CN111898178B

CN111898178B - Consolidation degree calculation method for layered foundation combined preloading

Info

Publication number: CN111898178B
Application number: CN201910628493.6A
Authority: CN
Inventors: 周伟; 朱晶晶; 刘益平; 任亚群; 韦华; 陈念军; 陆伟岗; 何小飞; 王志楠; 沈锦儒
Original assignee: Jiangsu Keneng Geotechnical Engineering Co ltd
Current assignee: Jiangsu Keneng Geotechnical Engineering Co ltd
Priority date: 2019-07-12
Filing date: 2019-07-12
Publication date: 2021-03-26
Anticipated expiration: 2039-07-12
Also published as: CN111898178A

Abstract

The invention discloses a consolidation degree calculation method of layered foundation combined prepressing, which adopts a method of dividing first and then combining, namely, dividing vacuum prepressing and stacking preloading which form the combined prepressing into three subjects, then using a layering method consolidation theory and a formula to calculate one by one to respectively obtain an initial value of each layering consolidation degree, a layering average consolidation degree, a layering consolidation degree contribution value and a whole layer total average consolidation degree when vacuum negative pressure, water level decline and stacking pressurization of the layered foundation are independently acted, then according to the proportions of the three in the combined prepressing, obtaining respective weights of the vacuum negative pressure, the water level decline and the stacking pressurization in the combined prepressing, and finally synthesizing the three into each layering average consolidation degree, each layering consolidation degree contribution value and the whole layer total average consolidation degree in the combined prepressing according to the weights. Or the total average consolidation degree of the whole layer when the vacuum negative pressure, the water level drop and the stacking pressurization respectively act is multiplied by the weight of each whole layer and then added to obtain the total average consolidation degree of the whole layer when the three act together.

Description

Consolidation degree calculation method for layered foundation combined preloading

Technical Field

The invention belongs to the technical field of soft soil foundation reinforcement in geotechnical engineering, and particularly relates to a consolidation degree calculation method for layered foundation combined prepressing.

Background art:

for the calculation of the consolidation degree of the consolidated layered foundation by the combined prepressing method, the stacking pressure and the vacuum pressure are mostly superposed, and then the calculation is carried out according to a single soil layer by adopting a method of a weighted average consolidation coefficient. Although the method can simplify calculation and calculate the average consolidation degree of the whole soil layer, the method cannot calculate the consolidation degree, the layered settlement and other results of each soil layer. This method neither distinguishes the difference between the stacking pressure and the vacuum pressure in the downward transfer process, nor does it relate to the difference in the degree to which they each perform in the combined action. In other methods for calculating the consolidation degree of the layered foundation, research results are more in recent years, the general theory and formula are complex, and the solution of the consolidation equation can be obtained by means of a deep and complex mathematical method. Some adopt numerical methods and some adopt analytical methods. The numerical method mainly uses a finite difference method and a finite element method, and the analytical method adopts methods of variable separation and Fourier expansion, a Lagrange interpolation method, Laplace integral transformation and the like. This is relatively complicated for designers, and is inconvenient for engineering practice. Consolidation analytical solution studies in combination with precompression are relatively rare. The combined preload is a combination of both the surcharge preload and the combined preload. Calculation of a calculation formula directly referring to conventional surcharge preloading may cause a large error. The engineering community urgently needs a special method for calculating the consolidation degree of the consolidated layered foundation by combining a pre-pressing method.

Disclosure of Invention

The invention aims to provide a consolidation degree calculation method for layered foundation combined preloading, which aims to solve the defects caused in the prior art.

A consolidation level calculation method of stratified foundation joint preloading, the method comprising the steps of:

because vacuum negative pressure can be generated in the process of combined prepressing to act in the layered foundation, the underground water level can be reduced at the same time, and the dead weight of the soil layer with the subsided buoyancy is increased. This gravity acts on the layered foundation to increase the compressive deformation. Vacuum negative pressure and soil layer water level drop are symbiotic. The two actions have different stress distribution modes, the vacuum negative pressure is of an attenuation type, the action depth is limited, the whole compression layer cannot be reached, the water level reduction is stable, and the pressure below the underground water level after the reduction is invariable. The two effects are applied in different modes, the vacuum negative pressure is applied instantly, and the water level is linearly and uniformly applied. According to the characteristics, the two working conditions cannot be calculated together and must be synthesized after being calculated respectively. Therefore, the calculation of the consolidation degree of the combined prepressing reinforced layered foundation is decomposed into the calculation of the consolidation degree under two working conditions of vacuum negative pressure (A working condition) and water level reduction (B working condition). The dump load pressurization is another function, and the stress distribution mode of the dump load pressurization is different from that of the A, B working condition, so that the dump load pressurization is called a 3 rd working condition-C working condition.

Finally synthesizing into the original combined prepressing working condition (called J working condition).

The consolidation degree calculation subject of the combined prepressing (J working condition) is decomposed into consolidation degree calculation subjects of 3 working conditions of vacuum negative pressure (A working condition), water level reduction (B working condition) and heaping pressurization (C working condition). And finally, combining the consolidation degrees of A, B, C working conditions into the consolidation degree of J working conditions. This is the core of the present invention.

Firstly, the attenuation value of each layer and the amplitude of the underground water level reduction when the vacuum degree is transmitted downwards are set.

And respectively calculating the stress values of the vacuum pressure, the water level drop pressure and the pile loading pressure at the midpoints of the layers in the foundation, and drawing A, B, C the stress distribution diagram in the foundation under the working condition.

And respectively calculating A, B, C working condition final settlement of each layer and the whole layer final settlement, and calculating A, B, C working condition contribution rate of each layer, layer weight and whole layer weight. And adding the final settlings of the layers under the A, B, C working conditions to obtain the final settlings of the layers under the J working conditions, and adding the final settlings of the whole layer under the A, B, C working conditions to obtain the final settlement of the whole layer under the J working conditions. And calculating the layering contribution rate of the J working condition according to the above.

Respectively calculating A, B, C working condition initial values of each layering consolidation degree;

and multiplying the initial value of each layering consolidation degree of the A, B, C working condition by the stress reduction coefficient of the corresponding A, B, C working condition respectively to obtain the average layering consolidation degree of the A, B, C working condition.

Multiplying the average layering consolidation degree of A, B, C working conditions by the layering contribution rate of A, B, C working conditions to obtain the contribution value of the layering consolidation degree of A, B, C working conditions;

respectively obtaining the total average consolidation degree of the whole layer under A, B, C working conditions by the sum of the contribution values of the layered consolidation degree under A, B, C working conditions;

and the total average consolidation degree of the whole layer under the condition of A, B, C is multiplied by the weight of each whole layer, and then the total average consolidation degree of the whole layer under the condition of J is obtained.

Preferably, the overall average consolidation degree of the whole layer can be obtained by the following calculation method:

respectively multiplying the layered average consolidation degree of A, B, C working conditions by corresponding layered weights and then adding the layered average consolidation degrees to obtain the layered average consolidation degree of J working conditions;

multiplying the layering average consolidation degree of the J working condition by the respective layering contribution rate of the J working condition to obtain the layering consolidation degree contribution value of each layering of the J working condition;

and obtaining the total average consolidation degree of the whole layer of the layered foundation under the J working condition by summing the contribution values of the layering consolidation degrees under the J working condition.

Preferably, the method for calculating the drainage distance includes the steps of:

distance of water discharge H_iThe distance from the bottom surface of the laminate to the top surface of the compression layer was calculated using the following formula:

in the formula: h is_mThe thickness of the mth layer soil is shown, and the unit m and the unit i are the calculated layering serial number.

Preferably, the method for calculating the full-path vertical consolidation coefficient includes the following steps:

the calculation requires distinguishing between the vertical layer and the sub-well layer.

When the ith zone is located in a shaft zone:

in the formula: c. C_vmIs the vertical consolidation coefficient of the m-th layer of soil, h_mIs the thickness of the mth layer of soil, m.

