Abstract: with the expansion of the area covered bridge, viaduct project more and more, the main bridge variable cross-section of the continuous box construction and foundation treatment, become a bridge engineering often face a problem. To put the whole project premise, must choose the correct solution, and the demonstration of the scheme.
Keywords: continuous box foundation treatment scheme comparison
A project survey,
Even the "line of provincial highway 221 bridge is located in HaiAnXian territory, across new Ⅲ level channel even" canal (tongyu river), bridge spans layout for 11 × 25 + 11 × 25 m, bridge is a 768.28 m, the main (60 + 90 + 60) m span prestressed concrete cross-section of three continuous box, cross and edge in across the beam height of 2.3 m, 5.2 m high beams fulcrum place, the bottom of the box girder wide and 7.0 m, 14.0 m DingKuan, for single box single room structure. The main construction scheme for the cantilever construction method amplified stents, namely when construction cast-in-situ amplified, LaJia cantilever structure is after. The scheme has a section cast-in-site length is hanging basket poured long suspension characteristics, there are six main suspension for water, 1 fold section, shorten the construction period. Which blocks 0 # 12.4 m long box girder, the stents cast-in-situ piece of a, 1 ~ 6 piece of longitudinal section length for water which is 6.3 m, cast-in-site segments at the side spans length of 13.92 m, side cross section is the closed 2.0 m.
Second, foundation treatment scheme is selected
(1) the main variable cross-section continuous box for the shallow ground water stents (20 m) of geological conditions introduction:
1 layer: grain filling, silty clay is given priority to, contain a few plant roots, the bottom buried deep 0.2 ~ 1.9 m,.
2-1 layer: silty clay clip powder soil, belongs to the compressibility of foundation soil, and the buried depth of 1.6 ~ 9 m, thick layer of 1.1 ~ 7.10 m,.
2-2 layer: the muddy silty clay, saturated flow model, belong to high ground compressibility, bottom buried deep 5.8 ~ 20 m, thick layer of 2.5 ~ 8.60 m,.
2-3 layer: silty clay to clay, of the foundation soil for compressibility, bottom buried deep 17 ~ 21.0 m, a thick layer of 2.5 ~ 7.00 m,.
The above 2-2 soil for the muddy silty clay, has the characteristics of liquefaction, so deal with in the foundation for processing.
A plan to deal with a: PC pile reinforcement scheme
PC pipe diameter of 0.6 m, pile model for PC-600 (110) A-C60-15, to hammer the pile, the longitudinal row spacing 3.15 m, transverse 3.5 m, namely the lateral 3 root, longitudinal 2 root, each section 6.3 m standard of section 6 root pile stress. The pile bottom elevation-11.4 m, the pile length 15 m, into 2-3 soil layer. According to the calculation of the whole bridge common PC pile 352 root, plan 5280 m. Each root pile appraisal about 3480 yuan, the bridge of about 1226300 yuan, the PC pipe pile prefabricated in advance, and procedures, influence period.
A plan to deal with two: clean surface soil, the original ground turned loose 60 cm, with 6% of lime soil mixed with grey processing, degree of compaction quartile 93%, width support build-up to meet demand, the 15 cm thick C25 used on of the hardened.
Measurement engineering cost: the whole bridge share 6% lime soil 3024 m3, 35 yuan per cubic meter of the unit price, plan 105840 yuan. C25 concrete 756 m3, each cubic meters unit price is 360 yuan, 272160 yuan project. Scheme ii cost is 378000 yuan.
Obviously scheme ii cost less than a third of the cost of the scheme. To save the project cost and ensure the quality of construction, the scheme ii feasibility calculating theory. Take the whole bridge section for watering the largest weight of # 1 piece (1 # piece of volume, the weight of 241.9 tons of 93.04) as the most unfavorable factors are analyzed.
1 # piece of box girder beams high 4.8 m, 0.7 m redesign of box girder thickness, for straight webs, roof wide 14 m, bottom width 7 m, bridge panel cantilever length of 3.5 m, cantilever plate at the end of the 20 cm thick, root thick 70 cm. Box girder 28 cm thick roof and floor thick 70 cm. Built for stent 6.1 m high, stents, longitudinal spacing 0.9 m, horizontal spacing: in web 0.3 m, plan 4 row, close to the lateral template spacing for 0.4 m, 0.6 m for the spacing, take action to support the width 40/2 + 3 by 30 + 60/2 = 140 cm, length 90 cm. Here is the most negative stress area, checking the foundation bearing capacity.
