CN105486836A - Calculation method for saturated-clay frost heaving ratio in closed system - Google Patents

Abstract

The invention discloses a calculation method for saturated-clay frost heaving ratio in a closed system. The method comprises getting soil from an on-site clay layer, obtaining the standard soil sample mass and the residual soil mass at a natural state through an indoor geotechnical test, measuring the residual soil particle mass by utilizing a drying process, and measuring the relative density by utilizing a pycnometer process, so as to obtain the water content and the soil-particle relative density of the soil sample; saturating the soil sample by utilizing a vacuumizing process, measuring the mass of the saturated soil sample, and calculating the saturation water content; and calculating the soil-particle volume and water volume in soil according to the soil-sample total volume, and the soil-particle density and the water content, establishing a calculation formula of the saturated-clay frost heaving ratio related to the saturation water content and the soil-particle relative density in the closed system. The beneficial effects comprise that the method fills the blank for calculating the clay volume expansion in the closed system in the artificial freezing field, establishes a function formula employing the saturation water content and the soil-particle relative density as independent variables, and is capable of relatively effectively determining the saturated-clay frost heaving ratio in a closed environment.

Description

The computing method of saturated clay frozen-heave factor in closed system

Technical field

The present invention relates to Artificial Frozen Soil technical field, be specifically related to the computing method of saturated clay frozen-heave factor in a kind of closed system.

Background technology

In the process of engineering with artificial freezing method strengthening stratum, along with heat interchange is carried out, formation temperature declines gradually, when soil temperature reaches the freezing point, along with the formation of the ice intrusive body such as crystalline solid, phacoid, ice band of freezing because of pore water and migration water in soil, soil body volume increases, and then makes the soil body produce frost heaving.Body frost heaving phenomenon in the freezing process application process of artificial stratum is all the focus paid close attention in Practical Project all the time.

Especially for the Metro Tunnel adopting construction freezing method, due to subway tunnel multidigit in city bustling location, above ground structure and peripheral facility more, the pipeline buried underground of stratum is various, intricate simultaneously.If there is design inconsiderate in detail or construction means improper, cause stratum frost heaving amount effectively estimated and monitor, direct harmful effect will be produced to Around environment, and cause huge economy and personal casualty loss.This just requires, before the construction freezing method of artificial stratum, to predict for body frost heaving effect.Therefore, research and develop a kind of frozen-heave factor computing method of saturated clay, simulation and forecast is carried out to the stratum freezing heave behavior that may cause, the cost and risk of freezing process application is dropped to minimum, there is Important Project practical value.

In engineering cognition practice, it is found that soil in open system and in closed system the frost-heaving deformation of saturated clay be different.Under open system, the frost heave of saturated clay is except volumetric expansion after water freezing about 9%, and the water cut also having water translocation in freezing process to make carefully to stick grain soil increases, and the volume of migration water exacerbates the frost heave of saturated clay.But the water translocation of soil in process of frost heave, the current also more not complete reliable theory of computation, to the understanding of Moisture Transfer Rule, also stay in qualitative interpretation, not yet carry out determining quantifier elimination in a lot, theory calculate is also very immature, and is substantially confined to inquire into one-dimensional problem by method of difference.Therefore, still immature for the research and development of the computing method of saturated clay frozen-heave factor in open system, need a large amount of scientific research personnel constantly to further investigate body frost heaving rule.

In closed system, the frost heave of saturated clay is mainly caused by saturated clays pore water original position frost heave, and in soil, capillary water is not owing to having outside moisturizing, and in freezing process, water translocation amount is extremely small, does not have an impact to saturated clays frost heave effect.Sum up forefathers simultaneously and study discovery, although each component has breathing phenomenon in soil due to temperature change, in frozen soil, the volume expansivity of ice is about 120 × 10 ^-6k ^-1, the volume expansivity of water is about 200 × 10 ^-6k ^-1, the volume expansivity of clay grain is about 20 × 10 ^-6k ^-1, their breathing effect is very little, can ignore, thus only need consider soil water freeze produce volumetric expansion change.These factors determine that the computing method application of saturated clay frozen-heave factor in closed system is simple and accuracy is high.

Therefore, summary present stage numerous scholar on the basis of the frost heave variation characteristic cognition of soil, a kind of computing method of saturated clay body frozen-heave factor in research closed system, and apply the method simulation and forecast is carried out to the stratum freezing heave behavior that may cause, the cost and risk of freezing process application is reduced, there is great theory significance and engineering practical value.

Summary of the invention

In order to solve the problems of the technologies described above, the object of this invention is to provide the computing method of saturated clay frozen-heave factor in closed system, be beneficial to easy, calculate body frost heaving rate quickly.

