Segmental Method for Installing Wick Drains

This application is a continuation of U.S. patent application Ser. No. 18/132,057, filed Apr. 7, 2023, which claims benefit of priority of U.S. Provisional Pat. App. Ser. No. 63/329,023, the contents of which are incorporated herein by reference.

The present invention relates generally to geotechnical engineering and, in particular, an improved method for installing wick drains using segmental mandrel sections.

The ground improvement and deep foundation industries rely on various types of drainage systems. For example, wick drains, also known as Prefabricated Vertical Drains (PVD) are prefabricated geotextile filter-wrapped plastic strips with molded channels. The flexible strip or “core” is typically manufactured of polypropylene and both sides have grooves allowing water to flow unimpeded. The core is wrapped in a strong and durable geotextile filter fabric with excellent filtration properties, allowing free access of pore water into the drain. This also prevents piping of fines from adjacent soils without clogging.

Wick drains are typically installed in soft, saturated fine-grain soils, such as silts, clays, peat, sludges, mine tailings and dredge fills, all permeable and normally filled with water (fully saturated). The wick drains act as drainage paths to take out pore water, accelerating drainage, and consolidating soil faster, often from decades to months.

At installation the wick drain is fed down through a hollow mandrel mounted on an excavator or crane mast, and is connected at the bottom to an expendable anchor plate. A vibratory hammer or static method is used to insert the mandrel to design depth. The mandrel is the extracted leaving the anchor plate and wick drain in place. The wick drain is cut at the ground surface, and the equipment is moved to the next location. A pattern of installed vertical wick drains provides short drainage paths for pore water, which accelerates the consolidation process and the construction schedule.

illustrates a conventional wick drain installation apparatus and method. The wick drainis fed from a spoolup to the top of an excavator mastand down through the mastinto a hollow mandrel. The typical mandrelis a rectangular hollow steel tube. The wick drainis fed from spoolthrough the entire mandreland is connected at the bottom of the mandrelto an expendable anchor platewhich is releasably inserted into mandrel. The mandrelis carried in a drive systemin the mastfor downward insertion. The drive system may be any suitable conventional drive system, including hydraulic/cable drive, hydraulic cylinder drive, bottom gear drive, sprocket drive, or the like. For example, American Pile Driving Equipment, Inc. (APE) offers it Bottom Drive™ wick drain drivers, OMS (Germany) offers sprocket drive wick drain drivers, and U.S. Pat. No. 4,755,080 to Cortlever et al. shows a chain or cable drive. As disclosed in U.S. Pat. No. 6,431,795 to White, a vibratory hammer or other assist may be used to help insert the mandrelto design depth. Once inserted the mandrelis removed leaving the anchor plateand wick drainin place. The wick drainis cut at the ground surface, and the mandrelis moved to the next location where a new length of wick drainis spooled and connected to a new anchor plate. The process is repeated and a pattern of installed vertical wick drainsmay be installed as shown to provide short drainage paths for pore water, which accelerates the consolidation process and the construction schedule.

Unfortunately, using a conventional wick drain installation apparatus and method, one needs a fixed length mast/mandrel to install an equal-length wick drain (e.g., a 100′ wick drain rig/mandrel to install a 100′ wick drain). However, there is a need for variability in installation length requirements that existing wick drain installation equipment cannot accommodate. For example, if a 100′ wick drain needs to be installed beneath 60′ power lines existing wick drain installation equipment simply cannot be used.

What is needed is a segmental installation method that splices together as many segments of wick as needed to reach a desired depth, thereby eliminating the need for a 100′ mandrel to install 100′ of wick drain.

It is, therefore, an object of the present invention to provide a segmental installation method that splices together as many segments of wick as needed to reach a desired depth, thereby eliminating the need for a fixed-length mast and mandrel to install that length of wick drain.

According to the present invention, the above-described and other objects are accomplished by providing a novel shoe coupler comprising an open ended receptacle having an identical aperture at both ends configured for slidable insertion of a mandrel. The shoe coupler has a constant cross-section except for a partition offset from one end, and a pair of bore-holes offset from the other end for insertion of two set pins. A plurality of mandrel sections are modified each by attaching a shoe coupler at one end by welding or the like, and by machining two transverse grooves at the opposing end. After calculating a proper number of modified mandrels needed to reach a desired depth, an operator undertakes segmental installation by installing and driving mandrel sections, and cutting and splicing wick drain sections together as needed to reach a desired depth. Once a first mandrel segment has been driven into the earth, the operator knocks out two release pins from the shoe coupler to disconnect that segment from the mast. They cut the wick drain with enough room to make a splice, attach another mandrel segment to the installer machine, feed another length of wick drain through it, splice it to the first, and couple the segments together at the shoe coupler, and repeat as necessary. The advantage is that one can install any length of wick drain with a standard 40′ wick drain rig.

