1 Scope

NOTE This standard covers the design, furnishing, installation, monitoring, and removal of temporary and permanent excavation support systems and the associated groundwater control (dewatering) required to construct deep excavations. (1.1)

NOTE This standard applies to excavations exceeding 5 ft in depth, and to any excavation in soil or groundwater conditions that requires an engineered protective system regardless of depth. (1.2)

NOTE Excavation support systems within scope include sloping and benching, trench boxes and shields, aluminum hydraulic shoring, soldier pile and lagging walls, steel sheet piling, secant and tangent pile walls, soil-mixed walls, slurry (diaphragm) walls, and soil nail walls. (1.3)

NOTE Lateral support systems within scope include cantilevered walls, internal bracing (struts, rakers, cross-lot and corner bracing), and tieback ground anchors with their proof, performance, and creep testing. (1.4)

NOTE Groundwater control within scope includes sump pumping, wellpoint systems, deep well systems, eductor (vacuum) well systems, cut-off walls used for hydraulic control, and the discharge handling and permitting associated with each. (1.5)

NOTE Instrumentation and monitoring within scope includes inclinometers, settlement monuments, piezometers, tiltmeters, survey benchmarks, and vibration monitoring, together with the trigger, action, and abort levels that govern the response to observed movement. (1.6)

1.7 The Contractor shall retain a licensed professional engineer to design every support and dewatering system that this standard or the governing code requires to be engineered.

1.8 The excavation support and dewatering systems shall be designed using the site-specific geotechnical investigation report prepared for the Project.

1.9 Excavation support and dewatering are means and methods that remain the Contractor's responsibility unless the Contract Documents assign a specific permanent system to the design of record.

NOTE Soil nail walls occupy the boundary between temporary support and permanent retaining construction. (1.9.1)

1.9.2 A soil nail wall built only to permit excavation and removed or abandoned at completion is within this standard; a soil nail wall that serves a permanent retaining function is outside this standard and shall be designed and detailed under Retaining WallsSite Retaining WallsResolves to the current edition.sync/retaining-walls.

2 Referenced Standards

2.1 Materials, design, installation, and testing shall comply with the latest adopted edition of each of the following unless a specific edition is cited or the authority having jurisdiction adopts a different edition.

2.2 Where referenced standards conflict, the more stringent requirement shall govern unless the Engineer of Record directs otherwise in writing.

Standard	Title
29 CFR 1926 Subpart P	OSHA Excavations (1926.650-1926.652, Appendices A-F)
IBC 2021	International Building Code (Section 1803 Geotechnical Investigations; Section 1805 Foundation Design)
ASCE 7-22	Minimum Design Loads and Associated Criteria for Buildings and Other Structures
ASTM A328/A328M	Steel Sheet Piling
ASTM A572/A572M	High-Strength Low-Alloy Columbium-Vanadium Structural Steel
ASTM A36/A36M	Carbon Structural Steel
ASTM D1785	Poly(Vinyl Chloride) (PVC) Plastic Pipe, Schedules 40, 80, and 120
ASTM D1587	Thin-Walled Tube Sampling of Fine-Grained Soils for Geotechnical Purposes
ASTM D4044	Field Procedures for Instantaneous Change in Head (Slug) Tests for Aquifer Properties
ASTM D4050	Field Procedure for Withdrawal and Injection Well Tests for Aquifer Properties
ASTM D4700	Soil Sampling from the Vadose Zone
PTI DC35.1	Recommendations for Prestressed Rock and Soil Anchors
PTI DC80.3	Specification for Unbonded Single Strand Tendons
FHWA NHI-14-007	Geotechnical Engineering Circular No. 4 - Ground Anchors and Anchored Systems
FHWA NHI-06-006	Geotechnical Engineering Circular No. 7 - Design and Construction of Driven Pile Foundations
FHWA SA-97-073	Manual on Design and Construction Monitoring of Soil Nail Walls

3 Submittals

3.1 Action Submittals

3.1.1 The Contractor shall submit the following action items for review before any excavation support or dewatering work begins:

