Construct DSM Cutoff Wall Checklist and QA Guide

Definition: Construct DSM cutoff wall checklist for field engineers and inspectors controlling mixing energy, overlap continuity, QA coring, and permeability performance during deep soil mixing installation.

Track real-time torque, RPM, flow, and pressure to validate energy.
Plan overlaps and sequencing to eliminate windows and ensure continuity.
Execute QA coring and permeability tests to verify design intent.
Interactive, commentable checklist with export and QR code verification.

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Checklist

Construct DSM cutoff wall requires disciplined controls over mixing energy, overlap continuity, QA coring, and permeability verification to deliver a continuous low-permeability barrier. This checklist targets deep soil mixing cutoff wall works and DSM barriers for groundwater control along embankments, cofferdams, and excavation perimeters. It excludes secant piles and diaphragm walls, keeping focus on wet mixing methods, data logging, and acceptance testing. By standardizing calibration, live monitoring, and test frequency, you minimize windows, segregation, and under-mixed zones that compromise hydraulic performance. The outcome is a traceable record set linking materials, equipment settings, energy curves, core strengths, and in-situ hydraulic conductivity to acceptance criteria. Use it to guide preconstruction, production, and verification—capturing photos, instrument screenshots, test IDs, and approvals. Start interactive mode to tick tasks, add comments with attachments, and export as PDF/Excel. Generate and affix the QR to field packs so crews access the latest version.

Establish a robust QA/QC regime around DSM mixing energy, penetration/withdrawal rates, and binder dosage to achieve uniform soil–cement. Validate overlap geometry and verticality to avoid windows that create seepage pathways, and verify permeability through lab and in-situ tests tied to traceable locations.
Drive reliability with instrumented rigs, calibrated torque, RPM, and grout flow meters logging at 1 Hz or better. Use alarms for low energy or flow anomalies, and base corrective actions on real-time dashboards and daily reviews. Align sampling, coring, and testing frequency with risk and geology variability.
Interactive online checklist with tick, comment, and export features secured by QR code. The QR-backed workflow links field data, photos, and signatures to each task, enabling faster nonconformance closure, transparent approvals, and searchable archives for audits and closeout documentation across contractors and owner teams.
Document wall continuity through as-built mapping of column centrelines, diameters, and overlaps. Integrate GNSS/total station coordinates, drilling depth profiles, and energy curves to demonstrate conformance. Where deviations occur, implement targeted re-mixing or grout injections and retest to confirm permeability recovery before acceptance.

Pre-Construction & Submittals

1. Confirm approved DSM mix design and wall geometry; record binder type, water-to-binder ratio, target diameter, and permeability criteria per approved project specifications and authority requirements; attach signed approvals and latest revisions.
2. Stake wall alignment and top-of-wall elevation using total station/GNSS; maintain horizontal tolerance ±20 mm and elevation ±10 mm; upload coordinate file, stake-out report, and photos of control points.
3. Verify materials traceability: cement/binder lot numbers, delivery tickets, and storage conditions; acceptance: tickets match mix design, moisture protected; upload tickets and silo level logs.
4. Approve construction method statement explicitly excluding secant and diaphragm wall methods; include sequencing, overlap geometry, spoil management, and contingency plans; evidence: signed method statement and ITP.

Equipment Calibration & Mixing Energy Control

5. Calibrate torque and rotation sensors on the DSM rig; acceptance: within ±2% of reference across operating range; attach calibration certificates and before/after check readings.
6. Calibrate grout flowmeter and pressure transducer with a prover tank; acceptance: flow error ≤ ±3%, pressure ≤ ±2% of full scale; upload calibration sheet and photos.
7. Configure data logger to capture depth, torque, RPM, penetration/withdrawal rates, flow, and pressure at ≥1 Hz; verify time sync; evidence: sample log file and timestamp check.
8. Complete trial columns to establish baseline energy curve versus depth; acceptance: actual curve within ±10% of target over 90% of length; attach plots and trial reports.

