CASE 015
:
THE CASE OF THE TILTING TOWER
A 22-storey tower under construction is found tilting 0.8 degrees from vertical. Construction halts. Nobody is hurt. The developer blames the engineer. The engineer blames the contractor. The contractor blames the soil survey. The question is why it is leaning — and who made the decision that caused it."
CASE BRIEFING
On a Tuesday morning in March, surveyor Daniel Osei was conducting a routine vertical alignment check on the Harwick Waterfront Tower — a 22-storey residential development under construction on the eastern edge of Millhaven's newly regenerated docklands.
He checked his instrument reading twice.
Then he called his supervisor.
The tower — currently at 18 storeys with four floors of steelwork still to be erected — was tilting.
Not catastrophically. Not visibly to the naked eye from street level. But measurably, precisely, and — as Daniel Osei would later tell the inquiry — in a direction and at a magnitude that should not have been possible given the foundation design he had reviewed six months earlier.
0.8 degrees from vertical. Tilting northwest.
His supervisor called the site manager. The site manager called the developer. The developer called the structural engineer. The structural engineer called the contractor. Within two hours the site had been evacuated and a cordon established around the base of the building.
Construction on the Harwick Waterfront Tower ceased at 9:47 AM on that Tuesday morning and has not resumed.
The three parties:
Harwick Properties — the developer — had commissioned the tower as the centrepiece of a £340 million waterfront regeneration project. Forty-seven residential units had already been sold off-plan. The tower's completion was eighteen months behind schedule before the tilt was discovered. CEO Marcus Webb, 52, issued a statement within hours of the evacuation:
"We commissioned the most thorough soil survey available and engaged one of the most respected structural engineering firms in the country. If the building has moved it is because the design or the construction failed to meet the standard we were assured it would. We will cooperate fully with the investigation."
Meridian Structural Engineering — the structural engineer — had designed the tower's foundation system. Lead engineer Dr. Elena Marsh, 47, responded to the developer's statement the same afternoon:
"The foundation design was based on the soil survey data provided to us by the developer's appointed surveyor. We designed within the parameters that data described. If the building has moved it is because either the survey data was inadequate or the construction deviated from our specification — or both."
Caldwell Construction — the main contractor — had built the foundations and the structural frame. Operations director Patricia Nolan, 44, issued the briefest statement of the three:
"Caldwell Construction built to the approved drawings. Any suggestion of deviation from specification is without foundation. We await the outcome of the investigation."
Three statements. Three deflections. One building tilting northwest over Millhaven's regenerated docklands.
The Millhaven Building Safety Authority appointed an independent investigation team led by structural engineer Dr. James Okoro — the same physicist who had investigated the Ashworth House phenomena the previous year, now seconded to the authority's specialist investigations unit.
He stood at the base of the Harwick Waterfront Tower on the morning of the investigation and looked up at eighteen storeys of steel and concrete tilting imperceptibly but measurably toward the northwest.
"Buildings do not tilt for no reason," he said. "The question is never whether there is an explanation. The question is how many people knew part of it and told nobody."
Your investigation begins now.
A 22-storey tower is leaning. Three parties are pointing at each other. The soil beneath the northwestern corner of the building is the beginning of the story — but it is not the whole story.
Examine all five Evidence Files. The survey data, the soil analysis, the foundation inspection records, the materials testing, and the load analysis all have something to say.
The building failed because of a series of decisions made by different people at different stages of its construction. The science will show you what happened to the structure. The records will show you who knew — and who chose not to say.
Why is the Harwick Waterfront Tower tilting — and who is responsible?
Instructions:
Play solo or with a team of up to 5 investigators. Examine the five Evidence Files together, or divide them among your team and have each investigator analyze different clues. Share what you discover, compare theories, and decide which evidence matters most.
When you've examined all the evidence, work individually or as a team to reach your final verdict—then reveal the solution to see if you cracked the case.