Excavation support system design drawings and calculations sealed by the design engineer
Dewatering system design, including predicted drawdown, flow rate, and well or wellpoint layout
Tieback ground anchor design, including bond length, unbonded length, inclination, and lock-off load
Internal bracing design, including strut and raker sizing, preload values, and bracing sequence
Excavation and bracing or anchoring sequence drawings
Instrumentation and monitoring plan with trigger, action, and abort levels
Mill certificates for sheet piling, soldier piles, wales, struts, and anchor tendons
Dewatering discharge plan and applicable discharge permit or permit application

Action submittals required before start of workcheckbox

☑ Support system design drawings and calculations (PE sealed)

☑ Dewatering system design (drawdown, flow, layout)

☐ Tieback anchor design (bond, unbonded length, lock-off)

☐ Internal bracing design (sizing, preload, sequence)

☑ Excavation and support sequence drawings

☑ Instrumentation and monitoring plan

☐ Mill certificates for steel and tendons

☐ Dewatering discharge plan and permit

3.2 Informational Submittals

3.2.1 The Contractor shall submit the following informational items:

Qualifications of the design engineer and the specialty support and dewatering subcontractors
Pre-excavation condition survey of adjacent structures, utilities, and pavements, including photographs and crack mapping
Utility location records for the work area and the zone of influence
Anchor testing program describing proof, performance, and creep test procedures and acceptance criteria
Manufacturer data for trench boxes, shields, and hydraulic shoring, including tabulated capacities and depth ratings

Informational submittals requiredcheckbox

☑ Designer and subcontractor qualifications

☑ Pre-excavation adjacent condition survey

☑ Utility location records

☑ Anchor testing program and acceptance criteria

☑ Manufacturer data for shields and shoring

3.3 Closeout Submittals

3.3.1 The Contractor shall submit the following closeout items:

Record drawings showing as-built support system geometry and any anchors or elements left in place
Final monitoring data report with movement and settlement history through completion
Tieback load test reports and lock-off load records with load cell verification
Dewatering operation log, including discharge volumes and any treatment performed
Documentation of anchor or wall steel left permanently in the ground and its location relative to property lines

Closeout submittals requiredcheckbox

☑ As-built record drawings (system and elements left in place)

☑ Final monitoring data report

☑ Tieback load test and lock-off records

☑ Dewatering operation and discharge log

☑ Record of elements left permanently in ground

4 Quality Assurance

4.1 Design Responsibility

4.1.1 Excavations deeper than 20 ft shall have their protective system designed by a registered professional engineer, as required by OSHA 1926.652(b)(1)(ii).

4.1.2 OSHA Appendix B tabulated shoring data is valid only to a depth of 20 ft and shall not be used to justify a system deeper than 20 ft.

4.1.3 The support system design engineer shall be licensed in the jurisdiction of the Project.

4.1.4 The dewatering system design shall be prepared by an engineer experienced in groundwater control and based on the measured or estimated hydraulic conductivity of the affected strata.

4.2 Geotechnical Basis of Design

NOTE A site-specific geotechnical investigation report is required by IBC Section 1803 and by every engineered support and dewatering design; selecting a system without it is the most common and most consequential omission on deep-excavation projects. (4.2.1)

4.2.2 The support and dewatering designs shall reference the boring logs, soil classification, groundwater elevations, and hydraulic conductivity values from the Project geotechnical report.

4.2.3 Soil sampling supporting the geotechnical report shall follow ASTM D1587 for thin-walled tube samples and ASTM D4700 for vadose-zone sampling.

4.2.4 Where the dewatering design depends on aquifer properties, those properties shall be established by slug testing per ASTM D4044 or pumping testing per ASTM D4050.

4.3 Soil Classification

NOTE OSHA classifies soil for sloping and shoring selection as Type A (cohesive, unconfined compressive strength ≥ 1.5 tsf, no fissures), Type B (0.5 to 1.5 tsf or granular), and Type C (less than 0.5 tsf, or submerged or otherwise unstable). (4.3.1)

NOTE Maximum allowable slope by OSHA soil type, for excavations to 20 ft, is 3/4H:1V for Type A, 1H:1V for Type B, and 1.5H:1V for Type C. (4.3.2)

4.3.3 A competent person shall classify the soil before each shift and reclassify it whenever conditions change.

Governing OSHA soil classificationradio

○ Type A (cohesive, ≥ 1.5 tsf)

● Type B (0.5 to 1.5 tsf or granular)

○ Type C (< 0.5 tsf, submerged, or unstable)

4.4 Inspection

4.4.1 A competent person shall inspect the excavation, the adjacent areas, and the protective systems daily, before each shift, and after every rainstorm or other hazard-increasing event, as required by OSHA 1926.651(k).