When the ith zone is located in the downhole formation:

c_wsi＝[1+μ(v_i-1)]×c_vi；

in the formula: c. C_wsiComposite vertical consolidation coefficient, cm, for the ith layer²S or m²D; mu is the ratio of the cross section area of the vertical shaft to the cross section area of the equivalent circle of the drainage vertical shaft, has no dimension and is calculated by the following formula;

ν_ithe vertical consolidation coefficient of the vertical shaft is the ratio of the vertical consolidation coefficient of the ith layered interwell soil, has no dimension and is calculated by the following formula.

v_i＝c_w/c_vi

In the formula: a. the_wIs the cross-sectional area of the shaft in cm²Or m²(ii) a A is the equivalent circular cross section area of the drainage shaft in cm²Or m²；c_wVertical consolidation coefficient of vertical shaft, cm²S or m²/d；c_viIs the vertical consolidation coefficient of the soil between the ith layering wells in cm²S or m²/d；n_wThe well diameter ratio is dimensionless and is calculated according to the following formula.

n_w＝d_e/d_w；

In the formula: d_eThe diameter of the equivalent circle of the drainage vertical shaft is cm or m; d_wDiameter of the shaft, cm or m.

Full path vertical consolidation coefficient of each layer in underground layer

Calculated using the formula:

in the formula: c. C_wsmIs the composite vertical consolidation coefficient of the mth layer in the vertical well layer, cm²/s；c_vmIs the vertical consolidation coefficient of the m-th layer soil in the underground layer, cm²S; w is the layering serial number of the lowest layer of the vertical shaft layer, and the dimension is avoided; w +1 is the layering number of the uppermost layer in the underground layer, and has no dimension.

Preferably, the calculation method of the initial value of the layering consolidation degree comprises the following steps:

working condition A-vacuum negative pressure:

the initial value of the layering consolidation degree is calculated by adopting a general expression for each layering in the vertical well layer and the underground well layer:

in the formula:

the initial value of the layering consolidation degree of the ith layering under the working condition A is dimensionless; α is a coefficient, α ═ π²/8；β_iIs the coefficient of the ith stratification, and t is the solid of vacuum negative pressureKnot length, s; wherein beta is_iAnd according to the position of the layering, calculating by adopting a formula of a layering method.

B working condition-water level drop:

in the formula:

the initial value of the layering consolidation degree of the ith layering under the working condition B is dimensionless; α is a coefficient, α ═ π²/8；β_iIs the coefficient of the ith layer; beta is a_iCalculating by adopting a formula of a layering method according to the position of the layering; t is the consolidation duration of vacuum negative pressure, s; the linear uniform loading mode of water level lowering action is replaced by an instant loading mode, and the consolidation duration is half of that of vacuum preloading consolidation.

C working condition-loading pressurization:

in the formula:

the initial value of the layering consolidation degree of the ith layering is dimensionless under the working condition C; eta_jThe load ratio of the j level load is dimensionless; t is_zAt the end of the pre-compression, the unit d, t_jThe delay time difference of the j-th level load is shown, and the unit d and k are the last level of the graded load without dimension.

Load ratio eta of j-th load_jCan be calculated using the following formula:

η_j＝Δp_j/p；

in the formula: Δ p_jAnd the j-th level load value is shown as kPa, and p is the final stacking load value, kPa.

Preferably, the coefficient β_iThe calculation method comprises the following steps:

when the stratification is in a shaft layer:

when the stratification is in the downhole layer:

in the formula: c. C_hiIs the radial consolidation coefficient of the ith layer, cm²/s；

Full path vertical consolidation coefficient, cm, for the ith layer²/s；H_iThe vertical drainage distance of the ith layer is cm; t is the consolidation duration in units of s, F_iParameters related to the well diameter ratio, well resistance and smearing influence of the ith layer are defined;

when the well foundation is ideal: f_i＝F_n；

When the well is a non-ideal well foundation: f_i＝F_n+F_si+F_ri；

In the formula: f_nThe well diameter ratio factor is used, all layers in the vertical well layer are the same, and the calculation is carried out according to the following formula:

when the well diameter ratio is n_wWhen F is not less than 15_nCan be simplified as follows:

F_n＝ln(n_w)-0.75；

F_sireflecting the influence of the i-th layer smearing disturbance, and calculating according to the following formula:

S_i＝d_si/d_w；

in the formula: k is a radical of_hi、k_siRespectively the permeability coefficients of the i-th layer of undisturbed soil and the soil in the smearing area, cm/s; d_wIs the diameter of the vertical shaft, cm; d_sIs the diameter of the smearing area, cm; s_iDiameter d of application area of ith layer_siDiameter d of shaft_wCan be taken as_i2-3. Taking a low value for medium sensitive cohesive soil and a high value for high sensitive cohesive soil;

F_rreflecting the well resistance effect, calculated as follows:

in the formula: h_iThe vertical drainage distance of the ith layer is cm; k is a radical of_wIs the vertical shaft permeability coefficient, cm/s; q. q.s_wFor water flow of vertical shaft, cm³/s；r_wIs the radius of the cross section of the shaft, cm.

Preferably, the method for calculating the breaking coefficient of the vacuum negative pressure layering stress comprises the following steps:

selecting a corresponding vacuum attenuation value according to the permeability difference of the soil layer and the permeability coefficient of the soil layer, wherein the influence depth of vacuum negative pressure is not more than 30 m;

according to the attenuation value of the vacuum negative pressure, calculating the vacuum pressure of the midpoint of each layer after attenuation, wherein the ratio of the pressure to the ground vacuum pressure is the stress reduction coefficient of the vacuum pressure, and calculating by using the following formula:

in the formula: omega_aiStress reduction for vacuum suctionCoefficient, p_i-1The vacuum pressure in kPa after the attenuation at the midpoint of the i-1 th delamination; h is_i-1、h_iThe thickness of the layers of the (i-1) th and (i) th is m; delta_i-1、δ_iVacuum pressure attenuation values of the i-1 th and i-th layers in units of kPa/m, p₀The vacuum pressure, kPa, corresponds to the vacuum degree under the film.

Preferably, the method for calculating the stratified stress reduction coefficient of the water level lowering effect includes the following steps:

and calculating the pressure generated in each layer by the water level reduction action according to the original underground water level and the predicted amplitude of the underground water level reduction. And calculated using the following formula:

ω_bi＝A_i/γ_wh_bh_i；

in the formula: omega_biReduction factor for water level lowering, A_iThe area of the ith stratified water level reduced pressure graph is kPa/m; gamma ray_wIs the water gravity, kN/m³；h_bM, the magnitude of groundwater descent; h is_iIs the thickness of the ith layer, m.

Preferably, the method for calculating the hierarchical contribution rate includes the following steps:

layered contribution ratio lambda of A working condition_aiCalculated using the formula:

layered contribution rate lambda of B working condition_biCalculated using the formula:

layered contribution rate lambda of C working condition_viCalculated using the formula:

layered contribution rate lambda of J working condition_jiCalculated using the formula:

in the formula: s'_ai、s′_bi、s′_ciDeformation amount, s, of the ith layer of foundation under A, B, C working conditions respectively_aif、s_bif、 s_cifThe final sedimentation value of the ith layer of A, B, C working conditions, cm and s respectively_af、s_bf、s_cfThe final settlement value of the whole layer under the working condition of A, B, C, cm and psi_v、ψ_sEmpirical coefficients are calculated for the settlement of the vacuum preloading and the surcharge preloading.

Preferably, according to the superposition principle of elastomer deformation, the sum of the settlement value of the layered foundation at A, B, C working condition is the settlement value of J working condition,

s_jit＝s_ait+s_bit+s_cit；

s_jt＝s_at+s_bt+s_ct；

s_jif＝s_aif+s_bif+s_cif；

s_jf＝s_af+s_bf+s_cf；

in the formula: s_jit、s_ait、s_bit、s_citRespectively representing the settlement value of the ith layer under the J, A, B, C working condition at the time t, cm; s_jt、s_at、s_bt、s_ctRespectively J, A, B, C sedimentation value of the whole layer at time t, cm; s_jif、s_aif、s_bif、s_cifThe final sedimentation value of the ith layer of J, A, B, C working conditions respectively; cm; s_jf、s_af、s_bf、s_cfThe final sedimentation value of the whole layer under J, A, B, C working conditions, cm, respectively.