EVIDENCE FILES
EVIDENCE FILE 01 +
EVIDENCE FILE 01 — SURVEY DATA AND TILT ANALYSIS
Case Reference: MBSA-2024-0319
Evidence Item: EV-01 — Structural survey and vertical alignment measurements
Prepared By: Dr. James Okoro, Millhaven Building Safety Authority
Date: Wednesday — 9:00 AM
BACKGROUND
A building tilts when its foundation settles unevenly — one side or corner sinking further into the ground than the others. The tilt observed in the Harwick Waterfront Tower was identified during a routine vertical alignment survey. Dr. Okoro's first task was to establish the precise nature and extent of the tilt — its direction, its magnitude, and whether it was stable or progressing.
SURVEY INSTRUMENT AND METHOD
Vertical alignment of tall structures is measured using a precision theodolite — an optical instrument that measures angles with an accuracy of 0.001 degrees. Measurements are taken from multiple positions around the base of the building and at multiple heights to produce a three-dimensional picture of the structure's deviation from vertical.
Dr. Okoro's team conducted measurements from eight positions around the tower perimeter over two consecutive days — comparing their results against the original construction survey baseline recorded when the foundations were completed fourteen months earlier.
CURRENT TILT MEASUREMENTS
The tower is currently 18 storeys — approximately 54 metres in height, with four storeys of steelwork yet to be erected.
At 54 metres height the top of the current structure is displaced from its original vertical position by:
Northward displacement: 41 centimetres
Westward displacement: 29 centimetres
Combined displacement: approximately 50 centimetres northwest
This corresponds to a tilt of 0.8 degrees from vertical — toward the northwest.
PROGRESSION ANALYSIS
By comparing the current measurements against the construction baseline Dr. Okoro established that the tilt has not been constant throughout construction.
The foundation baseline survey — conducted 14 months ago — showed the structure perfectly vertical at ground level.
Survey records taken at intervals during construction — standard practice on a development of this scale — showed the following progression:
At 6 storeys — 0.1 degrees — within normal construction tolerance
At 10 storeys — 0.2 degrees — at the upper limit of acceptable tolerance
At 14 storeys — 0.4 degrees — outside acceptable tolerance
At 18 storeys — 0.8 degrees — significantly outside acceptable tolerance
The tilt has been increasing consistently as the building has grown taller and heavier.
RATE OF PROGRESSION — CRITICAL FINDING
The progression data reveals something significant.
The tilt did not begin at ground level and remain constant as the building grew. It began small and accelerated — doubling between 6 and 10 storeys, doubling again between 10 and 14 storeys.
This pattern is characteristic of differential settlement — one part of the foundation sinking progressively further than the rest as the load above it increases.
Dr. Okoro noted:
"The progression pattern tells us the foundation is not failing uniformly. A specific area — almost certainly the northwestern corner — is settling at a significantly higher rate than the rest of the footprint. The increasing rate of tilt as the building rises is consistent with a foundation in that corner that is carrying load it was not designed — or built — to carry."
THE SURVEY RECORDS — A PROCEDURAL NOTE
The intermediate survey records — taken at 6, 10, and 14 storeys — were submitted to Harwick Properties as standard construction monitoring reports.
They were not submitted to Meridian Structural Engineering.
They were not submitted to the Millhaven Building Safety Authority.
Under standard practice surveys showing deviation outside acceptable tolerance at 10 storeys should have triggered a mandatory notification to the structural engineer and the building authority.
That notification was not made.
Dr. Okoro noted this in his preliminary report without further comment.
The implication — that Harwick Properties received survey data showing the building outside acceptable tolerance at 10 storeys and continued construction to 18 storeys without notifying the engineer or the authority — would be addressed in the investigation's later stages.
YOUR TASK
The survey data has established that the Harwick Waterfront Tower is tilting 0.8 degrees northwest — and that the tilt has been accelerating progressively as the building has grown taller.
Research what differential settlement is and what causes one part of a building's foundation to sink faster than another. Consider what the accelerating tilt progression tells you about the location and nature of the foundation problem — and why a tilt that begins at 0.1 degrees does not stay at 0.1 degrees as a building grows taller and heavier.
The survey records also raise a procedural question that the science alone cannot answer.
The tilt exceeded acceptable tolerance at 10 storeys. Construction continued to 18 storeys. What should have happened at 10 storeys — and what does the failure to notify the structural engineer or the building authority tell you about how seriously the survey findings were taken?
