
Step S103, respectively calculating the geometric clearance G p Three-dimensional elastic-plastic deformation U of soil body * 3d And considering a radial clearance omega generated by correcting and overexcavating during shield construction, and accumulating the three parts to obtain an equivalent soil loss parameter g.
Step S104, calculating the surface x 0 The stratum distribution and the soil body parameters are processed to obtain the calculated depth z 0 Has a major influence on the tan beta value i ′。
Step S105, based on the random medium theory, the actually measured data of the ground surface of a certain section is known, the ground surface displacement value is calculated according to the relevant parameters of the section through the method, then the calculated value is fitted with the actually measured data, the grouting filling rate delta, the shield eccentricity ratio kappa and the excavation surface convergence mode parameter gamma are determined through continuous adjustment of the calculated parameters and repeated fitting, and then the shield eccentricity ratio kappa is adjusted to position the same engineering on the calculated surface x 0 Calculating the depth z 0 And calculating the displacement value of the soil body.
And S106, guiding field construction according to the calculated soil displacement value of each section, so that control measures can be conveniently and timely adopted to control the soil displacement and optimize construction parameters.
Prior to the study, the following assumptions were first made: (1) The stratum along the y-axis direction is a horizontal layered stratum, and the soil quality of each layer is homogeneous, continuous and isotropic; (2) The soil loss caused by shield excavation is concentrated on a soft soil layer, the hard rock layer at the lower part does not deform, and all gaps formed by excavation are filled by grouting.
Specifically, the step S101 specifically includes:
collecting related engineering stratum parameters and shield tunnel design parameters, and establishing a three-dimensional coordinate system, wherein as shown in figure 2 (a), the tunnel axis is located on the xoz plane, and the excavation section burial depth is H 1 The tunneling direction is along the positive direction of an x axis and forms an angle theta with the horizontal plane, a plurality of layered stratums exist at the upper part of the tunnel, and the tunnel is arranged at the x position 1 ～x 4 The upper part of the excavation surface is a soft soil layer, and the lower part of the excavation surface is a hard rock layer. As can be seen from FIG. 2 (b), the RSI surface is simplified into a broken line segment, which forms an angle α with the horizontal plane and has a buried depth H 3 (ii) a And finishing the establishment of the three-dimensional calculation model. Determining a computational surface x 0 Calculating the depth z 0 Calculating the radius l, calculating the plane x 0 And taking the range of each l before and after the l as a calculation range, finding out the gradient alpha angle of the RSI surface and the change position of the gradient theta angle of the tunnel in the calculation range, and cutting the calculation range into N sections at the change positions of the alpha angle and the theta angle to obtain the tan alpha and tan theta values of each section. In the figure, the tunnel is at x 1 ～x 4 Cross the soil-rock composite stratum, within the range, the alpha angle is x = x 2 Is changed, theta angle is x = x 3 The process is changed and divided into 4 segments.
As shown in FIG. 3, the large circle represents the excavation cross-section P and has a diameter D d Center o 1 Buried depth of H 1 (ii) a The small circle represents the convergent profile Q, the center o 2 Buried depth of H 2 Since the soil quality of each layer along the y-axis direction is uniform, the center o 1 And o 2 Only a shift in the z-direction occurs. The excavation surface is divided into two layers, the upper part of the RSI surface is a soft soil layer, the lower part of the RSI surface is a hard rock layer, and the hard rock layer is filled with grouting materials in a shaded mode.
The formation parameters include the thickness h of each formation i Angle of internal friction
Burying of earth-rock interface (RSI surface)Deep H 3 The design parameters of the shield tunnel comprise the diameter D of the excavation section d Outer diameter D of tunnel segment and excavation section buried depth H 1 And the length L of the shield machine host.
