GT's structural engineer's report 2

PETER LODGE B.Eng C.Eng M.I.Struct.E
Consulting Structural Engineer

E-Mail: slack_house@tiscalli.co.uk

10th June 2004

Greentops Limited

Dear Sirs

Re: Retaining Wall at Spring Grove - Hebden Bridge

Following my recent inspection of the retaining structure at the rear of the properties on Spring Grove which form a section of the boundary to the parcel of land bounded by Windsor View at the higher level I would like to confirm the observations made: -

1. The majority of the masonry wall forming the retaining wall to the higher level was once part of a structural wall of a mill which originally occupied the site. The masonry adopted is a roughly coursed and thinly bedded local grit stone which was possibly originally bedded in a lime based mortar which has now weathered away leaving an open jointed block structure in some areas. The wall appears to be of a single skin to the earth face as can be seen on the end of the wall where a battered slope has been formed to retain the upper level.

2. There is evidence along the length of the remnants of the wall that within the original construction cross walls would have been built and bonded into the earth retaining wall these would have acted as buttresses for this structure. The floors of the mill would have also propped the wall resulting in the retaining wall adopting a two way spanning action. The original structural form was far less onerous than the present condition; which is free standing with only nominal buttressing effects drawn from the change in direction of the wall line.

3. During the development of Spring Grove remedial work/additional masonry has been added to the original walling. This construction again appears to be of a single skin of coursed bedded stone which has been fully pointed. Generally this work has been undertaken to the upper levels of the wall and acts in a retaining situation which could not be justified by calculation for the lateral pressures potentially generated.

4. In one instance where reconstruction work has been undertaken the wall appears to have moved due to the applied horizontal pressures and is now resting on timber garden shed. (Nƒ 21)

5. Trees have become established within and along the top of the wall. The effect of wind rock on the tree roots will cause the deterioration of the structure and these should be removed.

6. At the end of the masonry structure a battered face has been formed up to the higher levels. Trees have been felled from the earth slope leaving the stumps in place with erosion of the ground from around the roots evident The slope is in excess of 45ƒ which is above the normal natural safe angle of repose adopted for slopes of 27ƒ, there is evidence of the fall of material onto the path at the base of the slope.

From the visual appraisal it can be noted that remedial action is required to maintain the integrity of the retaining structure. Generally along the top of the wall where new masonry has been added and trees have become established there could be potential problems associated with the tree roots penetrating the construction which only a single skin resulting in the breakdown within the bed joints of the masonry. This along with the effect of tree rock could result in the dislodging of masonry in time.

The section of the wall which is resting on the garden shed should be reviewed to ascertain if movement is progressive and if a potential collapse could occur.

Recent masonry constructed at the top of the wall should not be in a retaining situation as the lateral forces may result in the overturning of these sections of wall; this will be aggravated by the presence of tree roots within the zone at the rear of the wall.

Maintenance of the wall is required with the removal of all embedded trees before they result in structural problems and their size present problems associated with felling. All trees within the vicinity of the added masonry on the top of the wall should be removed to prevent the possible future displacement of the stonework.

Yours faithfully

Peter Lodge