Evidence File 02 will examine what is actually beneath the northwestern corner of the tower — and why the foundation there is behaving differently from the rest of the footprint.
EVIDENCE FILE 02 +
EVIDENCE FILE 02 — SOIL ANALYSIS
Case Reference: MBSA-2024-0319
Evidence Item: EV-02 — Geotechnical investigation and soil composition analysis
Prepared By: Dr. Sarah Mensah, Geotechnical Engineering Laboratory
Date: Thursday — 11:00 AM
BACKGROUND
Evidence File 01 established that the tilt is concentrated in the northwestern corner of the tower — consistent with differential settlement in that area. Dr. Mensah conducted a detailed geotechnical investigation of the soil beneath the tower footprint — drilling new boreholes at nine positions across the site and comparing the results against the original soil survey commissioned by Harwick Properties before construction began.
THE ORIGINAL SOIL SURVEY
The original soil survey — conducted eighteen months before construction began by Hartwell Geotechnical Services on behalf of Harwick Properties — drilled boreholes at four positions across the site.
The survey identified the following soil profile across the site:
Surface layer — 0 to 2 metres: Made ground — rubble and compacted fill from previous industrial use of the docklands site.
Layer 2 — 2 to 8 metres: Soft alluvial clay — deposited by river action over centuries. Low bearing capacity. High compressibility — meaning it compresses significantly under load.
Layer 3 — 8 to 14 metres: Dense sand and gravel — significantly higher bearing capacity than the clay above.
Layer 4 — below 14 metres: London Clay — stiff, stable, high bearing capacity. Suitable for founding deep piles.
The survey described the alluvial clay layer as broadly consistent across the site — varying in depth between 6 and 9 metres.
The foundation design commissioned from Meridian Structural Engineering was based on this profile.
THE NEW INVESTIGATION — CRITICAL FINDINGS
Dr. Mensah drilled nine new boreholes — including positions in the northwestern corner of the site that were not covered by the original four-point survey.
The results revealed a significant anomaly the original survey had not detected.
Northwestern corner — boreholes NW1 and NW2:
The alluvial clay layer in the northwestern corner is substantially different from the rest of the site.
Depth: 11 to 13 metres — significantly deeper than the 6 to 9 metres recorded elsewhere
Composition: highly organic clay — containing decomposed organic material consistent with an ancient watercourse or marsh deposit
Compressibility: significantly higher than the clay recorded elsewhere — laboratory testing shows the northwestern clay compresses approximately 2.4 times more under equivalent load than the clay at other positions across the site
The dense sand and gravel layer — present at 8 metres across most of the site — does not appear in the northwestern boreholes until 13 to 14 metres depth.
This means the stable load-bearing layer is approximately 5 metres deeper in the northwestern corner than the original survey suggested for that area.
WHY THE ORIGINAL SURVEY MISSED IT
The original survey drilled four boreholes — positioned at the four corners of the site boundary.
The northwestern corner borehole was positioned 8.4 metres from the actual northwestern corner of the tower footprint — close enough to the site boundary to miss the anomalous clay pocket entirely.
The anomalous deposit — an ancient filled watercourse running diagonally beneath the northwestern portion of the site — has a surface footprint of approximately 12 metres by 9 metres. It sits almost entirely beneath the tower's northwestern corner.
Four boreholes across a site of this scale — with a tower footprint of 28 metres by 22 metres — provided insufficient coverage to detect a localised anomaly of this size.
Industry guidance for sites with known variable geology — such as a former docklands site with potential infilled watercourses — recommends a minimum of one borehole per 100 square metres of foundation footprint.
The tower footprint covers approximately 616 square metres.
The original survey drilled four boreholes — one per approximately 154 square metres on average — with the critical northwestern area effectively uncovered.
DR. MENSAH'S ASSESSMENT
"The anomalous clay deposit beneath the northwestern corner is the direct cause of the differential settlement. Under the load of an 18-storey structure the highly organic clay in this zone is compressing at a rate approximately 2.4 times higher than the surrounding soil — causing the northwestern corner to sink progressively further than the rest of the foundation.