The upper parameters are further explained as follows:
the x axis is along the direction of the tunnel axis, and the unit symbol is m;
the y axis is horizontally vertical to the axis direction of the tunnel, the vertical projection of the central axis of the shield coincides with the x axis, the y coordinate is the horizontal distance from the axis of the shield, and the unit symbol is m;
the z axis is along the vertical direction, the z coordinate is the depth below the earth's surface, and the unit symbol is m;
H 1 、H 2 、H 3 respectively as shield excavation section P center o 1 The depth of penetration (i.e. the depth of penetration of the tunnel axis), the centre o of the convergent rear section Q 2 The burial depth of the earth-rock interface (RSI surface) is m;
D d the unit symbol is m for the diameter of the excavated section;
the alpha angle and the theta angle are an RSI surface gradient angle and a tunnel gradient angle respectively, and the unit symbol is Degree (DEG);
specifically, the step S102 is as follows:
as shown in fig. 4, based on the random medium theory, the upper stratum soil mass loss volume should be equal to the difference between the convergent volume of the shield excavation section and the grouting filling volume of the hard rock stratum, that is, equal to the convergent volume of the excavation surface in the soft soil layer. In order to accurately calculate the displacement of the upper soil body caused by tunnel excavation, the convergence mode of the excavation surface needs to be determined. Through research, the convergence mode of soft soil on the upper part of the shield tunnel excavation surface comprises the following three typical modes: (1) equal convergence mode: the central position does not change before and after convergence, and g is an equivalent soil loss parameter (unit symbol is m) as shown in fig. 4 (a); (2) bottom tangent unequal radial convergence mode: the converged section sinks to the bottom of the excavation surface, as shown in fig. 4 (b); (3) top tangent unequal radial convergence mode: the converged section floats up to the top of the excavated surface as shown in fig. 4 (c). During the tunneling process of the shield in the upper soft and lower hard soil-rock composite stratum, the shield has the characteristic of deviating towards the soft soil layerSo that the tunneling attitude is difficult to control and upward deviation occurs; meanwhile, after the lower hard rock is excavated, the lower hard rock is slowly closed and mainly filled by slurry, and the slurry is in a flowing state for a long time and can generate buoyancy on the wrapped segment, so that the segment is upwardly displaced. In practical engineering, the convergence mode of the excavation surface is not limited to the above three modes due to the influence of the gravity of the duct piece. In the invention, in order to accurately represent the convergence mode which may occur in the tunnel, the convergence mode parameter gamma of the excavation surface is introduced, and the burial depth H of the excavation section P and the converged section Q 1 、H 2 Satisfies the following conditions:
in the formula: the range of γ is [ -1,1], and when γ =0, 1, -1, it corresponds to the excavation face convergence pattern of fig. 4 (a), 4 (b), 4 (c), respectively; when the soft soil stratum with the full section is excavated, the convergence mode of the excavation surface is close to the mode shown in fig. 4 (b), and gamma =1 is taken; along with the increase of the hard rock proportion in the excavation face, the section after convergence has a floating trend, the limit state corresponds to the mode shown in fig. 4 (c), gamma = -1 is taken, and the gamma value in the actual engineering can be reversely deduced according to the surface settlement data.
Specifically, the step S103 is as follows:
for the calculation of g, the following formula exists:
g＝G p +U * 3d +ω (2)
in the formula: g p Diameter D of excavated section d Geometric clearance (unit symbol is m) between the outer diameter D of the tunnel segment, namely G p ＝D d -D；U * 3d For the three-dimensional elastic-plastic deformation of the soil body (unit symbol is m), the present embodiment assumes U * 3d =0; omega is a radial clearance (unit symbol is m) generated by considering shield construction deviation correction and overexcavation.
As shown in fig. 5, the eccentricity of the shield machine main body is set to m, and there are two measuring methods: (1) Monitoring points are arranged around the tunnel excavation surface to measure the displacement S of each point in the vertical and horizontal directions H 、S V To calculate; (2) And measuring the eccentricity k of the shield by using a deviation correcting device to calculate the eccentricity m. Satisfies the following conditions:
in the formula: l is the length of the host machine of the shield machine; p is a shield eccentric angle; kappa is the eccentricity of the shield, and is generally 0-4% in the actual engineering.
