The optimization of the Big-bag removal is studied in
(Jaballah and Ramdane Cherif-Khettaf, 2021;
Ramdane Cherif-Khettaf et al., 2022) where a new
vehicle routing model called the Multi-Trip Pickup
and Delivery Problem, with Split loads, Profits and
Multiple Time Windows was proposed. This model
allowed mutualization of material delivery with Big-
Bag waste removal, using tail-lift truck fleet. In this
study, we focus only on waste bin removal, which
consists in performing a set of direct trips from the
platform to the construction sites to satisfy
construction site requests for full bins removal and
their replacement by empty bins. The remainder of
the paper is organized as follows. Section 2 describes
the problem and related literature; two MIP models
are presented in section 3. Experimental results with
the definition of benchmarks are given in section 4.
Finally, concluding remarks are given in section 5.
2 PROBLEM DESCRIPTION AND
RELATED LITERATURE
A limited heterogeneous fleet of tipper trucks
(vehicles) situated at the platform must perform
multiple direct trips between the platform and the
construction sites. The vehicles differ by their speed
and their distance limit. Each trip consists of loading
an empty bin at the platform, delivering it to a given
construction site, collecting a full waste bin from this
construction site, and unloading it in the recycling
center located just next to the platform. Each vehicle
has one or more periods of availability, which
represent the time windows when the vehicles are
available at the platform and so can move to the
construction sites to collect waste bins, outside of
these periods of availability, the vehicles can be
mobilized for other tasks external to the platform and
can’t satisfy the request of bin removal. The platform
also has a period of availability, that is given by the
platform's opening hours. The construction sites have
one or more types of bins depending on the specificity
of the works in progress in the construction site (bin
for wood, bin for metals, bin for plaster, bin for inert
materials, etc.). Each site has only one bin per type,
and must therefore send to the platform requests for
bin removal. The platform must manage the bins
waste removal with the available resources and
ensure the replacement of each full bin with an empty
one. The construction sites also have one or more
periods of availability during which vehicles access is
allowed, and thus the arrival and departure of vehicles
at the construction site location must be within one of
the availability time windows allowed by the
construction site. We denote by a bin removal task,
all operations that consists of loading the vehicle with
an empty bin at the platform, travelling from the
platform to the construction site, unloading the empty
bin at the construction site, loading the full bin,
travelling back to the platform and unloading the full
bin at the platform's recycling center. Platform
service time is the time required for loading and
unloading the bin on the platform.
This problem can be modelled as unrelated
parallel machine scheduling problem in which the
vehicles can be represented as machines with multiple
periods of availability and the bin removal tasks as
jobs that have one or multiple periods of availability,
and require a certain amount of processing time, that
depends on the vehicle that is used. In addition, the
constraint of availability of the tasks in our case
concerns only a part of the task processing time, it is
the loading and unloading part at the location of the
construction site and does not concern the part of the
travel to and from the site. The objective is to perform
the maximum number of bin removal tasks, to
determine the assignment of tasks to the availability
intervals of the vehicles; and to define the sequence
of satisfied tasks per available interval of each used
vehicle.
In terms of computational complexity (Lenstra et
al., 1977) proved that the single machine scheduling
problem with only release dates, which is a special
case of our problem is NP-hard. In literature,
extensive studies have been conducted in the area of
parallel machine scheduling with time constraints
without availability constraints (Arik et al.,2022;
Osorio-Valenzuela et al., 2019). In most of the
research reviewed in the area of parallel machine
scheduling, the availability constraints are defined on
resources (Such-Jeng, 2013). Very few studies
consider the availability intervals of tasks as in
(Gedik et al.,2016). A survey on parallel machine
scheduling under availability constraints can be found
(Kaabi and Harrath, 2014).
Despite the abundant literature on parallel
machine scheduling, the problem that we present here
is in our knowledge a novel one and allows us to
model a new constraint in unrelated parallel machine
scheduling problems, that is both resource and task
multiple availability interval constraint. Our
contribution can be summarized in the two following
issues:
─ Modeling a real problem of direct transportation
of bin waste in the construction sector as a
parallel machine scheduling problem with a new
specific constraint that is multiple periods of