4.4.2 The support system design engineer shall observe the installation of each new wall or bracing level and confirm conformance with the design before excavation proceeds below that level.

5 Environmental and Service Conditions

5.1 Protection of Adjacent Construction

5.1.2 A pre-excavation condition survey of adjacent structures, utilities, and pavements shall be performed and documented with photographs and crack mapping before any work begins.

5.1.3 Underground utilities within the work area and within the zone of influence shall be located and marked before excavation.

5.1.4 The support system shall limit lateral movement so that the angular distortion of adjacent framed construction does not exceed L/500, and of adjacent load-bearing masonry does not exceed L/750.

Adjacent-structure settlement limit (angular distortion)radio

● L/500 (framed construction)

○ L/750 (load-bearing masonry)

○ L/1000 (settlement-sensitive or historic structure)

5.2 Corrosion and Service Life

5.2.1 A temporary support element removed or abandoned at completion has a short design life and needs no permanent corrosion protection; a permanent element carries load for the structure's service life and shall be protected accordingly.

5.2.2 Permanent ground anchors and permanent wall steel shall be protected against corrosion by galvanizing, epoxy coating, or full encapsulation appropriate to the soil chemistry.

Design service life of support systemradio

● Temporary (construction duration only)

○ Permanent (incorporated into the structure)

Corrosion protection for permanent elementsselect

None (temporary system)

Hot-dip galvanizing

Fusion-bonded epoxy coating

Double-corrosion-protection encapsulation

6 Support System Selection

NOTE The choice among open-cut sloping, a disposable or reusable shield, and an engineered shoring wall is driven by excavation depth, soil and groundwater conditions, and how close the cut comes to structures or property lines. (6.1)

NOTE Sloping or benching is the simplest system but consumes the most lateral space; it is rarely feasible on a constrained urban site. (6.2)

NOTE A trench box or shield protects workers inside a trench but provides no support to the trench walls themselves and does not control settlement outside the box. (6.3)

NOTE An engineered shoring wall is required where the excavation is deep, the soil is unstable, or settlement-sensitive construction is close enough that an unsupported or sloped cut would damage it. (6.4)

6.5 The excavation support system shall be selected to suit the geotechnical conditions, the excavation depth and geometry, and the proximity and sensitivity of adjacent construction.

Primary excavation support approachradio

○ Sloping or benching (open cut)

● Trench box or shield

○ Aluminum hydraulic shoring

○ Engineered shoring wall

6.6 Shoring Wall Type

NOTE Shoring wall selection turns mainly on soil permeability and the settlement sensitivity of what is nearby: an open system such as soldier pile and lagging is economical in firm soils above the water table, while a closed system such as sheet piling, secant piles, or a slurry wall is needed where groundwater or settlement control demands a continuous, low-permeability face. (6.6.1)

NOTE Soldier pile and lagging is an open wall: vertical steel piles at intervals with lagging spanning between them, leaving gaps that pass soil and water unless they are sealed. (6.6.2)

NOTE Steel sheet piling is a continuous interlocking wall well suited to high groundwater and to sites needing a water cut-off. (6.6.3)

NOTE Secant and tangent pile walls are continuous walls of overlapping bored piles, used for deep excavations next to settlement-sensitive structures. (6.6.4)

NOTE A soil-mixed wall is built by overlapping auger-mixed soil-cement columns with steel sections inserted while the mix is fluid. (6.6.5)

NOTE A slurry (diaphragm) wall is a continuous reinforced-concrete wall cast in a bentonite-supported trench, used for the deepest and most settlement-critical excavations. (6.6.6)

6.6.7 The selected shoring wall type shall provide a face whose permeability and stiffness suit the groundwater regime and the settlement tolerance of the adjacent construction.