To achieve these goals, the technical solution used in the present invention is to provide the computing method of saturated clay frozen-heave factor in closed system, and the method comprises the following steps:

1) fetch earth in clay layer at the scene, will fetch earth according to appointment specification is processed as standard soil sample, and it is native to retain the residue after a certain amount of processing; First under recording native state, the quality m of described standard soil sample and the quality m ' of residue soil, then utilizes oven drying method to record the soil particle quality m of residue soil _s', and utilize pycnometer method to measure its specific density of solid particles d to the soil particle of the residue soil after oven dry _s, natural moisture content w and the grogs quality m of standard soil sample is drawn by following formula _s:

$w=\frac{m^{\′}-{m_s}^{\′}}{{m_s}^{\′}}\×100\%---\left(1\right)$

$m_s=\frac{m}{(1+w)}---\left(2\right)$

2) utilize vacuumizing method to carry out immersion saturated to standard soil sample, saturation time is 24h;

3) saturated complete after, take out standard soil sample weigh, record the saturated quality m of standard soil sample _sat, and calculate its saturation moisture content w _sat:

$w_{sat}==\frac{m_{sat}-m_s}{m_s}\×100\%---\left(3\right)$

4) the volume V before saturated standard soil sample being freezed ₀the volume V of soil particle in the standard soil sample that equivalence one-tenth is saturated _swith the volume V of water _wsuperposition, then

$V_0=V_s+V_w=\frac{m_s}{{\mathrm{\ρ}}_s}+\frac{m_{sat}-m_s}{{\mathrm{\ρ}}_w}=\frac{m_s}{d_s}+m_{sat}-m_s=\frac{m_s}{d_s}+w_{sat}{m}_s---\left(4\right)$

In formula, ρ _sfor soil particle density, numerically equal specific density of solid particles d _s; ρ _wfor the density of pure water, ρ _w=1g/cm ³;

5) the volume V after saturated standard soil sample being freezed ₁equivalence becomes to have freezed the volume V of soil particle in rear saturated standard soil sample _swith the volume V of ice _isuperposition, then

$V_1=V_s+V_i=\frac{m_s}{{\mathrm{\ρ}}_s}+\frac{m_{sat}-m_s}{{\mathrm{\ρ}}_i}=\frac{m_s}{d_s}+\frac{m_{sat}-m_s}{0.917}=\frac{m_s}{d_s}+\frac{w_{sat}{m}_s}{0.917}---\left(5\right)$

In formula, ρ _ifor the density of ice, ρ _i=0.917g/cm ³;

6) set up saturated standard soil sample and freeze front and back volume change formula, and freeze front and back volume equivalent transformation by saturated standard soil sample in formula (4) (5), obtain the computing formula of the frozen-heave factor α of saturated standard soil sample:

$\mathrm{\α}=\frac{V_1-V_0}{V_0}\×100\%---\left(6\right)$

$\mathrm{\α}=\frac{0.09w_{sat}{d}_s}{(1+w_{sat}{d}_s)}\×100\%---\left(7\right)$

Saturated clay frozen-heave factor α is obtained in closed system about saturation moisture content w by above-mentioned steps _satwith specific density of solid particles d _scomputing formula.

Effect of the present invention is the blank that the volumetric expansion that compensate for saturated clay in the closed system of manual pipe jacking field calculates, the function formula that to establish with saturation moisture content and specific density of solid particles be independent variable.The method is applied in engineering practice, more effectively, more quickly can carries out simulation and forecast to the stratum freezing heave behavior that saturated clay body in relative closure environment causes, the cost and risk of freezing process application is dropped to minimum.Therefore, the computing method researching and developing saturated clay frozen-heave factor in closed system have great theory significance and engineering practical value.

Embodiment

Below in conjunction with example, the computing method of saturated clay frozen-heave factor in closed system of the present invention are elaborated.

The computing method design philosophy of the frozen-heave factor of saturated clay in closed system of the present invention, mainly mainly caused by saturated clays pore water original position frost heave based on the frost heave of saturated clay in closed system, and in soil capillary water owing to there is no outside moisturizing, in freezing process, water translocation amount is extremely small, does not have an impact to saturated clays frost heave effect.Sum up forefathers simultaneously and study discovery, although each component has breathing phenomenon in soil due to temperature change, in frozen soil, the volume expansivity of ice is about 120 × 10 ^-6k ^-1, the volume expansivity of water is about 200 × 10 ^-6k ^-1, the volume expansivity of clay grain is about 20 × 10 ^-6k ^-1, their breathing effect is very little, can ignore, thus only need consider soil water freeze produce volumetric expansion change.These factors determine that the computing method application of saturated clay frozen-heave factor in closed system is simple and accuracy is high.Therefore, the saturation moisture content w of soil sample is adopted _satwith specific density of solid particles d _s, as the parameter affecting saturated clay frozen-heave factor α in closed system.

