CN103184052A - Unsaturated loess modification treatment method - Google Patents
Unsaturated loess modification treatment method Download PDFInfo
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Abstract
The invention discloses a method for modifying unsaturated loess, and aims to improve mechanical strength of the modified loess under dynamic load or under the condition of wet collapse compression. The method provided by the invention comprises the following steps: firstly, phosphoric acid aqueous solution, metaborate, heavy calcium carbonate, talcum powder and light calcium carbonate are added into the modified loess; and secondly, the added substances, 15 Wt percent of water and to-be-modified loess are mixed uniformly. After the loess is modified by the treatment method provided by the invention, not only is the mechanical strength of the loess improved, but also particles are more efficiently close-grained; and further, the modified loess has impact resistance, shearing resistance, flexibility, and the method does not pollute soil texture.
Description
Technical field
The invention belongs to the geotechnical engineering field, relate to the method for modifying to the unsaturation strength of loess, can reach and improve loess foundation in the mechanical strength purpose under the travelling load effect or under the saturated yielding condition.Be primarily aimed at the unsaturation loess that shake falls into property and collapsibility.Comprising the bigger sand yellow soil of grittiness composition, and the bigger low viscosity opaque loess of silt composition, and sticking loess etc.These unsaturated soils problem in engineering is outstanding, comprises meeting the later on strong saturated yielding distortion of water, and is subjected to vibrations landslide, landslide after the dynamic stress, problems such as the infratectal saturated yielding loess of highway asphalt cavity.Present technique adopts the easy working replacement cushion method of engineering (fetch earth on the spot, add material modifiedly, stir the back backfill).This modification foundation soil can be eliminated collapsibility effectively, reaches under 200KPa, and coefficient of collapsibility is reduced to 0.001, and shake falls into that coefficient is minimum reduces to 0.2%.Permeability coefficient 4.9 * 10
-6, shear strength is greatly improved, i.e. two of the sunken property of basically eliminate shake and collapsibilitys.Can reach the one-level anti-seismic foundation treatment technology requirement of buildings in general in loess subgrade scope construction construction, highway, railway.
Background technology
China's loess mainly is distributed in Gansu, Ningxia, the Inner Mongol, Shaanxi, the Shanxi of the Yellow River middle and lower reaches, Henan and Hebei Zhu Sheng also have the unsaturation loess distribution with Xinjiang northeastward, and area coverage reaches 640,000 square kilometres, account for 6.6% of China's territory area, account for 49% of world's loess area coverage.Western China particularly, the loess distribution scope is wide, and thickness is big.Owing to form close husky source at that time, belong to eolian loess more, namely unsaturation loess mainly comprises sand yellow soil, low viscosity loess and sticking loess.The constructional feature of low viscosity opaque loess especially wherein is silt content height, and clay content is low, generally has the sunken property of collapsibility and shake.Its special built on stilts weak glued microtexture causes that intensity is low under the travelling load effect, the shake notch distortion is big, for having proposed arduous ground, engineering construction handles a difficult problem, referring to Wang Lanmin. loess kinetics [M]. Beijing: Earthquake Press, 2003:12-82. (Wang Lan Min. The Loess dynamics [M]. Beijing:seismological press, 2003:12-82).
Need the saturated yielding of handling or shake sunken property loess widely distributed in China central and west regions, Zhengzhou to Xi'an high speed passenger transportation special railway line total length 458.8km for example, collapsible loess section along the line accounts for 65% of all fronts total length, and wherein self weight collapse loess accounts for 27% of circuit length overall.There is Thick Loess distribution more widely in western part, Gansu, and shake falls into the coefficient maximum and reaches more than 10%.Because the microstructure of loess has unique dynamic properties of soils, makes it show very high earthquake vulnerability.In Central and Western China loess area, all previous macroseism (Ms 〉=8 grade: 6 times; Ms 〉=7 grade: 22 times, Ms 〉=6 grade: 52 times) all once caused serious earthquake landslide, shake loess earthquake disasters such as sunken and liquefaction, even some little earthquakes also can cause many Building Deformation in the epicentral area and collapse (for example Yuncheng Ms=3.1-3.7 level earthquake swarm in 1986).Shake falls into property loess and generally also has very strong collapsibility.Therefore the sunken property of macroseism and collapsibility are one of main ground disasters in loess area.
The processing of unsaturation loess is comparatively complicated and difficult, because nonsaturation must adopt bigger grouting pressure, it is rare that unsaturated soil was in the milk, and causes the subsidence of foundations probably.Therefore, research is simple and the effective technology be badly in need of in geotechnical engineering construction of Loess Subgrade method is with a wide range of applications.
The general processing of loess has following several method: the loess shape silt that Treatment by Dynamic Compaction thickness is big, referring to Wang Lanmin. loess kinetics [M]. Beijing: Earthquake Press, 2003:12-82., make the shallow-layer microstructure that bigger variation take place, in, macrovoid reduces, degree of compactness improves between the particle, and shake falls into coefficient and can fall below 1%.Also has the silication slip casting method, compaction pile method and replacement cushion method etc., see the building aseismicity standard, see People's Republic of China's industry standard .GB/J 25-90 Code for building construction in collapsible loess zone [S]. Beijing: Chinese architecture press, 1990:12-18. (The industry standard of the People's Republic, GB/J 25-90.The collapsible loess area building codes [S]. Beijing:China architecture press, 1990:12-18.), urban district, Lanzhou building aseismicity design discipline. Gansu Bureau of Technical Supervision province-norm, in October, 2007, (Lanzhou city code for seismic design of buildings. Gansu province technical supervision bureau standard, in October, 2007.).The cushion method is that subbasal yellow soil horizon of collapsibility is all dug out, and the artificial bed course soil in generation is generally the dirt of 3:7, and the shake of the soil after the backfill under 200 kPa dynamic stress falls into coefficient less than 1%.
