Analysis method of foundation pit and slope anchorage

Mind map of analysis methods for foundation pits and slope anchors, a personal summary that is not rigorous, including the elastic fulcrum method, static balance method, and equivalent beam method. For reference only.

Edited at 2024-10-25 09:06:50

Mason·Carter

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Analysis method of foundation pit and slope anchorage

Mason·Carter

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Outline

Analysis method of foundation pit and slope anchorage

1. Elastic fulcrum method

1. Model features:

1. Before the vertical support: use soil springs for the embedded section and Kh point springs for the anchor fulcrums.

1. Calculation unit, the width of the soil spring supply spring is based on the pile width, and the pile width is expanded to a certain size.

2. For the anti-slide piles in the "Side Regulations", the soil spring in front of the support may also be partially provided by the soil side pressure or reverse residual anti-slip force provided by the anti-slip soil above the sliding surface in front of the support (above the embedded section). force

2. After vertical support: there is no spring in the whole section (it is fixed soil side pressure or remaining sliding force)

1. Calculation unit, earth pressure load supply width behind support, take pile spacing

2. According to the "Side Regulations", only soil springs are installed in the embedded section, and the soil side pressure after support is not included (this pressure is considered and deducted from the allowable transverse bearing capacity of the embedded section)

1. When there is no anchor: (similar to the foundation pit gauge) the soil side pressure behind the support is calculated as ea

2. When there is an anchor: the soil pressure behind the support shall be calculated according to p51, 52, e'a of the "Border Regulations"

3. Anti-sliding pile: After support, take the larger value of Ea and the remaining sliding force.

3. For the entire section behind the support of the "foundation pit", the soil side pressure is calculated according to ea.

Note: No matter what the value is, during the entire calculation process, the pressure value behind the support does not change with the deformation of the elastic support beam.

2. Engineering application

1. (relatively) accurately obtain the Htk value of the anchor fulcrum for further design calculations of the anchor rod.

1. More accurate than the traditional equivalent beam method and static balance method

2. "Border Regulations" p41, in anchor design, the value of Htk

1. Spring support method: obtained based on the initial anchor force at the fulcrum position, the final horizontal displacement, and the kh value of the anchor point.

2. No vertical support: (flexible beam) directly take Htk=e‘ah*sx*sy

3. Equivalent beam method and static balance method: calculated directly according to p117 and 119 of the "Side Regulations"

2. Accurately determine the soil side pressure of the embedded section (converted by the deformation of the soil spring), and determine the length of the embedded section.

0. The elastic support method is still a simplified approximation algorithm and is insufficient in determining the embedded length.

The "Border Regulations" rely on the elastic support method to determine the embedding length, but for safety, the characteristic value of lateral bearing capacity is introduced to replace Ep, ep

"Foundation Pit" does not rely on the spring support method to determine the embedding length (in the spring support method, the soil side pressure of the embedded section is only verified and reviewed), but follows engineering experience and selects settings based on overall stability, local stability, and anti-uplift stability. Embedded length

1. The "Border Regulations" introduce the lateral bearing capacity characteristic values in p69, 70, and 71, requiring the soil side pressure of the embedded section not to exceed this value to clarify whether the embedded length is sufficient.

0. The "Side Regulations" can roughly determine the embedding depth and support plan through the equivalent beam method or the static balance method - the "Side Regulations" do not clearly require that this method be used to roughly determine the embedding depth first. In practice, it is often Skip this step and continue using the pop-up method

1. The "Side Regulations" use the elastic fulcrum method and use the characteristic values of soil lateral pressure and lateral bearing capacity calculated in detail in the embedded section to clarify the embedded length.

2. "Foundation Pit" p25, there is a requirement that when using the elastic support method, the total soil side pressure of the embedded section does not exceed Ep, so as to double-check whether the embedded length is sufficient.

1. The embedding length of "Foundation Pit" is set according to p29 and 35 based on overall stability, local stability, etc.

Note: The formula for determining the embedding length of no anchor or single anchor in pages 25 and 26 of "Foundation Pit" is basically the same as the static balance method.

2. "Foundation Pit" calculates the soil lateral pressure of the embedded section in detail according to the elastic support method, and uses Ep for verification and review

Note 1: The characteristic value of lateral bearing capacity in the "Side Regulations" is basically similar to the ep value (both are the soil lateral pressure strength of soil and rock under certain special working conditions)

Note: The elastic fulcrum method is also an approximation method. Like the static equilibrium method and the equivalent beam method, it also has great limitations. As a result, this method is not used to determine the embedding of vertical supports in "Foundation Pit" depth

2. Static balance method

1. Model features: ea is taken as the whole section after the branch, and ep is taken as the front (block) of the branch.

2. Applicable to situations where the blocks are soft and shallow, and the rotation is large.

1. Based on the horizontal force of the anchor (all), ea after the anchor (full section) and ep before the anchor (block), calculate the Htk value of each anchor layer by layer (according to the inverse process characteristics)

2. Based on the rotational moment balance around the anchor fulcrum of the bottom layer, find the embedding depth.

3. Equivalent beam method

1. Model features: ea is taken as the whole section after the branch, and ep is taken as the front (block) of the branch.

2. Applicable to situations where the blocks are hard and deep and the rotation is small.

1. Based on the rotational moment balance around the block ep-ea=0 point, find the Htk value of the anchor rod at each layer.

Note: The calculation process at this stage does not involve or be affected by the embedding depth value.

1. Based on the balance between ep-ea=0 point above (earth pressure, anchor support force) and ep-ea=0 point below (earth pressure), reversely find the minimum embedding depth