$\mathrm{\α}=\frac{0.09w_{sat}{d}_s}{(1+w_{sat}{d}_s)}\×100\%$

The computing method of saturated clay frozen-heave factor in closed system of the present invention, the method comprises the following steps:

1) fetch earth in clay layer at the scene, will fetch earth according to appointment specification is processed as standard soil sample, and it is native to retain the residue after a certain amount of processing; First under recording native state, the quality m of described standard soil sample and the quality m ' of residue soil, then utilizes oven drying method to record the soil particle quality m of residue soil _s', and utilize pycnometer method to measure its specific density of solid particles d to the soil particle of the residue soil after oven dry _s, natural moisture content w and the grogs quality m of standard soil sample is drawn by following formula _s:

$w=\frac{m^{\′}-{m_s}^{\′}}{{m_s}^{\′}}\×100\%---\left(1\right)$

$m_s=\frac{m}{(1+w)}---\left(2\right)$

2) utilize vacuumizing method to carry out immersion saturated to standard soil sample, saturation time is 24h;

3) saturated complete after, take out standard soil sample weigh, record the saturated quality m of standard soil sample _sat, and calculate its saturation moisture content w _sat:

$w_{sat}==\frac{m_{sat}-m_s}{m_s}\×100\%---\left(3\right)$

4) the volume V before saturated standard soil sample being freezed ₀the volume V of soil particle in the standard soil sample that equivalence one-tenth is saturated _swith the volume V of water _wsuperposition, then

$V_0=V_s+V_w=\frac{m_s}{{\mathrm{\ρ}}_s}+\frac{m_{sat}-m_s}{{\mathrm{\ρ}}_w}=\frac{m_s}{d_s}+m_{sat}-m_s=\frac{m_s}{d_s}+w_{sat}{m}_s---\left(4\right)$

In formula, ρ _sfor soil particle density, numerically equal specific density of solid particles d _s; ρ _wfor the density of pure water, ρ _w=1g/cm ³;

5) the volume V after saturated standard soil sample being freezed ₁equivalence becomes to have freezed the volume V of soil particle in rear saturated standard soil sample _swith the volume V of ice _isuperposition, then

$V_1=V_s+V_i=\frac{m_s}{{\mathrm{\ρ}}_s}+\frac{m_{sat}-m_s}{{\mathrm{\ρ}}_i}=\frac{m_s}{d_s}+\frac{m_{sat}-m_s}{0.917}=\frac{m_s}{d_s}+\frac{w_{sat}{m}_s}{0.917}---\left(5\right)$

In formula, ρ _ifor the density of ice, ρ _i=0.917g/cm ³;

6) set up saturated standard soil sample and freeze front and back volume change formula, and freeze front and back volume equivalent transformation by saturated standard soil sample in formula (4) (5), obtain the computing formula of the frozen-heave factor α of saturated standard soil sample:

$\mathrm{\α}=\frac{V_1-V_0}{V_0}\×100\%---\left(6\right)$

$\mathrm{\α}=\frac{0.09w_{sat}{d}_s}{(1+w_{sat}{d}_s)}\×100\%---\left(7\right)$

Saturated clay frozen-heave factor α is obtained in closed system about saturation moisture content w by above-mentioned steps _satwith specific density of solid particles d _scomputing formula.

Whole computation process below in conjunction with a standard soil sample describes calculating effect of the present invention in detail:

(1) fetch earth in the clay layer of working-yard, Tianjin, will fetch earth according to appointment specification is processed as standard soil sample, and reserve part processing after remaining soil, calculate standard soil sample volume V ₀=196.25mm ³.

(2) the standard soil sample quality first recorded under native state is 369.2g and remaining soil property amount is 14.5g.Then drying the soil particle quality that remaining soil sample records remaining soil is 12.1g, and obtaining its natural moisture content is 19.5%, and carrying out pycnometer method to the soil particle of remaining soil after drying, to measure its specific density of solid particles be 2.73g/cm ³, obtaining standard soil sample soil particle quality by above step is 308.9g.

(3) utilize vacuumizing method to carry out immersion saturated to standard soil sample, saturation time is 24h.

(4) saturated complete after, take out standard soil sample weigh, recording its saturated rear quality is 410.3g, show that its saturation moisture content is 27.6% as calculated.

(4) by the standard soil sample after saturated, put into household freezer, household freezer temperature is-20 DEG C, and freeze-off time is 120h.

(5) standard soil sample freezed is taken out, the volume change of bioassay standard soil sample.First a soil sample diameter d is measured along standard soil sample height every 1mm _i, corresponding numerical value is in table 1, and calculating its mean diameter D is 5.13mm.Then measurement standard soil sample height, its height change is only 0.003mm, can ignore.Finally calculating the standard soil sample volume after frost heave is 206.93mm ³.