Preferably, the method for calculating the final sedimentation value of the whole layer comprises the following steps:

a working condition:

the final sedimentation value of the whole layer of the compression layer under the action of vacuum negative pressure is calculated according to a special formula of a vacuum preloading method provided by the invention:

in the formula: s_afThe final sedimentation value of the working condition A is mm; s'_aThe deformation of the whole compression layer under the working condition A is mm; p is a radical of_a0The negative pressure generated by the vacuum degree under the film, kPa; psi_vThe data are empirical coefficients and are taken according to regional experience without dimension; n is the number of divided soil layers within the depth range of the compression layer; omega_aiThe stress reduction coefficient of the ith layer is zero dimension; h is_iIs the thickness of the ith layer, m; e_siThe compressive modulus of the ith layer, MPa, is calculated from the pressure section from the dead weight pressure of the soil to the sum of the dead weight pressure and the additional pressure.

Working condition B:

the final sedimentation value of the whole layer of the compression layer under the action of water level reduction is calculated according to a special formula of the vacuum preloading method provided by the invention:

in the formula: s_bfThe final sedimentation value of the working condition B is mm; s'_bThe final sedimentation value under the working condition B is mm; psi_vThe value is an empirical coefficient, has no dimension and is the same as the value of the vacuum negative pressure; n is the number of divided soil layers within the depth range of the compression layer; omega_biThe stress reduction coefficient of the ith layer is zero dimension; h is_iIs the thickness of the ith layer, m; gamma ray_wIs the water gravity, kN/m³；h_bM, the magnitude of groundwater descent; e_siThe compressive modulus of the ith layer, MPa, is calculated from the pressure section from the dead weight pressure of the soil to the sum of the dead weight pressure and the additional pressure.

C, working condition:

calculated according to a formula recommended by national standard GB50007-2011 'design code for foundation base of building'.

In the formula: s_cfIs the final settlement value of the foundation, mm; s'_cfThe deformation of the foundation is calculated according to a layering summation method, and is mm; psi_sThe empirical coefficient is calculated by settlement without dimension; determining according to regional experience, and taking values according to the national standard table according to the equivalent value of the compression modulus in the depth range of a compression layer when no regional experience exists; n is the number of divided soil layers within the depth range of the compression layer; p is a radical of_c0An additional pressure at the base bottom corresponding to the quasi-permanent combination of actions, kPa; e_siThe compressive modulus, MPa, of the i-th layer of soil below the basal surface. And calculating the pressure section from the dead weight pressure of the soil to the sum of the dead weight pressure of the soil and the additional pressure. z is a radical of_i、z_i－1The distance m from the bottom surface of the foundation to the bottom surface of the ith layer of soil and the bottom surface of the (i-1) th layer of soil;

the average additional stress coefficient from the ground to the bottom surface of the i-th layer of soil and the i-1 th layer of soil can be adopted according to the annex of the national standard.

Preferably, the method for calculating the stacking loading pressurization layering stress reduction coefficient comprises the following steps:

stress reduction coefficient omega of ith layer_ciCalculated using the formula:

in the formula: z is a radical of_i、z_i-1The distance from the bottom surface of the foundation to the bottom surfaces of the ith layer of soil and the (i-1) th layer of soil,

calculating the average additional stress coefficient h from the foundation bottom surface to the bottom surface of the i-th layer soil and the i-1 th layer soil_iIs the thickness of the ith layer of soil, m.

Preferably, the method for calculating the layering average consolidation degree comprises the following steps:

and multiplying the initial value of the layered consolidation degree of A, B, C working conditions with the layered stress reduction coefficient of A, B, C working conditions respectively to obtain the layered average consolidation degree of A, B, C working conditions.

Preferably, the method for calculating the contribution value of the layered consolidation degree comprises the following steps:

and multiplying the layered average consolidation degree of A, B, C working conditions with the layered contribution rate of A, B, C working conditions respectively to obtain a layered consolidation degree contribution value of A, B, C working conditions.

Preferably, the method for calculating the total average consolidation degree of the whole layer under the A, B, C working condition comprises the following steps:

the total average consolidation level of the whole layer of A, B, C operating conditions is calculated by respectively summing the contribution values of the layered consolidation levels of A, B, C operating conditions.

Preferably, the method for calculating the total average consolidation degree of the whole layer under the J working condition comprises the following steps:

and multiplying the total average consolidation degree of the whole layer of the A, B, C working condition by the weight of each whole layer to obtain the total average consolidation degree of the whole layer of the J working condition.

In the formula:

the total average consolidation degree of the whole layer under the working conditions of A, B, C respectively has no dimension; q_a、Q_b、Q_cA, B, C, the integral layer weight is dimensionless and is calculated according to the following formula:

in the formula: s_af、s_bf、s_cfRespectively A, B, C working condition final sedimentation value of the whole layer, unit cm.

Preferably, the method for calculating the layering average consolidation degree of the J working condition comprises the following steps:

and the layered average consolidation degree of the J working condition is calculated by multiplying the layered average consolidation degree of the A, B, C working conditions by the layered weight of the A, B, C working conditions respectively and then adding the products.

U_ji＝U_aiq_ai+U_biq_bi+U_ciq_ci；

In the formula: u shape_jiThe average consolidation degree of the i th layered foundation in the combined prepressing (J working condition) is the layered average consolidation degree without dimension; u shape_ai、U_bi、U_ciThe average consolidation degree of the ith layered foundation under the working condition of A, B, C is zero dimensional; q. q.s_ai、q_bi、q_ciThe hierarchical weight of the ith hierarchical foundation under the working condition of A, B, C is calculated according to the following formula without dimension:

in the formula: s_aif、s_bif、s_cifRespectively the final settlement value of the ith layer A, B, C condition of the layered foundation.

Preferably, the method for calculating the contribution value of the layered consolidation degree of the J working condition comprises the following steps:

and multiplying the layering average consolidation degree of each layer of the J working condition by the corresponding layering contribution rate of the J working condition to obtain the layering consolidation degree contribution value of the J working condition.

and calculating the total average consolidation degree of the whole layer of the J working condition by the sum of the contribution values of the layering consolidation degree of the J working condition.

The invention has the advantages that: the consolidation degree calculation method for the layered foundation combined prepressing comprises the following steps:

(1) the invention decomposes the problem of the combined precompression method into three problems of vacuum negative pressure action, water level descending action and stack loading pressurization, and after respective solution, the results are synthesized into the result of the combined precompression method by using corresponding weights, so that the concept is clear and the operation is simple.

(2) The invention does not need to establish a partial differential equation additionally, avoids adopting a high-depth complex mathematical theory to solve, applies a ready-made theory and formula, utilizes an Excel spreadsheet and can obtain a solution with sufficient precision by only using an exponential function and four arithmetic operations, thereby greatly simplifying the calculation process.

(3) The invention can calculate not only the total average consolidation degree of the whole layer, but also the consolidation degree of each layer, and also the average consolidation degree of any layer, such as a vertical well layer or a downhole layer.

(4) Different stress reduction coefficients are adopted in 3 working conditions of vacuum negative pressure, water level reduction and stack pressurization, and the initial values of the layered consolidation degrees calculated by the 3 actions are reduced respectively to eliminate errors.

(5) No matter the vertical shaft layer or the underground layer, the layers are layered according to natural layers, and each layer is a homogeneous foundation. The layering consolidation degree of each layer can be calculated by using the existing consolidation degree formula. And calculating the contribution value of the layering to the total average consolidation degree of the whole compressed layer by using the layering contribution rate. The problem of layered foundation is transformed into the problem of homogeneous foundation.

Drawings

FIG. 1 is a flow diagram of the present invention for integrated prepressing;

FIG. 2 is a graph of pressure generated by groundwater level drop during vacuum preloading;

FIG. 3 is a schematic diagram of a water level drop pressure curve generated after the groundwater level drops in accordance with the present invention;

FIG. 4 is a vertical cross-sectional view of a single well consolidation model in the case of the present invention;

FIG. 5 is a graph of the stack pressure, vacuum pressure and combined pressure for the present case;

FIG. 6 is a graph of vacuum pressure after attenuation for the present invention case;

FIG. 7 is a graph illustrating the time course of the water level decreasing pressure according to the present invention;

fig. 8 is a time course graph of linear uniform loading and instantaneous loading of the case of the present invention.