This deposit would have been detectable had the original survey included a borehole within the tower's northwestern corner footprint. The decision to use four boreholes on a former docklands site with known variable geology was, in my professional assessment, insufficient for a structure of this scale and sensitivity."
YOUR TASK
The soil analysis has identified an anomalous deposit of highly organic clay beneath the northwestern corner of the tower — compressing 2.4 times faster than the surrounding soil under the building's load, causing the differential settlement that is tilting the tower.
The original survey missed this deposit because its four boreholes were too widely spaced to detect a localised anomaly beneath the tower's northwestern corner.
Research what differential settlement is and why organic clay compresses more than standard alluvial clay under load. Consider what industry guidance says about borehole spacing on variable geology sites — and whether a four-borehole survey was adequate for a 22-storey tower on a former docklands site.
The soil survey was commissioned by Harwick Properties and conducted by Hartwell Geotechnical Services. The foundation was designed by Meridian Structural Engineering based on that survey data.
Does an inadequate soil survey automatically mean the foundation design was wrong — or could a correctly designed foundation have accommodated the actual soil conditions even if the survey understated them? That question is addressed in Evidence File 03.
EVIDENCE FILE 03 +
EVIDENCE FILE 03 — FOUNDATION INSPECTION RECORDS
Case Reference: MBSA-2024-0319
Evidence Item: EV-03 — Foundation construction records and pile inspection
Prepared By: Dr. James Okoro, Millhaven Building Safety Authority
Date: Friday — 2:00 PM
BACKGROUND
Evidence File 02 established that the original soil survey was inadequate — missing an anomalous clay deposit beneath the northwestern corner. But the foundation design was based on that survey. This file examines what the foundation specification required and whether what was actually built matched that specification.
THE FOUNDATION DESIGN — SPECIFICATION
Dr. Marsh's foundation design used a bored pile system — a standard approach for tall buildings on variable urban ground conditions.
Bored piles are cylindrical columns of reinforced concrete drilled into the ground to transfer the building's load down through weak upper soil layers to stronger bearing strata below. Their effectiveness depends on two factors — the depth to which they reach and the quality of the concrete within them.
The approved foundation specification for the Harwick Waterfront Tower required:
Total piles: 48
Specified pile diameter: 750 millimetres
Specified pile depth — general: 16 metres below ground level
Specified pile depth — northwestern corner piles: 18 metres below ground level
Dr. Marsh's specification noted a marginal increase in pile depth for the northwestern corner — described in the design notes as a precautionary measure accounting for the slightly deeper alluvial clay suggested by the nearest original survey borehole.
The specification required all piles to reach the London Clay layer — confirmed as the stable bearing stratum — before termination.
THE FOUNDATION INSPECTION — FINDINGS
Dr. Okoro's team conducted a physical inspection of the foundation using borehole camera equipment and ground-penetrating radar — non-invasive techniques that allow the depth and integrity of existing piles to be assessed without excavation.
General pile inspection — 44 piles:
Depth: consistent with specification — ranging from 15.8 to 16.3 metres — within acceptable construction tolerance of plus or minus 0.5 metres.
Concrete integrity: no significant voids or discontinuities detected.
Bearing stratum reached: confirmed for all 44 general piles.
Northwestern corner piles — 4 piles designated NW1 to NW4:
This is where the inspection produced its most significant finding.
PileSpecified depthActual depthShortfallNW118 metres15.7 metres2.3 metresNW218 metres15.9 metres2.1 metresNW318 metres16.1 metres1.9 metresNW418 metres15.8 metres2.2 metres
All four northwestern corner piles fall significantly short of their specified depth — by an average of 2.1 metres.
More critically — given the actual soil conditions identified in Evidence File 02 — the stable London Clay bearing stratum in the northwestern corner does not begin until 13 to 14 metres depth. The specified 18-metre depth was intended to ensure piles achieved 4 to 5 metres of penetration into the London Clay — sufficient to develop reliable end bearing in stable ground.
At their actual depths of 15.7 to 16.1 metres the northwestern piles penetrate the London Clay by only 1.7 to 3.1 metres — insufficient to develop reliable end bearing under the load of an 18-storey structure.
