CN1206423C - Constructing method for treating soft foundation of highway by cement, flyash and macadam - Google Patents

Abstract

The present invention discloses a constructing method for treating soft foundations of a highway by cement, pulverized coal ash and gravel piles. The present invention is characterized in that the constructing method comprises: the pile length reaches 0.8 to 1.2 meters under a bonding layer; the pile diameter is from 400 to 500 millimeters, and the strength of the pile body is from C8 to C20; the pile spacing is estimated according to a formula, and according to the designed pile length, the pile diameter and the pile spacing, the composite foundations of cement, pulverized coal ash and gravel piles are formed by making use of a pile machine for distributing the piles. The flexible bearing platforms of the composite foundations are formed by making use of 2 to 4 level matched gravels and geotextile fabrics. The present invention has the advantages that the pile forming quality, the bearing capacity, the treatment depth, etc. of the soft foundation treated by the method are superior to those of the composite foundations of dry jet mixing piles, and the treating effects, the treating quality, etc. are also superior to those of the composite foundations. In addition, because of a complete set of quality detecting means provided by the present invention, the quality can be controlled to obtain the design requirements. The method can be used for the retreatment of the foundations of a construction, the transition sections of the construction and a bridgehead, the widened section of old road embankments and collapse sections, and the reinforcing treatment of section containing the construction section and the transition section of the bridgehead.

Description

The job practices of CFG in Expressway Ground Improvement

One, technical field

The present invention relates to a kind of construction technology of Expressway Ground Improvement, the job practices of particularly a kind of CFG (CFG) in Expressway Ground Improvement, it comprises design main points and quality examination means under the control of CFG stake pile quality, the different operating mode situation.

Two, background technology

Through the practice of Expressway Ground Improvement for many years, people are classified as three classes with soft basic problem on the basis of summing up experience, i.e. stability problem, settlement issues and contain the works highway section and difference settlement issues such as end of the bridge changeover portion.Improve the Expressway Ground Improvement quality, it is essential that minimizing contains difference sedimentations such as works highway section and end of the bridge changeover portion.

Before the present invention proposes, the DJM pile compound foundation processing method is adopted in the processing that contains works highway section and end of the bridge changeover portion etc. usually, all there is deficiency in this method at aspects such as pile quality, bearing capacity and the processing degree of depth, has seriously restricted the raising of treatment of soft foundation quality.

The construction period of treatment of soft foundation, settlement after construction etc. are the problems that people were concerned about always in expressway construction, and general soft base segment is handled and adopted surcharge preloading, vacuum preloading etc., and special road section such as end of the bridge, passage etc. often adopt powder spray piling to handle.From condition of construction, powder spray piling is handled many unsatisfactory places, as settlement issues, handle effective length problem, bearing strength problem and quality control on construction problem.Research and to the serious analysis of Expressway Ground Improvement characteristics etc. by inquiry, the applicant carries out the system test and the research of CFG stake at first on new platform Expressway Ground Improvement, many useful achievements have been obtained, for applying of this soft base processing method provides the reference foundation.

Three, summary of the invention

1, goal of the invention: the objective of the invention is in order to overcome the defective of DJM pile compound foundation processing method, introduce a kind of the processing and contain the method for reinforcement ground that works highway section ground, works ground, end of the bridge transition highway section ground, old road dike are widened Ground Treatment again, works and the end of the bridge transition highway section in highway section ground, slump highway section.

2, technical scheme: for achieving the above object, the job practices of CFG of the present invention in Expressway Ground Improvement is characterized in that this job practices is:

(1) getting stake grows to and treats under the bonding course 0.8～1.2 meter, 400～500 millimeters in stake footpath, strength of the mixing pile C ₈～C ₂₀

(2) according to formula $f_{\mathrm{sp},k}=m\frac{R_k}{A_p}+\mathrm{\α\β}(1-m)f_k$ Or f _{Sp, k}={ 1+m (n-1) } α β f _kAnd $S=\sqrt{\frac{A_p}{m}}$ The estimation pile spacing, S is pile spacing, f in the formula _{Sp, k}Be nominal value of bearing capacity of composite foundation; f _kBe the natural foundation bearing capacity standard value, m area replacement ratio; The n stress ratio; A _pThe single pile sectional area; α=f _Sk/ f _k, f _SkReinforce back inter-pile soil standard value of bearing capacity; β=0.75～0.95; R _kBearing capacity of single pile standard value A _pSingle pile sectional area, m area replacement ratio;

(3), stake footpath long according to the stake of design, pile spacing utilize a stake machine to lay out pile, and form the CFG composite foundation;

(4) use 2-4 graded broken stone and geotextile to form the flexible cushion cap of composite foundation.