The geotechnical engineering chemistry is one of main method that changes geotechnological Cheng Xingzhi, see Xiong Houjin, Lin Tianjian, Li Ning. geotechnical engineering chemistry [M]. Beijing: Science Press, 2001:7-100. (Xiong hou-jin, Lin tian-jian, Li ning. Geotechnical Chemistry. Beijing:Science Press,, 2001:7-100.), during to the chemical treatment of unsaturation loess, than complexity and effective means such as silicification method.Method is: inject CO
2Gas makes in the soil air and part pore water by CO
2Gas is replaced, and generates carbonic acid, and the surface forms hydrocarbonate, pours into sodium silicate solution, carbonate energy and CO in the soil
2Form supercarbonate, further play cementation with silicate effect precipitated silicic acid salt hydrate again, also (Ba K) forms hydrosilicate and SiO for Ca, Mg with other basic metal and the sodium silicate solution that does not solidify
2Gel, see Yang Zhongzheng. the carbonic anhydride silicification is reinforced application [the C] // national loess academic conference collected works of Central Shanxi Plain loessland. Urumchi: Xinjiang science and technology health press, 1994:23-28.(YangZhongZheng. The Carbonic acid gas silicification method to reinforce the application of Guan-zhong loess [C]. The national loess academic meeting collection. Urumqi:xinjiang technology health press, 1994:23-28.), this method is effective, but handle complexity, cost is higher.Its most important theories is to generate the hydration salt with weak acid, increases consolidation strength.Other method has, as handling collapsible loess with the densification injection process, prescription adopts the cement-sodium silicate slurry, cement-loess slurry, loess-cement-coal ash pulp etc., see striking chapter duty. densification method grouting treatment collapsible loess loess foundation [C]. the 4th ground handled the academic discussion collection of thesis. Hangzhou: press of Zhejiang University, 1995:35-42. (Fei Zhang Qin. Pressure grouting treatment secret collapsible loess foundation [C]. The 4 th foundation treatment seminar proceedings. Hangzhou, zhejiang university press, 1995,35-42.).People such as Deng An adopt sand one granules of polystyrene light filler etc. evenly to mix according to a certain ratio to carry out modification, see Deng An, Xiao Yang, Liu Hanlong. sand-granules of polystyrene light filler Study of engineering characteristic [J]. the geotechnical engineering journal, 2008,30 (8): 1141-1145. (DENG An, XIAO Yang, LIU Hanlong.Engineering behavior of lightweight fills of sand-EPS beads[J] Chinese J. Geot. Eng., 2008, V30 (8): 1140-1145).Also useful flyash improves the strength of loess characteristic, proportioning is: 10～30% lime, 2% cement and 10%～30%, see the summer fine jade, Yang Youhai, Geng Xuan. the experimental study [J] of flyash and lime, cement improvement loess filler. Lanzhou Jiaotong University's journal, 2008,27 (3): 40-43.(Xia qiong, Yang you hai, GengXuan. Fly ash and lime, cement improvement of loess packing test research [J]. Journal of lanzhou jiaotong university, 2008,27 (3) :-43..
Summary of the invention
The invention provides a kind of physico-chemical process that unsaturation loess is carried out modification.
Unsaturation loess method of modifying of the present invention is to add phosphate aqueous solution, metaborate and water-ground limestone in the loess that is modified, and talcum powder and light calcium carbonate, and mixes after the material that adds and the loess stirring that is modified.
Add concentration among the present invention and be 10% phosphate aqueous solution in the loess that is modified, the borate of adding is barium metaborate.
In the unsaturation loess method of modifying of the present invention, the barium metaborate granularity of adding is the 0.045-0.1 millimeter, and the light calcium carbonate granularity of adding is the 0.045-0.125 millimeter, and the talcum powder granularity of adding is the 0.01-0.05 millimeter, and:
A. for sand yellow soil, the phosphate aqueous solution amount of adding is 2-5%, and the barium metaborate amount of adding is 6-13%, and the water-ground limestone amount of adding is 1-2%, and the light calcium carbonate amount of adding is 2-5%, and the talcum powder amount of adding is 3-5%;
B. for low viscosity loess, the phosphate aqueous solution amount of adding is 5-8%, and the barium metaborate amount of adding is 6-13, and the water-ground limestone amount of adding is 2-5%, and the light calcium carbonate amount of adding is 1-2%, and the talcum powder amount of adding is 3-5%;
C. for viscosity loess, the phosphate aqueous solution amount of adding is 2-5%, and the barium metaborate amount of adding is 6-13, and the water-ground limestone amount of adding is 2-5%, and the light calcium carbonate amount of adding is 3-5%, and the talcum powder amount of adding is 1%.The ratio of the above various components that add all is weight percentage.
Modification theory of the present invention is as follows: the chemical ingredients of Chinese loess is based on SiO2, and its content is 47%-64%; Secondly be Al
2O
3, CaO, content are 9.6%-27.7%; Moreover be Fe
2O
3, MgO, Na
2O, FeO, TiO
2With MnO etc., content is 4.1%-28%.All the other are trace element, and content is lower than 1%, on the whole, and based on the weakly alkaline salt.Need the pH value of the original state collapsible loess of modification to be approximately 6.5-7.5, because multiform is formed in the semiarid climate condition, the powder composition is more, and its weak glued composition is with CaCO
3, Fe
2O
3, CaSiO
3Be main etc. weakly alkaline salt, water content is few, produces the hydrogen bond polymerization hardly, mainly presents the weak glued microtexture with abundant built on stilts hole, and its mechanical strength is extremely low.Fall into property loess as the shake that forms under the dry and cold weather condition such as area, the west of Gansu Province, Gansu, the cementing material that plays cohesive force is mainly CaO and CaCO
3, the grain size proportion of its particle is also unreasonable, and soil sample becomes weakly alkaline more, and bond is poor, is easy to generate destructive distortion.