As shown in fig. 6, the shield is excavated according to the designed excavation boundary, and an overexcavation region (shaded in the figure) is formed around the original excavation boundary under the influence of the eccentricity of the shield main body, and the shield excavation center is deviated from a point o to a point o' by taking the eccentric direction in the figure as an example. Area S of overbreak region Deflection Satisfies the following conditions:
in the formula: r d The radius of the excavation surface; the q angle has q = arccos (m/2R) d )。
Since the eccentric direction of the shield is dynamically changed in the excavation process, in order to comprehensively represent the thickness of the dynamic gap, the uniform treatment is performed by Zhucaihui and the like, as shown in fig. 7, the gap is assumed to be uniformly distributed around the shield shell, the area of the overbreak gap is equivalent to an annular area (shaded part) larger than the shield shell, and the outer diameter of the annular area is R d ', since the uniform thickness is Δ, there are:
by combining equation (4) and equation (5), we can obtain:
then ω satisfies:
in consideration of the filling effect of the backfill grouting on the gap, equation (2) is modified as follows:
g＝(1-δ)(G p +ω) (8)
in the formula: delta is the grouting filling rate, and the reverse thrust can be carried out according to the surface subsidence data in the actual engineering, and the value range is 60-90 percent generally.
Specifically, step S104 is as follows:
considering the condition that multiple layers of soil cover exist on the upper portion of the tunnel excavation section, the soil deformation caused by the shield in the excavation process can be diffused and transferred upwards layer by layer. According to the uniqueness of the random medium theory, the upper soil body settlement curve caused by excavation of a certain unit d zeta d eta of the stratum is unique, so that the settlement curve deduced layer by layer from the tunnel excavation layer upwards sequentially is consistent with the actual settlement curve. Similarly, the main influence angle β of the multi-layer formation can also be derived by upward transmission layer by layer. As shown in FIG. 8, the upper and lower strata have a thickness h 1 And h 2 Assuming that the center and the buried depth of the soil damage occurrence region are h (h = h) 1 +h 2 ) D ζ d η of the deformation unit of (a) has a primary angle of influence of the formation formed in the lower formation of β 2 After which the deformation continues to be transferred upwards, the formation formed in the upper strata having a prevailing angle of influence beta 1 Geometrically satisfying:
similarly, the n strata main influence angles β satisfy:
in the formula: h is i 、β i (i =1,2 · · n) is the height of the ith formation from top to bottom and the major formation influence angle, in that order.
The Han, li Ning establishes a connection between the random medium theory and the Peck formula, namely:
by substituting formula (11) for formula (10), it is possible to obtain:
in the formula: k is i 、
Is the width coefficient of a settling tank of the ith stratum from top to bottom and the internal friction angle of the soil body and has a->
Tan beta calculated by the formula (12) is a main formation influence tangent value at the earth surface, and can be further popularized to a random calculation depth z above the unit d zeta d eta, and if the calculation depth is positioned in a formation i (i is more than or equal to 1 and less than or equal to n), the main formation influence tangent value tan beta at the depth z is calculated i ' satisfy:
in the formula: h is i ' is the height of the calculated depth z from the bottom of the formation i.
For the calculated depth z 0 Has a major influence on the tan beta value i ', will z 0 Can be obtained by calculation after substituting the formula (13).
Specifically, step S105 specifically includes the following steps:
the random medium theory is proposed by Litwiniszyn, and the theory starts from a probability statistics theory, and the influence of excavation on the surrounding soil body is equivalent to the sum of the excavation influences of infinite micro units. As shown in FIG. 9, a calculation unit with the burial depth of eta is selected, the volume of the calculation unit is d ξ d ζ d eta, and the excavation unit is completely excavatedDisplacement value dU of upper arbitrary point (x, y, z) soil body in all directions caused by collapse x 、dU y 、dU z Comprises the following steps:
in the formula: d xi, d zeta and d eta are respectively integral units in the directions of an x axis, a y axis and a z axis, r (z) is an influence radius in the z direction, and r (z) = (eta-z)/tan beta i '; because the calculation unit needs to perform integration in the soil loss occurrence region V subsequently, the value range of η is in the upper and lower boundaries of the soil loss occurrence region V in the burial depth direction.
And in the convergence volume of the soft soil layer, integrating the soil displacement generated by all the soil units to obtain the total soil displacement caused by tunnel excavation. The soil loss occurrence area V meets the following requirements:
V＝V P -V Q -V S (17)
in the formula: v P Is the volume of the excavated section V Q Is the volume of the cross section after convergence, V S And the grouting filling volume of the hard rock stratum is obtained.