Process of the present invention comprises the following aspects:

(1) the determining of 5 design parameterss in the CFG pile composite foundation design, i.e. stake is long, stake footpath, pile spacing, strength of the mixing pile, cushion thickness and material.

A, long the determining of stake.

According to geologic information, get stake and grow to and treat 0.8m～1.2m under the bonding course, as about certain highway soft foundation highway section silt depth 20.6m, be severely-weathered argillaceous siltstoue below, designing pile length is got 21.6m.Hit (paddle type mill immersed tube technology) deflection with last 10 in the construction and control whole pile length.

B, stake footpath, pile spacing, strength of the mixing pile definite.

Consideration embankment filled soil height, road structure layer thickness, dynamic vehicle load and suitable safety are stocked, and following method is adopted in the estimation of bearing capacity:

$f_{\mathrm{sp},k}=m\frac{R_k}{A_p}+\mathrm{\α\β}(1-m)f_k----\left(1\right)$

Or f _{Sp, k}={ 1+m (n-1) } α β f _k(2)

In the formula: f _{Sp, k}Nominal value of bearing capacity of composite foundation; f _kThe natural foundation bearing capacity standard value, m area replacement ratio; The n stress ratio; A _pCFG single pile sectional area; α=f _Sk/ f _k, f _SkReinforce back inter-pile soil standard value of bearing capacity; β=0.75～0.95; R _kCFG bearing capacity of single pile standard value.Under the condition of known natural foundation bearing capacity standard value, bearing capacity of single pile standard value and nominal value of bearing capacity of composite foundation, try to achieve replacement ratio m by (1) formula.According to the Expressway Ground Improvement characteristics, and a large amount of tests and theoretical research, 400mm～500mm is got in the stake footpath, and strength of the mixing pile is got C ₈～C ₂₀, when calculating m, get inter-pile soil performance factor beta=0.9, inter-pile soil intensity improves factor alpha=1.5.When adopting square to lay out pile, pile spacing S presses the following formula estimation:

$S=\sqrt{\frac{A_p}{m}}----\left(3\right)$

As certain speedway slump section, situation, nominal value of bearing capacity of composite foundation f such as stock according to embankment filled soil height, road structure layer thickness, dynamic vehicle load and suitable safety _{Sp, k}Get 250Kpa, natural foundation bearing capacity standard value f _k=45Kpa.M=0.0687, A as calculated _p=0.19625m ², substitution (3) formula can get pilespacing S=1.69m, and the design pilespacing is got 1.50m.

Determining of D, cushion thickness and material.

In Expressway Ground Improvement, according to the estimation of pilespacing, on the basis of experimental study and theoretical research, cushion thickness is pressed formula and is calculated:

$\mathrm{\ΔH}=\mathrm{\λm}\×S\×\frac{f_{\mathrm{sp},k}}{f_k}----\left(4\right)$

In the formula: Δ H cushion thickness; The λ correction factor, span 0.5～0.6.As in handling certain highway soft foundation slump section, λ gets 0.526, and bed course estimation thickness is Δ H=0.3011m, design cushion thickness 0.30m.Remarks: a, pile spacing are generally at S=(3～5) d.

B, pile body test block compressive strength f _CuShould satisfy f _Cu〉=3 (R _k/ A _p), R _kThe bearing capacity of single pile standard value; A _pDowel section area.

C, course are generally selected the 2-4 graded broken stone for use.

D, the form that lays out pile adopt quincunx or quadrangle.

(2) CFG stake pile quality control.

In CFG pile driving construction process, the undergauge of pile body, hang phenomenons such as pin, broken pile and easily take place, therefore, guaranteeing pile body integrity, avoiding occurring broken pile is to need the emphasis problem that solves in the CFG pile driving construction.The integrality of pile body is by factor decisions such as the vertical extent of pile crown in the work progress and sleeve pipe, the height that promotes sleeve pipe, pipe-pulling speeds, so will pay special attention to below the control some when construction.Concrete control method is as follows:

Leveling pile machine before A, the immersed tube makes pile crown vertically be inserted in sleeve pipe, prevents from closely mud to be clamp-oned in the sleeve pipe because of sleeve pipe contacts with pile crown.When immersed tube, fall apart from can not be excessive, prevent to cause sleeve pipe to separate too greatly with pile crown because of momentum.The compound storage period can not be oversize in the immersed tube process, avoids occurring segregation phenomenon.