Detailed Description

In order to make the technical means, the creation characteristics, the achievement purposes and the effects of the invention easy to understand, the invention is further described with the specific embodiments.

As shown in fig. 1 to 8, a method for calculating consolidation degree of a layered foundation combined with a pre-pressing method includes the following steps:

(1) and designing and calculating various parameters required by geotechnical engineering data according to the vacuum preloading scheme.

(2) Determining the thickness of the whole compression layer according to the condition that the additional stress is less than or equal to 0.1 times of the self-weight stress. Dividing the compression layer into a plurality of layers according to the natural layer level according to the rule of the layering method, and calculating the drainage distance and the whole-path vertical consolidation coefficient of each layer.

(3) The combined prepressing (J working condition) is decomposed into three working conditions of vacuum negative pressure (A working condition), water level descending pressure (B working condition) and stacking pressure (C working condition). The attenuation value of each layer of vacuum pressure and the amplitude of the drop of the underground water level are set. Stress values of midpoints of the working conditions in all the layers in the foundation are calculated A, B respectively, and a stress distribution diagram in the foundation of A, B working conditions is drawn.

(4) Calculating A, B, C final sedimentation value of working condition

The final settlement value of the working condition A (vacuum negative pressure) is calculated by using a special formula (1) provided by the invention:

in the formula: s_afThe final sedimentation value of the working condition A is mm; s_aThe' is the deformation of the compression layer under the working condition of vacuum negative pressure A, which is mm; p is a radical of_a0The negative pressure generated by the vacuum degree under the film, kPa; psi_vThe settlement empirical coefficient is a dimensionless value and is taken according to regional experience; n is the number of divided soil layers within the depth range of the compression layer; omega_aiThe stress reduction coefficient of the ith layer is zero dimension; h is_iIs the thickness of the ith layer, m; e_siThe compressive modulus, MPa, of the ith layered soil is calculated from the pressure section from the dead weight pressure of the soil to the sum of the dead weight pressure and the additional pressure.

And (3) calculating a final settlement value of the working condition B (water level reduction):

the final sedimentation value of the whole layer of the compression layer under the action of water level reduction is calculated according to a special formula (2) provided by the invention:

in the formula: s_bfIs the final sedimentation value of the water level descending function, mm; s'_bThe deformation of the compression layer is mm when the water level is lowered; psi_vThe coefficient is a sedimentation experience coefficient without dimension, and the value is the same as the value of the working condition A; n is the number of divided soil layers within the depth range of the compression layer; omega_biThe stress reduction coefficient of the ith layer is zero dimension; h is_iIs the thickness of the ith layer, m; gamma ray_wIs the water gravity, kN/m³；h_bM, the magnitude of groundwater descent; e_siThe compressive modulus, MPa, of the i-th layer of soil is calculated from the pressure section from the dead weight pressure of the soil to the sum of the dead weight pressure and the additional pressure.

C, calculating the final sedimentation value of the working condition (stacking):

and (3) calculating the final settlement value of the compression layer during preloading according to a settlement formula of a layering summation method of the national standard GB50007-2011 building foundation design standard:

in the formula: s_cfThe final deformation of the foundation is mm; s'_cfThe deformation of the whole foundation layer is calculated according to a layering summation method and is mm; psi_sThe empirical coefficient is calculated by settlement without dimension; determining according to the regional experience, and taking values according to the equivalent value of the compression modulus in the depth range of the compression layer in a national standard table when no regional experience exists; n is the number of divided soil layers within the depth range of the compression layer; p is a radical of_c0An additional pressure at the base bottom corresponding to the quasi-permanent combination of actions, kPa; e_siThe compressive modulus, MPa, of the i-th layer of soil below the basal surface. And calculating the pressure section from the dead weight pressure of the soil to the sum of the dead weight pressure of the soil and the additional pressure. z is a radical of_i、z_i－1The distance m from the bottom surface of the foundation to the bottom surface of the ith layer of soil and the bottom surface of the (i-1) th layer of soil;

(5) Calculating the final settlement value of the combined prepressing (J working condition):

based on the superposition principle of elastomer deformation, the settlement value of the combined prepressing is the sum of the surcharge prepressing settlement value and the combined prepressing settlement value:

s_jit＝s_ait+s_bit+s_cit (4)；

s_jt＝s_at+s_bt+s_ct (5)；

s_jif＝s_aif+s_bif+s_cif (6)；

s_jf＝s_af+s_bf+s_cf (7)；

(6) The method for calculating the laminated stress reduction coefficient comprises the following steps:

a working condition:

calculating the vacuum pressure of the midpoint of each layer after attenuation according to the attenuation value of the vacuum negative pressure, wherein the ratio of the pressure to the ground vacuum pressure is the stress reduction coefficient of the vacuum pressure, and calculating by using the following formula:

in the formula: omega_aiStress reduction coefficient, p, for vacuum negative pressure_i-1The vacuum pressure in kPa after the attenuation at the midpoint of the i-1 th delamination; h is_i-1、h_iThe thickness of the (i-1) th and (i) th layered layers respectively,the unit m; delta_i-1、δ_iVacuum pressure attenuation values of the i-1 th and i-th layers in units of kPa/m, p₀The vacuum pressure, kPa, corresponds to the vacuum degree under the film.

Working condition B:

ω_bi＝A_i/γ_wh_bh_i (13)；

in the formula: omega_biReduction factor for water level lowering, A_iThe area of the ith stratified water level reduced pressure graph is kPa · m; gamma ray_wIs the water gravity, kN/m³；h_bM, the magnitude of groundwater descent; h is_iIs the thickness of the ith layer, m.

C, working condition:

stress reduction coefficient omega of ith layer_iCalculated using the formula:

(7) The method for calculating the contribution rate of each layer comprises the following steps:

layered contribution rate lambda of B working condition_biBy the formulaAnd (3) calculating:

in the formula: s'_ai、s′_bi、s′_ciRespectively A, B, C working condition ith layered foundation deformation amount s_aif、 s_bif、s_cifThe final sedimentation value of the ith layer of A, B, C working conditions, cm and s respectively_af、s_bf、s_cf is the final settlement value of the whole layer under the working condition of A, B, C cm and psi_v、ψ_sEmpirical coefficients are calculated for the settlement of the vacuum preloading and the surcharge preloading.

(8) The hierarchical weight and the whole hierarchical weight of each hierarchical layer of the working condition are calculated A, B, C.

The hierarchical weight for the A condition is calculated as follows:

the hierarchical weight of the B working condition is calculated by the following formula:

the hierarchical weight for the C condition is calculated using the following formula:

the whole layer weight of the A working condition is calculated by the following formula:

the whole layer weight of the B working condition is calculated by the following formula:

the whole layer weight of the C working condition is calculated by the following formula:

(9) the method for calculating the drainage distance comprises the following steps:

(10) The method for calculating the full-path vertical consolidation coefficient comprises the following steps of:

When the ith zone is located in a shaft zone:

When the ith zone is located in the downhole formation:

c_wsi＝[1+μ(v_i-1)]×c_vi (27)；

v_i＝c_w/c_vi (29)；

n_w＝d_e/d_w (30)；

Full path vertical consolidation coefficient of each layer in underground layer

Calculated using the formula:

(11) The calculation method of the initial value of the layering consolidation degree comprises the following steps:

working condition A-vacuum negative pressure:

in the formula:

the initial value of the layering consolidation degree of the ith layering under the working condition A is dimensionless; α is a coefficient, α ═ π²/8；β_iThe coefficient of the ith layering is shown, t is the consolidation duration of vacuum negative pressure, and s; wherein beta is_iAnd according to the position of the layering, calculating by adopting a formula of a layering method.

B working condition-water level drop:

in the formula:

the initial value of the layering consolidation degree of the ith layering under the working condition B is dimensionless; α is a coefficient, α ═ π²/8；β_iIs the coefficient of the ith layer. Beta is a_iAnd according to the position of the layering, calculating by adopting a formula of a layering method. t is the consolidation duration of vacuum negative pressure, s. The linear uniform loading mode of the water level descending effect is replaced by an instant loading mode, and the consolidation time length of the linear uniform loading mode is half of that of the vacuum negative pressure consolidation mode, and is shown in figure 3.

