BT2 DeepExcavation TYT

 

Tr ần Yến Thanh

MSSV: 81303617

1. Excavation Method

Description

Advantag e

Disadvanta ge

Quite

In deep

1.1. 

Full open cut method 1.1.a. Sloped open cut method

1.1.b. Cantilevered open cut method

1.2. 

Braced excavatio n method

1.3. 

Anchore d excavatio n methods

excavation or slopes are very gentle, the cost in not low   Not Requiring necessitat the e the slope constructio and n of  backfillin retaining g walls Any Struts and excavatio center n depth or  posts width. obstruct the excavation  process Deficiency of lateral resistance  Not Short constructi application on period. to weak soil layer Large cheap the if excavatio n is not deep 

areas and shallow depths excavatio n projects

Large settlement if anchors is not good

 

Tr ần Yến Thanh 1.4. 

Island excavatio n method

1.5. 

Topdown construct ion method

1.6. 

Zoned excavatio n method

MSSV: 81303617 Efficiency Water and the leakage shortened and weak constructi structural on period.  joints. In large area excavatio ns, it can avoid the drawbacks  both of the braced excavatio n and anchored method The shortened constructi on period More operationa l space The safety of excavatio n

Reduce wall deformati on or ground settlement

Higher cost If the constructio n period of  basement is lengthened, the lateral displaceme nt may increase The worsened ventilation and illuminatio n

 

Tr ần Yến Thanh

MSSV: 81303617

2. Strutting system

According to the material of a strut  

Strutting systems Wood struts

Excavations Narrow and not deep

RC struts

Various shapes

Steel struts

-no information-

Advantage Low cost (in countries that are abundant in wood) The axial stiffness is high Easy to install, dismantle, and be  preloaded Low cost Short construction  period

According to the function of a strut Strutting systems Earth berm Horizontal strut Raker

Material Soil Wood, RC, Steel Wood, RC, Steel

3. Retaining Wall Dimension: 3.1.Wall Penetration Depth: 

Excavation methods Island All Island

Disadvantage The axial stiffness is low Heavy weight Waste times Cannot easily be used in site of great topographical undulation or of great width

 

Tr ần Yến Thanh

MSSV: 81303617

Where: su: the undrained shear strength (kPa)

σ’v: vertical effective stress (kPa) As shown in the figure, if the normalized of the soil is su/ σ’v=0.36, deformations for above wall penetration depth Hp=1 5mstrength Hp=15m and Hp=20m are the same. When the Hp=10.0m, though the deformation increases a little, the excavation system is still  basically stable. The above figure also shows the relationships between the ddeformations and penetration

depths with normalized strength su/ σ’v=0.28 under the same excavation conditions. The deformation is slightly larger for Hp=15m Hp =15m than that for Hp=20m. When Hp=10m, the  phenomenon of kicking at the bottom of the retaining wall grows worse and the excavation fails. Therefore, we can see that as long as the retaining retain ing wall is in a stable stab le state, the growth of the penetration depth does not affect the deformation of the retaining wall. We can use the finite element method to analyse anal yse the stable state of retaining wall and the relationship between wall deformations and penetration depths. Besides, we must care about the possibility of the decrease groundwater in basement construction process as well as the decreased flow go into the excavation. The depth of retaining wall is dependent on the above analytic resault. 3.2.Wall Thickness:

Theoretically, the increase of wall thickness will increase the wall stiffness and reduce wall deformation. However, the amount decrease does not have a linear relationship with the increment of stiffness, so it is only decreased to a certain extent. So we can choose the wall thickness dependent on lateral wall deformation condition.