Unsaturation loess method of modifying of the present invention is the acidifying modification technology, its principle is that phosphoric acid of utilizing lower concentration etc. carries out acidification to silt, destroy the granular built on stilts microstructure based on gluing a little less than the calcium carbonate that forms under the arid climate, add weak borate family then, again formed the chemical bond of cementation, as boron oxygen key, phosphorus oxygen key, hydrogen bond etc.; Add stopping composition then, be used for adjusting the grain diameter proportioning as calcium carbonate or talcum powder, increase soil body shear strength, shock resistance, water permeability etc. are eliminated the modification purpose that shake falls into property and collapsibility thereby reach.
The characteristics of this modification technology are: 1), with the acid-basicity of phosphoric acid modification soil, adjust pH value, and adopt metaborate to increase the chemical bond strength of loess cementing material; 2) adopt the filler formulation of different grain size proportioning to improve native whole mechanical strength, comprise shearing resistance, travelling load intensity, water repelling property etc.Specific as follows:
1) adds small amounts of phosphoric acid and boric acid barium salt and increase consolidation strength.
Among the present invention, the boron salt that adds after dehydration under the effect of acid can with the boron bridged bond of other metal ion formation-B-O-B-as shown in Equation 1, the boron bridged bond can form title complex with other metal-salt, forms strong chemical bond between particle, thereby plays glued reinforcement effect.
Formula 1(boron salt chemical bond formula)
Phosphoric acid among the present invention and other salt effect can form as hydrosilicate, hydrated carbonate, hydrated iron hydrochlorate etc.The main effect of phosphoric acid is to allow basic oxide generate a series of salt hydrates, and the dehydration back produces following: boron oxygen key (1-2), siloxane bond (1-3), hydrogen bond are as (1-4), (1-5), (1-6), (1-7) formula.Therefore, the interaction energy of acid strengthens the come out salt of weak acid of cementation of leaching and forms stronger chemical bond, thus the increase consolidation strength.Its reaction is as follows
3M
++3（—BO2—）=3MBO2- (M: K+, Na+,H+,Mg2+….) (1-2)
SiO2+CaCO3+H+=CaSiO3·H2O +CO2 (1-3)
3CaCO3 +H3PO4+3H2O=2Ca(HCO3)2·H2O +Ca(H2PO4)2·H2O (1-4)
Fe2O3+ 6H++3H2O= 2Fe(OH)3·3H2O (1-5)
MgCO3+2H++2H2O=Mg(HCO3)2·2H2O (1-6)
Al2O3 +6H++ 5H2O=2Al(OH)3·2H2O (1-7)
2) add multiple filler among the present invention, thereby overcome the single shortcoming of particle size of a kind of powder (other method of modifying such as cement or lime modified), reached the purpose that increases soil strength.
Consider the granular size of multiple original state unsaturated soil among the present invention, adjust the grain diameter grating, add fillers such as the talcum powder of corresponding granularity or calcium carbonate, make after the modification grain size proportion of soil property particle reasonable, improve its mechanical property, make particle more effectively closely knit, comprise shock resistance, anti-shear performance and snappiness.Simultaneously, method of modifying of the present invention can not produce soil property and pollute.
Description of drawings
Fig. 1 is the residual strain-dynamic stress correlation curve of Yongdeng acid modification loess
Among the figure: h0, h1, h2, h3, h4 are respectively undisturbed soil and four sour modified formula curves.
Residual strain-dynamic stress the correlation curve of Fig. 2 Yongdeng acid modification loess
Among the figure: h0, h5, h6, h7 is respectively undisturbed soil and three correlation curves that sour modification soil is filled a prescription.
1000 times of microstructure photos of the undisturbed soil microtexture of Fig. 3 unsaturation loess
Show among the figure that original state loess has abundant built on stilts hole and weak glued supporting structure.
Fig. 4 is the energy spectrogram of the undisturbed soil of unsaturation loess
The peakedness ratio of the calcium of undisturbed soil (Ca) element is bigger as seen from the figure, is silicon (Si) secondly, aluminium (Al), and the peak value of iron (Fe) element is less, this is the built on stilts loose accumulation microtexture that forms under a kind of dry and cold weather condition.
1000 times of microtexture photos of Fig. 5, Fig. 6 and modification soil after Fig. 7 is different modified formula modifications
Among the figure: h1, h2 are respectively different modified formulas with h3, and more built on stilts hole is arranged in the h1 prescription microstructure; H2, forms the hydration mineral aggregate and is embedded between the silt particle with the boric acid barium salt that adds because the eluviation of phosphoric acid has produced a large amount of salt hydrates, plays tangible cementation; The microtexture photo of h3 prescription modification soil, for intensity higher inlay cement structure, cementing material wherein is more transparent cement particle, glued situation is better.
Fig. 8, Fig. 9 and Figure 10 are respectively the energy spectrogram of h1, h2 and h3 prescription modification soil
The Fe element increases in the cementing material of h1, h2 and h3, wherein h
3The power spectrum ultimate analysis of cementing material shows, the content of Fe element obviously increases, even surpass the content of Ca element, barium (Ba) element peak value clearly, and Ba element peak value does not almost have in undisturbed soil, can be defined as the boric acid barium salt in the modified feedstock, and between particle, form the material of cementation.
Figure 11 and Figure 12 are the modification dried 1500 times of microtexture photos of soil and the energy spectrogram of h4 prescription
The shake of the modification soil of h4 prescription falls into the coefficient minimum, is 0.7% under 200KPa,, h4 number prescription, in air, place the soil sample microstructure photo behind a couple of days complete drying.Change the very high cotton-shaped glued microtexture of intensity into after showing drying; Power spectrum shows that the barium constituent content in the granule is very high, is the modified material that adds.
Figure 13, Figure 14 is 1500 times of microtexture photos of h4 prescription modification soil (natural moisture content 13%) and can spectrogram
Figure 13 is the h4 number soil sample photo under the prescription natural moisture content, and structure shows particles filled more full and uniform, the cementing matter showed increased between the particle, and particle is horizontal distribution, and hole is very little; The microstructure photo shows the clay particle of bulk, and power spectrum shows that the clay barium constituent content of bulk wherein is very high, and the cement structure of bulk obviously strengthens than the built on stilts pore texture of undisturbed soil.