Let x = x 0 For calculating the section at will, in order to obtain the displacement value of the soil body at any depth in the section, the calculation is carried out with x = x 0 In the central, two-sided influence range l, and in the range (x) 0 -l,x 0 + l), there may be a change point of the angle θ or angle α as described above (e.g., point a in fig. 2) 3 、A 2 ) Or the intersection of the RSI surface with the upper and lower tunnel boundaries (e.g., point a in fig. 2) 1 、A 4 ) At these locations, a cross-sectional cut is made to divide the whole (x) 0 -l,x 0 + l) the study period was divided into N small segments. The random medium theory has a superposition principle, so that the soil deformation caused by the excavation of each small segment of shield can be superposed. Due to x 0 The selection of the point (x, y, z) is arbitrary, so that the soil displacement U of any point (x, y, z) in all directions can be obtained x 、U y 、U z Respectively as follows:
in the formula: b 1 、a 1 And b 2 、a 2 Upper and lower limits of integral, d, along the z-axis before and after convergence, respectively 1 、c 1 And d 2 、c 2 Upper and lower limits of integral, f, along the y-axis before and after convergence, respectively j 、e j (j is more than or equal to 1 and less than or equal to N) are respectively the upper limit and the lower limit of each small section, and satisfy the following conditions: a is a 1 ＝H 3 、b 1 ＝H 1 -R d 、a 2 ＝H 3 、b 2 ＝H 2 -(R d -0.5g)、
tanβ i Is a depth z 0 The main influence tangent value of (d); xi, zeta and eta respectively represent coordinate values of the computing unit on an x axis, a y axis and a z axis, and the value range corresponds to the boundary value of the soil loss occurrence area V; x, y, and z represent coordinate values of an arbitrary point (x, y, z).
On the basis of the step S105, the calculated parameters (including the grouting filling rate δ, the shield eccentricity κ and the excavation face convergence mode parameter γ) may be repeatedly fitted by using the actually measured surface subsidence data of the known cross section, and then used to calculate surface or underground soil displacement values of more other cross sections. The method comprises the following specific steps: (1) The method comprises the steps of knowing actual ground surface measurement data of a certain section, calculating ground surface displacement values according to relevant parameters of the section by the method, fitting the calculated values with the actual measurement data, and determining grouting filling rate delta, shield eccentricity kappa and excavation surface convergence mode parameter gamma by continuously adjusting the calculated parameters and fitting repeatedly; (2) As the hard rock ratio of other sections of the same engineering is possibly different, the shield eccentricity kappa needs to be adjusted, and the specific adjustment rule can refer to the result (the change relation between the shield eccentricity kappa and the hard rock ratio) obtained by the reverse analysis of the known section of the engineering; (3) And predicting the displacement value of the earth surface or the underground soil body of other sections of the same project according to the adjusted shield eccentricity ratio kappa.
As shown in fig. 10, fig. 11 and fig. 12, the invention takes three domestic shield tunneling through upper soft lower hard composite stratum projects as examples to analyze cases and verify the reliability of the prediction method of the invention.
Case 1-Guangzhou certain underground comprehensive pipe gallery
Fig. 10 (a) is a schematic diagram of engineering calculation of a certain central office of Guangzhou, and fig. 10 (b) is a comparison diagram of calculation results. The stratum crossed by the engineering shield tunnel comprises: (1) miscellaneous fill, (2) silty clay, (3) silty clay, (4) strongly weathered carbonaceous limestone (soft rock), and (5) air-weathered carbonaceous limestone (hard rock). Taking 398 rings and 446 rings as research sections, firstly, carrying out back analysis on data parameters (delta, kappa and gamma) by using measured data of the 398 rings, then adjusting the shield eccentricity kappa according to hard rock distribution difference, and finally predicting the surface subsidence value of the 446 ring. The whole research range is divided into 4 sections according to the changing positions of the alpha angle and the theta angle, and the lengths of the sections from left to right are 66m, 72m, 58.5m and 63m in sequence; the tangent value tan theta of the tunnel slope angle of each section is 0; the RSI surface gradient angle tangent tan alpha of each segment is-0.022, -0.021, -0.026 and-0.024 from left to right in sequence.
The main parameters needing to be input in the Matlab program calculation process comprise two blocks, namely stratum parameters and shield tunnel parameters.