Box girder dead weight: 4.8 by 0.7 by 0.9 by 26 = 78.6 KN
Stents dead weight: 6.1 x 0.06 x 4 x 2 = 2.9 KN
Template dead weight: 4.8 x 2 x 0.5 = 4.8 KN
The total load: F = 91 KN
Foundation stress for P = 91/1.26 = 72.2 KN/M2
According to the calculation of rectangular concrete cushion bottom additional stress
: basic bottom self-respect pressure (in filling) (concrete density of 23 KN/M3, lime soil for 18 KN/M3), = 0.15 by 23 + 0.6 by 18 = 14.25 KN/M 2
: foundation soil stress diffusion Angle, take = 400, t = 0.6 m
According to the geological prospecting report, the department lime soil foundation bearing capacity under at least for 65 KPa,
Safety coefficient 65/15.91 = 4.09, safety.
(3) additional stress calculation under the action of the settlement of foundation soil
According to the elastic mechanics calculation final settlement of foundation soil
: average settlement influence coefficient, check a watch w = 1.1
: of foundation soil poisson coefficient, take = 0.26
(4) stent elastic deformation
Check the bowl buckle stents, steel pipe diameter, each role by 2 lines of face, 4 in each row root calculation, each pieces of steel under 91/8 = 11.4 KN.
In the main girder in steel webs vertical every 0.9 M set a horizontal bars, so to ensure that every root made stem bearing capacity is up to 40 KN > 11.4 KN.
Made stem rod deformation
Box girder bottom-formwork can use bamboo veneer, back for 15 by 15 cm jandova pine two layers, each layer elasticity and the elastic deformation of 2 mm, plan 4 mm.
Stents, template and is expected to foundation settlement 2.09 + 2.4 + 4 = 8.49 mm.
Three, scheme comparison
According to the second option, the contractor in the choice a glade, actual area is equal to 1 # piece of area: 14 x 6.3 = 882 m2.
Take turn dig 0.6 m, each layer is more than 20 cm, three layers using 6% lime soil construction, each layer detection compaction degree, grey dose, ensure the compaction quartile 93%. Complete after subgrade soil LiMo, highly 15 cm, using C25 concrete one-time casting. Concrete strength of 90%, according to the calculation of # 1 piece of dead weight + template, support iso-effect load weight (2518 KN, according to drawings, combined with geometric feature of box girder, the ShaDai under preloading. After 10 days for observation, for three days accumulative total settlement is not more than 3 mm, namely recognized settlement stability, can discharge, and the measurement summary statistics, the largest elastic deformation of foundation settlement is 3.6 mm, meet the design requirements of 10 mm settlement.
Lime soil foundation treatment settlement observation summary form
Project content observation time date observation on observation
Settlement (mm) accumulative total sink
Drop volume (mm)
4.12 loading (1/2) 9:00 a.m. at 3.4 3.4
4.13 loaded morning 1.9 5.3 "
4.14 the first morning which of 1.2 6.5
4.15 the second day morning 6.5 "0
4.16 the third day 8:50 a.m. when 0 6.5
4.17 the fourth day morning at 8:45 0 6.5
4.18 the fifth day 8:30 am 0 6.5
4.19 the sixth day morning 8:55 0 6.5
4.20 the seventh day morning the 0 6.5
The eighth day morning 4.21 and 6.5 0
4.22 the ninth day
(uninstall 1/2) at 9:09-2.2 4.3
4.23 the first ten days
(uninstall finish) morning if-0.7 3.6
Four, the conclusion
Through the second plan checking and on-site validation, show that the lime soil shallow processing and certain thickness can effectively make up for the concrete surface layer of foundation soil layer the defect that soft berth bearing capacity, and the scheme has a deal with a simple, economic, short construction period advantage of long-span in cast-in-site structure to promote the use of foundation treatment. Now even the "line the main bridge has been successfully completed, the bridge, the linear smooth, beautiful. The whole bridge good foundation treatment plan and construction quality to meet the hpa cantilever bracket need, achieved great results.