With inadequate end bearing the piles are forced to transfer a greater proportion of their load through shaft friction — the friction developed along the pile surface through the overlying soil layers. In the highly organic clay identified in Evidence File 02 — which is significantly more compressible than standard alluvial clay — shaft friction is particularly unreliable.
Under sustained load from the growing structure the organic clay has been consolidating — compressing progressively around the pile shafts and reducing the friction it can develop. As shaft friction reduces the load transfers further downward toward the pile tips — which are themselves inadequately embedded in the London Clay to develop full end bearing.
The result is progressive settlement — the northwestern corner sinking slowly but consistently as the organic clay consolidates and the piles find no reliable load transfer mechanism in the ground conditions they were built into.
CONSTRUCTION RECORDS — WHAT CALDWELL KNEW
Dr. Okoro requested Caldwell Construction's pile construction records — the daily logs maintained during foundation drilling that record drilling depths, concrete volumes, and termination decisions for each pile.
The records for the four northwestern piles showed the following termination notes:
NW1: "Terminated at 15.7m — drilling resistance adequate — supervisor approval"
NW2: "Terminated at 15.9m — drilling resistance adequate — supervisor approval"
NW3: "Terminated at 16.1m — drilling resistance adequate — supervisor approval"
NW4: "Terminated at 15.8m — drilling resistance adequate — supervisor approval"
The phrase "drilling resistance adequate" is used by drillers to indicate they believe they have reached a suitable bearing stratum — based on the resistance felt through the drilling equipment as it advances.
Dr. Okoro noted one significant problem with these termination records.
The specified termination criterion in Dr. Marsh's design was not drilling resistance. It was minimum depth of 18 metres combined with confirmation of London Clay penetration by a qualified geotechnical engineer present on site.
The construction records show no geotechnical engineer was present during the drilling of any of the four northwestern piles.
The termination decisions were made by a site supervisor — based on feel rather than measurement — at depths 1.9 to 2.3 metres short of specification.
CONCRETE VOLUME DISCREPANCY
A secondary check on actual pile depth uses concrete volume — the quantity of concrete poured into each pile should correspond to its depth and diameter.
Theoretical concrete volume for an 18-metre pile at 750mm diameter:
π × (0.375)² × 18 = 7.95 cubic metres per pile
Actual concrete volumes recorded for the four northwestern piles:
PileTheoretical volumeRecorded volumeImplied depthNW17.95 m³6.94 m³15.7 mNW27.95 m³7.03 m³15.9 mNW37.95 m³7.12 m³16.1 mNW47.95 m³6.98 m³15.8 m
The concrete volumes independently confirm the depths recorded by the borehole camera — the piles are exactly as short as the inspection found them to be.
The concrete volume records were available to Caldwell Construction, to the building inspector, and — on request — to Harwick Properties throughout the construction period.
Nobody checked them against the specification.
YOUR TASK
The foundation inspection has revealed that all four northwestern corner piles were terminated 1.9 to 2.3 metres short of their specified depth — without a qualified geotechnical engineer present and based on subjective drilling resistance rather than the measurement and verification the specification required.
The concrete volume records independently confirm the shortfall — and were available throughout construction to multiple parties.
Research how bored pile foundations work and why pile depth is critical to load transfer in variable ground conditions. Consider what the termination records tell you about the decision made on site — and whether "drilling resistance adequate" is an acceptable substitute for the specified termination criteria.
Three failures have now been identified across three evidence files:
The soil survey was inadequate — it missed the anomalous clay deposit.
The foundation specification had insufficient depth margin for the actual conditions.
The construction deviated from the specification — by 1.9 to 2.3 metres on four critical piles.
Consider how these three failures interact. Would the tower be tilting if only one of them had occurred — or does the tilt require all three to combine? And what does the concrete volume data — available throughout construction and never checked — tell you about the systems that were supposed to catch this kind of deviation?
Evidence File 04 will address the whistleblower's claim about concrete quality — and whether substandard materials contributed to the failure.