1. Parameters of the formation
The section where the 398 ring is located sequentially comprises (1) miscellaneous fill, 2) silty clay, 3) silty clay and 4) strongly weathered carbonaceous limestone (soft rock) from top to bottom, the layer thicknesses are 5m, 5m and 9.75m sequentially, and the internal friction angles of the strata are 7.8 degrees, 9.3 degrees, 25.1 degrees and 28 degrees sequentially. RSI surface buried depth H 3 22.5m, hard rock ratio B0.25.
The section where the 446 ring is located sequentially comprises (1) miscellaneous fill, 2) silty clay, 3) silty clay and 4) strongly weathered carbonaceous limestone (soft rock) from top to bottom, the layer thicknesses are sequentially 5m, 5m and 7.5m, and the internal friction angles of the strata are sequentially 7.8 degrees, 9.3 degrees, 25.1 degrees and 28 degrees. RSI surface buried depth H 3 21m, hard rock ratio B0.5.
2. Parameters of shield tunnel
398 rings corresponding to excavation section burial depth H 1 21m, diameter of excavated cross section D d 6.3m, the outer diameter D of the pipe piece is 6m, the length L of a main machine of the shield machine is 8.75m, the grouting filling rate delta is 89%, the convergence mode parameter gamma of the excavation surface is-1, and the eccentricity kappa of the shield machine is 0.01%.
446 ring corresponding excavation section buried depth H 1 21m, diameter of excavated section D d The diameter of the pipe piece is 6.3m, the outer diameter D of the pipe piece is 6m, the length L of a main machine of the shield machine is 8.75m, the grouting filling rate delta is 89%, the convergence mode parameter gamma of the excavation surface is-1, and the shield eccentricity kappa is 4%.
Case 2-Buddha guan intercity railway
FIG. 11 (a) is a schematic diagram showing the calculation of a construction of an inter-city Foguan railway, and FIG. 11 (b) is a comparison diagram showing the calculation results. The stratum crossed by the engineering shield tunnel comprises: (1) plain filling, (2) plastic powdery clay, (3) fully weathered granite, and (4) strongly weathered second-long granite (hard rock). Taking the 1322 ring and the 1346 ring as research sections, firstly, performing inverse analysis of data parameters (delta, kappa and gamma) by using the measured data of the 1322 ring, then adjusting the shield eccentricity kappa according to the hard rock distribution difference, and finally predicting the surface subsidence value of the 1346 ring. The engineering divides the whole research range into 3 sections according to the changing positions of the alpha angle and the theta angle, and the lengths of the sections from left to right are 80m, 38.4m and 40m in sequence; the tunnel slope angle tangent tan theta of each section is 0.042, 0.042 and-0.064 from left to right in sequence; the RSI surface gradient angle tangent tan alpha of each segment is 0.016, -0.013-0.018 in sequence from left to right.
The main parameters needing to be input in the Matlab program calculation process comprise two blocks, namely stratum parameters and shield tunnel parameters.
1. Parameters of the formation
The section where the 1322 ring is located sequentially comprises (1) plain filling soil, (2) plastic powdery clay and (3) completely weathered granite from top to bottom, the layer thicknesses are 5m, 6.5m and 15.05m sequentially, and the internal friction angles of the strata are 7 degrees, 17.03 degrees and 21.3 degrees sequentially. RSI surface buried depth H 3 29.74m, hard rock ratio B0.25.
The section where the 1346 ring is located sequentially comprises (1) plain filling soil, (2) plastic powdery clay and (3) fully weathered granite from top to bottom, the layer thicknesses are 6.25m, 3.75m and 17.13m in sequence, and the internal friction angles of the strata are 7 degrees, 17.03 degrees and 21.3 degrees in sequence. RSI surface buried depth H 3 29.25m, hard rock ratio B0.5.
2. Parameters of shield tunnel
The 1322 ring corresponds to the buried depth H of the excavated section 1 27.61m, diameter of excavated section D d 8.8m, the outer diameter D of the pipe piece is 8.5m, the length L of a main machine of the shield machine is 10m, the grouting filling rate delta is 75%, the convergence mode parameter gamma of the excavation surface is-1, and the shield eccentricity kappa is 2.2%.