C working condition-loading pressurization:

and calculating the initial value of the layering consolidation degree by adopting the following expressions for each layering in the vertical well layer and the underground well layer:

in the formula:

the initial value of the layering consolidation degree of the ith layering is dimensionless under the working condition C; eta_jThe load ratio of the j level load is dimensionless; α is a coefficient, α ═ π²/8；β_iIs the coefficient of the ith layer, T_zAt the end of the pre-compression, the unit d, t_jThe delay time difference of the j-th level load is shown, and the unit d and k are the last level of the graded load without dimension.

Load ratio eta of j-th load_jCan be calculated using the following formula:

η_j＝Δp_j/p (35)；

(12) The coefficient beta_iThe calculation method comprises the following steps:

when the stratification is in a shaft layer:

when the stratification is in the downhole layer:

Is divided intoFull path vertical consolidation coefficient of layer, cm²/s；H_iThe vertical drainage distance of the ith layer is cm; n is_wIs the well diameter ratio, n_w＝d_e/d_w， d_eThe diameter of the equivalent circle of the drainage vertical shaft is cm; d_wIs the diameter of the shaft, cm; f_iParameters related to the well diameter ratio, well resistance and smearing influence of the ith layer are defined;

when the well foundation is ideal:

F_i＝F_n； (38)；

when the well is a non-ideal well foundation:

F_i＝F_n+F_si+F_ri (39)；

F_n＝ln(n_w)-0.75 (41)；

S_i＝d_si/d_w (43)；

in the formula: k is a radical of_hi、k_siRespectively the permeability coefficients of the i-th layer of undisturbed soil and the soil in the smearing area, cm/s; d_wIs the diameter of the vertical shaft, cm; d_sIs the diameter of the smearing area, cm; s_iDiameter d of application area of ith layer_siDiameter d of shaft_wCan be taken as_i2-3. And taking a low value for the medium sensitive cohesive soil and a high value for the high sensitive cohesive soil.

F_rReflecting the effect of well resistance, is calculated as follows：

(13) The method for calculating the layering average consolidation degree comprises the following steps:

Working condition A-vacuum negative pressure:

b working condition-water level drop:

c working condition-loading pressurization:

in the formula: u shape_ai、U_bi、U_ciThe average layering consolidation degree of the ith layering under the A, B, C working conditions is respectively, and the average layering consolidation degree is dimensionless; omega_ai、ω_bi、ω_ciThe stress reduction coefficients of the ith lamination under the A, B, C working conditions are respectively, and the stress reduction coefficients are dimensionless.

(14) A, B, C condition layered average consolidation degree U_iRide onA. B, C respective layered contribution rates λ of working conditions_iObtaining A, B, C working condition layering consolidation degree contribution value lambda_iU_i；

(15) A, B, C condition total average consolidation degree of whole layer

The contribution value lambda of the layered consolidation degree of each layered under A, B, C working conditions_iU_iThe sum of the above;

working condition A-vacuum negative pressure:

b working condition-water level drop:

c working condition-loading pressurization:

in the formula:

a, B, C working conditions are respectively used for the total average consolidation degree of the whole layer, and the dimension is avoided;

λ_aiU_ai、λ_biU_bi、λ_ciU_cithe average consolidation contribution of the i th layer under A, B, C working conditions is zero dimension.

(16) The overall average consolidation for the J case is calculated using the following equation:

(17) and when the layered average consolidation degree of the three working conditions is obtained through calculation, the calculation can be continued by another way. And (3) multiplying the layered average consolidation degree of A, B, C working conditions by the corresponding layered weight to calculate the layered average consolidation degree of each layer of the J working conditions.

U_ji＝U_aiq_ai+U_biq_bi+U_ciq_ci (53)；

(18) And (4) multiplying the layering contribution rate of the J working condition by the layering average consolidation degree of the J working condition calculated by the formula (53) to obtain the layering consolidation degree contribution value of the J working condition.

(19) The total average consolidation for the J case is calculated as follows:

based on the above, the invention adopts the following cases to carry out experimental analysis:

case (2): surcharge vacuum combined prepressing reinforcement project for Huaneng pouring cloud combined heat and power generation project

The Huaneng Shuyun cogeneration project is located in a swallow-tailed harbor town of Shuyun county, the east faces yellow sea, the north and the west are both Shuxi salt farms, and the south is the intersection of a new Yihe and a river mouth entering the sea. The geomorphic unit of the plant site area is a sea area plain, the terrain is basically flat, the terrain is low, and the ground elevation is generally 2.50-3.00 m. The soft soil in the field is widely distributed, the layer thickness is larger, the physical and mechanical indexes are poorer, and the soft soil is not suitable to be used as a foundation bearing layer and a foundation subjacent layer without being treated.

The total area of the plant area foundation treatment is 11.35 multiplied by 10⁴m²The three-dimensional space is divided into 4 fields, wherein the Z2 field is a main factory building area, the plane is in a rectangular shape of 144.5m multiplied by 218m, and the area is about 3.15 multiplied by 10⁴m²。

The main physical and mechanical parameters of each soil layer of the stratum of the reinforced field are shown in the table 1.

TABLE 1 indexes of main physical and mechanical properties of soil layer

The vertical drainage wells are plastic drainage plates which are arranged in a square shape, and have the space of 1.2m and the length of 21.6 m. The vertical shaft does not perforate a compression layer and belongs to an incomplete well foundation. FIG. 4 shows a vertical cross-section of the single well consolidation model of this example.

The Z2 field starts to be vacuumized at 27 days of 5 months in 2014, and is vacuumized for 159 days at 11 days of 11 months (affected by typhoon, tide rise and power failure, and pumps are stopped for 10 days in midway). The soil loading is 38kN/m²The first earthwork stacking is carried out at 20 days after 7 months, and the stacking load is 19kN/m². The second batch of earth is piled at 29 months 8 in 2014, and the earth piling load is 19kN/m². The first-stage stacking time length is 104 days and the second-stage stacking time length is 54 days by 11 months and 11 days Z2 in 2014. The time course curves of the ground vacuum pressure, the surcharge pressure and the combined pressure are shown in fig. 5.

16 ground subsidence marks are arranged on the Z2 field, and judged by the Grubbs criterion, when the confidence level is 99%, the 16 actually measured subsidence values are all reliable effective values, and the average value is the subsidence value s when the pre-pressing is finished_t＝105.3cm。

The invention provides a method for calculating the consolidation degree of a layered foundation combined prepressing method, which comprises the following steps:

step (1): and calculating each parameter of the surcharge preloading according to a layering method.

(1.1) calculating the shaft parameters: the following parameters were calculated from the dimensions and the pitch and shape of the planar arrangement of the plastic drainage plates:

the width b of the drainage plate is 10 cm;

the thickness d of the drainage plate is 0.45 cm;

cross sectional area a of drain board_e＝10×0.45＝4.5cm²；

Equivalent reduced diameter d_w＝6.65cm；

Equivalent diameter d of shaft_e＝1.356m；

Equivalent circle cross-sectional area A of shaft_e＝1.443m²；

Shaft depth h_w＝21.6m；

Area ratio mu of shaft to equivalent circle is 0.31 multiplied by 10^-3；

And (1.2) calculating the composite vertical consolidation coefficient of each layer in the vertical well layer, and calculating the drainage distance, the directional consolidation coefficient and the like of each layer of the compression layer.

Permeability coefficient k of shaft_w＝5×10^-4cm/s＝0.432m/d；

Longitudinal water flow q of shaft_w＝40cm³/s＝3.46m³/d；

Reduced vertical shaft compression modulus E_s＝36Mpa；

Vertical consolidation coefficient c of shaft_w＝4.32×36×1000/9.8＝1587m²/d；

Consolidation ratio v₁＝c_w/c_v1＝1587/0.056＝28338；

v₂＝c_w/c_v2＝1587/0.065＝24414；

v₃＝c_w/c_v3＝1587/0.265＝5988；

Composite vertical consolidation coefficient c_ws1＝0.55m²/d；

c_ws2＝0.56m²/d；

c_ws3＝0.76m²/d；

The consolidation coefficients calculated from the compressibility and permeability coefficients of the respective layers of soil are shown in table 2.