B, after reaching projected depth, in the stake pipe, pour into certain compound, should shake 10～15S earlier, begin tube drawing again, avoid occurring hanging the pin phenomenon.Each tube drawing height should be controlled at 0.5～0.8m, stops to dial vibrations 10～15S at interval or instead inserts the degree of depth 0.3～0.4m (both should decide on the site operation situation).In the tube drawing process, answer segmentation to add compound, compound is higher than tube drawing height 1.2m all the time in the stake pipe, and tube pulling speed is controlled in the 1.4m/min, to guarantee the integrality of pile body.

C, when tube drawing when the sludge interlayer, should suitably slow down pipe-pulling speed, the undergauge phenomenon appears to prevent pile body.

D, concrete slump are controlled at 60～80mm, and water/binder ratio should be between 0.6～0.8; The stake position should guarantee that accurately its deviation allows to be not more than 100mm, and it is vertical that pile body keeps, and perpendicularity deviation should be greater than 1%.

E, the plumb bob under hanging according to stake machine top can be controlled verticality, and verticality is controlled in 1%.

Should adopt according to actual conditions in F, the work progress and jump the technology of beating according to the order of sequence, to emit with preventing.Scale is buried on stake top at pile underground, observes construction to the extruding situation of pile, prevents that pile body is squeezed and ruptures, and understands ground, ground and emit situation.

G, if meet boulder, the stake position should suitably be shifted, and meets design requirement to guarantee pile body.Regularly the stake machine is detected, guarantee the continuity of construction.

(3) the flexible cushion cap of CFG pile composite foundation is a bed course.

Flexible cushion cap technology is CFG stake one of key technologies for application in Expressway Ground Improvement, and the step that forms flexible cushion cap is as follows:

A, employing 2-4 graded broken stone, the thickness of flexible cushion cap by formula (4) calculates.

B, in order to guarantee the globality of cushion cap, macadam respectively is provided with layer of geotextile (geo-grid or geotextiles) up and down.

C, employing door sprig be geotextile fixedly, the wide 0.20m～0.25m of door sprig, high 0.15m～0.20m; Press line space 2.5m～3.0m, vertical clearance 5.0m～6.0m.

(4) to the processing of particular case.

A, for the Soft Roadbed that carried out treatment of soft foundation, end of the bridge changeover portion with contain the situation in works highway section, in 1/3～1/4 ratio sand pile (available with the machine construction) is set, the longitudinal drainage passage is provided; The macadam side opens wide, and the transverse drainage passage is provided.

Add reinforcing cage in B, the CFG stake and can play the antislide pile effect, to solve unusual sedimentation, the end of the bridge reinforcing soft foundation problem during speedway is operated.

C, CFG stake do not add water in stirring, and directly pour into immersed tube (immersed tube diameter 0.10m～0.15m), can solve the consolidation process problem of deep soft foundation section.

3, beneficial effect: the present invention compared with prior art, its remarkable advantage is: no matter this method all is better than DJM pile compound foundation at aspects such as pile quality, bearing capacity and the processing degree of depth, and, also be better than DJM pile compound foundation at aspects such as treatment effect, processing quality.A whole set of quality examination means provided by the invention in addition can be controlled quality and reach designing requirement.The present invention can be used for the reinforcement processing of handling, contain works highway section and end of the bridge transition highway section again that works ground, works and end of the bridge transition highway section, old road dike are widened highway section, slump highway section.

Four, description of drawings

Accompanying drawing is a CFG pile composite foundation design flow diagram of the present invention

Five, the specific embodiment

In order to verify the reliability of present techniques, applicant and new platform speedway Co., Ltd cooperate, and carry out the system test and the research of CFG stake on new platform Expressway Ground Improvement at first, have obtained many useful achievements.

Embodiment 1: to the processing of end of the bridge section roadbed.