Figure 15 is the microtexture photo of 500 times in h1 prescription modification soil
Produced transparent clay cementing material between the h1 particle, but in the h1 prescription microstructure more built on stilts hole has been arranged.
Figure 16 is the microtexture photo of 500 times in h4 prescription modification soil
The microstructure photo is shown as the clay particle of bulk, power spectrum shows that barium constituent content wherein is very high, the cementation of bulk obviously strengthens than the built on stilts pore texture of undisturbed soil, changes the very high cotton-shaped glued microtexture of intensity into, satisfies the requirement of one-level seismic design standard substantially.
Figure 17 is 1500 times of microtexture photos of h5 prescription modification soil
Disperse more evenly between the h5 particle, glued fully h5 is 0.75% in the residual strain of 100 kPa, the requirement of basic meeting tier 2 seismic design standard.
Figure 18 can spectrogram for h5 prescription modification soil
Since be calcium material 10% in the h5 prescription, boron material 2%.Energy spectrum analysis shows that the content of Ca element is than other soil sample height; Because of the eluviation that phosphoric acid rose, making has more Zn in the cement particle, Fe, S, K element deposition simultaneously.Compare with undisturbed soil sample, these constituent contents increase, and also have tangible Ba element peak value simultaneously.
Figure 19 and Figure 20 are 1500 times of microtexture photos of h6 prescription modification soil and can spectrogram
The h6 cementing material becomes dispersed to arrange rather than the reunion shape, so cementation does not have the h5 prescription strong.
Figure 21 and Figure 22 are 1500 times of microtexture photos of h7 prescription modification soil and can spectrogram
H7 makes somebody a mere figurehead the quantity showed increased of hole owing to there not being boratory adding, and the h7 prescription has significantly built on stilts hole, has influenced cement structure intensity, and demonstration h7 fills a prescription significantly built on stilts hole, has influenced cement structure intensity, the vital role of visible boron salt.
Figure 23,24,25 is respectively the microstructure photo of 500 times in three prescriptions of h5, h6, h7 modification soil
Being uniformly dispersed of the h5 prescription cement particle that moving residual strain is less, the cementing matter contact area is big; The h6 cementing material disperses inhomogeneous, and bond is low.H7 prescription soil sample microstructure has significantly built on stilts hole.Therefore the h5 granule is uniformly dispersed, and is glued effective, and shake falls into property and obviously weakens.
Figure 26 modification soil shear strength correlation curve
The curve that indicates prismatic black among the figure is sour method modification loess, and the square dot mark curve among the figure is original state loess curve.Detect through shearing test, the mechanics shear strength of soil has obtained tangible improvement.What especially will say is the native saturated certain shearing resistance that still has later of modification, shown in the curve that indicates positive triangle among Figure 26, illustrate modification of the present invention soil after saturated mechanical strength also can reach certain requirement, under at 200KPa, still have shear strength.
Figure 27 saturated yielding deformation coefficient and pressure dependence curve
By shown in Figure 27, the compression factor of water immersion test coefficient of collapsibility under (100-200kPa) is 0.058mPa, saturated gravity pressure 26.8kPa, self-collapsibility coefficient 0.001.
The geotechnical test achievement summary table of Figure 28 given the test agent
As seen from Figure 28, the native optimum water content after the modification is 1.72g/cm3, and the maximum dry density water content is 18%, and void ratio only is 0.57.Plastic limit index 18.5, liquid limit 27.1.After the modification soil coefficient of collapsibility only be 0.001, be 4.55 * 10-6 to permeability coefficient vertically, level to permeability coefficient be 5.65 * 10-6, the compression set coefficient is 0.058, the cohesive force of original soil and sliding angle are 50.8KPa and 30.50C.
Figure 29 is the compaction test results of modified test sample of the present invention
Test sample water content of the present invention and dry density figure after modification is handled, namely P σ-W relation curve is seen Figure 29, the heavy 2.5kg of the hammer of employing, hammer floorage 19.64cm2, fall apart from 30cm, hit real three layers, every layer 25 is hit, compaction test records, and maximum dry density is 1.72, and optimum water content is 18%.Embodiment
(1) at first judges the classification of the loess sample of handling.The lithologic character of loess comprises grain size characteristic, mineral characteristic, chemical feature and constitutional features etc.The particulate component of Chinese loess belongs to sandy silt and viscosity silt based on powder in rock-soil classification.For example the granularity of Chinese loess has certain Changing Pattern at space-time.In time, the stratum is from experienced new, and loess grain size is by thin chap; Sand grain content increases, and clay content reduces; Spatially, from the north-westward southeast, loess grain size from the coarse to fine, sand grain content reduces, clay content increases.As table 1, because the grain diameter of original state loess is divided into sand grains (0.05-0.25mm); Powder (0.005-0.05mm); Clay (＜0.005mm).But the content of these particulate components is different in three different class soil.Be that sand yellow soil is based on the sand grains particle; Opaque loess (i.e. low viscosity loess) is based on the powder particle; Sticking loess clay content is more.Therefore, at first should judge needs to handle the loess sampling spot, and judgement is to belong to sand yellow soil, loess (mainly comprising sandy silt and viscosity silt), and that in the sticking loess is a kind of, to determine to add the prescription of filler.
Table 1 actual measurement loess sand grains, powder and clay
(2) adding phosphate aqueous solution adjusts the pH value of soil sample and adds material modified; Need the original state loess pH value of modification to be generally 6.5-7.5, because multiform is formed in the semiarid climate condition, the powder composition is more, and its weak glued composition is with CaCO
3, Fe
2O
3, CaSiO
3Be main etc. weakly alkaline salt, water content is few, produces the hydrogen bond polymerization hardly, and its mechanical strength is extremely low.Therefore suggestion at first adds 10% phosphate aqueous solution and adds and stir slaking in burying when handling, and pH value drops to about 5-6, and it is material modified to add barium metaborate etc. again, just can reach effect preferably.
