Analysis on the Surface Subsidence & Control Approach of Shenzhen

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ABSTRACT

(Analysis on the Surface Subsidence & Control Approach of Shenzhen Metro Line 11 Housong section) In Shenzhen railroad line eleven Housong section the subway construction because the background, combined with the scene of the subway construction observance scenario, observance and method analysis was dispensed the surface on the pine of Housong section. per observance knowledge and website condition, the Housong section is summarized within the underground construction ways of the surface subsidence caused by the explanations and rules, and consequently puts forward some measures to manage the surface subsidence, because the steerage of consequent railroad engineering construction, and supply reference for similar subway engineering.

 INTRODUCTION

With the speedy economic process and accelerated pace of urban construction in China, we've entered a stage of speedy urbanization. Some students have pointed that the twenty first century is that the century of development and utilization of underground area [1-3]. because the wide application of tunneling technique of construction technology, subway construction has been developed ceaselessly. variety of subway routes still be launched in some metropolis. However, due to the distinction of geography options, construction conditions and different aspects within the subway tunnel construction, it's an enormous impact on surface and surroundings. a way to scale back the impact of subway construction has being the topic involved by underground engineering and geotechnical engineering [4-5]. Therefore, it's essential to investigate the rule of surface subsidence within the method of subway construction. It ought to be a concrete analysis of specific problems. This has a very important technical worth and economic significance to ensure the amount and increase economic potency. This paper analyzed the observance and mensuration results of surface subsidence within the railroad subway construction method of the Housong section of line eleven in Shenzhen, obtained the law of surface subsidence and analyzed the explanations that result to ground subsidence. Some acceptable management measures are projected to supply steerage for the development of the next project.

PROJECT summary

Project introduction

Shenzhen railroad Line eleven from south to north through the district of Futian, Nanshan and Baoan. Connected central space of Futian, Nanshan, Qianhai, Baoan, it additionally connect the district of Fuyong, Shajing, Songgang and airports. placed in west of town development axis,It is a specific line between town center space and therefore the western coastal region and each with the perform of landing field specific line. on the route there ar seventeen stations that as well as thirteen underground stations and four elevated stations. Line average station spacing of three.2km. the most distance between stations placed in Bihai station-airport station (7.2km).The minimum distance between stations placed in Qiaotou station-Tangwei Station (1.7km).

Housong section placed between Houtin station of Baoan district and Songgang station. The section outward-bound from the Houtin station and consecutive passed Maozhou watercourse, the Guangzhou-Shenzhen main road bridge and Songgang watercourse, on Baoan road go straightly to Songgang station.

Geological conditions

Housong section belongs to ocean sediment plain, Original landscape as coastal fish ponds.Now it's been unnaturally full of comparatively flat parcel of land and therefore the ground elevation is three.12 meters to five.84 meters. On either side of the road ar in the main industrial district , dormitories, residential areas so on. Section field geologic structure ar in the main regional dynamic thermal geological process of the Sinian, below the weathering mixed granite and leucoleptite shaped eluvium.The higher portion of the soil ar in the main layer of loose clay and sand that belong to the Paralic. The surface soil is artificial plain fill, from prime to bottom followed by Paralic of mucky loose clay layer and sand layer, sediment of mucky loose clay layer, loose clay layer and sand layer.

SURFACE SETTLEMENT ANALYSIS

Monitoring spot arrangement

Depending on circumstances and therefore the close construction in Housong section, the subway construction section close to MaoZhou watercourse was choosed for the stationing observance, the development section through the MaoZhou watercourse, within the method of the development of an excellent influence on surface subsidence. on the Baoan avenue, a complete of seventy three observance points were set. Specific observance arrange is shown in figure one.

Change of surface subsidence

The surface subsidence of Housong section has been monitored and therefore the observance frequency is once daily. Some special sections were choosed for analyzing all told observance programs. Take 2 sections for every eleven observance points for analysis, the article is to require a cross-channel that below construction in Housong section. the chosen observance sections were NO + 004 and NO + 017. The points accumulated most settlement worth as shown in Table one.

According to the observance knowledge obtained the most settlement worth of every observance purpose horizontal curve distribution. The results were shown in figure a pair of and figure three.

From figures a pair of and three it are often found the surface observance most settlement at each purpose horizontal curve has the subsequent rules,

1. The most settlement seems to near variety of points within the NO + 004 + DB-O and NO + 017 + DB-O. specifically close to the highest of cross-channel center that was below construction. Settlement step by step decreases toward either side and type a subsiding tank curve. 
2. The subsiding tank curve is considerably rendered as Gauss distribution. Scope of influence is concerning cross-channel thirty meters on both sides of the midplane. 
3. Cross-channel center line on either side of the symmetrical purpose settlement is completely different. Settlement on the left facet of cross-channel typically larger changes, on the correct is comparatively moderate.

Select components of observance points as analysis object in section NO + 004, got the accumulative settlement of the observance points dynamical with time curve as shown in figure four.

From figure four the subsequent rule are often found.

1. Settlement versus time curve is or so a reverse "S" formed curve. There ar 3 stages of settlement in time. that's settlement stage of development, settlement surge part and settlement stable stage. 
2. Overall, the settlement surge part period of forty days, once every purpose of the settlement ar roughly maintain around a set value and have a tendency to leveling off. The nearer the observance points to subway tunnel construction, the larger the number of subsidence. 
3. Points on either side once the development amount, the settlement quantity was considerably rebound, some purpose recovery rate is comparatively massive.