EVIDENCE FILE 04 +
EVIDENCE FILE 04 — CONCRETE CORE TESTING
Case Reference: MBSA-2024-0319
Evidence Item: EV-04 — Materials testing and whistleblower assessment
Prepared By: Dr. Sarah Mensah, Geotechnical Engineering Laboratory
Date: Monday — 10:00 AM
BACKGROUND
Two days after the investigation began the Millhaven Building Safety Authority received an anonymous communication from a person identifying themselves as a former Caldwell Construction site foreman.
The communication alleged that concrete used in the Harwick Waterfront Tower foundations was below the specified grade — specifically that the concrete supplied for the northwestern corner piles was a lower strength mix than the specification required, delivered from a different batch to avoid detection.
If true this would represent a second and independent structural failure — weakening the piles themselves in addition to their insufficient depth.
Dr. Mensah conducted core sampling and laboratory testing of the foundation concrete to assess the claim.
CONCRETE SPECIFICATION
The foundation specification required all piles to be constructed using concrete of grade C35/45 — meaning the concrete achieves a minimum compressive strength of 35 megapascals when tested on cylindrical samples and 45 megapascals on cube samples after 28 days of curing.
C35/45 is standard for bored pile foundations in urban environments and represents a well-established and widely available concrete grade.
CORE SAMPLING METHOD
Concrete core samples were extracted from six piles using a rotary diamond core drill — standard practice for in-situ concrete assessment. Cores of 100 millimetres diameter were taken from each pile at two depths — near the pile head and at mid-depth.
Sampled piles:
Two general piles — G12 and G27 — as reference samples
All four northwestern corner piles — NW1 through NW4
Cores were submitted to an independent laboratory under blind testing conditions — the laboratory was not informed of the investigation context or which piles the samples came from.
LABORATORY RESULTS
General piles — G12 and G27:
Average compressive strength: 38.4 megapascals — above the minimum C35/45 requirement.
Northwestern corner piles — NW1 through NW4:
Pile NW1 showed an average compressive strength of 37.0 megapascals — above the minimum requirement.
Pile NW2 showed an average compressive strength of 37.8 megapascals — above the minimum requirement.
Pile NW3 showed an average compressive strength of 37.0 megapascals — above the minimum requirement.
Pile NW4 showed an average compressive strength of 37.1 megapascals — above the minimum requirement.
Average compressive strength across all four northwestern piles: 37.2 megapascals — above the C35/45 minimum requirement of 35 megapascals.
Strength values were consistent between pile heads and mid-depths across all four piles — indicating uniform concrete quality throughout each pile's length.
DR. MENSAH'S ASSESSMENT
"The concrete in all six sampled piles — including all four northwestern corner piles — meets the C35/45 specification. The strength values are consistent across pile heads and mid-depths, and between the general and northwestern corner piles. There is no evidence of a lower-grade concrete mix in the northwestern corner or anywhere else in the sampled foundation.
The whistleblower's allegation is not supported by the physical evidence."
THE WHISTLEBLOWER — FURTHER INVESTIGATION
Following the laboratory results Dr. Okoro requested that the authority's investigators identify and interview the source of the anonymous communication if possible.
Cross-referencing the communication's language, timing, and specific details against Caldwell Construction's employment records identified a likely candidate — Gary Nolan, a site foreman who had worked on the Harwick Waterfront Tower foundations and had been dismissed by Caldwell Construction seven months before the tilt was discovered — following a disciplinary process he had formally contested.
Gary Nolan agreed to be interviewed.
He confirmed he was the source of the anonymous communication. He stated he had witnessed what he believed to be a concrete delivery from a non-approved supplier on one occasion during the foundation works — but acknowledged he had not recorded it formally at the time, had not raised it through official channels, and could not provide documentary evidence to support his recollection.
When asked about his dismissal — and whether it had influenced his decision to contact the authority — he declined to answer directly.
Dr. Okoro noted in his assessment:
"The absence of documentary evidence, combined with the laboratory results showing specification-compliant concrete across all sampled piles, means the whistleblower's allegation cannot be substantiated. The concrete is not the problem. The concrete never was the problem. The investigation should not be distracted from the findings of Evidence Files 01 through 03 by an allegation that the physical evidence does not support."
YOUR TASK
The concrete testing has eliminated the whistleblower's allegation. All sampled piles — including all four northwestern corner piles — show concrete meeting or exceeding the C35/45 specification.
