Question

In: Civil Engineering

A corner of a five-story commercial building resting on a raft foundation settled down a few...

A corner of a five-story commercial building resting on a raft foundation settled down a few inches in the last few years of its construction due to a pocket of loose soil underneath. As a result of undesirable settlement, the usage of building was affected, and the owner seeks the help of a consultant to suggest the proper method of underpinning to avoid any further settlement. Soil investigation reports showed that the hard rock stratum is available at a depth of 10 meters from the natural ground level. Considering the above scenario, answer the following questions:
i. Suggest a suitable underpinning method as a solution for the above problem. [1]
ii. Write the step by step procedure aided with a neat sketch for the above suggested method. [5]
iii. State any two advantages and limitations each of the suggested method. [2]
iv. Comment on the ‘cost effectiveness’ of the method used.

Solutions

Expert Solution

Answer:

given that

A corner of a five-story commercial building resting on a raft foundation settled down a few inches

1) Under pinning is technique to repair/strengthen the existing foundation of structure. Selection of under pinning method depend upon foundation type.

For current problem, under pinning using "Hicropies" will serve the issue of ground improvement.and reduce the settlement.Since "Hicropies" will transfer building loads to bearing layer.

2) Step by step procedure:-

Firstly problem of ecentricity causing settlement due to vertical loads need to check.Total expected vertical load is calculated & corresponding stress points are marked & location of Hicropies are located.

Step 1:-

Step 2:-

Step 3:-

(or)

step 3 may same times proceed by lowering of reinforcement lage & than grounding.

Step 4:-

Step 5:-

3) Advantage:-

1) Reduction is settlement, increase in bearing capacity of foundation due to increased soil structure interation & transfer of stress to bearable strata.

2) Micropile under pinning can be used in retricted headroom access.

Dis advantage:-

1) less lateral capacity when used without casing.

2) potential buckling at seismic condition.

3) costly method.

4) Inclusion of steel casings at micropiles periphery increases the cost which otherwise, if used only with steel case or steel bar at middle of micropile with grount can be economic.


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