The soil body diameter at table 1 respective heights place

(6) formula is utilized calculate the theoretical frozen-heave factor α of standard soil sample ₁, wherein w _satfor saturation moisture content, w _sat=32.8%, d _sfor specific density of solid particles, d _s=2.75g/cm ³, calculate α ₁=3.88%.

(7) formula is utilized calculate the actual frozen-heave factor α of standard soil sample ₂, wherein V ₀for freezing front standard soil sample volume, V ₀=196.25mm ³, V ₁for having freezed rear standard soil sample volume, V ₁=206.93mm ³, calculate α ₂=5.16%.

(8) contrast step (6), the result of calculation of (7) finds, in closed system, the calculated value of saturated clay frozen-heave factor and actual measured value are closely.Can reach a conclusion, in the closed system that the present invention sets up, the computing formula of saturated clay frozen-heave factor, is very reliable.Analyze and there is the reason of error: one is that soil sample cubing after freezing exists slight error; Two is the free frost heaves of soil sample, and constraint, does not produce some frost heave cracks; Three is that soil particle in soil sample and soil water (ice) are subject to breathing effect, there is microdeformation.The method is applied in engineering practice, more effectively, more quickly can carries out simulation and forecast to the stratum freezing heave behavior that saturated clay body in relative closure environment causes, the cost and risk of freezing process application is dropped to minimum.Therefore, the computing method researching and developing saturated clay frozen-heave factor in closed system have great theory significance and engineering practical value.

Claims (1)

1. the computing method of saturated clay frozen-heave factor in closed system, the method comprises the following steps:

1) fetch earth in clay layer at the scene, will fetch earth according to appointment specification is processed as standard soil sample, and it is native to retain the residue after a certain amount of processing; First under recording native state, the quality m of described standard soil sample and the quality m ' of residue soil, then utilizes oven drying method to record the soil particle quality m of residue soil _s', and utilize pycnometer method to measure its specific density of solid particles d to the soil particle of the residue soil after oven dry _s, natural moisture content w and the grogs quality m of standard soil sample is drawn by following formula _s:

$w=\frac{m^{\′}-{m_s}^{\′}}{{m_s}^{\′}}\×100\%---\left(1\right)$

$m_s=\frac{m}{(1+w)}---\left(2\right)$

2) utilize vacuumizing method to carry out immersion saturated to standard soil sample, saturation time is 24h;

3) saturated complete after, take out standard soil sample weigh, record the saturated quality m of standard soil sample _sat, and calculate its saturation moisture content w _sat:

$w_{sat}==\frac{m_{sat}-m_s}{m_s}\×100\%---\left(3\right)$

4) the volume V before saturated standard soil sample being freezed ₀the volume V of soil particle in the standard soil sample that equivalence one-tenth is saturated _swith the volume V of water _wsuperposition, then

$V_0=V_s+V_w=\frac{m_s}{{\mathrm{\ρ}}_s}+\frac{m_{sat}-m_s}{{\mathrm{\ρ}}_w}=\frac{m_s}{d_s}+m_{sat}-m_s=\frac{m_s}{d_s}+w_{sat}{m}_s---\left(4\right)$

In formula, ρ _sfor soil particle density, numerically equal specific density of solid particles d _s; ρ _wfor the density of pure water, ρ _w=1g/cm ³;

5) the volume V after saturated standard soil sample being freezed ₁equivalence becomes to have freezed the volume V of soil particle in rear saturated standard soil sample _swith the volume V of ice _isuperposition, then

$V_1=V_s+V_i=\frac{m_s}{{\mathrm{\ρ}}_s}+\frac{m_{sat}-m_s}{{\mathrm{\ρ}}_i}=\frac{m_s}{d_s}+\frac{m_{sat}-m_s}{0.917}=\frac{m_s}{d_s}+\frac{w_{sat}{m}_s}{0.917}---\left(5\right)$

In formula, ρ _ifor the density of ice, ρ _i=0.917g/cm ³;

6) set up saturated standard soil sample and freeze front and back volume change formula, and freeze front and back volume equivalent transformation by saturated standard soil sample in formula (4) (5), obtain the computing formula of the frozen-heave factor α of saturated standard soil sample:

$\mathrm{\α}=\frac{V_1-V_0}{V_0}\×100\%---\left(6\right)$

$\mathrm{\α}=\frac{0.09w_{sat}{d}_s}{(1+w_{sat}{d}_s)}\×100\%---\left(7\right)$

Saturated clay frozen-heave factor α is obtained in closed system about saturation moisture content w by above-mentioned steps _satwith specific density of solid particles d _scomputing formula.