Wet Mixing Operations & Overlap Continuity

9. Survey start point and verify drill to design depth (toe elevation) with depth encoder; tolerance: depth −0/+100 mm; evidence: log extract and stake photo.
10. Maintain penetration and withdrawal rates per procedure (e.g., 0.2–0.6 m/min); acceptance: within specified band; upload rig trend chart showing steady rates without stalls.
11. Control binder dosage via flow vs. advance rate; acceptance: dosage within ±5% of target; capture flow/pressure plots and batch records for each column.
12. Ensure column overlap meets design (≥150 mm or ≥15% of diameter, whichever is greater); verify by layout checks and drilling logs; evidence: as-built overlap calculations and field photos.
13. Monitor real-time energy index (torque×revs) and set low-energy alarms; acceptance: not below target for more than 0.5 m of depth; attach alarm screenshots and corrective action notes.
14. Check tool verticality with inclinometer; tolerance: deviation ≤ 1:100; capture inclinometer readings at start, mid-depth, and toe for each column.
15. Observe and record returns/spoil consistency to confirm mixing; acceptance: continuous returns without segregation; upload photos and supervisor sign-off.

Quality Assurance Coring & Lab Testing

16. Select core locations using a risk-based plan covering overlaps and variable soils; mark on as-built; evidence: core location map with coordinates and IDs.
17. Extract 100 mm diameter cores after specified curing (e.g., 7/28 days); seal ends to prevent moisture loss; evidence: core logs, photos, and chain-of-custody.
18. Test UCS and lab permeability per approved project specifications; acceptance: parameters meet target values; attach lab reports with sample IDs and curing records.
19. Assess core quality (RQD-like assessment, defects, inclusions); acceptance: no open voids or unmixed zones; upload inspection sheets and annotated photos.

In-Situ Permeability Verification

20. Conduct falling-head or single-hole packer tests in selected columns; acceptance: hydraulic conductivity meets target (e.g., ≤ 1×10⁻⁷ m/s) per approved specifications; attach raw data and calculations.
21. Investigate anomalies (rapid head loss or high k) by coring or GPR; implement remedial re-mixing or grout injection; evidence: corrective action record and passing retest.

Documentation & Acceptance

22. Compile daily reports with instrument logs, batch tickets, crew notes, and weather; supervisor signs; upload PDF and native data files.
23. Produce as-built wall plan showing column centres, diameters, overlaps, and test locations; georeference to site grid; evidence: CAD/PDF and exported coordinate list.
24. Complete final acceptance review against ITP: mixing energy compliance, overlap continuity, core and permeability results; obtain client/engineer digital signatures.
25. Archive all records with QR-linked index; store photos, logs, approvals, and test certificates; verify backup to project server/cloud.

Control Mixing Energy for Uniform DSM Columns

Mixing energy unifies soil and binder into a low-permeability matrix. Track torque, rotation speed, penetration/withdrawal rates, grout flow, and pressure against target curves. Calibrate sensors so the energy index reflects true conditions. Use alarms to flag low energy that might create unmixed streaks or lenses. Trial columns help tune tool selection, blade wear limits, and rate bands before production. During drilling, aim for steady torque and RPM; spikes may indicate obstructions or overly rapid advance. Document any pauses and corrective passes. Align binder dosage with advance rate to avoid under-cemented zones that elevate hydraulic conductivity. Daily reviews of depth-registered plots catch trends like energy decline with wear or water ingress. When deviations occur, stop, re-mix the affected interval, and annotate logs so laboratory results correlate with field actions.

Calibrate torque, RPM, flow, and pressure instruments.
Log depth-indexed data at 1 Hz or better.
Use alarms and pause to re-mix low-energy intervals.
Tune penetration/withdrawal to maintain steady torque.
Correlate dosage with advance rate and depth.