TABLE 2 table of parameters such as consolidation coefficient of each layer

(1.3) coefficient considering influence of well resistance and smearing effect

Well diameter ratio n ═ d_e/d_w＝20.37；

Well diameter ratio factor F_n＝2.26；

S₁＝S₂＝d_s/d_w＝3 S₃＝d_s/d_w＝2.5；

Suppose K_h/K_sSmearing effect F ═ 2_s1＝F_s2＝1.10，F_s3＝0.92；

F_r3＝(3.14²×22²/4)×(4.406×10^-4/3.46)＝0.152

The remaining parameters are shown in Table 3

Table 3 summary of coefficients of floors in shaft

Step (2): layering according to natural layers. The method comprises the following substeps:

(2.1) the depth of the compressed layer was determined to be 65.3m under the condition that the additional stress was 0.1 times or less the self-weight stress. The compression layer is divided into two combined layers, a vertical well layer and a downhole layer, by taking the bottom of the drainage well as a boundary.

(2.2) dividing the vertical well layer and the underground layer according to the natural layer position, wherein the vertical well layer comprises 3 layers, and the underground layer comprises 8 layers. Numbering is continued from top to bottom for a total of 11 layers, see FIG. 4.

And (3): the combined prepressing (J working condition) is decomposed into three working conditions of vacuum pressure (A working condition), water level descending pressure (B working condition) and stacking pressure (C working condition). And setting the attenuation value of the vacuum pressure of the working condition A and the descending amplitude of the underground water level. Are divided into the following:

(3.1) the vacuum pressure decay values set forth in Table 4. The plotted post-attenuation vacuum pressure curve and the plot of the mean vacuum pressure for each segment are shown in FIG. 6.

TABLE 4 attenuation value δ of vacuum pressure_iAverage vacuum pressure p of each layer_aiAnd stress reduction factor omega_ai

(3.2) the set groundwater level was dropped by 2.8m, and the average pressures of the respective layers are shown in Table 5. The pressure curve generated after the groundwater level has dropped is plotted schematically in figure 7.

TABLE 5 mean pressure p for each layer of groundwater table descent_biAnd stress reduction factor omega_bi

And 4, step 4: calculating A, B, C final sedimentation value of working condition

(4.1) calculating the final settlement value of the working condition A (vacuum negative pressure): the results are shown in Table 6. Wherein the layered settlement has been multiplied by the empirical coefficient psi of settlement_v. Empirical coefficient of sedimentation psi_vIs obtained according to regional experience_v＝1.00。

TABLE 6A Table of stratified Final Settlement, cumulative Final Settlement and stratified contribution

(4.2) calculating the final settlement value of the working condition B (water level drop): the results are shown in Table 7. Wherein the layered settlement has been multiplied by the empirical coefficient psi of settlement_v. Empirical coefficient of sedimentation psi_vTaking the same as the working condition AValue psi_v＝1.00。

TABLE 7B Table of stratified Final Settlement, cumulative Final Settlement and stratified contribution

(4.3) drawing a loading time course curve, and calculating load values delta p of all levels_kLoad ratio eta_kDelay time difference t_kAnd a consolidation duration T_k。

The time course curve of the gradual loading is shown as "actual loading time course curve" in fig. 8. The 2 times of stacking are all linear and uniform loading, and each time is 19kN/m²Now, a mode of 2-level instantaneous loading is adopted to replace the original 2-time linear uniform loading mode, and a design loading time course curve chart is shown in fig. 8. The load detailed parameters are shown in table 8.

TABLE 8 load parameter Table

Load order k	1	2
			Load value Δ p_k/kN/m²	19	19
Ratio of loads eta_k	0.5	0.5
			Time difference t of delay of loads at all levels_k/d	59	109
Each stage of load consolidation duration T_k/d	100	50

(4.4) calculating the final sedimentation value of the working condition C (stacking pressurization): the results are shown in Table 9. Wherein the sedimentation values have been multiplied by an empirical sedimentation coefficient psi_s. Empirical coefficient of sedimentation psi_sCalculated from the value of the compression modulus equivalent of the compression layer, #_s＝1.00。

TABLE 9C Table of stratified Final Settlement, cumulative Final Settlement and stratified contribution

And (5): and calculating the final settlement value of the combined prepressing (J working condition).

The stratified final settlement and the full-layer final settlement of the J-condition are the linear sum of the settlement of A, B, C three conditions. The calculation results are shown in Table 10.

TABLE 10J behavior stratified final settlement, cumulative final settlement and stratified contribution table

And (6): the stress reduction factor for the condition A, B, C was calculated and the results are shown in Table 11.

TABLE 11A, B, C layered stress reduction factor Table for the operating conditions

And (7): the hierarchical weight and the whole hierarchical weight of each layer of the working condition are calculated A, B, C, and the results are shown in tables 12 and 13.

TABLE 12 hierarchical weighting table for the 12A, B, C operating conditions

TABLE 13 Whole layer weight table for the 13A, B, C operating mode

And (8): and calculating the initial value of the layering consolidation degree, the layering average consolidation degree, the contribution value of the layering consolidation degree and the total average consolidation degree of the whole layer of each layering under the working condition of A, B, C.

(8.1) calculating coefficients β of respective layers_iThe value is obtained.

(8.2) the initial values of the consolidation of each layer under A, B, C were calculated from the expressions (32), (33) and (34), and the results are shown in Table 14.

TABLE 14 initial value table of consolidation degree for each layer under 14A, B, C working conditions

(8.3) the average consolidation level of each layer under A, B, C conditions was calculated by multiplying the initial value of consolidation level of the corresponding condition and layer by the reduction coefficient of stress of each layer under A, B, C conditions, and the results are shown in Table 15.

TABLE 15 table 15A, B, C table of average consolidation for each layer

(8.4) the contribution rate of each layer of A, B, C was multiplied by the average consolidation rate of each layer of the corresponding layer and A, B, C condition to calculate the value of the contribution rate of each layer of the A, B, C condition, and the result is shown in Table 16.

TABLE 16A, B, C Table of average consolidation for each layer and total average consolidation for the entire layer

And (9): the overall average consolidation for the J case is calculated as equation (52).

＝0.5846×0.3357+0.8246×0.2766+0.8485×0.3877

＝0.7533；

Step 10: and calculating the layering average consolidation degree of each layer under the J working condition according to the formula (53). Then, the average layering consolidation degree of each layer under the J working condition is multiplied by the layering contribution rate of each layer under the J working condition to obtain the layering consolidation degree contribution value of each layer under the J working condition, and then the sum of the layering average consolidation degree and the layering contribution rate is used for obtaining the total average layering consolidation degree under the J working condition, which is shown in a table 16.

TABLE 16J working condition table for each layer of average consolidation degree and contribution value of consolidation degree

Can see twoMethod for calculating total average consolidation degree of whole layer by combined prepressing method

The method is 'special way congruence', and the calculation results are completely the same. Only the total average consolidation degree of the whole layer of the combined prepressing is calculated by the formula (52), and the calculation method of the step (10) can calculate not only the total average consolidation degree of the whole layer of the combined prepressing, but also the average consolidation degree of each layer of the combined prepressing, the contribution value and the like.

Calculating the final settlement value s of the combined prepressing (J working condition) by a layering method_jfThe settling value at the end of the combined precompression should be 140.2 cm:

calculating a settlement value generated by the working condition A when the combined prepressing is finished by using a layering method:

calculating a settlement value generated by the working condition B when the combined prepressing is finished by using a layering method:

calculating a settlement value generated by the working condition C when the combined prepressing is finished by using a layering method:

s_jt＝s_at+s_bt+s_ct＝27.5+32.0+46.2＝105.7cm；

and another 'special way congruence', the calculation results are completely the same. Therefore, the method for calculating the combined prepressing consolidation degree of the layered foundation by adopting the 'separation before combination' completely accords with the scientific law.

The results of the layering calculation are compared with the measured values in Table 17, and the results of the design calculation are compared with the measured values in Table 18.

And (3) calculating the consolidation degree: the error of the layering method is 0.4%, and the error of the design is 23.6%;

calculating a settlement value when the pre-pressing is finished: the error of the layering method is 0.4%, and the error of the design is 38.0%.