Research how concrete compressive strength is tested and why the C35/45 grade is appropriate for bored pile foundations. Consider what the whistleblower's motivation might have been — and what the absence of corroborating documentary evidence tells you about how seriously an unsubstantiated allegation should be weighted against laboratory results.
The concrete is not the cause of the tilt.
Three independent failures established in Evidence Files 01 through 03 remain the explanation — an inadequate soil survey, a foundation with insufficient depth margin for the actual conditions, and piles terminated 1.9 to 2.3 metres short of specification.
Before reading Evidence File 05 — consider which of these three failures you believe is most significant, and whether the tilt would have occurred if any single one of them had been avoided. That question is what the final analysis will address.
EVIDENCE FILE 05 +
EVIDENCE FILE 05 — LOAD ANALYSIS AND RESPONSIBILITY RECONSTRUCTION
Case Reference: MBSA-2024-0319
Evidence Item: EV-05 — Structural load analysis and failure mechanism assessment
Prepared By: Dr. James Okoro, Millhaven Building Safety Authority
Date: Tuesday — 3:00 PM
BACKGROUND
Four evidence files have established the physical facts of this case. The tower is tilting 0.8 degrees northwest. The cause is differential settlement in the northwestern corner driven by anomalous organic clay. The original soil survey missed the clay deposit. The foundation piles in the northwestern corner were terminated 1.9 to 2.3 metres short of specification. The concrete is not at fault.
This file addresses two remaining questions.
First — what does the structural load analysis tell us about whether any single failure alone would have caused the tilt?
Second — what do the records tell us about who knew what and when?
PART ONE — LOAD ANALYSIS
The Harwick Waterfront Tower at 18 storeys has an estimated total structural weight — including the concrete frame, floor slabs, and permanent fixtures — of approximately 42,000 tonnes.
This load is distributed across 48 foundation piles. The northwestern corner piles — NW1 through NW4 — carry approximately 17% of the total load — reflecting the tower's structural geometry and the column positions above.
Load carried by the four northwestern piles: approximately 7,140 tonnes
Dr. Okoro assessed the load-bearing capacity of the northwestern piles under three scenarios — actual conditions, specification conditions, and a hypothetical in which the soil survey had been adequate.
SCENARIO 1 — ACTUAL CONDITIONS
Pile depth: 15.7 to 16.1 metres — as built
Bearing stratum at northwestern corner: London Clay beginning at 13 to 14 metres
Penetration into London Clay: 1.7 to 2.1 metres
Anomalous organic clay present: yes — undetected by original survey
Load-bearing capacity of four northwestern piles under actual conditions:
estimated 4,200 to 4,800 tonnes
Load applied: 7,140 tonnes
The piles are carrying approximately 50% more load than their capacity under actual conditions.
The result is progressive settlement of the organic clay under the pile tips — causing the differential settlement and the observed tilt.
SCENARIO 2 — SPECIFICATION CONDITIONS
Pile depth: 18 metres — as specified
Bearing stratum at northwestern corner: London Clay beginning at 13 to 14 metres
Penetration into London Clay: 4 to 5 metres — as the specification intended
Anomalous organic clay present: yes — undetected by original survey
At 18 metres depth with 4 to 5 metres of penetration into the London Clay the pile tips would be well below the anomalous organic clay layer. The load would be transferred into the stable London Clay rather than the compressible organic material above it.
Load-bearing capacity of four northwestern piles at specified depth: estimated 8,500 to 9,200 tonnes
Load applied: 7,140 tonnes
At the specified depth the piles would have been adequate even given the undetected organic clay.
SCENARIO 3 — ADEQUATE SOIL SURVEY
If the original soil survey had detected the anomalous clay deposit — using the industry-recommended borehole spacing of one per 100 square metres — Dr. Marsh's foundation design would have been modified.
Dr. Marsh confirmed in interview that had she been aware of the organic clay deposit and its depth she would have specified the northwestern corner piles at a minimum of 20 to 21 metres — ensuring adequate penetration into stable London Clay regardless of local variation.
At 20 metres depth the load-bearing capacity of the four northwestern piles is estimated at 10,500 to 11,200 tonnes — well in excess of the applied load.
