blossom street, e1blossom street Warehouses structural method statement

november 2015

100 St John Street London EC1M 4EH

T +44 (0)20 7250 7777

F +44 (0)20 7250 7555

info@akt-uk.com

www.akt-uk.com

NOTE: UNDERPINNING OF EXISTING BLOSSOM

STREET WAREHOUSES

Project Name Blossom Street Project No. 3461

Rev: 04 Date 19/11/2015

PURPOSE

This note has been prepared to accompany the planning addendum for the retention of the

existing Blossom Street warehouses no. 12-13. These two buildings will now be retained as

existing, where as the previous application involved re-setting the floor levels. In line with the

previous planning application and extant scheme, the façade of numbers 14-15 Blossom Street

will also be retained.

As with the previous application, it is proposed to lower the level of the basement slab in the

warehouses to provide adequate head height in the basement floor. Neighbouring works adjacent

to the rear of the warehouses also involve the excavation of a lower basement level. In order to

carry out these excavations safely, without undermining the existing footings, it is necessary to

underpin all existing vertical load bearing structure and façade being retained. The main load

bearing elements of the warehouses are the masonry walls, façades and the cast iron columns.

This revised scheme retains more of the existing structure at basement level therefore the extent

of underpinning required has grown proportionally. Underpinning brings the level of the base for

the existing footings down to a lower level than the proposed excavations in proximity so that the

stability of the footings is maintained. It is carried out in a hit and miss sequence, in small sections

typically 1m long, using mass concrete which is quick to place so that the stability of the existing

masonry above can be maintained during the works.

This note sets out the assumed method for underpinning in the preparation of the permanent

works design. The extent of the works will be developed during the following design stages and

the final method statement will be prepared by the contractor.

ASSUMED METHOD

- Confirm locations and type of incoming services that may be affected by the works, get any

permissions required and carry out disconnection before commencing underpinning works

- Monitoring of neighbouring/retained structures so be set up and initial readings taken

before commencing works

- Underpinning to be carried out in a hit and miss sequence of 1 in 5 for sound supported

structure above, this may be reduced to 1 in 7 for heavily loaded structure or weak cracked

wall. It is proposed to adopt 1 in 5 here, alternative to be proposed by the contractor.

- Underpinning width to match existing footing width unless specified otherwise.

- Underpinning to be carried out in 1m lengths.

- Depth of underpinning required will be developed during the next design stage considering

the depth of neighbouring excavation required. It is anticipated that this will not be more

that 2m therefore the works can be carried out in single pins. Should site conditions require

a depth of more than 2.5m the contractor may wish to carry out underpinning in 2 layers.

100 St John Street London EC1M 4EH

T +44 (0)20 7250 7777

F +44 (0)20 7250 7555

info@akt-uk.com

www.akt-uk.com

- Excavate block and work space together. Temporary stability of structure and retained

ground during underpinning works is the contractor’s responsibility, propping to be

provided.

- Remove or compact loose material.

- Protect the area with a cover of 50mm thick concrete if there will be a delay of more than 4

hours between completion of excavating and casting of concrete underpinning.

- Provide front shutter, dowels, and protection to any services passing through underpin

where required.

- Cast pin in one lift leaving a gap for packing/pinning up beneath existing foundation.

- On completion of concrete curing period, hard pack gap between underpinning block and

existing foundation. Allow packing to cure before commencing excavation for next

sequence of pins.

- Minimum period for curing of 24 hrs between casting underpin and pinning up. Minimum

period for curing of 24 hrs between pinning up and commencement of excavation for next

sequence of underpinning. Extended curing periods to be allowed for inclement weather.

- Shear connection to be provided between underpinning blocks using reinforcement dowels

- Should any perched ground water be encountered during the works the contractor must

take adequate measures to exclude the water from excavations and stop flow. Depending

on flow rate proposals may include tight boarding where flow rates are low, de-watering, or

grouting of the gravels where flow rates are higher, contractor to send proposals.

A detailed method statement will be prepared and submitted to the Structural Engineer by the

contractor prior to any works commencing on site.

EXAMPLE OF AN UNDERPININGSEQUENCE ON PLAN

SEQUENCE NUMBER OF PINS BEINGEXCAVATED SIMULTANEOUSLY

UNDERPINNING WIDTHTO MATCH EXISTINGWALL FOUNDATION

EXISTING WALL

6 1 4 2 5 3 6 1 4 2 5 31 2 34 55

EXISTING INTERNAL LEVEL +17.500

EXTERNAL LEVEL VARIES

T.O.C. +17.00

630

TOOK’S COURT

TO MATCH EXISTING BOUNDARY WALL FOUNDATION

50mm BLINDING

+16.550

C ATION

B.O.C. +15.500

INTERNAL

B.O.C.

TYPICAL SECTION THROUGHUNDERPINNED WALL

MASS CONCRETEUNDERPINNING

Application Documents

Application forms

CIL Additional Information form

Addendum Planning Drawings

Addendum Design and Access Statement

Addendum Planning Statement

Replacement Environmental Statement I

Replacement Environmental Statement II(Townscape and Visual Impact Assessement)

Replacement Environmental Statement III

Replacement Environmental Statement Non-Technical Summary

Addendum Heritage Appraisal

Addendum Regeneration Statement

Energy Statement Update

Addendum Sustainability Statement

Addendum Transport Assessment

blossom street Warehouses structural method statement