(3) calculate proportioning according to the situation of soil, add the calcium filler.After phosphate aqueous solution, metaborate adding mixing, according to the proportioning of table 1, according to sand yellow soil, loess still sticking loess judged result is determined proportioning, adds water-ground limestone, light calcium carbonate, talcum powder etc. again.At construction process, for easy construction, also can be with phosphate aqueous solution, metaborate and water-ground limestone, and disposable addings such as light calcium carbonate and talcum powder, but effect is less better.In the construction material that adds and the loess that is modified are mixed, backfilled roadbed supported after the stirring, can reach soil mass consolidation intensity, improve the purpose that saturated yielding and shake fall into.
In the embodiments of the invention three kinds of unsaturation loess have been carried out the modification processing, these three kinds are respectively: sand yellow soil, low viscosity loess and sticking loess.The design of the granularity of these three kinds of loess and the different grain size material modified proportioning of shared table 2 in loess.
The design of the material modified proportioning of table 2
To be all the other total filler content of 6-13%. be 6-12% to barium metaborate in the table 2.
Below be embodiments of the invention.
Falling into property loess with the shake that forms under the dry and cold weather condition such as area, the west of Gansu Province, Gansu is example, and the cementing material that plays cohesive force is mainly CaO and CaCO
3, the grain size proportion of its particle is also unreasonable, and soil sample becomes weakly alkaline more, and bond is poor, is easy to generate destructive distortion.Be example with opaque loess sample, because this layer soil is the dry and cold settling that falls by force under the husky condition, grain diameter is bigger, is approximately 0.09-0.120mm and accounts for more than 55%.Therefore, to add the thinner light calcium carbonate (0.045-0.125mm) of particle, fillers such as talcum powder are main (0.045-0.05mm) and an amount of water-ground limestone (0.32-0.4mm) during processing.Adjust prescription according to test, among the embodiment in the loess that is modified: 1) dig out 1000 kilograms of original state loess, 10% phosphate aqueous solution of adding, total weight percent is 3%, i.e. 30 kilograms of phosphate aqueous solutions; Add the back and add barium salt 10%, i.e. 100 kilograms of boric acid barium salts; Place to stir 2) add then such as, water-ground limestone, weight percent are 5%, namely 50 kilograms; 2%, 20 kilogram of light calcium carbonate, 4%, 40 kilogram of talcum powder; 3), also need according to the optimum moisture content under the maximum dry density (18%), add suitable water according to the degree of drying of soil, according to 18% weight percent, need add 150 kg of water again as the soil of complete drying, add the back and stir, it is backfilled roadbed supported to mix the back.
Shake falls into the testing method of coefficient
Shake of the present invention falls into coefficient (being residual strain) testing method, all adopts the test of electromagnetic type vibration triaxial apparatus.This pilot system can be applied directly to the xial feed of random waveform on the sample by moving up and down of loading ram.
In the place that needs are tested, take the undisturbed soil sample of different depths, fixed on the electromagnetic type vibration triaxial apparatus under original burden pressure, test.Consolidation ratio is determined by following formula:
General to northwest loess
About 24o, get usually
=1.69.
The definition that falls into according to shake is adjusted to shake under the different amplitudes in same earthquake motion time history to 5～7 samples of same group and is fallen into test, according to the axial stress (peak value in the trial sheet
) and strain time-histories (residual strain
) corresponding relation just can obtain a seismic subsidence of loess curve.(maximum dry density according to optimum formula is 1.72g/cm to need to control soil specimen moisture content and dry density in concrete test
3, optimum water content is 18%).Come the treatment effect of soil sample is compared judgement to shake the residual strain coefficient that falls into test.The correlation test data of low viscosity opaque loess below only are provided, this loess in three kinds of loess, shake fall into property and collapsibility all very big, for example the sunken coefficient of maximum shake is very representative up to 6-10%.
In the test of the present invention, isobaric fixed after-applied different dynamic stress, the residual strain that records is drawn following Fig. 1 and Fig. 2.H wherein
0Be undisturbed soil sample curve, h
0Residual strain under 100 kPa dynamic stress is up to 6-10%, and h1-h7 is that the shake of corresponding prescription soil sample test falls into curve.
Concrete test recipe and test result
Get the low viscosity opaque loess soil sample of place, Yongdeng, Lanzhou typical case, be mixed with test sample by the mix proportion scheme of table 3 and table 4, wherein the boron material mainly is the boric acid barium salt.Filler comprises: light calcium carbonate, water-ground limestone, talcum powder etc., wherein phosphorylated ligand is set to 10% solution.Additional proportion such as table one.The h0 prescription is not for adding the undisturbed soil sample of modification, and h1-h4 is the soil sample numbering behind the adjustment different ingredients.The test soil sample of preparation is filled a prescription according to h0-h4 and is made the earth pillar of high 10 * 5 cm2 respectively, and the water content of preparation is 15%, and dry density is adjusted into 1.58 g/cm3.Each sample stirs then adding filling mixture ratio as shown in Table 1.The test shake falls into coefficient.
The sour modification proportioning of table 3 loess shape silt, the h1-h4 prescription
Show following results according to table 3 and Fig. 1:
(1) residual strain of h1 and h2 prescription under the 100kPa dynamic stress is respectively 1.8% and 2%.The difference of two prescriptions is: h1 prescription calcium material and boron material add-on are respectively 10% and 2%; H2 prescription calcium batching and boron material amount are respectively 15% and 2%; As seen the calcium batching namely has more significantly improvement to the sunken property of the shake of loess for major ingredient reaches 10%.
(2) h3 number prescription is for increasing boron material proportioning to 6%, and the residual strain of soil sample under the 100kPa dynamic stress reduces to 1.1%, and fatigue resistance is enhanced, and reaches the second-stage treatment standard.But the residual strain under the 200kPa dynamic stress but is 3.5%, and the shake that does not reach primary standard falls into the purpose of coefficient below 1.5%.H3 prescription filler total amount is 22%, and wherein the amount of boron salt is 6%, and the calcium batching is 16%.