Shoring wall typeselect

Soldier pile and timber lagging

Soldier pile and precast concrete lagging

Soldier pile and shotcrete lagging

Steel sheet piling

Secant pile wall

Tangent pile wall

Soil-mixed wall (SMW)

Slurry (diaphragm) wall

Soil nail wall (temporary)

6.7 Lateral Support Method

NOTE A wall may stand as a cantilever, lean on internal bracing, or be held by tieback anchors; the choice is set by depth, by the room available for struts inside the cut, and by whether anchors may extend beyond the property line. (6.7.1)

NOTE A cantilevered wall needs no bracing or anchors but is limited to shallow excavations because deflection grows quickly with depth. (6.7.2)

NOTE Internal bracing keeps all work within the site but obstructs the excavation and complicates the permanent structure built around it. (6.7.3)

NOTE Tieback anchors leave the excavation clear but extend beyond the wall and require subsurface easement rights wherever they cross a property line. (6.7.4)

6.7.5 Tieback anchors shall not be installed beyond the property line unless a subsurface easement or right-of-entry has been secured from the affected adjacent owner.

6.7.6 The lateral support method shall be designed for the lateral earth pressures and surcharge loads determined in accordance with ASCE 7-22 and the Project geotechnical report.

Lateral support methodradio

○ Cantilevered (no bracing or anchors)

○ Internal bracing (struts and rakers)

● Tieback ground anchors

○ Combined bracing and anchors

Number of support (bracing or anchor) levelsrange

levels

06

Default: 2 levels

7 Soldier Pile and Lagging Walls

NOTE A soldier pile and lagging wall is the economical default in firm soils above the water table, but its open lagging gaps are also its principal weakness where groundwater is present. (7.1)

7.2 Soldier piles shall be ASTM A572 Grade 50 or ASTM A36 wide-flange (H-pile) sections, installed by drilling and grouting or by driving.

NOTE Soldier pile spacing typically ranges from 6 to 10 ft on center, with 8 ft on center a common starting point in medium-dense granular soils. (7.3)

7.4 The soldier pile spacing shall be specified, sized to suit the soil conditions and the design lateral earth pressures at this excavation.

Soldier pile spacing (on center)range

ft

610

Default: 8 ft

Soldier pile section steelradio

● ASTM A572 Grade 50 (Fy = 50 ksi)

○ ASTM A36 (Fy = 36 ksi)

Soldier pile installation methodradio

● Drilled and concreted in place

○ Driven

7.5 Lagging

NOTE Lagging spans horizontally between soldier piles to retain the soil exposed as the excavation advances. (7.5.1)

7.5.2 Timber lagging shall be a minimum 3 in. nominal thickness for spans up to 8 ft in Type B soils, and a minimum 4 in. nominal thickness in Type C or soft conditions.

NOTE Open lagging in high-groundwater conditions allows soil and water to migrate through the gaps; unless the gaps are sealed, the wall loses ground behind it and adjacent settlement follows. (7.5.3)

7.5.4 Where groundwater is present behind a soldier pile and lagging wall, the gaps between lagging boards shall be sealed with filter fabric or lean-mix grout to prevent soil and water migration.

Lagging materialselect

Rough-sawn timber (Douglas fir or southern yellow pine)

Precast concrete panels

Shotcrete

Timber lagging nominal thicknessradio

● 3 in. (spans to 8 ft, Type B)

○ 4 in. (Type C or soft conditions)

8 Steel Sheet Piling

NOTE Steel sheet piling forms a continuous interlocking wall that both retains soil and cuts off groundwater, which makes it the common choice below the water table. (8.1)

8.2 Sheet piling shall conform to ASTM A328 with a minimum yield strength of 38.5 ksi, or to ASTM A572 Grade 50 where higher strength is specified.

8.3 Sheet piles shall be installed with their interlocks fully engaged for the full driven length to maintain wall continuity and the water cut-off.

NOTE Vibratory or impact driving of sheet piles transmits ground vibration that can crack masonry and damage buried utilities, so driving near existing structures shall be monitored rather than assumed safe. (8.4)

8.5 Where sheet piles are driven within the influence zone of existing structures or utilities, vibration monitoring shall be performed and driving shall stop if the measured peak particle velocity exceeds the established limit.