With an adequate soil survey the foundation would have been designed to accommodate the actual ground conditions.
THE CRITICAL INTERACTION
The three scenarios reveal something precise about how this failure occurred.
If the soil survey had been adequate — the foundation would have been correctly designed and the tilt would not have occurred regardless of whether Caldwell terminated the piles at 18 metres or 15.7 metres.
If the piles had been built to specification at 18 metres — the load would have been transferred to stable London Clay and the tilt would not have occurred despite the inadequate survey and the undetected clay.
If both the survey and the construction had been correct — the tilt would certainly not have occurred.
The tilt required both failures to occur simultaneously — an inadequate survey that left the design with insufficient depth margin, and a construction shortfall that removed the margin that did exist.
Either failure alone was survivable. Together they were not.
PART TWO — WHO KNEW WHAT AND WHEN
Dr. Okoro compiled a chronology of knowledge across the three parties.
Harwick Properties:
Commissioned a four-borehole survey on a former docklands site — below industry-recommended coverage for a structure of this scale. Received intermediate survey reports at 10 and 14 storeys showing tilt outside acceptable tolerance. Did not notify Meridian Structural Engineering. Did not notify the Millhaven Building Safety Authority. Continued construction to 18 storeys.
Caldwell Construction:
Terminated four northwestern corner piles at 15.7 to 16.1 metres — 1.9 to 2.3 metres short of specification. Used drilling resistance as a termination criterion rather than the specified minimum depth verified by a geotechnical engineer.
Concrete volumes consistent with the reduced depths were recorded throughout — and were available to multiple parties. No deviation from specification was reported to Meridian Structural Engineering or to Harwick Properties.
Meridian Structural Engineering:
Designed the foundation based on the soil survey data provided. Specified 18-metre pile depths for the northwestern corner — a precautionary increase that would have been sufficient had it been built as specified. Was not notified of the intermediate survey findings showing tilt outside tolerance at 10 storeys. Was not notified of the pile depth deviation during construction. Learned of the tilt when the site was evacuated.
DR. OKORO'S CONCLUSION
"This building is tilting because of two independent failures that combined to exceed the foundation's capacity. The soil survey was inadequate for a site of this geological complexity — it missed an anomalous deposit that was detectable had the survey been conducted to industry standards. The foundation piles in the critical corner were built 1.9 to 2.3 metres short of specification — without the verification procedure the specification required.
Either failure alone would not have caused this outcome. Together they did.
The records show that Harwick Properties received survey data indicating tilt outside acceptable tolerance at 10 storeys and continued construction without notifying the structural engineer or the building authority. The records show that Caldwell Construction terminated piles short of specification without disclosure. Meridian Structural Engineering designed correctly for the data it was given and was not informed of findings that would have required design review.
The building is still standing. Whether it remains standing depends on remediation work that cannot begin until responsibility has been established and a remediation design has been approved. Every day of delay carries structural risk.
The investigation's findings are now complete. The determination of legal responsibility is a matter for others."
YOUR TASK
You now have all five Evidence Files.
The survey missed the anomalous clay. The foundation design had insufficient margin for the actual conditions. The piles were built short of specification without disclosure. The developer received tilt data outside acceptable tolerance at 10 storeys and continued construction to 18 storeys without notifying the engineer or the authority. The contractor terminated piles early based on subjective feel rather than the required measurement and verification. The engineer designed correctly for the data provided and was kept uninformed of the deviations that followed.
Using evidence from all five files — what caused the Harwick Waterfront Tower to tilt, and who bears responsibility? Build your case identifying each failure, each party's role, and the critical interaction that made this outcome unavoidable once both failures occurred simultaneously.
Consider the load analysis carefully. The scenario comparison shows that either failure alone was survivable — it took both to cause the tilt.
What does that tell you about how complex systems fail — and about the difference between a single point of failure and the accumulation of smaller decisions that individually seemed acceptable but collectively were not?
HAVE YOU SOLVED THE CASE?
Review the evidence and decide what you think happened. If you're investigating with others, discuss your findings and agree on your final verdict before revealing the answer.
Once your team has reached a conclusion, reveal the answer.