TABLE 17 comparison of the layering method with the measured values

TABLE 18 comparison of design values with measured values

As can be seen from tables 17 and 18, the difference between the design value and the measured value on site is large, and it is the problem of the theory and method of computing application. The parameters and assumptions used in their calculations are not analyzed one by one, and it can be seen that: the existing theory and formula for calculating single foundation are applied to the layered foundation. Compared with the layering method, the layering method of the invention has the inevitable result of high precision of the calculation result of the layering method. See tables 19, 20.

Table 19 design and layering method comparison table in settlement calculation

TABLE 20 comparison of design and layering methods in consolidation calculation

It will be appreciated by those skilled in the art that the invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The embodiments disclosed above are therefore to be considered in all respects as illustrative and not restrictive. All changes which come within the scope of or equivalence to the invention are intended to be embraced therein.

Claims

1. A consolidation degree calculation method for layered foundation combined prepressing, which is characterized by comprising the following steps:

the method is divided into A, B, C working conditions, and a J working condition is obtained after A, B, C working conditions are combined;

dividing the layered foundation into a vertical well layer and a downhole layer, dividing the vertical well layer and the downhole layer into a plurality of layers according to natural layer positions, and calculating the vertical drainage distance, the radial consolidation coefficient and the full-path vertical consolidation coefficient of the layers;

calculating A, B, C layered stress reduction coefficient, final sedimentation value and whole layer final sedimentation value of working condition;

calculating A, B, C, J the layering contribution rate of the working condition according to the final settlement value;

calculating to obtain initial values of the consolidation degrees of all layers under the A, B, C working conditions according to the consolidation coefficient and the vertical drainage distance;

obtaining the layered average consolidation degree of A, B, C working conditions according to the corresponding initial value of the layered consolidation degree and the layered stress reduction coefficient;

multiplying the average consolidation degree of each layer under A, B, C working conditions by the layering weight of corresponding A, B, C working conditions respectively, and adding to obtain the average consolidation degree of each layer under J working conditions;

calculating the average consolidation degree of each layer under the J working condition by multiplying the contribution rate of each layer corresponding to the J working condition to obtain the consolidation degree contribution value of each layer under the J working condition;

the total average consolidation degree of the whole layer of the J working condition is obtained by summing the contribution values of the layering consolidation degrees of the J working condition.

2. The consolidation degree calculation method of the stratified foundation combined preloading according to claim 1, wherein: the method for calculating the vertical drainage distance comprises the following steps:

vertical drainage distance H_iThe distance from the bottom surface of the laminate to the top surface of the compression layer was calculated using the following formula:

in the formula: h is_mIs the layer thickness of the mth delamination, m; i is the calculated tier number.

3. The consolidation degree calculation method of the stratified foundation combined preloading according to claim 1, wherein: the method for calculating the full-path vertical consolidation coefficient comprises the following steps of:

when the ith zone is located in a shaft zone:

in the formula: c. C_vmThe vertical consolidation coefficient of the mth layer soil; h is_mIs the thickness of the mth delamination;

when the ith zone is located in the downhole formation:

c_wsi＝[1+μ(v_i-1)]×c_vi；

in the formula: c. C_wsiComposite vertical consolidation coefficient, cm, for the ith layer²S; mu is the ratio of the cross section area of the vertical shaft to the cross section area of the equivalent circle of the drainage vertical shaft, has no dimension and is calculated by the following formula;

v_ithe vertical consolidation coefficient of the vertical shaft is the ratio of the vertical consolidation coefficient of the ith layered interwell soil, has no dimension, and is calculated by the following formula;

v_i＝c_w/c_vi；

in the formula: a. the_wIs the cross-sectional area of the shaft in cm²(ii) a A is the equivalent circular cross section area of the drainage shaft in cm²；c_wVertical consolidation coefficient for shaft, cm²/s；c_viIs the vertical consolidation coefficient of the soil between the ith layering wells in cm²/s；n_wThe well diameter ratio is zero dimension and is calculated according to the following formula;

n_w＝d_e/d_w；

in the formula: d_eThe diameter of the equivalent circle of the drainage vertical shaft is cm; d_wIs the diameter of the shaft, cm;

full path vertical consolidation coefficient of each layer in underground layer

Calculated using the formula:

4. The consolidation degree calculation method of the stratified foundation combined preloading according to claim 1, wherein: the method for calculating the laminated stress reduction coefficient comprises the following steps:

the reduction coefficient of the layering stress under the working condition A is as follows:

in the formula: omega_aiThe stress reduction coefficient under the working condition A; p is a radical of_i-1The vacuum pressure in kPa after the attenuation at the midpoint of the i-1 th delamination; h is_i-1、h_iThe thickness of the layers of the (i-1) th and (i) th is m; delta_i-1、δ_iRespectively representing the vacuum pressure attenuation values of the ith-1 and ith layers in unit of kPa/m; p is a radical of₀The vacuum pressure corresponding to the vacuum degree under the film is kPa;

the reduction coefficient of the layering stress under the working condition B is as follows:

according to the original underground water level and the amplitude of the estimated underground water level reduction, the pressure generated in each layer by the water level reduction action is calculated, and the pressure is calculated by the following formula:

ω_bi＝A_i/γ_wh_bh_i；

in the formula: omega_biThe reduction coefficient of the layered stress under the working condition B; a. the_iThe area of the ith stratified water level reduced pressure graph is kN/m; gamma ray_wIs the water gravity, kN/m³；h_bM, the magnitude of groundwater descent; h is_iIs the thickness of the ith layer, m;

the reduction coefficient of the layering stress under the working condition C is as follows:

stress reduction coefficient omega of ith layer_ciCalculated using the formula:

in the formula: z is a radical of_i、z_i-1The distance from the bottom surface of the foundation to the bottom surfaces of the ith layer of soil and the (i-1) th layer of soil;

is a baseCalculating the average additional stress coefficient from the bottom surface to the bottom surface of the i-th layer of soil and the i-1 st layer of soil; h is_iIs the thickness of the ith layer, m.

5. The consolidation degree calculation method of the stratified foundation combined preloading according to claim 1, wherein: the method for calculating the initial value of the layering consolidation degree comprises the following steps:

initial value of layering consolidation degree under A working condition:

in the formula:

the initial value of the layering consolidation degree of the ith layering under the working condition A is zero dimension; α is a coefficient, α ═ π²/8；β_iIs the coefficient of the ith layer; t is the consolidation duration of vacuum negative pressure, s; wherein beta is_iCalculating by adopting a formula of a layering method according to the position of the layering;

initial value of layering consolidation degree under B working condition:

in the formula:

the initial value of the layering consolidation degree of the ith layering under the working condition B is dimensionless; α is a coefficient, α ═ π²/8；β_iIs the coefficient of the ith layer, beta_iCalculating by adopting a formula of a layering method according to the position of the layering; t is consolidation of vacuum negative pressureDuration, s; the linear uniform loading mode of the water level descending effect is replaced by an instant loading mode, and the consolidation time length is half of the vacuum negative pressure consolidation time length;

initial value of layering consolidation degree under C working condition:

in the formula:

the initial value of the layering consolidation degree of the ith layering is zero dimension under the working condition C; eta_jThe load ratio of the j level load is zero dimension; t is_zD, the moment when the pre-pressing is finished; t is t_jDelay time difference of j-th load, d; k is the last stage number of the grading load without dimension;

load ratio eta of j-th load_jCalculated using the formula:

η_j＝Δp_j/p；

in the formula: Δ p_jIs the j-th level load value, kPa; p is the final stack load value, kPa.