Sheet pile section seriesselect

PZ / PZC hot-rolled Z-section

PS hot-rolled straight-web section

AZ cold-formed Z-section

Sheet pile installation methodradio

● Vibratory driving

○ Impact driving

○ Press-in (silent) installation

Vibration monitoring near existing structuresradio

● Required (structures or utilities within influence zone)

○ Not required (no adjacent structures)

9 Tieback Ground Anchors

NOTE Tieback ground anchors hold a wall by transferring its lateral load through a prestressed tendon to a grouted bond zone in competent soil or rock, leaving the excavation clear of internal bracing. (9.1)

9.2 Tieback design and testing shall conform to PTI DC35.1 and FHWA NHI-14-007; unbonded single-strand tendons shall additionally conform to PTI DC80.3.

NOTE An anchor has a bond length that develops capacity in competent ground and an unbonded (free) length that transfers load past the failure surface; placing the bond zone short of competent ground is the classic anchor design error. (9.3)

9.4 The unbonded length shall extend at least 5 ft beyond the theoretical failure plane into competent material, with typical unbonded lengths between 15 and 40 ft.

9.5 Anchors shall be locked off at 80 percent of the design load unless the design engineer specifies otherwise.

Tieback tendon typeradio

● Strand tendon (prestressing strand)

○ Bar tendon (threaded bar)

Anchor inclination below horizontalrange

degrees

1045

Default: 15 degrees

Anchor lock-off load (fraction of design load)range

percent

70100

Default: 80 percent

Anchor design loadrange

kips

50300

Default: 120 kips

Per drawings

9.6 Anchor Testing

NOTE Anchor testing exists because a grouted bond zone cannot be inspected; the load test is the only proof that the anchor will hold, so the acceptance criteria and the remedy for a failed anchor shall both be stated explicitly. (9.6.1)

9.6.2 Every production anchor shall be proof tested to a minimum of 1.33 times its design load.

9.6.3 Selected anchors shall be performance tested over five load cycles to a minimum of 1.5 times the design load, in the quantity and locations directed by the design engineer.

9.6.4 Anchors in creep-susceptible soils shall be subjected to an extended creep test, with the acceptable creep movement limited per PTI DC35.1.

9.6.5 An anchor that fails its proof or performance test shall be re-grouted and re-tested, or replaced, to the satisfaction of the design engineer.

9.6.6 Each accepted anchor's lock-off load shall be documented and verified with a load cell or equivalent measurement.

Anchor test type for this anchor rowselect

Proof test (1.33 x design load)

Performance test (1.5 x design load, 5 cycles)

Extended creep test

Proof test load (multiple of design load)range

x design load

1.21.5

Default: 1.33 x design load

10 Internal Bracing

NOTE Internal bracing supports a wall with compression members inside the excavation when anchors are precluded by property lines or subsurface obstructions, accepting the obstruction the bracing creates inside the cut. (10.1)

10.2 Cross-lot struts, corner braces, and rakers shall be ASTM A572 Grade 50 or ASTM A36 wide-flange or pipe sections sized by the design engineer for the design lateral load.

10.3 Struts shall be preloaded to the value shown on the bracing design to engage the wall and limit deflection before further excavation proceeds below the strut level.

10.4 Rakers shall bear on a footing designed to transfer the inclined strut reaction into competent subgrade.

Internal bracing configurationselect

Cross-lot struts (wall to wall)

Corner braces and corner wales

Rakers to base footings

Combined struts and rakers

Strut preload (fraction of design strut load)range

percent

30100

Default: 50 percent

11 Aluminum Hydraulic Shoring and Shields

NOTE Pre-engineered trench shields and aluminum hydraulic shoring protect workers in trenches without a full engineered wall, within the depth and soil limits of the manufacturer's tabulated data. (11.1)

11.2 Trench shields and shoring shall be selected from the manufacturer's tabulated capacities for the actual trench depth and OSHA soil type, and shall not be used beyond their rated depth.

11.3 Aluminum hydraulic shoring cylinders shall develop a minimum axial capacity of 18,000 lb for 2 in. cylinders and 30,000 lb for 3 in. cylinders, per OSHA 1926 Subpart P Appendix D.