In order to reduce end of the bridge section settlement after construction, avoid problem of bumping at bridge-head, the applicant has carried out the CFG stake and has handled.According to reality condition of construction (sand wick, sand cushion construction are finished) and geological condition, the CFG stake is designed to diameter 50cm, pile spacing 1.8m, requires to squeeze into 1.0m under the bearing stratum (by ceasing driving standard control).Former drainage system can be avoided the dissipation problem of the ground excess pore water pressure that causes because of piling, and pile spacing and ceasing driving standard are determined by the ground upper load (embankment, vehicle etc.) and the settlement after construction of allowing.After the process of setting and construction are finished, bridge pier is carried out settlement observation, construction period accumulative total sedimentation 43mm, accumulative total sedimentation 12mm (time: on 3～March 5 January, it is stable that sedimentation has become) behind the worker.The CFG stake is handled, and bankets to shorten to ten days by two months, has shortened the duration greatly, and the back settlement after construction that is open to traffic simultaneously is also very little, illustrates that the CFG stake is successful in the processing of this end of the bridge section.

Embodiment 2: to the processing of landslide section roadbed.

Because complicated geology, mud change sharply, slump takes place near the K18+380～K18+545 the grade separation of the Xin Tai of Guangdong Province speedway ox gulf.Completely embankment had been filled to design height at that time, if according to a conventional method or vacuum preloading handle, except that the duration will prolong, the differential settlement of the old and new's embankment also can produce the crack.In order to address the above problem, the specialists meeting decision is adopted the CFG stake to add sand pile and is handled.In order to reduce cost, designing institute has adopted the change pitch arrangement, and pile spacing adopts 1.5m, left and right sides curb pile spacing to adopt 2.0m, slope, road pile spacing to adopt 2.5m in the road.For the excess pore water pressure that dissipates, improve the degree of consolidation of mud between stake, add the sanding stake between the CFG stake, the ratio of sand pile and CFG stake is 1: 3.Sand pile and CFG stake were handled 40 days, and 7m multichannel dike bankets and hardcore bed and stake detect 15 days.The CFG stake has not only been shortened the duration greatly, but also has solved the uneven subsidence of the old and new's embankments.

According to design theory and calculating, the design scheme of slump section treatment of soft foundation is, the long 21.6m of average stake, and stake footpath 500mm, strength of the mixing pile C15, pilespacing 1.5m adopts arranged in squares, and the thick 0.3m of bed course adopts the 2-4 graded broken stone.According to designing institute's drawing, CFG stake on October 9 in 2000 begins construction, and November 11, the CFG pile driving construction was finished; 7.4m high embankment was finished and is filled in 10 days, had guaranteed the duration that is open to traffic.

Embodiment 3: to the processing of widened section roadbed.

The Xin Tai of Guangdong Province speedway ox gulf grade separation mainline toll station widened section adopts the CFG stake to handle, and finishes early because main line bankets, and does not produce differential settlement in order to make widened section and main line, and the CFG pile spacing adopts 1.5m, hardcore bed 30cm.The CFG stake in 3 months that is open to traffic handle and former roadbed between, promptly the crack that produces because of differential settlement does not appear in widened section and main line.

Embodiment 4: to the processing of passage pipe culvert roadbed.

The auxilliary K10+911.5 place, road of connecting line before Guangdong Province Xin Tai speedway department, because the depth of fill changes, former foot bridge changes to 2-4*3 steel bar concrete slab culvert.For also having adopted the CFG stake, handles the bearing capacity that improves ground.The result shows that not only original drain function is constant, but also has reduced cost.

Embodiment 5: the reinforcement to the end of the bridge roadbed is handled.

For preventing that bridge pier from causing skew because of the soil body pushes it, in work progress, setting two sediment outflow stakes near the bridge pier place earlier.Both reduced the extruding of the soil body, water can be discharged from sand pile, thereby improved the bearing capacity of ground bridge pier.Sequence of construction near bridge pier to carrying out away from the bridge pier place.Because science reasonable in design does not find that in the process of setting bridge pier has shift phenomenon

In work progress, adopt and jump the new technology of beating according to the order of sequence according to actual conditions: when the reinforcing end of the bridge in response to from platform embankment filled soil one side injection dorsad; Should be if reinforce embankment from embankment injection outside embankment; Same campshed will jump to beat and advance gradually to a direction, to emit with preventing.Scale is buried on stake top at pile underground, observes construction to the extruding situation of pile, prevents that pile is squeezed and ruptures and emit situation with understanding ground.

Embodiment 6: to the processing of unusual sedimentation roadbed of operation phase.