(3) because the shake that the auxiliary agent that adds in the h1-h3 prescription and boron filler help to improve loess falls into property, in the h4 prescription, further improve the amount of boron salt, original 6% amount is increased to 13%, the filler total amount still is 22%, the calcium batching is reduced to 8%, the residual strain of reducing under 0.2%, the 200kPa dynamic stress in the residual strain under the 100kPa dynamic stress is reduced to 0.7%, reaches antidetonation and falls into the primary standard treatment effect.
The residual strain of Yongdeng, Gansu modification loess-dynamic stress correlation curve as shown in Figure 1, h1 and h2 prescription is compared with the h0 prescription, shake falls into property and has clear improvement, the h3 improved effect is better, h4 reaches the improved effect of eliminating residual strain fully substantially.
Because the add-on of phosphoric acid directly has influence on glued salt power, so need test definite to the add-on of phosphoric acid.Preceding four prescriptions are the test-results that increase filling adding amount under the constant condition of phosphorus acid content.Change change to modification soil mechanics performance in order to study phosphorus acid content, the amount of filler is reduced, increase phosphorus acid content, see Table 4 and h5, h6, the h7 prescription of Fig. 2.
(1) prescription h6 compares with the original soil h0 curve that does not add phosphoric acid with h7, though the amount of calcium filler is very low, is 5% add-on, but still plays the effect that reduces residual strain.From Fig. 2 and table 3, under 100 kPa, the residual set coefficient is reduced to 1.5% (104 kPa) from 4.5% (101kPa) of original state sample, has strengthened the fatigue resistance of modification soil significantly.But the phosphorus acid content of h6 and h7 prescription is increased to 3.98% from 3.76%, does not play the effect of further gaining in strength.
(2) modifying function of prescription h5 is comparatively obvious, this prescription is as the h5 curve of table 3 and Fig. 2, the content of its phosphoric acid is 2.9%, light calcium carbonate content is 10% of dry ground, the content of boron material is 2%, under 100 kPa dynamic stress, the residual strain coefficient of original soil is reduced to 0.75% from 4.5%, can reach the second-stage treatment requirement substantially.Therefore, the add-on of phosphoric acid is defined as about 3 ± 0.1%.
The sour modified feedstock proportioning h5-h7 of table 4 Yongdeng loess shape silt
The improvement situation of loess microtexture and mechanical property after the modification
For further checking the improvement situation of loess modification front and back microstructure difference and mechanical property, the natural loess before and after the modification is carried out Electronic Speculum and energy spectrum analysis.
Shown in the electromicroscopic photograph as shown in Figure 3, undisturbed soil sample particle aerial construction is apparent in view, the rare Fig. 4 of the cementing material between the particle.Analysis revealed, the content of calcium (Ca) element is bigger, is silicon (Si) secondly, aluminium (Al), and the peak value of iron (Fe) element is less.This is the built on stilts loose accumulation microtexture that forms under a kind of dry and cold weather condition.
The microstructure photo of soil sample after adopting method modification of the present invention see Fig. 5 to the microtexture photo that Figure 7 shows that prescription modification soil and Fig. 8 can spectrogram to shown in Figure 10.Produced transparent clay cementing material between the h1 particle.The power spectrum ultimate analysis of cementing material shows, the content of Fe element obviously increases, even surpass the content of Ca element, barium (Ba) element peak value clearly, and Ba element peak value does not almost have in undisturbed soil, can be defined as the boric acid barium salt in the modified feedstock, and between particle, form the material of cementation.
Shown in the power spectrum of h2 number prescription sample, the clay aggregate about 2 μ m of photo square frame part shows the content of ferro element up to 74%, considerably beyond other element, and Ca, K(potassium), constituent content such as Al also rolls up.Confirm the analysis of front, because the eluviation of phosphoric acid has produced a large amount of salt hydrates, with the boric acid barium salt that adds, form the hydration mineral aggregate and be embedded between the silt particle, play tangible cementation.
The microtexture photo of h3 prescription modification soil, for intensity higher inlay cement structure, cementing material wherein is more transparent cement particle, glued situation is better.Residual strain under the 100kPa shows that h3 recipe ratio h1 prescription and h2 prescription have bigger raising, energy spectrum analysis to show that the content of Fe element all increases as shown in the figure.
Figure 11 falls into the microtexture photo of the h4 number dry post-modification soil of filling a prescription of coefficient minimum for shake, and Figure 12 falls into the energy spectrogram of the h4 number dry post-modification soil of filling a prescription of coefficient minimum for shake, and wherein Figure 11 is the soil sample microstructure photo behind placement a couple of days complete drying in air.Figure 13 is the h4 number soil sample photo under the prescription natural moisture content, and Figure 14 is the energy spectrogram of this soil sample.The microstructure photo of Figure 13 is shown as the clay particle of bulk, and power spectrum shows that barium constituent content wherein is very high, and the cementation of bulk obviously strengthens than the built on stilts pore texture of undisturbed soil, changes the very high cotton-shaped glued microtexture of intensity into.
Contrast h1 and h4 prescription modification soil, be respectively the microtexture photo (500 times) of Figure 15, Figure 16.Particles filled more full and uniform as among Figure 16, the cementing matter showed increased between the particle, particle is horizontal distribution, and hole is very little; And in the h1 prescription microstructure more built on stilts hole is arranged among Figure 15.Therefore the treatment effect of h4 prescription has reached the weak cement structure that changes undisturbed soil substantially, and shake falls into coefficient and is down to 0.7% (200 kPa are following).
H5 among the present invention, h6, three prescriptions of h7 modification soil design phosphorus acid content is respectively 2.96%, 3.76%, 3.98%.Institute's soil sampling is the loess of 10 m soil layers of Yuzhong County, Gansu Province.Figure 17 is h5 prescription soil sample microstructure photo, owing to be calcium material 10% in the h5 prescription, boron material 2%.Energy spectrum analysis shows that the content of Ca element is than other soil sample height; Because of the eluviation that phosphoric acid rose, making has more Zn in the cement particle, Fe, S, K element deposition simultaneously.Compare with undisturbed soil sample, these constituent contents increase, and also have tangible Ba element peak value simultaneously, see Figure 18.H5 is 0.75% in the residual strain of 100 kPa, the design requirements of basic meeting tier 2 antidetonation standard.