Trench protection systemradio

● Trench box (steel)

○ Trench box (aluminum)

○ Slide-rail shield system

○ Aluminum hydraulic shoring

Hydraulic shoring cylinder sizeradio

● 2 in. (min 18,000 lb axial)

○ 3 in. (min 30,000 lb axial)

12 Dewatering

NOTE Dewatering lowers the groundwater table so the excavation can be made and the subgrade kept stable and dry; the method that fits a site is governed first by the soil's hydraulic conductivity and then by the required drawdown depth. (12.1)

NOTE The available methods, ordered by the soil permeability and drawdown each suits, are: (12.2)

Sump pumping collects water in a pit and pumps it out; it suits high-permeability gravels where hydraulic conductivity exceeds about 10^-2 cm/s.
Wellpoint systems use closely spaced shallow wells on a vacuum header and suit sands with hydraulic conductivity from about 10^-4 to 10^-2 cm/s, but a single stage can lower water only about 15 to 18 ft.
Deep well systems use individually pumped boreholes and can lower water 30 to 100 ft or more, making them the choice for deep drawdown in permeable soils.
Eductor (vacuum) well systems use a high-pressure circulating water loop with no moving parts in the well and reach into low-permeability silts from about 10^-6 to 10^-4 cm/s where wellpoints lose suction.
Electro-osmosis dewaters very low permeability clays by applying a direct current; it is a specialty method rarely used in standard commercial construction and is included here only for completeness.

12.3 The dewatering method shall be selected to suit the hydraulic conductivity of the dewatered strata and the required drawdown depth, as established by the Project geotechnical and aquifer testing data.

Dewatering methodselect

Sump pumping (gravels, k > 1e-2 cm/s)

Wellpoint system (sands, k 1e-4 to 1e-2 cm/s)

Deep well system (permeable, deep drawdown)

Eductor / vacuum well (silts, k 1e-6 to 1e-4 cm/s)

Cut-off wall (hydraulic exclusion)

Required drawdown below existing groundwater tablerange

ft

5100

Default: 15 ft

Per drawings

12.4 Wellpoint Systems

12.4.1 Wellpoints shall be spaced 3 to 6 ft on center along the header pipe, with the spacing tightened in lower-permeability soils.

12.4.2 Where the required drawdown exceeds the single-stage limit of about 15 to 18 ft, the wellpoint system shall be installed in multiple stages.

12.4.3 Wellpoint and header materials in contact with groundwater shall be PVC conforming to ASTM D1785 or equivalent corrosion-resistant material.

Wellpoint spacing along headerrange

ft

36

Default: 4 ft

Number of wellpoint stagesrange

stages

13

Default: 1 stages

12.5 Deep Well Systems

12.5.1 Deep wells shall be drilled to a diameter of 6 to 12 in. and fitted with a slotted PVC or HDPE screen sized to the surrounding soil gradation.

12.5.2 Each deep well shall be equipped with an electric submersible turbine pump set 3 to 5 ft above the bottom of the screen.

Deep well borehole diameterrange

in

612

Default: 8 in

12.6 Dewatering Discharge

NOTE Pumped groundwater is a regulated discharge; failing to secure the discharge permit and treatment before mobilizing is a frequent cause of project delay. (12.6.1)

12.6.2 Dewatering discharge shall be covered by an NPDES stormwater permit, a local municipal permit, or a sewer discharge agreement, as required by the authority having jurisdiction, before pumping begins.

12.6.3 Where the discharge requires treatment, the water shall be treated for sediment, turbidity, and pH to the permit limits before it leaves the site.

12.6.4 The discharge point, route, and pump capacity shall be coordinated with the civil site drainage so a pump failure does not flood the excavation or adjacent property.

Dewatering discharge destinationselect

NPDES-permitted surface water discharge

Municipal storm sewer (permitted)

Sanitary sewer (discharge agreement)

On-site infiltration or recharge

Discharge treatment requiredcheckbox

☑ Sedimentation (settling tank or basin)

☐ pH adjustment

☐ Turbidity reduction (filtration or flocculation)

13 Instrumentation and Monitoring

NOTE Instrumentation turns wall and ground movement from an after-the-fact discovery into a measured trend; the value of the program is the pre-set trigger, action, and abort levels that tell the team when to slow down, intervene, or stop. (13.1)

13.2 A monitoring program shall be established with inclinometers to measure lateral wall movement, settlement monuments on adjacent structures and grade, and piezometers to track groundwater response.

