Question

A building company has been awarded the contract to undertake the construction works for a multi-storey office project in a city centre location. A deep basement is to be installed under one half of the building, within a layer of dense gravel.

The site is surrounded by public roads and buildings on all sides and it is expected that the water table is extremely close to the ground surface on a year-round basis.

You have been asked by the contractor to advise their company with regard to a number of issues on the project, in advance of the construction works.

1. (a) What details would you provide to the contractor in relation to the options and methods available to dewater the soil on the project, to facilitate both the basement construction and trench excavations for utility ducting installation on the site? How would the range of dewatering methods be combined to produce a suitable solution?

2. (b) Given the basic information available in relation to the location and ground conditions on this site, describe the particular options that you would recommend to the contractor for use on this specific site to assist in supporting the sides of the deep excavations during the basement construction.

Answer 1

1.

(a) What details would you provide to the contractor in relation to the options and methods available to dewater the soil on the project, to facilitate both the basement construction and trench excavations for utility ducting installation on the site?

i. Details that would be required is : type of soil, saturation, water depth, field density, bulkiness index of soil, free area available beside construction space to set up plant and machinery. Topography of area, traffic details, peak traffic time, type of buildings nearby, peak hours of office, permissions to be taken, permission already available

(b) How would the range of dewatering methods be combined to produce a suitable solution?

i. Given the details that location is congested, there is very less space for works which are to be done. For dewatering the soil whose Ground Water table is extremely close to ground level, pumps of higher capacity can be deployed and tanks can be placed on a mobile equipment which will enable movement of water pumped out easy. Since the space is very less, using a rig and structural steel sheets, sheet pile shall be placed and trench excavation can be executed.

2.

(a) Given the basic information available in relation to the location and ground conditions on this site, describe the particular options that you would recommend to the contractor for use on this specific site to assist in supporting the sides of the deep excavations during the basement construction.

            Being a deep excavation to the existing building, proper shoring method to be adopted. To support the sides of excavation, excavation to be done with slope as per approved codal provisions for the type of soil at site. Also, a sheet pile shall be inserted along the length of the excavation to avoid fall of soil or overburden.