Factors influence of surface subsidence

Combined with the geologic condition and close atmosphere, have an effect on the surface subsidence for the subsequent reasons.

1. Shenzhen belongs to the coastal areas with loose soil, rock and soil layer exists the muddy clay powder, organic sand, filling soil, silt, crushed stone, etc. Soil was disturbed throughout the subway tunnel construction, below the gravity influence of the higher soil, the layer tend to be a lot of at risk of disturbances and would manufacture subsidence. near subway construction website, heaped-up with the subway construction needed instrumentation, like steel, cement and steel, etc, that increased the load on the surface, leading to surface settlement.
    
2. In construction method of subway tunnel, as a result of support isn't timely or structure isn't stable, additionally the soil and tunnel excavation disturbance lots, that has made settlement additive impact and therefore the accumulated settlement has increased.
    
3. Shenzhen belongs to rainy areas with ample downfall, once the tunnel construction, owing to the rain infiltration into the layer, so leak to the tunnel, build stratum continued loss of water, soil pores and fissures consolidation shrinkage, caused an oversized vary of surface subsidence. Housong section is found within the neighborhood of MaoZhou watercourse, soil consolidation settlement caused by water penetration was a lot of obvious. The region is ample downfall, and round the bottom of the water is saturated, that cause all-time low a part of soil softening. Some municipal pipelines lie on either side of subway lines, at all-time low of the pipeline excavation construction method, saturated water are lost, which may cause the soil consolidation and therefore the surface subsidence.
    
4. Interval lines across the fault zone is especially composed of cataclastic rock, tectonic fractures ar developed close to the fault zone, and therefore the crack cut rock into fractional Structural. Fault impact on the general stability of close rock isn't massive, except for cutting harm of rock mass is powerfully, on either side of the fault with broken rock mass, Weathering fault could deepen, that might destroy the integrity of rock mass and scale back the strength of rock mass. The groundwater in fractures ar sometimes a lot of advanced, rock mass integrity was greatly stricken by geologic structure, the soundness of close rock is greatly reduced, ar at risk of collapse or gushing, accelerate strata consolidation settlement. Combined with the sphere scenario, there ar several factors which may influence the surface subsidence, the mutual influence between factors, below the perform of varied factors, makes the surface subsidence a lot of highlights.

DISCUSSION ON SURFACE SUBSIDENCE MANAGEMENT MEASURES

In the method of subway construction, as a result of the influence of some factors on construction technology, causes the surface subsidence, must take corresponding measures to manage, to make sure the security of subway construction and different aspects. On the surface subsidence influencing factors Housong section of Shenzhen railroad line eleven, discussing some measures to manage the surface subsidence [6-8].

1. Improve construction technology to cut back subsidence. Do the development preparation and construction organization seriously, elaborate the development technology, do a decent job to "fast" and "tight" of early supporting construction, "fast" is that the speedy construction, quick closed."Tight" represent the highest tight between the first support and therefore the soil while not gaps. Strengthen the backfill grouting and fill the gap between the soil and therefore the primary support timely.
    
2. According to the results of detection, completes promptly wealthy water anomaly process, particularly to be completed before the excavation and construction, improve the compactness of soil to cut back the settlement. within the method of the tunnel construction, as a result of the water penetration into the formation, most within the tunnel within the drop of water, therefore rushing up the consolidation settlement of soil layer, such consolidation settlement manifested by ground subsidence. At an equivalent time, Shenzhen belong to the wet space with ample water in stratum, merely consider pump to pumping groundwater wasn't appropriate, different effective measures ought to be taken.
    
3. Reinforce the grouting to tunnel construction space, improve the density of stratum. components of sections exist artificial fill soil and severe weathering rock, grouting is needed within the stratum to vary the property, that have the impact of reinforcement to avoid the surface settlement is just too massive.
    
4. Under the premise of safety construction, it ought to be applied in time for the secondary lining. Considering the existence of an exact content of weathering rock in operating face, the excavation can cause massive disturbance and loose. If not handled in time, tunnel can presently deformation and cannot type a natural arch, such influence on tunnel structure is larger, which is able to cause an excellent influence on deformation of stratum and surface subsidence. Completes promptly once tunnel excavation support, scale back the deformation of tunnel and therefore the surface subsidence.
    
5. In the method of shaft passage construction, owing to the cross section size is larger and plenty of steps of excavation sequence with part overlap excavation. every step within the excavation will bound effects the settlement of the highest shaft passage, therefore causes the surface subsidence. Therefore, within the method of construction, try and management the gap of excavation between every step.
    
6. To strengthen the observance within the construction and analyze knowledge in time, so as guide the development from feedback. In accordance with the wants of construction observance programme, ground surface settlement and therefore the settlement observance of buildings have to be compelled to be done once daily, analysis of subsidence observance data and feedback in time, to supply the reference for the subway construction, make sure the safety of subway construction.

CONCLUSION

In subway construction, it must opt for appropriate activity technique and knowledge analysis technique to attain the target for the key and make sure the safety of construction and therefore the close buildings. within the speedy development of subway, a way to management the surface subsidence within the method of subway construction, become an issue purpose. particularly close to a settled and traffic is comparatively developed areas. If the surface subsidence management isn't smart, not solely have an effect on the road traffic, however additionally have an effect on the near buildings on it. a lot of serious will cause building collapse, threaten the security of life. Therefore, within the method of subway construction, it's essential to organize enough to the surface subsidence observance and prediction, which may offer steerage to subway construction. At an equivalent time, take corresponding management measures visible of the intense scenario of the surface that will return up to make sure the security of subway construction.

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