13.3 Trigger, action, and abort levels shall be defined for each instrument, with the response to each level stated in the monitoring plan.

13.4 Inclinometers shall be read daily during active excavation within one excavation width of the wall, and weekly during bracing or anchor installation.

13.5 A trigger level of 0.5 in. and an action level of 1.0 in. of lateral movement shall apply unless the design engineer specifies project-specific levels.

13.6 Settlement monuments at adjacent structures shall trigger review at an angular distortion of L/500 for framed construction and L/750 for load-bearing masonry.

13.7 Where drawdown occurs near existing buildings founded in fine-grained soils, settlement monitoring shall be performed because consolidation settlement from dewatering can damage adjacent structures on shallow foundations.

Monitoring instruments deployedcheckbox

☑ Inclinometers (lateral wall movement)

☑ Settlement monuments (adjacent structures and grade)

☑ Piezometers (groundwater response)

☐ Tiltmeters (adjacent structure rotation)

☑ Survey benchmarks (reference)

☐ Vibration monitors (during driving)

Lateral movement trigger level (inclinometer)range

in

0.252

Default: 0.5 in

Lateral movement action level (inclinometer)range

in

0.53

Default: 1 in

14 Installation

14.1 Sequence of Construction

NOTE The excavation and support sequence ties together every system in this standard: the wall, the bracing or anchors, and the dewatering are installed in an interleaved order that keeps the cut stable at every stage. (14.1.1)

14.1.2 Excavation shall not proceed below any bracing or anchor level until that bracing or anchor has been installed, preloaded or stressed, and accepted.

14.1.3 Dewatering shall achieve and demonstrate the required drawdown before excavation proceeds below the groundwater table.

14.1.4 Where staged berms are used to support a wall during raker or anchor installation, the berms shall be maintained until the supporting elements are in place and accepted.

Excavation sequenceradio

● Top-down (support installed as excavation descends)

○ Bottom-up (open cut, then build)

○ Berm-staged (perimeter berm retained during support installation)

14.2 Dewatering Acceptance

14.2.1 The dewatering system shall demonstrate stable drawdown to the required elevation for a continuous period of 24 to 48 hours before excavation proceeds below the groundwater table.

14.2.2 Standby pumping capacity and backup power shall be provided so that a pump or power failure does not allow the groundwater to rebound into the open excavation.

Dewatering acceptance hold periodrange

hours

2448

Default: 24 hours

15 Delivery, Storage, and Handling

15.1 Steel sheet piling, soldier piles, wales, struts, and anchor tendons shall be stored off the ground on dunnage and protected from damage that would impair interlock engagement, straightness, or coating.

15.2 Prestressing tendons and their corrosion-protection sheathing shall be protected from mechanical damage, kinking, and contamination before installation.

15.3 Dewatering pumps, wellpoints, and header pipe shall be stored to keep screens and interlocks free of debris that would reduce flow.

16 Removal and Restoration

16.1 Temporary support elements no longer needed shall be removed unless the Contract Documents permit them to be cut off and abandoned in place.

16.2 Elements left permanently in the ground shall be documented on the record drawings with their location relative to the property lines, particularly tieback anchors that extend beyond the site boundary.

16.3 Voids left by extracted sheet piles, soldier piles, or wellpoints shall be backfilled and compacted to prevent surface settlement, in accordance with EarthworkEarthworkResolves to the current edition.sync/earthwork.

16.4 Dewatering shall be discontinued in a controlled manner that allows the groundwater to recover without inducing uplift on the completed permanent construction.

Disposition of support elements at completionradio

● Fully removed

○ Cut off below subgrade and abandoned in place

○ Incorporated into permanent structure

17 Warranty

17.1 The Contractor shall warrant the excavation support and dewatering systems against failure to perform their protective function for the duration of the excavation and until the permanent construction provides equivalent support and groundwater control.

17.2 Permanent support elements incorporated into the structure shall carry the warranty applicable to the permanent work into which they are incorporated.