6. The consolidation degree calculation method of the stratified foundation combined preloading according to claim 5, wherein: beta is the same as_iThe determination method comprises the following steps:

when the stratification is in a shaft layer:

when the stratification is in the downhole layer:

Full path vertical consolidation coefficient, cm, for the ith layer²/s；H_iThe vertical drainage distance of the ith layer is cm; s; f_iParameters related to the well diameter ratio, well resistance and smearing influence of the ith layer are defined; d_eThe diameter of the equivalent circle of the drainage vertical shaft is cm;

when the well foundation is ideal: f_i＝F_n；

When the well is a non-ideal well foundation: f_i＝F_n+F_si+F_ri；

when the well diameter ratio is n_wWhen F is not less than 15_nThe method is simplified as follows:

F_n＝ln(n_w)-0.75；

S_i＝d_si/d_w；

in the formula: k is a radical of_hi、k_siRespectively the permeability coefficients of the i-th layer of undisturbed soil and the soil in the smearing area, cm/s; d_wIs the diameter of the vertical shaft, cm; s_iDiameter d of application area of ith layer_siDiameter d of shaft_wTaking S as 2-3; taking a low value for medium sensitive cohesive soil and a high value for high sensitive cohesive soil;

F_rreflecting the well resistance effect, calculated as follows:

7. The consolidation degree calculation method of the stratified foundation combined preloading according to claim 1, wherein: the method for calculating the J working condition settlement value comprises the following steps:

according to the superposition principle of elastic body deformation, the sum of the settlement values of the layered foundation under A, B, C working conditions is the settlement value of J working conditions:

the settlement value of the ith layer of the J working condition at the moment t:

s_jit＝s_ait+s_bit+s_cit；

and (3) settlement value of the whole working condition layer at the moment of t:

s_jt＝s_at+s_bt+s_ct；

final sedimentation value of i-th layer of J condition:

s_jif＝s_aif+s_bif+s_cif；

j condition final sedimentation value of the whole layer:

s_jf＝s_af+s_bf+s_cf；

the settlement value of the whole layer under the working condition A at the moment t:

and (3) settling value of the whole layer under the working condition B at the moment t:

and (3) settling value of the whole layer under the working condition C at the moment t:

in the formula: s_jit、s_ait、s_bit、s_citRespectively representing the settlement value of the ith layer under the J, A, B, C working condition at the time t, cm; s_jt、s_at、s_bt、s_ctRespectively J, A, B, C sedimentation value of the whole layer at time t, cm; s_jif、s_aif、s_bif、s_cifThe final sedimentation value of the ith layer under the working condition of J, A, B, C is cm; s_jf、s_af、s_bf、s_cfThe final sedimentation value of the whole layer under the working condition of J, A, B, C is cm; n is the number of divided soil layers within the depth range of the compression layer.

8. The consolidation degree calculation method of the stratified foundation combined preloading according to claim 1, wherein: the method for calculating the final sedimentation value of the whole layer comprises the following steps:

the final sedimentation value of the whole layer under the working condition A is as follows:

in the formula: s_afThe final sedimentation value of the whole layer under the working condition A is mm; s'_aThe deformation of the whole compression layer under the working condition A is mm; p is a radical of_a0Is the vacuum degree under the filmRaw negative pressure, kPa; psi_vThe data are empirical coefficients and are taken according to regional experience without dimension; n is the number of divided soil layers within the depth range of the compression layer; omega_aiThe stress reduction coefficient of the ith layer is zero dimension; h is_iIs the thickness of the ith layer, m; e_siCalculating a pressure section from the dead weight pressure of the soil to the sum of the dead weight pressure and the additional pressure in the compression modulus of the ith layer, MPa;

the final sedimentation value of the whole layer under the working condition B:

in the formula: s_bfThe final sedimentation value of the working condition B is mm; s'_bThe compression deformation of the whole compression layer under the working condition B is mm; psi_vThe coefficient is an empirical coefficient, has no dimension, and takes the value same as the working condition A; n is the number of divided soil layers within the depth range of the compression layer; omega_biThe stress reduction coefficient of the ith layer is zero dimension; h is_iIs the thickness of the ith layer, m; gamma ray_wIs the water gravity, kN/m³；h_bM, the magnitude of groundwater descent; e_siCalculating a pressure section from the dead weight pressure of the soil to the sum of the dead weight pressure and the additional pressure in the compression modulus of the ith layer, MPa;

the final sedimentation value of the whole layer under the working condition C:

in the formula: s_cfThe final sedimentation value of the whole layer under the working condition C is mm; s'_cfThe deformation of the whole foundation layer is calculated according to a layering summation method and is mm; psi_sThe empirical coefficient is calculated by settlement without dimension; determining according to the regional experience, and taking values according to the equivalent value of the compression modulus in the depth range of the compression layer in the national standard table when no regional experience exists; n is the number of divided soil layers within the depth range of the compression layer; p is a radical of_c0For additional pressure at the base bottom in response to quasi-permanent combination of actions，kPa；E_siThe compressive modulus, MPa, of the i-th layer of soil below the bottom surface of the foundation; calculating a pressure section from the dead weight pressure of the soil to the sum of the dead weight pressure of the soil and the additional pressure; z is a radical of_i、z_i-1The distance m from the bottom surface of the foundation to the bottom surface of the ith layer of soil and the bottom surface of the (i-1) th layer of soil;

the average additional stress coefficient from the ground to the bottom surface of the i-th layer of soil and the i-1 th layer of soil is adopted according to the annex of the national standard.

9. The consolidation degree calculation method of the stratified foundation combined preloading according to claim 1, wherein: the method for calculating the layering contribution rate comprises the following steps:

layered contribution rate lambda of C working condition_ciCalculated using the formula:

in the formula: s'_ai、s′_bi、s′_ciThe deformation of the ith layered foundation under the working condition of A, B, C respectively; s_aif、s_bif、s_cifThe final sedimentation value of the ith layer under the working condition of A, B, C is cm; s_af、s_bf、s_cfRespectively A, B, C working condition final sedimentation value of the whole layer, cm; psi_v、ψ_sEmpirical coefficients were calculated for the settlement.

10. The consolidation degree calculation method of the stratified foundation combined preloading according to claim 1, wherein: the method for calculating the layering average consolidation degree comprises the following steps:

A. b, C condition average consolidation for delamination:

multiplying the initial value of the layered consolidation degree of A, B, C working conditions with the layered stress reduction coefficient of A, B, C working conditions respectively to obtain the layered average consolidation degree of A, B, C working conditions;

average consolidation for J conditions:

respectively multiplying the layered average consolidation degree of A, B, C working conditions by the layered weight of A, B, C working conditions, and adding to obtain the layered average consolidation degree of J working conditions;

U_ji＝U_aiqa_i+U_biq_bi+U_ciq_ci；

in the formula: u shape_jiThe method is combined prepressing, namely the average layering consolidation degree of the ith layering foundation under the working condition J, and has no dimension; u shape_ai、U_bi、U_ciThe average consolidation degree of the ith layered foundation under the working condition of A, B, C is zero dimensional; q. q.s_ai、q_bi、q_ciThe hierarchical weights of the ith hierarchical foundation under the A, B, C working condition are calculated according to the following formula without dimension:

hierarchical weight under A condition:

layering weight in B working condition:

hierarchical weight under C condition:

11. The consolidation degree calculation method of the stratified foundation combined preloading according to claim 1, wherein: the method for calculating the contribution value of the layered consolidation degree comprises the following steps of:

A. b, C condition layered consolidation contribution:

the layered average consolidation degree under A, B, C working conditions is multiplied by the layered contribution rate under A, B, C working conditions respectively to obtain a layered consolidation degree contribution value under A, B, C working conditions;

contribution value of layered consolidation degree of J working condition:

12. The consolidation degree calculation method of the stratified foundation combined preloading according to claim 1, wherein: the method for calculating the total average consolidation degree of the whole layer comprises the following steps:

A. b, C condition overall average consolidation throughout layer:

adding the contribution values of the layered consolidation degrees of the A, B, C working conditions respectively to obtain the total average consolidation degree of the whole layer of A, B, C working conditions;

the total average consolidation degree of the whole layer under the working condition A is as follows:

b, working condition total average consolidation degree of the whole layer:

c, working condition total average consolidation degree of the whole layer:

wherein, the lambda aiUai, the lambda biUbi and the lambda ciUci are respectively the contribution values of the layered average consolidation degree of the ith layered under the working condition of A, B, C, and have no dimension; n is the number of divided soil layers within the depth range of the compression layer;

overall average consolidation of the whole layer under J conditions:

and respectively multiplying the total average consolidation degree of the whole layer under the A, B, C working conditions by the weight of each whole layer, and adding to obtain the total average consolidation degree of the whole layer under the J working conditions:

in the formula:

the whole layer weight under the working condition A:

and (3) the whole layer weight in the working condition B:

and (3) the whole layer weight under the working condition C:

in the formula: s_af、s_bf、s_cfThe final sedimentation value of the whole layer in cm under A, B, C working conditions respectively.