1346 ring corresponding excavation section buried depth H 1 29.25m, diameter of excavated section D d The diameter is 8.8m, the outer diameter D of the pipe piece is 8.5m, the length L of a main machine of the shield machine is 10m, the grouting filling rate delta is 75%, the convergence mode parameter gamma of the excavation surface is-1, and the shield eccentricity kappa is 4%.
Case 3-Shenzhen subway No. 7 line
Fig. 12 (a) is an engineering calculation diagram of a Shenzhen subway No. 7 line, and fig. 12 (b) is a calculation result comparison diagram. The stratum crossed by the engineering shield tunnel comprises: (1) plain filling soil, (2) conglomerate cohesive soil, (3) completely weathered granite (soft rock), (4) strongly weathered granite (soft rock), (5) weathered limestone (soft rock), and (6) slightly weathered granite (hard rock). Taking an observation surface 1 and an observation surface 2 as research sections, firstly performing inverse analysis on data parameters (delta, kappa and gamma) by using the measured data of the observation surface 1, then adjusting the eccentricity kappa of the shield according to the hard rock distribution difference, and finally predicting the surface subsidence value of the observation surface 2. The engineering divides the whole research range into 4 sections according to the changing positions of the alpha angle and the theta angle, and the lengths of the sections from left to right are 49m, 20m, 18m and 12m in sequence; the tangent value tan theta of the tunnel slope angle of each section is 0; the RSI face gradient angle tangent tan α of each segment is-0.24, 0, 0.47, 0 in order from left to right.
The main parameters needing to be input in the Matlab program calculation process comprise two blocks, namely stratum parameters and shield tunnel parameters.
1. Parameters of the formation
The section of the observation surface 1 is sequentially provided with (1) plain filling soil and (3) completely weathered granite (soft rock) from top to bottom, the layer thicknesses are 5m and 5.8m in sequence, and the internal friction angles of the stratums are 22.6 degrees and 24 degrees in sequence. RSI surface buried depth H 3 12.6m, and a hard rock ratio B of 0.4.
The section where the observation surface 2 is located sequentially comprises (1) plain filling soil, (2) conglomerate cohesive soil and (3) completely weathered granite (soft rock) from top to bottom, the layer thicknesses are 3m, 3m and 3.7m sequentially, and the internal friction angles of the strata are 22.6 degrees, 22 degrees and 24 degrees sequentially. RSI surface buried depth H 3 10.4m, hard rock ratio B0.77.
2. Parameters of shield tunnel
Excavation section buried depth H corresponding to observation surface 1 1 12m, diameter of excavated section D d 6.4m, the outer diameter D of the pipe piece is 6m, the length L of a main machine of the shield machine is 8.75m, the grouting filling rate delta is 86.8%, the convergence mode parameter gamma of the excavation surface is-1, and the eccentricity kappa of the shield machine is 0.01%.
Excavation section buried depth H corresponding to observation surface 2 1 12m, diameter of excavated section D d 6.4m, the outer diameter D of the pipe piece is 6m, the length L of a main machine of the shield machine is 8.75m, the grouting filling rate delta is 86.8%, the convergence mode parameter gamma of the excavation surface is-1, and the eccentricity kappa of the shield machine is 4%.
As shown in the figures 10, 11 and 12, the measured data points of each project are uniformly distributed on two sides of the theoretical calculation curve, the method has high coincidence degree of the predicted values and the measured data, and the reliability of the method is verified. The method has certain accuracy in calculating the soil displacement value caused by the shield crossing the upper soft and lower hard soil-rock composite stratum, and can be used for analyzing the soil displacement value of each section of an unset section, so that corresponding reinforcement measures can be taken in advance for some sections with larger soil displacement, or the shield construction process or construction route can be adjusted in a targeted manner, the influence of shield construction on the surrounding environment is reduced, and the method has certain significance in guiding the actual engineering design.