Reference will now be made in detail to preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.

The present invention generally comprises a segmental installation method for wick drains (a.k.a. PVDs) that incrementally inserts and splices together as many segments of wick drain as needed to reach a desired depth. The method employs multiple mandrel segments coupled together by a unique shoe coupler also disclosed.

With reference to, the shoe couplercomprises an open ended receptacle having an identical aperture at both ends configured for slidable insertion of a mandrel sectionat both ends. One skilled in the art will understand that mandrels may take a variety of shapes but are typically rectangular, and so a rectangular shoe couplerembodiment is disclosed. The shoe couplerhas a constant cross-section along its entire length except for a partition() offset from one end by approximately one third lengthwise, and a pair of countersunk bore-holesoffset from the other end by approximately one third. The full or partial partitionsubdivides the interior into two sections A and B. Section A of the shoe coupleris intended to be permanently affixed by welding or the like onto one end of a first mandrelsection. The other end section B of the shoe coupleris intended to be removably affixed as will be described onto one end of a second mandrelsection. Each mandrel sectionto which shoe coupleris installed should be modified at the other end by machining two transverse grooves() on opposing sides, the groovescorresponding in position to bore-holes.

The bore holesfully traverse the interior section B of shoe couplermidway and are configured for insertion of retaining pins. When inserted the retaining pinspartially interrupt the interior channel of shoe couplerand engage the transverse grooveson opposing sides of mandrel sectioninserted therein to secure it.

also provides a set of exemplary dimensions, although dimensions may be scaled as needed or altered for different mandrel shapes (diamond, square, etc.).

After calculating a proper number of modified mandrelsneeded to reach a desired depth, conventional mandrelsare modified each by welding a shoe coupleronto one end as shown in, and by machining the other end with two transverse grooves on opposing sides. Thus, in practice, a number of modified mandrelswill be provided at a job site, each with a shoe couplerpre-welded on one end (pinsinserted) and machined at the other with the two transverse grooves on opposing sides.

The segmental installation method for wick drains proceeds as follows.

At step(), the operator lays the mastdown and inserts a modified mandrel into the drive systemand mast, loading the wick drainthrough this section of mandrel. The wick drainis fed from a spoolup to the top of the excavator/crane mastand down through the hollow mandrel. An anchor plateis installed into the end of mandreland the wick drain is attached to the anchorall in a known manner.

At step(), the operator drives the mandrelto depth using optional vibratory hammer, overdriving the shoe couplerbeyond the drive systemleaving the mandrel, anchor plateand wick drainall in place. The wick drainis cut where indicated leaving enough room to make a splice.

At step(), the operator lays the mastdown and inserts another modified mandrel into the drive systemand mast, loading the wick drainentirely through this second section of mandreland out the end.

At step(), the free end of the wick drainis spliced to the cut end protruding from the ground. This is best accomplished by telescoping the two ends together and stapling.

At stepthe second section of mandrelprotruding from the drive systemis inserted into the open upper end of shoe coupler(see) and is affixed therein by insertion of pins.

At step() the operator again drives the second section of mandrelto depth, and out of the drive systemagain leaving the mandrel, anchor plateand wick drainall in place. The wick drainis cut where indicated leaving enough room to make a splice

The operator repeat steps-as many times as needed to reach design depth, leaving the anchor plateand wick drainin place.

Finally, at stepthe mandrel sectionsare removed one by one. Each section of mandrelis extracted until the shoe coupleris exposed above ground. The operator knocks out the two pinsout to uncouple the shoe couplerfrom the mandrelsection in the mast, ejects the mandrelsection from the mast, and repeats until all sections are removed.

In practice, it is even more efficient to work two PVD installation sites together, extracting each section of mandrelfrom the first site, uncoupling and immediately inserting the extracted section into the next PVD site after putting a new anchoron.

The foregoing disclosure of embodiments of the present invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Many variations and modifications of the embodiments described herein will be obvious to one of ordinary skill in the art in light of the above disclosure. The scope of the invention is to be defined only by the claims, and by their equivalents.