From Site Distress to Investigation Scope: A Field-Based Study of Suspected Sewer-Related Ground Deterioration

Typically, road cracking, local settlement and suspected soil loss above the urban sewers are reported to a construction manager well before the cause is known. In between that report and the commissioning of an investigation, there are a series of judgements that are seldom written down: what observations are important, which records to believe, which specialists to call in, which competing explanations to exclude, and what questions the subsequent repair design needs to address. This paper questions what information should be gathered before determining investigation and repair work to specify. It builds a six-stage Distress-to-Scope (D2S) framework that takes an explicit register of Decision Information Requirements (DIRs) as a basis for defining the scope of the investigation and maps each item tendered (location, measurement, deliverable, provision for the unexpected) to the DIR and competing hypothesis that it addresses. The framework is then applied to six documented field records; four urban ground-loss incidents in London, Guatemala City, Hong Kong, a national cavity-survey programme in Japan and an urban sinkhole investigation in Zaragoza, as a natural-ground comparator. Each record was coded with respect to eight generic DIRs. DIR closure ranged from 0.00 to 1.00. For the three incidents which were eventually judged to be sewer and drain related, five of six answers whose route could be identified were only found after excavation or failure, while the two investigated with several explicit hypotheses found their answers through planned investigation. The constant gaps were the lack of information on groundwater, competing explanations with the absence of discriminating evidence, and the reliance on a single source of pipe inspection information. The study provides documented and auditable decision path for the pre-investigation phase, hypothesis–evidence matrix for ground deterioration due to sewer, closure metrics for assessing case records, and specification guidance for the Ausschreibung in Germany.