Design on soil-nailing wall Supporting of Foundation Pit in Bao Tou

Project Summary

Proposed site is located in the north of the west of the east river road at bao tou . The side of the building has leisure square and commercial shop and underground garage on the north and south of village .The excavation depth is11 meters .

Engineering geology

According to the geological survey report, the soil is divided into miscellaneous fill,collapsible loess, silt, coarse sand. The physical and mechanical indexes of soil are shown in table 1.

Table 1 Physical and mechanical properties of soils

Layer soil type name Layer thickness(m) Severe(kN/m3) cohesive force(kPa) Angle of internal friction(°)
1 miscellaneous fill 2.60 16.0 5.0 15.0
2 collapsible loess 3.40 16.1 13.1 22.0
3 scoarse sand 1.40 19.0 0.0 40.0
4 silt 9.10 18.9 13.9 22.0

edetermination of supporting schemes

According to the construction of foundation pit supporting technology regulations
(JGJ120-2012)[1],the engineering safety set the secondary level.Considering the surrounding area is smooth and the soil quality is good, no buildings around,soil nailing can meet the requirements, but we will strictly control the deformation of foundation pit.

5th International Conference on Advanced Design and Manufacturing Engineering (ICADME 2015)

The calculation of soil nailing
Calculate of soil nailing

According to the engineering geology and the surrounding environment, the foundation pit engineering arrange7 soil nail.Index of soil nailing are shown in table 2 .

Calculation of earth pressure

The earth pressure calculation method is the Rankine’s earth pressure theory of foundation pit supporting technology regulation.The lateral earth pressure of graphics is the triangular distribution,the soil pressure distribution pattern of soil nail length increases with the increase of the depth of foundation pit.

Coefficient of earth pressure: Ka=tan2(45°-φ/2) (1)
Intensity of soil nail force:gs (2)

In the formula:q-ground overload ri-i row of soil nailing in severe soil layer soil hi-i row of soil nail distance on the surface of the side slope distance Kai-i row of soil nailing in the active earth pressure coefficient of soil layer soil

Table2 Design parameters of soil-nail

number of soil nail Vertical distance
(m)
horizontal spacing
distance(m)
horizontal
angle(°)
Soil nail
aperture(mm)
1 1.5 1.5 10 110
2 1.5 1.5 10 110
3 1.5 1.5 10 110
4 1.5 1.5 10 110
5 1.5 1.5 10 110
6 1.5 1.5 10 110
7 1.5 1.5 10 110

calculate of tensile load standard value

In accordance with the provisions of slope of soil nail wall, so it need put on slope soil pressure reduction. This project adopts the single-stage slope soil nail wall. In accordance with the relevant provisions, single soil nail tensile load standard values can be pressed.gs (3)

In the formula:Tjk – tensile load standard values of the j root soil nail ξ- load reduction factor
Eajk – j root soil nail location of foundation pit horizontal load standard values
Sxj, Syj -horizontal and vertical spacing of the j root soil nail and soil nailing adjacen
αj – angle of the soil nailing with horizontal plane
β – soil nail wall slope and the horizontal plane angle φk -angle of internal friction values
The first layer of soil:miscellaneous fill(2.6m),β=63.4°, = k j 15°,ξ1=0.554
The second layer of soil:collapsible loess(2.6m-6.0m),β=63.4°,φk=22°,ξ2=0.485
Similarly,ξ3=0.276,ξ4=0.485

Therefore, the above results are shown in table 3.

length of soil nail design

Length of soil nail design is directly related to the safety of the foundation pit slope stability, it is
also the important factors that affect the project cost. Length of soil nail Divided into anchorage
length and free length.
anchorage length:gs2 (4)

Table3The calculation results of soil parameters

The number of
soil nail
Earth pressure
(KN)
Reduction factor Tensile load
standard values
(KPa)
Length of soil nail
(m)
1 14.43 0.554 18.26 5.8
2 9.45 0.485 10.47 5.4
3 20.42 0.485 22.62 5.7
4 31.38 0.485 35.28 4.6
5 33.61 0.276 21.19 6.6
6 64.08 0.485 70.99 8.8
7 76.95 0.485 85.30 6.4

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