Figure 19 and Figure 21 are the microtexture photo of h6, h7 prescription modification soil, and Figure 20 and Figure 22 are respectively the energy spectrograms for h6, h7 prescription modification soil.Wherein the boron filling adding amount of h6 prescription is reduced to 1.7%, h7 prescription and does not add the boron filler.The h6 cementing material becomes dispersed to arrange rather than the reunion shape, so cementation does not have the h5 prescription strong.What is interesting is that Figure 19 shows that the h7 prescription has significantly built on stilts hole, has influenced cement structure intensity.H7 makes somebody a mere figurehead the quantity showed increased of hole owing to there is not boratory adding, and visible boron material has play a part important.As shown in Figure 2, the residual strain under 100 kPa of h6 and h7 is 1.5% more greatly, and h5 is 0.75%.
Further analyze phosphoric acid and barium borate salts contg to the influence of modification soil sample microstructure.Contrast as follows: h5, h6, the phosphorus acid content of three prescriptions of h7 is respectively 2.96%, 3.76%, 3.98%, and boron material content is respectively 2%, 1.7%, 0.The microstructure photo of three prescriptions under contrasting 500 times is shown in Figure 23,24 and 25, and the characteristics of the h5 prescription that moving residual strain is less are that the dispersion of cement particle is comparatively even, and cementing matter becomes bulk more; The h6 cementing material disperses inhomogeneous, and bond is low.H7 prescription soil sample microstructure has significantly built on stilts hole.Therefore the h5 granule is uniformly dispersed, and is glued effective, and shake falls into property and obviously weakens.
The boratory adding of above-mentioned analysis revealed is discrete particles obviously, reduces the built on stilts hole quantity of soil sample.Cementing material is scattered between the particle with floss, the built on stilts weak cement structure of the soil particle that disperses is become inlay cement structure more closely and strengthened native structural strength, and the strong treatment effect that shake falls into coefficient that reduces is arranged.The borate add-on is 2%-13%.
The proportioning index of method of modifying of the present invention and with the contrast of other method referring to table 5.Sour modification loess is than the improved performance of undisturbed soil as seen from the table: 1) compression factor is reduced to 0.05 of low compressibility by original 0.6; Internal friction angle brings up to 30.5 from 16.1 of undisturbed soil; These two indexs and cement and lime conditioned soil are close.In addition, 2) maximum dry density after the modification is 1.72, and optimum water content is 18%.Plastic limit, liquid limit, plasticity index be all improvement also.Modification result of the present invention is that intensity has obtained bigger enhancing, compares with other method, and advantage is that full water-based strengthens no season cracking, the disadvantages such as fragility of modified cement method.
Table 5 method of modifying of the present invention and other method performance comparison
The experimental result of following examining report is provided by the ground feeler mechanism of Gansu Province water conservancy department with ground detection first class qualification.(Gansu Province ground feeler mechanism special seal, certificate number, 20100031.Qualification geotechnical engineering first class, concrete works first class.）
Shear strength
Through detecting, after the peracid modification, structural strength obtains very big improvement, is sour method modification loess referring to the curve that indicates prismatic black among Figure 26, and the square dot mark curve among the figure is original state loess curve.Detect through shearing test, the mechanics shear strength of soil has obtained tangible improvement.For example under 400 kPa, shear strength is brought up to 280 kg/cm3 by the 200kg/cm3 of undisturbed soil.What especially will say is that modification soil still has certain shearing resistance after saturated, shown in the curve that indicates positive triangle among Figure 26, illustrates that the mechanical strength of modification soil of the present invention after saturated also can reach certain requirement, still has shear strength under at 200KPa.
The coefficient of collapsibility test-results
The saturated yielding test-results of modification sample of the present invention, saturated yielding deformation coefficient and pressure dependence curve are seen Figure 27.Show that by Figure 27 the compression factor of water immersion test coefficient of collapsibility under (100-200kPa) is 0.058mPa, saturated gravity pressure 26.8kPa, self-collapsibility coefficient 0.001.
Lyotropic salt is analyzed
The lyotropic salt analytical results sees Table 6 Figure 28.By table 6 Figure 28 as seen after modification soil become weakly alkaline, pH value is 9.46, the corrodibility salt is as SO
4 2-Ion content only is per kilogram soil 0.064 gram, non-corrosiveness.
The analysis of table 6 lyotropic salt
Basic geotechnical test mechanical index
The geotechnical test of the test sample of the present invention after modification is handled the results are shown in Figure 29.As seen from Figure 29, the native optimum water content after the modification and maximum dry density are 1.72g/cm3 and water content 18%, and void ratio only is 0.57.Plastic limit index 18.5, liquid limit 27.1.After the modification soil coefficient of collapsibility only be 0.001, be 4.55 * 10-6 to permeability coefficient vertically, level to permeability coefficient be 5.65 * 10-6, the compression set coefficient is 0.058, the cohesive force of original soil and sliding angle are 50.8KPa and 30.50C.
Maximum dry density and optimum water content
The compaction test data of the test sample of the present invention after modification is handled are seen pd-W relation curve of Figure 29.The heavy 2.5kg of the hammer that adopts in Figure 29 test, hammer floorage 19.64cm2 falls apart from 30cm, hits real three layers, and every layer 25 is hit, and compaction test records, and maximum dry density is 1.72, optimum water content is 18%, sees pd～W relation curve.
Grain size analysis
The data of screen analysis test see Table 7(date of test: 2012-05-09).Screen analysis test shows that the flour sand grain (0.075-0.05mm) of optimum modified formula sample accounts for 25.4%; Coarse dust (0.05-0.01) accounts for 57.4%; Fine silt (0.01-0.005) accounts for 7.5%; Clay and micelle account for 13.8 altogether.