Fig. 13 shows the comparison of the lateral surface settlement values under different hard rock ratio (B) conditions. With the Foguan intercity railway engineering as background, part of parameters are adjusted as follows: h 1 The method comprises the steps of =25m, delta =80%, k =2%, gamma =1, tan alpha =0 and tan theta =0, sequentially taking the hard rock ratio (B) as 0, 0.2, 0.4, 0.6 and 0.8, respectively calculating the horizontal and vertical surface subsidence values under different hard rock ratios, and being noted that the hard rock ratio B is the ratio of the thickness of the hard rock layer to the excavation diameter in the excavation section and has the following characteristics that
This calculation case holds H 1 Unchanged, with adjustment of hard rock ratio B, H 3 The correspondence will change. As shown in fig. 13, the horizontal surface subsidence value is significantly affected by the hard rock ratio, and as the hard rock ratio increases, the surface subsidence value decreases as a whole, the subsidence tank becomes shallower, but the decrease of the subsidence value decreases gradually; when the hard rock ratio is 0, 0.2, 0.4, 0.6 and 0.8 in sequence, the width of the settling tank is gradually reduced, and the settling deformation is more centralized.
FIG. 14 is a graph showing the longitudinal surface sedimentation value comparison under different hard rock ratio (B) conditions. The longitudinal surface subsidence value is obviously influenced by the hard rock ratio, the surface subsidence value is reduced along with the increase of the hard rock ratio, and the reduction amplitude is gradually reduced; the influence of the shield on the deformation of the earth surface mainly starts from about 35m in front of the cutter head (the sedimentation value is about 1% of the final sedimentation value), and increases until about 40m behind the cutter head reaches stability (the sedimentation value is about 99% of the final sedimentation value); the longitudinal settlement curve of the earth surface changes violently in the range of [ -20m,20m ], and the settlement change amount accounts for about 80% of the final stable value, which means that the region of the earth surface, which is most influenced by shield excavation, is located in the region of about 20m in front of and behind the cutter head; when the hard rock ratio is 0, 0.2, 0.4, 0.6 and 0.8 in sequence, the proportion of the sedimentation variation in the range of [ -20m,20m ] to the final sedimentation value is 74.6%, 77.7%, 79.7%, 81.6% and 83.7% in sequence, which shows that the longitudinal sedimentation variation interval is more concentrated and the influence range is reduced as the hard rock ratio is increased. By combining the above, the rule reflected by the calculation result of the method is similar to the research conclusion obtained by the army and the like (2018) and the Liu Chongqing and the like (2018), and the reliability of the method is laterally verified.
The invention relates to three engineering cases which come from the thesis of settlement analysis and prevention and control measures of upper soft and lower hard strata by shield construction [ J ] Guangdong civil engineering and construction, 2019,26 (9): 43-47.", the thesis of Zhongli, zhang Mengxi, wangwei, and the like. Most parameter values come from the case itself, and a few parameters are reasonably determined according to actual engineering experience.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and amendments can be made without departing from the principle of the present invention, and these modifications and amendments should also be considered as the protection scope of the present invention.
Claims (6)
1. A method for predicting soil body displacement caused by shield tunneling in a soil-rock composite stratum is characterized by comprising the following steps:
collecting related engineering stratum parameters and shield tunnel design parameters, establishing a three-dimensional calculation model among the shield tunnel, the upper part layer covering soil and the lower part hard rock, and determining a calculation surface x 0 Calculating the depth z 0 Calculating the radius l, calculating the plane x 0 Taking the range of each l before and after as a calculation range, finding out the gradient alpha angle of the RSI surface of the soil-rock interface and the change position of the gradient theta angle of the tunnel in the calculation range, and cutting the calculation range into N sections at the change positions of the alpha angle and the theta angle to obtain tan alpha and tan theta values of each section;
utilizing the convergence mode parameter gamma of the excavation surface, the excavation section P and the buried depth H of the section Q after convergence 1 、H 2 Representing a convergence mode of a tunnel excavation surface in actual engineering;
calculating the geometric gap G p Soil body three-dimensional elastic-plastic deformation U * 3d Calculating a radial gap omega generated by considering shield construction deviation correction and overexcavation based on the shield eccentricity kappa, accumulating the three parts and correcting by combining the grouting filling rate delta to obtain an equivalent soil loss parameter g;
according to the calculation plane x 0 The stratum distribution and the soil body parameters are processed to obtain the calculated depth z 0 Has a major influence on the tan beta value i ′；
Based on a random medium theory, the actually measured displacement data of the surface soil body of a certain section is known, the surface displacements in different directions caused by shield excavation of all sections in a calculation range are respectively superposed according to relevant parameters of the section to obtain a displacement calculation value of any point of the surface soil body, then the calculation value is fitted with the actually measured data, the grouting filling rate delta, the shield eccentricity ratio kappa and the excavation surface convergence mode parameter gamma are determined by continuously adjusting the calculation parameters and repeatedly fitting, and then the shield eccentricity ratio kappa is adjusted to position the same project on a calculation surface x 0 Calculating the depth z 0 And (6) predicting the displacement value of the soil body.