Assure Overlap Continuity and Verticality

Continuity depends on precise layout, verticality control, and disciplined sequencing. Set out centers with the required offset to achieve designed overlaps, and verify with survey before drilling. Inclinometer checks at start, mid, and toe keep deviations within tolerance. Plan a systematic column sequence to minimize time between adjacent columns, preventing slurry loss and soil relaxation that can open windows. Review returns visually to confirm intermixing at overlaps. Where verticality or position drifts, adjust subsequent centrelines or perform corrective columns. Document each overlap’s achieved geometry in an as-built and flag any potential gaps for targeted verification. Avoid mixing adjacent columns too far apart in time or depth; consistent energy during overlap passes is essential for continuity.

Stake centers to deliver the designed overlap.
Check verticality; target deviation ≤ 1:100.
Sequence columns to limit gap time between overlaps.
Inspect returns for continuous intermixing.
Record achieved overlaps in as-built maps.

Verify Performance with Coring and Permeability Testing

QA coring and permeability testing demonstrate the cutoff’s hydraulic integrity. Choose core locations to sample overlaps, variable strata, and critical zones such as under utilities or near tie-ins. Extract and seal cores after designated curing periods to preserve moisture. Laboratory programs typically include UCS and permeability; where needed, add index tests to diagnose variations. Complement lab work with in-situ falling-head or packer tests to confirm performance in place. If results exceed target conductivity, execute corrective re-mixing or injection and retest until compliant. Maintain traceability by linking samples to column IDs, depths, and energy logs so nonconformances can be resolved efficiently. Acceptance is based on meeting permeability targets and demonstrating continuity, not on structural capacity.

Select cores using a risk-based plan.
Seal and label cores with chain-of-custody.
Test UCS and permeability against targets.
Use packer or falling-head tests in situ.
Retest after any remedial works.

How to Use the DSM Cutoff Wall Interactive Checklist

Preparation: gather approved mix design, method statement, ITP, rig calibration certificates, and survey control. Ensure access, spoil management, lighting, and emergency equipment. Equip the crew with PPE, tablet/phone, and camera for logging evidence.
Open the checklist on your device and switch to interactive mode. Assign roles to crew members so torque/RPM monitoring, survey, batching, and QA sampling tasks have clear owners.
During production, tick each task as completed, attach photos (stake-out, instrument screens), and upload data logs. Use comments to record anomalies, pauses, and corrective re-mixing.
At verification stages, add lab reports and field test sheets. Cross-reference sample IDs to column numbers and depths to maintain traceability.
Export progress snapshots to PDF/Excel for daily briefings. Share links with stakeholders to review comments and request clarifications before the next shift.
Sign-Off: obtain digital signatures from contractor, engineer, and owner. Generate a QR-linked final export and place it on the as-built drawing set for quick authentication.

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Miguel Garcia GeoMiguel

Dec 02, 2025

FAQ

Question: How do I know the mixing energy is sufficient throughout the DSM column?

Use calibrated torque and RPM sensors with depth-indexed logging at 1 Hz or better. Compare the live energy curve to the approved baseline from trial columns. Set alarms for low energy and immediately re-mix affected intervals. Document deviations, causes, and corrective passes, then verify with consistent energy on rework.

Question: What is the best way to prove overlap continuity and avoid windows?

Stake precise centrelines, maintain verticality within tolerance, and follow a tight sequence to minimize time between adjacent columns. Verify overlap in real time by reviewing drilling logs and returns. After production, produce an as-built map and, where risk is higher, core the overlap or perform targeted in-situ tests.

Question: How often should I core DSM columns for QA and what tests are typical?

Frequency should follow the approved project specifications and authority requirements, adjusted for risk and geology. Typical tests include unconfined compressive strength and laboratory permeability. Seal cores immediately, maintain chain-of-custody, and link samples to column IDs and depths to ensure traceable, defensible results.

Question: Which in-situ permeability tests are suitable for a DSM cutoff wall?

Falling-head tests in standpipes and single-hole packer tests are commonly used. Choose methods suited to the site’s groundwater and access. Define acceptance against the project’s hydraulic conductivity target, document raw readings and calculations, and retest after any remedial works to confirm restored performance.