Table 7 screen analysis test
Correlation test shows:
The built on stilts weak cement structure of low viscosity opaque loess causes loess foundation to present under the travelling load effect that intensity is low, the shake notch distortion is big, and character such as strong collapsibility handle to have proposed a challenging difficult problem for ground in the engineering construction.And the method for modifying of present technique unsaturated soil is by changing its microtexture, the purpose that reaches effective reduction dynamic deformation amount reduces the generation of the residual set under the travelling load effect, can alleviate the landslide depression of earthquake groundwork effectively, run into the later problems such as loess subgrade landslide of water.Present technique adopts sour method of modifying to handle loess, namely the borate of tying effect than strong rubber is arranged as modified material by adding, with fillers such as light calcium carbonates, adjusts the grain diameter grating, reconciles the pH value of soil with the phosphoric acid diluent.Soil sample behind the adjustment test recipe is shaken the notch distortion test, analyze modification front and back changes of microstructure, the definite optimum formula of contrast.The microstructure test shows, the present invention can make can generate a large amount of hydration salt of weak acid cementing matters in the unsaturation loess particle, make that bond is obviously strengthened between the silt particle, can change or eliminate the sunken property of shake of soil from microstructure, reduce the residual strain of unsaturation loess greatly, the basically eliminate shake falls into property, and can significantly eliminate the collapsibility of unsaturation loess.
Test-results shows that sour method of modifying of the present invention can effectively improve the microtexture of loess, makes the shake notch distortion coefficient of soil sample obviously reduce, and coefficient of collapsibility reaches 0.02%, basically eliminate.Optimum formula also basically eliminate shake fall into property, shake falls into that coefficient is minimum to reach 075%.And the modified feedstock chemistry that adds is nontoxic, can not produce environmental pollution to soil layer.
Claims (3)
1. unsaturation loess method of modifying, it is characterized in that in the loess that is modified, adding phosphate aqueous solution, metaborate and water-ground limestone, and talcum powder and light calcium carbonate, and mix after the water of the material that adds and 15 Wt % stirred with the loess that is modified.
2. unsaturation loess method of modifying according to claim 1 is characterized in that adding concentration and is 10% phosphate aqueous solution in the loess that is modified, the borate of adding is barium metaborate.
3. unsaturation loess method of modifying according to claim 1 and 2, it is characterized in that: the barium metaborate granularity of adding is the 0.045-0.1 millimeter, the light calcium carbonate granularity that adds is the 0.045-0.125 millimeter, and the talcum powder granularity of adding is the 0.01-0.05 millimeter, and:
A. for sand yellow soil, the phosphate aqueous solution amount of adding is 2-5Wt%, and the barium metaborate amount of adding is 6-13Wt%, and the water-ground limestone amount of adding is 1-2Wt%, and the light calcium carbonate amount of adding is 2-5Wt%, and the talcum powder amount of adding is 3-5Wt%;
B. for low viscosity loess, the phosphate aqueous solution amount of adding is 5-8Wt%, and the barium metaborate amount of adding is 6-13Wt%, and the water-ground limestone amount of adding is 2-5Wt%, and the light calcium carbonate amount of adding is 1-2Wt%, and the talcum powder amount of adding is 3-5Wt%;
C. for viscosity loess, the phosphate aqueous solution amount of adding is 2-5Wt%, and the barium metaborate amount of adding is 6-13Wt%, and the water-ground limestone amount of adding is 2-5Wt%, and the light calcium carbonate amount of adding is 3-5Wt%, and the talcum powder amount of adding is 1Wt%.
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Cited By (6)
| Publication number | Priority date | Publication date | Assignee | Title |
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| CN103936375A (en) * | 2014-03-24 | 2014-07-23 | 番禺珠江钢管有限公司 | Curing agent for salinized sludge to achieve soil hardening and applications thereof |
| CN106049417A (en) * | 2016-06-22 | 2016-10-26 | 张耀 | Method for treating collapsible loess foundation using acid-adding presoaking method |
| CN107033911A (en) * | 2017-04-14 | 2017-08-11 | 洛阳理工学院 | A kind of unsaturation loess modification processing method |
| CN109142410A (en) * | 2017-06-19 | 2019-01-04 | 天津大学 | Consider the engineering classification method of the carbonate containing sand of each factor interaction |
| CN110510979A (en) * | 2018-05-21 | 2019-11-29 | 中国石油天然气股份有限公司 | A kind of loess pipe trench waterproof chemical slurry and preparation method thereof |
| CN112878125A (en) * | 2021-03-23 | 2021-06-01 | 姚震 | Technical scheme of regenerative material for replacing collapsible loess subgrade |
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2012
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| Publication number | Priority date | Publication date | Assignee | Title |
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| CN103936375A (en) * | 2014-03-24 | 2014-07-23 | 番禺珠江钢管有限公司 | Curing agent for salinized sludge to achieve soil hardening and applications thereof |
| CN106049417A (en) * | 2016-06-22 | 2016-10-26 | 张耀 | Method for treating collapsible loess foundation using acid-adding presoaking method |
| CN106049417B (en) * | 2016-06-22 | 2018-08-07 | 张耀 | A kind of method of acid adding presoaking processing collapsible loess foundation |
| CN107033911A (en) * | 2017-04-14 | 2017-08-11 | 洛阳理工学院 | A kind of unsaturation loess modification processing method |
| CN109142410A (en) * | 2017-06-19 | 2019-01-04 | 天津大学 | Consider the engineering classification method of the carbonate containing sand of each factor interaction |
| CN109142410B (en) * | 2017-06-19 | 2020-12-15 | 天津大学 | Engineering classification method of carbonate-containing sandy soil by considering interaction of various factors |
| CN110510979A (en) * | 2018-05-21 | 2019-11-29 | 中国石油天然气股份有限公司 | A kind of loess pipe trench waterproof chemical slurry and preparation method thereof |
| CN112878125A (en) * | 2021-03-23 | 2021-06-01 | 姚震 | Technical scheme of regenerative material for replacing collapsible loess subgrade |
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