The long 180m of Guangdong highway soft foundation section K17+820～K18+000, after pavement construction was finished, the long unusual sedimentation of nearly 30m to largest cumulative sedimentation 18.4cm on the 24th, took place on the 25th, maximum in 3～6 observation point largest cumulative sedimentation 14.4cm

The sedimentation of settlement point accumulative total reaches 29.7cm, and with the outer protuberance of roadbed, there is the continuation development trend in the crack on the road surface.In test operation phase situation, it is impossible to carry out treatment of soft foundation on a large scale for this speedway, and it is comparatively suitable to adopt mud jacking reinforcement in the embankment, embankment toe to add dozen antislide pile processing method.In actual process, the scope raising 2m berm with superloading of elder generation's protuberance outside roadbed, outside, side slope of embankment gutter sets the antislide piles of 2 rows by CFG stake remodeling, and antislide pile adopts tube-sinking cast-in-situ pile, a footpath 0.5m, spacing 0.8m, strength of the mixing pile C ₂₀, require to beat 4.0m to the mud, press the equilateral triangle layout.After immersed tube sets projected depth, the good reinforcing cage (main muscle 10 φ 12, stirrup φ 8a35) of welding is put into immersed tube, begin concrete perfusion then.Sequence of construction is carried out to the sedimentation smaller part from the sedimentation larger part.The every 6.9m in stake top establishes cap stake is got in touch.28d detects antislide pile after the antislide pile construction is finished, and pile body adheres to specification, and shear strength has reached intended purposes.Handle the unusual sedimentation of back embankment and stop, it is steady that subgrade settlement is tending towards.

In order to ensure construction quality, assurance embankment safety, carry out on-the-spot surface settlement observation and horizontal displacement observation, on-the-spot surface settlement observation is provided with 5 observation points, and horizontal displacement observation is provided with 3 observation points.

Claims (6)

1, the job practices of a kind of CFG in Expressway Ground Improvement, this job practices comprises:

(1) getting stake grows to and treats under the bonding course 0.8～1.2 meter, 400～500 millimeters in stake footpath, strength of the mixing pile C ₈～C ₂₀

(2) according to formula $f_{\mathrm{sp},k}=m\frac{R_k}{A_p}+\mathrm{\α\β}(1-m)f_k$ Or f _{Sp, k}={ 1+m (n-1) } α β f _kAnd $S=\sqrt{\frac{A_p}{m}}$ The estimation pile spacing, S is pile spacing, f in the formula _{Sp, k}Be nominal value of bearing capacity of composite foundation; f _kBe the natural foundation bearing capacity standard value, m area replacement ratio; The n stress ratio; A _pThe single pile sectional area; α=f _Sk/ f _k, f _SkReinforce back inter-pile soil standard value of bearing capacity; β=0.75～0.95; R _kBearing capacity of single pile standard value A _PSingle pile sectional area, m area replacement ratio;

(3), stake footpath long according to the stake of design, pile spacing utilize a stake machine to lay out pile, and form the CFG composite foundation;

(4) utilize 2-4 graded broken stone and geotextile to form the flexible cushion cap of composite foundation;

When it is characterized in that utilizing rubble to form the flexible cushion cap of composite foundation, at macadam layer of geotextile is set respectively up and down, and fixes with a sprig.

2, the job practices of CFG according to claim 1 in Expressway Ground Improvement is characterized in that a sprig wide is 0.2～0.25 meter, high 0.15～0.20 meter, 2.5～3.0 meters of line spaces, 5.0～6.0 meters of vertical clearances.

3, the job practices of CFG according to claim 1 and 2 in Expressway Ground Improvement is characterized in that the thickness of flexible cushion cap is estimated according to following formula: $\mathrm{\ΔH}=\mathrm{\λm}\×S\×\frac{f_{\mathrm{sp},k}}{f_k}$

In the formula: Δ H cushion thickness; The λ correction factor, span 0.5～0.6.

4, the job practices of CFG according to claim 1 in Expressway Ground Improvement, it is characterized in that Soft Roadbed, end of the bridge changeover portion and contain the processing in the slump highway section in works highway section, widen the processing in highway section, be equally applicable to carry out the situation of treatment of soft foundation, can be provided with sand pile this moment in 1/3～1/4 ratio, and the longitudinal drainage passage is provided; The macadam side opens wide, and the transverse drainage passage is provided.

5, the job practices of CFG according to claim 1 in Expressway Ground Improvement is characterized in that adding reinforcing cage and forms antislide pile in stake.

6, the job practices of CFG according to claim 1 in Expressway Ground Improvement is characterized in that not adding water in stake is stirred, and directly pours into immersed tube, 0.10～0.15 meter of stake pipe diameter.