2. The method for predicting the soil displacement caused by shield tunneling in the soil-rock composite stratum according to claim 1, wherein relevant engineering stratum parameters and shield tunnel design parameters are collected, and a three-dimensional calculation model among the shield tunnel, the upper layer covering soil and the lower hard rock is established, specifically:
collecting related engineering stratum parameters and shield tunnel design parameters, and establishing a three-dimensional coordinate system, wherein the tunnel axis is positioned on the xoz plane, and the excavation section burial depth is H 1 The tunneling direction is along the positive direction of an x axis and forms an angle theta with the horizontal direction; the upper part of the tunnel is provided with a plurality of layered stratums, the tunnel penetrates through a soil-rock composite stratum with soft upper part and hard lower part in the tunneling direction, the upper part of the excavation surface is a soft soil layer, and the lower part of the excavation surface is a hard rock stratum; will be provided withThe RSI surface is simplified into a broken line segment which forms an angle alpha with the horizontal and has the buried depth H 3 And completing the establishment of the three-dimensional calculation model.
3. The method for predicting soil body displacement caused by shield tunneling in soil-rock composite stratum according to claim 1, characterized in that the excavation face convergence mode parameter γ, the excavation section P and the buried depth H of the section Q after convergence are utilized 1 、H 2 The convergence mode of the tunnel excavation surface in the actual engineering is shown as follows:
in the formula: the value range of gamma is [ -1,1], and g represents an equivalent soil loss parameter.
4. The method for predicting soil body displacement caused by shield tunneling in the soil-rock composite stratum according to claim 1, wherein an equivalent soil body loss parameter g is expressed as follows:
5. the method for predicting the soil displacement caused by shield tunneling in the earth-rock composite stratum according to claim 1, wherein the method is characterized in that the method is carried out according to a calculation plane x 0 The stratum distribution and the soil body parameters are processed to obtain the calculated depth z 0 Has a major influence on the tan beta value i ', indicated as follows:
in the formula: h is a total of i Is to calculate the depth z 0 The height from the bottom of the stratum i, the depth z is calculated 0 In the stratum i (i is more than or equal to 1 and less than or equal to n), K i 、
The coefficient of the width of a settling tank of the ith stratum from top to bottom and the internal friction angle of the soil body have->
h is the burial depth of the center of the soil damage occurring area, and n is the number of strata.
6. The method for predicting the soil displacement caused by shield excavation in the earth-rock composite stratum according to claim 1, wherein the earth surface displacements in different directions caused by shield excavation of all sections in the calculation range are respectively superposed to obtain a displacement calculation value of any point of the earth surface soil, and the method comprises the following specific steps:
in the formula: b is a mixture of 1 、a 1 And b 2 、a 2 Upper and lower limits of integral, d, along the z-axis before and after convergence, respectively 1 、c 1 And d 2 、c 2 Upper and lower limits of integral, f, along the y-axis before and after convergence, respectively j 、e j (j is more than or equal to 1 and less than or equal to N) are respectively the upper limit and the lower limit of each small section, and satisfy the following conditions: a is a 1 ＝H 3 、b 1 ＝H 1 -R d 、a 2 ＝H 3 、b 2 ＝H 2 -(R d -0.5g)、
tanβ i Is a depth z 0 The main influence of (A) on the tangent, H 3 For RSI surface burial depth, H 1 For digging section buried depth, H 2 Depth of penetration of converged cross section, R d In order to excavate the surface radius, xi, zeta, eta respectively represent the coordinate value on x-axis, y-axis, z-axis of the computational unit, the value range corresponds to the boundary value of the soil mass loss occurrence area V; x, y, and z represent coordinate values of an arbitrary point (x, y, z). />
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